Effects Of Combined Application Of Organic And Inorganic Fertilizers On Yield And Soil Fertility And The Fate Of Organic Fertilizer Nitrogen In Dryland Wheat Field Based On ¹⁵N Labeling

The cultivation of wheat in the northwest dryland plays an important role in ensuring the food security of China.In the process of wheat production in this region,heavy application of chemical fertilizers,no or little application of organic fertilizers,and excessive fertilization are common problems.Organic fertilizers can adjust the physical and chemical properties of soil,activate soil nutrients,improve soil fertility,and increase soil productivity.The rational application of organic fertilizer and chemical fertilizer can reduce the input of chemical fertilizer,improve the efficiency of fertilizer utilization,and increase the yield of crops.It is an effective way to solve the problem of excessive input of chemical fertilizer and stabilize grain output.At present,the research on the combination of organic and inorganic fertilizers mainly focuses on how much chemical fertilizers can be replaced by organic fertilizers or the simple combination of chemical fertilizers and organic fertilizers.Few people pay attention to the organic fertilizer itself,and there are few studies on the ability of organic fertilizer to provide nitrogen fertilizer after it enters the soil and the residue of organic fertilizer in the soil.Only some scholars estimate the fertilizer supply capacity of organic fertilizer through indirect methods.¹⁵N isotope tracing technology can be used to quantitatively study the whereabouts of N in soil and plants,and can be used as an auxiliary means to study the contribution of nitrogen in organic fertilizers to plants and soil.This study was based on the plant-soil system of dryland in northwest China.Through field trials for 6 consecutive years(30 t hm^-2 of organic fertilizer with 0,75,150,225,300 kg N hm^-2),research on the fate of fertilizer nitrogen in plant-soil under the condition of long-term organic fertilizer and nitrogen fertilizer application.A three-year field micro-plot experiment was carried out using isotope tracer technology(30 t hm^-2 of ¹⁵N-labeled organic fertilizer was applied with 0,75,150,225,300 kg N hm^-2),research on the fate of nitrogen in the organic fertilizer in the plant-soil under the condition of combining organic fertilizer with nitrogen fertilizer.Through the culture test(¹⁵N labeled organic fertilizer was applied with 0.1g N kg^-1 soil and 0,0.05,0.1,0.15,0.20 g N kg^-1 soil was applied),the mineralization of nitrogen in organic fertilizers treated with organic fertilizers and nitrogen fertilizers was studied.The main findings and conclusions are as follows:In the field experiment of organic fertilizer combined with nitrogen fertilizer for 6consecutive years,when 30 t hm^-2 organic fertilizer was combined with 150 kg N hm^-2（M+N150）or 225 kg N hm^-2,the yield of wheat was significantly higher than other treatment.The 6-year average yield of M+N150 treatment was 40.6%,8.8%and 8.7%higher than that of M,M+N75 and M+N300 treatments,respectively.Nitrogen fertilizer effect curve calculation showed that 30 t hm^-2 organic fertilizer combined with 190 kg N hm^-2 had the highest wheat yield;M+N150 treatment of wheat biomass,nitrogen uptake and chemical nitrogen use efficiency were significantly higher than M and M+N75 treatments.The nitrate nitrogen content of the 0-200 cm soil layer in the M+N150 treatment was close to that in the M treatment and the M+N75 treatment,M+N150 treatment was significantly lower than that of M+N225 treatment and M+N300 treatment at harvest stage.M+N150 treatment has less risk of nitrate leaching.Compared with M+N300 treatment,M+N150 treatment significantly increased soil MBC and MBN contents,and M+N150 treatment NAG（β-1,4-N-acetylglucosaminidase）,LAP（L-leucine）Acid aminopeptidase),βG（β-1,4-glucosidase）,CBH（cellobiohydrolase）,and AKP（alkaline phosphatase）had the highest activity.It shows that the application of organic fertilizer with appropriate amount of nitrogen fertilizer can increase wheat yield,biomass,nitrogen absorption,soil MBC,MBN content and soil enzyme activity in 0-20 cm soil layer,improve the utilization efficiency of chemical nitrogen fertilizer,and reduce soil nitrate content in 0-200 cm soil layer.30 t hm^-2organic fertilizer combined with 150 kg N hm^-2 is the best ratio.In the experiment