| [Objective]Farmland shelterbelt is an important barrier to improve ecological environment and agricultural productivity in oasis area.However,the water resources of desert oasis are very limited,and the long-term coexistence of forest trees and farmland may cause and aggravate the potential water conflict between agriculture and forestry,affecting the cotton field environment and cotton growth.However,long-term real-time monitoring is time-consuming and labor-intensive.Therefore,this study explores the accuracy of calculating the net primary productivity（NPP）,evapotranspiration（ET）and water use efficiency（WUE）of cotton fields and shelterbelts through remote sensing models,so as to clarify the water use efficiency of shelterbelts and cotton fields.The law of time change and the synchronicity of its water consumption were discussed.At the same time,UAV images were obtained at the same time as satellite remote sensing images,and a simple water use efficiency model was used to estimate the WUE and real-time transpiration water consumption of cotton fields at different distances from the shelterbelt,so as to clarify the water use relationship between shelter forest and cotton field,and the influence range and degree of shelter forest on cotton field water.On the one hand,the conclusions of this study can verify the simulation effect and feasibility of remote sensing model technology in estimating NPP and WUE of farmland shelterbelt and cotton field in arid desert area,and realize large-scale and long-term continuous observation of ET and NPP of farmland shelterbelt and cotton field in desert oasis area;On the other hand,by clarifying the impact of farmland shelterbelt on farmland water use in oasis area,it can also provide a scientific basis for better regulating agricultural and forestry water supply in desert oasis area,realizing agricultural water-saving,high yield and high efficiency in arid area,and strengthening the management of farmland shelterbelt.[Methods]From 2020 to 2021,the experiment will be carried out in the 10th Company of the 150th Regiment of the Eighth Division of the Xinjiang Production and Construction Corps.The farmland shelterbelt and its adjacent cotton fields are used as the research objects.The test cotton field is 295m long and 50m wide;the shelterbelt is 295m long and 15m wide.First,Landsat8 series remote sensing images combined with CASA model,SEBAL model,meteorological data and related data,were used to simulated the NPPRS and ETRS of the cotton fields and shelterbelts,then the WUERS of cotton fields and shelterbelts were obtained by the ratio of NPPRS and ETRS.The UAV combined with a simple water use efficiency model were also used to estimate the NPPUAV,ETUAV and WUEUAV of forest cotton.Finally,the simulated estimation results of satellite remote sensing and UAV remote sensing are compared with the measured data to verify the satellite remote sensing and UAV remote sensing respectively.Therefore,a water use efficiency model with higher accuracy was selected to estimate the impact of shelterbelt on the water use status of cotton fields.[Main results]（1）Based on satellite remote sensing,combined with CASA model and SEBAL model,the net primary productivity(NPPRS)and evapotranspiration water consumption(ETRS)of shelterbelt and cotton field are estimated.Through npprs/ETRS,the remote sensing water use efficiency(WUERS)model can be obtained;The spatial resolution of the model is 15 m and the temporal resolution is 16 D.The NPPRS,ETRS and WUERSestimated by satellite remote sensing were verified by using the measured nppme and etme in cotton field.It was found that there was a significant linear correlation between the simulated value and the measured value in cotton field.The verification results of NPPRS in cotton field were R2 0.78,RMSE 5.48 and deviation 5.21;The ETRS verification result is that R2 is 0.95,RMSE is 1.30 and the deviation is 1.32;The WUERSverification result is that R2 is 0.89,RMSE is 0.56 and the deviation is-0.54.Therefore,the calculation accuracy of the WUE model can meet the calculation of the time scale of water use efficiency of forest and cotton in farmland shelterbelt system.（2）The validated model was used to estimate the NPP of shelterbelt and cotton field.From the time scale,the water consumption of cotton field and shelterbelt was significantly correlated with the growth of cotton and trees.The water consumption of cotton in the early stage was lower than that of shelterbelt,but with the growth of cotton,the water consumption was greater than that of shelterbelt;In addition,it was found that the NPP,apar,NDVI and light energy conversion rate of cotton field and shelter belt had obvious seasonal changes.The NPP,apar and NDVI in summer were significantly higher than those in spring and autumn,showing a trend of first increasing and then decreasing;the light energy utilization has an obvious relationship with NDVI and apar,showing the same trend.（3）The NPP,ET and WUE estimated by UAV remote sensing are verified by using the ground measured data.It is found that there is a significant linear correlation between the simulated remote sensing values and the field measured values.Among them,the verification results of NPP are R2 of 0.94,RMSE of 2.08 and deviation of 0.69;The ET verification result is that R2 is 0.93,RMSE is 0.73 and the deviation is 0.36;The WUE verification result is that R2 is 0.97,RMSE is 0.31 and the deviation is-0.30.The verification results show that the accuracy of crop water use efficiency and transpiration water consumption simulated by UAV image combined with simple water use efficiency model is higher than that simulated by satellite remote sensing.（4）From the spatial scale of the whole growth period,the etc of cotton fields at different distances has an obvious gradient.There is water competition between farmland shelterbelt and adjacent cotton fields in the area of 0.1H～1H.When it is greater than 1h,the water stress effect of shelterbelt on cotton fields begins to weaken,and the total transpiration water consumption of cotton fields at different distances in the whole growth period is 3H>2H>1H>0.5h>0.1H;At the same time,the transpiration water consumption of cotton field and shelter forest at different distances increased first and then decreased.（5）The simple water use efficiency model with higher accuracy was used to estimate the water use efficiency of cotton in cotton fields at different distances.It was found that the shelterbelt had a significant impact on the cotton field,but the shelterbelt greater than 1h had little impact on the growth of the cotton field;In addition,the water use efficiency of shelter forest and cotton field increased first and then decreased.The water use efficiency of cotton field was up to 1.91 times that of shelter forest in August.[Conclusion]Based on satellite remote sensing and UAV remote sensing,the WUE of forest and cotton is estimated respectively.It is found that the deviation between satellite remote sensing estimation value and UAV smoke sensing estimation value and field measured value is 0.54 and 0.30 respectively.Both of them can meet the estimation requirements of field scale,but the UAV remote sensing estimation accuracy is higher（UAV R2 is 0.97 and satellite R2 is 0.89）.NPP,ET and WUE of forest and cotton increased first and then decreased,which were significantly correlated with the growth period of shelter forest and cotton.The WUE and biomass of cotton fields at different distances were 3H>2H>1H>0.5H>0.1H,and the ET of cotton fields at different distances was 3H>2H>1H>0.5H>0.1H. |
