Effect of nitrogen fertilizer application and nitrogen use efficiency of early, mid and late rice in Hubei Province

Multipoint field experiments of rice were conducted to study the effect of nitrogen (N) fertilizer application on rice yield, to investigate the N use efficiency, and to compare early, mid and late rice in their response to N application in 18 counties of Hubei Province during 20062009. The results show that the average yields of the NPK (with nitrogen) treatment of early, mid and late rice are 1641, 1717 and 1695 kg/ha, respectively, which are higher than those of the PK (without nitrogen) treatment. It is concluded that the N application increases grain yield significantly, with the yield increase rates of 37.6% for early rice, 27.5% for mid rice and 35.0% for late rice. And the increase of the yield is resulted from the increase of panicles per unit area and grains per panicle in early and mid rice, and the increase of panicles per unit area and 1000-grain weight in late rice. At present production conditions, N agronomic efficiencies (NAE) of early, mid and late rice are 10.7, 10.0 and 10.4 kg/kg, partial factor productivities of applied N (PFPN) are 46.2, 50.1 and 45.3 kg/kg, N recovery efficiencies (NRE) are 31.0%, 33.2% and 24.8%, and N physiological efficiencies (NPE) are 31.8, 31.8 and 41.1 kg/kg in Hubei Province, respectively. The average soil N dependent rates (SNDR) of early, mid and late rice are all above 60.0%, which means that nitrogen absorbed by rice mostly comes from soil rather than fertilizer. And in three kind of rice, late rice has the highest SNDR.