Research On Grain Production Pattern And Regulation Mechanism In Guanzhong-Tianshui Economic Zone

Guanzhong-Tianshui Economic Zone(Hereinafter referred to as Guantian Economic Zone)is an important agricultural production base and experimental demonstration base in China.Due to excessive exploitation of groundwater resources,uneven temporal and spatial distribution of precipitation and poor capacity of surface runoff regulation and storage,the economic zone is an area with poor water resources.With the continuous increase of population in the region,the demand for food will be further increased.How to improve the utilization rate of agricultural water resources and improve the water productivity of food crops under the premise of stable production and high yield has become a key issue in solving regional water shortages and ensuring food security.In this thesis,GIS.RS technology and Matlab software are combined to extract the annual crop distribution area of the economic zone by using long-term and short-term memory network,and the grain yield is spatialized by BP neural network in the crop distribution area,and the evapotranspiration data of the economic zone is estimated by means of the Penman-Monteith method;The temporal and spatial dynamic evolution of various time series statistical methods is used to analyze the dynamic changes of grain yield and actual evapotranspiration of food crops in Guanzhong-Tianshui Economic Zone.Based on this,the dynamics of water productivity of grain crops in economic zone are evaluated comprehensively and quantitatively,and the key influencing factors and influencing mechanisms of water productivity of food crops are excavated by using the geographical detector.This study has important theoretical significance and practical guidance for realizing the coordinated development of agricultural modernization(precision irrigation,water-saving irrigation)and ecological environment,increasing regional grain output and stabilizing the pattern of food security in China,realizing the sustainable agricultural development and building a well-off society in an all-round way.The main conclusions are as follows:1.The grain production of Guantian Economic Zone shows a declining trend from 2001 to 2016.The Hurst index of grain production is 0.48,and the future change is a decrease→increasing trend.(1)The decline trend of grain production in cultivated areas from 2001 to 2016 was-1.21 t/(km2·a),which indicated that food security in Guantian Economic Zone has been threatened to a certain extent.(2)Spatially,the higher grain yield areas are mainly distributed in alluvial plain and loess plateau.In terms of cropping system,the grain yield per unit area of two grain crops per year was 119.15 t/km2,followed by three grain crops in two years and one grain crop per year.Spatially,the significant increase of grain yield in the past 16 years was mainly distributed in the eastern part of Weinan City,Shaanxi Province.The distribution of the decreasing area is scattered,mainly in the Tianshui area,followed by the periphery of the city.(3)The change of grain yield shows anti-sustainability,combined with a decreasing trend in the light of 16 years of grain production,reflecting that the future changes in grain production in Guantian Economic Zone are generally a trend of decreasing to increasing.2.From 2001 to 2016,the actual evapotranspiration of Guantian Economic Zone showed an upward trend.The Hurst index of actual evapotranspiration was 0.50,and the future change of the real evapotranspiration is unclear.(1)The increasing trend of evapotranspiration in cultivated area was 10.69 kg/(m2·a)from 2001 to 2016.From the perspective of different cropping system,the increasing trend of actual evapotranspiration of one grain crop per year and three grain crops in two years is similar to that of the whole cultivated area,and the increasing trend of actual evapotranspiration of two grain crops per year is lower than that of the whole cultivated area.(2)The average evapotranspiration of grain crop cultivation area is 476.00 kg/m2,and the high evapotranspiration area is mainly distributed in the western part of the economic zone.The low evapotranspiration area is mainly distributed in the loess plateau area around Xi’an urban area and in the north of the economic zone.(3)The randomness of evaporation variation is strong,which reflects that the future trend of evapotranspiration in the Guantian Economic Zone is not clear in general.3.From 2001 to 2016,water productivity of grain crops of Guantian Economic Zone showed a downward trend.The Hurst index of water productivity of grain crops was 0.5 1,and the future change is a continuous decrease.(I)The decreasing trend of water productivity of grain crops in cultivated area from 2001 to 2016 was-0.59x 10-2 kg/(m3·a),which reflected the decrease of agricultural water resources utilization efficiency.From the perspective of different cropping system,the water productivity of two grain crops per year was higher,followed by three grain crops in two years and one grain crop per year.From the point of view of the changing trend,the downward trend of water productivity of grain crops in the whole study area is mainly caused by the change of water productivity of grain crops once a year.