Research On Nitrogen Use Efficiency And Environmental Effects Of Rice Field Under Different Nitrogen Application In Hangjiahu Plain Region

Rice is one of the main cultivated crops in Hangjiahu plain of Zhejiang Province. In the past few years, the amount of fertilizer used in unit land area decreased with the promotion and application of formula fertilization by soil testing.But the farmers in pursuit of high-yield excessive application of nitrogen fertilizer remains widespread. Large number of nitrogen fertilizer brought about many disadvantages, such as reduced nitrogen use efficiency, declined fertilizer economic value, intensified the process of eutrophication, resulted in nitrate pollution to ground-water and posed a threat to ecological environment. The study of recommended fertilization system based on comprehensive assessment has significance on improving fertilizer use efficiency, reducing the negative effects of fertilization on environment. This study is located in Hangjiahu Plain in Hangzhou, the Ministry of Agriculture focus on the ecological environment of rice field soil scientific monitoring station (Haining Yangdu Town) in the coastal mud field light coating of soil. The purpose of this research is, chosing hybrid rice Zheyou 12 as materials for field localization test, using ¹⁵N isotope tracer studies and other methods of nitrogen application, to study rice growth and nutrient uptake, nitrogen migration and transformation in the soil and nitrogen use efficiency, filter optimal amount of nitrogen fertilizer recommendation based on rice yield, economic and environmental effects of fertilizer integrated assessment, evaluate ecological effects under different N levels, and provide scientific basis for scientific fertilization to Hangjiahu plain region . The major findings are as follows:1,The plant height, tiller number and nitrogen rate of hybrid rice Zheyou 12 increased with the rise of nitrogen, the number of tillers reached largest level after transplanting 35 days in Hangjiahu plain, the tillering was inhibited when ammonium concentrations in soil less than 15mg·kg^-1. The dry matter accumulation increased with the nitrogen applied level increasing at the range of 0²10kg·hm^-2 nitrogen and trend to decline when nitrogen applied amoumt over 210kg·hm^-2. Nitrogen applied level under the range of 0²70kgN·hm^-2,the content of nitrogen, phosphorus and potassium increased with the rise of nitrogen, rice nitrogen, phosphorus and potassium accumulation decreased with increased nitrogen, nitrogen uptake reached largest in jointing to heading positive correlation between rice grain yield and nitrogen, phosphorus and potassium accumulation in whole growth. And the correlation coefficient was significant maximum about grain yield and nitrogen accumulation between rice grain yield and N accumulation.2,When nitrogen fertilizer appilied level between 0³30kgN·hm^-2, rice production output by absorption of per unit weight nutrients (internal nutrient use efficiency) is decreased within nitrogen increased, internal nutrient use efficiency is increase with the organic manure. The highest nitrogen use efficiency (PNUE) and nitrogen uptake efficiency (NRE) is in 210kg·hm-2 of nitrogen treatment, which compared with nitrogen-free zone were increased 34.1g·g^-1 and 58.6%. When the nitrogen fertilizer more than 210kgN·hm^-2, the nitrogen use efficiency and nitrogen uptake efficiency decreases with the amount of nitrogen increases. This also confirmed by using ¹⁵N isotope tracer method. Combined with appropriate organic fertilizer in 150kgN·hm^-2 treatment will improve rice nitrogen use efficiency (PNUE) and nitrogen uptake efficiency (NRE), and reduce nitrogen consumption and environmental pollution.3,When nitrogen fertilizer applied level between 0²10kgN·hm^-2, the yield of hybridization rice of Zheyou 12 increases with nitrogen fertilizer increasing. The highest yield rate is 210kgN·hm^-2 treatment, which increased 54.4% (2008) and 54.91% (2009) compared with nitrogen-free zone. Nitrogen fertilizer increased is mainly to improve the number of rice grains per panicle and panicles of rice grain, and has little effect in improving the weight of 1000-seed and seed rate. When chemical nitrogen fertilizer application at the range of 0¹50kgN·hm^-2, increasing organic manure applied level played an important role for improving rice production. Application of Coase principles from environmental economics, according to 2008 and 2009 two years'field test results, comprehensive analysis of nitrogen application rate on the marginal production and marginal loss of nitrogen, proposed the hybridization rice of Zheyou 12 in Hangjiahu plain desalting mud polder's economic nitrogen is 219.9²34.8kg·hm^-2, corresponding rice yield is 9116.7⁹796.4kg·hm^-2, concern both rice production and environmental benefits of a reasonable amount of nitrogen is 217.3²40.1kg·hm^-2, the corresponding ecological suitable for production of 9119.8 9801.9kg·hm^-2.4,In the 28 days after transplanting, NH₄⁺-N,NO₃^--N concentrations in paddy field surface water increased with the raise of nitrogen applied in different periods,and the appear of peak value was related to fertilization time.The change of NH₄⁺-N,NO₃^--N concentration in farming layer soil was consistent with surface water. NH₄⁺-N,NO₃^--N concentration in runoff water increased with nitrogen applied increasing, and has a great consistency between the concentration in surface water and farming layer soil. It means excessive nitrogen applied has great risk on water pollution. NH₄⁺-N and NO₃^--N concentration in soil seepage water is lower than corresponding nitrogen concentration in runoff water, the concentration change was relate to nitrogen concentrantion,but the change is slighter than runoff water. NH₄⁺-N concentration in soil seepage water was beyond the ground water quality standards (ammonium nitrogen was 0.5mg·L-1) when nitrogen applied level was over 270kgN·hm-2. Ammonia volatilization rate increased with the nitrogen applied level increasing, reached fastest level after the base fertiliaer applied, and the cumulative ammonia volatilization loss come to largest at the same time, has a great consistency to NH₄⁺-N concentration change in surface water and farming layer soil.The cumulative ammonia volatilization has no significant difference among different nitrogen applied treatments.