Effect of continuous application of manures and fertilizers on productivity of cotton-sorghum rotation

Abstract

Field experiments were conducted from 1985 through 2001 on medium deep vertisol to determine the effect of the continuous application of manure and fertilizers on a two-year cotton-sorghum rotation. The results indicate that the response to N was greatest during the initial years, while after five to six rotation cycles the yield levels declined to the zero level in the N and NK plots. The application of P along with N prevented the decline in seed cotton and sorghum grain yields. The effect was more pronounced at the higher level. K application did not result in any yield increase. Balanced fertilizer at the higher level (N90P19K37) resulted in a significant yield increase over the recommended dose (N60P13K25); however, the percentage increase declined with duration, indicating a decline in factor productivity. Seed cotton yields were the highest when part of the fertilizer N was applied from an organic source (farmyard manure: FYM). Of the eight years, a significant response was observed in four years at the lower level (N30P13K25 + 5 t FYM ha-1) and six years at the higher level (N45P19K37 + 7.5 t FYM ha-1), while in sorghum a response was only observed in two years. The cotton crop should, therefore, be preferred to sorghum for the application of organic manure. In areas where no organic manure is available, N60P13K25 is sufficient for cotton, while sorghum needs to be fertilized at 1.5 times the recommended dose (N90P19K37).