THE PROBLEM OF MAINTAINING SOIL FERTILITY IN EASTERN KENYA: A REVIEW OF RELEVANT RESEARCH

J. R. SimpJol/, J. R. Okafehl e.3 G. Luhllfwa)

J -10 HOIIIlCJ CreJcent, Campbell, ACT, AllJtralia 2612

2 Department of Soil Sciencc, fi10i UrziIJerJity, PO Bo.r: 1125, EIJoret, Kenya , ACIAR, GPO Bo.\: 157 L Canberra, AlItJrall.'a

AllJtralian Centre for International A.lJriCllI tllml ReJearcb 1996 The Australian Centre for International Agricultlll'al Research (ACIAR) was established in June 1982 an Act of the Australian Parliament. Its primary mandate is to help identi(y agricultural problems in developing countries and to commission collaborative research between AustI'alian and developing country researchers in fields where Australia has special competence. \Vhere trade names are used this does not constitute endorsement of nor discrimination against any product by the Centre,

SERTES series contains the results of original research supported by ACIAR. or' material deemed relevant to ACIAR's research and development objectives, The series is distributed internationall:v, with an emphasis on developing countries.

© Australian Centre for International Agricultural Reseal'ch GPO Box 1571. Canberra. Australia 2601. Simpson. J. R .. Okalebo. J. R. and Lubulwa. G. 1996. The Problem of Maintaining Soil Fertllity in Eastern Kenya: a review of relevant reseal'ch. ACL\R Monograph No, 41. 60p.

ISBN I 86320 1920

Design and production: (J,'.'l.qll ONE. Canberra. Australia

Printed Goanna Print PI'y Ltd. Canberra. Australia THE AUTHORS The ;\ustralian Centre for International Agricultural Research (ACIAR) supported collaborative research vvith the Kenya Agricultural Research Institute (KARI) in Machakos and Kitui Districts between 1984 and ]993. Drs Simpson and Okalebo \vere collaborators in that research, affiliated \vith ACL-\R and KARI respectivel,)·. Or Lubulwa is a Senior Economist with ACIAR in Canberra.

2 PURPOSE OF THE REVIEW

TllIS REVIEW TRACES n lE IIISTORY with two crops taken every yeal~ learned how to manage the and progress of research in puts heavy pressure on the soil resource base better'. eastern Africa into the problems resource. TiFfen and colleagues This review aims to show that of maintaining soil fertility and (1994) described the excellent progress is indeed being made sustainable productivity on the progress that has been made in towards better land croplands, with particular reducing soil erosion by contour managemen t 111 reference to the 'medium banks and especially districts like :Vlachakos. Several potential' areas of the 'moist in the rainfall hill areas of examples are of farmers savanna'. These are the areas of j\lacha koso \Vhi le they working towards affordable medium but unreliable rainFall recognised that soil Fertility has techniques for better soil (average 600-800 mm/year). declined, these authors fertility management. 11000,vever, They span the E"-O (Food and suggested no feasible and the overall progress in soil Agriculture Organization) com prehensi ve solu tion to this fertility management is slow; classifications of 'semi-arid' and increasingly important problem. very uneven, and is hampered into the less-favoured end of the They did not mention that the by major socioeconomic hurdles. adjacent 'sub-humid '. The conservation of soil and water The low rates of adoption of review deals mainly with has, by increasing the supply of better soil management studies in eastern Kenya, but soil moisture, actually' practices, despite the also calls on reports from other the potential for the 'mining' of conclusions of recent on-farm areas of eastern and sou thern the remaining soil nutrients by research and modelling, Africa ;vith related agricultural crops. \Vith current 10Y.,' that further on-farm research systems, and ;,;hel'e similar nutrient inputs, this can and extension are urgently problems of maintaining soil produce short-term gains in needed. Apparently many small­ fertility are experienced. crop yields but will scale farmers need education on As an exam pIe of the the problem of maintaining soil their possible options, and problem, the present study fertility in the long term. assistance in selecting centl'es on the situation in English and co-workers (1994) appropriate sol u tions. \Vi thou t Machakos District, Kenya, also did not recognise this such effort. and enabling where population and reality~ stating (p. 35) that 'any Facilities such as financial credit agricultural production have deleterious eFFects of changes in and better fertilizer increased some sixFold during the nature of the resource base distribution, the improvement the years 1930-1990. I n this (due to cu/til'atioll and croppill/l) rate in soil fertility management 'medium potential' area, have been more than offset by in eastern Kenya is likely to intensification of agriculture, improvements due to terracing, remain generally lo\'.: etc., and the farmers have

3 Some of the options in better are explored in the light of relative economic attractions soil fertility management for recent research, and their and risks surve.ved. farmers wi th modest resources

BACKGROUND

TI lE j\i\PlD['{ INCREASING forecasts increasing Food deficits Fertilizer use has been declining, populations in sub-Saharan if Llrming practices are not e.g. in Uganda, where usage has Africa linked ,vith low inputs of improved, and estimates that decreased by 40-60% between soil nutrients and increasingly food sufficiency can be achieved 1980 and 1990 and farmers now intensive cropping over much only if ferti lizer usage rises to rely heavily on local organic of the cultivated lands have 90 kglha by the year 2010 and sources (Swift et a!. 1994). It is resulted in the stagnation of, 160 kglha by 2030, not surprising that soil then gradual decline in, per Total inorganic fertilizer productivity is decreasing capita production of Food grains usage in su b-Saharan Africa generally apart from the over the period 1960--90 during 1992 was about relatively few cases where (Makhn 1993a). Gerner and 1.28 million tonnes (Gerner farmers wi th better financial Harris (1993) surveyed the and Harris 1993). Kenya and resources are able to afford the recent histor,Y of inorganic Tanzania used roughly equal nutrient inputs necessary tor fertilizer consumption in sub­ amounts, and together sustainable crop production. Saharan Africa. Average rates of accounted for some 100000 Generally, rhroughou t su b­ fertilizer application across tonnes of this total. Saharan AFrica, the existing Africa are outstandingly low by Consumption during 1975-90 low-input agriculture results in world standards, ranging from had been growing at 3.4% depletion of the major soil about 1 kg/ha cropland in annually, overall; in East Africa nutrients nitrogen (N), Central Africa to 15 kglha in the rate was nearly 5%; in phosphorus (P) and potassi um southern Africa. These national southern Africa, 1. 7%. However, (K). Overall, this depletion has averages disguise large structural adjustment policies of been calculated at 22 kg N, variations between agro­ many governments have led to a 2.5 kg P and K 15 kg/ha/year ecological zones wi thin stagnation in fertilizer (Stoorvogel et al. 1993), wi th countries and even between consum ption since the late much higher values For Kenya. individual farmers. FAO (1993) 1980s. In some countries The extent of the problem varies

4 both within national boundaries highland areas of Ethiopia, In the densely populated, and on national scales, Kenya, Rwanda, Burundi, heavily cropped district of Kisii, depending on the inherent soil Malawi and Lesotho (Smaling SW Kenya, aggregated nutrient fertility and the intensity of 1993). For these countries, even losses were calculated at 112 kg cropping imposed. Annual national average cropland losses N, 3 kg P and K 70 kg!ha/year, nutrient losses are particularly are calculated to exceed 40 kg wi th some serious P acute in the densely populated N,6 kg P and K 15 kg/ha/year. deficiencies.

EARLY SOlL FERTlLlTY RESEARCH

CAB! (1994) recently reviewed started in 1936, was designed to Later work (Simpson 1961; soil fertility research in East establish what ratios of time Stephens 1967) at Kawanda, near Africa (1930-1990) and under crop to time under fallow, Kam pala, showed that the published an annotated supplemented by varied inputs beneficial effects of resting bibiliography with over 1000 of manure, could produce fallows of deep-rooted grasses, abstracts. sustainable crop yields. The e.g. Cf:,/O/"l~1 .qayana and Pen/ll~ld{11ll Early soil fertility work, experiment continued for at PIII"PIII"CIIIIl, were due largely to starting soon after 1930, was least 25 years (i .e. fi ve of its the capture of leached nitrate and largely concerned wi th the rotational cycles). The results bases, particularly K, from the effecti veness of vegetati ve were reviewed by Jameson and subsoil and the return of these fallows, combined with animal Kerkham (1960), 1vlills (1960) nutrients to the surface as manure applications, designed and McWalter and Wimble increased organic Nand to restore ferti li ty after a period (1976). Essentially, the associated exchangeable cations. of cropping. This work was in experiment showed that the The physical effects on soil the context of a gradual demise beneficial effects of resting from structure and rainfall acceptance, of shifting cultivation, as cropping under a grass/bush which had previously been communities became more fallow could be largely (not thought to be important, were settled and populations entirely) replaced by the found to be only short-term increased (Padwick 1983). application of manure once in transient improvements. A major long-term fertility each 5-year rotation, but would experiment in Eastern Uganda require application rates greater at Serere Research Station, than 5 t!ha.

5 At Katumani, Machakos, in a var'iations in parent material, or large quantities of cations \vere drier climate, Bennison and reactions ,vi Ih ferric and leached into the subsoil, Evans (1968) found that aluminium ions in the more oxic accompanyi.ng the nitrate accumulations of' nitrate in the profiles. movement previously observed, soil profile after ~,re fallov\; Concurrent with general soil during three years of cropping legume crops or short-duration fertility research were many at Namulonge, north of maize could have significant detailed studies on the dynamics Kampala. A subsequent three effects on subsequent crop of the mineralisation of soil years of restol'ative hillow under yields. The size of the l'esidual organic l\' as affected by perennial grasses recaptured effect varied greatly with the moisture regimes. Cycles of much of the leached nutrients. amount of seasonal rainfall in dr)ing and rewetting were which otherwise were beyond both the first and second found to greatly stimulate N the reach of the annual crops cropping seasons, as ,veIl as OIl mineralisation (Birch 1958. and grown, and bmught them bac k the sequence of crops in the many subsequent repol"ts - see to the sllrf~lce soil. Jones found rotation. CAB! 1994). The accumulation that crop )ields could be Aluch of the early soil of nitrate near the soil surface maintained in the three-year fertility work pointed to the and its movement to the 10'wer cropping phase v,·hen the fallow importance of organic sources of pmfile by leaching during the phase was reduced to only one nutrients in controlling cropping phase of rotations also year, if inorganic nutrients were nutrient availability lJVical are captured the attention of several applied in the amounts required the studies of Birch and Friend workers across Sast Africa (ap to replace the nutrients lost by (1956) throughou t East Africa, GriHlth 1951; Mills 1 leaching. In this case, ground Stiven (1972) in western Leutenegger 1956; Robinson limestone had to be included to Tanzania, and roster (1969. 1981) 1960; Simpson 1960; Stephens neutralise the gradual in southern and eastern Uganda. 1962). acidiFication of the poorly buffered soils. /\nalyses shovved a close Studies during the 1960s also correlation between soil organic in vestiga ted the ca uses of soi I These results (Jones 1967, carbon (C) content, organic N, fertility decline under 1968) appeared to offer the and the availability of most continuous cropping. and the possibility of continuous other nutrients. Soil pH was su bsequent restorati ve processes cropping without the resting or also generally higher in the soils under vegetative fallow. fallow phase. This promoted a of high organic matter content. Pro~,bly the most signifIcant of period of research. particularly Available P was much less these was the work of Jones in Uganda. on the intensive use closely associated with organic (1967, 1968) on ferrallitic soils in of inorganic fertilizers on cash C, and could be associated with southern Uganda. It showed that and ~,sic food crops (Stephens 1969a,b). Souza Machado (1969)

6 reported that the responses to The limited impact of The 1980s brought major fertilizers obtained in farmers' research on small-scale farmers changes in research approaches trials throughou t eastern methods of' maintaining soil to problems of low productivity Uganda could be economic if fertility up to the 1980s can be on small-scale farms. The farmers raised their level of blamed partly on poli tical socioeconomic attitudes of the husbandry. or a 50% subsidy was factors sllch as continuing civil farm household became a pri me placed on fertilizers. strife in Uganda in the 1970s. consideration with the rise of Much of the research on the unsuccessful Ujamaa farming systems research (FSR). intensive use of fertilizers up to movement in Tanzania. and The increasingly impOl'tant about 1970 (or even later in continuing land subdivision and question was why farmers are so some areas of East Africa) failed resettlement schemes in Kenya slow to adopt the options so to have much impact on small­ which released new land, of a ttracti ve to researchers. This scale farmers in the medium varying qualities, for question is addressed beIO\\; potential areas. It probably cultivation. after a survey of the natural supplied useful information for There were other factors. resources and farming systems large-scale farming and researchers did not often of eastern Kenya, and some of plan tations, and assisted the stop to ask farmers their the problems that have adoption of hybrid maize attitudes to using the advocated developed. varieties in the higher potential range of possible inputs and areas of western Kenya. During new practices. This was the 1970~72 the area planted to period of 'transfer of hybrid maize by small-scale technology' or 'top-down farmers in Kenya more than approach'. in which social and doubled to 280 000 ha, and economic realities tailed to fertilizer sales also increased by influence the course of research. about 200%. Since then, The researcher was regarded as however; fertilizer use has fallen the source of all knO\vledge. back to about the 1969 leveL ,-,,'hich simply had to be largely because of economic conveyed to the uneducated structural adjustments and farmer ( L... H. Brown )968, on consequent instability in the the attitudes in Kenya circa fertilizer market (Gerner and 1945; reported in Tiffen et al. Harris 1993). 1994. p. 252).

