Incorporation of Relay Intercropping in Wheat–Fresh Maize–Fresh Soybean Cropping System Improves Climate Resource Utilization and Economic Benefits in Yangtze River Delta

In the Yangtze River Delta region, demand from consumers for fresh maize and fresh soybeans is increasing. The cropping systems applied in agricultural production have a low utilization of light and temperature resources. In order to construct a novel planting pattern for fresh maize and fresh soybean with a high-efficiency utilization of climate resources, we conducted a field experiment to compare the annual yield, allocation, and utilization efficiency of climatic resources and the economic benefits between the conventional double-cropping system with wheat-fresh soybeans (CK) and the triple-cropping planting patterns comprising wheat-fresh maize/fresh soybeans (W1) or wheat-fresh maize/fresh maize(W2) at Nantong, Jiangsu, China, from 2016 to 2020. Compared with the conventional double-cropping system, the triple-cropping planting patterns increased the annual yield by 6547 kg ha−1 and 11,979 kg ha−1 and increased the annual biomass by 4389 kg ha−1 and 10,425 kg ha−1, respectively. The annual economic benefit of triple-cropping planting patterns increased by 2775 RMB ha−1 and 12,765 RMB ha−1, respectively. The triple-cropping planting patterns respectively increased the annual radiation production efficiency by 0.08 g MJ−1 and 0.28 g MJ−1, the annual temperature production efficiency by 1.65 kg ha−1 °C−1 and 4.30 kg ha−1 °C−1, and the annual precipitation production efficiency by 4.40 kg mm−1 ha−1 and 9.67 kg mm−1 ha−1. Considering the yields, resource-use efficiency, and economic benefits, the wheat–fresh maize–fresh soybean system is suitable for application in YRD region and worth extending in the Yangtze River region. However, ways to improve fertilizer utilization efficiency in the wheat–fresh maize–fresh soybean system need to be studied.