The enhancement of saline soil yield potential by biochar was well-documented, but the changes brought by biochar particle size on soil properties and crop performance are not well understood. To investigate the changes in soil properties and tomato yield due to biochar particle size under varying salt stress, we conducted a pot experiment in China Northwest’s solar greenhouse. A total of nine treatments were applied, with three different salt amounts of [S0 (no salt), S1 (0.3% dry weight), and S2 (0.6% dry weight)], and three biochar treatments of B0, B1, and B2 (0, 0.5% of large particles and 0.5% of small particles). Adding biochar did not significantly affect the measured soil chemical properties, except for pH, total nitrogen (TN), and Ca²⁺. Specifically, the addition of biochar significantly increased soil pH and TN, while reduced soil Ca²⁺ content likely due to biochar selective adsorption of Ca²⁺. Biochar particle size had opposite effects on tomato yield under varying salt stress levels. Compared to S0, the yield under B1 was 19.1% and 36.5% higher, whereas under B2, the yield was 33.1% and 44.2% lower for S1 and S2, respectively. Under no salt stress, small-size biochar increased yield by 51.0% compared to B0, largely due to the improved soil water and nutrient status. These results are of great value for developing better strategies for adding biochar with appropriate properties into saline soils to achieve greater productivity gains. Highlights Biochar addition significantly reduced soil Ca²⁺ by 16.7–37.9%, while there was no significant difference in the other cations. Large-size biochar alleviated salt stress and improved tomato yield by promoting salt leaching and enhancing soil nutrients. Small particle size biochar exacerbated salinity stress and reduced tomato yield under higher salinity treatments. Small particle size biochar boosted tomato yield in soils without salinity stress. Graphical Abstract

Quantifying the interactive effects of different irrigation and fertilization strategies on soil water and mineral N dynamics provides an important insight for developing more effective water and N use management practices. This experiment was carried out in a tomato ( Solanum lycopersicum L.) (2016)–cucumber ( Cucumis sativus L.) (2016)–tomato (2017) rotation, with 12 treatments in total combining two irrigation methods (drip and furrow), two irrigation levels (high and low), and three fertilizer types (control [N0], organic N [N1], and inorganic N [N2]). Soil water content (SWC) and soil mineral N concentration were measured for soil depth of 0–80 cm. Relative to furrow irrigation, drip irrigation led to lower temporal variation and smaller differences between soil depths and treatments in SWC and soil NO ₃ ⁻ –N concentration. A high irrigation level led to higher SWC and soil NO ₃ ⁻ –N concentration for N1 and N2 treatments under drip irrigation, whereas furrow irrigation had the opposite results. About 42.8% mineral N (over soil depth of −20 to 80 cm) was stored at the ridge under furrow irrigation. Relative to the start of the experiment, N2 fertilizer application increased the soil mineral N content by about 450 kg ha ⁻¹ , whereas N0 and N1 application decreased soil mineral N content by about 200 kg ha ⁻¹ by the end of the rotation. Yield for N1 was similar or higher than that of inorganic N treatments, with drip irrigation–high irrigation–organic N having the highest soil mineral N and the greatest yield, indicating that a combination of organic N fertilizer with appropriate irrigation practices can achieve the balance of high yield and low environmental risks.

Growing crops in salt-affected soils has become increasingly important for sustainable development in arid and semi-arid regions. Knowledge on the responses of alfalfa root development, yield, and quality to soil salinity is critical for assessing the productivity and profitability of salt-affected soils. A field experiment with a total of six treatments combining three soil salinity levels and two biosolids fertilizer levels was conducted in 2018 and 2019 in northwest China. For salinity treatments, the salt addition rates were 2‰, 4‰, and 6‰ of 0–60 cm soil dry weight, while a commercial biosolids fertilizer was added at a rate of 0 and 1.5 Mg·ha⁻¹ of 0–10 cm soil for biosolids treatment. Root parameters of root length (RL), surface area (RSA), diameter (RD), volume (RV), and dry matter (RDM) were obtained at the end of each year, while yield and quality parameters of crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF) were measured for each cut of the two years. Most root parameters were significantly reduced by the highest soil salinity treatment in 2018, but not affected by salinity in 2019. Higher salinity treatments consistently led to lower plant height and yield, higher CP, and lower ADF and NDF in both years. The absolute slope value of the regression between yield of each cut with the respective soil salt content was smaller for the later cuts. The relationship between plant height and quality parameters varied depending on soil salinity levels and between the two years, and plant height was found to be a good predictor for alfalfa quality in 2019. Biosolids fertilizer had no significant effect on any alfalfa root, growth, or quality parameters. The results are expected to assist determining the proper soil salinity range, maximizing the productivity that takes both yield and quality into consideration.