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Biochar may prove to be long-lasting solution to soil amendment
Jill Odom | December 5, 2016
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With biochar a little can go a long way, around five percent by volume is the good rule of thumb.
Photo: Sonoma Biochar Initiative

Every landscaper knows that aside from water and sunlight, soil is one of the most important elements needed for plants to grow.

Yet sometimes when the soil is unfavorable steps must be taken to amend it. There are organic and inorganic options to choose from, but one that has been gaining attention is biochar.

Biochar has been around for millennia and has been used to improve soil throughout the Amazon Basin to create rich black soil known as “terra preta.” Even though these soils were amended thousands of years ago by Amazonian civilizations the soil remains highly fertile to this day.

Biochar is a highly purified form of charcoal that is designed to improve plant growth and health. It can be created from various source materials, such as wood chips or manures, but depending on the type of matter used affects its properties.

Organic source material that has a higher water content often results in more porous biochar, providing extra space for beneficial bacterial and fungi to colonize. Biochar positively impacts soil in a number of ways.

It increases a soil’s water holding capacity by increasing the soil surface area. It is water adsorbent in conditions with greater than 60 percent relative humidity and releases water if the relative humidity is below 40 percent.

Increased soil surface area also overcomes the problem of too much water retention. It improves pore space for better drainage and reduces standing water on surfaces, as found with clay or compacted soil.

Biochar reduces acidity, accelerates decomposition and provides a habitat for valuable microorganisms that in turn help increase plant productivity. The porous nature of biochar also allows it to adsorb heavy metals like lead and cadmium, and enzymes produced by plant pathogens like Phytophthora root rot.

When using biochar, it augments the efficiency of fertilizers used because it creates a higher nutrient retention level, reducing leaching.

To test biochar’s effectiveness, the Bartlett Tree Research Laboratories conducted case scenarios to see if biochar provided any noticeable benefits to Yoshino cherry trees that were planted in barrier-lined planting pits 5.9 feet by 11 feet by 1.9 feet.

Trees were planted with biochar at 5 and 10 percent by volume, 5 and 10 percent biochar combined with compost and fertilizer, compost and fertilizer alone, and control soil with no amendment.

After three growing seasons, it was found trees with the biochar and compost at 5 percent volume had the best results. There was improved tree growth, canopy quality, soil nutrient levels, and volumetric soil moisture.

“The take-home on biochar right now is that we’re seeing some positive responses in growth with it,” Bryant Scharenbroch, soil scientist at The Morton Arboretum, told Bartlett Tree Experts. “We’re seeing some improvements in organic matter and soil properties with char. What the different improvements are and what the magnitude will be, we just don’t know yet.”

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