Biochar Agriculture for Arid and Semi-arid Agricultural Soils

WHAT IS BIOCHAR?

Biochar is a black carbon or charcoal made from biomass—biological, organic materials derived from plants and animals. Biochar is created by heating biomass in an environment that has little or no oxygen a process called pyrolysis. The net effect of pyrolysis is the production of a solid material that has a high concentration of carbon and does not easily break down in the soil. By applying biochar agriculture to the soil, the soil’s carbon content can be increased significantly. This added carbon can persist in the soil for a very long time.

One could say that biochar is charcoal for soils. There are some important distinctions between biochar and other materials. Biochar is made from biomass of recent origin. This means that it is made from recent woody or plant waste materials. Some biochars are also made from animal wastes, such as manure and poultry litter. Biochar is not made from coal or coke, which is a carbon-rich product from petroleum refining. Biochar fertilizer can be used as a soil amendment in that it can improve certain soil properties. Although it does contain some nutrients, biochar is not considered a fertilizer.

IMPACTS OF BIOCHAR ON SOILS AND HOW DIFFERENT SOILS RESPOND

Soil moisture and soil physical properties

One of the cited benefits of biochar presented in many studies is its effects on soil moisture retention. However, the impact of biochar for soil moisture improvement depends on the biomass feedstock, pyrolysis conditions. They found both soils had improved moisture retention due to biochar addition. They also discovered the switchgrass biochar produced at 500°C and added at 2% by soil weight gave the best moisture retention in the soils, which was about 10% more than soils without biochar. Other authors found an increased benefit in moisture retention due to the addition of biochar in sandy soils more than in clay soils.

Therefore, when applying biochar for soil moisture improvement, producers need to consider their soil type because of not all biochars can improve moisture retention in all soil types. Other soil physical properties shown to be positively impacted by biochar applications include soil bulk density, soil aggregate stability, and moisture flow within the soil.

Soil nutrients and soil chemical properties

Depending on biomass feedstock and pyrolysis conditions, biochar can add nutrients to the soil and modify the soil’s chemical environment. Ultimately, biochar’s effect on soil fertility depends on the initial fertility of the soil; therefore, the effect of biochar on soil fertility or crop productivity may not be apparent in soils that are already fertile. Many studies show biochar can improve soil fertility by delivering important nutrients to the soil, such as nitrogen, phosphorus, potassium, and calcium. The amount of nutrients delivered to the soil, however, is highly dependent on the feedstock from which biochar is made. For example, wood biochars were shown to have lower total nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium than manure-based biochars. 

Biochar made from animal wastes have been shown to contain significant amounts of nitrogen that led to improved crop yields compared to the control soil without biochar, and also improved nutrient use efficiency. Chan et al. In arid regions, caution must be exercised when using biochar since it can affect soil pH and salinity. Generally, the pH of most arid soils is already in the high range, and raising the pH further can create management challenges for crop production and nutrient availability. Similarly, arid soils are prone to salt accumulation, and any practice increasing soil salinity should be avoided. Therefore, when using biochar products as a soil amendment in arid soils it is important to know and account for the pH and salinity characteristics of the biochar being applied.

EFFECT OF BIOCHAR ON CROP PRODUCTIVITY

Many studies have reported yield increases for different crops due to biochar application. The impact of biochar production on crop yields varies depending on the crop, type of biochar, and rate of application. Yield increases are generally attributed to increased phosphorus and nitrogen added to the soil through biochar. Therefore, biochar uses to increase crop yields, the feedstock from which the biochar is made must have high levels of nutrients. It is important to know the initial fertility of the soil receiving biochar since the impacts of activated biochar on soil fertility and crop nutrition are more pronounced in low fertility soils. It is vital to know the crop-available nutrient contents of the biochar, especially when used for crop production. Based on soil test results, fertilizer applications can be adjusted to credit the amount of nutrients delivered by the biochar.

CONCLUSION

Biochar can be a valuable resource for amending soils in arid and semi-arid regions with regards to short- and long-term soil health and productivity.

Before using biochar as a soil amendment, follow these recommendations:

1. If buying from biochar suppliers, know the feedstock source of the biochar and request the analytical results; compare those results to available standards for biochar quality and sustainability from the International Biochar Initiative and the European Biochar Foundation. The feedstock used to make the biochar should be clean and fully “cooked”.

2. Carefully consider the salinity and pH of the biochar material, especially for soils with already elevated salinity and/or pH levels.

3. Adjust fertilizer applications according to the measured available nutrient content of the biochar.

4. Expect the effect of biochar on soil moisture retention to be more pronounced in coarse and medium-textured soils than in fine-textured soils.

5. Start small and begin with a small area; the biochar cost can be high, and most of the effects will be long-term.