Nitrogen fertilization of dry-seeded rice in south-east Australia

Abstract

Dry-seeded rice is often fertilized by broadcasting prilled urea on the soil surface shortly before permanent flood commences. Although this method is more efficient than nitrogen application at other stages, nitrogen loss is still substantial (up to 40%). Therefore we compared the efficiency of broadcast urea prills with various forms of urea banded below the soil surface shortly before permanent flood.

Banding urea prills increased plant recovery of applied¹⁵N from 37% (broadcast) to 46% (banded), while recovery with point-placed urea supergranules was even higher (49%). Plant recovery from banded urea treated with DCD (dicyandiamide) or PPD (phenylphosphorodiamidate) was not higher than from banded urea prills. Loss of applied¹⁵N averaged 25%, with no significant differences between treatments. The increased plant nitrogen recovery with banding was associated with reduced immobilization of¹⁵N in the soil, rather than reduced losses. The increase in plant nitrogen recovery was relatively small compared with total nitrogen uptake by the plants, and consequently there was no significant improvement in yield or agronomic efficiency.

There are practical difficulties associated with banding before permanent flood. When the soil is too wet, unacceptable amounts of soil disturbance and plant damage occur. On the other hand, when the soil is dry and cracked, the depth of banding is no greater than the depth to which broadcast urea prills are transported by the irrigation water at the commencement of permanent flood.