Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5–2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared.

Microbial biomass phosphorus (MBP) and its relationships with other biological and chemical properties were studied on loess soil with an 11-year long-term fertilization experiment. The results indicated that inorganic fertilizers (F) improved soil microbial biomass carbon (MBC), nitrogen (MBN), and MBP levels and F plus maize stalk (SNPK) improved MBC and MBN. Manuring markedly increased soil MBC, MBN, and MBP levels. Fertilization decreased the ratios of MBC/MBN, MBC/MBP, and MBN/MBP. Microbial biomass phosphorus was positively and linearly correlated with MBC, MBN, organic carbon (SOC), total phosphorus (TP), water-soluble P, and Olsen P but negatively correlated with soil pH. Microbial biomass phosphorus constituted 2% of TP on control (CK) and inorganic fertilizer treatments and 12% on manure plots. Microbial biomass phosphorus to Olsen P ratios were 50% on CK, F, and SNPK and 80% on manure treatments. Measurements of MBP in soil containing high Olsen P were subject to analytical problems of unknown reasons.

Background: Diverse phosphorus (P) fractionation procedures presented varying soil P fractions, which directly affected P contents and forms, and their biological availability.Purpose: To facilitate the selection of phosphorus (P) fractionation techniques, we compared two procedures based on a long-term experiment on a calcareous soil.Methods: The soils containing a gradient P levels were sampled from seven treatments predictor under various long-term fertilizations. The P fractions were then separated independently with both fractionation procedures modified by Tiessen-Moir and Jiang-Gu.Results: The results showed that the labile P in Jiang-Gu is significantly lower than that in Tiessen-Moir. The iron and aluminium-bounded P were greater in Jiang-Gu by a maximum of 46 mg kg⁻¹than Tiessen-Moir. Jiang-Gu fractionation gave similar Ca bounded P to that Tiessen-Moir did at low P level but greater contents at high P level. The two methods extracted much comparable total inorganic P. However, Tiessen-Moir method accounted less total organic P than ignition or Jiang-Gu method (the organic P (Po) estimated by subtract the total inorganic P (Pi) in Jiang-Gu fractionation from the total). P uptake by winter wheat was significantly and positively correlated with all phosphorus fractions in Jiang-Gu; Resin-P, NaHCO₃-Pi, D. HCl-P, C. HCl-Pi, NaOH-Po, total-Po in Tiessen-Moir; P fraction categories of Ca-P, Fe & Al-P and total-Pi in both fractionations. Path coefficients indicated that Ca₂-P in Jiang-Gu, NaHCO₃-Pi and D. HCl-P in Tiessen-Moir had the higher and more significant direct contributions to P uptake among P fractions measured.Conclusions: Our results suggested that Jiang-Gu procedure is a better predictor in soil P fractionation in calcareous soils, although it gives no results on organic P fractions.

Soil organic matter (SOM) is a recognized determinant of nitrogen-use efficiency (NUE), but its quantitative control over the fate of fertilizer N remains unclear. Using a ¹⁵N tracer study within a winter wheat–summer maize region, we quantified the recovery of initially applied N from wheat and subsequent crops in relation to SOM and N application rates. We found that while N fertilization boosted yields by 85–340% in low-fertility soil, its effectiveness exhibited diminishing returns in high-fertility soils. Crucially, the total recovery efficiency of fertilizer N (cumulative ¹⁵NUE) across three cropping seasons was fundamentally governed by SOM content, following a linear–plateau relationship. The model revealed that the maximum ¹⁵NUE (54.3%) at an optimal application rate (105 kg N ha⁻¹) was achieved when SOM exceeded a critical threshold of 21.3 g kg⁻¹ (equivalent to 57.51 t ha⁻¹ in the 0–20 cm soil layer). Below this threshold, ¹⁵NUE increased linearly with SOM (R² = 0.956). Furthermore, residual ¹⁵N in soil was primarily stabilized in organic forms (58–64%), while recovery by subsequent crops was minimal (≤4.3%). This confirms that high SOM content minimizes the amount of unaccounted ¹⁵N by enhancing N fixation within the soil organic pool. Our findings establish a quantifiable SOM threshold for maximizing NUE, thereby providing a scientific basis for reducing fertilizer waste and enhancing the sustainability of intensive agriculture in the region.

Mitigating climate change necessitates a thorough understanding of soil organic carbon (SOC) decomposition and its response to warming. The overuse of synthetic fertilizers can alter SOC composition and affect carbon cycling, potentially changing the temperature sensitivity (Q₁₀) of SOC decomposition. This study evaluated the Q₁₀ of SOC decomposition after long-term (37-year) excessive fertilization in a loess soil. Four treatments were compared: control (no nutrient input, CK); recommended rates of synthetic nitrogen (N) and phosphorus (P) fertilizers (CF_r); excessive rates of N and P fertilizers (CF_h); and CF_h plus organic manure (MCF_h). The Q₁₀ of SOC decomposition was investigated via an incubation experiment at temperatures of 15 °C, 25 °C and 35 °C within 63 days. Compared with CF_r, long-term CF_h and MCF_h significantly increased SOC contents by 14% and 67%, and this increase was driven primarily by rises in mineral-associated organic carbon (MOC) of 28% and 62% and particulate organic carbon (POC) of 32% and 79%, respectively, under CF_h and MCF_h. While CF_h and MCF_h did not change the SOC composition, they increased the proportions of fine POC (fPOC) to SOC by 10% and 91%, and the ratio of light POC to SOC by 78% and 143%, respectively. Q₁₀ values ranged from 2.18 to 3.00 across all treatments, with a mean of 2.64. Both CF_h and MCF_h drastically enhanced the Q₁₀ values by 38% and 25% compared with CF_r at 15–25 °C. However, MCF_h significantly decreased the Q₁₀ value by 31% relative to CF_r at 25–35 °C. Partial least squares path modeling showed that soil physicochemical properties and labile carbon fractions differed significantly among treatments, with physical properties regulating labile carbon fractions. Fertilization significantly increased the Q₁₀ value at 15–25 °C owing to increased proportion of labile carbon fractions and decreased labile carbon content. Our results suggest that SOC gains from continuous addition of synthetic fertilizers are vulnerable to loss under warming. However, this loss could be alleviated by incorporation of organic manure. Thus, integration of organic manure into nutrient management practices could be an efficient way to counteract warming-induced SOC decomposition.