This study aimed to elucidate the impacts and dominant factors of combined application of nitrogen, phosphorus, and potassium fertilizers with manure (NPKM) and manure alone (M), compared with application of nitrogen, phosphorus, and potassium fertilizers (NPK), on soil properties and maize yield across different soil types, soil textures, soil pH levels, and initial SOC contents, to provide a scientific basis for mitigating black soil degradation and promoting high and stable maize yields.

Based on 75 published studies and 477 paired datasets regarding the effects of fertilization on soil fertility and maize yield, this study employed a meta-analysis to quantitatively assess the impacts of NPKM and M treatments (relative to NPK) on soil physicochemical and biological properties and maize yield of the black soil in Northeast China, considering soil types, textures, pH levels, and initial SOC contents. Furthermore, principal component analysis and a random forest model were employed to identify the relative importance of different soil properties in determining the soil fertility index and maize yields.

Compared with NPK, NPKM significantly reduced soil bulk density (BD) by 6.2%, with the largest reduction in pH<6.5 (12.3%). The NPKM treatment increased SOC by 24.0%, with the highest increase (30.6%) when initial SOC was less than 20 g·kg^-1. It also enhanced AN, AP, and AK, with larger increments under pH 6.5-7.0. Regarding maize yield, NPKM increased it by more than 25% on average, with the largest increase (43.7%) at pH 6.5-7.0. The M treatment increased SOC by an average of 21.1%, with the greatest increase (42.5%) at low initial SOC, but its enhancing effect gradually weakened as the initial SOC content increased. Overall, the effect of the M treatment was weaker than that of NPKM, and under some conditions, it even reduced total phosphorus (TP) by 12.6% and total potassium (TK) by 3.7%. The soil fertility indices for NPKM and M treatments were 0.7 and 0.6, respectively, both indicating a high fertility level. The PCA and random forest analyses showed that SOC was the core driver of increasing maize yield. The increment of maize yield under NPKM was primarily dependent on SOC, TN, SMBC, and BD, with a cumulative explanatory rate of 60.2%. In contrast, the yield increase under M was mainly dependent on SOC, BD, pH, SMBC, and SMBN with a cumulative explanatory rate of 63.7%.

In the black soil region of Northeast China, NPKM significantly reduced BD and enhanced SOC, nutrient availability, microbial biomass, and maize yield, having a more comprehensive effect than that under M. Our study demonstrated that NPKM was more effective for improving soil fertility and securing high and stable maize yields. It also identified SOC as the key driver of soil fertility and maize yield under NPKM treatment, and concluded that this fertilization method is the optimal approach for enhancing black soil fertility and achieving high and stable maize yields. Additionally, NPKM represented an effective strategy for enhancing soil fertility, preventing degradation, ensuring food security, and promoting sustainable agricultural development.

To provide theoretical guidance for mitigating global warming, the comprehensive effects of manure amendment on soil organic carbon sequestration and greenhouse gas emissions were studied.

Based on the long-term experiment, the validated process-based model-SPACSYS, combined with regional database and ArcGIS, was used to clarify the spatial characteristics of average annual soil organic carbon sequestration rate (SOC_SR), average annual soil N₂O emission and average annual net global warming potential (NGWP) under three long-term fertilization scenarios (equal nitrogen fertilization), namely, chemical fertilizers only (NPK), 50% of chemical fertilizers combined with 50% of manure (NPKM(5:5)) and 30% of chemical fertilizers combined with 70% of manure (NPKM(3:7)), from dry land in the North China Plain from 2010 to 2050.

The SOC_SR from dry land in the North China Plain was higher in the east and lower in the west, and the higher regions mainly included Jiangsu Province and Shandong Province. Correlation analysis showed that there was a significant negative correlation between SOC_SR and initial soil organic carbon content. Stepwise linear regression analysis further indicated that initial soil organic carbon content, mean annual temperature and soil pH were three important factors affecting SOC_SR, which accounted for 24% of the variation of SOC_SR. The average annual soil N₂O emission was higher in the central part of the North China Plain, lower in the north and south, and the higher regions included parts of Shandong Province and Jiangsu Province. Correlation analysis showed that there was a significant positive correlation between average annual soil N₂O emission and initial soil organic carbon content. In general, compared with NPK, NPKM(5:5) and NPKM(3:7) both increased SOC_SR and decreased average annual soil N₂O emission from dry land in the North China Plain, of which SOC_SR (233 and 236 kg C·hm^-2·a^-1) increased by 79% and 82%, respectively, the average annual soil N₂O emission (15.8 and 14.4 kg N·hm^-2·a^-1) decreased by 21% and 28%, respectively. As a result, NGWP (6.6 and 5.9 t CO₂-eq·hm^-2·a^-1) decreased by 26% and 34%, respectively.

Compared with the application of chemical fertilizers, the application of chemical fertilizers combined with manure was beneficial to SOC sequestration, soil N₂O emission reduction and mitigation of glowing warming from dry land in the North China Plain over the long-term.

The decomposition, nutrient release characteristics and driving factors of straw under different C/N ratio were studied based on coal mining area, so as to provide as theoretical basis for the full utilization of straw resources and reclaimed soil fertility improvement.

Air-dried maize straw and wheat straw were cut into 2 mm pieces and were selected for decomposition experiment of a coal mining reclamation area in Shanxi Province. Two C/N ratio levels of 25 and 10 were designed in maize straw and wheat straw by supplementing urea, taking no nitrogen application that C/N ratio levels was 52 and 74 as the control. All the straws (8 g in organic carbon) were put into a nylon mesh bag (0.38 µm aperture), and horizontally buried into 15 cm deep of soil. On the 12, 23, 55, 218, 281 and 365 days after buried, samples were collected from the bags to analyze the dynamic of the dry matter residue and nutrient (carbon, nitrogen, phosphorus and potassium).

During the first 55 days, the adjusting the C/N on 25 with the application N was the best way to accelerate the decomposition of maize straw. Meanwhile, the adjusting the C/N on 10 was the best way to accelerate the decomposition of wheat straw. Application N could significantly promote the release of carbon and phosphorus from maize straw during the first 55 days. Application N could significantly accelerate the release of carbon, nitrogen and phosphorus from wheat straw, but had no significant effect on the release of potassium. The thermal equation of straw decomposition and nitrogen and potassium release was better than the temporal equation, and phosphorus release from straw was not suitable for the exponential decay equation. When the accumulated temperature was 4 600 ℃, the average release rates of carbon, nitrogen, phosphorus and potassium from straw were 49.2%, 39.5%, 40.8% and 90.3%, respectively; When the accumulated temperature reached 1 125 ℃, more than 85% the potassium of straw was released. The decomposition of straw was mainly influenced by the temperature, organic carbon, lignin and hemicellulose.

Application N could accelerate the decomposition of maize straw and the release of carbon and phosphorus in the early stage, which could significantly accelerate the wheat straw decomposition and the release of carbon, nitrogen and phosphorus too. Temperature could better reflect the process of straw decomposition and nitrogen, potassium release than time, the decomposition of straw was mainly regulated by the temperature, organic carbon, lignin and hemicellulose. Therefore, combined with the hydrothermal conditions in the coal mining area, the straw with an appropriate amount of urea should be returned to the field in the right time to improve the content of nitrogen, phosphorus and potassium of the reclaimed soil.