Effects Of Organic Fertilizer Substituting Chemical Fertilizer And Film Mulchig On Soil Fertility Quality And Water And Nitrogen Utilization In Wheat-Maize Double-Cropping System

Drought and water shortage is an important factor affecting fertilizer efficiency and agricultural production.Long-term excessive application of chemical fertilizers caused by crop quality decline,soil structure damage,microbial activity reduced,soil fertility decreased and greenhouse effect aggravated problems such as prominent.The combination of mulching and organic fertilizer instead of chemical fertilizer can not only improve soil fertilizer and coordinate the nutrient balance,but also has important practical significance for crop yield increase,efficient use of water and nitrogen and sustainable agricultural development.A winter wheat-summer maize double-cropping field experiment was conducted in the Guanzhong Plain of China.In this experiment,the two main experimental factors were mulching（M）and no-mulching,and the secondary experimental factors included no fertilizer application（CK）,organic fertilizer substituting chemical fertilizer at 0%（T0）,25%（T25）,50%（T50）,75%（T75）,and 100%（T100）,for a total of 12 treatments.The time of this experiment was from June 2021 to June 2022.By exploring its effects on soil physical and chemical properties,biological properties,crop growth and yield,and water and nitrogen use efficiency,the optimal organic fertilizer substitution and mulching measures were proposed to improve local crop yield and soil quality.The main research results are as follows:（1）Organic fertilizer substituting chemical fertilizer and mulching effectively improved soil physical and chemical properties,especially the organic fertilizer substitution 75%treatment.In the 0-20 cm and 20-40 cm soil layers,compared with chemical fertilizer treatment,MT75/T75 reduced soil bulk density by 4.9%/3.9%and3.3%/3.3%,increased saturated water content by 13.4%/20.9%and 8.0%/5.2%,and soil porosity by 1.8%/20.9%and 5.4%/5.2%,respectively.The effect of mulching on the improvement of soil physical properties was not significant.Compared with the chemical fertilizer treatment,MT75/T75 increased the total nitrogen content（0-40 cm soil layer）of summer maize and winter wheat by 26.1%/23.3%and 14.4%/14.8%,and organic matter content（0-20 cm soil layer）by 23.2%/26.2%and 33.9%/26.3%.Soil nitrate N content showed that:chemical fertilizer treatment>organic fertilizer substituting chemical treatment>no fertilizer treatment.Ammonium N content was more stable,and fertilizer application could play a certain increase effect.Compared with the no-mulching treatment,the mulching increased the total N content（0-20 cm soil layer）of summer maize and winter wheat by 15.8%and 7.6%,and the organic matter content by 17.8%and 2.4%.Mulching increased soil nitrate nitrogen content and had no significant effect on ammonium nitrogen.（2）Organic fertilizer substituting chemical fertilizer and mulching improved soil biological fertility and organic fertilizer substitution 50%treatment had a better carbon sequestration and emission reduction effect.Fertilization,mulching and the interaction of two factors had significant effects on soil CO₂-C emission and emission efficiency.Compared to chemical fertilizer treatment,MT50 reduced 30.3%CO₂-C emissions and MT50/T50 reduced 35.5%/5.5%CEE in summer maize season.CO₂-C emissions of organic fertilizer treatments in winter wheat season showed an increase under mulching and a decrease under no-mulching.The T0 treatment(0.54 kg·kg^-1)had the lowest CEE followed by T25(0.56 kg·kg^-1)and T50(0.57 kg·kg^-1)among the fertilizer treatments applied under no-mulching.Mulching increased total soil CO₂-C emissions by 165.0%and205.0%in summer maize and winter wheat,respectively.Microbial biomass increased with increasing percentage of organic fertilizer replacement.Compared to MT0/T0,MT100/T100 increased 77.3%/107.4%MBC and 36.6%/28.3%MBN in summer maize,and 37.4%/25.4%MBC and 25.4%/26.6%MBN in winter wheat.Compared to no-mulching treatment,mulching increased 6.8%MBC and 9.7%MBN in summer maize and 16.5%and 11.4%MBN in winter wheat.（3）Organic fertilizer substituting chemical fertilizer and mulching promoted crop growth and increase yield,and organic fertilizer substitution of 50%had higher annual yield and economic benefits.Organic fertilizer substitution 75%and mulching treatments had higher plant height,leaf area index and above ground biomass.Organic fertilizer substitution treatments all had significant effects on spike traits.Compared to chemical fertilizer treatments,MT50/MT75 increased summer maize yield by 5.6%/7.5%and winter wheat yield by 13.7%/9.1%,respectively;T50/T75 increased summer maize yield by 10.5%/14.3%and winter wheat yield by 11.8%/6.9%,and annual yield of organic fertilizer substitution 50%higher.Mulching increased 8.4%to 22.4%of summer maize yield and 0.9%to 13.1%of winter wheat yield.Compared to the chemical fertilizer treatment,the planting cost of organic fertilizer treatments increased by 221.6%and 240.2%in summer maize season and 144.1%and 155.9%in winter wheat season,respectively.The economic benefits of the organic fertilizer treatment decreased with the increase in the percentage of organic fertilizer substitution.Organic fertilizer substitution of 50%was the best economic benefit if the excess fertilizer input over chemical fertilizer was not considered.Mulching increased the economic benefits of MCK,MT0,MT25 and MT50 in summer maize season and MCK,MT50,MT75 and MT100 in winter wheat.（4）Organic fertilizer substituting chemical fertilizer and mulching improved water and nitrogen use efficiencyand organic fertilizer substitution of 50%had a better water and nitrogen utilization effect.Mulching,fertilization and the interaction of two factors had significant effects on on NPE,WUE and PUE.Compared to the chemical fertilizer treatment,the MT50/T50 increased nitrogen accumulation（NA,and nitrogen uptake efficiency,NUE）by 14.4%/21.8%and 9.5%/12.3%and NPE by 8.5%/10.5%and13.7%/11.8%in summer maize and winter wheat,respectively.Mulching increased NA by18.7%,NPE by 19.1%and N harvest index（NHI）by 2.6%in the summer maize season.Mulching increased NA by 7.1%in the winter wheat season,and NPE and NHI were lower than in the no-mulching treatment.Soil water content in summer maize season was"water storage",and in winter wheat season was"water consumption".Compared with chemical fertilizer treatment,MT50/T50 increased WUE by 19.4%/10.4%and PUE by 8.5%/10.5%in summer maize,and WUE by 4.5%/12.4%and PUE by 13.7%/11.8%in winter wheat.MT75/T75 increased WUE by 24.5%/18.6%and PUE by 7.5%/14.3%in summer maize,and PUE by 9.1%/6.9%in winter wheat The mulching increased WUE by 14.8%and PUE by 17.3%in the summer maize season and WUE by 7.2%and PUE by 4.1%in the winter wheat season.In conclusion,organic fertilizer substitution of 50%and 75%and mulching could significantly improve soil physical and chemical properties,improve biological fertility,promote crop growth,and improve water and nitrogen use efficiency,with higher annual yield,lower carbon emission efficiency and better economic benefits（without the excess fertilizer cost）for the organic fertilizer substitution 50%.Thus,this study recommends a combination of 50%organic fertilizer substitution and mulching measures for field management in order to provide a reference basis for achieving high crop yield,improving soil fertility and achieving green and sustainable agricultural production in the Lou soil type.