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Maintaining soil productivity and sustainability remains a challenge in the face of a changing global agricultural framework, which includes the primary threat of soil degradation in many regions. Although soil erosion contributes to land degradation, how reductions in fertiliser nitrogen (N) affect erosion and soil microbial communities in sloped farmland remains unclear. In this study, effects of reductions in fertiliser N from 300 kg ha−1 (N1) to 225 kg ha−1 (N2), 150 kg ha−1 (N3), and 75 kg ha−1 (N4) on runoff, sediment yield and microbial community structure were evaluated in 12 maize farmlands with a 10° slope in Southwest China. Soil chemical properties were analyzed, and bacterial 16S rRNA and fungal ITS1 were sequenced from extracted DNA. Runoff and sediment yield in maize were significantly lower in N1 and N2 than in N3 and N4 (p < 0.05). The microbial diversity was higher in N1 and N2 than in N3 and N4. The severe erosion associated with reductions in N input resulted in significant decreases in abundances of the bacterial phyla Proteobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes, Firmicutes, and Nitrospirae and fungal phyla Basidiomycota, Mortierellomycota, and Olpidiomycota. By contrast, abundances of the phyla Acidobacteria (bacteria) and Ascomycota and Glomeromycota (fungi) increased significantly with severe erosion. Distance‐based redundancy analysis indicated that cation exchange capacity, organic matter, and nitrate strongly influenced structure of bacterial and fungal communities. Reductions >25% in N fertiliser (N3 and N4) did not meet crop N requirements, and because of the reduction in surface coverage, soil erosion was exacerbated, and soil fertility and diversity and complexity of microbial communities decreased. The results elucidated effects of N input on soil erosion and soil microbiomes in a sloped agroecosystem with the aim to rehabilitate or restore degraded land and increase sustainable agriculture development. [ABSTRACT FROM AUTHOR]

Simple Summary: Excessive accumulation of reactive oxygen species (ROS) during semen preservation can disrupt the balance of the antioxidant system in sperm, resulting in oxidative damage to lipids and damage to their structure and function. Curcumin is a natural plant extract that neutralizes ROS and enhances the function of endogenous antioxidant enzymes. The effect of curcumin on the preservation of semen has not been reported. This study determined the effects of curcumin on refrigerated sperm (4 °C) and analyzed the effects of curcumin on sperm metabolism from a Chinese native sheep (Hu sheep). The results showed that adding curcumin significantly improved (p < 0.05) the viability of refrigerated sperm at an optimal concentration of 20 µmol/L. Plasma membrane and acrosome integrity in semen were significantly improved (p < 0.05). Adding curcumin to refrigerated semen significantly increased (p < 0.05) the levels of multiple antioxidant enzymes and significantly decreased (p < 0.05) ROS production. We identified 50 differentially expressed metabolites (DEMs) in sperm between the negative control and curcumin-treated groups, suggesting that curcumin affects ovine sperm ROS production by regulating DEMs expression. This finding provides a new way to optimize the refrigerated preservation of sheep semen. Reactive oxygen species (ROS) are important factors that lead to a decline in sperm quality during semen preservation. Excessive ROS accumulation disrupts the balance of the antioxidant system in sperm and causes lipid oxidative damage, destroying its structure and function. Curcumin is a natural plant extract that neutralizes ROS and enhances the function of endogenous antioxidant enzymes. The effect of curcumin on the preservation of sheep semen has not been reported. This study aims to determine the effects of curcumin on refrigerated sperm (4 °C) and analyze the effects of curcumin on sperm metabolism from a Chinese native sheep (Hu sheep). The results showed that adding curcumin significantly improved (p < 0.05) the viability of refrigerated sperm at an optimal concentration of 20 µmol/L, and the plasma membrane and acrosome integrity in semen were significantly improved (p < 0.05). Adding curcumin to refrigerated semen significantly increased (p < 0.05) the levels of antioxidant enzymes (T-AOC, CAT, and SOD) and significantly decreased (p < 0.05) ROS production. A total of 13,796 metabolites in sperm and 20,581 metabolites in negative groups and curcumin-supplemented groups were identified using liquid chromatography–mass spectrometry. The proportion of lipids and lipid-like molecules among all metabolites in the sperm was the highest, regardless of treatment. We identified 50 differentially expressed metabolites (DEMs) in sperm between the negative control and curcumin-treated groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEMs were mainly enriched in the calcium signaling pathway, phospholipase D signaling pathway, sphingolipid metabolism, steroid hormone biosynthesis, 2-oxocarboxylic acid metabolism, and other metabolic pathways. The findings indicate that the addition of an appropriate concentration (20 µm/L) of curcumin to sheep semen can effectively suppress reactive oxygen species (ROS) production and extend the duration of cryopreservation (4 °C) by modulating the expression of sphingosine-1-phosphate, dehydroepiandrosterone sulfate, phytosphingosine, and other metabolites of semen. This discovery offers a novel approach to enhancing the cryogenic preservation of sheep semen. [ABSTRACT FROM AUTHOR]