Effects Of Reduction And Deep Placement Of Nitrogen Fertilizer On Rice Yield And Ammonia Volatilization

Heavy nitrogen fertilizer is often applied to produce rice,the staple food for nearly half of the global population.Large amount of reactive nitrogen is lost during the production process.To reduce nitrogen loss and improve the nitrogen use efficiency（NUE）,In this study,Seven fertilization treatments were used:N0（no N fertilizer）,S300(300 kg N ha^-1 and conventional application),S210(210 kg N ha^-1 and conventional application),R5(210 kg N ha^-1 and row application at 5cm depth),R10(210 kg N ha^-1 and row application at10cm depth),B5(210 kg N ha^-1 and application in large granular fertilizer at 5cm depth),B10(210kg N ha^-1 and application in large granular fertilizer at 10cm depth).we studied the effect of application depth and shape of nitrogen fertilizers on ammonia volatilization,soil N distribution and rice growth,the results provide scientific basis for ensuring food security production and reducing agricultural ammonia emissions.The main results are as follows:（1）The results showed that the ammonia volatilization loss decreased by 16.9%-61.3%in the treatment of reduced deep application compared with the treatment of reduced scattered application,and the ammonia volatilization loss decreased by 7.1%-30.9%in the treatment of large granular fertilizer deep application compared with the treatment of row deep application.Compared with the fertilization depth of 5 cm,the ammonia volatilization loss decreased by 7.1%-11.7%at the fertilization depth of 10 cm.It indicated that large granular fertilizer deep application could better inhibit the production of ammonia volatilization,and the deeper the fertilization depth was,the better the effect was.When nitrogen fertilizer was applied to paddy soil,the p H,NH₄⁺-N concentration and total nitrogen concentration in surface water were significantly positively correlated with ammonia volatilization.Therefore,deep application of nitrogen reduction can effectively reduce NH₄⁺-N concentration in surface water,thereby reducing ammonia volatilization loss in paddy field and improving nitrogen utilization rate.（2）The distribution of NH₄⁺-N in the soil with N fertilizer reduction was mainly centered on the fertilization point and gradually spread to the surrounding areas.Inorganic nitrogen in paddy soil is mainly NH₄⁺-N,NO₃^--N is relatively low,and the effect of fertilization on soil NO₃^--N concentration has no obvious regularity and difference.NH₄⁺-N concentration in soil under large granular fertilizer deep application was finally concentrated in the soil layer of 3-15 cm in the vertical direction and 0-7.5 cm in the horizontal direction.NH₄⁺-N concentration in soil under 5 cm row deep application was mainly concentrated in the soil layer of 3-9 cm in the vertical direction and 0-5 cm in the horizontal direction.The concentration of NH₄⁺-N in the soil at the depth of 10 cm was mainly concentrated in the range of 3-15 cm in the vertical direction and 0-7.5 cm in the horizontal direction.（3）The results showed that the dry biomass of different organs was closely related to the nutrient accumulation of nitrogen,phosphorus and potassium,and the nutrient accumulation was affected by the dry biomass.Because the panicle organs gradually developed and matured after full heading stage,the nitrogen accumulation gradually transferred to the panicle organs after full heading stage,and most of them were stored in the grain.The content of phosphorus itself in the plant is not high,most of the phosphorus is adsorbed by soil,and the total phosphorus accumulation shows a steady trend after maturity.The accumulation of potassium was more than that of phosphorus,which was equal to that of nitrogen.The accumulation of potassium was mainly stored in the stem,sheath and root of the plant.With the growth period,potassium showed an upward trend.（4）The results showed that on the basis of reducing nitrogen by 30%,deep fertilization could make rice roots fully contact with fertilizer,provide higher nutrient concentration during rice growth and development to promote rice tillering,increase dry biomass in various organs of rice,enhance root activity,accelerate grain filling,and maintain or improve rice yield.Deep application significantly increased the yield by 12.2%-56.4%compared with S210 treatment.At the same time,the nitrogen recovery rate of deep application treatment was 50.2%-59.5%,the nitrogen agronomic efficiency was17.8%-20.6%,and the grain production efficiency was 19.9%-22.8%,which was significantly higher than that of traditional nitrogen application treatment.（5）The effect of large granular fertilizer deep application on rice yield and nitrogen use efficiency was better than that of row deep fertilization,and the effect of fertilization depth of 10 cm was better than that of 5 cm.The main reason is due to the slow release of fertilizer and the longer duration of nutrients in the soil,so that the rice growth period has sufficient nutrient absorption;and the fertilization depth of 10 cm was consistent with the distribution area of rice roots,which could improve the nitrogen absorption of rice roots and increase the nitrogen utilization rate.In summary,deep fertilization can reduce the NH₄⁺-N concentration in surface water,thereby reducing ammonia volatilization and nitrogen loss in paddy field.Large granular fertilizer deep application slows the rate of nitrogen release and extends the cycle of fertilizer in the soil.After the reduction of nitrogen fertilizer by 30%,large granular fertilizer deep application and fertilization depth of 10 cm was consistent with the fertilizer requirement rule of rice,which improved the utilization efficiency of nitrogen in rice.