7 NATURAL RESOURCES IN EASTERN KENYA (MACHAKOS)

THE SOILS landscapes where the ferralsols and cropping. Soil physical on the upper slopes grade into properties include high The soils of ~vlachakos District are acrisols, luvisols, etc., then to erodibilitj\ surface capping typical of the platea ux of poorly drained grey soils in the under cultivation and poor eastern Africa. They are derived valJeys. In some valleys, soils of infiltration of rainfall. This has from the pre-Cambrian vertic properties occur led to serious erosion and losses 'basement-complex'rocks expanding through to wide of soil nutrients on many of the consisting mainly of granites, plains of Vertisols, but such steeper cropland sites in the gneisses, and sometimes of areas are often too dry for past (Okwach et al. 1992; Tiffen schists, sandstones or phylli tic cropping and have other unique et al. 1994). Cation exchange shales. There are volcanic physical problems for capaci ty is generally low to very influences on the periphery of cultivation. Alfisols occur low but the soils are often deep the District. including the widely through the semi-arid and well structured, allowing basaltic xatta plateau. but these and subhumid regions of eastern deep penetration of plant roots have little overall effect on the Africa, including parts of and a moderately good capacity soils or agriculture or Kenya, Tanzania, and Uganda, to hold available water. Machakos. The better-drained and much of southern Africa. red soils are mainl:y ,-\lfisols The Alfisols of eastern Kenya THE CLIMATES (USDA Soil 'Dlxonomy), ,vith are generally lov\' in organic varying degrees of ,veathering Average annual rainfall matter (t,ypically about 1.0% C and acidification, bringing them distribution through central and 0.1 % N) and often are into the luvisols, alisols, lixisols Kenya. Tan2"-ania and Uganda marginally to acutely deficient and acrisols of the suggests large areas of good in P (Okalebo et al. 1992). l:'l\O~UNESCO classification agricultural potential receive Phosphorus availability varies system. In areas of more more than 800 mm/year. greatly with parent material and extreme weathering and clay rlowever; this is misleading cropping history. \Vith the low degradation, the soils grade into because great seasonal rates of nutrient inputs that Oxisols (USDA) or ferralsols variations in rainfall, especially prevail on the great majority of (FAO). A catena sequence, more in eastern Kenya and much of small-scale t~H·ms, soil fertility common in central Uganda and Tanzania, have been described usually declines markedly north-eastern Tanzania, may by many authors (e.g. McCown during continued cultivation develop on undulating et aL 1991; Keating et al. 1992a).

8 In Kenya, Uganda and northern dry forest and moist woodland. exceed 500/km2, e.g. in Kisii in Tanzania, and also southern vvith a high climatic potential SW Kenya. 680/km2 (Smaling Ethiopia, there are two for cropping (rainfall >900 mm) et al. 1993). In Machakos cropping seasons eHch yeHr. In and suitable for growing coffee. District. population densities Kenya these are known as the Zone 4 is transitional, 'semi­ vary with agro-ecological zone long rains (;Vlarch-June) Hnd humid to semi-arid', with (Jaetzold and Schmidt 1983) the short rains (October­ average but unreliable rainfall from 285/km2 in AEZs 2 and 3, January) but the timing and of 700-850 mm, and suitable for to 11 0/km2 in AEZ 4 and relative lengths of each growing cotton, sunflower and -i0/km2 in AEZs 5 and 6. period vary substantially with legumes. Zone 5 high However. since 1930 there has location. Further south, the two potential for livestock-raising, been a relative shift of growing seasons merge with average rainfall of 500-800 population to the more marginal progressively into one long wet mm, greater seasonal variability areas. i.e. AEZs 5 and 6 (English season (November April in and higher tem peratures. et al. 1994), where populations Zimbab,ve) with unreliable Although m uch of this zone is have incl"eased nearly ten times times of onset. Total rainfall more suitable for sorghum and taster than in AEZs 2 and 3. The generally increases with altitude millets, maize has become a rapid population changes have and proximi ty to hill masses. popular crop. Main discussion necessitated corn plete changes There are, however. substantial in here centres on the problems in farming sj/stems, i.e. rain shadow effects on the of zones 4 and 5, which cover intensification of crop north-west slopes of mountains, most of the District and production, major earth works especially near ''''It Kilimanjaro resemble m uch of eastern and to control soil erosion. and Mt Kenya. southern Africa. The main clarification of land ti ties and, of The agro-ecological zones conclusions are relevant to great im portance to this (AEZs) of eastern Kenya were zones 2 and 3 also. discussion, increasing problems classified by Jaetzold and of soil fertility decline and how Schmidt (1983). Machakos DEMOGRAPHIC AND to prevent it. District contains hill areas ECONOMIC CHANGES The District economy in (<10%) in the wetter zones 2 and I\1achakos has also changed Populations in Kenya and 3, through drier zones 4 and 5 substantially in response to Uganda have increased fivefold (about 80%) to marginally arid better rCk'ld commul1lcations and to sixfold between 1930 and areas in zone 6 (10%), suitable social factors. Cash crops have 1990, typical of the whole only for range land or occasional increased greatly in importance eastern African region. \Vithin drought-tolerant crops (see and seasonal trade between the highly productive highland 1). The 'semi-humid' families in staple foodgrains, areas. population densities can zones 2 and 3 were originally particularly maize, beans and

9 Agro-ecological zones (AEZs): Semi-hu mid (Dry Forest and moist woodland) Semi-humid to se mi-arid (Dry woodland and bushland) Semi-arid (Bush land) Semi-arid to arid (Bushland a nd scrubla nd)

® District capital

Towns and vi llages

o 10 20 30 40 50 I I I I I ki lometres

5

.MAKINDU

KIBWEZI ~ • 'l \\ II " 5

J\VO

Figure 1. Kenya Agro-ec%g£ca/ :zoneJ, M achakOtf D£Jtr/ct.

10 cowpeas. is important llowevel~ in ;vlachakos this is Among countries with mixed (R ukandema 1984). There are not a major difficulty. since climates. Ethiopia, Kenya, now manyoppot,tunities for there has been a rapid rate of Malawi. Rwanda and Uganda trade in farm products and commercialisation in the were grouped along with India purchase of farm inputs. District since 1930. There are and Nigeria as already having Nevertheless, cashflow is alwa,Ys now at least 700 regular APDs exceeding 250 people per a problem in poorer households markets and more than million kilocalories potential and demands such as school fees 8000 licensed shops and kiosks production. In producing these fot, children often take priority in rural communities impressive data, Binswanger over farm inputs. (Tiffen et al. 1994). and Pingali did not consider Engl ish and col ( 1994) Binswanger and Pingali present trends in soil fenility. notE' that 'the efTect of {I 988) classified countries on and assumed that an market access in bringing their 'agroclimatic population intermediate level of information and stim u lating densities' (APDs), i.e. the agricultural technology would agricultural change and number or people present per be achieved nationally in each investment is well known '. million kilocalories of potential case between now and the year U therE' are easily accessible food pl'oduction, in contrast to 2025. Their findings highlight markets where produce can be the usual 'population/km2' basis. the importance maintalllll1g sold to generate 1'01' the On the APD basis, Kenya and and improving the productivity purchase of fertilizers and other Niger share the highest ranking of the land resource base in inputs, thE're is no incentive to in the world, both now and in Kenya (er NlcCown and adopt high yield technologies. projections to the year 2025. Keating 1992) and its neighours.

11 SPECIAL PROBLEMS OF THE MEDIUM POTENTIAL AREAS - MACHAKOS AS AN EXAMPLE

TIlE CmlPONENTS OF TilE ,\UXED year simply to supply members Livestock have traditionally farming systems of Nlachakos, of the family with 2000 been a means of raising cash involving food crops, cash calories/da.r Considering the when needed. crops, tree crops and livestock, probabilities of seasonal and soil Table I shows selected have been described by Lynam constraints and losses due to socioeconomic aspects of the (1978), Rubndema (1984), Lee pests, it is not surprising that farming systems in i'Vlachakos. (1993) and Tiffen et al. (I 99LJ). periodical food shortages occur, In this study Ockwell and Interacting demands for labour, particularly as farm sizes colleagues (1987), the farmers nutrients, cash resources and gradually decrease. Here, only were gr~uped according to their management decisions are found those aspects of the farming rates of adoption of various ;1 t various levels. ;v\ost farmers systems pertaining to soil selected technologies. The use ox-drawn ploughs for major fertility management are technologies adopted by the cultivation, but much weeding discussed. different groups are shown in is done by hand "vi th hoes, and There is strong in teraction the second row of the table. other farm equipment is often between livestock and cropping Average farm sizes of the groups minimal. \Vhere all cultivation activities. Livestock provide ranged 5-24 ha; individual farm is with hand-tools, the cultivated manure and draught power. 1.2-32 ha. The farms were area is usually restricted to while cropping activities all multi-enterprise crop and about 1 bJfi1rm. The use of provide crop residues for livestock production units. A animal draught power allows livestock feed. However; there is trend of' increasing prosperity about three ha of cultivated significant conflict between can be traced from group 1 to cropland \l\·hereupon the livestock and soil fertility group 4, e.g. in expenditure on availability of labour for enhancing activi ties. For school fees. weeding becomes limiting, even example, crop residues and Table 1 indicates that, on though rotal f~lnn area may be maize stover which could be average, at least one member of 5-10 ha (Rukandema 1984). returned to the field to reduce each household works off-farm. Since a typical household may run-off and provide nutrients Tiffen and colleagues (1994) contain about 10 people, a single for future crops are commonly estimated that, for farmers in hectare of cropland would have used as feed. Food security AEZ 4, 52% of their cash income to yield around one tonne of remains an important objective was from non-farm work; for cereal grain equivalent twice a for f:,rmers in Machakos. farmers in AEZs 2 and 3, about

12 39% income is from non- THE SOIL SITUATION and consequent soil erosion of farm activities. Most able men the cropped lands in the last ;Vlachakos District has soil have at least part-time off..f~ll·m 50~60 years (TifTen et al. 1994). work. This ranges from local resources and rainfall Machakos and its similar work as labourers to employment expectancies typical of much of neighbouring District Kitui outside the District, e.g. in eastern Africa. It is a well­ have undergone large increases Nairobi or in Coast Province as studied area from an in agricultural production, soil migl'atory'.vorkers. agricultural viewpoint because conservation and other aspects of its periods of overexploitation of development. Howevel~

Table 1. HOllJe/wtd c/Jaracten~lticLI and pattern'! of tec/mofl~qy adoptioll 0/ {h//'ermt fJrtlll/Mo//armerd (tneall I'aflle,1 per/arm).

Gwup 1 Group 2 Group 3 Group 4 No. of fiums 5 5 4 2

Technologies adopted EUlllJ'

h A/al'lII "'ith a lIIale (J""i.li"Il-lI1aker i,1 rt'CIJr{)er) a,1 1.1), with a h",,/!all') flnd Wife tealll, tl.5, alii)

, ,~farlll ",it!! (/ ,1I'CI:'I,m,maker 60 .'leaI', I ,J/' le", 1:1 re,""',)",) ,1.1 IJ.{I, IIwr,' tball 6{1, Ill. S,'{[r,,': Ockll'c/ll'l al. (l9S7)

13 because of the strain on the soil High yields, resource imposed intensive Low low inputs long cropping with 10\,\' nutrient inputs, many farmer households in "vlachakos are still threatened by encroaching poverty. Unless their economic position can be alleviated quickl}~ they are likely to descend further into poverty spiral from which escape becomes increasingly d i Hlc ul t (Fig. 2). The main physical factors contributing to the decline in soil productivit.>j and hence to farm povert.)~ have been described by Okwach and colleagues (1992) and are shown in Figure 3. Largely in parallel with the operation of the poverty spiral, Figure 3 depicts a cycle of i nc reasi ng soi I Figure 2. The dowllll'aN) ,Iplm! to the pVl'crtv trap degradation as and (AlcCOII'1l alld )0111',11992) . nutrient inputs diminish along with increasing household potentially productive water are poverty and reduced crop THE CLIMATIC RISKS lost. Figure 3 also shows the .>~elds. With reduced soil The erratic nature of rainfall priori ty of a poorer household to organic matter in the surface feed crop residues to livestock, patterns during the t\VO wet (i.e. layers, infiltration rates for and possibly to sell the vital crop-growing) seasons has been rainwater are 100,\'ered and the nutrient-containing manure or described by Stewart and Hash run-off of excess \vater to sell the resid ues directly, (1982) and Tiffen and colleagues increases, carrying with it the rather than returning them to (1994). Coefficients of variation relatively nutrient-rich surf~\ce the land. This contributes in seasonal rainfall commonly soil. Thus both val uable soi I and 50% (Keating, Siambi further to general soil depletion. and Wafula 1992). Because of this seasonal unreliability.

