Effects Of Combined Application Of Inorganic Fertilizer And Organic Manure On Nitrogen Fertilization Rate Wheat Grain Yield And Soil Environment On The Loess Plateau Dryland

Loess Plateau dryland is an important wheat production area in China.The lower fertility and less rainfall in this area result in the lower wheat grain yield about 3600 kg/hm~2.Excessive fertilization that farmer applied is widespread to get higher yield.Excessive application of nitrogen fertilizer not only can not improve wheat yield,but also lead to a large number of soil nitrate residue,increase of agricultural greenhouse gas emissions,and a series of environmental problems such as surface water and groundwater pollution.It provides an important way that organic manure replace partial chemical nitrogen fertilizer to reduce nitrogen fertilization rate,improve wheat grain yield,ameliorate soil fertility and reduce environmental pollution,and to achieve the goal of zero growth of chemical fertilizer use in 2020.The nitrogen fertilization rate was determined by different N fertilization rate(0,75,150,225,300 kg/hm~2)combined with organic manure(30 t/hm~2)to explore the effects on reducing N fertilization rate and increasing wheat yield.The results showed that:1.The grain yield and biomass of winter wheat increased with the amount of nitrogen applied,and it showed an overall trend of first increase and then decrease.The wheat grain yield was highest when the nitrogen application rates were 225 and 150 kg/hm~2 in the single fertilizer application treatment and organic fertilizer treatment respectively.Compared with fertilizer application alone,combined application of inorganic fertilizer and organic manure could increase grain yield by 2.0%~18.3%in the case of reducing nitrogen fertilization rates by 12.9%~21.3%.Among three years,the organic nitrogen fertilizer had more obvious effect of reducing nitrogen and increasing yield in dry years.By analyzing the three elements of yield,it could be found that the combined application of inorganic fertilizer and organic manure mainly increased the number of effective panicles,which was increased by 6.4%~29.5%compared to the treatment with single inorganic fertilizer.Applying nitrogen fertilizer could significantly increase the photosynthetic rate and chlorophyll content of wheat flag leaf.The application of organic fertilizer was also beneficial to delaying leaf senescence and prolonging the photosynthetic validity period of wheat flag leaves.When the nitrogen application rate was 75 kg/hm~2 and below,combined application of organic manure could significantly increase flag leaf SPAD value2.Compared with nitrogen application alone,combining organic manure could significantly increase nitrogen uptake in above-ground and wheat grains.In normal rainfall years,the application of organic manure had no effect on nitrogen use efficiency,but it had significant improvement in dry years.The combination of organic and inorganic fertilizers could promote absorption of P and K by wheat,and the P content in grains increased significantly.The contents of organic matter,total nitrogen,available phosphorus and available potassium in the soil after winter wheat harvest increased significantly by organic manure applied,which increased by 25.4%,12.5%,114.5%and 44.8%respectively compared to nitrogen application alone.3.The deeper soil water content before sowing and after havesting was reduced by adding organic manure,especially in the 60~120cm soil layer,and it would tend to move deeper with the year extension.In the case of organic manure applied,the soil moisture content before sowing could be improved when the nitrogen application rate was less than or equal to 75 kg/hm~2 in dry years,and it increased in all treatment in normal rainfall years.In dry years,the application of organic manure could improve water consumption during wheat growing period and improve water use efficiency by 11.6%,but the difference was not significant in normal rainfall years.4.Appropriate rate of nitrogen fertilization combined with organic manure could keep more nitrate-N in root layer and inhibit its movement and accumulation in deeper layers.Excessive amount of nitrogen application could easily lead to the leaching of nitrate-N.Nitrate-N accumulation in 0~200cm increased with the nitrogen application rate increase.The accumulation of nitrate-N in 200cm soil layer in adding organic manure treatment was higher than that of single nitrogen fertilizer treatment in each nitrogen level.In the dry years,the nitrate accumulation in root layer was significantly higher in adding organic manure treatment,and it was opposite in deeper soil layer(mainly concentrated in the 80~120cm).In the normal rainfall years,when the nitrogen application rate was less than 150 kg/hm~2 in the case of organic manure applied,nitrate-N residue was significantly higher in tillage layer,and if nitrogen application amount was more than 225 kg/hm~2,it was found in deeper soil layers(40~80 cm).