Spatiotemporal evolution and carbon emission on non-grain production of cultivated land in the Northern Plains of Zhejiang Province, China

Non-grain production refers to the mode in which the farmland of grain cultivation is occupied by cash crops, forests, fruits, or the stock-breeding industry. It is very necessary to identify the spatial and temporal evolution of non-grain production and then to examine the carbon emission, particularly for the national food security and low-carbon green agriculture. However, it is still lacking in the different types and their carbon emission of non-grain production at a fine scale. Differentiated control and management have been hindered on the non-grain production from a low-carbon perspective. Taking the Tongxiang City of Zhejiang Province in east China as an example, this study aims to explore the different types of non-grain production in the cultivated land, including nursery plantation, pit-pond aquaculture, livestock and poultry farming, and greenhouse vegetable production. Their spatial and temporal evolution was also determined using remote sensing and GIS spatial analysis. Global Moran’s I index and local Moran’s I statistics were used to evaluate the spatial distribution and agglomeration of non-grain production types over the years. The life cycle and the opportunity cost method were then applied to assess the carbon emission using field survey data. The results showed that: 1) The non-grain production rate of cultivated land increased from 1.56% to 7.50% from 2005 to 2020, where the non-grain production area had a net increase of 2,464.74 hectares. In terms of the distribution of non-grain production, there was significant spatial clustering, where the high-value agglomerations were distributed in the far southwestern suburbs with a dense water network. 2) Pit-pond aquaculture accounted for the largest proportion of non-grain production, followed by nursery plantation and greenhouse vegetable production. The evolution of non-grain production was shifted from the dominant type of nursery plantation to the staggered distribution of multiple types in the end. 3) Carbon emissions due to non-grain production increased from 22 232.56 to 98 945.40 t from 2005 to 2020, of which pit-pond aquaculture contributed the most. Moreover, the carbon emission from the pit-pond aquaculture accounted for 83.7% of the total in 2020. The largest contributors to the carbon emissions of nursery plantation and greenhouse vegetable production were various fertilizer inputs and plastic film inputs, respectively, while the main sources of carbon emissions from the pit-pond aquaculture and livestock and poultry farming were direct emissions of CH₄ and N₂O. Meanwhile, the carbon emissions of non-grain production showed a trend of high-value agglomeration in the far southwest and low-value ring distribution in the central suburbs. The carbon emission should consider the different types of non-grain production for regional food security. The management of non-grain production should be implemented under the regional types. The synergistic development can be achieved in cultivated land protection and low-carbon emission reduction in agricultural production.