Effects of Real-Time and Site-Specific Nitrogen Managements on Rice Yield and Nitrogen Use Efficiency

Using hybrid rice Shanyou63, the agronomic and economic characters of different nitrogen(N) managements were evaluated. The results showed that the grain yield of the control(N omission plots) ranged from 6.8 to 7.4 t ha-1, indicating the high indigenous N supplyof the soil. Compared with farmers fertilizer practice (FFP, 240 kg N ha-1), the modifiedFFP (70% N of FFP), real-time N management (RTNM, applying N based on values ofchlorophyll meter) and site-specific N management (SSNM, applying nitrogen based on thetiming, amount of N and values of chlorophyll meter) increased the grain yield by 9.2-10.3%, 3.3-7.0% and 8.9-9.3%, and agronomic N efficiency (the increase in grain yieldper unit N applied) by 110.5-135.6%, 204.3-297.0% and 200.9-276.4%, respectively. Theresults suggested that RTNM and SSNM have great potential for improving N use efficiencywithout sacrificing the grain yield. In addition, RTNM and SSNM also decreased chalkygrain percentage and chalkiness to improve grain appearance quality.

Studies on the Photosynthetic Characteristics andAssimilate's Accumulation and Transformation inHeavy Panicle Type of Rice

Using 18 indiea rice varieties with different panicle weight, the photosynthetic characteristics and assimilate's accumulation and transformation in heavy panicle type of rice (HPT) were studied. The resuits showed that the net photosynthetic rate of the flag leaf in HPT after heading was obviously higher than that in medium panicle type(MPT) and light panicle type(LPT). The reason for the high net photosynthetic rate in HPT was the increase of Rubisco activities and chlorophyll content, and keeping high assimilate ability to CO2 under high and low light intensity, high temperature and low CO2 content, and light midday depression and wide adaptability to environmental conditions. The high net photosynthetic rate of HPT might be also the results of its excellent stomatal characteristics and higher total quantity of stomatal opening degrees(stomatal density X stomatal opening degrees). There was a large amount of dry matter production after heading and obvious high assimilate's transformation to panicle in HPT.

Effect of Different Water Management and Nitrogen Forms on Characteristics of Iron Nutrition of Rice Cultivated Under Aerobic Condition

Although available iron is usually abundant for the growth of rice cultivated in waterlogged condition, the rice crop may suffer from its deficiency when cultivated in aerobic soil since the soil properties are totally different from waterlogged. Solubility of iron is very low in soils with high Eh and/or high pH. A field experiment with five different depth (10, 20, 30, 40 and 50 cm) of groundwater, and a pot experiment with five treatments of ammonium nitrate ratio (100/0, 75/25, 50/50, 25/75 and 0/100) were conducted to study the characteristics of iron nutrition of rice in non full irrigation condition. Moreover, the contents of iron extracted by 1 mol L 1 HCl of rice plant samples of 8 cultivars from both aerobic and waterlogged cultivation were analyzed to study the effect of water regimes on iron content of rice plants. The results were as follows: (1) The average content of available Fe (2.70 mg kg 1 ) of 5 layers of the soil treated with 10 cm depth of groundwater was significantly higher than that (0.83 mg kg 1 ) with 50 cm depth of groundwater, and the iron concentration of rice plant of the former was much higher than that of the later. (2) Iron deficiency of rice became much severe when high ratio of nitrate (more than 75 percent) in nitrogen fertilizer applied at different intervals in aerobic cultivation. (3) The iron concentrations of 3 cultivars, Wuyujing3 (99 mg kg 1 ), Yangdao4 (87 mg kg 1 ) and 9520 (95 mg kg 1 ), of rice plants cultivated in aerobic condition were significantly less than those(195, 197 and 175 mg kg 1 ) respectively in waterlogged condition at tillering stage. And even much significant differences existed in the iron concentrations of different cultivars growing in the aerobic and waterlogged condition at maturity.