The amelioration effects of canola straw biochar on Ultisol acidity varied with the soil in which the feedstock crop was cultivated

Purpose Regional differences in the alkaline properties and base cation richness of canola straw biochars, and their amelioration effects on an acidic Ultisol, were studied in the present investigation. Materials and methods The biochars were produced using straw from canola crops grown in four different regions and soils from south to north of China as feedstock, namely Yingtan biochar (YTBC), Xuancheng biochar (XCBC), Nanjing biochar (NJBC), and Huaiyin biochar (HYBC), and were used to correct an acidic Ultisol. Results and discussion The concentrations of exchangeable base cations (EBCs) varied among the biochars produced under the same conditions from the different feedstocks and correlated significantly with other variables of the studied biochars, namely carbonate concentration, pH, and alkalinity. The pH of the test Ultisol amended with 2% 600 °C biochar by weight, increased by 1.08, 0.77, 0.66, or 0.42 U after 56 days of incubation with HYBC, NJBC, XCBC, or YTBC, respectively, when compared with the unamended Ultisol in an incubation trial. The concentration of EBCs in the Ultisol amended with HYBC, NJBC, XCBC, or YTBC was in the range 70.90–83.04, 75.90–92.85, 55.53–66.42, and 22.38–35.33 mmeq kg −1 during incubation, respectively. The amelioration effects of the biochars on soil acidity and EBC supply remained effective over a 56-day incubation period, with the effects increasing incrementally with increasing pyrolysis temperature and application rate. Conclusions Further studies on the alkaline properties of crop straw biochar and its effect in correcting soil acidity should consider not only the crop and pyrolysis conditions but also the conditions under which the feedstock crop was grown.