(2)From 2001 to 2016,the high-value areas of water productivity of grain crops were mainly distributed in the west of Tianshui,the periphery of Xi’an,the middle-north of Weinan,the southwest of Xianyang and the west of Baoji;the middle-value areas were mainly distributed in the Weihe Basin and the east of Tianshui farming area;and the low-value areas were mainly distributed in the south of Weinan and Xianyang.(3)The change of water productivity of grain crops shows sustainability,combined a decreasing trend of water productivity of grain crops,which reflects the trend of continuous decrease of water productivity of grain crops in Guantian economic zone as a whole.4.The surface parameters of Guantian Economic Zone have a strong influence on the spatial differentiation of crop water productivity and its interaction with other factors.The effects of topographic parameters,surface parameters and meteorological factors on the spatial variation of crop water productivity increased with time.(1)Land surface parameters have the relatively highest explanatory power to the spatial differentiation of crop water productivity,in which evapotranspiration and surface temperature determine the speed and amount of water dissipation between crops and soil,and vegetation cover determines the grain yield.Soil water and precipitation are the water recharge sources of crops,and they all have the same explanatory power.However,there is a high correlation between elevation and air temperature,so the explanatory power of the two factors is also similar.(2)The interaction between each factor and surface parameters on crop water productivity is stronger,followed by the interaction with meteorological factors,and the interaction with topographic parameters is the weakest.Among them,the evapotranspiration of surface parameters has the strongest interaction with other factors,followed by the interaction of surface temperature,vegetation cover and soil moisture with other factors;the interaction between various factors and meteorological factors on crop water productivity is weak,and the interaction between precipitation and temperature is 0.29,followed by the interaction between precipitation and DEM,and the interaction between precipitation and slope with the interaction value of 0.23 and 0.16 respectively;in addition to the high interaction between air temperature and precipitation,the interaction values between air temperature and DEM and slope direction both are 0.12.(3)There is no significant difference in the effect of slope and slope direction,temperature and elevation on the differentiation of crop water productivity.There is a strong correlation between air temperature and elevation,so there is no obvious difference in the effect of temperature and elevation on the differentiation of crop water productivity.However,the cultivated areas of the economic zone are generally distributed in a relatively flat area,the change of slope and slope direction is not obvious at first,and there is no significant difference between the two on the differentiation of crop water productivity.(4)From the perspective of irrigation time,the critical period of water demand for one grain crop per year is in late March and mid-July;the critical period of water demand for three grain crops in two years is mainly concentrated in the middle of the year and the second half of the year,which is mainly distributed before the germination period of the crop and between the middle of June and the middle of September;for two grain crops per year,the critical period of water demand of the first mature crop is mainly concentrated in the period after the peak of vegetation coverage of the crop;the critical period of water demand of the second mature crop is mainly distributed between the germination stage and the peak of crop vegetation coverage to the end of the growing season.The innovations and important progress of this thesis are as follo ws:(1)Based on the in-depth learning method,this thesis,aiming at the multi-band time series data,has established a long-term and short-term memory network between the multi-band time series and the land type within a year from the perspective of time,and has provided a relatively novel method for remote sensing recognition of land object categories.(2)Based on geographical detectors,this thesis has explored the key influencing factors that affect the spatial difference of water productivity of grain crops,and from the perspective of time,analyzed the temporal variation law of the in:fluence degree of each factors on the spatial difference of water productivity of grain crops.(3)In the light of the geographical detectors,this study has discussed the influence of soil moisture on water productivity of grain crops at all times of the year,and analyzed the relationship between the annual growth of grain crops and soil moisture and the timeliness of effects on soil moisture on grain crops in the combination with the annual vegetation coverage,soil moisture change and the average q value of the grain crops in Guantian Economic Zone,so as to accurately grasp the critical period of crop water demand.