Due to the excessive application of ammonium nitrogen fertilizer and the effect of acid deposition, the accelerated acidification of farmland soil in the subtropical region of China in the past 30 years has led to a decline in soil fertility, aggravation of aluminum and manganese poisoning, endangering crop growth, reducing crop yield and reducing farmers' income. Although the application of an alkaline modifier can neutralize soil acidity, it reduces the risk of acidification.
However, as agricultural activities such as crop cultivation and fertilization continue, soil acidification will occur again. If the chemical resistance of the soil can be improved by certain technical measures, the process of soil acidification can be slowed down and the acidification hazard can be alleviated. The soil pH buffer capacity is the key factor determining the difficulty of soil acidification. Increasing the soil pH buffer capacity can improve the acid resistance of the soil.
Previous studies have shown that straw biochar can increase soil pH buffer capacity, but the relevant mechanisms are still unclear.
The Xu Renshu team of Nanjing Institute of Soil Science, through simulated acidification experiments combined with attenuated total reflection infrared spectroscopy (ATR-FTIR), revealed the mechanism by which straw biomass carbon increased soil pH buffer capacity. The study found that adding straw biochar not only increased soil pH, but also significantly increased soil pH buffer capacity, thereby improving soil acid resistance.
Among the common crop straws, the biomass charcoal prepared from peanut straw has the most significant effect on improving the acid resistance of soil. The surface of the biomass carbon is rich in oxygen-containing functional groups. The anions of these weakly acidic functional groups associate with H+ to form neutral molecules, and simultaneously release the previously adsorbed exchangeable base cations into the solution. This process is biomass. The main mechanism by which charcoal increases the pH buffer capacity of the soil.
The experimental results show that the release of salt-based ions on the surface of biomass carbon is linearly related to the proton consumption. The absorption peak associated with -COO- in the ATR-FTIR spectrum of biomass carbon decreases with the decrease of pH of the system, and -COOH The relevant absorption peaks show opposite trends. These results provide experimental evidence for the above mechanisms.
This study will provide theoretical basis and technical support for soil acidification prevention in subtropical regions of China. The results are published online in the Journal of Agricultural and Food Chemistry.
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