SUGAR-BEET TOPS AS A SOURCE OF NITROGEN FOR MAIZE AND RICE GROWN IN ROTATION WITH SUGAR-BEET IN SUBTROPICAL NORTH-WEST INDIA

Field experiments were conducted to determine the fertilizer N-equival ence of sugar beet tops for maize-sugar beet and rice-sugar beet rotat ions. Treatments consisted of 0, 60, 90, 120, and 150 kg N ha(-1) as u rea and 0, 60, 90, and 120 kg N ha(-1) as urea + sugar beet tops conta ining 90 kg N ha(-1). Tops were applied only to the first crops. Incor porating tops increased grain yields more in the presence of urea-N an d in rice than in maize. The estimated urea-N equivalence of tops in m aize-sugar beet rotation varied from 20 to 29 (mean of 25) kg ha(-1) f or maize and 17 to 20 (mean of 18) kg ha(-1) for the succeeding sugar beet. These crops utilized 19% and 11%, respectively, of the N of the applied sugar beet tops. The urea-N equivalence values in rice-sugar b eet were estimated to be 32 to 40 (mean of 37) kg ha(-1) for rice and 12 to 16 (mean of 14) kg ha(-1) for sugar beet. Apparent recovery of N in tops for this rotation was 26% for rice and 19% for sugar beet.