Soil moisture based optimum nitrogen requirement for sustainable productivity of sorghum grown in vertisols of Solapur district, Maharashtra.

Abstract

An attempt was made to optimize fertilizer N at varying levels of available soil N and soil moisture for rainfed sorghum grown in Vertisols under semi - arid condition at Solapur. The study was based on 20 field experiments conducted with 8 combinations of organic and inorganic fertilizer~ under receding moisture conditions in a permanent site from 1985 to 2004. The soil had a mean moisture profile of 219 mm with variation of 34.7'« at sowing. Similarly, the soil had a mean available N of 148 kg ha·1 with variation of 11.2'1f· and P of 16 kg ha·1 with variation of 42.rk. The mean sorghum yield of 946 kg ha· 1 with variation of 40.2'7r was attained over years. The results indicated that combination of 25 kg N ha· 1 crop residue + 25 kg N ha·i (Leucaella) was superior with a significant yield predictability (0.85 * * ) and minimum prediction error of 193 kg ha·j • This was efficient with maximum mean yield of 1109 kg ha·1 and sustainable yield index of 0.54 over years. The pooled model of treatments gave a significant predictability (0.38 * "") with prediction error of 282 kg ha·l . The study further indicated that when soil moisture ranged from 100 to 300 mm, optimal ferti izer N ranged from 26 to 76 kg ha" at a soil - N of 120 kg ha" and 14 to 64 kg ha·1 at a soil - N of 140 kg ha' At a soil - N of 200 kg ha·j and soil moisture of 160 mm, fertilizer N of 26 kg ha" was optimum for attaining sustainable sorghum yield. Since the treatment 50% N (crop residue) + 50% N (Leaucaena) ,gave maximum sustainable yield index, mean yield and yield predictability with minimum prediction error, optimum fertilizer N could be applied at the rate of 50' * through crop residue and the remaining through Leaucaena.