| N2O,NH3,CO2,and CH4 emitted from agricultural production activities are all important sources of greenhouse gases,which contribute more than 20%of the greenhouse gases.At the same time,the harm caused by nitrogen loss also poses a serious threat to human survival and development.Therefore,in order to clarify the impact of different water and fertilizer control measures on the fate of nitrogen in orchards and the net greenhouse effect,this study conducted a 3-year field trial at Danfengshan apple orchard plantation base in Tang County,Baoding City,Hebei Province.There are 5 treatments in this experiment:traditional water and fertilizer(CT),elemental fertilizer+biogas slurry(A1),optimized water and fertilizer(A2),fertilizer saving and water control+humic acid+microbial agent(B),fertilizer saving and water reduction +humic acid+microbial bacteria(C).The 15N tracer technique was used to study the fate of nitrogen in apple-soil system under different control measures,and the leaching loss of nitrogen was determined by soil drilling method.Meanwhile,the emission fluxes of N2O,NH3,CO2 and CH4 during the critical growth period of apples are monitored to determine the nitrogen gaseous loss and greenhouse gas emission.Finally,combined with LCA method,the net greenhouse effect of different water and fertilizer control measures was calculated,and the ways of nutrient absorption and loss were integrated to determine the water and fertilizer control mode with both environmental friendliness and benefits.The main results of this study are as followed:(1)The water and fertilizer management mode of adding humic acid and microbial inoculants can significantly increase the yield and quality of apples.Compared with the traditional water and fertilizer treatment,the output of fertilizer saving and water control +humic acid+microbial inoculants treatment in 2019 and 2020 increased by 10.66%and 16.86%,and the net income increased by 2.13*104yuan/hm2,4.06*104yuan/hm2,and effectively reduced.At the same time,the fruit hardness,the soluble solid content and the fruit taste are improved.(2)The treatment of fertilizer saving and water control+humic acid+ microbial inoculants can promote the absorption of nitrogen by fruit trees and improve the efficiency of nitrogen fertilizer use.The order of 15N absorption of fertilizer in each organ is as followed:the main root>perennial branch>fine root>central stem>fruit>leaf>annual branch.The order of 15N absorption of fertilizer in each organ under traditional treatment is as followed:the main root>perennial branch>fine root>central stem>fruit>leaf>annual branch.The 15N absorption and utilization rate of fertilizer control water+humic acid+microbial inoculants were 3.2 g and 23.18%,respectively,while that of traditional water fertilizer was 2.39 g and 17.33%.(3)Using fertilizer saving and water control+humic acid+microbial inoculants can increase the 15N residue in the 0?60 cm soil layer.The maximum 15N residue in the 40?60 cm soil layer is 0.157 g.The 15N residue of traditional water and fertilizer treatment is 0.20 g at 80?100 cm.The cumulative increase in the 60?100 cm soil layer during two years under treatment with humic acid and microbial agents is 22.60-29.25 kg·hm2,while the leaching amount of traditional water and fertilizer treatment is 1.12?1.75 times of it.(4)In 2019,the N2O emission of each water and fertilizer regulation was between 0.219?0.409 kg·hm-2,and the NH3 volatilization was between 0.651?0.733 kg·hm-2.The N2O emission in 2020 was between 0.150?0.248 kg·hm-2,and NH3 volatilization was between 0.653?0.801 kg·hm-2.Adding humic acid and microbial inoculants can reduce soil N2O emission by 7.77%?22.2%,and reduce NH3 volatilization loss by 3.40%?7.61%.The N2O emission flux is significantly correlated with the inorganic nitrogen content of the surface soil,and the correlation coefficients are 0.242*,0.374**,respectively;NH3 volatilization is significantly correlated with the ammonium nitrogen content of the surface soil,and the correlation coefficient is r=0.412**.(5)The main way of nitrogen input is external fertilizer input,which accounts for 68.01%?73.14%.Soil residue and crop absorption are the main destinations of nitrogen.Leaching is the main way of nitrogen loss,and the amount of leaching loss is 4.13?11.95 kg·hm-2,accounting for 7.48%?19.61%of the total nitrogen input.Compared with the traditional water and fertilizer treatment,fertilizer saving and water control+humic acid +microbial inoculants effectively reduced the soil nitrogen surplus by 32.29%and improved the nitrogen utilization rate.(6)The soil CO2 emission rate is mainly affected by seasonal effects.The highest emission rate is 194.47 mg·m-2·h-1(elemental fertilizer+biogas slurry)in summer,and the lowest is 4.36 mg·m-2·h-1(Elemental fertilizer+biogas slurry)in winter.Optimized water and fertilizer,fertilizer saving and water control+humic acid+microbial inoculants,fertilizer saving and water reduction+humic acid+microbial inoculants,the cumulative emission of CO2 is between 1208?1864 kg?hm-2,which is more than traditional water and fertilizer The emission of the treatment was reduced by 0.5%to 3.79%;the CH4 absorption of each water and fertilizer regulation was between 0.957 and 1.529 kg·hm-2,and the CH4 emission was reduced by 1.89%to 5.93%after adding humic acid and microbial agents.Soil CO2 emissions are significantly positively correlated with soil surface moisture and temperature,and soil CH4 emissions are significantly correlated with temperature.(7)The CO2 equivalent produced by the use of fertilizer and the CO2 equivalent emitted by the soil itself in the short-stock densely planted apple orchard are the main factors affecting the net greenhouse effect.The use of various optimized water and fertilizer measures can effectively reduce the net greenhouse effect.The reduction range of water and fertilizer regulation is between 8.37%and 28.80%.The total GWP of fertilizer saving and water reduction+humic acid+microbial inoculants is reduced by 13.26%to 29.80%compared with traditional water and fertilizer treatment,which has the best reduction and emission reduction effect and maximize reduce the impact of agricultural activities on the greenhouse effect.In summary,the management model of saving fertilizer and controlling water+humic acid+microbial inoculants can increase nitrogen by 5.85%,reduce nitrogen gas loss by more than 11.17%,effectively reduce net greenhouse effect by more than 8%,and increase production by 10%above,while improving fruit quality,which is the best water and fertilizer control measures for short-stock densely planted apple orchards. |
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