Jpn.J.TroP.Agr.45(3):167-175,2001

Potato (Solanum tuberosccm) Intercropped with Maize (Zea mays) in the Eastern Hills of Nepal

S. P. CHAND, H.C. LEE*, D.H. SCARISBRICKand E E. TOLLERVEY

Imperial College at Wye,University of London, Wye,Ashford, Kent TN25 5AH, UK * Corresponding author

Abstract The yield of potato (Solarium tuberosum) was evaluated when intercropped with maize (Zea mays) in Nepal. The objective was to study ways of increasing potato yield within the intercrop by altering planting dates and using a fungicide to reduce the incidence of late blight. Two field trials were carried out in 1994 and 1995 at 2200 m a. s.l. Three local potato cultivars, Rato Aalu, Sarkari Seto and Hale were intercropped with the local maize cultivar Seti Makai. Both trials tested the planting times of local potato cultivars. The effect of chemical control of late blight infection was also monitored in 1995. Results for time of planting suggested that the potato cultivars Ratu Aalu, Sakari Seto and Hale gave higher yields when planted early, medium, and late respectively, as followed by local smallholders. Fungicide spraying against blight led to potato tuber yields of up to 19 t/ha for sole crops and slightly lower increases for intercrops but all in excess of unsprayed treatments. Maize yields were not affected by the enhanced potato performance. For both experiments intercropping resulted in yield improvements with LERs (Land Equivalent Ratios) ranging from 0.93 to 1.89. It is concluded that intercropped potato cultivars could achieve short-term tuber yield increases. The sustainability of such yield increases are discussed. Key words Intercropping, Nepal, Potato, Maize

ネ パ ー ル 東 部 丘 陵 地 帯 に お け る トウ モ ロ コ シ(Zea mays)と の 間 作 に よ る ジ ャ ガ イ モ(Solanum tuberosum)の 最 大 限 持 続 的 可 能 な 生 産 高 の 追 求S. P. CHAND・H. C. LEE・D. H. SCARISBRICK・EE. TOLLERVEY Imperial College at Wye, University of London, Wye, Ashford, Kent TN25 5AH, UK

要 約 ネパ ール の丘 陵 地 帯 にお い て,ト ウ モ ロ コ シ(Zea mays)と 間 作 され た ジ ャ ガ イ モ(Solanum tuberosum)の 収 量 を 調 査,検 討 し た.調 査 は,(1)植 付 け時 期 の 違 い に よ る間 作 ジ ャガ イ モ の 収 量 変 化,お よび(2)生 育 後 期 に 発 生 す る ジ ャ ガ イ モ疫 病(potato blight)軽 減 の た め の殺 菌 剤 使 用,の 各 項 目 につ い て検 討 す る こ と を 目的 に実 施 した.1994, 1995の2ヵ 年 に わ た って,標 高2,200メ ー トル の 圃 場 に お い て,ジ ャ ガ イ モ在 来3品 種(Rato Aalu, Sarkari Seto, Hale)を トウ モ ロ コ シ 在 来 品 種(Seti Makai)と 間 作 し,生 育 を調 査 し た.ジ ャガ イモ の 植 付 け時 期 の 違 い に よ る調 査 は 両 年 と も実 施 し,ジ ャ ガ イモ 疫 病 と殺 菌 剤 に関 す る調 査 は1995年 に 実 施 した. Rato Aalu, Sarkari Seto, Haleの 各在 来 品 種 の 収 量 は植 付 け時 期 が早 ま る と高 く な り,植 付 け時 期 が遅 くな る に つ れ 収 量 も低 下 した. ジ ャ ガ イモ 疫 病 防 除 を 目的 と した 殺 菌 剤 施 用 に よ り単 作 で 塊 茎 収 量 は19t・ha-1ま で 増 加 した が,間 作 した 場 合 の 収 量 増 加 分 は 僅 か で あ った.し か しい ず れ も殺 菌 剤 施 用 区 は無 施 用 区 の 収 量 水 準 を いず れ も上 回 っ て い た.ト ウ モ ロ コシ の 収 量 は ジ ャ ガ イ モ 収 量 の 増 加 に は 影 響 され な か っ た.両 実験 と もLERs (Land Equivalent Ratios)は0.93～1.89の 値 と な り,2作 物 の 間 作 は収 量 増 加 を もた ら して い た.間 作 され た ジ ャ ガ イモ 在 来 品 種 は塊 茎 収 量 の 増 加 を短 期 間 に成 し得 る こ とが 認 め られ た.こ の 様 な 収 量 増 加 の持 続 性 に つ い て も考 察 し た. キ ー ワー ド 間 作,ジ ャガ イ モ,ト ウモ ロ コ シ,ネ パ ー ル

