Nitrogen Loss in Conjunction with Transpiration from Rice Leaves as Influenced by Growth Stage, Leaf Position, and N Supply 1

An understanding of the fate of the N used or discharged by crop plants is important to cost‐efficient producton. Recent reports from our laboratory show that leaves of several crop and weed species lose volatile N in conjunction with transpirational water vapors. This study has investigated the effects of growth stages, leaf position, transpiration rate, and N supply in relation to rate of this loss on rice ( Oryza sativa L.). A pyro‐chemiluminescent method was used to quantify the volatile N loss along with the transpirational water vapors from rice leaves. Calculations, based on collected data, estimate N loss of 14.1 (‘Bonnet 73’) to 15.2 (‘Starbonnet’) kg/ha from plant leaves over a l00day period. Rate of N loss decreased during the period between tillering and 1 to 3 weeks beyond panicle initiation after which it increased as plants progressed to the heading stage. The most recently matured leaf lost N at a higher rate than older leaves. The N concentration in nutrient solution did not affect rate of volatile N loss per unit of leaf area of the most recently matured leaf; however, older leaves supplied with high rates of N lost N at a higher rate than those grown in low‐N medium. Volatile N lost per plant increased with N supply mainly due to higher leaf area and higher N loss rate from older leaves. Quantifying the physiological influences on volatile N loss can help to determine the time for application and the amounts of N fertilizers needed for optimum rice production. Additional