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.

The aim of this study was to clarify the response of different rice varieties to zinc fertilizer and the differences in the effects of different zinc fertilizer application methods on rice yield and grain zinc bioavailability.

The field experiments were conducted in 2019 and 2020. The first field experiment (Experiment 1) in 2019 aimed to explore the response of different rice varieties to zinc fertilizer application. Four rice varieties were selected, including Xiadao No.1, Xiadao No.2, Runxiangyu, and Longliangyou3463, with two treatments of no zinc application (CK) and zinc application (+Zn), and the differences in the response of different rice varieties to zinc fertilizer application were investigated. The second field experiment (Experiment 2) in 2020 aimed to explore the effects of different zinc fertilizer application methods on rice yield and grain zinc bioavailability. Based on the experiment in 2019, two high-yielding rice varieties, including Xiadao No.1 and Longliangyou3463, were selected to continue the study. Six treatments were set: no zinc application to soil (S0F0), soil application of 15 kg·hm^-2 zinc (S1F0), soil application of 30 kg·hm^-2 zinc (S2F0), foliar spray of 0.5% ZnSO₄ at flowering stage (S0F1), soil application of 15 kg·hm^-2 zinc + foliar spray of 0.5% ZnSO₄ at flowering stage (S1F1), and soil application of 30 kg·hm^-2 zinc + foliar spray of 0.5% ZnSO₄ at flowering stage (S2F1), and the differences in the effects of different zinc application methods on yield and grain zinc bioavailability of two rice varieties were investigated.

In experiment 1, there were significant differences in the response of different rice varieties to zinc fertilizer. After zinc application, the yields of Xiadao No.1, Xiadao No.2, Runxiangyu, and Longliangyou3463 increased by 4.4%, 11.6%, 7.9%, and 4.8%, respectively. The increase in yield was mainly attributed to the increase in effective panicle number and grain-setting rate. Compared with CK, the average effective panicle number of the four rice varieties with zinc application increased by 19.8%, 3.9%, 9.9%, and 24.0%, respectively, and the average grain-setting rate increased by 5.4%, 9.7%, 6.7%, and 4.0%, respectively. In addition, the molar ratio of phytic acid to zinc in brown rice and polished rice of the four rice varieties with zinc application decreased by averages of 24.3%, 30.9%, 21.3%, and 37.2%, and 29.5%, 32.4%, 33.9%, and 35.3%, respectively. In experiment 2, there were significant differences in the effects of different zinc application methods on the yield and grain zinc availability of Xiadao No.1 and Longliangyou3463. Soil zinc application significantly outperformed foliar zinc spray in increasing yield, and foliar zinc spray further increased rice yield when it combined with soil zinc application. Compared with S0F0, the yields of Xiadao No.1 under S0F1, S1F0, S1F1, S2F0, and S2F1 increased by 12.1%, 14.1%, 17.2%, 22.2%, and 29.3%, respectively, and the yields of Longliangyou3463 under S0F1, S1F0, S1F1, S2F0, and S2F1 increased by 2.0%, 10.1%, 15.2%, 28.3%, and 31.3%, respectively. The effects of different zinc application methods on grain zinc availability varied, and there were significant differences in grain zinc availability between the two rice varieties. Foliar spray had a significantly greater zinc enhancement effect on grain compared with soil application, and the bioavailable zinc content in grains of Longliangyou3463 was higher than that in Xiadao No.1.

Selecting high-yielding and zinc-enriched rice varieties (Longliangyou3463) and adopting appropriate zinc fertilizer application methods (30 kg·hm^-2 soil application + foliar spray of 0.5% ZnSO₄ at flowering stage) could achieve the goals of increasing rice yield and enhancing rice zinc nutrition, thereby helping to increase income and improve rice quality.