Impacts of urban sprawl on agricultural land quality grade structure and potential production based on remote sensing

Abstract: China is undergoing rapid urbanization and industrialization over the last three decades. Agricultural land loss and degradation due to urban occupation is one of the most serious issues in China. There were many studies on the quantity of agricultural land loss, however few researches focused on the agricultural land quality change due to urbanization. The impact of urban occupation on agriculture land quality was assessed in this paper by using remote sensing images and agricultural land quality data. We proposed 2 indicators to show the impacts of urbanization on agricultural land resource. One was quality index of agricultural land which can indicate the structure of agricultural land quality due to occupation by urban sprawl. The other was loss of production potential that is a comprehensive indicator of both quantity and quality change of agricultural land. We used the satellite data and agricultural land quality data sets of Jiangsu Province to evaluate the change of quantity, quality and potential production of agricultural land due to urbanization process from 1985 to 2015. The results showed that the total area of 3 500 km2 was lost dramatically due to urban sprawl in recent three decades, which accounted for 7% of total area of agricultural land in Jiangsu Province. In South Jiangsu Province which is the most developed area of Jiangsu, the loss of agricultural land accounted for 20% of total area. The loss rate of the central and north Jiangsu was 3.6% and 3.1%, respectively. The tendency of agricultural land loss due to the urban occupation would increase with the economic development and urbanization. Urban sprawl occupied the land around the city which was the high quality agricultural land. This process has led more and more loss of high quality land, the first, second and third level land of which accounted for 60% of total lost land. Although China implements the strictest land policy of requisition-compensation balance in arable land, high quality agricultural land loss became a serious problem due to their occupation around cities. Structure of land quality indicator was used to indicate comprehensive change of agricultural land. The research showed that the structure of land quality became worse, and the first, second and third level high quality land decreased by 1.5%. By the reason of the loss of high quality agricultural land in the urbanization process, the quality structure of agricultural land decreased, which would affect the crop production. In fact, the crop production decreased by about 5×106 t, which accounted for 14% of total crop production in Jiangsu Province in 2015. Therefore, the agricultural land quality change caused by urban sprawl should be paid more attention. The decreasing tendency of quantity and quality of agricultural land in short term will not change because urbanization is ongoing rapidly in China. The conservation of agricultural land is the base for food quality and food security. The protect object of agricultural land should be changed from quantity balance to quality and potential production balance.