2.2. Crop culture and management
Two rice seasons and one crop rotation season were conducted from June 2019 to November 2020. The field had always been cropped with rice-wheat rotation before the experiment. The paddy rice (Oryza sativa L.) with the variety of “Nanjing 46” was planted on June 14, 2019, and harvested on November 7, 2019, for the first season (Rice2019), and on June 13, 2020, and harvested on November 17, 2020, for the second season (Rice2020). The winter wheat (Triticum aestivum L.) with the variety of “Yangmai 13” was seeded on November 17, 2019, and harvested on May 22 in 2020 (Wheat). The oilseed rape (Brassica napus L.) with the variety of “Huayouza No.8” and the green manure of Chinese milkvetch (Astragalus sinicus L.) with the variety of “Zhezi No.5” were seeded at the same time as wheat. Straws of rice and wheat were turned over after grain harvesting by a rotary cultivator. Shoots of oilseed rape and Chinese milkvetch were also turned over after maturing. Crops were planted by a planter with the conventional plant density. The base fertilizer was incorporated into the 10−15 cm soil layer before planting and the topdressing fertilizer was broadcasted artificially. Conventional weeding, irrigation, and UAV plant protection were carried out to maintain crop growth.