14 Low (known by the Kiswahili term / income ~ as 'fimya juu terraces). These Loss of Low Low very necessary structures ",,'ere ~goiland crop fiU'll1 I nutrients yield input gradually developed to prevent t the and huge soil losses + which occurred in the 1930s and runoff POOR ____" Lowplant in some subsequent periods of t DEGRADED Low SOILS population neglect (Tiffen et al. 1994). infiltration ___ L-____~ t RECENT RESEARCH Low soil No ,"",,'," L-__~ nrgallle .... --~ of crop J ON INTERACTIONS matter residues AFFECTING MAIZE t + YIELDS Crop residues no red to The extent of the seasonal to soi I livestock variations, the varied degrees of Pigure 3. TI,e con/fidel that lead to IlIlJuJtm'naMe lalld we for a typ~cal depletion in the nutrient

15 Keating. Siambi and W,fula conservation, and changes of The conclusions of this (1992) and Keating and maize variet.y. Of particular research are discussed in greater col leagues (I 992a,b; 1994) significance to the present detail below. In briefest tackled this research problem, at discussion, the CMKEN model sunllnar)\ research has indicated least for maize agronom), by has been used to predict the and continues to confirm, that developing and adapting a crop likelihoods of profitable '\'ith a fairly high standard of simulation model. derived from increases in crop yields when management, which should be CERES-ivlaize 4Jones and soil fertility has been improved. feasible for many farmers in Kiniry 1986) and named The most commonly deficient Machakos. use of inOl'ganic C;\lKEN, which can predict the nutrient is N, which can be fertilizers to complement locally interacting effects of seasonal applied as organic manures or produced organic manures rainfall. soil conditions and in soluble inorganic forms as should be economically management practice on maize fertilizer. The quality and attractive vvith tolerably low growth, development and grain availability of nutrients in boma levels of risk. However. a great yield, manure are largely uncontrolled deal of adaptive on-farm The CMKEN model has (Probert et a!. 1992) therefore research and demonstration in proved its ability to predict the model has been used to collaboration with farmers maize J':ields over' a wide variety investigate effects and climatic remain to be completed. Many of field conditions with tolerably risks of using fertilizer N in farmers still need to be good precision (typical I)'. eastern Kenya, rather than the convinced that affordable r = 0.95). Csing typical soil data use of manure (Keating et al. techniques to improve and and the detailed daily rainfall 1991; 1992a). The economics and maintain soil fertility can be records for differen t locations risks of supplementary fertilizer developed within their own throughout Machakos and Kitui, N application were further particular financial constraints the model has enabled explored at seven selected and continual crop production researchers to explore the likely locations, representing a variety demands. outcomes of changes in farm of rainfall regimes across practice such as plant Machakos and Kitui Districts, population densit); moisture matched with two contrasting types of soi I condi tions. by Probert and colleagues (1994).

16 MArNTAINING SOIL FERTILITY rN MACHAKOS SOME POSSIBLE INTERVEI\lTIONS FOR FARMERS

RATES OF SOIL with low reserves of available N corroborates that yields decline FERTILITY DECLINE and P, even under natural to very low levels in just a few vegetation. Denudation under seasons unless substantial UNDER CONTINUOUS grazing and sheet soil erosion amounts of nutrients are LOW-INPUT CROPPING over the past few decades are applied (Greenland 1994). The Research into the farming partly res ponsi ble for this in following examples provide systems of lVlachakos during some locations (Tiffen et al. additional evidence that a 1980-93 has examined 1994). Further; there is evidence decline in fertility occurs quite socioeconomically feasible ways that nutrient deficiences emerge rapidly in soils related to those of restoring and maintaining soon after the cultivation of in Machakos when they are soil fertilit}: Before considering previously rested land if continually cultivated and these it is logical fl rst to su pplementary nutrients are not cropped with little or no establish, as far as possible, just applied (Okalebo et al. 1996). nutrient inputs. how much the soil has declined First principles dictate that In north-eastern Tanzania, in fertility with farmerS current such nutrient deficiences must Haule and colleagues (1989) methods. Careful analysis has to occur on the Alfisols of eastern working on a soil sequence be made of the available Kenya with the current low (catena) from chromic luvisols to evidence. nutrient inputs because each ferralsols found a rapid loss of I t is beyond dou bt tha t soi I I tlha crop of maize can be soil C in the cultivated layer fertility is very low on many calculated to remove 20-40 kg and associated reductions in farmers' cropland fields. There N, 2-4 kg P and 15-30 kg K maize yields under annual is overwhelming evidence that (using the data of Qureshi 1987). cropping. Organic C decreased soil fertility on the croplands of These figures agree with the by 30-40% on all of three soi I eastern Kenya (Machakos and negative nutrient balances types from the fIrst four-year Kitui Districts) is already derived for similar agro­ period to the next four years. seriously limiting crop yields in ecological zones by Stoorvogel Exchangeable K decreased many seasons (Nadar and et al. (1993). Evidence from similarly by 17-40% on the same Faught 1984b; Okalebo et al. long-term cropping soils, accompanied by decreases 1992; Probert and Okalebo experiments in other parts of in pH. During the same periods, 1992). Most soi Is in eastern Africa, notably northern Nigeria unfertilised maize yields Kenya are low in organic C, and western Tanzania, decreased by up to 45%, e.g. on

17 the luvisol, from a 4.2 cultivated layer aFter long-term chromic luvisol near Katumani. average to 2.6 1/11<1 in the next cultivation in the Kilungu area. Machakos. during 16 years of four years. Comparing sites under natural low-input cmpping. Here, the On a more fertile l1itisol vegetation. under grazing and cultivated soil contained about under continuous cropping at under cultivation and cropping. 33% less C to 50 cm depth than Kabete near Nairobi, Qureshi Mbuvi found a marked contrast soil at an adja.cent site under

(l987) also Found it decline in from 2,49 to 1.25 to 0.74% C for grassland. The changes in C, and unfertilised maize yields the respective sites (Table 3). In parallel changes in N, occurred about 40% (3.3 1111a to 1.9 t/ha) the same soi I sam pies, organic in each lO-cm depth layer from from one Five-year period to the N, available P. and exchangeable the surface. At 0-10 cm the next. Yields in the second five K had all decreased in parallel change. comparing several sites years were i m proved to levels wi th the changes in C. The in each categor); from 1.85% to above those in the first period changes in crop yield with time 1.23% C (and 0.172% to 0.120% (from 4.6 tfha to 5.2 rib) could not be established but N) \vas highly significant applying combinations of major reductions are probable statistically organic manure and inorganic (Pmberr and Okalebo 19(2). It is probable that some of the fertilizers. lVlanul'e or fertilizer lVlbuvi also sampled cultivated organic matter and nutrient loss applied singly produced r

18 erosion, according to analyses of problem (McCown and Jones The cause of fertility decline, the run-off soil after the worst 1992). This practice is discussed apart from the obvious drain on erosive events. At this site, further in later sections (as P and soil cations by crop return of maize stover as a 'fertilizer-assisted soil removal, is ultimately a mulch each season, and enrichment' or, more commonly, negative balance in soil organic applications of 70 kg N plus 'integrated nutrient matter. The rates of depletion of 10 kg Piper ha to each crop as management} organic C and N through inorganic fertilizer, prevented In summar}\ it is clear from microbial mineralisation and soil depletion and produced a the evidence presented and crop removal in the intensive doubling of average maize yields corroborated elsewhere that soil cropping systems described from 1.3 to 2.8 tlha. fertility in eastern Kenya, as in often exceed thei r rates of The continual application of comparable soils in other parts replenishment from crop roots, inorganic N fertilizer, mainly as of the world, declines fairly residues, other farm organic calcium ammonium nitrate, for quickly under low-input inputs and biological N2 five years (l0 crops) was found cropping to levels of nutrient fixation. Soil organic matter is by Okalebo et al. (1996) to have supply which restrict crop an important repository for caused some acidification of the growth. When this happens, the plant nutrients (N, S, P and surface soil (a decrease from return to a farm household for exchangeable cations). It reduces pH 6.14 to pH 5.78 at 0-15 cm its labour inputs falls, even in acidifIcation and improves both depth). This observation is a good rainfall seasons. It is not soil aeration and water reminder that the long-term use possible to state accurately the infiltration. Maintenance of a of such fertilizers, although not ann ual rates of fertili ty decline moderate soil organic matter causing any detectable loss of for various soil types under content thus becomes an soil productivity on this site so different farming systems. The essential part of sustainable land far, has to be managed wi th answer to this question would management. caution on the poorly buffered require tedious, expensive long­ The use of inorganic fertilizer Alfisols of eastern Africa. Use of term research which has not N alone, on soils already inorganic fertilizer in modest been completed. Certainly there depleted in organic N, enables amounts strictly to supplement is overwhelming evidence that substantial crop yields to be applications of organic nutrient present management practices maintained only as long as the sources, such as animal manure, cannot sustain acceptable yields supply of other nutrients, where supplies of such sources for typical farm households - particularly P, is adequate and are inadequate to satisfy crop which could avoid their descent problems of soil water loss due nutrient demands, is one way of in to the poverty spiral. to surface capping can be avoiding or reducing the avoided. A combination of organic inputs and

19 supplementary applications of (g) integrated nutrient 1994). Other Zimbabwean fertilizer N thel'efore looks a management (combining researchers (Sithole and Shoko more attractive management organic and inorganic 1991) also fou nd high use of option to researchers (NlcCown inputs). manure (63% and 83% and Jones 1992). But 'what can a Each of these inputs and respectively) in the communal resource-poor farmer do, within technologies has characteristic areas of Shurugwi-Chiwundura socioeconomic constraints and benefits and costs to the farming and Wedza. using materials available around system, summarised in Table 2. Despite this high popularit.), the farm, to maintain cropland The following section discusses manure use

2D Technology (in put) Advantages Disadvantages soil effects

Boma manu re Oll~{ilrm pmduction labour costs of Increases soil C and N, and COIll posts - no cash outlay extraction, pr'm'cssing, and availability of both transport and spreading, moisture and other nul rients Often not available in recluired amounts

Crop residuE's On~rarm production Labour needed for h,lrvesting Increases soil organic C, as mulch .---- no cash outlay Im proves and returning to land after reduces erosion and impl'oves rainwater inlilt rat ion, ploughing, Deprives farm soil moisture availability reduces ,,'ater losses livestock of dry. Season from rlll1~Orr fodder: May increase some pest problems Green manures On-{;/rm product ion of Occupies cropland which Residual effects on soil N biologically~fixed Nand would otherwise be under are less than those of animal C food or cash crops III all ure Grain legumes in Biological N-fixation Do not satis(y the full Residual effects are the cropping accompanied by high- N demands of the posit i ve but small rotation protein Residues can accompanying (intercropped) 1)(' returI!"d to soil. The or subsequent cereal crop, break in cereal cropping Effects are modest may reduce diseases Ag rofo rest ry The trees SlI pply a variety Possible compet ition Still a potentially useful of products, including animal bet\veen t H?CS alld all 11 ual technique [or some medium­ fodder, mulching materials, crops for critical soil potential al'eas, but only if new fuelwood and fruit. Effects moisture and nutrients adaptations can be satisfactorily 011 soil C and N are incorporated into farming positive, May recycle I? K systems and other nutrients Inol'ganic Lovv labour costs in IIigh cash outlay for Will help to maintain fertility re I't iI ize rs application, A source of resource~poor farmers, if lIsed together with organic rapidly available uut rients Risks of crop failure in inputs (manure, composts, dc), (especially Nand P). Csually poor seasons Continual use of heavy produce good crop yield applications may cause soil responses. Reliable quality acidification. It is the only final Can be lIsed (N) after basal resort to maintain nutrient appplications of organic supply and yields when organic inputs to satisfy crop Ilutrient lIutl'ient SOUlTes have been demands as modified exhausted by seasonal rainfall events

