Saline soil represents an important reserve of cultivated land in China, yet poor soil conditions and low-nitrogen use efficiency constrain crop production. Biochar has been widely applied to improve soil properties; however, its interactive effects with nitrogen fertilization in saline soils remain unclear. A pot experiment using coastal saline soil collected from the northern Jiangsu province was conducted to evaluate the combined effects of biochar (0%, 4%, and 8% w·w⁻¹) and nitrogen fertilizer (0, 150, and 200 mg·kg⁻¹) on the growth performance, photosynthetic indices, yield, quality, and nitrogen use efficiency of water spinach (Ipomoea aquatica Forssk.). Moderate biochar application significantly improved vegetative growth of water spinach, as indicated by higher plant height, stem diameter, leaf area index, and SPAD values. In addition, biochar substantially enhanced photosynthetic performance, dry matter accumulation, and yield, whereas excessive biochar or nitrogen application generally inhibited plant performance. The combined application of 4% biochar with 150 mg·kg⁻¹ nitrogen consistently produced the highest yield and nitrogen partial factor productivity, while simultaneously increasing soluble protein, soluble sugar, and vitamin C contents and reducing nitrite accumulation. These research results demonstrated a clear synergistic interaction between biochar and nitrogen fertilization. In coastal saline soils, reducing the usage of nitrogen fertilizer moderately and adding approximately 4% of biochar is an effective strategy.

Searching for a low-cost soil amendment that can reduce the reliance on chemical fertilizers while maintaining crop yields is a vital issue to sustainable agricultural development. In this study, bio-organic matter derived from harmless disposal of livestock and poultry carcasses was used to discuss its potential for substitute chemical fertilizer. An incubation experiment was conducted by incorporating bio-organic matter into the soil at the rate of 0% (CK), 1%, 2%, 3%, 4%, 5%, 6% and 7% (T1, T2, T3, T4, T5, T6, T7) of soil mass to investigate the effects of bio-organic matter on soil physical properties and the nutrient release dynamics. A pot experiment was conducted with three treatments: 150 mg·kg⁻¹ nitrogen from compound fertilizer (CK), 150 mg·kg⁻¹ nitrogen from bio-organic matter (B1) and 300 mg·kg⁻¹ nitrogen from bio-organic matter (B2), to evaluate the potential of bio-organic matter as a substitute for chemical fertilizers in influencing the yield and quality of Chinese cabbage (Brassica chinensis L.). Results showed that in the incubation experiment, bio-organic matter addition reduced soil bulk density of 1.5% to 8.9% and increased soil porosity by ranging from 1.5% to 10.9%. The soil physical properties were significantly improved when addition rates ≥ 4% (by soil mass). The interaction effects of addition rate and incubation time had a significant effect on soil nutrients. In the pot experiment, substitution of chemical fertilizer with bio-organic matter did not reduce the yield, and the increasing application rate of bio-organic matter led to significantly higher soluble protein, soluble sugar and total phenol content of vegetables. Additionally, nitrite content in the vegetables was slightly lower with bio-organic matter compared to that under CK. It is concluded that bio-organic matter derived from the harmless disposal of livestock and poultry carcasses is feasible; it has great potential to partially or entirely replace chemical fertilizers, thereby contributing to realizing chemical fertilizer reduction.

The newly reclaimed soil is an important reserve land resource, while it faces challenges such as poor water retention and low fertility. Therefore, it requires improvement through the use of soil amendments. Attapulgite (ATP) is abundant in northwest China with excellent properties and can be used as an amendment for newly reclaimed soil. The effects of ATP and its addition rate on infiltration and evaporation characteristics in newly reclaimed soil were studied by experiments and model simulation. Three addition gradients (2%, 4%, and 6%) were set in this study, and no ATP addition was used as a control (CK). The results show that ATP treatment prolonged the infiltration duration, reduced the wetting front migration distance, and reduced the accumulated evaporation. Both the Philip model and the Kostiakov model can accurately describe the infiltration process of newly reclaimed soil with ATP addition; the soil evaporation process can be fitted well with the Rose model. In this study, ATP addition affected both sorptivity and the stable infiltration rate of the reclaimed soil. During the evaporation, the soil evaporation effect was inversely proportional to the addition rates of ATP, and the ATP addition rate at 2% had the best effect on reducing soil evaporation. In summary, the ATP addition was beneficial top soil infiltration and evaporation, thus improving the poor water retention of newly reclaimed land and is a reasonable choice for efficient construction of new reclaimed land.