Effect of different transplanting leaf age on rice yield, nitrogen utilization efficiency and fate of 15N-fertilizer

Field experiments were conducted to study rice yield, N uptake and fate by using 15N-urea at transplanting leaf age of 2-, 4-and 6-leaf, respectively. The results showed that rice yield significantly decreased with delay of transplanting leaf age, and 15N-fertilizer uptake by grain and straw of rice, nitrogen utilization and residue also decreased, but loss of 15N-fertilizer increased. Under different transplanting leaf age, N absorption by rice mainly came from the soil. Almost 1/3 of total N was supplied by fertilizer, and 2/3 came from soil. The efficiency of fertilizer was 20.8% ∼ 25.7%, 15N-fertilizer residue ratio was 17.9% ∼ 32.2%, and 15N-fertilizer loss was 42.1% ∼ 61.3%. 15N-fertilizer residue mainly distributed in 0 ∼ 20 cm top soil under different treatments. The results indicated that transplanting young leaf age could increase rice yield and nitrogen utilization efficiency, and decrease loss of nitrogen fertilizer and pollution level on environment. (authors)