Weed levels did not alter rice grain yield response to nitrogen

Rice (Oryza sativa L.) research field plots are likely to have nearly compl ete weed control whereas normal farmer field-grown rice often have consider ably greater weed populations. Consequently a disparity might exist between nitrogen (NZ requirements for producing maximum yields, in weedy (such as in some farmer fields) versus weed-free rice (such as field research plots) . We conducted a 2-year field study at Keiser, AR.. Using paired plots, we compared weed control effects, at several preflood N rates (0-112 kg N ha(- 1)) on yield, yield components, harvest index and weed weights. Rice yield responses to preflood N fertilization were similar with and without weed pr essure. Consequently, N fertilization recommendations based on research plo ts with little or no weed pressure are valid for research plots and grower fields with much greater levels of weed pressure.