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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 4, Num. 2, 1996, pp. 151-158
African Crop Science Journal
Vol.5. No.2, pp.151-158 1997

On-farm evaluation of soybean and cassava intercropping in south-west Nigeria

H. TIJANI-ENIOLA and F. K. AKINNIFESI

Agronomy Department, University of Ibadan, Ibadan, Nigeria

(Received 30 January, 1995; accepted 25 September, 1995)

Code Number: CS96052 Sizes of Files: Text: Graphics: Tables (gif) - 55.2K

ABSTRACT

Farmer-participatory and researcher-managed trials were conducted at Ayepe, in south-west Nigeria, between July, 1991 and October, 1992, to determine the biophysical compatibility of soybean and cassava intercrop and the optimum time for introducing cassava (Manihot esculenta Crantz) in soybean-based intercropping systems. Soybean (Glycine max L. ) was planted in monoculture and also intercropped with cassava at varying stages of soybean development. Results indicated that seed yield of soybean was depressed by intercropping. Land equivalent ratio (LER) increased with growth stage of soybean prior to introduction of the cassava intercrop. Yield of soybean ranged from 327 kg ha^-1 to 642 kg ha^-1 in farmers' fields, and from 723 kg ha^-1 to 1201 kg ha^-1 in the researcher managed field. Intercropping caused slight etiolation during the early growth of cassava but this disappeared after soybean harvest. Tuberous root yield of cassava was improved by intercropping irrespective of the stage of development of soybean. Relative total yield increased with growth stage of soybean prior to introduction of cassava. Both crops were least competitive with each other when intercropped at 6 weeks after sowing soybean. Introducing cassava into soybean in a relay-intercropping system is advantageous for this agroecological zone.

Key Words: Cassava, soybean, relay intercropping, yield advantage

Resume

Des essais en collaboration avec des fermiers et geres par des chercheurs ont ete menAe entre juillet 1991 et octobre 1992 e eyepe (sud-est du Nigeria) afin de dAterminer la compatibilite biophysique du soya et du manioc pour la culture intercalaire et le temps optimal pour introduire le manioc (Manhiot esculenta Crantz) dans un systeme intercalaire e base de soya. Le soya (Glycine max L.) Atait plante en monoculture ainsi qu'en culture intercalaire avec manioc e des stades variables du soya. Les resultats indiquaient que le rendement du soya est diminue par la culture intercalaire. La proportion d'Aquivalence de terre (LER) augmente avec le stade de developpement du soya au moment de l'introduction de la culture intercalaire. Le rendement de soya variait de 327 kg par ha jusque 642/ha sur les champs des fermiers, et de 723 jusque 1201 sur les champs geres par les chercheurs. La culture intercalaire causait un etiolement pendant la croissance initiale du manioc, mais ceci disparait apres la recolte du soya. Le rendement des racines tubereuses de manioc augmentait en culture intercalaire et ceci etait independant du stade de developpement du soya. Le rendement relatif total augmentait avec le stade de developpement du soya avant l'introduction du manioc. La concurrence entre les deux cultures atteignait son niveau le plus bas quand l'intercalation se faisait 6 semaines apres le semis de soya. L'introduction du manioc en intercalation avec la culture du soya est avantageuse dans cette zone agroecologique.

Mots Cles: Manioc, soya, culture intercalaire en relais, avantage au rendement

INTRODUCTION

The interest in production and utilisation of soybean (Glycine max L. ) in Africa has been on the increase during the past decade. Nigeria is the largest soybean producer in West and Central Africa (Root et al., 1987). Soybean was introduced into Nigeria in 1908 (Root et al., 1987) and has received much research attention in the country, yet few farmers have adopted it into traditional farming systems. However, the demand for soybean as source of edible oil and protein has increased tremendously since the Nigerian government ban on importaion of edible oil in 1986.