For subsistence of farmers in Nepal the Introduction enhanced production of potato when intercropped The intercropping of potato is important to with maize has importance for local food security smallholder crop production systems across and also as a cash crop.5) However, potato yield parts of the Andes in South America, central and improvements when intercropped with maize in west Africa and most of Asia.13)In Nepal, potato this region of Nepal are limited by: (i) average and maize are grown as relay intercrops and are farm sizes of <0.5 ha; (ii) limited access to an important smallholder farming system in inorganic fertilizers and to cash for their higher altitude (1700.2500 m) areas of the eastern purchase; (iii) foliage damage caused by heavy hills, covering about 63% of available farmland.4) hail storms between March and May; and (iv) The relay intercropping allows the peaks of late blight (Phytophthora infestans) when the foliage growth for both species to occur separately monsoons begin in May. and is thought to allow the best use of local and Some research works have studied the environmental resources across the Season,14,10) potential of potato intercropped with maize in Received Feb. 8, 2000 tropical regions of South America,13) Africa9) and Accepted Feb. 9, 2001 other parts of Asia.10) In most cases, attempts to 168 Jpn. J. Trop. Agr. 45 (3) 2001 increase yields were only moderately successful. control of plant densities, and is widely practiced The main objective of the present investigation elsewhere in Asia. 10 was to study the effect of intercropping planting ) Maize was planted in rows 1 m apart, with times on the yield of potato when grown in 25 cm between plants. Two potato rows were set conjunction with maize on a smallholding in the between the maize rows, with 50 cm apart and eastern hills of Nepal. 25 cm spacing between plants. The planting

Materials and Methods pattern was therefore two potato rows equally spaced between each maize row. This was Two field experiments were conducted during equivalent to 40,000 plants/ha and 80,000 the periods of December, 1993 to October, 1994 plants/ha for maize and potato, respectively and (Experiment 1), and January, 1995 to October, was maintained for all intercrop and sole crop 1995 (Experiment 2). Both experiments were treatments. Each plot, which measured 4.5m•~ situated in Sindhuwa village, in the Koshi hills of 5.0m, accommodated five maize and ten potato eastern Nepal (27•K17••N, 87•‹17••E) at 2200 m a. s. l. rows. Two interior rows of maize and the One farmer's hillside terrace in Sindhuwa village surrounding six potato rows were hand harvested was sequentially used for both experiments. at maturity, giving plot areas of 12m2 for potato This was because of the limited availability of and 8m2 for maize. relatively large terraces for field experiments. Apart from the planting pattern, techniques The terrace measured approximately 120m by for potato and maize planting and management 30m, just large enough to accommodate each were the same as for local smallholder production. experimental design. For both experiments seed potato portions, each The annual total rainfall at the experimental containing one'eye•fwere planted individually in site was 1292 mm in 1994 and 1603 mm in 1995, holes 5cm deep and composted buffalo manure with nearly 90% falling between May and was added at the equivalent rate of 33 t•Eha 1 fresh September during both years. Average maximum weight. The compost used in both experiments and minimum air temperatures, respectively was analysed. Variation between years was small; varied from 20.8•Ž and 16.5•Ž in August to 9.4•Ž the mean analyses were 0.61% N, 0.51% P and and 3.1 •Ž in January. The soil was classified as 2.14% K, with 29% organic matter. The maize a free-draining acidic loam (pH 5.6). Prior to the seed was planted by hand at a depth of 3 cm. start of experiment 1, the soil macronutrient After the potato harvest, 30 kg N•Eha 1 as urea characteristics were determined using samples (46% N) was added to the maize as per local taken from the surface 10cm of every experimen- practice. Leaf Area Indices (LAIs) were deter- tal plot. Chemical analytical methods used are mined for potato and maize at 20-40 day intervals. described in ANDERSON and INGRAM.1) Means and standard errors (in parentheses) were: soil Experiment 1 Experiment 1 involved three local organic matter content 4.50% (0.10); available N potato cultivars (cvs): Rato Aalu (R. Aalu-early 0.22% (0.004) dry weight; P 25.31 mg•Ekg-1 maturity normally planted early January),

