Biochar is a carbon rich substance produced from pyrolysis-a process involving thermal degradation of biomass (such as manure, leaves, wood) in the absence of oxygen. It is used as a soil enhancer in agriculture because it has the capacity to enhance crop growth by retaining nutrients in the soil for crop uptake (1,2,3). Biochar is also gaining popularity because it has the potential to reduce emission of nitrous-oxide a potent greenhouse gas from soil (4).
The idea of using pyrolysed biomass as a soil enhancer, originates from old traditional soil management practices in the Amazon basin which produced the famous fertile Amazonian dark earth (10). It is speculated that practices such as cooking fires and intentional spread of charcoal on soil by the natives of this region led to the accumulation of its rich dark earth (1, 10). Biochar also occurs naturally in soils affected by vegetation fires (1).
Biochar can be enriched when mixed with manures, clay and minerals (5,9). Enriched biochar is high in exchangeable cations such as; (calcium (Ca2+), magnesium (Mg2+), sodium (Na+) and potassium (K+); high in plant available phosphorus and it also has a high acid neutralizing ability (9). Recently, a study by scientists in Australia and China (5) looked at the effects of biochar-mineral complexes (biochar coated with minerals) combined with compost (poultry manure) on soil bacteria, soil quality and some plant growth properties for Pakchoi (Brassica rapa L. spp. chinenesis). This article summarises the methodology and some interesting results of this study.
• Seeds were sown: Pakchoi seeds were sown into pots filled with soil, biochar mineral complex (BMC), compost (CO) or biochar mineral complex combined with compost (BMCO). Plants were grown in a growth controlled chamber and were harvested 40 days after planting. Soil and plant samples were then collected for analysis.
• Some soil and plant properties measured: Soil moisture was measured by drying the harvested soil at 60°C for 4 days. Other soil properties measured include soil pH, electrical conductivity, total soluble nitrogen, nitrate, ammonium, organic carbon, available potassium and available phosphate content. Soil microbial analysis was carried out by DNA extraction and sequencing. The plant fresh and dry weight, the leaf area, leaf height and leaf chlorophyll content were also measured. The effects of compost, biochar mineral complex or biochar mineral complex combined with compost on the measured properties were analysed using statistical methods; principal coordinates analysis, permutational analysis of variance, and analysis of variance.
Some results of the study
• Biochar mineral complex combined with compost (BMCO) increased bacteria population and nutrient levels of the soil. They attributed this increase to the presence of compost in the mixture; as organic manure applied to soil increases microbial population (6,7).
• Comparing the compost only treatments to BMCO there was a higher content of total soluble nitrogen, organic carbon, nitrate and available potassium in the BMCO than the compost. In particular, soil nitrate was double the amount in BMCO than in the compost pots. They explained that the increased nitrate levels in BMCO, were as a result of increased soil nitrification caused by the abundance of nitrifying bacteria. Nitrification is a process in the nitrogen cycle which ends with the release of nitrate (the plant available form of nitrogen) in soil.
See-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4824760/table/T3/ for detailed results.
• Plants grown in BMCO filled pots showed increased leaf size. The authors suggested that the increased leaf size in these plants were as a result of increased nitrate levels caused by BMCO.
• BMCO did not increase the level of available phosphate required for plant growth. They explained that the high pH levels of compost and ions in BMCO might have restricted the availability of this nutrient (see Cao and Harris, 2010; for further reading).
This work indicates that BMC (biochar mineral complex) can combine successfully with organic manure to increase soil microbial population and soil nutrient levels which in turn boosts crop growth and soil quality. The benefits of this combination will lead to a rise in the demand for biochar used in organic farming.
References and further reading
1. What is biochar? https://www.biochar-international.org/biochar
2. Brennan RB, Healy MG, Fenton O, Lanigan GJ (2015) The Effect of Chemical Amendments Used for Phosphorus Abatement on Greenhouse Gas and Ammonia Emissions from Dairy Cattle Slurry: Synergies and Pollution Swapping. PLOS ONE https://www.ncbi.nlm.nih.gov/pmc/articles/PM. accessed 16th November 2015
3. Clough TJ, Condron LM, Kammann C, Müller C (2013) A Review of Biochar and Soil Nitrogen Dynamics Agronomy 3:275-293.
4. Cayuela ML, Sa´nchez-Monedero MA, Roig A, Hanley K, Enders A, Lehmann J (2013) Biochar and denitrification in soils: when, how much and why does biochar reduce N2O emissions? Scientific Reports 3 : 1732.
5. Ye et al (2016) A Combination of Biochar–Mineral Complexes and Compost Improves Soil Bacterial Processes, Soil Quality, and Plant Properties. Frontiers in Microbiology 7: 372.
6. Hartman et al (2015) Distinct soil microbial diversity under long-term organic and conventional farming. ISME Journal 9: 1177-1194.
7. Zhen et al (2014) Effects of Manure Compost Application on Soil Microbial Community Diversity and Soil Microenvironments in a Temperate Cropland in China. https://dx.doi.org/10.1371/journal.pone.0108555
8. Cao X and Harris W (2010) Properties of dairy-manure-derived biochar pertinent to its potential use in remediation. Bioresource Technology 101:545-553.
9. Chia et al (2014) Characterization of an enriched biochar. Journal of Analytical and Applied Pyrolysis 108:26-34.
10. A brief history of biochar- https://www.pronatura.org/wp-content/uploads/2013/02/History-of-biochar.pdf
Feature Image: Biochar.jpg Via wiki.