| In northern China,the rain is rare and the land is droughty.As the water resources are relatively scarce,the water used to irrigate water is also fairly rare.As a result of it,the decrease in crop yield due to drought has always occurred.In order to alleviate the pressure on water resource and improve the yield of crop,mulching film-based water-saving agricultural measures have been widely promoted.With the maturation of mulching technology,the water-permeable ground film based on the unidirectional water seepage principle has emerged.This has enabled the effective use of small rainfall resources in the north and has received extensive attention.Based on the unique seepage performance of water-permeable plastic film,in order to realize the maximum utilization of water-permeable plastic film,guide agricultural management,and increase agricultural output,it is indispensable for the study of soil water,fertilizer,gas,and heat conditions under water-soaked plastic film.The permeable and common film had been covered on the soil,and bare ground was used as a control.During the whole growth period of crop,the soil bulk density,soil water content,soil salinity,crop yield and other climate parameters such as rainfall and temperature in the test area had been monitored.Based on field monitoring data and the theories of soil hydrodynamics,soil solute transport,and soil physics,the characteristics of soil moisture and salt transport,the physicochemical properties of soil and the utilization of water under permeable plastic mulch had been investigated.The changes about bulk density of surface and soil water and salt in the tillage layer had been analyzed.The relationship between bulk density of soil surface and cumulative rainfall in bare soil surface,and the relationship between salt content in surface soil under plastic film and the growth days of corn had been quantified.The characteristics of distribution and the laws of migration of water and salt in the soil during non-rainy season and rainy season had been explored and the water use efficiency of corn under different treatments had been compared.Finally,based on the prediction model of BP neural network,the soil salinity in farmland had been predicted.The results of the study were as follows:(1)Rainfall was the main factor leading to the change of bulk density of bare surface soil,and there was a significant logarithmic relationship between cumulative rainfall and surface soil bulk density.Based on the Pearson correlation test of two-side,the correlation coefficient was 0.876 in the case of?=0.05 and the correlation coefficient under Logarithmic fitting between them was R~2=0.8834.(2)During the growth period of corn,the changes of the bulk density of surface soil on bare soil showed a staged characteristic.The change phase could be divided into five:steep increase in seeding period,gentle growth after sowing,steep increase in rainy season,gentle increase in rainy season,and flat decline in harvest period.(3)The differences of the variation law of soil bulk density between these three measures were obvious.During the growth period,the bulk density of surface soil always remained the largest in the bare land,followed by the common plastic film,and the smallest under the water-permeable plastic film;The change stage of surface soil bulk density under mulching film could be divided into three:initial gentle growth,medium-term growth,and late-term decline.(4)The water-permeable mulch had more significant water-saving and yield-increasing effects than the ordinary mulch,and could greatly increase water use efficiency.Under the experimental conditions,the ET of corn covered with water-permeable mulch was 459.5mm,which was 9.78%less than bare land;the yield of corn was 778.98kg/mu,which was 32.6%higher than bare land;the water use efficiency was 2.54kg/m~3,which was 46.8%higher than bare land.Corn covered with the ordinary mulch had an ET of 485.7mm,which was4.63%less than bare;the yield of corm was 685.6kg/mu,which was 16.7%higher than bare land;water use efficiency was 2.12kg/m~3,which was 22.5%more than bare land.(5)The distribution characteristics of soil water content under different types of mulching showed obviously differences,and the differences were mainly reflected on the upper layer of soil.During the non-rainy season,the soil moisture content of the upper layer under bare land conditions was significantly lower than that under mulching,and the change of per depth was significantly greater than that under mulching.During the rainy season,the relationship of the soil moisture content between bare soil and common mulching covered soil was changed on the 40cm.(6)There were obviously differences in distribution characteristics of soil salinity under these three different mulching,and the most obvious difference in depth was the range of 0-100cm in the distribution curve.The soil salt content in bare soil was significantly higher than that under plastic film coverage in the depth of 0-100cm during the test period,and the salt content under the permeable plastic film was the lowest.Under bare ground,the soil salinity content continued to decrease with depth,but under the mulching,the minimum salinity value appeared at the 40cm soil layer,and the salt content first decreased and then increased with the depth.(7)There were significantly differences in the variation law of volumetric soil water content between these different types of mulching during the growth period of corn.Under bare ground,the change of surface soil moisture content could be divided into four:slow decline,significant increase,stable transition,and sharp decline;the changes under permeable film could be divided into five:initial rise,initial stable,rise again,stable again and significant decline.The changes under common mulch could be divided into two:steady rise and steady decline;and During the whole growth period,the volumetric moisture content of the surface layer under the permeable film was always higher than that of ordinary film and bare land.(8)There was a linear relationship between the salt content in the surface soil under the plastic film and the growth days of corn.The linear correlation coefficient between the salt content of soil covered with normal film and the growth days of corn was R~2=0.988.The linear correlation coefficient between the salt content of soil covered with permeable film was R~2=0.996.(9)Using the predicted method of BP neural network to predict soil salinity was feasible.Based on the BP neural network,choosing initial salt content,initial volumetric moisture content,volumetric moisture content,surface soil bulk density,soil texture,soil depth,soil organic matter content,and cumulative rainfall as input factors,the predicted model of soil salinity had been built.Under this predicted model,the error of training sample was 4.86%,the correlation coefficient between the predicted value and the actual measurement value was R~2=0.8798,the error of verification sample was 5.45%,which indicates that the model could achieve the prediction of soil salt in farmland.Due to the limit of knowledge and multidisciplinary ability,the mechanism analysis of some data was poor in depth and breadth,and the further refine and refine of the experimental conclusions was necessary.In this paper,the soil salinity in farmland had been predicted successfully,and the concept of soil transfer function could be further extended to the study of other physical and chemical properties of farmland soil to enrich the content of soil transfer function. |
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