Optimizing Biochar Amendment to Improve Soil Property and Cotton Seedling Growth in Saline Soils

【Background and objective】 Soil salinization is a biotic stress facing agriculture production in almost all countries. It not only destroys soil structure but also reduces bioavailable nutrients and the ability of soil to sequester carbon. Amending stalinized soil with biochar is a technology to improve soil quality and productivity, but its efficacy depends on soil texture and the amount of biochar being applied. The objective of this paper is to study the optimal biochar amendment for improving soil quality and fertility for cotton growth. 【Method】 The experiment was conducted in pots with the cultivar Medium S9612 used as the model plant. The soil was amended by biochar at ratios of 0 (CK), 1% (BC1), 1%(BC1), 3% (BC3) and 5% (BC5), respectively. In each treatment, we measured physicochemical properties, enzyme activities of the soil, as well as growth indexes of the cotton at seedling stage. 【Result】 Biochar amendment improved moisture content in the 0~20 cm soil layer, but the increase was negatively correlated with biochar amount; biochar also reduced salt content in the 0~20 cm soil layer. The amendment did not show significant effect on soil pH, total phosphorus, and available phosphorus, but increased soil organic carbon, total nitrogen, total potassium, available potassium, peroxidase (POD), and fibro two glycosidases (FTG), especially BC1 which significantly increased the activity of POD and FTG. In general, biochar reduced soil alkali-hydrolyzable nitrogen and polyphenol oxidase (PPO). BC1 increased stem diameter and above-ground dry matter accumulation of the crop, both significantly, but did not show noticeable impact on plant height. BC3 did not show significant effects on plant height, stem thickness, and above-ground dry matter, while BC5 reduced plant height, stem diameter, and above-ground dry matter. Also, addition of biochar reduced the total nitrogen content in stems and leaves. 【Conclusion】 Biochar can improve soil nutrients and enzyme activities but only when applied at an appropriate ratio. For the saline soil we studied, the optimal biochar amendment was 1%.