21 (80-90%) and ,,,ere therefore detectable patches of high and Similar systems of moveable largel.y soiL Nutrients easily 10\\' available P in the same bomas have been noted in available to plants included cropland terrace. and lower Tanzania (Sukumaland), parts of mineral 1\ (47-135 mg/kg). high available P at increasing SenegaL lviadagascar and extractable P (185-946 mg/kg distances From the boma Ethiopia (Ruthenberg 1980, by the Bray 2 method) and large (Okalebo et aL 1992; Probert p. 84). In Kenya such systems amounts of K. et aL 1992). are uncommon. but have been Evidence indicates that There are feaSible ways of observed in use on a Few farms animal excreta lying in the improving the efficiency of in central and western Kenya bomalkraaI becomes badly manure collection and use. (E.M. Cichangi, pers. comm). weathered so that much of its These include roofing the boma i\ more attracti ve practice, valuable N. especially the (Materechera et a!. 1995), which seems to be growing in soluble and rapidly building it on a well-drained popu larity as the demand for mineralisable fractions. is lost. rise where the interior does not manure continues to exceed the This occurs either by become boggy in the wet suppl); is to extend the quantity volatilisation to the atmosphel'e seasons, heaping the man ure to of manure by composting it as ammonia or by nitrification one side away from the cattie, with whatever organic residues to nitrate tOlhwed by a and better means of transport to are available. These may be crop combination of leaching and the fields. Some of these ideas residues, weeds with attached denitrification to r\2 gas during have been tried in eastern soil or litter and loppings from periods of excessi ve wetness Kenya (Tiffen et a!. 1994) but surrounding trees. This (Freneyand Simpson 198,,). none seems to have been technique is being promoted in \Vhen the manure is finally dug adopted wide I): Kenya by the Institute for out from the boma. it is so 1\lore broadb; other Organic Farming (KIOF), the mixed with the underlying soil techniques have had greater Tropical Soil Biology and that its removal means impact. In some areas of Fertility Programme (TSBF) transporting much unnecessary Malawi, the bomalkraal is and other NCO and mwethya weight of soil. Considering the moved periodically across the (self-help) groups. Just how simple tools many farmers cropland so that the noted much the composting effectively emplo)" i.e. transport by ox-cart. beneficial effects 01' the animal conserves nutrients in the wheelbarrow, sledge or even on excreta on subsequent crops can manure does not appear to have the shoulder. application to the be exploited. The system is been studied. Using materials of fields farthest from the boma in known as ' khohi (Makken high C to N ratio can prolong the limited time between crops 1993b) and enables large plots to the composting process. 1Vluch is a major problem. The result is be systematically manured. crop residue is likely to be uneven application with easily valued more highly as livestock

22 feed in the dry season than as RETURN OF CROP exchange capacity of the surface composting material, so RESIDUES AS MULCH soil (Okwach 1994). materials less palatable to OR GREEN MANURE In a context of integrated livestock tend to be used. nutrient management (Janssen r\ project promoted by KIOF The corn pe ti ti ve uses wi thi n 1993; TSBF 1994). the use of at Makaveti in Machakos is mixed brming systems for crop resid ue mulch together wi th using a ubiquitous shrub weed. residues. i.e. as a source of modest applications of inorganic [,all/ana cami/ra. mixed "",ith animal feed during the later fertilizer has a compounding or boma man u re to prod uce part of the season when feed interactive effect (lVlcCown and corn post. The project is reported is scarce. and as a soil additive Keating 1992). On the one hand. to be having a useful impact on to maintain matter and the m ulch creates greater more than 50 farmers (Tiffen et su pply some nutrients. are moisture availability enabling al. 1994 p. 243). Similar or already noted. A.t present the the subsequent crop to respond related composting methods are livestock usually win and obtain better to applied fertilizer N. promoted by other the feed. even if some is The crop then produces more mwethya or NGO groups in tram pled uneaten In the boma stover so that, unless the farmer Nlachakos District (Simon to become cam posted with buys more animals to consume Wambua. pers. commJ. In the manure. the extra feed. or sells the excess Central Highlands of Kenya Research has shown that to neighbours, there will not be KIOF has many other successful return of crop residues, a demand for all the stover as mwethya groups which actively particularly maize stover, as a fodder and the surplus can promote farming mulch after maize planting is again be used for subsequent (Cheatle and Njoroge 1993). valuable in reducing rainwater mulching. Such a scenario Farm households without run-off, thereby increasing allows greater hope fora livestock have the choice of water infiltration, producing grad ual u pgradi ng of the returning crop residues. as greater available moisture for farming system tov,'ard higher compost or mulch. or selling the crop growth in the subsequent production. greater efficiency of material to livestock-owners. season. and reducing the labour and better sustainability TSBF network programs in probability of soil nutrient Green manuring. i.e. the eastern and southern A.frica losses in the run-off (Okwach of growing a (TSBF 1994) attempt to et al. 1992; Okalebo et aL 1996). leguminous crop solely or promote the val ue and adoption These beneficial effects are in mainly for the purpose of of integrated nutdent addition to the nutrients, obtaining biological N2 fixation management. including especially K. added in the mulch and ploughing under the crop to residues and composts. and the positive effects on the enrich the soil in organic N. has physical structure and cation not been adopted to any

23

,- important extent in East Afric:i crop against root diseases. an It m ust be concl uded that because of press 1I re to prod lice alleviation of the process of soil legumes in the cropping food and cash crops every N depletion and possibly a rotation are a very valuable season on all available cropland. source of residual soil N of inclusion but do not solve the Nevertheless. researchers in value to the subsequent maize problem of sustaining soil some countries continue to crop (Nadar and Faught 1984a). Fertility. ;\:loreover, legumes experiment with this appealing On the N-depleted soils of the make a positive contribution idea. motivated by the recent eastern African medium only to the N problem. They do increases in costs of inorganic N potential crop lands. there is no not grow well ifavailable soil P fertilizers. In Jv1alawi. current doubt that grain legumes fix is low (Okalebo et al. 1992; investigations centre on much of their ~ requirement Probert and Okalebo 1992) and underso\'>.ing maize with annual from the atmosphere. Howevel; do not fix atmospheric N2 legumes which are grown on much of the N contained in the eFficiently in this situation after the maize is harvested. crop at maturity is harvested in (Probert et al. 1994. and many then dug or ploughed into the the seed and pods. Only some others). soil (Materechera et al. 1995). leaves. roots and nodules are OF special interest here is the Such a practice is unlikely to usually left to improve soil value of pigeon pea, Caiallll.l appeal to f~lrmers in ,vlachakos fertility. Thus Simpson and ca/all. in crop rotations. In because crops frequently incur colleagues (1992). working 011 eastern Kenya, and a number of moisture stress during the later an N-depleted farm site near other semi-arid tropical stages of growth -- this would W~1munyu. Machakos. found environments, pigeon pea is be aggravated by competition that legumes (cow pea. pigeon grown as a rela,Y intercrop with from an understorey of growing pea and lablab) grown for two maize or other cereals. This legume. seasons in rotation with maize shrub legume species stays in left behind an additional 40 kg the ground for up to 12 months. GRAIN LEGUMES IN Nlha in the soil profIle, nearly flourishing on residual moisture THE CROPPING all as nitrate. This was sufficient after the cereal crop has been to increase subsequent maize ROTATION harvested and providi ng green yield by 300-400 kg/ha. but still pods, dry mature pods. then Legumes play a vital role in well below maize yields on finally fuel from its woody African cropping systems, often adjacent plots supplied with stalks. Because of its deep root intercropped with maize but fertilizer N. The result is typical system. enabling it to exploit also as sole crops alternated of experience in other African subsurl~'lce soil layers for their with cereals. The legumes form and semi-arid tropical available P, this species is a vi tal source or protein in environments \,.. ·ith a range of observed to thrive on many human diets. as well as a break grain legume species. nutrient-poor sites, and to

24 produce a useful yield during grown in aJieys some five leguminous trees of Acacia drought seasons v"hen the metres wide between t"rtl!l~' (Bel sky et al. 1989) and cereals have failed to establish. hedgerows of leguminous trees, Acacia alhida (Sanchez 1995) is Pigeon pea is thus a valuable is heavily discounted in often noted. Even non­ inclusion in cropping systems Sanchez's review, as the result of leguminous trees such as on most farms in i\lachakos recent analytical research. Grel'tllea roblldta are prized on District. Studies of hard.}\ Although the trees, which are many farms as a source of woody crop legumes of this type periodically pruned or lopped, fuelwood and building have influenced agroforestry do provide organic matter, materials. researchers toward the current mulch and nutrients to the crop, Current agrotorestry research thrust to use leguminous tree competition between the is pursuing and designing species such as Se"I'I1Il/a "C"IJilIl. perennials and the annual crop better systems for the With relay intercropping, plants for moisture, nutrients juxtaposition of trees and Sesbania can be used in a andlor light prohibits this annual crops in small-scale promising new technique of formalised alley-cropping farming, to exploit the short-term ameliorative becoming established as a robust advantages that some tree t~dlowing, For soil improvement technique for resource-poor species offer in captUl'ing with a minimum disruption to f~lrmers. subsoil nutI'ients, especially P, the cropping rotation (Sanchez On the other hand, in steep leached nitrate and K, 1995). areas, planting perennial grasses providing organic C and and fruit trees on contour banks bri ngi ng all these into the reach THE PLACE OF (fanya ju u terracing) is well of crop roots. To be successfuL AGROFORESTRY IN established as a beneficial however, all this m ust be THE MEDIUM stabilising practice to protect achieved vvithout incurring the the banks from erosion (Hudson detrimental competition for POTENTIAL AREAS 1993). IVl.ixtures of crops and moisture observed in alley­ In his recent review of the trees are grown widely across cropping. The leguminous developing science of the varied agro-ecosystems of multipurpose trees being agroforestry, Sanchez (1995) East Africa, apparently to studied, such as SedL'ania spp., critically surveyed the possible farmers' advantage and can provide valuable high­ benefits and disadvantages of satisfaction. Frui t trees such as protein fodder for cattle to growing annual crops in some pawpaws, mangoes, bananas and supplement the low quality dry sort of geometric arrangement citrus are grown in strategic feed which remains in the dry alongside trees. The previously locations on many farms in season, as ,veil as improving soil acclaimed formula of 'alley eastern Kenya. The increased nutrients (Dzowe!a and Kwesiga cropping', whereby the crop is fertility surrounding 1994). There appear to be two

2E mai n research approaches to RENOVATIOI\J OF THE revegetated by sowing cowpeas capturing the advantages of GRAZING LAI\JOS as a cash crop to recou p the such a system on small farms. labour costs, and a mixture of USING PITTING AND The first is that described by fodder legumes to provide a AGROFORESTRY Sanchez (1995) and referred to canopy. to fix atmospheric N2 TECHNIQUES above, of interplanting the tree and provide grazing. The seedlings (or sowing the seed) A promising technique to technique aroused the interest of between rows of a young crop, involve agroforestry and several farmers, but clearly then allowing the trees to grow multipurpose trees in the requires further study because on with protection from grazing, amelioration of exhausted of the labour costs involved and after the crop has been harvested. croplands has been considered the need to fi t the construction This method would be above. Sometimes in eastern of the pits into the long dry appropriate for a si te of Kenya, however, as in other season (July-September in exhausted cropland producing parts of eastern Africa, the Machakos) when labour is very little crop, allowing it to grazing land within farm available. The Katumani group become a source of browse and boundaries and adjacent to the noted the possibility of growing fodder, or loppings and mulch for protected cropland terraces can trees within the pits, but did not adjacent cropland, for one, two or also be seriously degraded. initiate studies along these lines. more years (Dzowela and These areas are usually denuded Leguminous tree species such Kwesiga 1994), with the at some times of the year due to as Sesbania planted in the expectation of improved crop excessive grazing by farm Katumani pi ts could provide a )ields after the trees ha ve been livestock. On sloping ground means of ameliorating the site removed for fuelwood or sale. the continual denudation for future cropping as the needs Such a method is showing good accentuates the run-off and loss of the farm family expand. promise at a number of of valuable water, and leads Alternatively. the tree prunings experimental sites in Zambia, but eventually to serious soil could be spread on the considerable adaptive research erosion. Researchers at the neighbouring cropland as a and extension are still required. National Dryland Farming source of nutrients and organic The second possible technique Research Centre, Katumani C. The established trees would also requires substantial research (Simiyu et al. 1992) developed a remain a valuable source of and adaptation, but could evolve pitting technique to capture the fodder for farm livestock. The out of research into the potentially lost run-off water in economics of such techniques, in renovation of denuded grazing a contiguous series of micro­ terms of milk and meat lands in eastern Kenya, as catchments or pits, each about production, have been assessed discussed below. 2 m2 in area, constructed down very positively (Lubulwa et al. the slope. The area was 1995).