(1.35); K 280.82 mg•Ekg 1 (16.83). Soil sampling Sarkari Seto (S. Seto-medium maturity normally was repeated prior to the start of experiment 2. planted late January) and Hale (late maturity Means were mainly similar except for K which normally planted mid February), grown as sole was 171.32 mg•Ekg 1 (7.88), less than in the crops and intercropped with the maize cultivar

previous year. Seti Makai in a randomised complete block For both experiments potato and maize were design with three replicates. A total of 19

planted in rows. This was not similar to the treatments were allocated to each block as in normal smallholder practice, where potatoes are Table 1. There were 5 intercropped planting

planted first in a checkerboard pattern approxi- times for each of the three potato cvs at Ti (16th mately 40•`50 cm apart, followed by maize seeds of December, 1993), T2 (6th of January, 1994), sowing with equi-distance to the emerged potato T3 (27th of January, 1994), T4 (17th of February,

plants. Local plant populations vary widely 1994) and T5 (10th of March, 1994). These 15 between 30,000 and 80,000 plants•Eha 1 for both treatments were included to explore the range

potato and maize. Row planting was used in the of possible planting times and also to mirror experiments because it allowed a more exact those normally recommended by local farmers S. P. CHANDet al.: Potato Intercropped with Maize in Nepal 169

Table 1. Effect of intercropping on potato and maize leaf area index (LAI) during 1994 at Sindhuwa, Nepal (Experiment 1)

Int.=intercrop; potato cultivar abbreviations: R. Aalu=Rato Aalu; S. Seto=Sarkari Seto Potato planting dates: Ti=16th of December, 1993; T2=6th of January, 1994; T3=27th of January, 1994; T4 =17th of February, 1994; T5=10th of March, 1994.

for the chosen potato cvs. The remaining 4 planting and were continued at 40 day intervals. treatments were sole crops of the 3 potato cvs, Potato tubers and grain maize were hand each planted at their recommended times, and harvested on 20-24th of July and 10thof October, the chosen maize cv. The maize was sown on 10th 1994, respectively. of March, 1994, a typical date for smallholder production. All potato cvs were grown from Experiment 2 The second experiment used the seed tubers and multiplied near the trial site in same potato and maize cvs. A total of 18 the previous year. treatments (Table 3) was included in each of LAI was measured by passing leaf segments three blocks; 12 were sprayed with Fubol 75 through a Delta-T Leaf Area Meter (Delta-T WP (metalaxyl mancozeb) at a rate of 1.3 Kg Devices Ltd., Cambridge, UK). TATmeasurements a.i./ha. against late blight. This fungal pathogen for potato began 40 days after first emergence destroys local potato crops and limits tuber and then 40 day intervals. LAI measurements yields (CHAND,personal communication), and for maize were commenced 40 days after the intention was to monitor potato performance 170 Jpn. J. Trop. Agr. 45 (3) 2001

Table 2. Effect of intercropping on tuber and maize grain yield (t•Eha-1) and Land Equivalent Ratio (LER) during 1994 at Sindhuwa, Nepal (Experiment 1).