Although there is considerable potential for soybean production in southwest Nigeria (Mutsaers, 1991), there is high variability in seed yield ranging from 150 to1500 kg ha^-1 in farmers fields (Baten et al., 1992). Tropical agriculture is confronted with the challenges of identifying management options that will maximise productivity of compatible crops in the traditional multiple cropping system. Soybean is frequently intercropped with cassava (Manihot esculanta Crantz) and other crops.

Cassava, a root crop, has been ranked as the second most important staple food in Africa after maize (Nweke et al., 1988) while soybean, a protein-rich grain legume is increasingly becoming a pre-eminent cheap source of protein and edible oil in the continent (Singh and Rachie, 1987). Under intercropping, the yield of soybean depends on sowing time relative to the planting of other crops, and on plant population density (Tijani-Eniola and Akinnifesi, unpublished data). However, research information is scarce on the effect of crop-mixes on yield dynamics in farmer-based soybean production systems.

The study reported here was undertaken to determine the optimum time of introducing cassava into soybean-based systems with a view to exploring the possibility of improving soybean production by optimising temporal compatibility in soybean and cassava intercropping systems.

MATERIALS AND METHODS

The experiments were conducted at Ayepe in Irewole Local Government area of Osun State, Nigeria. Ayepe lies at 5o 90' S and 7o 15' N. It receives about 1350 mm rainfall annually during the rainy season extending from April to November. The rainfall pattern is bimodal, with long and short rainy seasons separated by a short dry spell of uncertain length, usually during the month of August. Soybean thrives well in the area if sown by late July or early August (Mutsaers, 1991).

The relative humidity of the area ranges from 63% to 85% depending on time of day, while the average daily temperature is about 27.5 + 2.5oC with small diurnal fluctuations. The soil has been classified as an Alfisol, belonging to the Egbeda series with various associations at different positions in the catenae (Onasanya, 1992). Table 1 presents some physical and chemical properties of 16 representative farmers' fields in Ayepe area.

Experiment I. A farmer-participatory trial was set up in July in six cluster villages at Ayepe area in both 1991 and 1992. The experiment was a randomised complete block design with six replications. Each farmers' field represented a replication. Treatments were sole soybean, and cassava introduced into soybean at planting (0), 2, and 4 weeks after planting (WAP). Cassava variety TMS 30572 and soybean variety TGX 1497-ID were planted at 1 x 1m and about 75 cm x 5 cm, respectively. Plot size ranged from 24m^2 to 60m^2 depending on farmers' field size. Fields were managed by farmers as desired without researchers interference. Crop growth parameters were measured at 50% soybean flowering, and seed yield determined at harvest.

Experiment II. A researcher-managed trial was set up at Ayepe in July 1992 to complement farmer-participatory trials above (Experiment I). The same soybean (TGX 1497-ID) and cassava (TMS 30572) varieties were planted at 1 x 1m and 75 x 5 cm spacing, repsectively, in a randomised complete block design (RCB) with four blocks. Plot size was 4 x 5m. Treatments were four crop mixes and their sole crops: (i) sole soybean (0 WAP), (ii) sole cassava (0 WAP), (iii) soybean + cassava (planted same day), (iv) soybean + cassava (2 WAP), (v) sole cassava (2 WAP), (vi) soybean + cassava (4 WAP), (vii) sole cassava, (4 WAP), (viii) soybean + cassava (6 WAP), and (ix) sole cassava (6 WAP).

Sole cassava was planted at the same time in each crop mix. Crop growth was measured at 50% flowering of soybean, while yields were determined at harvest. Soybean grain yield was measured at 12% moisture content. All data were subjected to analysis of variance using Statistical Analysis System (SAS, 1985). Indices for assessing competitive abilities and yield advantage in the intercrop were estimated as described by Palaniappan (1985).

