The application of persulfate (PS) for the remediation of petroleum hydrocarbon contamination is among the most widely employed in situ chemical oxidation (ISCO) techniques, and it has received widespread attention due to its limited impact on soil integrity. This study employed a FeSO₄-activated PS oxidation method to investigate the feasibility of remediating soil contaminated with total petroleum hydrocarbons (TPHs). The factors tested included the TPH concentration, different PS:FeSO₄ ratios, the reaction time for remediation, soil physical and chemical property changes before and after remediation, and the effect of soil before and after remediation on soybean growth. The TPH degradation rate in soil was highest for high-, medium-, and low-TPHs soils—81.5%, 81.4%, and 72.9%, respectively, with minimal disruption to the soil’s physicochemical properties—when PS:FeSO₄ = 1:1. The remediation verification results indicated that the condition of the soybeans was optimal when PS:FeSO₄ = 1:1. Under this condition, the net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, and transpiration rate all remained high. Therefore, the best remediation effect was achieved with PS:FeSO₄ = 1:1, which also minimized the damage to the soil and the effects on crop growth.

To investigate the long-term effects of combined organic and inorganic fertilizer application on the structural stability and fertility of soil in paddy fields located in the cool northeastern region of China, a long-term fixed-site experiment was initiated in 2017. The experiments included the following five treatments: 100% conventional chemical fertilizer NPK (CK), conventional PK fertilizer without N fertilizer (T1), 30% organic N and 70% chemical N fertilizers with conventional PK fertilizer (T2), 50% organic N and 50% chemical N fertilizers with conventional PK fertilizer (T3), and 100% organic N fertilizer (T4). Notably, the total amount of fertilizer applied remained consistent across treatment groups. The results revealed that the combination of organic and inorganic fertilizers significantly increased rice yields and nitrogen use efficiency, with the T3 treatment performing the best. Compared with CK, T3 resulted in a 24.26% greater rice yield, and it increased the nitrogen agronomic efficiency by 71.05%. There were no significant differences among the treatment groups in terms of the proportions of soil aggregates larger than 2 mm or smaller than 0.053 mm. Nitrogen fertilizer application reduced the proportion of 0.053–0.25 mm aggregates and promoted the formation of predominantly 0.25–2 mm aggregates. However, the different organic–inorganic combinations did not cause significant differences in soil aggregate structure or stability. Compared with the CK treatment, the application of both organic and inorganic fertilizers increased soil organic matter content, decreased N₂O emissions, and increased soil catalase activity. In summary, the application of 50% organic N and 50% chemical N fertilizers with conventional PK fertilizer (T3) was determined to be the optimal combination for achieving high and stable rice yields in the cool northeastern region of China while increasing the structural stability and fertility of the soil.

In order to immobilize heavy metals in livestock and poultry manure and promote the safe utilization of pig manure resources, this experiment utilized three types of dried pig manure mixed with soil as raw materials. A combination of biochar and bentonite was established, including treatments with the addition of pig manure (CZ), 2.5% bentonite (F1), 7.5% bentonite (F2), 2.5% biochar (F3), 7.5% biochar (F4), 2.5% biochar + 2.5% bentonite (F5), 2.5% biochar + 7.5% bentonite (F6), 7.5% biochar + 2.5% bentonite (F7), 7.5% biochar + 7.5% bentonite (F8), and with zero addition (CK). After the passivation treatments had been applied, a soybean pot experiment was established to measure various physiological indicators at different soybean development stages. The results revealed that the passivated Cu was predominantly in the reduced and residual states. The passivation rates for F8 in LPS, F7 in MPS, and F8 in HPS were 34.10%, 29.90%, and 39.50%, respectively. Among the three concentrations of a pig manure–soil mixture, the impact of low copper concentration on soybean growth was relatively minimal, whereas medium and high copper concentrations significantly impaired soybean health, resulting in varying degrees of interveinal chlorosis and leaf yellowing from the tip to the base of young leaves, thereby affecting photosynthesis. The combined application of biochar and bentonite enhanced copper passivation and facilitated soybean growth and development.