Fertilizer-N Use Efficiency And Its Regulation Approaches In Rice

Low fertilizer-nitrogen use efficiency (FNUE) is a serious problem in rice production in China. This study investigated possible approaches to increasing FNUE from various aspects of genetic improvement (GI), real-time and site-specific nitrogen (N) management, growth and development and nutrient uptake in super high-yielding rice (SHY), indigenous N supply of soil (INS), source-sink characteristics of cultivars, water management and the system of rice intensification (SRI). The main results were as follows:1. Effect of GI in mid-season indica rice on yield and FNUE With 16 representative mid-season indica cultivars during the past 60 years in China as materials, effect of GI on grain yield and FNUE was studied. The results showed that GI increased grain yield gradually, and the increase in grain yield was due mainly to the increase of total spikelets per unit area. From early tall cultivars to dwarf cultivars, synchronous increase of biomass and harvest index increased grain yield; from dwarf cultivars to current super rice combination, the yield increase was attributed mainly to the biomass increase. GI increased spikelets per unit leaf area, root weight and the ratio of root to shoot, reduced the angle of top three leaves, leading to upper leaves more erect.GI significantly increased physiological efficiency (PE), agronomic efficiency (AE) and partial factor productivity (PFP) of N fertilizer of modern rice cultivars, but it did not increase recovery efficiency (RE). GI increased biomass and N uptake before heading stage and enhanced N remobilization after heading stage. N uptake at heading stage and N translocation efficiency were significantly correlated with the grain yield. Activities of glutamine synthetase (GS), nitrate reductase (NR) and Fd-glutamate synthase (GOGAT) in leaves at panicle initiation and GS and NADH-GOGAT in grains at early grain filling stage played important roles of biomass accumulationand N uptake before heading stage and N remobilization during grain filling. Activities of GS, NR and GOGAT in rice plant were significantly regulated by N application. Increase in activities of main enzymes involved in N metabolism at panicle initiation and early grain filling stage enhanced N uptake and biomass accumulation before heading stage, facilitated N remobilization from vegetative tissues to grains and increased the grain yield and N use efficiency.2. Leaf color diagnosis of high-yielding rice for N requirement and application SPAD (Soil and Plant Analysis Department) readings of leaves were significantly and positively correlated with chlorophyll content (g m-2) and N content (g m-2) in leaves. Significant correlation was also observed between leaf color chart (LCC) scores and SPAD values. SPAD values and LCC scores could reflect N nutrition status in rice plant and could be an important diagnosis index for dynamic N management in rice. SPAD values of 35 and 37 could be used as critical values for N application at key growth stages for most indica and japonica rice cultivars in Jiangsu, respectively, and the corresponding LCC score was 3.0. It was proved to be reliable and feasible in the demonstration and production of rice.3. Effects of real-time N management (RTNM) and site-specific N management (SSNM) on rice yield and FNUE SSNM model was established according to the available nutrient supply from soil, target grain yield, seasonal RE of N-fertilizer, SPAD values at main growth stages and source-sink characteristics of cultivars. Plot experiment showed that SSNM reduced amount of N application by 51.9-56.3%, increased grain yield by 0.2-9.3% and AE by 39.1~276.4%, respectively, relative to conventional fertilizer practice (CFP). SSNM was demonstrated in 20 farmers' fields in two villages during 2003-2004 in Wuxi, Jiangsu province. Compared with CFP, SSNM reduced N rate by 38.7-41.3%, increased grain yield by 2.5-3.5% and AE by 88.3-117.7%, respectively. In 2004, the demonstration on a large scale in Wuxi, Yangzhou and Liangyungang showed that SSNM reduced N rate by 42.0%, increased grain yi...