RESULTS

Soybean in farmers' field. In the farmer-participatory trials, intercropping with cassava did not significantly affect the stand count, branching, and height of soybean at 50% flowering when cassava planting was delayed by 2-4 weeks (Table 2). However, pod production and grain yield were significantly depressed when soybean was intercropped with cassava on the same day. Soybean grain yields were reduced by 49% when intercropped with cassava on the same day and by 22% when cassava was introduced into soybean at 4 WAP. Estimated land equivalent ratios (LER) were 0.51, 0.86 and 0.88 in soybean when cassava was introduced at 0, 2, and 4 WAP, respectively.

Soybean in researcher's field. In the researcher managed trial (Table 3) stand count at 50% flowering and pod production were not statistically different whether sole or intercropped. Soybean height was greatest when intercropped with cassava on the same day. Planting cassava at 6 WAP coincided with 50% flowering of soybean crop. As in the farmer-participatory trial, soybean grain yield was significantly depressed by intercropping with cassava up to 4 WAP. Intercropping did not significantly affect grain yield of soybean when cassava was introduced at 6 WAP. Soybean yield in the intercrop increased with growth stage of soybean prior to intercropping with cassava. This ranged from 723 kg ha^-1 in soybean intercropped at 0 WAP to 1173 kg ha^-1 when cassava was introduced at 6 WAP, and 1201 kg ha^-1 in sole soybean.

Cassava in farmers field. Table 4 shows the growth as measured by plant height and stem diameter and tuberous root yield of cassava intercropped with soybean at various stages of soybean growth under farmer-managed conditions. Plant height of cassava was consistently highest when intercropped with soybean at 0 WAP. This may be attributed to early competition for light between the two crops. Tuber yield of cassava was not significantly affected by time of intercropping with soybean crop. Land Equivalent Ratios (LER) of cassava tuber at harvest were 0.98, 0.88 and 1.02 when intercropped with soybean at 0, 2, and 4 WAP, respectively.

Cassava in researcher's field. In the researcher-managed field, cassava height at 50% soybean flowering was consistently higher in the intercrop compared to sole crop (Table 5), while stem diameter was slightly depressed by intercropping. This indicated consistent etiolation of cassava under intercropping compared to sole cropping. Cassava introduced into soybean at late vegetative stage of growth was little affected by intercropping. Etiolation in cassava, however, disappeared after soybean harvest. Number of stems per stand were significantly lower in intercrops at 2 and 4 WAP. Stem fresh weights were similar in both sole and intercrops. Total number of cassava tubers at harvest did not show any definite trend except a significant increase in tuber number at 6 WAP. Tuberous root length in monoculture and intercrop were also statistically similar. Except when cassava was introduced into soybean at planting, cassava root yield was not affected by intercropping.

Competition and yield advantage. Table 6 shows the yield advantage and competitive abilities of soybean + cassava intercrop. LER in soybean was generally <1, and indicated yield disadvantage of 40% when both crops were intercropped on the same day and 2% when cassava was introduced at 6 WAP. LER in cassava indicated a slight yield disadvantage when intercropped with soybean on the same day, and yield advantages of 17, 10 and 8% when intercropped at 2, 4 and 6 WAP, respectively. Relative yield total (RYT) increased with growth stage of soybean prior to introduction of cassava and ranged from 1.54 to 2.06 when intercropped on the same day and 6 WAP, respectively. This suggested increased compensation effect of crop mixtures. Aggressivity values for the crop mixture declined from 0.52 in soybean + cassava (2 WAP) to 0.10 in soybean + cassava (6 WAP). This showed that yield gap between actual and expected, and competitive abilities of crop mixture were highest at 2 WAP and lowest at 6 WAP, respectively, due to intercropping. Positive aggressivity for cassava and negative value for soybean indicated that relative yield increase in cassava was greater than that of soybean which appeared to be dominated in the mixture.

DISCUSSION

Farmers in Africa have for long recognised the role of intercropping not only as insurance against crop failure, but also as a convenient strategy for meeting dietary needs.

