Use of Alkaline Slag and Crop Residue Biochars to Promote Base Saturation and Reduce Acidity of an Acidic Ultisol

This investigation was conducted by using alkaline slag and crop straw biochars to reduce acidity of an acidic Ultisol through incubation and pot experiments with lime as a comparison. The soil was amended with different liming materials: lime (1 g kg−1), alkaline slag (2 and 4 g kg−1), peanut straw biochar (10 and 20 g kg−1), canola straw biochar (10 and 20 g kg−1) and combinations of alkaline slag (2 g kg−1) and biochars (10 g kg−1) in the incubation study. A pot experiment was also conducted to observe the soybean growth responses to the above treatments. The results showed that all the liming materials increased soil pH and decreased soil exchangeable acidity. The higher the rates of alkaline slag, biochars, and alkaline slag combined with biochars, the greater the increase in soil pH and the reduction in soil exchangeable acidity. All the amendments increased the levels of one or more soil exchangeable base cations. The lime treatment increased soil exchangeable Ca2+, the alkaline slag treatment increased exchangeable Ca2+ and Mg2+ levels, and the biochars and combined applications of alkaline slag with biochars increased soil exchangeable Ca2+, Mg2+ and K+ and soil available P. The amendments enhanced the uptake of one or more nutrients of N, P, K, Ca and Mg by soybean in the pot experiment. Of the different amendments, the combined application of alkaline slag with crop straw biochars was the best choice for increasing base saturation and reducing soil acidity of the acidic Ultisol. The combined application of alkaline slag with biochars led to the greatest reduction in soil acidity, increased soil Ca, Mg, K and P levels, and enhanced the uptake of Ca, Mg, K and P by soybean plants.