Study On Temporal And Spatial Variation Of Cultivated Land Quality In Longhai City Based On Trend Surface Analysis

Cultivated land is the material basis for human survival,ensuring the national food security and social stability.In recent years,with the rapid development of social economy,the acceleration of urbanization,the expansion of the scale of construction land and the increase of the contradiction between human and land,the basic national conditions of China’s large population and small land have forced China’s agricultural production to be in a high-input and high-output mode.And resulting in soil pollution,soil nutrient imbalance,effective soil thickness reduction,soil biota decline and the soil degradation are serious.In October 2015,the Ministry of Agriculture issued the Action Plan for the Protection and Promotion of the Quality of Cultivated Land.The plan pointed out that to promote the sustainable development of grain and agriculture,ensure the effective supply of agricultural products,and enhance the international competitiveness of China’s agriculture,we must vigorously improve the quality of cultivated land and effectively achieve the goal of "storing grain on the ground".Longhai City has an excellent geographical location.It is the first coastal open county in the country.It is adjacent to the Xiamen special economic zone.The establishment of the "one belt and one road" economic circle brings new opportunities for Longhai City.In this paper,the Longhai City is taken as the study area.This paper takes Longhai City as the research area,and builds the indicator system to evaluate the quality of cultivated land in Longhai City in 2013 and 2017 by using the grading unit in the database of cultivated land quality and other data.Through the deployment of monitoring points,the trend surface analysis model is established,and the mapping and spatial analysis functions of ArcGIS are combined to analyze the distribution of cultivated land quality and the characteristics of cultivated land quality in Longhai City.The main obstacles factor affecting the quality of cultivated land in Longhai City are analyzed by introducing the obstacle degree model.The main conclusions are as follows:(1)Ten indexes were selected from three aspects of soil condition,site condition and cultivated land management to evaluate the quality of cultivated land based on plots.The results showed that the cultivated land area of Longhai City decreased by689.33 hectares in 2017 and 2013,and the pattern division was more fragmented.The cultivated land area of Longhai City in 2017 decreased by 711.76 hectares compared with that in 2013,which indicated that part of the high-quality cultivated land was occupied and part of the cultivated land quality was declining gradually.(2)Thirty-six monitoring points were set up and a trend surface analysis model was established with the data of monitoring points.The results showed that the cubic trend surface fitting degree of the two time points was high,and the equation was more significant.It made a new contribution to the low-order trend surface equation and could fit the characteristics of cultivated land quality distribution in Longhai City.ArcGIS was used to draw the equivalence map of cultivated land quality trend surface and the boundary of cultivated land quality zoning between 2013 and 2017 in Longhai city,and the distribution characteristics and temporal and spatial changes of cultivated land quality in Longhai city were analyzed.The results show that the cultivated land quality of Longhai City decreases from the center to the surrounding area.The central area composed of the northern part of Bangshan Town and the western part of Zini Town has the best cultivated land quality,and the western border of Chengxi Town has the worst cultivated land quality.According to the quality of cultivated land,the cultivated land in Longhai can be divided into three regions,the cultivated land in high-quality area is mainly paddy field,the scale is large and the distribution is concentrated,and the spatial differentiation of cultivated land quality is small in this region;the cultivated land in sub-optimal area is mainly paddy field,and the distribution of cultivated land in the eastern part of the region is more concentrated than that in the western part,and the spatial differentiation of cultivated land quality is small in the inferior area.The distribution of cultivated land is the most evacuated in the western part of the region,paddy field is the main cultivated land,small and sporadic plots,spatial differentiation is greater,the eastern part of the region is mainly dry land,land fragmentation,poor quality of cultivated land but small spatial differentiation.In 2017,compared with 2013,the cultivated land area in the high-quality area is decreasing,the cultivated land area in the sub-optimal area is increasing,and the cultivated land area in the low-quality area is basically unchanged.(3)By constructing the trend surface analysis model of cultivated land quality change in Longhai City,drawing the trend surface equivalence map of cultivated land quality change,the cultivated land in Longhai City is divided into quality decline area,quality rise area I and quality rise area II.The quality declining area accounted for two-thirds of the cultivated land area in Longhai City,mainly paddy fields;the quality rising area I was mainly woodland,more supplementary cultivated land;the quality rising area II was one-third dry land.By introducing the obstacle degree model,the main obstacle factors of cultivated land quality in Longhai city are organic matter content,effective soil thickness and land scale,which are caused by the long-term high input and high harvest of cultivated land and the weakening of soil fertility.In order to improve the quality of cultivated land in Longhai City,it is necessary to protect the high-quality cultivated land,improve the sub-optimal cultivated land,upgrade the inferior cultivated land,take appropriate fallow and take certain biological measures.