lnt.=intercrop; potato cultivar abbreviations: R. Aalu=Rato Aalu; S. Seto=Sarkari Seto Potato planting dates: T1=16th of December, 1993; T2=6th of January,1994; T3=27th of January, 1994; T4=17th of February, 1994; T5=10th of March, 1994. when protected. Spraying was commenced on The following 6 treatments did not receive 30th April 1995, and was repeated every 20 days fungicide: until potato harvest on 2024th of July, 1995. R. Aalu, S. Seto and Hale planted as intercrops There were three intercropped planting at T2, T3 and T4, respectively. times for each of the 3 indigenous potato cvs. R. Aalu and S. Seto planted as sole crops at T2 The dates corresponded exactly with T2, T3 and and T3, respectively. T4 in Experiment 1, and are given the same Sole maize. coding. There were also three sole crop treatments for R. Aalu, S. Seto and Hale, each Lack of trial space on the mountain terrace planted at T2, T3 and T4, respectively and a sole excluded the use of Hale as an unsprayed sole maize plot. The maize was sown on 10th of crop treatment. A description of the 18 March, 1995. The presence or absence of treatments tested in Experiment 2 is given in application of Fubol was compared for inter- Table 3. cropped and sole cropped treatments of R. Aalu LAI measurements for potato and maize at T2, S. Seto at T3 and Hale at T4. began 40 days after first emergence and then at 20 day intervals. Potato tubers and grain maize S. P. CHAND et al.: Potato Intercropped with Maize in Nepal 171

Table3. Effect of intercropping on potato and maize leaf area index (LAI) during 1995 at Sindhuwa, Nepal (Experiment 2).

Int.=intercrop; potato cultivar abbreviations: R. Aalu=Rato Aalu; S. Seto=Sarkari Seto Potato planting dates: T2=6th of January, 1995; T3=27th of January, 1995; T4=17th of February, 1995. + S=sprayed with Fubol against late blight; - S=not sprayed

were hand harvested respectively on 20-24 of there is no advantage of intercropping and July and 10thof October, 1995. values more or less than 1 show the advantages Intercrops were compared with sole crops and disadvantages of intercropping, respectively. using the land equivalent ratio (LER) as All data were subjected to analysis of described by MEAD and WILLEY.12) LER is an variance (ANOVA). Means and the respective index which is defined as the relative total land least significant difference (LSD) is shown, to area required by sole crops to produce the same allow pair wise comparisons, such that differences yields when they are intercropped: between means greater than the LSD denotes significance (GOMEZand GOMEZ.8)) LER=LA+LB=YA/SA+YB/SB Results

where LA and LB are the LERs for the Experiment 1 Leaf Area Indices (LAI) for potato individual crops A and B, YA and YB are the and maize are shown in Table 1. Intercropped R. individual crop yields when intercropped and SA Aalu and S. Seto, respectively showed the and SB their yields as sole crops. When LER=1, development of LAI peaks of 0.80 and 0.57 on 7th 172 Jpn. J. Trop. Agr. 45 (3) 2001 of May at T5, and 1.32 and 1.08 on 27thof May at led to a slight enhancement of LERs. However T4. These latter peaks were significantly (P<0.05) the general suggestion is that LERs were greater higher than the value (0.43) achieved by Hale than 1.0 due to a yield benefit of intercropping on 27th of May at T4. In a comparison of sole over sole cropping. For R. Aalu/maize intercrop with intercrop for the three cvs, R. Aalu showed treatments there was a trend for the LER to almost no difference at T2, S. Seto showed a decline from Ti to T5 but this effect was not higher (P<0.05) LAI for sole (1.40) than for clear for the other potato cvs. For partial LERs intercrop (0.88) on 27th of May at T3. Late blight R. Aalu and S. Seto contributed approximately 50•` attack was first observed in mid June which 60% of the total except at T5 when values were destroyed almost all potato foliage by early July. much lower at 13% and 38%, respectively. Potato tuber fresh yields are shown in Conversely, Hale contributed the lowest to LER Table 2. Intercropped R. Aalu gave the highest at 27% (T1) and 33% (T2) and c. 40%•`50% at T3•`T5. yield at the earlier planting times, with a peak of 10.11 t/ha at T2 falling to 1.17 at T5. S. Seto and Experiment 2 Leaf Area Indices for potato and Hale produced smaller yields than R. Aalu at maize are shown in Table 3. Comparisons can earlier planting times but larger yields at T4 and be made with experiment 1, for the unsprayed

