Livestock manure recycling in farmland is an effective measure to dispose of livestock waste, reduce chemical fertilizer usage, and achieve green sustainable development in agriculture. Based on a two-year field experiment, this study explored the impacts of applying different types of manure under reduced chemical fertilization on crop yield, nutrient uptake, and utilization efficiency in a rice-rapeseed rotation system, which aimed to provide scientific guidance for the rational application of manure in rice-oilseed rape rotation production systems.

The field trial was conducted in Dafasi Town, Wuxue City, Hubei Province, from 2022 to 2024. Under the condition of straw return to the field, the trial was set up with seven treatments: conventional fertilization (Con), 15% nitrogen fertilizer reduction on the basis of Con (85%N), pig biogas slurry fertilizer application on the basis of Con replacing 15% chemical nitrogen fertilizer (85%N+PS), Con application on the basis of chicken manure-based solid fertilizer to replace 15% chemical nitrogen fertilizer (85%N+CM), 30% nitrogen fertilizer reduction on Con basis (70%N), pig biogas slurry fertilizer to replace 30% chemical nitrogen fertilizer on Con basis (70%N+PS), and chicken manure-based solid fertilizer to replace 30% chemical nitrogen fertilizer on Con basis (70%N+CM). Based on the crop yield, yield constituting factors, and nutrient accumulation in conjunction with the nutrient harvest index, nutrient apparent balance and fertilizer contribution rate were analyzed comprehensively.

The results of the two-season experiment showed that the application of different types of manure under the condition of nitrogen fertilizer reduction could improve the crop yield and nutrient uptake of the rice-oilseed rape rotation system. There was no significant difference in yield, nitrogen and potassium accumulation and harvest index of oilseed rape and rice under 85%N+CM and 85%N+PS treatments compared with Con treatment. However, different types of manure showed significant effects on enhancing crop nutrient uptake and regulating the annual nutrient balance across the rotation cycles, and the 85%N+CM treatment significantly increased the phosphorus accumulation in oilseed rape and rice (the increases were 22.1%-24.8% and 16.6%-16.9%, respectively), but the annual phosphorus surplus and profit and loss ratio increased by 155.9% and 60.3%, respectively, due to the large amount of phosphorus input brought by chicken manure-based solid fertilizer. In contrast, the 85%N+PS treatment reduced the annual nitrogen and phosphorus surplus by 23.5% and 5.9%, respectively, and the corresponding profit and loss ratios decreased by 17.9% and 6.7%, respectively, while maintaining crop nutrient uptake. Compared with 85%N+CM treatment, the FCR of 85%N+PS treatment in oilseed rape and rice increased by 17.4%-27.0% and 24.1%-35.5%, respectively, this not only achieved an efficient substitution of chemical N fertilizer but also substantially alleviated the pressure of soil nutrient surplus : the surplus of nitrogen, phosphorus and potassium was reduced by 28.6%, 63.2% and 35.5%, respectively, and the profit and loss ratio was reduced by 19.3%, 41.8% and 20.5%, respectively. When the nitrogen reduction ratio reached 30% (70%N+CM/PS), compared with the 85%N+CM/PS treatment, the yield of oilseed rape and rice decreased by 7.2%-18.5% and 6.9%-15.7%, respectively, and the accumulation of nitrogen, phosphorus and potassium in the shoots decreased significantly, the annual nutrient surplus and profit and loss ratio increased.

In conclusion, compared with conventional fertilization, the application of different types of manure under the condition of a 15% reduction in nitrogen could not only ensure the crop yield of the rice-oilseed rape rotation system, but also effectively promote the absorption of nutrients by crops, among them, combined with pig biogas liquid fertilizer (85%N+PS) treatment to further improve nutrient uptake and FCR while maintaining yield, and reduce the annual nutrient surplus of rotation, and achieve the level of conventional fertilization. Therefore, it was recommended as the best manure return model for the rice-oilseed rape rotation system.

The objective of this study was to investigate the changes in basic physical and chemical properties of soils in the main winter oilseed rape producing areas in the Yangtze River Basin over the past 40 years, and to clarify the characteristics of changes in comprehensive soil fertility of arable land in winter rape growing areas, in order to provide a scientific basis for conservation and soil fertility improvement in low and middle yielding fields in the Yangtze River Basin.

By collecting and organizing the data from published literatures, master’s and doctoral dissertations at home and abroad in the past 40 years, the temporal variation characteristics of basic soil properties in winter oilseed rape growing areas in the Yangtze River Basin were analyzed. Then the variation characteristics of integrated soil fertility (IFI) and its correlation with basic soil physical and chemical properties were evaluated.

The average values of soil organic matter, total nitrogen, available phosphorus and potassium, and pH in the main winter oilseed rape producing areas of the Yangtze River Basin were 18.54 g·kg^-1, 1.16 mg·kg^-1, 8.60 mg·kg^-1, 42.90 mg·kg^-1, and 6.26 during the period of 1981-1990, respectively, but enhanced to 25.60 g·kg^-1, 1.41 mg·kg^-1, 18.66 mg·kg^-1, 108.98 mg·kg^-1, and 6.31 by 2016-2020, respectively. Clearly, the soil basic physical and chemical properties have been improved extensively in planting area of winter oilseed rape in the Yangtze River Basin. The average annual increase rate was 1.2% in soil organic matter and 0.7% in soil total nitrogen. Soil available phosphorus and available potassium were enhanced by 3.0% and 4.0% per year, respectively. Soil pH remained stable in the past 40 years, with the mean range of 6.21-6.45 among different periods. Based on the improved Nemerow index method, soil IFI value was also found enhanced in the past four decades. Compared with the mean IFI in the period of 1981-2000, the value was significantly increased by 14.8%-30.4% during the period of 2001-2020. The IFI was positively correlated with soil organic matter, pH, total nitrogen, available phosphorus and available potassium. Path analysis showed that soil available potassium was the most important index affecting IFI, followed by soil total nitrogen and available phosphorus.

The basic physical and chemical properties and comprehensive fertility of the soil was significantly improved in the past 40 years in the planting area of winter oilseed rape. Developing the planting area of oilseed rape would be benefit for soil fertility and productivity improvement in the Yangtze River Basin, especially for the farmland with low yield productivity.