Water Demand Characteristics of Rice-Oilseed Rape Rotation System in the Middle Reaches of the Yangtze River

This study aimed to clarify the water demand characteristics of the rice-oilseed rape rotation system in the middle reaches of the Yangtze River, so as to provide the theoretical support for water allocation in this cropping system.

This study analyzed the water demand of the rice-oilseed rape rotation system in the middle reaches of the Yangtze River using the single crop coefficient method. The supplementary irrigation amount was calculated based on the effective precipitation, and the water surplus/deficit characteristics of the rotation system were identified according to the crop water surplus-deficit index.

The rice-oilseed rape rotation pattern in the Middle Reaches of the Yangtze River required an average annual water demand of 1 172 mm, with rice accounting for approximately 898 mm (76.6%) and oilseed rape accounting for approximately 274 mm (23.4%). Rice required an average annual supplementary irrigation of 643 mm, while oilseed rape required drainage of 54 mm on average per year. Years with moderate, severe, and extreme drought in the rice accounted for 77.5%, 15%, and 2.5%, respectively. Years with moderate, severe, and extreme flooding in the oilseed rape accounted for 10%, 17.5%, and 2.5%, respectively. Special attention should be paid to the field water conditions during the tillering, joint-booting, and heading and filling stages of rice, and flood prevention measures should be taken during the seedling and maturity stages of oilseed rape. The early rice-late rice-oilseed rape rotation pattern required an average annual water demand of 1 161 mm, with early rice accounting for approximately 550 mm, late rice accounting for approximately 401 mm. The total water demand of the two seasons accounts for 82.0% of the total water demand of the whole rotation system. while oilseed rape accounting for approximately 210 mm (18.0%). Early rice required an average annual supplementary irrigation of 322 mm, late rice requires 272 mm, and oilseed rape requires drainage of 59 mm on average per year. Years with moderate, severe, and extreme drought in the rice season account for 40%, 15%, and 1.3%, respectively. Years with moderate, severe, and extreme flooding in the oilseed rape season account for 12.5%, 17.5%, and 17.5%, respectively. The special attention should be paid to the water conditions during the joint-booting and heading and filling stages of late rice, and flood prevention measures should be taken during the seedling and maturity stages of oilseed rape.

In the middle reaches of the Yangtze River, the water demand of rice-oilseed rape rotation mode was 1 172 mm, and the water demand of rice and oilseed rape accounted for 76.6% and 23.4%, respectively. The water demand of early rice-late rice-oilseed rape rotation mode was 1 161 mm, and the water demand of rice and oilseed rape accounted for 82.0% and 18.0%, respectively. Supplementary irrigation was required to prevent water deficits during the rice season, while drainage measures were necessary during the oilseed rape season. In years with extreme precipitation, special attention should be paid to excess water conditions during the seedling stage of rice and the seedling and maturity stages of oilseed rape, and corresponding measures should be taken. In years with extreme drought, special monitoring of water deficits should be conducted during the tillering, joint-booting, heading and filling stages of rice and the flowering stage of oilseed rape, and the timely supplementary irrigation should be provided.