T5. The comparison of soles with intercrops plots of each cv, at T2, T3 and T4. Intercropped demonstrated that all cvs tended to decrease but unsprayed R. Aalu, S. Seto and Hale planted at showed no significant differences at their T2, T3 and T4, respectively reached [Al peaks respective recommended planting times of T2, of 0.80, 0.86 and 0.62 on 29th of May and declined T3 or T4. Planting at times which differed from thereafter. These values are similar to those in these did not appear to enhance yields, though the first experiment. As in experiment 1, there attack by late blight may have confounded this were no significant differences between R. Aalu effect. and S. Seto Intercropped and sole treatments There was a large increase in Intercropped when unsprayed. Hale could not be compared maize LAI between 31st of May (minimum 0.09) due to the absence of a sole treatment. and 20th of June (maximum 2.20). This was Late blight appeared again on 8th of June, during the time of late potato blight infection 1995, one week earlier than in experiment 1, and and a general decline in potato LAIs. However, killed all unsprayed potato foliage by the end of some residual effects of intercrop competition that month. Sprayed treatments showed a are evident, as the sole maize LAIs were slower rate of blight infection and developed generally greater than intercropped treatments much larger LAI peaks for T2, T3 and T4 than at 20thof June and 30thof July. unsprayed, many differences being statistically Maize grain yields at 15% moisture content significant (P<0.05). Of these, intercropped R. are shown in Table 2. There was a decline in Aalu produced the highest LAI peaks for T2 intercropped maize grain yield from Ti to T4 (R. (1.82), T3 (1.58) and T4 (1.37) on 18th of June, Aalu), Ti to T3 (S. Seto) and Ti to T2 (Hale) 1995. S. Seto and Hale gave peaks which were followed by small, non significant increases quite close to those for R. Aalu also on 18th of thereafter. When compared with sole maize by June. The lower rate of blight infection for ANOVA, intercropped yields showed significant sprayed plots resulted in approximately a one reductions (P<0.05) with R. Aalu (T2 to T4) and month extension of foliage cover during which S. Seto (T2 to T5). With Hale, maize grain yields blight infection was almost absent. Eventual were either larger than sole (Ti) or not foliage senescence and decline in LAI was due significantly different. Thus, maize grain yields to natural maturity of the crop. For sprayed were adversely affected by intercropping with at plots, differences between intercropped and least two of the local potato cvs. sole treatments for the three local cvs were non Land equivalent ratios (LER) are shown in significant (P>0.05). Table 2. They ranged from 0.93 to 1.89, though Potato tuber fresh yields are shown in Table when determining LER the relative yield of the 4. Yields for all unsprayed treatments ranged sole crop is very important. In this experiment from 9.47 t•Eha-1 (R. Aalu) to 13.22 t•Eha (S. the use of sole crop planting densities which Seto). The mean for all unsprayed treatments were the same as when intercropped may have was 11.29 t•Eha-1. Yields for sprayed treatments S. P. Con et al.: Potato Intercropped with Maize in Nepal 173

Table 4. Effect of intercropping on tuber and maize grain yield (t/ha) and Land Equivalent Ratio (LER) during 1995 at Sindhuwa, Nepal (Experiment 2).

Int.=intercrop; potato cultivar abbreviations: R. Aalu=Rato Aalu; S. Seto=Sarkari Seto Potato planting dates: T2=6th of January, 1995; T3=27th of January, 1995; T4=17th of February, 1995. + S=sprayed with Fubol against late blight; - S=not sprayed

ranged from 9.64 to 18.86 that•Eand some potato cvs showed relatively higher LAIs, comparisons were significantly (P<0.05) greater, especially at the later T4 planting time (Table 3). by LSD comparison, than when unsprayed. Sole Maize grain yield at 15% moisture content is sprayed R. Aalu, S. Seto and Hale showed the shown in Table 4. Yields ranged from 1.07 to 2.7 greatest yields at T2, T3 and T4, (18.86, 17.92 t•Eha-1 lower than for experiment 1. Grain yields and 17.83 t/ha, respectively). Differences between when intercropped with potato, both unsprayed sole and intercropped were non significant and sprayed, were mostly lower than for sole. (P>0.05) when unsprayed. However, spraying Total LERs are shown in Table 4. They led to significantly greater (P<0.05) sole yield mainly show a similar range of yield benefits of for R.Aalu than when intercropped and similar intercropping over sole cropping (LERs>1.0) but non significant trends for the other two cvs. even allowing for the slight effects of similar Sole maize LAI reached a peak of 1.9 on 8th sole versus intercrop planting densities as of July. When intercropped with potato, both shown in Experiment 1. The LERs for S. Seto unsprayed and sprayed treatments were mostly were the highest and significantly greater than lower (P<0.05) than sole from 29th of May those for the other two cvs. For partial LERs all onwards. Maize intercropped with sprayed local potato cvs contributed approximately 50•`60%. 174 Jpn. J. Trop. Agr. 45 (3) 2001

