Cultivar and Nitrogen Rate Influence on Nitrogen Uptake and Partitioning in Rice

Abstract

AbstractNumerous empirical studies have shown that semidwarf rice (Oryza sativa L.) cultivars require higher N fertilizer rates for optimum yields than standard‐statured cultivars; however, these studies do not indicate the reason for this increased N requirement. Field studies were conducted with semidwarf ‘Lemont’ and standard‐stature ‘Lebonnet’ rice to evaluate N uptake and partitioning as related to fertilizer 15N rates and developmental stages. Four fertilizer N rates bracketing the recommended ranges for the two cultivars were applied as 15N‐labeled urea in split applications at preflood (PF) and panicle differentiation (PD). Aboveground plant portions were sampled at PD, heading, and heading + 21 d for dry matter, total N, and fertilizer 15N. Lebonnet produced more total dry matter at all N rates and had higher panicle weights at the lower two N rates, whereas Lemont had higher panicle weights at the highest N rate. Lemont continued to accumulate total N between heading and heading + 21 d, whereas Lebonnet showed either a decline or leveling. Fertilizer 15N uptake and accumulation decreased after heading for both cultivars, thus Lemont appears to continue accumulating soil N through grain filling. Nitrogen harvest index for total and fertilizer N with Lemont was greater than with Lebonnet, therefore, N utilization differences between the two cultivars may be associated only with total N uptake and partitioning after heading.