Effect of Exchangeable Sodium Percentage on the Efficiency of Diammonium Orthophosphate and Ammonium Polyphosphate in Wheat

In a greenhouse experiment, effect of exchangeable sodium percentage (ESP) on the efficiency of diammonium orthophosphate (DAP) and ammonium polyphosphate (APP) for wheat was investigated on a Typic Ustochrept. Dry matter (DM) yield, P uptake and per cent utilization of added P decreased, while shoot P concentration and available P content of soil increased with increasing ESP. Sodification of soil with ESP 9.6 to ESP 32.8 and 48.0 reduced 9.3 to 33.6 per cent and 23.8 to 41.1 per cent DM yields, respectively. Dry matter yield increased exponentially with P levels and mean response of wheat per unit of applied P was lower at higher ESP. Increase in DM with unit increase in shoot P concentration was also lower at higher ESP. Both the sources of wheat were equally effective in increasing DM yield, whereas shoot P concentration, P uptake, per cent utilization of added P and available P content in soil were generally higher with APP as compared with DAP treatment owing to continued hydrolysis of condensed phosphate fraction of APP for longer period and lesser sorption of pyrophosphate than orthophosphate by soil.