Soils of the Northern Kenya Aridlands
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Journal of Soil Science and Environmental Management Vol. 2(1), pp. 1-8, January 2011 Available online at http://www.academicjournals.org/JSSEM ISSN 2141-2391 ©2011 Academic Journals Full Length Research Paper The physical and chemical characteristics of soils of Northern Kenya Aridlands: Opportunity for sustainable agricultural production E. M. Muya1*, S. Obanyi1, M. Ngutu2, I. V. Sijali1, M. Okoti2, P. M. Maingi1 and H. Bulle2 1National Agricultural Research Laboratories, P.O. Box 14733, Nairobi, Kenya. 2Kenya Agricultural Research Institute (KARI) P.O. Box 147, Marsabit, Kenya. Accepted 22 November, 2010 Biophysical characterization was carried out in the mountain and oasis areas within the Northern Kenya Arid Lands with a view of identifying, soil constraints and opportunities for sustainable agricultural production in the area. The soil aspects were studied through desk-top analysis of the existing databases and collection of secondary data at regional scale, site evaluation surveys at site level and detailed soil survey at farm level. Based on biophysical data, the mountain and oasis area of the region was divided into three major eco-zones, namely (1) upper regions: mountains, hills and uplands, (2) middle level: footslopes and (3) low-lying areas: riverine, plains and bottomlands, which were found to occupy 20, 5 and 54% of the total land area of Kenya Arid and Semi-Arid Lands (KASALs) respectively. In these areas, soil structural degradation has taken place at varied rates through pulverization in the upper regions, compaction in the middle level and dispersion in the low-lying areas. The mean productivity index for the upper zone, middle slopes and the lowest zone was found to be 18.5, 19.6 and 1.3%, the most limiting factors being high acidity, increased compaction and high sodicity/salinity respectively. The opportunities for sustainable agriculture was found to be elimination of acidity and increased water saving for supplementary irrigation in the upper zone; harnessing run-off water and improving water holding capacity through subsoiling on the footslope; and precision and market oriented irrigated farming for improved water use efficiency in the lowest zone. Key words: Biophysical characterization, soil quality and productivity index. INTRODUCTION The challenge to any project with an objective to improve sustain agricultural production in these fragile and the productivity of the area is to have baseline on land resource limited environments. This is because these productivity and identify soil-related constraints in communities have a pastoral background with limited different zones or ecosystems. This can be the basis of farming skills and knowledge to face the challenges of formulating appropriate intervention packages and sustainable agriculture – for example crop diversification, identifying areas with reasonable agricultural potentials use of locally available resources (for example organic for the selected areas. In most of these ecosystems, inputs), water harvesting techniques and conservation. efficient use of limited water and nutrient resources is In addition, such research efforts should also come up required for both livestock and crop production. In this with tangible outputs and data on environment-agriculture context, efforts for improving the productivity through interactions, which has been one of the major impedi- sustainable approaches will bear fruits if they are ments in formulating appropriate land use and environ- accompanied by participatory methods and initiatives to mental policy for dry lands. Therefore, land resources improve the capacity of the pastoral communities to inventory through systematic characterization of the area using appropriate soil quality indicators is one of the major steps required to trigger of the agricultural develop- ment processes. In this regards, stepwise and hierarchi- *Corresponding author. Email: [email protected]. cal approaches are required at different scales of 2 J. Soil Sci. Environ. Manage. Table 1. Climatic zones of drylands. Zones r/Eo (%) r mm Eo mm Climate designation III 50 to 55 900 to 960 1750 to 1800 Semi-humid IV 40 to 50 750 to 900 1800 to 1880 Semi-humid to semi-arid VI 25 to 40 525 to 750 1880 to 2095 Semi-arid VII 15 to 25 320 to 525 2095 to 2150 Arid VIII <15 170 to 320 2150 to 2280 Very arid r=rainfall, Eo=potential evapotranspiration. Source: Van Kekem (1986). biophysical data collection in order to capture adequate each of the soil quality attributes selected and yield of maize. The information which are commensurate with different levels soil quality attributes selected were those with known influence on of determinations. This can provide decision support tools crop growth such as nitrogen, phosphorus, potassium and organic carbon. The productivity index of different soils was calculated by in formulating the appropriate intervention packages to be the method provided by Aune and Lal (1997). Base on this method, implemented at the farm level. Against this background, the critical