Soybean producers–in fact, all crop producers–are constantly assessing the potential of soil amendments for increasing yield and/or economic return and for improving soil quality for crop production. However, some amendments that are touted as beneficial may not be beneficial enough to increase a producer’s net return. Thus, all such soil additives should be assessed both agronomically and economically.
It is an established fact that irrigation of crops in the Midsouth 1) increases yields and net returns from crop production, and 2) has resulted in a declining water level in the Mississippi River Valley Alluvial Aquifer (MRVAA). Thus, continued crop irrigation in the Midsouth is not sustainable using current practices on an ever-increasing irrigated acreage when the main water source is the MRVAA. Therefore, more attention should be given to sustainable dryland crop production in the region.
Promotion of dryland agriculture in the Midsouth is a worthy cause. However, less than 35% of the region’s average annual rainfall is received during the growing season months of May through September. Also, the year to year vagaries in rainfall pattern during this period frequently result in extended periods of little or no rainfall, and this is exacerbated by high temperatures that are normal during this period (thus the frequent drought periods). This compromises dryland crop production, and often results in poor yields from dryland systems in the Midsouth.
Now back to the opening paragraph of this article. Biochar is being touted as a promising soil amendment to address the above challenges in sustaining dryland agriculture. Biochar is widely regarded as a soil amendment that will enhance water and fertilizer use efficiency in crop production because of its positive effects on soil pH, soil porosity and bulk density, cation exchange capacity (CEC), hydraulic conductivity, nutrient availability, soil water holding capacity, soil microbial activity, diversity, and abundance, and sequestration of carbon into agricultural soils. This perceived enhancement of these soil properties should result in crop yield increases in dryland systems.
The following definitions are presented to aid in the discussion of biochar as a soil additive.
• Pyrolysis: A process that uses the application of high temperatures (in an environment with negligible or limited oxygen) to organic compounds to cause chemical decomposition.
• Biochar: The product of pyrolysis of biomass waste materials such as crop residues, forestry/logging wastes, poultry litter, and animal manure.
• Biochar feedstocks: These come from biomass waste materials such as crop residues (e.g. corn stover, sugarcane residue), forestry/logging wastes, poultry litter, and animal manures. The composition of biochar–i.e. the amount of carbon, nitrogen, potassium, calcium, etc.–depends on the feedstock used in its production and the duration and temperature of the pyrolysis. Thus, any biochar product used as a soil amendment should be tested on a batch by batch basis to determine its specific chemical composition. The choice of biochar feedstocks also will be determined by their availability in the area of intended use–e.g. in the Midsouth, poultry litter, sugarcane bagasse, logging residue would be available feedstocks.
• Bagasse: The residue or fibrous matter that remains after sugarcane stalks are crushed to extract their juice. Most bagasse is used as a fuel for sugarcane processing, but the percentage that is not used for fuel can be used as a feedstock for biochar production. The amount of this material that would be available for biochar production on a large scale is not known.
Making biochar from its various feedstocks: 1) should not compete for land used for crop production; 2) prevents these materials from being burned or left to decompose (thus releasing CO2 and methane back into the air) and from polluting local ground and surface waters; and 3) can result as a byproduct of producing energy from various biomass feedstocks. A consistent supply of biochar feedstock will depend on availability both within and among years, and this will likely be related to producer planting decisions, weather vagaries, and government programs that may influence choice of crop to plant or diversity of farming operation.
Consider the following points related to biochar use in agricultural systems.
• Long-term studies are needed to properly assess biochar’s impact on soil attributes before widespread biochar use is promoted.
• Since biochar’s carbon sequestration is based on its ability to slow the release of carbon into the atmosphere, its carbon stability must first be optimized, and this will also require a major long-term research effort to determine the optimum feedstock(s) and the optimum pyrolysis conditions for the various feedstocks.
• Research needs to be conducted to determine the long-term gains from applying biochar to soil used for agricultural production.
• Since the high variability in chemical composition among biochar feedstocks and their biochar products requires that users know the specific properties of any biochar product they use as a soil amendment, biochar should not be referred to as a single entity. Rather, recommendations for its use and predicted performance should be based on the specifics of the feedstock and pyrolysis conditions.
• It is doubtful if there exists sufficient facilities for the production of a selected biochar product in an amount that would be required for its use on a large acreage in the Midsouth. So even if sufficient research determines its value for any or all of the above-stated potential benefits, it will likely take a number of years to ramp up to the required large-scale production of needed biochar from any feedstock.
• If sufficient research determines biochar’s value as a soil amendment in the Midsouth, there will be a need to determine if in fact production and use of a selected biochar product in the amount needed will be economical in the region.
Click here for a White Paper on this website that summarizes biochar issues gleaned from various sources that are linked in that White Paper.
Composed by Larry G. Heatherly, Mar. 2020, firstname.lastname@example.org