Biochars and their feedstocks differ in their short-term effects in ameliorating acid soils grown with aluminium-sensitive wheat

Purpose: Biochars have potential to reduce soil acidity and Al3+ toxicity, and increase the availability of soil nutrients. This study aimed to compare the effectiveness of biochars and their raw feedstocks in amelioration of soil acidity. Materials and methods: Ten ameliorants comprising of five biochars (pyrolyzed at 550°C) and their corresponding feedstocks (wheat chaff, canola stubble, vetch hay, lucerne pellets, and poultry litter) were added (1% of soil weight) to sandy Tenosol and loamy Chromosol with both having similar Al3+ concentrations but Chromosol having nine times greater pH buffer capacity. The soils with the ameliorants were incubated for 7 weeks (incubation phase), before being planted with an Al-sensitive wheat (ES8) for 18 days (plant phase). Results and discussion: Biochars outperformed their feedstocks in increasing soil pH, leading to a significant reduction of Al3+ toxicity. Biochar additions increased shoot growth by 137‒341% for Tenosol and 10‒295% for Chromosol, whereas their feedstocks increased shoot growth by 25‒233% for Tenosol and -38‒136% for Chromosol. Poultry-litter biochar increased soil pH greater than the corresponding poultry-litter treatments by 1.59 units in the Tenosol and 0.79 units in the Chromosol at the end of the plant phase. In addition, all organic amendments (except wheat-chaff and its biochar) significantly increased shoot P concentrations with poultry-litter biochar achieving the highest Olsen P and shoot P concentrations in both soils. Evidently, high alkalinity and nutrient contents of poultry-litter biochar resulted in the greatest increases in soil pH and shoot biomass in both soils. Conclusions: Biochars were more effective at ameliorating soil acidity than their corresponding feedstocks primarily via increasing soil pH and supplying plant nutrients, depending on soil type. Poultry-litter biochar was the most effective on both soils.