Research on biochar to improve soil acidity and salinity

Biochar from rice husks is more effective in improving saline acid soil than products from other agricultural by-products , according to research by scientists at Ho Chi Minh City University of Industry.

Potential left open

Biochar has been studied quite a lot on the mechanism of reducing the concentration of heavy metals in water and soil . Using biochar helps increase the amount of organic carbon in the soil, reduce greenhouse gas emissions and improve soil properties, improving crop productivity.

Biochar can also increase soil fertility and crop productivity by reducing soil acidification, improving nutrient retention, enhancing soil structure and increasing nutrient content. such as N, P and K. Biochar is also reported to have the ability to limit the negative effects of saline soil, helping to increase plant growth and productivity.

In Vietnam, agricultural by-products for biochar production are quite abundant. However, these by-products are still mainly thrown away, burned after harvest. causing environmental pollution and wasting renewable resources.

Biochar can increase soil fertility and crop productivity. (Illustration).

Therefore, recovering and converting agricultural by-products into biochar and fertilizing them back to the soil, especially problematic soils such as saline soil, is a creative and meaningful way. environmental, economic and social implications. However, research on biochar to improve alum saline soils is very limited in the country.

Faced with that reality, a group of authors at Ho Chi Minh City University of Industry carried out the project 'Research on the mechanism and potential of salinity improvement of agricultural land using biochar produced from agricultural by-products'.

Associate Professor, Dr. Nguyen Thanh Binh, project leader, said that four types of biochar were produced by the group from rice husks, corn leaf stems, longan stems and coconut fiber , using the manual anaerobic pyrolysis method.

These four types of coal are used to evaluate the ability to adsorb sodium (Na). Most biochars are highly alkaline (pH 7.2 - 9.4), while saline alum soils are strongly acidic (pH 3.8).

The results show that rice husk charcoal is a potential adsorbent because of its large surface area, high porosity (60.5%) and Na adsorption capacity of 33.9 (mg/g coal); Next is longan charcoal and corn charcoal.

Coir charcoal has a small surface area and has the lowest adsorption capacity, reaching 15.5 (mg/g of charcoal). Biochar adsorbs Na, while releasing other cations such as K, Ca, and Mg. Coir charcoal contains high levels of Na and Cl, so it has the lowest potential for improving saline and alum soils.

Change soil properties

According to the authors, adding biochar to saline alum soil has changed soil properties in a way that is beneficial to plants, such as reducing soil acidity (increasing pH), reducing element content. potentially toxic such as Al and Fe, and increase the content of soil nutrients such as K, Ca, P.

Therefore, all types of biochar have the ability to improve soil quality to different degrees, depending on the rate of charcoal used and soil properties. Charcoal types help improve soil quality by 33 - 46%.

Because coir charcoal has poor potential to improve saline alkaline soil, the group only used three types of biochar from rice husks, corn leaf stems and longan stems to mix with alkaline soil (taken from rice-shrimp rotation fields in Can Gio district, Ho Chi Minh City), at rates of 0.7% and 1.5% to grow wet rice.

Test results show that charcoal from rice husks is more effective than longan charcoal and corn charcoal in improving soil, increasing productivity by 5 - 6%/ha/crop (an increase of 0.46 kg/m2/crop). when using longan charcoal and 0.47kg/m2/crop when using rice husk charcoal) compared to not using biochar.

Therefore, the authors recommend that rice husk charcoal should be given priority when using alum soil. In addition to being effective in improving soil, rice husk charcoal also has a cheaper production cost than other charcoal. The coal rate that should be applied is 8 - 10 tons/ha/crop.

Biochar has a lasting effect of up to 4 crops , so it can be applied to the first crop and not applied to the next 3 crops while still ensuring rice production efficiency. The group also recommends not using charcoal from coconut fibers, corn stems and leaves, as well as plants living in coastal areas and salt water because they can accumulate large amounts of different salts.

Currently, the authors have completed the process of using biochar on saline soil, which can be applied on a large scale to replicate the research results of the project.