Study On The Soil Water And Nitrogen Coupling Characteristics And Synergistic Effects Of Mountain Apple Under Surge-root Irrigation In The Loess Plateau

The Loess Plateau is the largest apple cultivation area in China.At present,local orchards are,for the most part,rain-fed,and developing water-saving irrigation in mountain orchards is urgent.Severe water shortages limits sustainable development of apple production.The purpose of this study was to make known the controlling effects of water and nitrogen coupling on physiology,growth,fruit yield,quality,economic benefit,water-nitrogen utilization effectiveness,and movement and distribution of soil water and nitrogen and enzyme activity in root zone of mountain apples under surge-root irrigation in the Loess Plateau were evaluated in 2018 to 2021 at the Zizhou Mountain Apple Demonstration Station of Science and Technology Experiment in Yulin,Shannxi Province,China.Six years was selected for the mountain apple test material.The subjective weight attained by analytic hierarchy methods and the objective weight achieved by enhanced coefficient of variation method were examined to find the comprehensive weight based on the notion of game hypothesis.Then,the weighted TOPSIS process was utilized to comprehensively assess the yield,quality,economic benefit,and water-nitrogen use efficiency of apples,and a binary quadratic regression model was created between comprehensive evaluation index and water-nitrogen inputs.The main research results are as follows:(1)The distribution of soil water and nitrogen in apple root zone and the response of soil enzyme activity to water and nitrogen input were revealed.The study on the coupling experiment of water and nitrogen of mountain apple in 2020-2021 showed that the soil moisture content,the NO3-N content and NH4+-N content were the largest at the depth of 40 cm,and gradually decreased from the center of the emitter outlet to the periphery.The change of NO3--N content in 0 to 40 cm of soil layer was greater than that in 40 to 100 cm of soil layer.The NH4+-N content increased with the increase of nitrogen amount under the same irrigation level.The coupling of water and nitrogen significantly affected the mean values of catalase,urease and sucrase activity in apple root zone.Catalase,urease and sucrase activity first increased and then decreased with the increase of soil depth.Under the same nitrogen level,the catalase activity increased with the increase of irrigation amount.Under the same irrigation level,the urease activity first increased and then decreased with the increase of nitrogen amount.The sucrase activity first increased and then decreased with the increase of irrigation and nitrogen amount.(2)The water and nitrogen transport and infiltration models of single and double point source of surge-root irrigation were established by using the Hydrus-3D software.Based on unsaturated soil hydrodynamics theory,using the Hydrus-3D finite element model,numerical simulation of the water and nitrogen transport of soil under surge-root irrigation in mountain apple orchard on the Loess Plateau,and calibration and verification of model parameters based on field measured data.The results showed that the simulated values of the model are in good agreement with the measured values,which indicated that it is reliable to use the Hydrus-3D model to simulate and analyze the water and nitrogen transport characteristics of single and double point source infiltration of surge-root irrigation in the mountain orchard of the Loess Plateau.The wetting front migration distance increased rapidly at first and then slowly with the infiltration duration.The soil profile moisture content,NO3--N content and NH4+-N content decreased with the increase of the distance from surge-root irrigation emitter.(3)The effects of regulated deficit surge-root irrigation at different growth stages on photosynthetic characteristics,fruit yield,quality and economic benefits of apple were revealed.According to the research on regulated deficit irrigation of mountain apples from 2018 to 2019,after regulated deficit irrigation during the sprout leaves stage(stage I)and fruit expansion stage(stage III)of apple,the leaf net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),and carboxylation efficiency(CE)of the apples decreased with the increase of water deficit,and the intercellular CO2 concentration(Ci)increased with the increase of water deficit.The shoot length and fruit diameter of severe(DIs)and extreme(DIE)regulated deficit irrigation decreased significantly.The photosynthetic capacity,shoot length and fruit diameter of the DIL-treated trees(light regulated deficit irrigation)was nonsignificantly different from that of the full irrigation,and the apple yield,irrigation water use efficiency(IWUE),water use efficiency(WUE),net income and return were all increased,but the increase was not significant,and these indicators of other treatments were reduced.The comprehensive quality was highest for the I-DIL-treated apples,second highest for the III-DIL-treated apples,and lowest for the III-DIE-treated apples.