The Effect of Crops/Crop Combinations on Some Indices of Yield and Some Soil Nutrient Dynamics

ABSTRACT
Crop production in peasant cropping systems in the semi-arid areas of West Africa is generally constrained by low and uncertain rainfall, poor soil fertility and lack of credit facilities to purchase inputs such as fertilizers and improved varieties. In this study, two field experiments
(September to November 1996 and March to June 1997) were conducted on an Ultisol (Bekwai series) at Kwadaso, Kumasi in the semi-deciduous forest zone of Ghana. An assessment was made of production potential and nutrient depletion or conservation of sole crops cowpea (Vigna unguiculata L. Walp) (C), maize (Zea mays L. var. obatcmpa) (M), sweet potato (Ipomea batatas) (P) as well as their intercrops, maize-cowpea (MC), cowpea-potato (CP) and maize-potato (MP), The cultivation of the sole crops particularly cowpeas and maize least depleted soil nutrients than the intercrops with the MP combination resulting in the greatest fall in soil nutrients. At the end of the first cropping season, cowpea total dry matter yield reduced to about 50 % in the intercropped maize and intercropped sweet potato possibly due to shading by the companion crop. Rainfall amount and distribution in the study site (minor cropping season) is insufficient for full expression of maize yield potential especially if planted in late September. Evidently, low November rainfall appears to be most critical in influencing maize yield if planting is done in September. Land equivalent ratio (LER) and the area-time equivalent ratio (ATER) demonstrated the superiority of MC intercrop to sole crops in terms of grain yield when moisture was adequate for crop growth in the 1997 cropping season. The results provide useful information for fine tuning choice of appropriate crops and cropping systems that will respond to prevailing rainfall conditions and soil nutrients; results of the present study can be used as a guide.