| The Weibei dryland in Shaanxi has long sunshine time,high altitude,and large temperature difference between day and night,which is beneficial for apple growth.It not only meets the production indicators of high-quality apples,but also serves as an advantageous industrial belt for apple production in China.The combination of orchard grass planting and organic and inorganic fertilizers can increase the content of soil organic carbon pool and reduce greenhouse gas emissions,which is of great significance in improving soil quality,improving soil fertility and reducing non-point source pollution of chemical fertilizers.This study is based on a 14 year long-term positioning experiment,using a trial design of green grass coverage and combined application of organic and inorganic fertilizers.The main treatment is green grass coverage and clear tillage,and the secondary treatment is four different fertilization treatments: no fertilization(CK),single application of chemical fertilizer(NPK),single application of organic fertilizer(M),and combined application of organic and inorganic fertilizers(MNPK).The study investigated the effects of combined application of organic and inorganic fertilizers on greenhouse gas emissions in apple orchard soil under green grass coverage from September 2021 to September 2022 The effects of physical and chemical properties and soil carbon pool were calculated,and the warming potential of greenhouse gas emissions,emission intensity,soil organic carbon storage and organic carbon component sensitivity index were calculated.The effects of grass growing and mulching combined with organic and inorganic fertilizers on soil environment were further clarified,providing a theoretical basis for reducing greenhouse gas emissions and improving soil carbon pool in Weibei dryland apple orchard.The following main research results were obtained.1.Grass mulching significantly increased fruit yield,with an increase of 11.33%.Under grass mulching conditions,the MNPK treatment had the highest single fruit weight and yield,with a significant increase of 31.01% and 15.87% in yield compared to M and NPK treatments.Under clear tillage conditions,the single fruit weight of MNPK treatment was significantly higher than that of M treatment by 24.96%,and the yield of MNPK treatment was also the highest,with a significant improvement effect compared to M and NPK treatments.2.Grass coverage is beneficial for improving soil nutrient content.The content of total nitrogen,available nitrogen,available phosphorus,and available potassium in the soil significantly increased after planting grass,with an increase of 6%,37.14%,and 32.44%,respectively.There were significant differences in the content of available nitrogen,available phosphorus,available potassium,and total nitrogen in the soil under different fertilization treatments.NPK,M,and MNPK treatments were all able to improve soil nutrients,among which MNPK treatment had a significant improvement effect.The content of total nitrogen,available potassium,and available phosphorus in the soil was increased by 40.51%,55.12%,and 127% compared to the single fertilizer treatment under grass cover,and increased by28.01%,73.72%,and 66.1% under clear tillage.There are significant differences in the impact of apples on soil microbial biomass carbon(MBC)at different growth stages,as evidenced by a gradual increase in soil MBC content as the growth stage progresses,namely,germination stage<fruit setting stage<fruit swelling stage<mature stage;There are also significant differences in the MBC content among different fertilization treatments,with the overall performance being in the germination,fruit expansion,and maturity stages.The MBC content is highest in the M treatment,and grass mulching significantly increases the soil MBC content compared to tillage.Soil microbial biomass nitrogen(MBN)showed relatively stable changes throughout the entire growth period,with the highest MBN content in all four stages of treatment M.During the germination and maturity stages,grass mulching significantly increased MBN content compared to clear tillage,but there was no significant difference between the fruit setting and swelling stages.3.The single application of chemical fertilizer has little impact on soil organic carbon and its active carbon components,while the combined application of organic fertilizer significantly increases soil organic carbon,microbial biomass carbon,soluble organic carbon,readily oxidizable organic carbon and particulate organic carbon.The single application of chemical fertilizer has no significant impact on organic carbon storage,and even reduces the soil carbon pool management index(CPMI),but after the combined application of organic fertilizer,the storage of soil organic carbon and CPMI are significantly increased.The application of organic fertilizer significantly increased the sensitivity index of soil organic carbon and its active components under the conditions of grass mulching and clearing tillage.Compared with clearing tillage,grass mulching had a significant improvement effect on the sensitivity index of particulate organic carbon.Combined application of organic and inorganic fertilizers reduced the proportion of some organic carbon components in Total organic carbon.After planting grass,the proportion of active organic carbon components in Total organic carbon was significantly different from that of clean tillage.Correlation analysis shows that there is a significant positive correlation between soil organic carbon,soil carbon pool management index(CPMI),and active organic carbon components,whether it is covered with grass or cleared tillage.There is also a significant positive correlation between each active organic carbon component.4.From the perspective of the entire growth period of apples,the methane emission rate is negative,indicating that methane is mainly absorbed in dry land.Under the conditions of grass coverage and clear tillage,there was no significant difference in nitrogen oxide among different fertilization treatments,and the application of organic fertilizers increased carbon dioxide emissions.Single application of organic fertilizer increased greenhouse gas emissions,increased warming potential and greenhouse gas emission intensity,but the combination of organic fertilizer significantly reduced warming potential and greenhouse gas emission intensity.Among all fertilization treatments,the combination of organic and inorganic fertilizers had the lowest greenhouse gas emission intensity.Compared with grass mulching,orchard tillage reduces greenhouse gas emissions and warming potential,but there is a trend towards increasing the intensity of greenhouse gas emissions.Correlation analysis shows that there is a significant positive correlation between soil organic carbon and the warming potential of greenhouse gases.In summary,planting green grass in apple orchards significantly improved fruit yield and soil nutrients.Whether it was covered with green grass or cleared tillage,MNPK treatment had the highest yield and soil available nutrient content.The application of organic fertilizer increased soil organic carbon storage and soil carbon pool management index.Planting green grass increased greenhouse gas emissions,but decreased overall warming potential and gas emission intensity.Under green grass coverage conditions,MNPK treatment significantly reduced soil greenhouse gas emission intensity compared to other fertilization treatments,and the difference was not significant under clear tillage conditions.Therefore,the combination application of organic and inorganic fertilizers under grass coverage can improve yield and soil quality while reducing greenhouse gas emissions,achieve quality and efficiency improvement in dryland apple orchards,and reduce environmental impacts.It is a key technology for reducing fertilizer application and green sustainable development in dryland apple orchards on the Loess Plateau. |
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