Search

Biochar was prepared from rice straw and modified with 15% H 2 O 2 and 1:1 HNO 3 /H 2 SO 4 , respectively. The unmodified biochars and HCl treated biochars for carbonate removal were used as control. The biochars were added to the acid paddy soil collected from Langxi, Anhui Province, China at the rate of 30 g/kg. The paddy soil was flooded and then air-dried, and soil pH and Eh were measured in situ with pH electrode and platinum electrode during wet-dry alternation. Soil pH buffering capacity (pHBC) was determined by acid-base titration after the wet-dry treatment. Then, the simulated acidification experiments were carried out to study the changing trends of soil pH, base cations and exchangeable acidity. The results showed that soil pHBC was effectively increased and the resistance of the paddy soil to acidification was apparently enhanced with the incorporation of H 2 O 2 - and HNO 3 /H 2 SO 4 -modified biochars. Surface functional groups on biochars were mainly responsible for enhanced soil resistance to acidification. During soil acidification, the protonation of organic anions generated by dissociation of these functional groups effectively retarded the decline of soil pH. The modification of HNO 3 /H 2 SO 4 led to greater increase in carboxyl functional groups on the biochars than H 2 O 2 modification and thus HNO 3 /H 2 SO 4 -modified biochars showed more enhancement in soil resistance to acidification than H 2 O 2 -modified biochars. After a wet-dry cycle, the pH of the paddy soil incorporated with HNO 3 /H 2 SO 4 -modified biochar increased apparently. Consequently, the addition of HNO 3 /H 2 SO 4 -modified biochar can be regarded as a new method to alleviate soil acidification. In short, the meaning of this paper is to provide a new method for the amelioration of acid paddy soils. Increase the soil pHBC, slow down the decline of soil pH, and improve the resistance to acidification. [Display omitted] • The addition of modified biochars obviously increased pHBC of an acid paddy soil. • HNO 3 /H 2 SO 4 -modified biochar increased soil resistance to acidification more evident. • Modified biochars increased the pH of the paddy soil after a wet-dry cycle. • Protonation of organic anions on biochars was main mechanism for soil pHBC increase. [ABSTRACT FROM AUTHOR]