26 THE STRATEGIC USE from the farm). 1\ioreoveI; Woomer 1995) adopted the term OF INORGANIC knowledge and skill are . integrated nutrient required to obtain a release of management' (lN1Vl). FERTILIZERS TO nutrients from organic sources SUPPLEMENT lViachakos District farmers at the times most by the who have adopted Ei.SE or ORGANIC INPUTS crop (1Vlyers et al. 1994). INNl find that it provides From the work of Stoorvogel To overcome these problems. flexibility in seasons of and colleagues (1993), Smaling a resourceful farmer may uncertain rainfall because a (J 993) and others, the crop lands to supplement local supplies of minimal basal application of of much of sub-Saharan Africa nutrients purchasing and inorganic Nand P (as are being drained of their plant­ applying modest amounts of diammonium phosphate) can be available nutrients during inorganic fertilizers. The applied at maize planting, after intensive cropping, "vith only and economic the organic inputs. Then, after minor inputs of nutrients from potential of this technology the initial nutrients have been outside. The main economicall:y seems attractive for substantial utilised. the young crop depends feasible 'vvays in ',',(hich the areas of nutrient-poor cropland on mineralisation of N from the nutrient drain can be slowed in AEZs 4 and 5 of eastern organic sources until seasonal using methods and inputs Kenya (Keating et al. 1991; prospects become clearer. generated on the f::~rm, with McCown and Keating 1992; Continuing good rainfall on the household or hired labouI~ are Probert et al. 1994). Several growing crop becomes the reviewed above. These organic authors have acknowledged that signal for a late side-dressing of inputs are extremely valuable in the most robust and soluble, quick-acting N fertilizer the medium potential areas. socioeconomicallyattractive (e.g. calcium ammonium nitrate Hm,vever, the materials are technology is to complement some 30 days after planting). A bulky to transport and often, as locally grown resources \vith conditional use of is the case for animal manure. purchased inorganic fertilizer, supplementary N fertilizer in just not available in the rather than aggressively attempt this way offers some advantages quantities required. Farm to replace organic supplies with in economic risk management equipment and labour supply inorganic sources. lVlcCown and (Wafula et al. 1992). are often inadequate for the Keating (1992) use the term The potential for tasks of loading. pruning, 'rerti lizer-a ugmen ted soi I nutrient management in sub­ transporting and enrichment' (FASE) to describe Saharan Africa has been spreading and burying the the combined resources critically reviewed by van materials (especially when the approach. Others (Janssen 1993; Reuler and Prins (1993). These most able-bodied men are absent Swift et al. 1994; Okalebo and authors, while conceding that a

27 substantial lift in food 63% of the planted cotton area, adoption of this technolog); In production can come onl)' from only 1617% of the maize and Kenya, a very positive move applications of externally sorghum areas received been made recently small derived nutrients to cropland, inorganic fertilizer. These data packets of fertilizer. 2-10 kg, are sti 11 place high val ue on IN 0'l. could be somewhat biased now lIyailable in some locations. They advocate optimising the toward largercscale producers Among possible P sources. a use of all possible local sources vvith greater financial resources. material cheaper than of nutrients before importing as they account for less than half superphosphate now available in inorganic fertilizer; pointing out the total consumption of Kenya is the ground rock that the successful introduction fertilizer. phosphate from a natural of fertilizers requir>es a good Government moves to cut deposit at Minjingu in northern infrastructure of traders and su bsid ies and pri vatise the Tanzania. This high grade transport. plus a major effort in distribution systems in many material (30% P) had good farmer education. countries have led to sudden residual availability to crops Results of a survey price rises and local scarcity of when tested on 11 RdeFicient soil Gerner and Harris (1993) of 14 supplies. The great value of near Katumani. M.achakos countries indicate that most of inorganic N fertilizer is that it (Probert and Okalebo 1992). In the fertilizer consumed in sub­ can produce a rapid response in partially (50%) acidulated form Saharan Africa is applied to cash the crop, if it is applied vIe,hen it produced yield responses in crops, e.g. cotton (17%), wheat moisture and other seasonal maize almost equal to the effects (14%), sugarcane (11 and conditions are favourable. Thus of equal amounts of P applied as tobacco but some 24% of to have supplies of the si ngle su perphosphate (the more the total was applied to maize appropriate forms of nutrients, expensive 100% acidulated and 8% to sorghum. \Vhereas in affordable packages when form). nearl,yall the sugarcane and and 'vvhere farmers need them. is toi:k'lCCO recei ved feni lizer and essential for the successful

28 ECONOMIC ASPECTS OF MAINTAINING SOIL FERTILITY

AN l.\lPORTAl':T ASPECT OF THE similar point is made by PI'I',!Cllt alld/lltllre ,I{)cidy, thcre I~' economics of maintaining soil Sanders and colleagues (1995) (/ need/or ifllwi'ati,'c policy fertility is the sustainability of who comment th.n: il1itiati,'c,I. Soil eralioll I;' a farm productivity through the pl'o/J/em ill political economy, III much o/,1[16-Sa/Jarall nutrient-supplying capacity of {/,qrt~'Il//11reJ tbe l'rcakdoH'1l 0/ tbe On the other band. Tiffen and soils. Tandon (995) recently fa/ /0'.1' dyd/em Jm to popu/ation co-workers (1994) strongly defined sustainable agriculture: pl'ed,IIlI'C alld tile (h;'ilppearallc'C 0/ argue that the steady A ,lIl"tainahlc p/"{JcJ{(ctl~J/l ,1]ptCIll the frontier bm'e !lot heell improvement in knowledge and ,Iholltd not jwt draw/rom thc accompanieci hy increa,'cd inpllt in the resource base of farmers rc,IOllrC,'.I, it "houM hm"- a prc­ I'lIl'cha,'e,' to I't1{;IC ,Ioil /ertility, in Machakos cannot simply be p/allned pI'Of'l~I{~m to p/oll.q!, hack Iwtcad, ti'e re,l/tit ba,1 heen ,Iod ascribed to government action, part of the profit" illlo cJc.qradatioll tbroll.qb minin.q the rather it is the resul t of con,lcl"I'ation and illl pra.·cml'nt 0/ ,Ioil for th(~ lIl'ai/able lIutricntJ or individual and village level thl' re,'ourCl' ha,11' to e/lha nee it,f hy plI,lhill,q crop pl'(}()lldion into investments and initiatives.

29 • assess the quantity (erosion) changes in the resource stock ill{J/catol' productil'ity, and a/,!o and quality of soils over and flow. does not decrease of "ll<'tail1ability, "illCl' jallill,q time; (Ehui and Spencer 1993). Ollt pllt 111I:q/.'t illdicate {/ • examine the factors Ehui and Spencer (1993) also deterioration ill the r,',IOIII'CC badl'. determining the supply and suggest a measure of economic DIArict pr(}ductl~1/I 1:1 (,\'amilluJ demand for new land viabili t)\ a static concept which on a pCI' bead and pl'r hedal'(~ (population pressure) and refers to the efficiency with ba,II;I, ad mea,lure,I 0/ lI'elt~lre and possible imbalances; which resources are employed in productivity II'hic/) take into • assess costs to the economy the production process at a account till' ,qnwth of th,~ due to resource degradation; given time. A new production poplllatioll and the il1cl'('a,'e ill • design incentive packages to system can be said to be more IJt:ltl'ict area. Thl:' cl.1apta Improve resource economically efficient than an ti1cre/ore /,IYwide,' Olll' main management. existing one if its total factor (l'{del1ce jor all il1Crea,fe ill Ehui and Spencer (1993) productivity is greater at a a,qriclIl t lira 1 Pl'iJdlldil'l'ty ",I.,il'h suggest a measure of given point in time. A key tll1d ,fll/J.ltalltia/ly oil/paced , sustainabi li ty based on the component in constructing populatio/l ,qlYlil'tl. . 'intertem poral total factor either the ITFP (sustainability) In this analysis Tiffen et al. productivity' (ITFP) and a index or the economic viability (1994) made two main errors growth accounting framework. total factor productivity index which throw doubt on their ITFP is defined in terms of the is the inclusion of all inputs and conclusions about increased productive capacit:r of the all costs including the unpriced intertemporal total factor system over time. For a contribution from or impacts on productivity in Machakos. sustai nable this natural resources. Analyses that productive capacity includes the excl ude these un priced factors 61) IIlCOIMIAC:llcy ill the ci1()ice unpriced contributions from are flawed. 4 rej'el'mce pert'od" natural resources and their Tiffen and colleagues (1994. unpriced production flows. Tiffen et al. (1994, p. 94) state chapter 6) state: ITFP is an appropriate measure that to compare the value of of sustainability as it addresses /j.'Jricllltura/ollt put per 1''''','011 I:' output per head and per hectare the question of intertemporal all important lIIea,'lIre 0/ we/j~lrc over time, they converted all change in the productivity of a ill allY eCiJlwmy II'her(~ afll'l~:ltltllre production to its 1957 value in s)'stem between two or more I:' t/.l£ main occupatio/l and wl'ere maize. This means that for each periods. A system is sustainable locally/}I'oll't1jood I:' thc main year in their analysis. they undertake the following if the associated ITFP index, l"uI:' olj~lIllily Ililtritioll, Out put analysis: which incorpora tes and values pCI' /gctal'c t:, tIll important Group J: were si tes which had been under annual cultivation for 40-60 (1) years or more without any known additions of In the above equation; other commodities for both 1977 fertilizers and little P is the price of commodity j and 1987. making it impossible to manunng. where j L 2, 3, ... n; compare the changes in value of The results are summarized output 1961 and 1987. 0t'is the quantitvat time t of in Table 3. -.j ~ More importantly; the big commodi ty j; Tiffen et al. (1994) conclude increase in output between 1961 that there is a definite trend of t takes values for these years: and 1977 could be due to fertility decline at every site 1930, 1967, 1961, 1977 and nothing more than inflation in from Group I to Group 3 sites. 1987 the prices. Yet in their Chapter 6. where P _-, /P /9-- ' gives the terms I9)/d ' )/,Ollll Z,-' they construct sustainability of' trade between maize and (IJjllladeqllate empl.?l7,fl:1 Oil indices for Machakos. no commodity j. t/1e lUlprt'ced factor,1 attempt is made to correct for In the Tiffen et al. A more important omission in this obvious soil mining impact. (1994) seem to carry ou t the their analysis was inadequate These data and other evidence above analysis for 1930. 1957 emphasis on soil fertility in their presented earlier- on the impact and 1961. The index in equation construction of intertemporal cultivation and cropping on I is a modification of a well­ sustainability indices. They report the fertility of soils in Machakos known Laspeyres quantity (1994. Cha pter 8) results of their are grounds for serious concerns index (Hirshleifer 1980). It analyses of soil samples from the about sustainability of crop expresses all other outputs in following three categories of sites production there. U I1til an terms of 1957 maize values and in Kilungu. Machakos: analysis is completed which would provide an estimate as to Grollp 1: were sites which had take~ into account and explicitly whether quantities have not been cultivated for incorporates estimates of the increased 'on the average over 60 years and are cost of soil mining from the between 1\\'0 time periods. under natural value of output in Machakos Howevel; Tiffen et al. (1994) vegetation; District, the overoptimistic switch from equation I when it Group 2: were sites which had picture painted in Chapter 6 of comes to analysing output for been fallow for 20 years Tiffen et al. (1994) has to be 1977 and 1987. The,Y resort to or more and are interpreted with caution. current prices 9f maize and currently used as grazing land;

31 Table 5. Soil fertihty Cball!l,-,,1 at KiltlIlglI) 111aciuzkal.

Property Group I means Grot! p 2 means Group 3 means

-~--~--~-~~~--~-.. ---~~-~--~~~~;~.~.~.--~--~~--.

