The application of chemical fertilizers and organic materials is a crucial measure for increasing agricultural production. Rice-rapeseed rotation system is a primary paddy-upland crop rotation pattern in the Yangtze River basin of China. Clarifying the impact of chemical fertilizers and organic material inputs on the annual crop yield and nutrient utilization in rice-rapeseed rotation could provide a scientific basis for ensuring food and oil security and achieving green and sustainable agricultural development.

From 2017 to 2022, a continuous field experiment was conducted at the Huazhong Agricultural University's Shayang Experimental Station in Shayang County, Hubei Province. Four treatments were established: no fertilizer (CK), chemical fertilizer only (NPK), chemical fertilizer with straw return (NPK+S), and chemical fertilizer with straw return plus organic fertilizer (NPK+S+M). The crop yields, nitrogen (N), phosphorus (P) and potassium (K) nutrient absorption of rapeseed and rice were analyzed. The nutrient use efficiency, apparent nutrient balances, and their relationships with yield were also assessed.

The average results over 6 years showed that compared with no fertilization, the application of chemical fertilizers and organic materials significantly increased the yield of rapeseed (493.5%-758.8%) and rice (94.3%-106.4%), and enhanced crop yield stability (24.6%-72.1%) and sustainability (17.2%-85.0%). Compared with the NPK treatment, the NPK+S treatment increased the yield of rapeseed by 6.3%, but decreased yield stability and sustainability; it decreased the yield of rice by 0.8%, but increased yield stability and sustainability. The NPK+S+M treatment increased the yield of rapeseed and rice by 44.7% and 5.4%, respectively, and improved the sustainability of yield. Throughout the rotation cycle, nutrient uptake by rapeseed was consistently lower than that by rice across all treatments. The addition of organic materials significantly enhanced nutrient uptake in both rapeseed and rice. Relative to the NPK treatment, the NPK+S+M treatment resulted in increases of 5.1%-91.2% in average nutrient uptake and 12.2%-100.4% in trend nutrient uptake. The NPK+S treatment did not significantly differ from the NPK treatment in average nutrient uptake but exhibited a 7.7%-25.4% higher trend nutrient uptake. The input of organic materials decreased the physiological nutrient use efficiency of rapeseed and rice. Compared with the NPK treatment, the physiological N use efficiency of rapeseed and rice in the NPK+S+M treatment decreased by 3.0 and 3.7 percentage points, respectively, and the physiological P use efficiency decreased by 19.3 and 25.5 percentage points, respectively. Further analysis revealed that the application of organic materials led to higher apparent nutrient surpluses, which caused the annual increase in the cumulative yield of crops in the rice-rapeseed rotation. The cumulative apparent nutrient surplus was significantly positively correlated with the cumulative crop yield.

The application of chemical fertilizers and organic materials significantly increased crop yields and nutrient use efficiency, and its effects were jointly influenced by crop and nutrient type. Increasing organic fertilization along with chemical fertilizers and straw application could further enhance soil fertility and increase crop yield; however, efforts should focus on improving the physiological nutrient use efficiency to fully realize the potential of organic amendments for sustainable grain and oil production.

Rice-rapeseed rotation is an important paddy-upland crop rotation in China, and the application of nitrogen (N), phosphorus (P) and potassium (K) fertilizer plays an important role in guaranteeing high and stable crop yields. This study systematically assessed the effects of different types of nutrient inputs on the yield and nutrient utilization of the annual crop of a continuous term rotation, so as to provide a reference to the management of nutrients in rice-rapeseed rotation.

A rice-rapeseed rotation field trial was carried out for 8 continuous years from 2016 to 2024, with 4 treatments of equal application of N, P and K (NPK), and no N (-N), no P (-P), and no K (-K), to analyze the yield of annual crops, yield components, nutrient utilization, and apparent balance.

Imbalanced fertilization significantly reduced crop yields, compared with the NPK treatment, the -N, -P and -K treatments reduced yields by 26.7%, 36.7% and 2.8% in rice and 57.4%, 86.4% and 12.3% in rapeseed, respectively, and the reduction in the number of effective number of panicles in rice and the number of pods in rapeseed were the main reasons for the crop yields reduction. With the increase of rotation year, the cumulative crop yield under -N, -P and -K treatments gradually increased the degree of yield reduction; compared with NPK treatment, the yield stability and sustainability of rice and rapeseed were significantly reduced under -P treatment. In terms of annual nutrient allocation in crop rotation, the N, P₂O₅ and K₂O accumulation in rice was higher than that in rapeseed, and the trends of nutrient accumulation in rice, rapeseed and crop annual rotation under imbalanced fertilizer application conditions were consistent with yields. Fertilizer use efficiency analysis showed that the fertilizer contribution rates of N, P and K fertilizers were lower in rice than in rapeseed, while the agronomic efficiency of N and P fertilizers, and the recovery efficiency of P and K fertilizers were higher than those of rapeseed. From the nutrient apparent balance of the annual rotation, the nutrient surpluses of the soil in the rice season were all lower than those of the soil in the rapeseed season, and the annual rotation of the NPK treatment had surpluses of 135.1 kg N·hm^-2, 49.6 kg P₂O₅·hm^-2, and deficits of 225.1 kg K₂O·hm^-2, deficiency of a single nutrient exacerbated the surplus of other nutrients.

In the rice-rapeseed rotation system, the deficiency of any single essential nutrient notably diminished crop yield as well as the utilization of nutrients, and the rate of yield reduction was related to the basic soil fertility level. Under the conditions of this study, the -P treatment had the largest yield reduction, followed by the -N treatment, while the -K treatment showed the smallest reduction. The magnitude of yield reduction in rapeseed was significantly higher than that in rice. Therefore, it was necessary to pay attention to the input of N and P fertilizers to achieve high and stable crop yields, and appropriate supplementation of K fertilizer to alleviate the depletion of soil K reservoirs, in order to realize high yield, high efficiency and sustainable development of the long-term rice-rapeseed rotation system.