Study of Regional Spatial and Temporal Changes of Net Ecosystem Productivity of Crops from Remotely Sensed Data

Net ecosystem productivity (NEP) is a crucial indicator of the carbon balance and health of an ecosystem. Until now, few studies have estimated the NEP of crops and analyzed it in space and time. The study of NEP in crops is crucial for comprehending the carbon cycle of agroecosystems and determining the status of carbon sources and sinks in farmland at the regional scale. In this study, we calculated the net primary productivity (NPP) and NEP of agricultural crops in Jiangsu Province, China, from 2001 to 2022 by using remote sensing data, land cover data and meteorological data. The modified Carnegie Ames Stanford Approach (CASA) model was employed to estimate the NPP, and the soil heterotrophic respiration model was used to calculate the soil heterotrophic respiration (Rh). Then, the availability of the NPP was evaluated. On this basis, the NEP was obtained by calculating the difference between the NPP and Rh. We explored the spatial and temporal changes in the NEP of crops and analyzed the correlation between the NEP and crop cultivation activities and climatic factors under the context of agricultural production information using the NEP datasets of agricultural crops. The study indicated that (1) the NEP of crops in Jiangsu Province showed a north-to-south pattern, being higher in the north and lower in the south. Over the course of 22 years, the average NEP of the crops in Jiangsu Province stands at 163.4 gC/m2, highlighting a positive carbon sink performance. Nonetheless, up to 88.04% of the crops exhibited declining NEP trends. (2) The monthly fluctuations in the NEP of crops in Jiangsu Province exhibited a bimodal pattern, with peaks occurring during spring and summer. The changes in the NEP of the crops were significantly associated with various agricultural production activities. (3) Significant regional differences were observed in the NEP of the crop response to temperature and precipitation, both of which directly impacted the annual performance of the NEP. This study could serve as a reference for research on the carbon cycle in agriculture and the development of policies aimed at reducing emissions and enhancing carbon sinks in local farmland.