Biochar characteristics and application rates affecting corn growth and properties of soils contrasting in texture and mineralogy

• High temperature biochar had higher ash content than lower temperature biochar.
• Liming effect of biochar ash reduced Al phytotoxicity in a high-Al Ultisol.
• High K from biochar ash caused Ca and Mg deficiencies due to K antagonism in corn.
• High ash biochar affected coarsely textured soil more than high clay soil.
• Biochars enhanced soil Mn solubility but reduced Mn toxicity to corn in an Oxisol.

Benefits of biochar as a soil amendment may vary with its properties, time after its application, and in relation to soil texture and mineralogy. Effects of pyrolysis conditions on biochar properties which, in turn, influence soil fertility and plant growth in two different soils were investigated. A pot experiment employing two types of eucalyptus wood derived biochar, i.e. low (350 °C) and high (800 °C) pyrolysis temperatures, was applied at four rates, i.e., 0, 1, 2, and 4% w/w, once at the beginning of the experiment to a loamy-sand Ultisol and a silty-clay-loam Oxisol. Two consecutive corn crops were grown to investigate biochar temporal effect. Low temperature biochar had lower ash (2.4%) content than its high temperature counterpart (3.9%). Biomass of the first corn crop was significantly depressed under the highest rate of the high temperature biochar compared to control treatment in the sandy Ultisol, but not in the clayey Oxisol. Biomass depression was accompanied by a significant increase in soil pH (5.88) compared to control (4.74), as well as significant increases in tissue K concentrations (43 vs 10.8 g kg− 1), and decreases in tissue Ca (2.8 vs 3.8 g kg− 1) and Mg (1.3 vs 2.6 g kg− 1). Biomass of the second crop increased in most biochar treatments compared to the controls, due to the reduction in phytotoxicity of Al in the Ultisol and Mn in the Oxisol. Both biochars significantly increased soluble Mn concentrations relative to the control (1.39–4.61 vs 1.12 mg l− 1), while they decreased tissue Mn concentrations compared to the control (0.08–0.17 vs 0.41 g kg− 1) in the Oxisol. Possible mechanisms underlying biochar mediated increases in soil Mn solubility and decreases in corn Mn uptake were discussed. These results showed clearly that lower temperature biochar gave higher benefits to both contrasting textured soils than the higher temperature counterpart in both first (32 days after biochar application, DAA) and second (82 DAA) cropping cycles. The 1–2% w/w rate of the low temperature biochar was appropriate for these soils, the higher rate being more suited to the finer textured soil.