of ¹⁵N labeled organic fertilizer combined with nitrogen fertilizer for three consecutive years,M+N75 and M+N150 treatments had the highest grain dry weight,wheat biomass and nitrogen accumulation.M+N75 and M+N150 treatments had significantly higher uptake of ¹⁵N in organic fertilizers than M+N300 treatments.The three-year cumulative contribution rates of nitrogen in organic fertilizers to wheat grain nitrogen in the M+N75 and M+N150 treatments reached 6.2%and 5.2%,respectively,which were significantly higher than those in the M+N300 treatment（2.7%）.The utilization rate of nitrogen in organic fertilizer reached 10.8%and 10.1%in three years respectively,which was significantly higher than that of M+N300 treatment（6.1%）.The residual amount of ¹⁵N in mineral nitrogen was mainly distributed in the 0-40 cm soil layer,and decreased year by year.The residual amount of ¹⁵N in mineral nitrogen in the M+N225 and M+N300 treatments was higher than that in other treatments.After the organic fertilizer was applied to the soil,it mainly increased the content of acid-degradable ammonium nitrogen and acid-degradable amino acid nitrogen in the soil,and the higher the amount of combined nitrogen fertilizer,the higher the residual amount.In the third year of the experiment,M+N75 and M+N150treatments had higher ¹⁵N residues in 0-40 cm soil than M+N225 and M+N300 treatments,and ¹⁵N residues in 40-100 cm soils were lower than M+N225 and M+N300 treatment.70%of the nitrogen in the organic fertilizer remained in the 0-100 cm soil,the M+N75 treatment was the lowest,and the M+N300 treatment was the highest.It shows that the application of an appropriate amount of nitrogen fertilizer with organic fertilizer can promote the absorption of organic fertilizer nitrogen and acidolytic ammonium nitrogen and acidolytic amino acid nitrogen in the soil by plants.Increasing the contribution rate of organic fertilizer nitrogen to wheat grain nitrogen is beneficial to the formation of wheat yield.The application of an appropriate amount of nitrogen fertilizer with organic fertilizer can increase the use efficiency of organic fertilizer nitrogen,reduce the residue of organic fertilizer nitrogen in the soil,reduce the leaching risk of nitrogen in the soil and reduce the loss of nitrogen in the organic fertilizer.In the experiment of ¹⁵N labeled organic fertilizer combined with nitrogen fertilizer under the culture condition,M+N0.20 treatment significantly increased the nitrate nitrogen content in the soil.M+N0.15 treatment significantly increased soil microbial biomass carbon content.M+N0.05 treatment（chemical nitrogen/organic nitrogen=1/2）significantly increased soil microbial biomass nitrogen content,and the residual amount of nitrogen in soil was also the highest,which was significantly higher than that of M treatment The mineralization rate of organic fertilizer in M+N0.15 treatment reached the highest 6%,which was significantly higher than that in M,M+N0.05 and M+N0.20 treatments.It shows that the application of organic fertilizer with an appropriate amount of nitrogen fertilizer can increase the content of soil microbial biomass carbon and promote the mineralization of organic fertilizer,and M+N0.15 treatment（chemical nitrogen/organic nitrogen=3/2）is the best.In this study,the effect of organic fertilizer combined with nitrogen fertilizer was proved by analyzing the whereabouts of fertilizer nitrogen in plant-soil under the condition of long-term organic fertilizer combined with nitrogen fertilizer.Using ¹⁵N labeled organic fertilizer to study the contribution of nitrogen in organic fertilizer to plants and its residue in soil under the condition of combining organic fertilizer with nitrogen fertilizer,and clarifying the whereabouts of nitrogen in organic fertilizer.Under the culture conditions,the mineralization of nitrogen in organic fertilizer and nitrogen fertilizer was studied with ¹⁵N labeled organic fertilizer,and the optimal ratio of nitrogen and chemical fertilizer nitrogen in organic fertilizer to promote nitrogen mineralization of organic fertilizer was clarified.These results help to clarify the fate of nitrogen in organic fertilizers under the condition of combined application of nitrogen fertilizers with organic fertilizers,and can provide theoretical basis and guidance for the rational application of organic fertilizers and nitrogen fertilizers in northwest Dryland winter wheat.