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Abstract
The productivity of sorghum, an important staple food crops in semi-arid tropics of the world, is low due to scarcity of moisture and poor soil fertility. Response of crops to phosphorus (P) application in these soils is erratic and tricky, which depends upon the available P status in soils, distribution of rainfall, adsorption and desorption capacity of soil, and overall P sink created by crop depending upon its vigor. Delineation of optimum P level for higher productivity and to avoid wastage of precious P fertilizer thus becomes inevitable. Hence, an experiment was conducted at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad to i) study the external (relative grain yields, agronomic efficiency, harvest index) and internal response (fertilizer P use efficiency, P uptake harvest index) indicators of sorghum to various levels of P application, ii) development of prediction functions to arrive at optimum P dose and iii) P use - removal balance for grain sorghum for these rainfed semi-arid tropical Alfisols. Results of the study indicated that P application to sorghum in these Alfisol soils beyond 23 kg ha−1 might not be much economical and desirable. It was observed that the maximum grain yield of 87% could be achieved at a leaf P concentration of 0.39% at boot leaf or flag leaf stage and 0.30% at 50% flowering stage. The prediction functions were developed to understand the quantitative relationship between external and internal response indicators. The zero P balance (neither depletion nor excessive build up) obtained at 20 kg ha−1 level (per se near 23 kg P ha−1) indicates that this level is sufficient for sorghum crop to perform with an agronomic efficiency of 19.42 kg grain kg−1 P. The findings of this study would help in efficient use of P fertilizer for achieving desirable yield levels and will in turn reduce the expenditure on P fertilizers that are mostly imported by India and majority of other developing countries.