| Compared with traditional irrigation methods,the water-fertiliser coupling drip irrigation provides high water and nutrients utilisation efficiency by multiple-low-amount irrigation methods.This is because water and fertiliser in the root area maintain soil conditions favourable for crop growth.However,infiltration of irrigation water displaces air in soil pores,causing an imbalance of soil oxygen supply-demand and severe hypoxia stress in the high-texture root areas.Insufficient oxygen in the root region soil inhibits root respiration and growth,affects water and nutrients absorption,as well as their transportation in plants,eventually lowering crop yield and quality.Based on the water-fertiliser coupling drip irrigation,a new irrigation technique named water-fertiliser-air coupling drip irrigation is developed.This technique enables oxygen?or oxygen-containing material?transportation to the root area of plants by expelling subsurface drip irrigation system through the venturi air jet.The proposed technique,therefore,offers a realistic possibility for overcoming hypoxia in the root area caused by flooding,irrigation,salinisation and compaction.It also provides a path for evaluating the production potential of plants irrigated by the water-fertiliser coupling system.In this context,the effects of water-fertiliser-air coupling drip irrigation on soil aeration,soil health,crop growth and physiology,yield,quality,utilisation of nutrients were investigated.This involved integrating the barrel-growing?potting?and micro-plot experiments with the structural equation model,and establishing different methods for aeration and determining the added amounts of oxygen,water and fertiliser.The correlations between soil aeration,soil enzyme activity and soil microbial biomass with crop growth,physiology,yield,quality and nutrient utilisation were also analysed.The aims were to explore the effects of the water-fertiliser-air coupling drip irrigation on soil aeration,crop growth and physiology and the soil-crop system response mechanism.The main conclusions of this study are as follows:?1?Venturi cyclic aeration irrigation significantly improved soil aeration,crop growth physiology,yield and nutrient utilization compared with the control group,it was the best among the three aeration methods and could be used by water-fertiliser-air coupling drip irrigation.?2?The application of water-fertiliser-air coupling drip irrigation revealed a significant impact for gaseous and liquid oxygen on soil aeration,the dissolved oxygen concentration,oxygen diffusion rate,oxidation-reduction potential and soil respiration rate after oxygen aeration showed significant increase for more than 24 hours compared with the control group.The aeration treatment was the main driver for improving soil aeration and more than 90%of the improvement of soil aeration can be explained by aeration treatment,whereas the effects of oxygen-based aeration were below expectation.?3?The water-fertiliser-air coupling drip irrigation keep the root region soil in a suitable water-fertiliser-air environment,significantly improved soil enzyme activity and soil microbial biomass,especially,during fruit expanding period and mature period.In addition to affected the soil enzyme activity and soil microbial biomass directly,the venturi cyclic aeration also affected them indirectly by improving the soil aeration.Fertilizer amount affected the soil enzyme activity and soil microbial biomass directly,irrigation amount affected the soil microbial biomass directly.?4?Suitable soil aeration and soil health condition significantly promoted crops root growth,followed by the crop growth,physiological activities,yield and quality,the utilization of nutrients by crop plants also benefited from suitable soil aeration and soil health condition.The improved crop nutrient utilization and physiological activities were attributed to the aeration amount,the fertiliser amount and the irrigation amount,while the aeration and irrigation amounts largely positively impacted yield and quality.A suitable soil gas environment was also required for the crop roots area,but the addition of excess oxygen negatively affected the environment.The biomass accumulation and yield in air-based aeration treated crops were better than for those treated with oxygen-based aeration.?5?As revealed by the structural model based on the water-fertiliser-air coupling drip irrigation and soil-crop improvment,the water-fertiliser-air coupling drip irrigation increased crops yield and vitamin C content by 55.85%and 21.24%from improving the soil aeration,soil enzyme activity and microbial biomass.Water-fertiliser-air coupling drip irrigation can increase crops yield and quality by improving the soil environment in the root area,thereby promoting root growth..?6?The optimal irrigation parameters for the yields of peppers and tomatoes in a greenhouse under water-fertiliser-air coupling drip irrigation were determined by response surface analysis.Specifically,the optimal irrigation parameters for the yield of peppers included the irrigation amount with an evaporation pan coefficient set at 1.0,an aeration amount set at 25 mg·L-11 and a fertiliser amount set at 210 kg N·ha-1.Similarly,the optimal irrigation parameters for the yield of tomatoes were an irrigation amount with an evaporation pan coefficient set at 1.0,an aeration amount set at 23.5 mg·L-11 and a fertiliser amount set at240 kg N·ha-1. |
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