Effects of Late Nitrogen Fertilizer Application on Head Rice Yield, Protein Content, and Grain Quality of Rice

Abstract

Cereal Chem. 73(5):556-560 Rice yields of 10 and 6 t/ha can be achieved in the humid tropics dur- improved, but Kett whiteness decreased with late N fertilizer application. ing the dry and wet seasons, respectively. At these high yield levels, late Brown-rice weight was not affected by late N application. In most cases, nitrogen (N) fertilizer application at flowering at the International Rice there was a significant positive correlation between head rice content, Research Institute (IRRI) farm often results in increased rough rice yield milled rice protein, and translucency. Thus, when crop management of IR cultivars and is accompanied by higher milled rice protein and seeks to achieve yields that approach yield potential levels, late N fertilincreased total and head-milled rice contents. The combined effects of N izer application provides an option to improve milling and nutritional application at flowering resulted in a 30-60% increase in head-rice pro- quality of rice grain. tein yield in three field experiments. In general, milled rice translucency A yield decline has occurred in several long-term experiments where continuous irrigated rice is grown in the Philippines (Flinn and De Datta 1984, Cassman et al 1995). In recent studies to identify the cause of decreasing yield trends at the International Rice Research Institute (IRRI) farm, increased nitrogen (N) fertilizer rates including a top-dressing applied at flowering stage was found to increase the yield of IR rices (Cassman et al 1993, 1994). It was hypothesized that the current low yields at the IRRI farm were partly related to a change in the N supplying capacity of soil which results in low N concentration in the leaf canopy during the grain filling period, early senescence of leaves, and low rates of photosynthesis (Kropff et al 1993; Cassman et al 1995). Consistent with this hypothesis, grain protein content also appears to have decreased. For example, mean protein content of milled rice was typically =7% in the 1960's and 1970's at the IRRI farm in plots without applied N (Cagampang et al 1966, Eggum and Juliano 1975, Gomez and De Datta 1975), whereas grain protein from 0-N IRRI field plots (block B4) in the 1991 wet season was only 5.5% for IR72 and 5.0% for IR58109-113-3-3-2 (IRRI, un