In this trial, intercropping did not adversely affect the more genetically-controlled growth parameters in soybean, such as branching intensity, pod production and plant height, compared to more environmentally-affected variables such as grain yield. Patterns of yield and yield components in soybean were similar in both farmer and researcher fields. Thus, grain yields in both trials were superior in monoculture compared to intercrop. Grain yield also increased considerably with increasing delay prior to intercropping with cassava. However, soybean grain yield in researcher's field was about twice the yield obtained by farmers. These trends were due to differences in field managment, notably weeding, between researcher and farmer and also among farmers.

Introduction of cassava at the late-vegetative or early reproductive stage of soybean did not adversely affect soybean yield. Conversely, the greater reduction in yield at other stages of introducing cassava may be attributed to competitive interaction between both crops at earlier stages of crop growth. Intercrop competition, according to Palaniappan (1985), occurs essentially in a response of one species to the environment as modified by the presence of another species. Crop competition could be minimised by spatial arrangement and choosing crops best able to exploit soil nutrients, and with different times of maturity, thereby separating periods of maximum demand of growth resources above and below ground. In this study competition was reduced by introducing cassava into soybean at the late vegetative stage of soybean growth which probably coincided with period of critical demand for growth resources, especially light, nutrient and water.

Cassava yield components, such as tuber number and size, were little affected by intercropping at diferent growth stages of soybean crop. Positive yield advantage in cassava due to introducing it into the intercrop at 2, 4 and 6 WAP, measured by land equivalent ratios, could be ascribed to complementary N transfer from soybean to cassava especially at the end of soybean cycle. Both crops were least competitive when cassava was introduced into soybean at 6 WAP, which also coincided with 50% flowering of soybean. In the context of the traditional farming system, these results indicate the possibility of optimising soybean and cassava yield in a relay-intercropping system. Cassava is best introduced into soybean [+ cassava intercrop] at late vegetative or mid-reproductive stage of soybean growth.

Acknowledgements

The authors gratefully acknowledge the financial support of Ford Foundation and the technical advice of Profs. M.E. Aken'ova, A.A. Agboola, Drs. M.O. Akoroda and H.J.W. Mutsaers.

REFERENCES

Baten, M.A. 1991. Effects of NPK Fertilization on Soybean Production in Southwestern Nigeria. Ph.D. Thesis, University of Ibadan Nigeria, 200 pp.

Fisher, N.M. 1977. Studies in mixed cropping II. Population pressures in maize-bean mixtures. Experimental Agriculture 13: 185- 191.

Mutsaers, H.J.W. 1991. Opportunities for Second Cropping in Southwestern Nigeria. RCMD Research Monograph No. 4, IITA, Ibadan, Nigeria, 28 pp.

Nweke, F.I., Ezumah, H.C. and Spencer, D.S.C. 1988. Cropping Systems and Agroeconomic Performance of Improved Cassava in a Humid Forest Ecosystem. RCMD Research Monograph No. 2., IITA, Ibadan.

Onasanya, S.O. 1992. The Relationship Between Topographic Location, Soil Properties and Cultural Management and the Productivity of Maize-Soybean Intercrop. Ph.D. Thesis, University of Ibadan, Nigeria, 319 pp.

Palaniappan, S.P. 1985. Cropping Systems in the Tropics: Principles and Management. Wiley Eastern Limited, 215 pp.

Root, W.R., Oyekan, P.O. and Dashiell, K.E. 1987. West and Central Africa: Nigeria sets example for expansion of soybeans. In: Soybean for the Tropics Research Production and Utilization. Singh, S.R., Rachie, K.O. and Dashiell, K.E. (Eds.), pp. 81-87. John Wiley and Sons Ltd.

SAS, 1985. Statistical Analysis System Users Guide, 1985 Edition. Statistical Analysis Institute Inc. Carry, North Carolina, U.S.A.

Singh, S.R. and Rachie, K.O. 1987. In: Soybean for the Tropics Research, Production and Utilization. Singh, S.R., Rachie, K.O. and Dashiell, K.E. (Eds.), pp. xv-xx. John Wiley and Sons Ltd.

Copyright 1996 The African Crop Science Society


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