Effects Of Combined Application Of Organic And Inorganic Fertilizers On Soil Nutrient Availability And Enzyme Activity In Rainfed Wheat Field

The Loess Plateau is a traditional dry farming area in China,where the soil is poor,fertility is low,and crop yield is low.In order to obtain more food,people apply fertilizer over a long period of time,which has a series of adverse effects on the soil and the environment.Combined application of manure and inorganic fertilizers can significantly improve soil enzyme activity and improve soil nutrient supply.In order to give full play to the fertilizer benefits and achieve high and stable yields of winter wheat,it is necessary to understand the biochemical characteristics of soil under different nitrogen(N)application rates combined application of organic fertilizer.Different N application rates(0,75,150,225,300 kg N /ha)combined with organic manure(0 and 30 t/ha)were set up by split plot experiment.In the tillering,jointing,heading and filling stages of winter wheat,soil samples of 0–20 cm soil layer were taken,and soil samples of 0-200 cm soil layer were taken before sowing and maturity,and soil nutrient and enzyme activities were determined by conventional methods.During the harvest period,the grain yield,aboveground biomass and grain nutrient content of winter wheat were investigated.The results are as follows:(1)Fertilizer application under the condition of applying organic fertilizer can significantly increase grain yield,which can be increased by 12.5% compared with single application of chemical fertilizer,and the application of organic fertilizer can save 8.7% of nitrogen fertilizer input and ensure high yield and stable yield of winter wheat.In addition,with the increase of nitrogen application rate,the yield of winter wheat increased first and then decreased.Among them,N150+M is the best.It shows that only the right amount of nitrogen fertilizer can achieve the best level of wheat yield,and the nitrogen application rate is too high or too low to limit the increase of wheat yield.By analyzing the three elements of wheat composition,it was found that the application of organic fertilizer significantly increased the effective panicle number of winter wheat by 10.3% compared with single application of chemical fertilizer,but had no significant effect on the number of kernels per spike and 1000-grain weight.(2)Appropriate ratio of organic and inorganic fertilizers can promote the synergistic absorption of nitrogen,phosphorus and potassium in wheat.Compared with single application of chemical fertilizer,the application of organic fertilizer can significantly increase the phosphorus content of winter wheat grain,the nitrogen uptake of grain,the phosphorus uptake of grain,stem,leaf and hull,and the potassium uptake of grain,stem,leaf and hull,increased by 6.7%,11.9%,23.2%,58.9%,33.3%,12.1%,45.2%,and 27.6%,respectively.Under the condition of applying organic fertilizer,when the nitrogen application rate exceeded 75 kg N /ha,there was no significant difference in nitrogen uptake,potassium uptake and phosphorus uptake between treatments.(3)Appropriate amount of nitrogen fertilizer combined with organic fertilizer had obvious stimulating effect on soil enzyme activity.Compared with single application of chemical fertilizers,organic and inorganic fertilizers can increase soil sucrase,urease activities and alkaline phosphatase,with an average increase of 4.5%,3.5% and 4.2% in2016-2018,while catalase in 2016.However,there was no significant difference in catalase between 2016 and 2017,with a significant increase of 3.0% in 2017-2018.It shows that the cumulative effect of organic fertilizer on soil organisms is slowly reflected.In addition,soil sucrase,alkaline phosphatase and catalase activities generally increased first and then decreased with the increase of nitrogen application rate,among which N150+M was the best treatment.Soil urease activity increased first and then stabilized with the increase of nitrogen application rate,and N(255~300)+M treatment was the best.(4)In the whole growth period of winter wheat,the combined application of manure and inorganic fertilizers can significantly increase the soil total nitrogen,organic matter,available phosphorus and available potassium in 0-20 cm of ploughed soil.In the two years from 2016 to 2018,the average increase was 24.0%,34.6%,190.0%,and 39.9%.In addition,when the nitrogen application rate is 0-150 kg N /ha,the application of organic fertilizer can significantly increase the soil water content and nitrate nitrogen residue at0-20 cm soil layer.When the nitrogen application rate is 225-300 kg N/ha,the application of organic fertilizer will increase the water consumption in the deep layer(80-100 cm),and also cause the risk of nitrate leaching to the deep layer.It indicated that the appropriate amount of nitrogen fertilizer combined with organic fertilizer not only had the effect of fertilizing the soil,but also alleviated the environmental problems caused by the excess nitrate nitrogen residue.In summary,the application of 30 t/ha organic fertilizer with 150 N kg /ha nitrogen fertilizer is beneficial to fertilize the soil,ensure high yield and stable yield of wheat,reduce environmental pollution,and enhance the sustainability of winter wheat soil ecosystem in the region.