| The crop planting structure reflects the composition and distribution of crops in a region or production unit,and its historical changes are guided significance for rational distribution and scientific planning of grain.Previous research is mostly based on the statistical yearbook or only extracted and analyzed planting structure in specific years,which could not accurately and comprehensively describe the temporal and spatial evolution characteristics of the planting structures.This article selects the Hehuang Valley which is the main agricultural area of Qinghai-Tibet Plateau and the Qaidam Basin which is the important oasis agricultural area of Qinghai-Tibet Plateau as the research area.It is based on Google Earth Engine(GEE)remote sensing cloud computing platform,multi-source data such as field survey,remote sensing,climate,topography and population are comprehensively used.The random forest and ten-fold cross validation methods were used to construct hierarchical classification model of planting structure in the study area,so as to obtain the data set of annual distribution of cropland and planting structure in the study area from 2000 to 2021.Based on this data set,we analyzed the spatiotemporal change characteristics of cultivated land and planting structure in the study area.Firstly,the spatiotemporal change characteristics of cultivated land in the study area were defined from the perspectives of the proportion of cultivated land area and its changes,spatial distribution characteristics and type transfer,etc.Then,based on the data set of planting structure distribution,the spatiotemporal change characteristics of crop planting structure in the study area were analyzed statistically.In order to provide scientific basis for agricultural distribution and ecological environment protection in Qinghai-Tibet Plateau,the attribution of planting structure change was combined with the changes of temperature and precipitation in agricultural areas.The main conclusions are as follows:(1)The cultivated land in Hehuang Valley is concentrated and mainly distributed in the area of lower altitude.For more than 20 years,the change trend of cropland area increased firstly,and then decreased after reaching a peak in 2012.The conversion between cultivated land and non-cultivated land was mainly concentrated at the junction of cultivated land and non-cultivated land.The Qaidam basin is dominated by oasis irrigation agriculture,and its cultivated land is concentrated in Golmud,Delingha,Ulan and Dulan.In the past 20 years,the area of cultivated land in Qaidam Basin has been increasing continuously,and the areas with significant changes of cultivated land are Delingha City and Dulan County.(2)The crop planting structure in Hehuang Valley developed in the direction of diversification.Its planting structure changed from wheat,rape and highland barley to wheat,rape,highland barley,corn,potato and greenhouse crops in different combinations of planting structure.The spatial difference of planting structure in Hehuang Valley was obvious,and the area of agricultural area gradually expanded towards higher elevation.(3)The planting types in Qaidam Basin are mainly nursery,wheat,rape,highland barley,greenhouse crops and potatoes.In recent ten years,the large area of cultivated land in Qaidam Basin has increased,and the crop planting area has increased.However,the area proportion of different crop types changed.The planting area proportion of nursery,rape,greenhouse crops,potatoes and other types of crops increased,while the planting area proportion of wheat and highland barley decreased.(4)In the past 20 years,the change of planting structure in Hehuang Valley has been significantly affected by temperature.With the increase of temperature,the planting range of temperature-loving crops such as corn has expanded,and the farming area has expanded to the high altitude area where the temperature was originally lower.The increase of precipitation also makes the planting structure tend to be diversified.The oasis irrigated agriculture developed in Qaidam Basin is less affected by the change of precipitation,and the influence of temperature is mainly reflected in that the increase of temperature on the one hand aggravates the contradiction between water supply and demand and increases the cost of crop planting;on the other hand,it provides more heat resources for crop growth,thus promoting the expansion of planting area.In both places,the planting area of grain crops decreased to a certain extent and the planting proportion of cash crops increased,which cannot be separated from the support of the Great Western Development Strategy and government policies,vigorously developing characteristic agriculture and facility agriculture with high economic benefits,and constantly improving the crop management level and water-saving irrigation technology. |
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