| Controlled-release nitrogen(N)fertilizers(CRNF)are designed to release N into the soil solution at rates which closely match the N demands of crops,thus improving crop yield and fertilizer use efficiency,which are ideal choices to solve the problem of fertilizer.At present,there are many kinds of CRNF in the market,and the application effects were varying considerably.Choosing the appropriate types of CRNF and application methods is an important premise to reduce the production cost and increase crop yield.In addition,blending application of controlled-release urea(CRU)and uncoated urea is often used method in agricultural production,which can not only achieve the effect of controlling N release,but also greatly reduce the production cost.Elucidating the mechanisms for increasing crops yield and the long-term effect of application fertilizer mixture can provide strong theoretical support for the popularization and application of CRU in wheat and maize.Effects of 3 kinds of CRU application on yields and yield components of wheat and maize,enzyme activity in soil,soil nutrient,and N release characteristics of CRU under field conditions soil were investigated in a 7-year pond culture experiment under a winter wheat-summer maize rotation system in Shandong agricultural university,and the application of urea was control for comparison.From October 2013 to September 2015,the effects of a fertilizer mixture(CRU and uncoated urea)on crop growth,yields,N use efficiency(NUE),and economic profits were investigated in a field using a winter wheat(Triticum aestivum L.)and summer maize(Zea mays L.)rotation system in Shandong agricultural university.Besides,the effects of a mixture of CRU and uncoated urea(N ratios 7:3,respectively)on crop yields,NUE,N budgets,soil fertility,and economic benefits were investigated in a wheat-maize rotation system over an 8-year period at “Intensive agricultural ecosystem experimental station in North China” in Huantai County,Shandong Province,China.The main results were as follows: 1 Effects of application of different kinds of CRU on wheat and maize yield,NUE,and soil biochemical propertiesNutrient release rates of CRU in filed condition were not only affected by the coating material,but also significantly affected by soil temperature.Therefore,the choice of CRU should be based on the crops growth period and soil temperature in the planting area.Among those 3 kinds of CRU,the N release rate of sulfur-coated urea(SCU)was the fastest,the N release rate of polymer coating of sulfur-coated urea(PSCU)was the second,and the N release rate of polymer-coated urea(PCU)was the most slowly.Consequently,long-term application 3 kinds of CRU once improved wheat and maize yields by 4.9%-11.5% and 7.3%-13.0%,increased NUE by 28.7%-34.4% in wheat,and 65.9%-80.3% in maize,respectively,compared with urea split application at the same N application rates.Furthermore,PSCU achieved the highest and the most stable crop yields among CRU,and the yield of wheat and maize increased by 11.5% and 13.0%,respectively.Even reducing CRU rate by 30% produced the same yields as with the 100% rate of uncoated urea.The contents of soil NO3--N and NH4+-N were significantly increased in the late stages of winter wheat and summer maize by application of CRU.Applying of CRU once could meet the requirements of N during the whole growth periods of winter wheat,especially in the key growing period.In addition,soil total N and organic matter contents in CRU were effectively increased in the topsoil of 0-20 cm after 5-year.Long-term application of CRU had great potential to relieve soil pH decreased.In addition,3 kinds of CRU increased catalase,urease,invertase and neutral phosphatase activity compared with common urea,in which SCU and PSCU were better than PCU in improving soil enzyme activity.2 Effects of application of mixtures of CRU and uncoated urea on wheat and maize yields,NUE,and economic profitsBlended applications of CRU and uncoated urea fulfilled the wheat and maize plants demand for N during the entire growth periods.In addition,significant linear correlations between N release rate of CRU and N requirements of wheat and maize were observed during the whole growth periods.The yields in the mixture fertilizer treatments were increased by 4.8%-16.8% for wheat and 4.0%-21.0% for maize,compared with uncoated urea treatments at the same N application rates.The NUE in the mixture treatments were increased by 33.7%-56.4% for wheat and 16.7%-48.5% for maize,respectively,and the average annual net profit was also increased by 14.5%-19.9%,compared with uncoated urea treatments at the same N application rates.Although the mixture fertilizer supplied one-third less N,its yield was similar with 100% rate of uncoated urea.However,the uncoated urea supplied one-third less N,the yields were significantly decreased by 6.1%-11.1% for wheat and 7.2%-9.4% for maize than 100% rate of uncoated urea.In addition,the mixture treatments significantly increased the quality and quantity of tillering of wheat and kernels per row of maize.No significant difference was observed among mixture and uncoated urea treatments in 1000-grain weight of wheat,number of ears per plant of maize,and rows per ear of maize.Furthermore,the NO3--N and NH4+-N concentration in soil were enhanced especially during the later crops stages,and leaching of soil N was reduced by using the fertilizer mixture.The mixture treatments reduced the leaching of N in the soil profile by augmenting NO3--N and NH4+-N contents at the 0-40 cm soil depth and reduced the leaching of NO3--N into deeper soil layers.In addition,blended applications of CRU and uncoated urea significantly increased plant height,stem diameter,and leaf chlorophyll SPAD value of maize in the middle and later growth stages.Hence,the photosynthetic ability of maize in the middle and later growth stage was improved.3 Effects of long-term application of a mixture of CRU and uncoated urea on crop yields,NUE,N budgets,soil fertility,and economic benefitsThe results of 8-year of continuous positioning test showed that: applying the mixture increased grain yields of wheat and maize by 8.2%-11.9% and 6.8%-9.8%,respectively,compared with treatments of monotypic,uncoated urea.Mean NUE were increased by 35.7%-37.6% and 13.2%-14.3% for wheat and maize,respectively,and annual net profits increased 15.4%-21.8%,compared with uncoated urea treatments at the same rates of N application.Regardless of application rate,the mixed urea treatments reduced the leaching of N in the soil profile by augmenting NO3--N and NH4+-N contents at the 0-40 cm soil depth and reduced the leaching of NO3--N into deeper soil layers.Considering the N budget,apparent N losses were increased with higher N application rates,and applying the mixture significantly reduced N losses by 6.8%-11.3%,compared with monotypic urea.The pH of the surface soil was also lowered and exchangeable Ca2+ and Mg2+ were reduced by the long-term application of monotypic urea.In addition,total soil N and soil organic matter contents 0-20 cm deep from the Mix treatments were higher than from the uncoated urea treatments at the same N application rates. |
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