Changes in Soil Chemical Properties in Response to Application of Phosphorus Sources in Legume Sorghum Cropping Systems

Abstract

Field experiments to evaluate effect of phosphorus (P) fertilizers and integration of legumes in sorghum cropping systems on soil pH, available nitrogen (N) and P, were conducted in Njoro Kenya during the short (SRS) and long rain seasons (LRS) of 2012 and LRS of 2013. The experiments comprised either lupin or chickpea grown with sorghum. The design was a split plot in a randomized complete block design. Main plots were cropping systems; sorghum monocrop, legume - sorghum rotation and legume- sorghum intercrop. Subplots comprised P sources (60 kg P ha1 ); triple super phosphate (TSP) and minjingu phosphate rock (MPR). Application of TSP resulted in significantly higher nutrient concentrations in the soil than MPR addition in the first season. In the second and third seasons, the performance of MPRs approached that of TSP. Legume crops due to their release and accumulation of carboxylic acid lowered the pH to below 5.5 thus making solubilization of MPR and availability of P possible. Intercropping sorghum with lupin or chickpea with application of MPR gave comparable results with use of TSP. Since MPR is cheaper than TSP, growing lupin or chickpea in intercropping system with sorghum with application of MPR is recommended for improved chemical properties.