Yield Quantity And Quality And Field Ecological Effects Under Site-Specific Nitrogen Management

Nitrogen (N) fertilizer is one of the most important factors affecting grain yield in rice. High N inputs and low use efficiency is a main problem in rice production in China. Creation of a technology with high-yielding and high efficiency is a hot point in rice production. With typical rice cultivars as materials, this study investigated the characteristics of growth and development, grain yield and quality, and field ecological effects under site-specific nitrogen management (SSNM). The main results were as follows:1. Characteristics of growth and development and yield formation under SSNM SSNM could decrease N rate to a greater extent without any sacrifice in grain yield, and N agronomy use efficiency increased by 143-166% when compared with farmers'fertilizer practice (FFP). Productive panicles under SSNM were a little lower than those under FFP, but the percentage of productive tillers was much greater. Leaf area index (LAI) and root weight were lower under SSNM than those under FFP before panicle initiation, but the results were reversed after booting stage. SSNM increased ratios of efficient and high efficient LAI at heading stage, and it also increased dry matter accumulation from heading to maturity, and the ratio of root to shoot during the whole growth period.2. Physiological mechanisms of increasing fertilizer-N use efficiency under SSNM The peak of N uptake under SSNM was from panicle initiation to heading stage. The ratio of N absorbed during this period to total N absorbed during whole growth stage was ranged from 45.6% to 46.2% under SSNM, and was much higher that under FFP. The amount of N uptake after heading under SSNM was also much higher than that under FFP. From panicle initiation, root weight, root activity (especially root activity per stem) under SSNM were higher than those under FFP. SSNM also significantly increased the activities of glutamine synthetase, nitrate reductase and Fd-glutamate synthase in leaves at panicle initiation and heading stage. Photosynthetic rate, chlorophyll fluorescence, parameters of spectrum characteristics of the flag leaves were also obviously greater under SSNM than under FFP, indicating that SSNM could benefit root growth, promote nutrient absorption of plants, and increase the ability of matter production during the mid and late growth periods. 3. Effects of SSNM on grain quality When compared with FFP, SSNM increased milling quality and transparency, whereas decreased chalky grain percentage, chalky area and chalkiness, leading to an improvement in appearance quality. SSNM also decreased amylose content, gelatinization temperature and protein content, but increased gel consistency. In addition, SSNM increased peak viscosity and breakdown values and decreased setback values, indicating that SSNM could improve rice quality.4. Field ecological effects under SSNM Effects of different N management methods including SSNM on field ecology were studied using HOBO to monitor the changes in temperature and humidity outside and inside the canopy in rice. The results showed that, when compared with FFP, SSNM improved population structure, increased the differences of temperature, relative humidity between day and night and light transmission rate, and reduced the occurrence of sheath blight, suggesting that SSNM could created a better field ecological condition for high yield and good quality of rice.