Investigations on crop responses to applied phosphorus in semi-arid vertisols of India

Abstract

Pot studies were conducted to investigate the reasons for the lack of response to applied phosphorus (P) in six representative vertisols of semi-arid tropical regions of India having low available P status (2.8 to 7 ppm P). Studies with pearl millet and sorghum as test crops in two different seasons showed that these two crops responded significantly to the applied phosphorus in all the soils. The optimum P doses worked out from the regression of harvested biomass or grain on P doses, were found to be mostly above 27 ppm P in the range of 0 to 44 ppm P tried. The requirement of high doses of P for optimum yields was attributable to high P fixation capacities of these soils ranging from 43 to 75%. Regression analysis showed that P uptake by both the crops was significantly influenced by pH and P fixation capacity of the soils besides the applied and soil P. The differences between superphosphate and diammonium phosphate as sources of P were not consistent over crops or soils. Two consecutive applications of P resulted in marginal or no build up of soils' available P. Suggestions to manage the P fertilization problem of the semi-arid tropical vertisols on field scale were also made.