EVALUATING WATER-USE EFFICIENCY IN SORGHUM-PIGEONPEA (SORGHUM BICOLOR L. MOENCH-CAJANUS CAJAN [L] MILLSP.) DIVERSIFIED CROPPING SYSTEMS IN MARGINAL AREAS OF GHANA AND MALI

ABSTRACTEVALUATING WATER-USE EFFICIENCY IN SORGHUM-PIGEONPEA (SORGHUM BICOLOR L. MOENCH-CAJANUS CAJAN [L] MILLSP.) DIVERSIFIED CROPPING SYSTEMS IN MARGINAL AREAS OF GHANA AND MALIByPrincess HayfordWater use efficiency (WUE) is an important determinant of crop productivity in water-limited environments where crop yield is highly dependent on rainfall. Phosphorus and nitrogen are two major nutrients limiting crop production across farming communities in West Africa; however, fertilizers are often not affordable. Sorghum-pigeonpea cropping system could be an affordable, sustainable option for smallholder farmers to improve soil fertility and increase yields. WUE of field crops (cereals, legumes) can be quite variable which complicates the extrapolation of field results to other sites. Crop simulation models (CSM) are useful tools to evaluate the agronomic and environmental performance of farming systems, aiding to extrapolate field experimentation data across environments. The objectives of this study were to determine the soil moisture distribution in the root zone of sorghum and pigeonpea, assess the effect of sole vs intercrop systems on crop yield and WUE, and simulate WUE in a sorghum-pigeonpea cropping system using APSIM. Field experiments were established for the 2015 and 2016 seasons under rain-fed conditions at four sites: two locations at the experimental field station of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Samanko (Sko), Bamako; one at the field station of the Institut d’Economie Rurale (IER) in Farako (Fko), Mali; and one location at the field station of the Savanna Agricultural Research Institute (SARI) in Wa, Ghana. Sorghum was planted as a sole and an intercrop with a medium duration (MD) and a long duration (LD) pigeonpea, with a 4 replicate, randomized complete block design. Access tubes were installed in all treatments within the rows of plants, to a depth of 100 cm. Soil moisture content was monitored over the growing season in all cropping systems using Time domain reflectometry (TDR). Growth, plant biomass and yield parameters were collected and analyzed.Seasonal variation in rainfall, soil fertility, site and planting time affected phenology, grain yield and biomass production of sorghum and pigeonpea. Lack of adapted pigeonpea varieties limited grain yield, but biomass production in Mali at the adequate phosphorus fertility site SkoHP (7784 kg ha-1) was almost twice that observed at the low P site SkoLP (3400 kg ha-1). The LD variety was larger than the MD variety, and produced more grain yield. Intercropping sorghum with pigeonpea resulted in high grain yield, biomass and overall productivity in terms of land equivalent ratio. Also, plants under the ratoon system were highly productive. Soil water storage was more under sole sorghum than intercropped sorghum/pigeonpea (LD) plots due to deeper soil water extraction by pigeonpea. Cropping system significantly influenced water use (WU), with higher WU in the intercrop systems than in sole crop stands. Pigeonpea LD variety had higher WUE relative to the pigeonpea MD variety. The performance of the model in predicting crop phenology, WU and WUE under both sole and intercrop systems of sorghum were very well, with under-prediction of pigeonpea biomass and WUE. As pigeonpea is a novel crop to be grown in Ghana, adaptation of the crop to the environment needs work, and this poses a challenge to model parameterization as well. Overall these studies provided important contributions to understanding how to integrate pigeonpea into sorghum cropping systems in West Africa and the potential for multiple benefits associated with the integration of LD pigeonpea as a sorghum intercrop.