Study On The Climate Effect And Crop Yield Increase Mechanism Of Farmland Shelterbelt At Regional Scale

Farmland shelterbelt is an artificial forest ecosystem which can promote the improvement of farmland microclimate,improve soil,reduce natural disaster,achieve stable production and increase production.They are an important part of the construction of shelterbelts in Northern China.In order to explore the climate effect and yield increasing mechanism of farmland shelterbelt in Northeast China,this paper takes the Northeast area of the Three North Project which is typical as the research area.Firstly,by determining the spatial distribution,age and growth status of farmland shelterbelt in Northeast China,the protected level formed by farmland shelterbelt at the regional scale is quantified.Secondly,using MODIS(Moderate-Resolution Imaging Spectroradiometer)data to obtain the surface temperature during the growing season of the study area from 2015 to 2017,and analyze the impact of regional scale farmland shelterbelt on the surface temperature;using CCI(Climate Change Initiative)data to obtain the soil moisture during the growing season of the study area from 2015 to 2017,and analyze the impact mechanism of regional scale farmland shelterbelt on the soil moisture.Thirdly,based on the harvest index method and remote sensing estimation of grain yield,the impact of regional scale farmland shelterbelt on grain yield is analyzed.Finally,the contribution rate of climate effect of farmland shelterbelt in grain production mechanism is analyzed.The specific research results are as follows:(1)The average value of protected level of farmland shelterbelt in the whole Northeast area is 13.52%.Among them,the area of crops without farmland shelterbelt system accounts for 74.03% of the total area of crops;the area of crops with incomplete farmland shelterbelt system accounts for 19.95% of the total area of crops;the area of crops with a better farmland shelterbelt system accounts for 6.01% of the total area of crops.(2)The results of temperature effect show that the planting of farmland shelterbelt in semi-arid area has significant warming effect on the surface temperature.Among them,the temperature change rate at 8-day scale of full protected effect is 0.04~21.10% compared to when the protection level is 0,and the maximum temperature increase is 1.574? and the minimum is 0.008?.In the semi-humid area,planting farmland shelterbelt has significant cooling effect on the surface temperature.Among them,the temperature change rate at 8-day scale of full protected effect is 0.02~36.36% compared to when the protection level is 0,the maximum cooling is 1.720?,and the minimum is 0.036?.(3)The results of humidity effect showed that: in semi-arid area and semi-humid area,planting farmland shelterbelts has significant humidification on soil moisture.In the semi-arid area,the humidity change rate at 8-day scale of full protected effect is 0.07~10.86% compared to when the protection level is 0,and the maximum humidity increase is 0.0270 m3/m3,and the minimum is 0.0002 m3/m3;in the semi-humid area,planting farmland shelterbelts has significant dehumidifying on soil moisture.The humidity change rate at 8-day scale of full protected effect is 0.01~10.1% compared to when the protection level is 0,and the maximum humidity increase is 0.0277 m3/m3,and the minimum is 0.00005 m3/m3.(4)The results of yield-increasing effect showed that the farmland shelterbelt lead to a yield-increasing effect on crops in both semi-arid and semi-humid areas.From 2015 to 2017,the yield increase rate of farmland shelterbelt in semi-arid area was 4.47%,4.88%,4.34%,and the yield increase rate of farmland shelterbelt in semi-humid area was 1.10%,0.18%,1.01%.In the semi-arid area,the yield increase benefit of planting farmland shelterbelt is significantly higher than that in the semi-humid area.In the semi-arid area,due to the poor site conditions and severe wind damage,soil moisture is the key limiting factor for crop production,with an average contribution of 43.10% to crop yield;in the semi-humid area,the surface temperature is the key limiting factor of crop production,with an average contribution of 10.80% to the per unit yield of crops.To some extent,the planting of farmland shelterbelt has changed the regional microclimate and promote agricultural production.