in such circumstances, tuber yield increases Discussion were smaller but still statistically significant These experiments indicated that the (P<0.05). Plots sprayed with fungicide to control potato cvs R. Aalu, S. Seto and Hale gave higher late blight on potato also showed slight but non yields when planted early, medium and late, significant (P>0.05) increases in maize yield. respectively confirming local practice for their This suggested that the increases in potato yield management. The later planted cv Hale in had not compromised the effectiveness of this intercrops indicated slightly lower yield poten- intercrop in that year. tial in the first experiment but not in the second. This research clearly demonstrates that IFENKWE and ODURUKWE9) suggested that later smallholders plant local potato cvs at the times maturing potato cvs were unsuited for intercrop- best suited to their maturities and that altering ping with maize. There was also a clear trend these times of planting will not lead to potato towards higher tuber yields for Sarkari Seto for yield increases. However, there is potential for both Experiments, which matches the experi- short-term enhancement of potato yields if blight ences of local smallholders (CHAND, personal is controlled with a fungicide, though interspe- communication). cific competition may limit such improvements. For both experiments intercropping led to However, there are limitations to funds for yield benefits, with LERs ranging from 0.93 to purchasing fungicides or inorganic fertilizers 1.89. Researchers have confirmed this in other and also problems of agrochemical transporta- countries, with LERs for potato/maize inter- tion to mountain farms.6) With the scarcity of crops in the range 1.0 up to 2.1 in Peru13), 1.6 in potential inputs, there is a need for local crop Nigeria8), and for two studies in the Philippines production to be within the limits of maximum up to 1.252) and 1.4.18) For all of these agronomic sustainable yield (MSY).3) If fungicides are studies, actual tuber yields ranged from approxi- imported without inorganic fertilizers then it is mately 10 to 20 t•Eha 1 and agree with the results likely that a breach of MSY would result, with a of the current trials. The enhanced yield of rapid decline of soil fertility and subsequent potato tubers is especially important for Nepalese crop yields. However, no data are available for smallholders, since potatoes are both an important such trends on the study site. Further monitoring domestic food and can also be sold for cash over additional seasons would be needed to

(CHAND, personal communication). confirm this. A comparison of potato tuber and maize If the sustainable limits of the cropping yields when sole and intercropped should help system have been reached then perhaps this can to clarify the relative competitive dominance of be overcome by diversification. A potato/maize the two species. For both experiments it seemed study in China suggested that other crops in the that maize grain yields were reduced by rotation might be modified10) while others have intercropping more than the corresponding considered the benefits of intercropping maize potato tuber yield. However, the conclusion that with a legume, particularly Phaseolus vulgaris in potato is more competitive may be misleading. Kenya15)and Zambia.16)In Nepal the importance of Instead it might be that the potato plants introducing legumes into high-altitude subsis- benefited from intercropping perhaps due to tence cropping systems is being demonstrated17) shading and cooling of the soil by the maize. and may be the most sustainable option for This is suggested by MIDMORE3) in Peru, enhanced long-term crop yield improvements. especially during tuber bulking. Acknowledgements In experiment 2, spraying fungicide to control late blight was associated with a significant This research was undertaken whilst one increase in tuber yields for sole potato treatments author (SPC) was on a PhD research scholarship (Table 4). Observations suggested that all three funded by the Overseas Development Admini- potato cvs were susceptible to this pathogen, as is stration (now the Department for International the case for most potato cvs7). Visual observations Development) and based at the Pakhribas confirmed that blight control extended foliage Agricultural Centre, Nepal. Thanks are due to growth and thus allowed more time for tuber Imperial College at Wye IT staff, for help with bulking. However, when intercropped with maize computer software. S. P. CHAND et al.: Potato Intercropped with Maize in Nepal 175

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