Effect of density of acacia and phosphorus fertilization on yield and water expense efficiency of rainfed cowpea in arid environment

A field study was conducted to evaluate the effect of Acacia (Acacia albida) planted at three densities (100, 200 and 400 trees ha⁻¹) and phosphorus fertilization (0, 20 and 40 kg P ha⁻¹) on yield and water expense efficiency of rainfed cowpea (Vigna unguiculata) on a loamy sand soil. The interactive effects of tree density and phosphorus were non-significant. The yields of sole crop were at par with the 10×5 m spacing (200 trees ha⁻¹) but significantly higher than that under 10×10 m (100 trees ha⁻¹) and 5×5 m (400 trees ha⁻¹). Phosphorus application had no significant effect on crop yield, though the yield with 20 kg P ha⁻¹ was higher than the control. The water expense efficiency was maximum (3.71 kg ha⁻¹ cm⁻¹) in the sole crop which was thrice of that in 5×5 m spacing and twice of that in 10×5 m spacing. The results indicate that under arid conditions planting of A. albida at 10×5 cm spacing (200 trees ha⁻¹) is optimum for agri-silviculture system.