Abstract
A multi-season field trial was carried out to investigate the effect of the amendment of biochar, lime, ash and washed biochar on the growth of maize. A degraded, strongly acidic Ultisol (pHKCl 3.60), with a relatively high exchangeable aluminium content (2.4 cmolc/kg) and a low exchangeable calcium content (0.99 cmolc/kg), was used. Soil was treated once at the beginning of the field trial and crop growth was monitored over seven planting seasons (PS). All treatments increased maize yield. The average increases were; seven times for biochar, five times for lime, five times for washed biochar and eight times for ash treatment, when compared to the control across all PS. The effect of biochar, lime and ash treatments on maize yield were sustained over the seven PS. Soil pHKCl was significantly increased (p < 0.05 level) following the addition of all of the amendment materials. All treatments significantly reduced the concentration of Al3+ when compared to the control (p < 0.05), with the lowest concentrations for the lime and ash treatments. The ash treatment also increased the concentration of macronutrients (K, P and Mg) to the greatest extent. Results showed that there was a clear liming effect at play. The better performance of biochar compared to lime, despite lime having the highest pH and the lowest Al3+ concentration, can be explained by the additional K, Mg and P the biochar adds to the soil. Results also showed a clear nutrient addition effect where ash added the most nutrients. Overall, this work supports the fact that small scale farmers in Indonesia should produce biochar from their waste agricultural materials. Doing so not only provides an increase in crop productivity, but also sequesters carbon resulting in the best overall environmental benefit.
Highlights
Biochar is the solid carbonaceous material that remains following the pyrolysis of biomass
In a study with 371 independent experiments taken from 114 published articles, reported that the addition of biochar to soils resulted in increased aboveground productivity, crop yield, nodulation, plant K and P as well as soil P, K, N and C contents (Biederman and Stanley Harpole, 2013)
The soil itself was strongly acidic, with a cation exchange capacity (CEC) of 9.7 cmolc/kg, a relatively high exchangeable aluminium content (2.4 cmolc/kg) and a low exchangeable calcium content (0.99 cmolc/kg), resulting in a low Ca/Al molar ratio. These parameters are typical of degraded Indonesian soils and are limiting factors for the growth of crops
Summary
Biochar is the solid carbonaceous material that remains following the pyrolysis of biomass. A fiveseason field trial in Sumatra, Indonesia reported a positive effect of up to 15 t/ha biochar amendment in the second, third and fourth cropping cycles for maize. The response was ascribed to an increase in pH resulting from additive effects of the fertilizer and biochar amendment (Kätterer et al, 2019) Despite these positive results, there are some studies that report the opposite for long term field trials with maize. Sänger et al (2017) did not observe any significant increase in maize growth in a threeyear field study when a temperate German soil was tested The authors speculated this was because the biochar amendment improved the availability of plant nutrients, but this was not a limiting factor in the soil used (Sänger et al, 2017). The microscopic analysis provides information about the microstructure and chemical composition of the biochar
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