Improving Northeast China's soybean and maize planting structure through subsidy optimization considering climate change and comparative economic benefit

The planting structure of Northeast China (NEC) is greatly responsible for China's food security and selfsufficiency. Climate change promoted the northward expansion of the suitable planting area for maize in NEC, and its higher comparative economic benefit largely helped it occupy the soybean planting space. Yet, knowledge on how climatic suitability and comparative economic benefit affected the northward expansion of maize planting area is limited. To bridge this gap, this study quantified the climatic suitability of maize and soybean from 1981 to 2020 using the fuzzy mathematical method. Combined with yield, crop distribution and social economic data in 2000, 2010 and 2020, this study further calculated the comparative economic benefit between the two crops. Furthermore, a crop planting decision simulation model was developed to clarify the impact of climatic suitability and comparative economic benefit on the planting area of soybean and maize. Results showed that from 2000 to 2010, the maize planting area increased dramatically. This was due to the continuous northward expansion of the most suitable region (S1) for maize from 47.63 degrees N to 48.43 degrees N before 2010, along with the fact that 65% of the total area was more profitable to plant maize. From 2010 to 2020, the maize planting area partially retreated, mainly due to the shrinking trend of the northern boundary of S1 for maize and the implementation of soybean producer subsidy. The improvement of maize climatic suitability played a fundamental role in the northward expansion of its planting area. On this basis, the comparative economic benefit was critical for planting proportion adjustments. The current soybean producer subsidy largely reduced the profit gap between the two crops, but it was still insufficient in nearly one-third of the total area. This study suggested to increase amount of soybean subsidies in the identified soybean-maize imbalanced regions. Specifically, the average recommended increase amounts ranged from 756 to 2052 CNY/ha depending on the regions. These findings could provide valuable references for understanding the motivation of crop planting decisions and optimizing the corresponding subsidy policies.