Converting natural vegetation to other types of land utilization is presently the most common land use change around the world. Conversion of grassland plays an important role in estimating the regional nutrients budget and assessing ecological effects. However, few studies have estimated the impacts of grassland conversion on soil nutrients under different soil pedogenic horizons. This study selected three sites, which were covered by grassland, shelterbelt, and cropland. The study evaluated the effects of grassland conversion and soil pedogenic horizon (to a depth of 100 cm) on the soil organic carbon (SOC), soil total nitrogen (STN), and soil total phosphorus (STP) concentrations and stocks in the Chinese Chernozem region. The results revealed that significant (p < 0.05) differences were seen after grassland conversion for concentrations and stocks of SOC, STN, and STP. The transformation from grassland to shelterbelt and cropland plantations caused soil carbon and soil nitrogen losses but caused soil phosphorus accumulations. Moreover, conversion of grassland made SOC, STN, and STP all drop below the B_k-horizon. Changes in the SOC and STP on an area basis were the greatest after conversion of grassland to cropland, for concentrations of −16% and 26% and for stocks of −15% and 32%, respectively. Land use change and soil pedogenic horizon primarily influenced the distribution patterns of nutrients concentrations and stocks. However, grassland conversion effects on nutrients were mainly at surface horizons. Soil properties, such as calcium carbonate (CaCO₃) and soil texture, affected the nutrients from the B_k-horizon to the C-horizon. This study indicates that land use management policies should protect natural grasslands to minimize losses of SOC, STN, and STP.

Background: The unique physicochemical properties of soda saline-alkali soils significantly reduce soil nitrogen availability and crop nitrogen use efficiency. While high-yield and high-efficiency cultivation practice offer a key strategy for the synergistic improvement of both crop productivity and resource use efficiency. However, the optimal nitrogen input rate for these practices remains to be determined. Methods: Hence, a three-year field study was implemented with nitrogen fertilizer application rates ranging from 0 to 325 kg ha ⁻¹ (0, 125, 175, 225, 275, 325 kg ha ⁻¹ ) to assess their effects on ionic balance, stress physiology, nitrogen use efficiency, and grain yield in rice grown under soda saline-alkali soil conditions. Results: The findings indicate that additional nitrogen fertilizer, particularly at 275 kg ha ⁻¹ within the high-yield and high-efficiency cultivation practice, significantly reduced the leaf Na ⁺ /K ⁺ ratio and levels of superoxide anion (O ₂ ⁻ ) and malondialdehyde (MDA), while increasing K ⁺ concentration and enhancing the levels of soluble proteins and proline, as well as the activities of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Conversely, leaf Na ⁺ concentration increased significantly with rising nitrogen application rates. Furthermore, supplementary nitrogen fertilizer significantly improved total nitrogen uptake, nitrogen use efficiency (NUE), and nitrogen agronomic efficiency (NAE) in rice, which can be attributed to markedly enhanced activities of key nitrogen metabolism enzymes. Consequently, grain yields under the N4 (275 kg ha ⁻¹ ), N5 (325 kg ha ⁻¹ ), N3 (225 kg ha ⁻¹ ), N2 (175 kg ha ⁻¹ ), and N1 (125 kg ha ⁻¹ ) treatments exhibited significant increases of 94.34%, 62.40%, 56.15%, 37.78%, and 24.01%, respectively, relative to the N0 control. These results demonstrate that, within the high-yield and high-efficiency cultivation practice, nitrogen fertilization at a rate of 275 kg ha ⁻¹ plays a crucial role in improving rice productivity and optimizing nitrogen use efficiency in soda saline-alkali paddy fields.

The interaction between secondary phyllosilicate minerals and straw is crucial for preserving soil organic carbon (SOC) and fertility. However, the specific mechanism through which these minerals affect straw decomposition and its products in northeast China’s black soil remains unclear. In this study, montmorillonite, illite, and vermiculite were mixed with quartz sand and maize straw, inoculated with microbes, and incubated to analyze the effects of different secondary phyllosilicate minerals on the degradation of organic components in maize straw and the formation of soil humus. The results showed that montmorillonite significantly facilitated the decomposition of maize straw hemicellulose and lignin, which decreased by 95.85% and 76.38%, respectively. Conversely, vermiculite decelerated hemicellulose and lignin degradation. Regarding soil organic acids, lactic acid and malic acid were predominant, with the highest content being found after the montmorillonite treatment. Montmorillonite was the most effective in enhancing extractable humic-like substances, which increased by 71.68%. Montmorillonite increased the content of G0 (water dispersion group), G1 (sodium ion dispersion group), and G2 (sodium grinding dispersion group) complexes. The addition of secondary phyllosilicate minerals increased the organic carbon (OC) content in the G0, G1, and G2 samples, with montmorillonite demonstrating the most pronounced effect. Secondary phyllosilicate minerals increased the abundance of fungi, particularly Ascomycota, with the highest abundance being found after the montmorillonite treatment. In conclusion, our results indicated that montmorillonite facilitated the decomposition of lignocellulose in maize straw, enhanced the accumulation of humus, and promoted the formation of organic–mineral complexes. These findings provide valuable insights into the interaction between secondary phyllosilicate minerals and maize straw and have important implications for improving the quality of black soil in northeast China.

