Efficiency of soil and fertilizer nitrogen in relation to rice variety and application time using sup(15)N labelled fertilizer: pt. 3

Use efficiency of top-dressed labelled nitrogen (30% at ear formation stage) ranged 23 to 61%(five fields) with no clear difference between varieties. In high yield soil the use efficiency of top-dressed nitrogen was higher and more than 50% of fertilizer nitrogen in plant seemed to be taken up after ear formation, sup(15)N excess was greastest in grain indicating that top-dressed nitrogen translocates easily to grain. The differences of sup(15)N excess between grain and straw was greater in Tongil line than in the local indicating faster nitrogen translocation in Tongil. Percent nitrogen derived from top-dressed nitrogen ranged 14 to 27% in aerial part. Two 3-hill plots per treatment could be enough for sup(15)N experiment under field condition if there is specific care. (Author)