Processes Of Transpiration And Evapotranspiration In A Rainfed Maize Field And Their Responses To Plastic Mulch On The Loess Tableland

In this study,a pot experiment was conducted to useweighing method to calibrate the results determined bysap flow method,and use the gained calibration equationto correct the sap flow rate values measured by the sapflow gauge in the field experiment.And a field study on dryland spring maize was conducted to investigate the process and characteristic of transpiration?T?and evapotranspiration?ET?and the effects of plastic film mulching management practice on maize growth,leaf area index?LAI?,yield,water use efficiency?WUE?,leaf water potential,soil water potential,atmospherewater potential,meteorological factor,soil temperature,soil water storages?SWS?and the ratio between transpiration and evapotranspiration?T/ET?.We also used the universal formula of water flow through the soil-plant-systems which based on electric resistance-capacitance circuit to calculate the hydraulic resistance and water capacitance of hydraulic resistance in soil-spring maize system.The main results and conclusions are asfollowing:1.Inorder to calibrate the sap flow gauge,the sap flow rate was compared to the leaf T determined byweighing method.The sap flow value was measured per hour during 3 days and the mean of hourlyvalues in each day was taken as the daily value to avoid the influence of hydraulic capacitance.Therewas a significant linear relationship between leaf T and sap flow rate.The slope and intercept oflinear regression were 0.764 and 4.944,with a R² of 0.97?p<0.01?.2.By traditional planting,the diurnal variation of sap flow of single maize plant is a unimodal or bimodal curve.The cumulative amount of corn transpiration is an s-shaped curve.Under different weather conditions,there were significant differences in the transpiration of maize.There is a significant positive correlation between corn transpiration and total solar radiation,photosynthetic effective radiation,air temperature and saturation vapor pressure difference.The daily change in the water potential of maize leaves is higher in the morning and evening,lower at noon.The effect of temperature,saturation vapor pressure and radiation illumination on leaf water potential is negative.And relative humidity has a positive effect onleaf water potential.The T/ET of maizewas 63.3%from July to September and 53%in the whole period in 2012.The T/ET increased linearly with increasing LAI.3.Then the corn was mulched by plastic film and comparative study found that due to the increase of soil temperature,plastic film mulching treatment had a seedling emergence rate of 98.1%,which was significantly higher than 80.2%of the non-mulching treatment.Maize plants reached to different stages 1.6 days earlier and the whole growth period was shortened by 14 days under plastic film mulching.After the silking stage?R1?,plant height and LAI reached to peak values and increased by 17.1%and 40.3%under the plastic film mulching treatment as comparedto non-mulched treatment.At harvest,shoot biomass under the plastic film mulching treatment was 40.1%more than that under the non-mulched treatment.In 2015,the leaf area index was 92 percent higher after planting two months.Plastic film mulching promoted maize germination and advanced growth stages.4.The T and the peak of daily T change curve of single maize plant under plastic mulch were higher than that under non-mulching.The daily transpiration of mulched corn is always higher than that of non-mulching treatment.The T/ET of maize was 68.1%and 61.6respectively from July to September under non-mulching treatment.While the T/ET of maize was 85.5%and 85.9 respectively from July to September under plastic film mulching treatment.The daily mean ET under plastic mulch was lower than that under non-mulching,whereas the daily mean T was the opposite.The T/ET of maize was 68.10%under non-mulching and 85.50%under plastic mulch from July to September in 2013.The T/ET increased logarithmically with an increasing LAI.When the LAI increased from 1 to 3.5,the T/ET under plastic film mulching rapidly increased from 47.9%to 84.1%,whereas that under the non-mulching treatment increased from 29.6%to 68.8%.However,with the increase in the LAI,the increasing rate of T/ET under both treatments became smaller.Under the same LAI,the T/ET of plastic film mulching was greater than that under non-mulching conditions.The daily average T/ET values calculatedby kang shaozhong formula and the measuredT/ET values of this study were compared.The results show that there is little difference between the two,and the change trend is basically the same.5.Although no significant differences between two treatments were found in kernels per row,kernels per ear and 100-kernel weight of plastic film mulching plots were significantly higher than those of non-mulching plots.The grain yields under plastic film mulching treatment were significantly greater than those under non-mulching treatment,with concomitant increases in shoot biomass production,total T and harvest index?P<0.05?.The whole periodtranspiration of two years of mulching corn was 299.1 and 303.4 mm respectively,significantly higher than the non-mulching treatment of 224.7 and 235.0 mm.The T/ET of two years of mulching corn was 73.0%and 74.7%respectively,significantly higher than the non-mulching treatment of 55.1%and 54.0%.The WUE_ET of two years of mulching corn was 35.5 kg ha^-1 mm^-1 and 30.6 kg ha^-1 mm^-1 respectively,significantly higher than the non-mulching treatment of 18.7 kg ha^-1 mm^-1 and 20.9 kg ha^-1 mm^-1.The T under plastic film mulching treatment was significantly greater than that under non-mulching treatment.The plastic mulch decreased ET but increased WUE.6.The effect of mulch on soil temperature is mainly to increase temperature.At 8:00am,the mulching temperature was significantly higher than that of the non-mulching treatment in the 5 cm and 10 cm soil layer,and slightly higher than the bare land where no crops are grown.The mulch reduced the diurnal temperature difference of the corn soil.Compared with not mulched,mulched to improve soil temperature by 1-4?at early age.The soil temperature of each soil layer at all times under the mulching treatment was higher than that of the non-mulching treatment.From middle of July to early in August,because the leaves of maize plants have obvious effect on the soil shading,the effect of mulch on increasing soil temperature was not large in the early stage and late stage.7.Soil water storages under plastic film mulching treatment were consistently higher than under non-mulching treatment during the whole vegetative growth,with the maximum difference of 66.2mm.However,to the beginning of July,soil water storages under the non-mulching treatment were consistently higher than that in plastic film mulching plots.From V12 to R3,the plastic film mulching plots had higher water contents in the upper 40 cm soil layer but lower water content at depths from 40 cm to 150 cm compared with the non-mulching plots.Plastic mulch retained soil water in the early stage to promote maize development in the later stage,and consumed more water in the deeper soil during the reproductive stage.8.The effect of mulch is the result of the combination of temperature and water.It provides favorable hydrothermal conditions for the growth and development of maize.Compare with the non-mulchingtreatment,the increase of surface soil temperature of mulched cornsignificantly promotes the growth and development of plants.It increases the biomass and LAI,and strengthens the transpiration.At the same time,mulch increases the availability of water in soil reservoirs,and regulates the water supply to the corn.It reduces the plant's ineffective evaporation and increases T/ET.9.Study on water migration of soil-spring maize system.The results indicate that the difference in water potential from soil to leaf is small in morning and evening and larger at noon.Transpiration?stem flow?rate decreases with soil water potential,and peak gradually decreases.Daily transpiration?stem flow?decreased gradually.The daily variation of hydraulic resistance is smaller in the morning and larger in the afternoon.The soil water potential has a significant effect on the hydraulic resistance of the system.With the decrease of soil water potential,the hydraulic resistance of the system increases significantly.The system watercapacitance is small in the morning and large in the afternoon.The hydraulic resistance of the system is closely related to the water capacitance.When the hydraulic resistance decreases,the system water capacitance increases.When the soil water potential decreases,the time"constant"increases.