Analysis of influencing factors of agricultural productivity and cultivated land dynamics based on simultaneous formulas in Northeast China

Abstract: Northeast China is one of the major grain producing areas in China. However, issues are current outstanding, such as decrease in land productivity. Therefore, it is significant to carry out researches on mechanisms of cultivated land dynamics and agricultural productivity in Northeast China. In this study, we quantitatively analyzed the relationship between the endogenous and exogenous variables of three key regional ecological processes in the study area, including agricultural productivity, conversion of cultivated land to land for house or building, and conversion of cultivated land to forests or grasslands. The simultaneous equations were used in this study, which was based on the data of land use, natural environment, meteorology, location, traffic and socio-economy. Quantitative analysis was conducted from several aspects such as population size, society, economy, policy, location and natural conditions. The results showed that socio-economic factors played a decisive role in the agricultural productivity in a short period, and agricultural population growth and the role of input factors of agricultural productivity were also significant. In addition, policy was one of key influencing factors as well. Although the policy of Grain for Green has negative effect for agricultural production, it was noted that the policy of Grain for Green can not be terminated because environmental protection should be also considered. Air temperature and precipitation were also important for agricultural productivity, but they produced negative effect after reaching a certain level. In the process of cultivated land converted to building area, rapid urbanization and economic development were the main reasons, while investment in capital construction had no obvious effects. Therefore, population size and economic development were the key driving factors, and the amount of cultivated land converted to building area increased with the lagged agricultural productivity. This indicated that most of the expansion of building area was converted from fertile farmland, which had a high productivity, and it was one of the problems of urbanization and it needed attention. Geographic conditions and policy were the control factors, and the region with large slope and low plain area percentage had less conversion from cultivated land to urban area. Moreover the policy of Grain for Green also controlled the conversion from cultivated land to building area to some extent. The process of cultivated land converted to forest or grassland was mainly influenced by the key variables such as proportion of agricultural population, terrain slope, location and traffic condition, policy, climate and so on, while topography, whether was the major grain-producing county, agricultural productivity were not significant. First industry GDP promoted the conversion from cultivated land to forest or grassland, while second industry GDP and tertiary industry GDP had negative effects. The larger the proportion of rural population, the greater the increase of cultivated land converted to forest or grassland was. This suggested that larger proportion of agricultural population made more agricultural population liberate from the agricultural production process, and increased their revenue by the forestry, animal husbandry, fisheries and non-agricultural industry. Therefore, it was necessary to handle the relationship between population, economic and agricultural productivity correctly, so as to protect cultivated land and its supply functions, support functions and regulation functions and guarantee the quality and level of human life. These findings will provide important reference information for land use planning and cultivated land protection.