Study On The Difference Of Nitrogen Use Efficiency And Environmental Benefits Of Synchronous Deep Fertilization Of Rice Machine-transplanting

Nitrogen（N）fertilizer is widely used in agricultural production,which plays a very important role in high quality and high yield of crops.Excessive application of nitrogen fertilizer not only causes a large amount of N loss,but also causes nitrate pollution of groundwater,eutrophication of lakes and increase of greenhouse gas（GHG）emissions.Therefore,it is very important to discuss how to reduce N loss in paddy field to improve N use efficiency and reduce environmental pollution,and deep fertilizer application can effectively improve N use efficiency,which plays an important role in improving N application method in paddy field and realizing high yield and efficiency of rice.This study in a typical cropping area,based on soil testing and formula fertilization,combined with synchronous deep fertilization of rice machine-transplanting（MRSF）.The effects of MRSF with different N application rates on nutrient uptake,yield,ammonia volatilization,greenhouse gas emission,N loss and carbon footprint of double cropping rice were studied.The relationship between various factors was discussed,and the economic benefits of net ecosystem（NEEB）were calculated.The response characteristics of N loss,absorption and utilization in rice paddy field under MRSF were revealed.The results provide a reference for the application of high quality and high yield and new fertilization technology.The main results are as follows:1.Yield and population quality of double cropping rice under synchronous deep fertilization of rice machine-transplantingCompared with conventional fertilization（CF）,rice yield was significantly increased by 0.5～20.2%under different N application rates in Miluo and Yiyang.In2017,the early rice yield of 70%N deep fertilization（DF）treatment was the highest(8.7 t hm^-2),while the late rice yield of 80%DF treatment was the highest(6.1 t hm^-2).In 2018,the yield of early and late rice(7.5 and 7.9 t hm^-2)under 80%DF treatment was the highest.The high yield of MRSF is due to the higher leaf area index,chlorophyll content,and grain number per spike.MRSF increased the panicle rate,thus improving dry matter accumulation and nutrient uptake.In addition,compared with CF treatment,MRSF treatments increased the economic benefit by 9.9～31.8%（Miluo）and 15.0～25.7%（Yiyang）,respectively.The results showed that the increase of yield and population quality of double cropping rice was related to synchronous deep fertilization.2.Characteristics of nutrient uptake and utilization double cropping rice under synchronous deep fertilization of rice machine-transplantingWith the decrease of N application rates,N recovery efficiency of double cropping rice increased first and then decreased,N harvest index,N agronomic efficiency and N partial factor productivity increased,while soil available N content decreased.Compared with CF treatment,MRSF treatment increased N,P and K accumulations by 7.9～11.7%,9.4～25.9%and 2.0～6.5%（2017）,8.2～15.0%,9.0～12.1%and 14.0～18.1%（2018）,respectively.Late rice respectively 0.6～5.7%and9.1～14.4%and 3.7～19.6%（2017）,6.1～8.5%and 9.4～19.3%and 18.7～22.2%（2018）;N recovery efficiency,N agronomic efficiency and N partial factor productivity increased by 11.5～27.8,11.4～23.4 and 14.2～38.8 percentage points（2017）,11.8～23.7,5.7～12.1 and 9.2～33.4 percentage points（2018）,respectively.Late rice increased by7.1～16.9,3.7～8.6 and 6.1～22.9 percentage points（2017）,and 6.9～25.8,3.8～6.3 and11.1～34.6 percentage points（2018）,respectively.The N reduction of 20～30%in early and late rice was better.The integration and optimization of fertilization technology and mechanized transplanting model can effectively reduce N fertilizer application in paddy fields,facilitate the absorption and accumulation of N,P and K,and simultaneously improve the yield and N fertilizer use efficiency of double cropping rice.3.Characteristics of ammonia volatilization loss of double cropping rice under synchronous deep fertilization of rice machine-transplantingThere were differences in NH₃ volatilization flux in double cropping rice field under different N application levels.The ratio of NH₃ volatilization loss to N application was 41.2～45.3%（early rice）and 44.9～45.2%（late rice）,respectively.Compared with CF treatment,the cumulative NH₃ loss of early rice decreased by 24.8～26.9%and20.1～20.8%in 2017 and 2018,and that of late rice decreased by 18.6～23.0%and20.2～21.8%.The ratio of NH₃ volatilization loss to N application decreased with the decrease of N application.In 2017,the treatment of reducing N10%and 40%for early and late rice reached the lowest,and the treatment of reducing N40%reached the lowest in 2018.During the monitoring period,the NH₃ volatilization accumulation model constructed by elovich equation was established;It is worth noting that the field monitoring results are in good agreement with the calculated values.4.Characteristics of N footprint of double cropping rice field under synchronous deep fertilization of rice machine-transplantingMechanical transplanting simultaneous deep fertilization significantly reduced the loss of NH₄⁺-N and NO₃^--N in runoff and seepage.In the whole rice growing season,rice mechanical transplanting synchronous deep fertilization increased the mineral N content in the deep soil.Compared with CF treatment,mechanical transplanting synchronous deep fertilization significantly reduced the total N footprint of rice,which were 42.4～53.5%（early rice）and 45.2～57.2%（late rice）,respectively.Correlation analysis showed that the mineral N loss and total N footprint increased with the increase of N application rate under rice mechanical transplanting synchronous deep fertilization under different N application rates,and the difference between reducing N by 10-30%was not significant,but both were higher than that under reducing N by 40%.Simultaneous deep fertilization with mechanical transplanting could not only maintain soil N content,but also reduce the environmental risk of N loss caused by paddy leakage and runoff,so as to reduce the N footprint of double cropping rice system in south China,and the reduction of N footprint by 40%was the best.4.Characteristics of net ecological and economic benefits of double cropping rice under synchronous deep fertilization of rice machine-transplantingCompared with CF treatment,soil CH₄ and N₂O emissions under different N rates were significantly reduced by 13.2～45.6%and 5.4～28.7%（early rice）,21.3～42.3%and 19.1～35.6%（late rice）,respectively.The total carbon footprint of mechanical transplanting simultaneous deep fertilization decreased by 17.1～38.5%（early rice）and 17.0～32.3%（late rice）under different N application rates,respectively.In addition,MRSF treatments reduced soil CH₄ and N₂O emissions under different N rates,while reduced the total greenhouse gas emissions of early and late rice by10.1～35.8%and 5.2～25.5%,respectively,in which the reduction of N 40%was the best.The NEEB of MRSF treatments was significantly higher than that of CF treatment 16.3～25.7%（early rice）and 23.4～29.7%（late rice）.The NEEB of early and late rice reached the maximum when reducing N 30%,followed by reducing N 40%and reducing N 20%.All in all,MRSF is a green and sustainable planting measure which is friendly to ecological environment.