Potassium (meOfo) 0.56 0.40 0.29 Calc i UIll (Ill e%) 8.70 2.40 l.ID ,Vlagnesiulll (mc%) 3.40 IAO 0.90 Phosphorus (ppm) 23.00 14.00 13.00 Nitrogen (%) 0.18 O.ll Carix111 (')la) 2.49 1.25 0.74

The problem of unpr'iced in a context where farmers do then soils m ust be considered as impacts associated with soil not tradi tionally invest in soi I an exhaustible reSOUI'Ce. The mining is especially important fertility enhancing technologies possibility of irreversibility in the con tex t of 1Vlachakos can increase the extent of soil means that a higher cost should because the period covered by mining (Bennison and Evans be charged against soil TifFen et al. (1994) witnessed the 1968). degradation than just the introduction of higher ;yielding Sanders et al. (I 995) argue estimated relation bet\\'een yield cultivars of maize. sorghum and that if soil mining can lead to decline and soil degradation. other crops. Their introduction irreversible damage to soils,

32 FARMER RESPONSES TO NEW SOIL MANAGEMENT TECHNOLOGY

SOIL FERTILITY RESEA.RCH WILL Interest in the use of improving soil and water have an impact on soil fertility inorganic fertilizers is graduall,y management, which place high and productivity in East AFrica increasing in Machakos and the demands on available labour but when farmers adopt the neighbouring districts of Kitui do not necessarily require cash results of the research. \Vithout and Embu. However. for their implementation. adoption. the Financial and other Muhammad studied a Mulching is not used because resources invested in soil sample of 94 farm households in the most readily available Fertility-enhancing research eastern and fou nd that materials, maize stover or other have a negative return. Table 4 between 1980 and 1990 the rate crop residues, are valuable dry summarises literature on the of increase in adoption of season feed For livestock. adoption rates For fertilizers in Fertilizers was only selected areas of thl'ee countries. 1.6% per year. Rukandema et al. EXAMPLES OF High levels of adoption of (J 981) and ;\luhammad and FARMERS' inorganic fertilizers have been Parton (1992) estimated the EXPERIENCE reported in parts of Malawi rates of adoption levels For with favourable environments various technologies in eastern In his survey of the use of for growing hybrid maize. Kenya (Table 5). Compared with inorganic Fertilizers, Malav,rian growers of local other technologies such as Muhammad (1996) found that maize varieties use Fertilizers timely planting and use of some fiumers are at least more modestly. In ;vlachakos, the improved seed, the use of interested in trying new levels of adoption observed are inorganic fertilizers has methods of soil Fertility m uch lowel~ as m ight be progressed least along the improvement. The survey does expected considering the adoption path. not show. however. how much unpredictability of rainfall and Innovations requiring smaller Fertilizer those continue higher levels of risk. The final direct cash outlays (organic to use after their first example, from a semi-arid zone fertilizers, terracing and early experiments. The following of Zimbabwe, shows almost zero planting) are the most widely accounts summarise briefly the adoption of fertilizers on adopted. These comprise the experiences of four households sorghum. poor person's technology and a mwethya group over a GVluhammad and Parton 1992). number of years of Terracing and boma man ure are familiarisation \'\·ith Fertilizer complementary techniques for technolog)" Three of the farmers

33 Table 4. A cOmpal'l~f(}1l of rate'} of adoptioll of lllol:qatu'c/;'rtift'zerdj;", would have to be classified as t bra A/i'lea Il c(lulltrie,f, 'above average' in their

...... , .. ~... ~.-~~-~.-.-...... - ...... -~-... . \.villingness to invest in new Countrv & Rate of adoption Source Crop of inorgan ic management methods. Family fel't i1izer's (%1) 'C' and the members of the Miliawi rnwethya group would, by Gl'Owcrs of local contl'ast. be subject to all the lnaize varieties [i0 Smale et aL 1992 socioeconomic constraints Growen; of hybrid maizc 87 Small' et aL 1992 illustrated in Figures 2 and 3. Kcnya (l\1achakos) A summary of family l\'l.aizc 18 l\'l.uhammacl & Parton 1992 characteristics and experiences l\hize 16 "\luhammad 1996 is given in Table 6. Farm sizes Zimbabwe all lie in the 5-10 ha range. The Sorghum Low close to zero Chiduza ct al. 1992 soils in cases A and C would probably be similar if they had been in the same way Table 5. TbI' rate,1 0/ tl{)optioll of,lodFrtdity-mbaIlCl'Il.9 tecbn(}ll~ql'e" (sandy loam alisols); those in and tl'l'raclllg ill ,,11adwko,1 am) [(itut lJt~lt/,ld

Adopt Cl'S as proportion of all farms The farm in case D has a steeper topography. making control of Date 1980" 1990b water loss I'll n-off more Use of homa manure important. but this is (organic fCI,tilizcn;) 0,68 0,8,3 Use of N-fixing legumes not estimated 0,22c compensated by a slightly higher Use of inorganic N-fertilizcrs (W8 0,18 average rainfall than the other Mulching D. DO 0.00 cases. Terracing not est i mated O]8C Family A. This is an example

34 Table 6. Somc c.Yamp/c,} ofjarmcr,; C.l'!'C/'l·C/lCC ill "oil jcrtilt'ty maIW/JCIJ/Cllt.

Family i\ Family B FamilyC FamilyD Kivoto Mwethya Group ------Technologies BOTllKangundo, (AEZ4) Machakos Kitui District Machakos near Kangundo, Machakos District Machakos Soil type Sandy loam, low in Sandy clay loam, Sandy loam with The farm is on a Badly eroded soils, with organic matter. low in organic low soil organic steep site (16-20% low and declining soil matter~ but with carbon (0.4%); N, slope), badly eroded fertility Much water good P status. e and K all through previous lost through run-off. acutely deficient. denudation and abuse. Sandy clay loam, low in organic matter.

COl/filiI/er) m'l't' !,"!!I'

35 Table 6. COlltl'IlIlCd

Run;ly A Family B FamilyC Famil.v 0 Kivoto ;\lwt:thya Group

Source of A government Not stated, but Has had contact Head of the f~unily The driver/assistant to a information instructiDn course has had contact with researchers was a driver/assistant research grou p (sce about the on the correct liSt: with researchers for several years. to agricultural !~"ullily D) helped start technology of fertilizers. and extension. t'esearchcrs, and so this cooperativc, wOl'king became inren'sted with tilE' local in thE' problems of' COm!1Hlnit,Y. H., !lOW soil fE'J'tility helps to coordinate its nlanagen1ent. activies, teaching from his own expet'ience . Crops and Jvlaize, legumt:" ,'vlaize. legumes. tvlaize with ver.v tviaize. legumes .vlaize, ot her rood crops. livestock some citrus and some cash crops. and othE'r domestic and cattle pl'oduced dry season cash 1O~ l:l cattle. ptgeon food crops, a crop,':;! e.g. 101natoes few goats pea). citrus trees few small cattle and bt'assicas (using the limited supply of manure)

maize, and then was joi ned by integral part of \vhole-farm Kitui District. The f~lInily head her mother-in-law in producing management. All this was is retired from the army and crops such as tomatoes far sale. achieved without any outside therefore has some pension. This This cashflow enabled the family financing. The soil is lairly allows occasional purchases of to make further purchases of typical of the surrounding fertilizer or manure but, as fertilizel~ and a small shop was valleys - a sandy loam quite money is scarce, these purchases set up to sell produce in the low in organic matter. From the are made only for specific local village. The enterprise beginning, however. the family reasons. The farm layout is grey" V'.'ithin the family to the ,vas willing to invest in contoured around the hill with stage when a dam could be education and was enthusiastic the homestead and the cattle constructed below the about experimentation. In this boma on the hilltop, surrounded homestead, trapping runoff and respect, it seems to differ from by terraced cropland. This facilitating irrigation of plots of its neighbours who have done facilitates the transport and brassicas and dry season little to copy its methods even even distribution of manure tomatoes. though the larm is obviously from the boma to various Now, fertilizer use, together well managed and prosperous. terraces. The boma is in a well­ with manure application. Family B. This example drained position so that manure composting and a generally high shows moderately good can be removed 01' stored more srandard of farming. is an management in iYlutonguni, eFficiently and with less

36 nutrient loss than would be the family. who eventually will be were observed near the boma case in a wet or muddy location able to establish his own site where effluent occasionally (Probert et al. 1992). The 10 to household there. runs onto the cropland after 12 cattle and few goats graze in Family C. This family has an heavy rainfalL and close to trees it neighbouring valley and so impoverished farm where the of Acacia forti/i., where leaf and bring nutrients to the cropland. land is almost exhausted from pod litter accumulate (compare Phosphorus status of' the soil is continual cropping and very Belsky et al. 1989). There is also moderately good (22 ppm by the low nutrient inputs. The soil is an old disused boma site, where Olsen method), which enables a sandy loam alisol near residual fertility has persisted, legumes to be grown Wamunyu, Machakos. Soil that still produces good maize. successFully around the terraces. organic carbon is very low The family group is quite Some crop residues are (0.4%). Nitrogen and P are both large with about 15 dependent incorporated in the soil and tree acutely deficient; available K is children and all the men except plantings are made also low. Probably the soil one, who is not physically progressively around the nutrient resources have always robust, away working or margins. It seems that the family been 10\\; but have diminished looking for \\'ork off-farm. has been able through hard work further during a long period of Since there are only four or five and good thrifty management cropping. Experiments on the small cattle, the manure supply with just occasional outside site have shown marked is meagre. Off-farm income and purchases, to be self-sufficient responses to Nand P fertilizers. cash flow are insufficient to in staple foods, plus making lYlaize yields increased from purchase external inputs. The some cash sales of legume grain. 600 to 4000 kg/ha wi th only crop that does reasonably It is probably too early to judge applications of Nand P. and well is pigeon pea because of its that the soil is in a sustainable cowpea yields increased from extended root system, allowing equilibrium, but at least its 1000 to 2000 kglha, with P plants to exploit the limited fertility decline is being Nlaize yields on the farm are supplies of soil P. and its N­ controlled compared with many generally very low and soil fixing ability. The limited other farms. The family ,vas able fertility urgently needs supply of manure is currently to purchase additional land on a improvement. Legumes grO'.v used to establish ci trus trees. neighbouring degraded si te and somewhat better than cereals, Both equipment and draught to te!Tace it with hired labour in depending on the P status in power of the cattle are minimal. 1990. It then obtained sufficient their exact location, since P This family is struggling to find manure to improve the availability varies greatly both a way out of the poverty spiral. diminished nutrient status of within one terrace and among If appropriate techniques can be this new site. This is a main terraces. Good maize .yields found, agroforestry on parts of project for the eldest son of the the farm could help restore

37 f'ertilit)~ but an input of' fertilizers. With this knowledge f~tctor in building up the externally derived nutrients (at of possible techniques, suitably investment. least P and K) also seems modified in scope to fit the The t:1.mily has deep roots in essential for sustainability. household budget, the farmer the local communit• ." and Family D. This farm is in experimented with Nand NP knowledge of its success has Kakuyuni Location near fel·tilizers, appreciated their permeated to the extended Kangundo, lVlachakos. In compatibility 'with his other f~ll11ily and neighbours. The contrast to Eunily C, this small limited nutrient input resources family has held field filmily of only two adults and of manure from a few cattle, discussions and demonstrations one teenage chi Id demonstrates composts, ash and leaf litter. He with its neighbours, and this has what can be achieved to build therefore developed a system of helped the formation of a local up farm productivity in an IN;y\ (or E\SE) to improve the Kivoto mwethya (self-help) erratic rainfall and depleted soil fertility of his land. The rather group whose activities are environment similar to those steep farm site (16-20% slopes) described below. Through the already described, with a modest had become badly eroded mwethya group, the local cash income from off-f::u'm through previous denudation Salvation Army church, the employment and some and abuse, so that terracing to schools and the local political educational experience for the prevent further erosion was a committees, this rural household head. priority Nutrient inputs were community has been able to then used to improve fertility The most critical factor is broadcast messages on on the reclaimed terraces. The probably that the household head sustainable land management. investments have been has been able. as part of his and so become a valuable successful through the combined work as a driver and assistant, education efforts of the family, with some to travel around Kenya. Kivoto mwethya group. This hired help. The family S,"IY now particularly ;Y\achakos and is a cooperative self-help group that they never have to buy Kitui Districts, and talk with of some 120 farmers near food. and that purchases of agricultural researchers about Kangundo, i\lachakos District, fertilizer have been far more the problems of declining soil organised by the local profitable than being dependent fertility and Imv crop yields and community and started in 1990. on outside grain purchases. The their possible solutions. \Vhile The farmers are mainly women crops treated with combined working on a number of onO. because the younger men look organic and inorganic nutrients farm experiments, he was able 1'01' work elsewhere to maintain look heal th.)~ and the system now to and appreciate the a cashflow. leaving the women seems sustainable. IIowever. it effects of better management, in charge of day-to-day must be acknowledged that of1'­ including the application of management. The origins of the f~lrm income has been a critical group lie in the general poverty

38 of the area; soils have been badly Recent activities have have gradually responded more eroded and soil fertility has concentrated on soil enthusiasticall}, The group deteriorated. Seasonal rainfall is conservation and revegetation leaders are continually uncertain and spasmodic run­ of denuded grazing land, but instructing groups in better off has been a major loss of better crop management and agronomic practices. from potential soil moisture. There promoting correct fertilizer use planting and fertilizer use to are recurrent food shortages and are also priorities. Because correct use of insecticides. hardshi ps. ferti lizer is now expensi VI". and When the group obtained The primary aim of the group better hand tools were badly financial assistance from an is as enunciated by the group needed by the group, NCO, its first priority was to leaders, the promotion of fundraising has been a priority purchase new tools and practical and positive attitudes Despite this the group's wheelbarrows to transport to development in the achievements are impressive. manure from the bomas to the community'. :Viore specific The group leaders have found terraced croplands. The farmers agricultural aims are to protect that it takes much patient are developing a balanced the soil from erosion and discussion to convince fanners approach using organic inputs increase the uptake of nutrients to make any changes in their (manure and compost) together by crops. This involves practices (ct'. Liniger 1993). with supplementary inorganic minimising water loss through Farmers in the Kivoto m\vethya fertilizers. They are starting to run-off. thus also preventing group have shown suspicion of re-evaluate their limited soil loss, and finding and declared disappointment supplies of manure. using mixed economicall.y feasible ways of about the value of fertilizers. composts and mulches of crop improving the soil nutrient They reported damage to young residues or tree loppings as the supply by experimenting with plan ts by fertilizer. and poor means of extending the combinations of compost, results. Questioning revealed effectiveness of their organic manure and inorganic fertilizer. widespread ignorance and poor inputs, and minimising cash Longer-term aims include techniques of fertilizer outlay on comparatively growing more animal fodder by application. such as bad timing expensive fertilizer: grass plantings on the contour and use of the wrong chemical Greater food security has banks and wherever else is forms of fertilize!; e.g. calcium been achieved for the whole possible consistent with the soil ammonium nitrate for basal community. The work of this conservation objectives. By applications close to the seed, mwethya group is having a obtaining better- grade cattle. and diammonium phosphate for beneficial effect on the the group aims to promote milk late surface applications. community of its sub-Location, production both for home Nevertheless, \vith education and word is spreading to consumption and cash sale. and demonstration the farmers surrounding sub-Locations. The

