Impacts Of Coated Controlled Release Urea Application On Agronomy-Economy-Energy Consumption-Environmental Performance Of Rice Production

The application of nitrogen fertilizer is closely related to crop production and local ecological environment.Under the dual pressure of food security and environmental protection,coated controlled release urea is superior to common urea in improving nitrogen use efficiency,increasing crop yield and saving manpower.However,the market price of coated controlled release urea is higher than common urea,moreover,there is a lack of systematic performance evaluation to explore agricultural,economic and environmental aspects of its field application.The experiment was conducted in central hilly region of Sichuan Basin,and four treatments were considered:no fertilization as control（CK）,single urea（N1）,single coated controlled release urea（N2）,40%urea and 60%coated controlled release urea（N3）.Nitrogen application amount of the three fertilization treatments was the same as the local optimal fertilizer application amount.In this study,the separate evaluation of agricultural,economic and environmental performance was finished based on a two-year field experiment.Then,the energy consumption,and net global warming potential of the rice cropping system under different application ratios of urea and coated controlled release urea were calculated.Additionally,based on the database Ecoinvent,a new calculation method for calculating or updating unit emergy value was proposed and then unit emergy values of urea and polyurethane coated controlled release urea were updated.Finally,a comprehensive evaluation was conducted through emergy accounting and economic assessment,in order to provide data support for the application of coated controlled release urea in rice cultivation.The main results were summarized as follows:（1）Coated controlled release urea fertilization was superior to urea in enhancing rice yield,nitrogen use efficiency and growers’benefit.Compared with N1,N2 and N3enhanced rice yield through the increase of effective spike number and grain amount significantly（p<0.05）.Consequently,the rice yield of N2 and N3 was enhanced by11.40%-21.84%and 7.96%-10.98%respectively.Moreover,the four nitrogen use efficiency indicators all followed the trend of N2>N3>N1.Compared with N1,nitrogen agronomy efficiency（NAE）,nitrogen partial factor productivity（NPFP）,and nitrogen contribution rate（NCR）of N2 increased by 43.96%-91.79%,11.40%-21.83%and29.13%-61.43%in order,and nitrogen recovery efficiency（NRE）was 2.71-2.98 times larger than that of N1.And NAE,NPFP,and NCR of N3 increased by 30.65%-46.22%,7.97%-10.97%and 22.98%-33.93%,and NRE of N3 was 2.21-2.47 times higher than that of N1.The increase in yield also led to an increase in benefits.The benefit of N2 and N3increased by 13.02%-29.53%and 11.92%-16.83%.Overall,single coated controlled release urea application achieved better performance in terms of enhanced rice yield,economic benefit and nitrogen use efficiency.（2）Coated controlled release urea fertilization reduced nitrogen loss but promoted greenhouse gas emissions（CH₄ and CO₂）.Compared with N1,N2 and N3 significantly reduced the peak value and average value of NH4⁺-N concentration in surface water;therein,the two indicator values of N2 were reduced by 82.06%-97.53%and91.54%-95.47%,and the two indicator values of N3 decreased by 58.20%-64.03%and62.49%-76.95%.Then,the N loss rate of N2 and N3 declined by 86.02%-95.34%and54.66%-70.48%.Nevertheless,compared with N1,N2 and N3 accelerated greenhouse gas emissions;therein,CH₄ emissions increased by 12.10%-47.26%and CO₂ emissions increased by 1.64%-20.86%.Overall,single coated controlled release urea application performed better on the reduction of N loss than single urea application but promoted the emission of CH₄ and CO₂emission.（3）Generally coated controlled release urea fertilization can improve harmony degree of rice production（relationship among rice yield,economic benefit,energy consumption and carbon emissions）.There was a slight difference among all the three fertilization schemes in energy consumption and the value was between 15356.02-15409.02 MJ,while energy consumption per unit yield and energy consumption per unit benefit showed the complete reverse trend.Results of energy consumption structure showed that more than 85%of direct energy consumption came from diesel-burning and more than 78%of indirect energy consumption derived from nitrogen fertilizer production.For global warming potential,the amount of N2 and N3 were bigger than N1 due to the more greenhouse gas emission from paddy fields and agricultural materials production.Therein,the biggest direct global warming potential source was the paddy field（CH₄）,which accounted for94.75%-96.67%and the biggest indirect global warming potential source was nitrogen fertilizer production with a contribution rate of 71.54%-75.34%.Though the biomass of N2and N3 were greater than N1 which would result in bigger carbon sequestration,the net GWP（net global warming potential）of N2 and N3 were still higher than N1.Indicator values of the net GWP intensity increased in N2 while the trend was not obvious for N3during this study period.Generally coated controlled release urea fertilization can improve harmony degree of rice production（relationship between rice yield,economic benefit,energy consumption and carbon emissions）.The LDMI results indicated that yield and benefit were the guarantees of harmony degree of the rice cropping system,and reducing net GWP was the key to improving the harmony degree of rice cropping system.（4）Based on the Ecoinvent database,a new method for calculating or updating unit emergy values was proposed within the disciplines of emergy algebraic rules.This method elaborated the"allocation"principle,specific calculation steps and related details in life cycle assessment and emergy accounting then provided a theoretical and data basis for related system performance evaluation.Furthermore,an emergy analysis for the urea production system and coated controlled release urea production system was conducted and the unit emergy values of urea and polyurethane coated controlled release urea were calculated,which was 7.79E+12 sej/kg and 8.57E+12 sej/kg,respectively.And the emergy indicators revealed the high environmental load and low environmentally sustainable index of the two production systems.Consequently,they were unsustainable in the long run.（5）N3 could achieve the highest coordination degree of agronomic,economic and environmental performance.The total emergy of three fertilization treatments followed a trend of N2>N1>N3.The cropping system was driven by imported inputs and showed a heavy reliance on labor,services and nitrogen fertilizer.N2 and N3 could increase environmental load,but N3 performed better than N2 and N1 according to the adjusted emergy sustainability index.At last,results of system coordinative degree showed 40%urea and 60%coated controlled release urea achieved the best highest coordination level among agricultural,economic and environmental performance.