limits were derived and applied in developing the the objective of carrying out site characterization was to productivity index. According to Aune and Lal (1997), the critical identify, prioritize and document key constraints with a limit is defined as the numerical value of soil quality where crop view of formulating the most promising management yield is 80% of the maximum. The productivity index of a given soil mapping unit (PI) was calculated by the following equation: options to be tested and up scaled in broad geographical scales. PI = SQI1 + SQI2 + SQ3 + SQ4 + SQ5 +....... Where: MATERIALS AND METHODS PI = Productivity index SQI1, SQI2, SQI3, SQI4, SQI5 is the relative yield read off from the Characterization of the soils of Northern Kenya Arid Lands focused yield response curves under specified soil quality indicator. on the mountain and oasis areas, which are unique micro-climatic ecosystems that can support arable farming at subsistence or small-scale, commercial level. The areas covered were those in RESULTS AND DISCUSSIONS which high degree of land degradation has taken place, thereby impacting negatively on the quality of land resources. The study Climatic characteristics and status of land sites are located in very arid and semi-arid lands, with annual rainfall varying from 170 to 750 mm. In this area low soil quality is degradation one of the main causes of poor crop performance at farm level. The decrease in vegetation cover and diversity towards settled areas The results showed that the area has three major ecolo- indicates that settlement had impacted negatively on environmental gical zones, namely mountains, hills and uplands; foot quality and biodiversity, hence loss in ecosystem functions, low slopes; and plains, riverine and bottomlands. The three biophysical sustainability and poor crop performance (Muya et al., zones have different rainfall regimes and degree of land 2008). The study area is located in a typical dryland with arid to degradation (Table 3).In the mountain, hills and uplands, very arid climate (Table 1). These areas occurred mainly in Marsabit, Wajir North, Garissa, Turkana and Ijara districts. most land forms are as a result of geological and geo- Biophysical site characterization was carried out at three levels, morphological processes such as faulting, folding, vol- namely regional, site and farm level. At the regional scale, canic activities and erosion. The mountains have a relief description and maping of the major areas of Kenya Arid and Semi- intensity of 300 to 1000 m and slopes ranging from 8 to Aridlands (KASAL), were done by clipping on the exploratory soil 30%. The mountains are important water catchment maps (Sombroek et al., 1981) to indicate major soils of the region. areas. The volcanic mountains consist of various volcanic This was to provide an overview of the possible areas to be up scaled and the potential impacts of the developed technologies. rocks, and the dominating volcanic mountains are mount The type and quantity of data collected depended on the scale. At Kulal in the North-East and mount Marsabit in the East. the regional scale, the secondary data were studied to gather They rise to 1740 and 2230 m above the sea level biophysical information from the existing databases. The respectively. biophysical information from the secondary data included climatic Hills have relief intensity varying from 50 to 300 m, with characteristics of the study area, geomorphic processes, the slopes ranging from 8 to 30%, while uplands have relief degree of land degradation and general soil conditions. At the site level, the time and space dynamic soil degradation processes such intensity varying from 10 to 100 m. On the mountain tops, as aggregate collapse, compaction, pulverization, salinization, the soils are deep to very deep. They are reddish brown sodification and nutrient depletion were assessed. At the farm level, to brown clay. In some areas the soils are stony and detailed soil and topographical soil survey were carried on the basis gravelly. In places the soils are compact between 0 and of physical, hydraulic and chemical characteristics of soil. 20 cm depth. The footridges on the southern slopes of The chemical characteristics of soils were used to determine their mount Marsabit have moderately deep to deep clay loam productivity, based on the thresholds values indicated in Table 2, after Aune and Lal (1997) and Kamoni and Wanjogu, (2006). The to clay soils with favorable physical and chemical response functions applied were regressed relationships between properties. Muya et al. 3 Table 2. Soil quality attributes and their threshold levels. Indicators Threshold values Source K me/100g 0.2 to1.5 Kamoni and Wanjogu (2006) K me/100g 0.83 Aune and Lal (1997) N% 0.2 Kamoni and Wanjogu (2006) C% 2 to 4 (Kamoni and Wanjogu (2006) C% 1.08 Aune and Lala (1997) P ppm 20 to 80 Kamoni and Wanjogu (2006) P ppm 7.6 Aune and Lal (1997) Cation exchange capacity 15 to 25 Kamoni and Wanjogu (2006) pH 5.5 to 7.0 “ Electrical conductivity (EC) 4.0 mS/cm ‘’ Ca me/100g 2.0 to 10.0 ‘’ Mg me% 1.0 to 3.0 ‘’ Mn me% 0.1 to 2.0 ‘ Table 3.