39 Location Chief (Government TaMe 7. RlctO!',/ fimt might e,vplm:1l fi1e (It/l~'/'ill~q /"I'e{,1 0/ adoptioll appointee) is interested in the of ,foil fertility-ellha Ilcing techll%gied. ---_._--_.... work of the group and Findings of l\lethod publicising it as a good example l'vluhammad (1996) of what can be achieved. The a District Commissioner is aware 2 The cost of acquiring infi.)rmation alxmt ? a of the project and is reported to t he technology be t~lvourably impressed. 3 The cost of in! roducing and using the ? a Clearly the success of the technology com pared to benefits from existing enterprises group depends on the 4 Attitude to risk b continuing enthusiasm, 5 Farm size (average size 7. 2 ha) and resoUl'Ce knowledge and leadership of a endowment of hnllling household ns c few individuals on its 6 HOllsehold demographic characterist ics: c organising committee. The 6a . Ilollsehold size IlS c committee reports that 6b- Age IlS c government extension services 6c - Gender ""ere having no impact on the 6d Level of formal education IlS c farmers before the mwethya 6~· Nature of non-brill or occupation liS c group's activities became 7 Availability and quality of farm inputs IlS c organised. 8 The quality and adequacy of exten~ion serviccs '1'1

! FtlnUt!,,1 "re to fVl>/ac/Of' WHY IS PROMISING ?? Then' wen' {h/J~~r{'Il{'t',r bdwffll tlth, /~lrllll'r,; cl/ att'{J IItldt'r,!/ a Il(JiIl.'! 1.:/1 he ('.r/en/lOIl Ji/(·,i,jil/Jt~ (flU) NEW TECHNOLOGY t~ll'llli:r /wtlcti{'t·. S'!al{:I/t'c(lIl.v,,(qlll~f{"Ctl!l1 lac/tlr (l()llpft~Jfl. ,lion' !ban 1(Jf}b f!/lbc/arllll"'.1 arc to ADOPTED SO SLOWLY? lVluhammad (1996) investigated possible bctors that could a: Li!(ratllre l'l'l'i(ll: explain differing levels of h: F-lIcitf') IIliliIY/II!lcl';'Ib' anrillllllb"lIwliml n:.k 11r''.'jf"fl/l//JIill.'l' adoption of soil fertility­ c,' RCOl1o/l{(:lric flllfl(V-1l:1 (~r (Ia/ll //'(1111 tl enhancing technologies. i\ hinllry c/im't't' IIUJ(JC/ il'll,J u,led ill the summary of the factors investigated and conclusions as to their significance are compiled in Table 7.

40 The results of Muhammad addition, ,vomen generally have important facto!; and (1996) suggest that the most power in the rural government extension services i m portan t ex planatory variablt.,s community and therefore less are having only a minor impact. for adopting soil fertility­ access to extension advice and Also, farmers who appreciate enhancing technologies are credit. the need for soil ferti li ty gender of the farmer and the Farm households sometimes improvement but have little farmer's attitude to risk. The have to buy food during the ready cash may still regard the finding that male-headed hunger period (September to education of Cl child, or other households had a higher January) after the long dry family needs, as of higher probability of adopting high-cost season (Rukandema 1984). priority than purchasing soil f'ertilit:y-enhancing September, October and fertilizers. There are several technologies needs further Novem ber are periods of very other possible reasons: investigation. It is possible that busy activity - land (i) Fertilizer is often not farmer gender is correlated with preparation. planting and available locally in the another variable such as farm weeding. People in poor families required amounts at the size, level of formal education. are at their physically start of a good, wet seasonal nature of non-farm occupation, when they need most energy for onset. 1Vloreover. farmers' or availability and quality of field tasks. Such factors reduce credit and cash resources are farm inputs. If these variables adoption rates for new soil and often Jaw at the start of a are correlated with gender then fertilizer technology. ne,\, planting season. an analysis excluding gender as If research resu Its indicate so (ii) Because of unstable an explanatory variable could clearly that modest, strategic fertilizer markets in East change the level of significance use of inorganic fertilizers is a Africa, particularly now of these other factors. sound and profitable way of that privatisation and In Machakos District some suppl}1ng nutrients to crops termination of Government 50% of the are managed over most of Machakos District. subsidies are proceeding, by women (Rukandema 1984). could there other reasons prices can suddenly increase Growing numbers of households why many farmers are so markedly; e.g. prices of N are headed by women for most hesitant to adopt this technique? fertilizer in eastern Kenya of the year, due to male From experiences recounted in increased 3-4-fold between migration seeking off-farm the previous section, 1990 and 1993. rarmers have ,\'ork. Nevertheless, men may particularly those of the Kivoto also reported variations in retain the major mwethya group, poor farmer fertilizer quality and making responsibility for land education on soil fertility incorrect labelling, e.g. use and crop planning, even management appears to be an ground rock phosphate when absent (Douglas 1993). In

41 labelled as triple (v) Some farmers do not WHAT CROP YIELDS superphosphate. appreciate the CAN MACHAKOS (iii)The extra labour for complementary values of SMALL HOLDERS applying lx~sal fertilizer at organic sources of nutrients, planting is required in a as in manure and composts, ACHIEVE WITH period of maximum farm and of inorganic sources. FERTILIZERS? activity (W,ddington 1994) Inorganic N, especially the Research shows that, with a high when there is a strong nitrate form. is standard of crop husbandry in disincentive for involvement immmediatelyavailable to AEZ 4. applications of N 40-80 in further activities. the crop. but the organic C kg!ha to K-depleted soil should (iv) rarmers with low cash supplied in boma manure result in long-term average resources Ii ke to see thei r has indispensable beneficial maize yields of about 2.8 t!ha crops well established and effects on soil structure, (Keating et al. 1991; McCown be able to assess seasonal water infiltration and soil and Keating 1992; Okalebo et rainfall prospects before cation exchange. Whereas al. 1996) compared with average investing in fertilizer. \Vhen the K concentration of boma yields of less than 1.0 t!ha good establishment and soil manure may be so low that currently obtained by most moisture have been assured. it is not an effective source farmers. In this case, each kg of e.g. 30 days after crop of plant-available N, it may fel,tilizer N produces more than emergence, N fertilizer may still be a valuable source of 20 kg grain, which would be be applied. This strategy of P (Mobvunye 1980). quite profitable even when the !'esponse farming for (vi) BC'cause individual farmers' purchase price of each kg of reducing climatic and resources, farming systems fC'rtilizer N is 10 times the cost economic risks is quite and climatic environments of 1 of maize (Probert et al. appropriate for side­ vary wide],); advice on the 1994 ). applications of N (Stewart uses of inorganic ferti lizers Probert and colleagues (1994) and I~ught 1984; Wafula et for each t~1rm community also examined the most aL 1992). I Iowever; unless needs to be carefu lly attractive options 1'01' risk-averse any existing soil P tailored after on-tarm farmers in climatically less­ deficiency is corrected by an research in collaboration favoured locations. using a crop early application of readily with an appropriate group growth simulation model and available p, the effectiveness of fanners (Waddington and long-term records of daily of late-applied N is likely to Ransom 1995) . rainfall. In almost every location be reduced. studied these researchers concluded that, on N-depleted

42 soils, application of some N D'lctors are known to reduce the successfu I wi th the hew fertilizer (albeit only N 10 kg/hi expected crop response to technology' that research is in some drier locations) would applied nutrients (Keating et al. advocating. They can then be be an attractive option for 1992, Waddington 1994. and convinced. as other farmer farmers prepared to adjust their many others). Such examples considered, to planting density and moisture considerations might be continue and to recommend the conservation techniques expected to result in many ideas to their neighours. accordingl:y. farmers achieving only 50~70% Secondl,)!, because investment in This research assumes a good of the .vield found by the fertilizer is cash-demandi ng. in a standard of crop management. It researcher, even when the cash-scarce economy it is most has not so f:,u' made allowances relevant experiments were logically used as part of an for the many contingencies conducted on-farm ""irh farmer overall strategy of integrated small-scale resource-poor management. but with an all­ nutrient management to farmers may incur, e.g. important addition of a few complement nutrients available unavoidable delays in ploughing critical outside inputs such as from home-produced organic and planting due to meagre insecticide. and cash for a little sources. By Jx,tlancing these equipment and low draught extra labour to ensure timely varied inputs. a good farm power, or delays in weeding due operations. manager can bring down the to shortages of family laboUl; or To summarise. two important average unit cost of total an unusually severe attack of points emerge. Firstl.';" farmers nutrients applied and make stalk-borer which cannot be require et certain minimum level most effect of the limited labour controlled before it substantially of resources, knowledge and su pplies of the household. damages the crop. All these management ski lis to be

43 THE NEED FOR ADAPTIVE ON-FARM RESEARCH AND EXTENSION

RE\,IEWLKG THE EXPER!E~CES OF 1991). \Vhat can be done about There are several options and farmers shows ho\\' difficult it this si t uation? decisions Facing the small-scale becomes For poor households to It is now generally farmer in a 'medium potential' adopt new technology involving appreciated that the problem area on the problem of some cash outlay, and so extmct must be approached from the maintaining soil fel"tilit): themselves from the 'poverty fanner's viewpoint, whereas for Figure 5 shows some of the tmp'. ror some tamilies, many years the temptation has decisions to be made in improvement of food security been for the researcher to look integrated nutrient and financial status is virtually from a much more general management on a typical mixed impossible without outside help. viewpoint. Participation by the farm, with a !"Otation of crops This highlights the to fanner in the research and and some livestock in a involve farmers in better ways eval uation process from the climatically risky area of eastern of maintaining soil fertili!); very beginning (as represented Africa. before they descend too far into in Figure 4) is essential. the'trap'. Extension services in most sub-Saharan countries are Phase IV: Farmer evaluation Phase I: Diagnosis • evaluation and adoption • soil fertilitv constraints underfunded, and arc provided of managemcnt options • resource a~'ailabilitv by undertrained and for improving soil f'l>rtility • rapid rural apprais.~1 on-fium participatory underequipped staff. Yet wide research Farmer knowledge experience shows that, without ~ c.g.indigenous knowledge ------... major extension effort, widespread adoption of a new Bes;:~luti~ C~em deiW~ 101'. man~lg"~H,~:~t ) e,g, sod lertrli~:~" ') technique is unlikely to occur. ofsOllleltlll~ _-...... ______(~ even though it has been well ----""'--- ~ential solutio~...... -~ for im proving soil checked-out by on-f~H'm research fertility (Tripp 1991). That the linkage Phase HI: Adapting/testing Phase II: Seeking solutions between national agricultural • on-farm research biological characterisation • on-station t'f"search of resoll rcps and svstem research and the extension arm nutrient flows . is often too weak is also widely acknowledged (Tripp 1991; Low Figure 4. The farlllel,f,ad.'-t(l~/ilrlller parad<'JlII applL"ed tOJOIlkrtility et al. 1991; Merrill-Sands et al. /,;,Iearc/.] (S"'Lj! et al. /991).

44 HOCSEHOLD RESOURCES1

MANAGEMENT LAND. LABOUR CASH (or credit) DECISIONS 1 1 Animals Trees Crops ~ ...... - Fertilizer (rotations) (draught, (farm (inorganic r products) -] plantings) 1 (fodder) 1 (fodder) 1 , 1 Treatment Residues .\LlI1l1re2 L Prunings (1') (N) (!"f'"Il!' ,,/l{! and tmn'/¥}r/ 1111'11/,') Ash Compost , 1 --r------" 1/1 Application 1'v1ethod ;\llllch l -.. IneorpOlatioll Basal Late (/11/],1/11' 1111'11/,') (sid e-appl n.) , .­ -'" .. Timing Before At 1\t first Depends on the planting planting weeding rainf,tIl pattern+

Ratcs of application3 Various combinations of manure and fertilizers are possible to produce: (l!/htl pCI' crop) > 1000 organic C, > 40 mineral N, 5-10 inorganic I' (er. Janssen 1994; et al \994)

F(qure 5. !llailltainillg doilfertilt"ty in a typical /11 achakod mi;\.'edf~lrming dY'tem: dome p()ddlNe management choiced and illteracti(lfhl (t1,I['ng inlegratuJ Illltrient manapemclll) iV(J/e,1

J II tl"nll'~flria mi'\'l"'(ljilrmiu,q <1.tptetll.

