Abstract
Field experiments were conducted to determine the fertilizer N-equivalence of sugar beet tops for maize-sugar beet and rice-sugar beet rotations. Treatments consisted of 0, 60, 90, 120 and 150 kg N ha-1 as a urea and 0, 60, 90 and 120 kg N ha-1 as urea + sugar beet tops containing 90 kg N ha-1. Tops were applied only to the first crops. Incorporating tops increased grain yields more in the presence of urea-N and in rice than in maize. The estimated urea-N equivalence of tops in maize-sugar beet rotation varied from 20 to 29 (mean of 25) kg ha-1 for 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 beet 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.
