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Biochar Is a Valuable Soil Amendment

This 2,000 year-old practice converts agricultural waste into a soil enhancer that can hold carbon, boost food security, and increase soil biodiversity, and discourage deforestation. The process creates a fine-grained, highly porous charcoal that helps soils retain nutrients and water.

Biochar is found in soils around the world as a result of vegetation fires and historic soil management practices. Intensive study of biochar-rich dark earths in the Amazon (terra preta), has led to a wider appreciation of biochar’s unique properties as a soil enhancer.

Biochar can be an important tool to increase food security and cropland diversity in areas with severely depleted soils, scarce organic resources, and inadequate water and chemical fertilizer supplies.

Biochar also improves water quality and quantity by increasing soil retention of nutrients and agrochemicals for plant and crop utilization. More nutrients stay in the soil instead of leaching into groundwater and causing pollution.

The carbon in biochar resists degradation and can hold carbon in soils for hundreds to thousands of years. Biochar is produced through pyrolysis or gasification — processes that heat biomass in the absence (or under reduction) of oxygen.

In addition to creating a soil enhancer, sustainable biochar practices can produce oil and gas byproducts that can be used as fuel, providing clean, renewable energy. When the biochar is buried in the ground as a soil enhancer, the system can become "carbon negative."

Biochar and bioenergy co-production can help combat global climate change by displacing fossil fuel use and by sequestering carbon in stable soil carbon pools. It may also reduce emissions of nitrous oxide.

A Balanced View

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The following guest editorial was submitted by soil science professor David Laird of Iowa State University in response to a recent Farm Journal article about biochar titled "New Row-Crop Product Supports Soil Microbes".

I read your recent article in Farm Journal about "Cool Terra" biochar and I feel compelled to comment.

First, by way of introduction, I am a professor of Soil Science in the Department of Agronomy at Iowa State University, where I have been conducting research on biochar since the early 1990s and extensively since 2005.

My concern is that your article “over sells” biochar - makes promises that are not realistic. We typically apply 10 tons per acre. Your article says 15 to 20 lb. per acre, which is not enough to have any effect at all. Your article says that farmers can expect a yield bump of 12% to 15%, which is possible but by no means certain and certainly will not be achieved by applying only 15 to 20 lb. per acre.

In the scientific literature, crop yield responses to biochar applications average just 2.8% and vary greatly; a recent analysis of 507 greenhouse and field trials indicated that 22% of the trials showed statistically significant positive yield responses to biochar, 4% showed statistically significant negative yield responses, and the rest (74%) showed no statistically significant difference in yield between controls and biochar treated plots or pots. This is not surprising because crop yield response to biochar depends on very complicated interactions between biochar type and amount, soil type, climate, crop and management.

When I talk with farmers about biochar, the first question I ask is "What is the problem you are trying to solve?" If a field has a soil compaction problem or has low nutrient- or water-holding capacity, then applying the right amount of the right type of biochar may help solve the problem. But if something else is limiting yields, then biochar may not help.

There is tremendous variability among different types of biochar. And it is important to use the right type of biochar, one designed to solve a specific soil problem. Using the wrong type of biochar on the wrong soils can cause problems – do more damage than good.

As a general rule, biochar is most effective when applied on degraded and otherwise poor-quality soils and least effective when applied on high quality soils.

Most biochars are weak liming agents, but the calcium carbonate equivalent (CCE) is typically less than 20. So adding biochar to soil may reduce the amount of lime need, but unless you put an enormous amount of biochar on, it will not be enough to eliminate the need for ag lime. Most biochars contain some plant available nutrients, typically potash (potassium), phosphorous, calcium and magnesium but little or no nitrogen. So adding biochar to soil may reduce the amount fertilizer that you need to apply, but only by a small amount as the nutrient levels in most biochars is quite low. On the other hand, biochar is highly effective for build soil organic matter levels. Biochar is also effective for reducing soil bulk density and can increase both nutrient- and water-holding capacity of soils.

Our longest-running field trials in central Iowa (10 ton of hardwood biochar per acre applied in 2007) show an average of 13-bu.-per-acre corn yield increase in continuous corn with chisel-plow tillage and no residue removal relative to controls with the same management but no biochar. The reason for this yield increase is that biochar is helping to reduce the yield drag caused by high residue levels left from the previous year’s corn crop. Technically, it is reducing autotoxicity by adsorbing phenolic compounds released as residue decomposes. In fields where we are harvesting 50% or 90% of the crop residue every year, there is no corn grain yield response to biochar. But the biochar additions have improved soil quality and therefore made the harvesting of residue more sustainable.

My point is that biochar does have potential applications, but overselling it and making unrealistic promises does harm and gives biochar a bad name. Biochar is not a miracle cure, but it does have value. Farmers need to know the truth, not hype.