Ren-kou Xu An-zhen Zhao Jin-hua Yuan Jun Jiang. pH buffering capacity of acid soils from tropical and subtropical regions of China as influenced by incorporation of crop straw biochars. J Soils Sediments 2012 12:494–502.
Abstract
Purpose The key factors influencing pH buffering capacity of acid soils from tropical and subtropical regions and effects of soil evolution and incorporation of biochars on pH buffering capacity were investigated to develop suitable methods to increase pH buffering capacity of acid soils.
Materials and methods A total of 24 acid soils collected from southern China were used. The pH buffering capacity was determined using acid–base titration. The values of pH buffering capacity were obtained from the slope of titration curves of acid or alkali additions plotted against pH in the pH range 4.0–7.0. Two biochars were prepared from straws of peanut and canola using a low temperature pyrolysis method. After incubation of three acid soils pH buffering capacity was then determined.
Results and discussion pH buffering capacity had a range of 9.1–32.1 mmol kg–1 pH–1 for 18 acid soils from tropical and subtropical regions of China. The pH buffering capacity was highly correlated (R200.707) with soil cation exchange capacity (CEC) measured with ammonium acetate method at pH 7.0 and decreased with soil evolution due to the decreased CEC. Incorporation of biochars at rates equivalent to 72 and 120 t ha−1 increased soil pH buffering capacity due to the CEC contained in the biochars. Incorporation of peanut straw char which itself contained more CEC and alkalinity induced more increase in soil CEC and thus greater increase in pH buffering capacity compared with canola straw char. At 5% of peanut straw char added soil CEC increased by 80.2% 51.3% and 82.8% for Ultisol from Liuzhou Oxisol from Chengmai and Ultisol from Kunlun respectively and by 19.8% 19.6% and 32.8% with 5% of canola straw char added respectively; and correspondingly for these soils the pH buffering capacity increased by 73.6% 92.0% and 123.2% with peanut straw char added; and by 31.3% 25.6% and 52.3% with canola straw char added respectively. Protonation-deprotonation of oxygen-containing functional groups of biochars was the main mechanism for the increase of pH buffering capacity of acid soils with the incorporation of biochars.
Conclusions CEC was a key factor determining pH buffering capacity of acid soils from tropical and subtropical regions of China. Decreased CEC and content of 2:1-type clay minerals during evolution of tropical soils led to decreased pH buffering capacity. Incorporation of biochars generated from crop straws did not only ameliorate soil acidity but also increased soil pH buffering capacity.
