Mineral nutrition and water use patterns of a maize/cowpea intercrop on a highly acidic soil of the tropic semiarid

Due to global warming, water is expected to become scarce especially in semiarid regions. Therefore, there is a need to increase the efficiency in water use by crops under rainfed agriculture. The effect of nutrient availability on the growth, production, root development, water relations and water use efficiency (WUE) by the intercrop maize/cowpea was investigated in 2 contrasting years (dry and wet) in the semiarid region of Brazil. The crops were grown on a strongly acidic, sandy soil with three treatments: (i) application of NPK fertilizers plus lime (NPK + lime), (ii) application of NPK fertilizers (NPK) and (ii) control (Contr.) in low and high input regimes. The soil water balance was calculated with the crop model EPICSEAR. Application of fertilizers and lime increased biomass production and grain yield of the intercrop up to 400% and 550%, respectively, and maize suffered more from the effects of low nutrient availability and soil acidity than cowpea. The root development of both crops was strongly improved by the application of NPK and lime and cowpea developed a deeper root system which enabled this crop to keep a higher transpiration rate in the dry year. As a consequence of the shallow root system, maize was prone to water stresses caused by the dry spells and its harvest index was reduced when dry spells occurred during flowering and grain filling.Fertilizers and lime application reduced deep percolation and soil evaporation while increasing the productive transpiration flow. WUE were improved through the application of nutrients and lime and maize showed higher WUE than cowpea. The omission of lime showed only minor effects on the evaporation and transpiration WUE. The model probably over-emphasizes the effects of high Al saturation on the root growth and water uptake and consequently underestimated the transpiration rate of the crops. Nevertheless, the gross WUE was reduced up to 58% when lime was omitted and NPK applied at high inputs.A balanced fertilization in combination with lime improves the root development of a maize/cowpea intercrop in acid Acrisols of the semiarid NE of Brazil. The improved root development allows a better use of soil water reserves and increases the WUE of the system.