To identify the effect of fertilization on the heavy metal concentration and assess the soil environmental quality, Meadow Black Soil (MBS) samples were collected from Long-term location fertilization base located in the Changchun City, Jilin Province of China. Subsequently, MBS samples were analyzed to determine the total concentrations of specific elements (Pb, Cd, Cu, Zn, Ni and Cr), for which data were available for 1984, 1989 and 2012. Under long-term location fertilization conditions, this investigation revealed that the mean concentrations of Pb, Cd, Cu, Zn, Ni and Cr exceeded their corresponding background values and the accumulations of Pb and Cd were readily apparent in the MBS and were beyond of the second grade of China soil standards. Pb and Cd were accounted for mainly by chemical fertilizers. In addition, the accumulations of Cu, Zn, Ni and Cr did not appear to reach pollution levels, and no obvious pollution was observed in the MBS. Significant correlations were observed between Pb and Cd, Cu and Ni, Cu and Cr, Ni and Cr, suggesting that they might originate from a common source. However, Pb and Ni, Cu and Zn showed negative correlations, suggesting a different source. The quality of the soil environment and the heavy metal pollution were evaluated by the Single-Pollution Index and Nemerow-Pollution Index method. Each treatment soil sample had a low or slight pollution index (PI) of Cu, Zn, Ni and Cr，whereas the PI values of Pb and Cd were high, and samples were classified as being moderately or heavily contaminated by Pb and Cd. Although practically uncontaminated by Cu, Zn, Ni and Cr, a potential danger may emerge in the future depending on the agricultural activities in this region. The results of heavy metal assessment in the MBS will be helpful for the formulation of strategic sustainable agriculture in Jilin Province and improvement of corn quality and safety.

Long-term organic inputs increase soil organic carbon (SOC) in black soil; however, it remains uncertain if straw and manure enhance SOC via separate microbial necromass carbon (MNC) routes. Therefore, a 12-year field experiment was conducted to explore this mechanism. Treatments included inorganic fertilizer, partial substitution of inorganic fertilizer with straw, and partial substitution of inorganic fertilizer with manure, along with a no-fertilizer control. According to the results, compared with inorganic fertilizer alone, treatments involving both organic manure and straw returned markedly raised the levels of SOC, MNC, bacterial necromass carbon (BNC), and fungal necromass carbon (FNC). Notably, compared to the CK treatment, N75S showed a greater contribution of MNC to SOC (MNC/SOC), but in both N75M and M, the MNC/SOC was lower than in CK. The CAZyme genes related to hemicellulose, lignin, chitin, and peptidoglycan differed among treatments. Elevated gene abundances for plant-derived lignin and hemicellulose decomposition were observed under M and N75M, whereas they reduced the genes responsible for peptidoglycan and glucan. However, under N75S, there was a notable rise in the number of genes responsible for hemicellulose and lignin, as well as an increase in genes that degrade chitin and peptidoglycans. In conclusion, this finding demonstrates that long-term straw return tends to promote SOC stabilization primarily through the microbial necromass pathway, while the application of manure over the long term tends to increase the total SOC primarily through the input of exogenous organic carbon.

Soil organic carbon (SOC) is a core component of farmland fertility, and its content is significantly influenced by tillage practices. To clarify the effects of alternate tillage on soil organic carbon sequestration and soil aggregate stability, a tillage experiment was initiated in 2017. The study focused on the distribution of soil aggregates across different particle sizes and their organic carbon contents under four tillage treatments: (1) rotary tillage for two consecutive years after initial deep plowing (RT_DP); (2) no-tillage for two consecutive years after initial deep plowing (NT_DP); (3) continuous rotary tillage (RT); and (4) continuous no-tillage (NT). Compared with continuous rotary tillage (RT), RT_DP increased the crop yield by 14.78%, NT decreased the yield by 10.59%, and NT_DP increased the yield by 3.40%. In the topsoil, soil organic carbon (SOC) content increased by 21.57% under RT_DP, 24.47% under NT, and 21.57% under NT_DP. In the subsoil, SOC content increased by 36.91% under RT_DP, 24.80% under NT, and 42.52% under NT_DP. Compared with the RT treatment, practices such as RT_DP increased the SOC content and the proportion of macroaggregates. No significant differences were observed among all treatments in the topsoil. However, in the subsoil, RT_DP significantly increased the SOC content (by 36.91%), SOC content within >0.25 mm aggregates (by 35.75%), and the proportion of >0.25 mm aggregates (by 1.28%), relative to RT. Compared with NT, NT_DP also increased these three indices by 14.2%, 13.38%, and 0.32%, respectively. In the topsoil, the NT_DP treatment resulted in higher mean weight diameter (MWD) stability than the other treatments. In the subsoil, the NT treatment showed the highest MWD and geometric mean diameter (GMD) values, while both RT_DP and NT_DP had significantly higher MWD and GMD than RT. In the deeper soil layer, the NT treatment exhibited the highest aggregate stability. Further analysis indicated that the positive effects of alternate tillage (NT_DP and RT_DP) on aggregate distribution, aggregate stability, and subsoil SOC sequestration were mainly due to improvements in the soil’s nutrient availability, bulk density, porosity, and water content. The optimization of these soil properties further enhanced soil enzyme activity and ultimately promoted the stabilization and accumulation of SOC. In conclusion, incorporating deep plowing into rotational tillage can effectively promote SOC accumulation, especially in the subsoil of maize farmland, and enhance the physical protection of SOC. This study provides a practical tillage strategy for increasing the maize yield and enhancing soil organic carbon sequestration.