2 "let bad ,,/.1/0Fllfft' l~' !lUIJlIU'C qUilHly;

+ re. '1',,,.,,, jarm/II!1 may /]e {(.let) (fI(~·II.J{1II011,' tujutiliuT tlI'P/",tlti"w, !'Ilte.' IIlld Ilm/lIl" tljk!' cO/h,/(ierill," tbe (ial e

(~f,'efl£fiJIlfzl rain OIMct fI!ld farfy,;t?il,l(maf pro,1/h'ct,lj.

45 Such a matrix of In a recent paper. Pingali and then be the source of expertise managemen t possi bi li ties is colleagues (in press) discuss the for other farmers in the same bewildering to both farmers and hlctors involved in the location or farming This extension agents. Tiffen et al. successful adoption by Asian Asian model might not be (1994, p. 276 and elsewhere) rice farmers 01' more efficient appropriate for all farmers in suggest that the problem of soil nutrient management eastern Kenya, but the exam pie fertility maintenance will techniques. They emphasise that discussed of the Kivoto gradually be solved by farmers existing blanket mV\'ethya group, shows that it in .\lachakos, with only a recommendations for fertilizer can be adapted to work here modest amollnt of outside help. applications shot! Id no longer be too. Other examples of From the above considerations used, if greater fertilizer successFul m wethya acti vi ties and experience so far; it is efficency is to be achieved. Thus across Kenya (Cheatle and difFicult to believe sllch a the challenge For future Njoroge 1993) shO"v'll that the proposition. The problem of extension services becomes how expertise-sharing model could integrated nutrient to transfer knowledge and have much merit. management. based on few decision-making skills to Even in Kenyan high available resources, is too brmers, rather than make potential areas such as Kisii, challenging to be resolved generalised recommendations. decl i ni ng soi I ferti I i ty is a effectively and quickly by This approach seems to be true looming problem, despite high farmers unless they receive of eastern Africa too initial fertility (SmaJing 1993). well-informed outside help 111 (\Vaddington and Ransom 1995), \Vith competing demands, the forms of on-filrm research, though perhaps at a different across the countr}\ the lower education, extension and credit level of sophistication. An potential areas in AEZs 4 and 5 facilities. Delay in tackling the important component is to might receive lower priority in soil fertility problem creates understand the incentives that the allocation of government greater intractability and allov\'s would cause farmers to be funds lor agricultural soil degradation to continue. interested in acquiring and extension. Because of the large iyloreovel~ the extension advice using technologies for better areas suffering fertility decline will have to be supplied in the nutrient management. Pingali thl-ough eastern Africa, and the form of options on management et al. stress that. for successful necessari 1.'1' slow rates of decisions aimed at ually adoption, communication of adoption of' changes in soil upgrading soil nutrient status extension messages must be in management, it is urgent that and yield sustainabilit); which familiar terms and best done on efforts are made to accelerate the household can consider and a farmer-to-farmer level. A few the process. The more desperate choose (.\'lcCown and Keating progressive farmers will acquire a farming household becomes, 1992; Waddington 1994). the ne,,\' management skills, and i.e. the deeper it descends into

46 the poverty spiral or into CAN SIMULATION profitable long-term option far drought, the shorter can the MODELLING OF CROP risk-averse farmers growing planning horizon of the farmer maize in all AEZs, on N­ RESPONSES HELP? be. At these later stages of depleted soils similar to those desperation, the household will In view of the many variables, assumed in their model. Low have little thought for long-term the interactions of possible maize plant populations were conservation of soil resources, decisions in the mixed farming optimal, 1.1 up to 4.4 plants/m2, but will exploit remaining systems of medium potential and additional N advocated by resources for whatever they will areas, and the var'y1ng the simulations varied 10 to 80 yield quickly. viewpoints of different farm kg Nlha, depending on location. Making an impact will households to decisions, Profitability of N fertilizer use require carefully designed on­ sympathy with both farmers and was generally better in the farm research and extension, extension advisors is possible. short rains season than the plus emphasis on training The task is formidable. long. The farecasts of optimum extension agents and on However; recent developments N requirements decreased education and demonstration to in crop growth modelling bring from AEZ 2 (1100 mm pa create awareness of all the potential help in the formulation rainfall) where it was possibilities (Low et al. 1991). of best soil management N 40-80 kglha, through to AEZ 5 Opportunities vary with decisions (Carberry 1994; (500-600 mm/year), where it location. In AEZ 5, for instance, Keating et al. 1994). was N 10-40 kglha. sustainable soil management A good exam pie of possi ble Several points should be options will logically lie toward development was shown by remembered. Firstl}\ these are organic inputs because livestock Probert and co-workers (1994). forecasts of economic will remain an important part These authors used daily rainfall attractiveness in the long-term, of the farming system, and the records (collected over 25-60 i.e. there will be some seasons climatic risks for cropping are years) for seven locations in when crop failure will occur. In greater than in AEZ 4. In AEZs Machakos and Kitui Districts, AEZ 5, these will be around 3 and 4, emphasis shifts toward together with assumed soil 20-30% of long rains seasons including the strategic use of characteristics of a poor acrisol and about 10% of short rains inorganic Nand P fertilizers in (0.4% organic C and 82 mm seasons. For some, N applied in INM because of better crop total available moisture the drought season may be response prospects and a capacity) or; alternativel}; a largely recoverable in the next sparser supply of organic better luvisol (1.1% organic C, season (Bennison and Evans manures. 175 mm available moisture). 1968). As mentioned alread}\ They concluded that the farmers in AEZ 5, where addition of fertilizer N was a climatic risk is high, probably

47

,- prefer to rely whenever possible was felt that better focusing of Low and colleagues (1991) on cheaper organic inputs to the research and closer examined the impact of 53 on­ supply their crop N needs. collaboration wi th farmers and f~lI'In research initiatives in Su pply of boma man u re is likely with extension staff are much southern Africa. They list some to be better here than in AEZ 4 needed. The experiences of this of the f~l.ctors Found to have and, because population movement, especially in li In i ted the i m pact of these pressure is lower than in Zambia. Zimbabwe and ;V1alawi. initiatives on farming practices: western :Vlachakos, the potential have been the subject of several (i) the poor quality of the OFR use of'short-term fallows of reports associated with including superficial planted N-fixing trees, e.g. Cr;VL\YYT Loweta1.1991; diagnosis. poor Sesbania (Sanchez 1995), shall Id Tri pp 1992; Wldd i ngton 1994). experimental work, explored, The ultimate choice Tripp (1992) emphasised that inadequate analysis and a tOr the farmer is between the any planned changes in high I'ate of turnover of labour costs of farming, technolog;y must be developed research staff; and the cash purchase costs of in close collaboration with (ii) a need for better integration inorganic N fertilizer 01; more farmers if they are to be of the adaptive OFR with 10gicallJ; deciding on an optimal successfully adopted, He broader component research; combination of the two inputs re ported tha t technology (iii)a need for conditional or (\Vaddington and Ransom 1995). development for many farming suboptimal systems has proved more recommendations For SOUTHERN AFRICAN difficult than envisaged: farmers vvhose resources do EXPERIENCE IN ON­ 'a .qreat prop,wtltJil (if reJOllrceJ in not enable them to plan to FARM RESEARCH (il/farm re,INlrel, (0 FR) btU f,(,(,1l reach the 'best In a number of southern African rJel'at('() to til1kerill,q witb tbill/p recommended' practices countries. efforts have been like fer! dizer (}r deaJill,q ratt',I found by research; made over the last 10-15 years 11'1'O,JC rCdldtd lire eit!'cr IlwrJc,lt (iv? communication problems to revitalise agronomic research, ('Iwu.qb to e,!cape tbe attcntion between research and make it more relevant to (llld illtt'l'e.lt 0/ I/l(J,jf f~lI'll1e,." or extension; rcquire tI more cOllartcd farmerS immediate problems. a need for adjustments in e.l'fell.ll~)11 ,it;wt. OF R I:' (tu~i') and so i m prove the ra tes of extension approach billit 011 a m/peet j;wfarll/('/'d. adoption of new practices (methods, content and fbell' a.lpirati()/ld alld kfl(~Flcd"l', f~lrmers, Previous impact, training); and ad wcll a,l (J/l (/ ,IC!l.I( of IFonOcr al particularl.y in agronomic (vi) problems of input supply ('0//1 pie,w'fy 1'./ tl'eil' fal'lIIin.lJ operations and soil andlor availability. management, was modest, It ",lpt 1'111./ •

48 l'Ylerrill-Sands and colleagues government agricultural on-farm research and extension (1991) listed in detail the departments. In Malawi, the (COFRE); the arrangement is managerial and institutional Research Department at reasonably successfu l. In requirements for successful Chitedze controls and advises Zambia, the on-f:,l'm research is OFR and its exrension to the A.rea Development conducted by a specific fanners. Clearl}\ adaptive OFR Di visions which are responsible Adaptive Research Program cannot always be successful for both ada pti ve research and Team (ARPT) vvhich is not (Low et at. 199 I; Jeranyama extension, working with responsible for extension. 1992). To pnxluce a substantial individual farmers. This Extension is calTied out b,Y impact on the adoption of more arrangement creates a heavy liaison officers (RELOs) who sustainable soil fertility burden on the small adaptive are bmiliar with all aspects of management practices in research teams, and is not the the research and become the districts like l'Ylachakos is a best arrangement. In Zimbabwe, conduit for a two-way major challenge for both in contrast. the research information flow between research and extension. department (DR&SS) and the researchers and farmers. Low Low and co-workers (1991) extension service (AGRITEX) and colleagues (1991) suggest described three examples in both conduct adaptive on-farm that this last model is probably southern AJrica of coordination research. Their efforts, along the best. of on-farm adaptive research with filrmer effort, are with extension arms of coordinated by a committee for

49 CONCLUSIONS

SOIL FERTILITY IU':SI~{\RCH IN cropping systems which are both Current research has been eastern Africa has changed its acceptable to small-scale farmers aided by f::Cu'ming systems focus markedly since it began in and scientifically sound arc studies and fiinner-back -to­ the ] 930s. The changes are likely to involve both organic farmer ideas; it is moti vated b:r partly in response to the major and inorganic inputs. This the urgent need to boost food demographic putting approach of' integrated nutrient crop production if further increased pressure on the soils management' aims to optimise and human disasters of the croplands. Soils helve the use of locally prod uced are to be avoided. Computer become depleted through more organic inputs to provide both technologies of crop simulation intensive cropping, little or no nutrients and maintain soil modeJling and geographic restorative breaks in the organic C. Other household information systems are now rotation, and continuing lov\/ demands and the constraints of available to assist on-farm external inputs of nutrients and available household labour and researchers with very valuable organic materials. The main equipment. essential in handling analyses of the feasible options priority now is to improve and and processing these bulky available to farmers. using data restore fertilit)\ while materials, ""ill limit the on resources and climatic continuing production of vital utilisation of organic inputs. expectations at local level. This food crops for as long as These organic sources will not welcome focllsing and improved possible in the rotation. be sufficient to maintain fertility capacity of cUlTent research will Early research sought to in most fann situations, though have the desired impact on maintain fertility b.i' restorative the supply might sometimes be farming practices only if it can vegetati ve fallows and inputs of boosted through agroforestry. be closely linked with organic manures. Then, as the Therefore current research continuing extension eFFort to opportunities fOI' using these strives, with the aid and convey appropriate messages to methods gradually decreased, collaboration of to farmers, to demonstl'ate, discuss there followed a period of ways of combining the and ed llcate on the feasible intensive \-'.'ork searching for more expensive, but Iabour­ options befol'e them. Also, if economic responses to imported efflcient, inorganic nutrients external inorganic inputs are to inorganic fertilizers. Current from extel'l1ally purchased be used efflcentl,)', they will have researchers are finding, at least fertilizers with inputs of :ocal to be made available to I~lrmers ill the areas of' medium organic materials, both to satis(y by a much better and more agricultural potential such as crop demands and maintain soil reliable infrastructure of Machakos, that sustainable fertilit,)( providers and credit sources.

50 This has not existed previously For small-scale resource-poor Farmers in the medium potential areas of eastern Africa.

ACKNOWLEDGMENTS Many research Findings discussed in this review invoked staff of the National Oryland farming Research Centre. Katumani. Machakos, working as collaborators in the KARI~ACIAR Oryland Research Project between 1984 and 1993. Their contributions and those of other colleagues in the Kenya Agricultural Research Institute (KARI) are gratefully acknowledged, and documented in the list references. Ideas for the revie"v developed from discussions with Or R.L. McCown of the Agricultural Production Systems Research Unit, Tbowoomb..'!. Or ET. Cl'aswell, now of lBSR,\M. Bangkok, Professor D.J. Greenland of Reading, UK, and Or M.E. Probert of CSIRo. Brisbane made valuable comments on earlier drafts.

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