Rice responses to changes in floodwater and N timing in southern USA

Delayed application and/or early draining of floodwater to lowland irrigated rice (Oryza sativa L,) should allow producers in southern USA more time for ground application of chemicals while reducing potential hazards from aerial applications and conserving water. Two field studies were conducted to evaluate growth and yield responses of "Tebonnet", "Alan", and "Texmont" rice to reduced hood duration and altered N management. Depending upon the study, treatments consisted of normal (four- to five-leaf stage) or delayed timing of hood application in combination with recommended or earlier-than-recommended draining of the floodwater, and full-season hush irrigation. Nitrogen was either applied once at the four- to five-leaf stage or as a three-way split with normal- or earlier-than-recommended timing. Flush irrigation reduced shoot and root growth and yield of rice as compared to normal flood while delayed-flood irrigation reduced shoot dry weight but had no effect on root length density or grain and head-rice yields. Nitrogen uptake was greater with a single preflood application of N than with a three-way split application. Yields were not affected by N management or earlier-than-recommended draining of the floodwater. These data indicate that the duration of floodwater application currently practiced in rice production in southern USA may be reduced without sacrificing grain yield or quality. (C) 2000 Elsevier Science B.V. All rights reserved.