Yield response of semi-dwarf rice varieties to applied nitrogen in New South Wales

Abstract

Grain yields of two semi-dwarf varieties of rice were compared over a range of 0-225 kg applied nitrogen/ha in two seasons with yields of the tall varieties Calrose and Kulu, which were their major recurrent parents. Harvested yields of the semi-dwarfs increased over the entire range whereas those of Calrose and Kulu decreased above 100-150 kg nitrogen/ha. This appeared to be associated with a decrease in the number of panicleslm2 in the first season, and the inadequacy of the harvester to recover as much grain from lodged as unlodged crops in the second. Lodging was extensive in both experiments when the tall varieties received high applications of nitrogen, but was absent in the semidwarf varieties at all nitrogen levels. This appeared to influence the harvesting much more than the production of grain. However, it is suggested that other factors are also involved.The results indicated that the semi-dwarf character incorporated into current varieties could increase yields by about 1 t/ha with high nitrogen applications.