Value of Soil Macro- and Micro-Nutrient Balances in Predicting Fertilizer Needs of Irrigated Cotton-Wheat Aridisols?.

The >3 million ha irrigated cotton (Gossypium hirsutum L.)-wheat (Triticum aestivum L.) system in alluvial, low organic matter Aridisols suffers with deficiency of nitrogen (N), phosphorus (P), boron (B) and zinc (Zn). A 5-year cotton-wheat field experiment in two Fluventic Camborthids investigated the value of apparent soil nutrient balances in predicting crop fertilizer requirements. Various nutrient managements [i.e., Farmers’ fertilizer use (FFU; cotton, 110 kg N ha-1; wheat, 80 kg N + 26 kg P ha-1); (ii) Recommended fertilizer use (RFU; cotton, 170 kg N + 26 kg P + 1 kg B + 5 kg Zn ha-1; wheat, 140 kg N + 44 kg P ha-1); and (iii) Integrated nutrient management (INM; modified RFU, having 75% fertilizer N and 25% FYM N)] were compared with and without recycling of cotton stalks + wheat straw, in flat bed- and raised bed-sown cotton systems. Both RFU and INM enhanced SOM (P<0.05), more evidently in coarse loamy soil having less native SOM. Residue-driven SOM enhancement (P<0.05) improved soil physical properties (P<0.05). Minimum yields (Mg ha-1) were obtained with FFU in flat bed sites. Yield increases with RFU were: coarse loamy soil – cotton, 24%; wheat, 37%; fine silty soil – cotton, 18%; wheat, 24% (P< 0.05). Yield increases were slighly higher with INM. With FFU, without residue, apparent soil nutrient balances were: -22 to -118 kg N ha-1; -755 to -1063 kg K ha-1; +24 to +64 kg P ha-1; +0.31 to +1.07 kg B ha-1; and +0.35 to +0.88 kg Zn ha-1. Despite positive P, B and Zn soil balances with FFU, incidence of their deficiency is widespread. Contrarily, despite negative soil K balances, both the crops hardly respond to K fertlizer. Thus, soil K, B and Zn balances appear to be poor indicator of fertlizer needs of the crops.