| Nitrogen-fertilizer is the most important factor affecting the growth and grain yield of rice. At present, high nitrogen-fertilizer input and low nitrogen-fertilizer use efficiency are serious problems in rice production in China. This study investigated the situation of rice requiring nitrogen through measuring the color of leaves, and established a new method of site-specific nitrogen management (SSNM), and clarified the formation of grain yield, nitrogen-fertilizer use efficiency and characteristics of growth and development of rice under SSNM. The main results were as follows:1. Leaf color diagnosis of high-yielding rice for nitrogen-fertilizer requirement and application SPAD (Soil and Plant Analysis Department) readings of leaves were significantly and positively correlated with chlorophyll 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 nitrogen (N) nutrition status of rice plant and could be an important diagnosis index for dynamic N management in rice. SPAD values of 36 and 39 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 scores were 3.0 and 3.5. It was proved to be reliable and practibale in the demonstration and production of rice.2. Effects of site-specific N management (SSNM) on rice yield and N-fertilizer use efficiency SSNM model was established according to the available nutrient supply from soil, target grain yield, seasonal recovery efficiency (RE) of N-fertilizer, SPAD values at main growth stages and source-sink characteristics of rice cultivars. Plot experiment showed that SSNM reduced amount of N application by 54.2%~63.0%, increased Agronomic efficiency (AE) by 169.6%~250.6%, respectively, relative to farmers, fertilizer practice (FFP) at the condition of without sacrificing, or even an increase in, the grain yield. SSNM was demonstrated in 20 farmers'fields in two villages during 2003~2004 in Wuxi, Jiangsu province. Compared with FFP, 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 2005, the demonstration in Yangzhou, Wuxi, Lianyungang showed that when SSNM reduced N rate by 30.9%, and increased grain yield by 10.5% and AE by 104.9%.3. Characteristics of growth and development in rice under SSNM Compared with FFP,leaf area index and root weight were lower before heading, but higher at and after heading. During the whole growth period, the ratio of root to shoot under SSNM was greater than that under FFP. Biomass accumulation after heading was about 36.7%~39.4% of the total biomass accumulation at maturity. The peaks for nutrient uptake of N, P2O5 and K2O in rice under SSNM appeared in the period from panicle initiation (PI) to heading stage, and the amount of N, P and K uptake during this period ranged from 45.6%~46.2%, 39.6%~43.6%, 44.2%～45.2%of the total amount at maturity.4. Participatory farmers, research Twelve to 15 farmers were randomly selected in each village in each year for a dialogue between farmers and the research team and for a rapid evaluation on SSNM. Based on the information obtained from the evaluation, a modification of SSNM (MSSNM) was developed through dialogue between a research team and farmers in a workshop at each village. In each village, more than 95% of the farmers were willing to adopt SSNM and MSSNM techniques, more than two thirds of the farmers preferred to adopt MSSNM rather than the standard SSNM. Based on farmers, willingness, 49 farmers were selected to conduct the experiment to compare SSNM or MSSNM with FFP. SSNM and MSSNM, as compared to FFP, maintained rice yields with less N-fertilizer application. The research of farmers, participatory accelerated the demonstration and extension of SSNM.
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