Effects Of Reduction Application Of CRNF On The Growth Of Spring Maize And The Losses Of Soil N

Polymer-coated urea?PCU?is a new type of nitrogen?N?fertilizer.N release of PCU is affected by soil moisture and temperature.The rate of N release basically corresponds with N demand for crops during growth period.PCU application can increase N uptake and N utilization efficiency?NUE?in cropping system,even significantly decrease N losses to environment.At present,the severity of agricultural non-point source pollution has led to the application of PCU as a hot spot.How to apply PCU rationally for optimal yield,minimum N losses and the best coupling economic benefit of input-output-environmental cost?This problem needs to be done through systematic research.Hence,the effects of PCU application with different reduction of N rates on spring maize cropping and N loss in 3 consecutive years were researched by long-term field plot trial in dry land of southern China,which aimed to provide some reference for maize cropping of scientific fertilization in this area.The results were as follows:?1?Relative to CU,a 0²0%reduction in the PCU-N application rate did not significantly affect the maize yield during the three consecutive years,however,a 30%reduction in the PCU-N application rate led to significant yield loss?by 13.07%?in the third year despite the consistent yields achieved in the first two years.?2?Relative to CU,a 20%³0%reduction in PCU-N application significantly increased NUE by 15²3 percentage points and PFPN?partial factor productivity from applied N?was significantly improved by 12.49%³1.80%after 10%³0% reduction in PCU-N application.?3?Relative to CU,0¹0%reduction in PCU-N application didn't present significant effects for mitigating gaseous-N losses,while 20%³0%reduction in PCU-N application significantly decreased N₂O emissions ammonia volatilization by 25.50%⁵5.12%and 15.62%⁴3.90%,respectively.?4?Relative to CU,0¹0%reduction in PCU-N application performed poorly for reducing runoff-N losses,but 20%³0%reduction in PCU-N application significantly reducing runoff-N losses by 23.03%⁴8.52%.The main forms of losses of runoff-N were NO₃^--N and PN?particulate N?which accounted for 76.32%⁹0.44%of total runoff-N losses.0³0%reduction in PCU-N application significantly reducing leaching-N losses by 15.67%⁵8.92%?P<0.05?,and the major forms of leaching-N were NO₃^--N and DON?dissolved organic nitrogen?, accounted for 70%⁹3%and 6%²8%of total leaching-N losses,respectively.?5?PCU application significantly abated N loss via N₂O emission,NH₃ volatilization, runoff and leaching to the environment,and as N application rate decreased,N loss significantly reduced.Our results showed that a 0³0%reduction in the PCU-N application rate mitigated N loss by 12.83⁴6.13%,and the two main N-loss pathways were leaching?55.22⁶2.26%?and NH₃ volatilization ?29.81³6.03%?.?6?Based on output-input for three years spring maize cropping in this area,PCU application with 0³0%reduction in N rates didn't get additional economic returns,even suffered deficits of 563³615 yuan·hm^-2 caused by high price of PCU.And based on net economic benefits?NEB?considering the combination of more yield economic returns and less environmental costs,the annual average NEB was-5463¹3211 yuan·hm^-22 for CU,-3463¹2836 yuan·hm^-2 for 100PCU,-1204¹3005 yuan·hm^-2 for 90PCU,792¹3098 yuan·hm^-2 for 80PCU,2565¹2829 yuan·hm^-2 for 70PCU.?7?It is a necessary requirement for the sustainable development of agriculture to determine the optimal nitrogen application rate of controlled release nitrogen fertilizer should not be confined to the guarantee of input and output,but also to environmental protection.In summary,the results shown that a 0¹0%reduction in the PCU-N application rate underperformed environmental protection because of the deficit of economic benefit of output-input was lower but higher NEB deficit;a 20%reduction in the PCU-N application rate presented moderate deficit in economic benefit of output-input but earned NEB;a 30%reduction in the PCU-N application rate underperformed the earnings of farmers because of the higher deficit of economic benefit of output-input although the NEB was the best for spring maize cropping.Thus,our findings suggest that reducing the PCU-N application rate by 20%(192 kgN·hm^-2)is a reasonable environmental and economic optimal N rate for spring maize cultivation in hilly areas of southern China and we considered above-mentioned deficit of producer can be made up by reducing production cost through PCU production technology reform or policy subsidy.