In this study, the effects of the soil application and foliar spraying with magnesium fertilizers on rice yield and quality in Liaoning Province were investigated. Field experiments were conducted at Kaiyuan, Xinmin, and Dawa in 2022 and 2023. Magnesium fertilizers were used in the soil as magnesium sulfate monohydrate and silicon–magnesium fertilizer and on leaves was magnesium sulfate heptahydrate. The results showed that the application of 12 kg magnesium hm⁻² in the soil at the Kaiyuan site can significantly increase rice yield by 14.8% compared with sites without magnesium fertilizer. The use of silicon–magnesium fertilizer showed a more obvious yield increase of 22.2%. The application of 3 kg magnesium hm⁻² or 6 kg magnesium hm⁻² on the leaf surface increased the rice yield at Kaiyuan by 19.4% and 21.6% and at Xinmin by 17.8% and 5.4%, respectively. The yield increase was more significant under the optimal fertilization treatment compared with the conventional fertilization treatment. The application of magnesium fertilizer increased the magnesium, nitrogen, and phosphorus contents in rice shoots and the potassium and crude protein contents in rice grains. The effect of foliar spraying with magnesium fertilizers was more obvious than soil application. Therefore, the magnesium fertilizer used on the leaf surface plays an important role in improving rice yield and quality in rice-growing areas with relatively rich soil magnesium content. Magnesium fertilizer can compensate for the yield decrease caused by the reduced use of nitrogen and phosphorus fertilizers by promoting nitrogen and phosphorus absorption in rice. Conclusively, the application of magnesium fertilizer is a promising measure to improve rice production in Liaoning province under a reduced nitrogen and phosphate fertilizer background.

The combined application of manure and chemical fertilizers has been recognized as a critical factor driving significant changes in crop yield and nutrient use efficiency, holding the potential to optimize agricultural management to achieve high yields. In this 40-year study, we investigated the effect of manure amendment on soybean and maize yields, water and nitrogen use efficiencies (WUE and NUE), and water and mineral N storage at 0–100 cm soil depths from 2017 to 2018 to explore the optimization of fertilization management strategies for soybean and maize production in Northeast China. To elucidate the impact of chemical fertilizers and manure, twelve treatments—control (CK); single N fertilizer at a low rate (N₁) and that at a high rate (N₂); N₁, phosphorus (P), and potassium (K) fertilizer (N₁PK); manure alone at 13.5 and 27 t ha⁻¹ (M₁ and M₂); and those combined with N, P, or K fertilizer (M₁N₁, M₁N₂, and M₁N₁PK and M₂N₁, M₂N₂, and M₂N₁PK)—were selected and studied. The results showed that long-term amendment with manure significantly increased crop biomass and yield in the soybean–maize–maize rotation system. Combining with manure increased the WUE, the partial factor productivity of N fertilizer (PFP_N), and N physiological efficiency (PE_N) in both the soybean and maize seasons; conserved soil water (mainly at 40–60 cm); and increased soil N retention (in the upper 60 cm layer), which reduced the risk of N leaching, with a better effect being observed after the application of 13.5 t ha⁻¹ manure. These results provide insight into the potential of using fertilization management strategies that include amendment with 13.5 t ha⁻¹ manure in combination with N, P, and K fertilizer in the maize season and only chemical fertilizer in the soybean season, as these results indicate that such strategies can achieve high yields and be used to implement agricultural sustainable development in brown soil regions in Northeast China.

Various environmental factors and anthropogenic practices can affect the Fe biogeochemical cycles in soils. Nitrogen and carbon states are closely associated with Fe dynamics. However, we still have a limited understanding of the complex response of Fe biogeochemical processes to long–term nitrogen– and organic–fertilization regimes. This study investigated the Fe fraction and distribution, as well as the link between Fe and nitrogen/carbon, in bulk soil and in soil aggregates. The results showed that the long–term application of the nitrogen fertilizer increased the contents of water–soluble iron (Ws–Fe) and carbonate–bound iron (Ca–Fe) in the bulk soil and various sizes of aggregates, as well as the iron contents in soybeans. The decreased pH and enhanced Feammox reaction in response to the nitrogen–fertilizer treatments were responsible for the increase in the Ws–Fe and Ca–Fe fractions. By contrast, the long–term application of the organic fertilizer decreased the contents of Ws–Fe and Ca–Fe, while it increased the contents of Ox–Fe and Or–Fe. Moreover, the contents of Ox–Fe and Or–Fe were positively correlated with the organic–carbon contents in the micro–aggregates of 0.053–0.25 mm and <0.053 mm. These results indicated that the long–term use of the organic fertilizer encouraged Fe immobilization in organo–inorganic compounds. However, the application of the nitrogen fertilizer alleviated the Fe retention induced by the organic fertilizer. In conclusion, long–term nitrogen and organic fertilization have contrasting influences on the mineralogy and availability of Fe in soil. This study is useful for understanding the mechanism underlying the interaction between Fe and nitrogen/carbon, as well as Fe’s phytoavailability in response to different fertilization practices in brown soil.

Copper (Cu) is an essential nutrient for plants. Fertilizer application is a key factor influencing the migration and transformation of Cu in the soil-plant system. However, limited studies have assessed the distribution, speciation, and transformation of Cu as well as its bioavailability under long-term fertilization conditions. In this study, we investigated the distribution and enrichment pattern of Cu in bulk soil and aggregates based on a 43-year long-term fertilization experiment on brown soil. The results present that long-term N fertilizer application can maintain total soil Cu at a stable level across the monitored 43 years, simultaneously increasing the Ws-Cu and Ca-Cu, thus increasing the Cu contents in maize and soybean. While long-term manure fertilizer application significantly enhanced Cu accumulation and availability in soil in terms of total Cu and various Cu fractions, Cu content declined in maize and soybean. The combined application of N fertilizer and manure fertilizer led to further accumulation of total Cu, DTPA-Cu, Ca-Cu, Ox-Cu, and Or-Cu, as well as Cu in 1–2 mm and 0.5–1 mm aggregates, but resulted in a decrease in Cu content in the 0.25–0.5 mm, 0.053–0.25 mm and <0.053 mm aggregates only under M2 treatments. In addition, the combined use of N fertilizer and manure fertilizer mitigated the reduction in plant Cu content caused by sole manure application. These findings provide a scientific basis for regulating Cu transport and transformation in the soil-plant system via combined organicinorganic fertilization in agricultural production.