Lay summary of the article published under the DOI: 10.1016/j.heliyon.2021.e07089
This study investigated how biochar, a highly stable, carbon-rich material made from discarded biomass, can be used to improve the quality of soils in sub-Saharan Africa. The study found that biochar improves soil quality in the same way as alternative methods that are more costly and not easily available.
One of the biggest problems facing crop production in sub-Saharan Africa is a decline in the fertility of soil. Better soil quality would lead to better crop yields, which would reduce rural poverty and reverse natural resource degradation
Research has shown that biochar, a highly stable, carbon-rich material, can be used to improve soil fertility. Biochar is the byproduct of heating organic matter, or biomass, in the presence of low or no oxygen. Biochar has been shown to increase the surface area of soil, increase water and air availability, and activate microorganisms in the soil.
This study tested the effect of biochar and compost on soil quality using indicators such as soil respiration, soil pH, the presence of microbes, the amount of carbon, and the amount of nitrogen available.
The researchers produced corn cob, coconut and rice husk biochars using pyrolysis, which involved heating organic matter in the absence of oxygen, at 450 C in a locally produced kiln. The researchers produced coconut husk biochar using pyrolysis at 300C and at 700 C.
The researchers then incubated soil samples mixed with the biochars for 30 days. Each sample contained specially prepared soil called Haplic acrisol, which was mixed with different combinations of biochars made from corn cob, rice husk or coconut husk, and a poultry manure compost.
Other samples contained a mix of soil and poultry manure compost , with rice husk biochar, and corn cob biochar, respectively. Each of the samples contained 1 % compost, 1% for each biochar, so that the researchers could investigate the effect of each mixture on soil quality.
The researchers found that adding biochar and compost to the soil, either separately or together, increased the pH value of the soil from 0.28–2.29 pH units, compared to unmixed soil. An increase in pH means the soil became less acidic.
The study found that basal respiration, or the minimum amount of carbon dioxide being released by the soil, increased when either compost alone was added, or when compost was mixed with rice husk, or corn cob biochar or combined biochars. The soil samples showed an increase in total organic carbon content of 37% when compost alone was used, and an increase of 117% when corn cob biochar was mixed with compost.
The amount of microorganism activity increased by 132% where the soil had a mixture of compost and rice husk biochar, compared to an increase of 247% in soil samples that had compost alone.
The results of this research show that it is possible to decrease soil acidity using biochar, which is easily and cheaply available. This is in contrast to the alternative practice of liming the soil, which is costly and scarcely available to smallholder farmers in sub-Saharan Africa.
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Soil fertility decline is a major constraint to crop production in sub-Saharan Africa. The positive effect of biochar and compost applications on soil fertility has been reported by many authors. In this study, a 30-day laboratory incubation experiment was done using 120 g samples each of a Haplic acrisol amended with corn cob biochar (cbio), rice husk biochar (rbio), coconut husk biochar (coco300 and coco700) or poultry manure compost (compost); and co- composted rice husk biochar (rcocomp) or co-composted corn cob biochar (cococomp) at rates of 1 % w/w amendment: soil, respectively. Other treatments in the study were combined poultry manure compost and corn cob biochar or rice husk biochar (1 % compost + 1% biochar: 1% soil w/w), respectively, to examine their effects on basal soil respiration, soil pH; soil microbial carbon; cation exchange capacity; total organic carbon, total nitrogen and available nitrogen concentration. Biochar and compost applied solely or together, and composted biochar increased soil pH by 0.28–2.29 pH units compared to the un-amended control. Basal respiration from the sole compost or composted rice husk, or corn cob biochar or combined biochar and compost were higher than the un-amended control, which was similar to that from the biochar only treatments. TOC in the sole compost and combined corn cob biochar and compost treatments were up to 37% and 117% higher, respectively, than the control. Combined application of rice husk biochar and compost increased MBC by 132% while sole compost addition increased MBC by 247%, respectively, compared to the control. In conclusion, the study demonstrated that sole or combined application of compost and biochar, or composted biochar improved soil quality parameters such as soil pH and MBC, and promoted soil C stabilization through enhanced TOC and reduced soil C loss through basal respiration.
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