(4)The regulation effect of water and nitrogen coupling on photosynthetic characteristics,fruit yield,quality and economic benefits of apple,and the mechanism of water and nitrogen high use efficiency were clarified.According to the research on partial root-zone surge-root irrigation and nitrogen coupling of mountain apples from 2019 to 2020,compared with no irrigation,alternate surge-root irrigation significantly enhanced the physiological activity of mountain apples,promoted growth and development,improved comprehensive quality,increased yield,WUE and economic benefits.The apple yield,fruit diameter,WUE,nitrogen agronomic use efficiency(NAE),and economic benefits first increased and then decreased with the increase of water and nitrogen input.The irrigation water production efficiency(IWPE)and IWUE decreased with the increase of irrigation amount,the nitrogen partial factor productivity(NPFP)decreased with the increase of nitrogen amount.The principal component analysis and cluster analysis in 2019 and 2020 showed that the comprehensive quality of the combination of light deficit irrigation and moderate nitrogen under alternate surge-root irrigation,and the combination of light deficit irrigation and moderate nitrogen under fixed surge-root irrigation were in the top six,and the comprehensive quality difference between the two combination modes was not significant,and the comprehensive quality of the combination mode without irrigation and nitrogen was the worst.According to the research on water and nitrogen coupling of mountain apples from 2020 to 2021 showed that the effects of irrigation levels and nitrogen levels on chlorophyll content,photosynthetic characteristics,fruit yield,water and nitrogen use efficiency,quality and economic benefits of mountain apple were significant.Deficit irrigation and nitrogen deficiency significantly reduced the chlorophyll content and photosynthetic capacity.The new shoot length and the growing days showed a power function at first,and then a quadratic function.Insufficient water and nitrogen severely reduce apple diameter,fruit yield,WUE,NAE,NPFP and economic benefits.The largest apple yield,NPFP,apple income and net income was achieved under irrigation level was 75%～85%θf and nitrogen level was 450 kg/ha compared with other treatments.The highest comprehensive quality was obtained using irrigation level was 75%～85%θf and nitrogen level was 450 kg/ha,followed by the irrigation level was 85%～95%θf and nitrogen level was 600 kg/ha,the lowest quality was obtained using no irrigation and no fertilization.(5)A model of water and nitrogen input under surge-root irrigation of mountain apples was established.The improved TOPSIS method,and the regression model between comprehensive evaluation indexes and irrigation amount and nitrogen amount shows that the best comprehensive evaluation index of regulated deficit irrigation was light regulated deficit irrigation during the fruit expansion stage,followed by light regulated deficit irrigation during the sprout leaves stage,and the worst comprehensive evaluation index was extreme regulated deficit irrigation during the fruit expansion stage during 2018-2019.The highest comprehensive evaluation index of partial root-zone surge-root irrigation and nitrogen coupling was obtained using the combination of light deficit irrigation and moderate nitrogen under alternate surge-root irrigation,followed by the combination of light deficit irrigation and high nitrogen under alternate surge-root irrigation,the lowest comprehensive evaluation index was obtained using no irrigation and no fertilization during 2019-2020.The comprehensive evaluation index was highest for the irrigation level was 75%～85%θf and nitrogen level was 450 kg/ha,second highest for the irrigation level was 75%～85%θf and nitrogen level was 300 kg/ha,and lowest for no irrigation and no fertilization.The comprehensive evaluation index for apples showed an opening downward paraboloid with the input of irrigation-nitrogen amount,and it first increased and then decreased with the increase of irrigation amount and nitrogen amount.The interval of irrigation and nitrogen attained under surge-root irrigation of mountain apples in the Loess Plateau from the mathematic model ranged in 85-105 mm and 390-525 kg/ha,respectively.