Study On The Mechanism Of Water And Heat Transfer In Film-mulching Soil-crop System And The Simulation Of Leaf Stomatal Conductance

Irrigation from the Yellow River is crucial for ensuring the normal growth and development of crops in the Hetao Irrigation District,with little precipitation and strong evaporation.Based on the high-quality development of the Yellow River Basin,the quota for diverting water from the Yellow River has gradually decreased,and the shortage of agricultural water resources has become increasingly serious,severely limiting crop productivity in the Hetao Irrigation District.Plastic film mulching provides an effective way to solve the problem of irrigation water shortage,it changes soil water and heat conditions and farmland microclimate,thereby affecting plant photosynthesis and transpiration processes.Only exploring the changes in soil water and temperature under plastic film mulching cannot well explain the differences in crop physiological and ecological characteristics.This will hinder the mechanism research of water and heat in the soil-crop system under plastic film mulching,leading to uncertainties in the regulation of water and heat.Field experiments of spring maize were conducted in 2019 and 2020 at the Hetao Irrigation District,Inner Mongolia,China.The field experiment consisted of different optical properties of plastic film mulching（transparent film mulching;black film mulching;no mulching）and irrigation amount（500 mm;300 mm）.The objectives of this research were to:investigate the effects of plastic film mulches having different optical properties and irrigation amount on water and temperature transfer in the soil-crop system;explore the leaf photosynthetic performance;identify the characteristics of grain filling process;calibrate and validate the modified stomatal conductance models and evaluate the applicability of the modified model under plastic film mulching in arid irrigation area.The main research results are as follows:（1）investigated the effects of mulching and irrigation on water and temperature transfer in the soil-crop systemPlastic film mulching significantly increased soil moisture,especially below the 40 cm soil layer.Plastic film mulching and irrigation increased canopy relative humidity.Mulching stimulated alternating wet-dry behavior of soil water,especially under deficit irrigation.Alternating wet-dry behavior of soil water induced by plastic film mulching was an effective water utilization strategy that increased crop water productivity.The wet and dry status of soil under mulching was characterized by the increase and decrease of water,respectively,relative to the soil water content in the FN treatment.Alternating wet-dry behavior of soil water mainly occurred in the 0–80 cm soil layer,whereas the 80–120 cm soil layer was mainly characterized by intense fluctuation in the wet range.Alternating wet-dry behavior of soil water in the 0–80 cm soil layer changed from wet to dry at V12 and then changed from dry to wet at R3.Plastic film mulching significantly increased soil temperature,especially at V6,and significantly decreased the canopy temperature.（2）evaluated the effects of mulching and irrigation on photosynthetic performanceThe limiting factor for photosynthesis under plastic film mulching（especially under deficit irrigation）was mainly stomatal limitation,but the limiting factor under no-mulched treatment was mainly non-stomatal limitation.The limiting factors for photosynthesis under no-mulched treatment changed from being driven by stomatal limitation to non-stomatal limitation at 14 days after irrigation.Plastic film mulching and irrigation significantly increased leaf chlorophyll concentration,mulching significantly increased net photosynthesis rate.Plastic film mulching improved chlorophyll fluorescence parameters,significantly increased the values of Phi PS2,F_v’/F_m’,q P and ETR,decreased q N.Plastic film mulching remarkably improved light compensation points,quantum efficiency and leaf carboxylation efficiency.（3）evaluated the simulation of three models on leaf stomatal conductance under plastic film mulchingPlastic film mulching significantly increased stomatal conductance and leaf-air temperature difference.The stomatal conductance of transparent film mulching was higher than that of black film mulching,and the stomatal conductance under full irrigation was higher than that under deficit irrigation.The leaf-air temperature difference of transparent film mulching was lower than that of black film mulching,the leaf-air temperature difference under full irrigation was lower than that under deficit irrigation.The performance of the BWB model was wrost,the performance of the USO model was better than BBL model.After introducing modification factors,the R² and E₁ of the modified models increased 5.8%–90.6%and 6.5%–145.4%,respectively,and the RMSE and RE decreased3.5–67.9%and 4.8–65.6%compared with the initial models.The f（θ）-modified models performed better than?T-modified models under plastic film mulching.The performance of the two factors multiply modified models were inferior than one factor modified model and initial model.The applicability of models was improved by introducing f（θ）or?T,and the modified models were more applicable under the differing SRWC conditions or the current varying?T conditions.The simulated g_s curves of the modified models were all within the95%confidence intervals of the observed g_s and were closer to the observed g_s in both year.（4）identified the effects of mulching and irrigation on grain filling process and productivity of spring maizeMulching and irrigation improved kernel weight and volume in the superior,middle,and inferior portions of the maize ear after silking.The grain filling process conforms to the logistic equation model,the R² values were all above 0.95.Mulching significantly increased grain-filling rate and active grain-filling period.Compared with DN,the grain-filling rate for FT,FB,FN,DT and DB were significantly increased by 20.0–78.5%、5.0–64.6%、2.5–30.8%、6.3–60.0%、5.0–50.8%,respectively,in 2019 and 2020,and the active grain-filling period were significantly increased by 31.8–40.3%、26.9–34.8%、12.5–15.8%、26.3–34.3%、25.2–33.3%.Mulching produced earlier seedling emergence and significantly increased the duration of reproductive stage.Plastic film mulching significantly increased plant height,stem diameter,LAI and dry matter accumulation,improving maximum growth rate of plant height and maximum accumulation rate of dry matter.Compared with DN,grain yield for FT,FB,FN,DT and DB were significantly increased by 32.5–45.8%,19.0–41.8%,3.4–17.0%,12.1–33.4%,and 9.6–32.1%,respectively,in 2019 and 2020,increased by 400–3798 kg ha^–1in 2019 and 1947–5234 kg ha^–1 in 2020.Deficit irrigation significantly increased irrigation water use efficiency,compared with full irrigation,DT,DB and DN improved IWUE by41.0–52.5%,53.4–54.6%and 42.4–61.1%in the two study years.This study identified the effects of plastic film mulching on the growth and yield formation of spring maize under irrigation conditions,revealing crop physiology and growth mechanisms under different mulching and irrigation conditions from the perspectives of water and heat conditions in the soil and crop system,photosynthetic characteristics,grain filling process,and crop growth process.Overall,transparent plastic film mulching coupled with 300 mm irrigation ensures crop productivity and can be used as a reasonable treatment for spring maize production in arid irrigation areas.