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Fostering Sustainability and Innovation in Agriculture
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From Paper Mill Residuals to Seaweed Byproducts, Tilth Expert Provides Sustainable Solutions to Invigorate Soil

May 9, 2012 |

Organic waste is too precious to go unused—take it from a soil scientist.

Andrew Carpenter, founder of Belfast, Maine-based consulting company Northern Tilth, makes a living helping others set up organic waste recycling plans for the purpose of improving soil fertility. Carpenter helps his clients make use of all kinds of organic matter-based byproducts, such as paper mill residuals, seaweed byproducts, wood ash, manure composts and biosolids (sludge from waste water treatment plants). Northern Tilth’s clients include organic waste generators who want to recycle their waste (such as paper mills and food processors) as well as those who want to use it (such as farmers).

Carpenter says using organic waste in place of chemicals fertilizers has many sustainable benefits. It has the potential to reduce some of the leaching and runoff commonly associated with chemical fertilizers. It creates stronger, healthier soil in which plants can more efficiently take up the appropriate nutrients. It also creates a closed-loop system where natural resources are recycled.

In 2010, 250 million tons of municipal solid waste was generated in the United States, according to the U.S. Environmental Protection Agency. Organic materials—which include yard trimmings, food scraps, wood waste, paper products and paperboard products—make up more than two thirds of our solid waste stream.

Farmers looking to use sustainable growing practices should be aware of the benefits of using organic waste for their soil, Carpenter said. He noted that they should also realize there’s no “one size fits all” approach involved.

Healthier Soil

Carpenter grew up in suburban Cleveland, but he spent his summers working on his uncle’s farm in Virginia. As an undergraduate college student, he studied environmental science before receiving a master’s degree in plant, soil and environmental science from the University of Maine in 1998. As a graduate student, Carpenter’s research and field work focused on the soil chemistry and soil fertility in soils manufactured from paper mill residuals and manures. He started Northern Tilth in 2003.

Through his journey, Carpenter says he has seen the difference between using chemical commercial fertilizers and organic-based materials. Chemical inputs feed nutrients directly to the plants as opposed to “feeding the soil itself” in order to create a healthier ecosystem, he said. Carpenter calls soil a “living, breathing thing” that houses billions of microbes per gram of soil (which are considered part of the soil’s organic matter), which need certain nutrients to live and prosper.

“(With chemical fertilizers) you’re adding just the nutrients in chemical form that the plants need to thrive,” Carpenter said. “When you do that … the organic matter that’s in the soil that’s been there for centuries, or even millenniums, naturally decomposes over time and it’s lost.”

Carpenter noted that many commercial chemical fertilizers mainly provide three main macronutrients nutrients—nitrogen, phosphorus and potassium. However, sometimes this isn’t enough for the plants, which also need secondary macronutrients such as calcium, magnesium and sulfur, and micronutrients such as zinc, copper and iron, he said.

“Generally, when you’re recycling organic matter byproducts like manures, bio-solids and wood ash, you’re adding back some of these micronutrients that you might not otherwise be adding back,” Carpenter said. “Sometimes you see unexpected results from that, improvements that you couldn’t attribute to just what are called macronutrients.”

Farmers can expect several results when they use organic waste for soil amendments, he said. There will be fewer threats of pest damage and fungi, lessening the need for pesticides. There will be better soil aggregation, meaning the soil particles will better stick together. (This means less erosion, better water infiltration and an increased ability for the soil to “breathe.”) There will also be a lower likelihood of nutrient leaching (or the carrying away of nutrients when water drains the soil) because organic matter tends to work in a “slow-release” form, Carpenter said.

Before and after pictures of a spent gravel pit converted to agricultural land using a topsoil made from organic matter-based by-products. Northern Tilth provided technical assistance on this project managed by Resource Management, Inc. This field, which was completely barren before reclamation with the topsoil, has become the highest yielding hay field for the farmer that owns and manages this land.

Organic Waste Selection

There are many different kinds of organic matter-based byproducts to choose from. Some can be used for certified-organic agriculture (which is a different kind of “organic” than Carpenter refers to when discussing “organic matter”). Others cannot.

Certified-organic farmers can usually use manure and food waste composts, as well as wood ash from power plants that burn non-treated wood. However, due to national certified-organic standards, they cannot use biosolids, and they generally cannot use paper mill residuals, Carpenter said.

Paper mill residuals are particularly useful for manufacturing topsoils from scratch and using them to reclaim disturbed land, such as mined areas that have become eroded and barren.

“The paper mill residuals that I work with have a very high organic matter content and a very low nutrient content, so unlike manures, you can add these to soil at a very high rate without overdoing it on the nutrients,” Carpenter said, noting that they are usually used with low-valued sands and different composts. “We can actually make a soil itself and kick-start a healthy soil ecosystem without having to strip topsoil from somewhere else or bring in a lot of chemical fertilizers.”

Seaweed byproducts run a fine line for certified-organic farmers, Carpenter said. One of Northern Tilth’s clients is a company that imports seaweed from all over the world and extracts carrageenan (a complex mixture of sulfated polysaccharides) from the seaweed at its plant in Maine. Before the extraction takes place, the dried seaweed is mechanically shaken, allowing for the collection of the sands and salts that have become encrusted on it. Carpenter said this shaken byproduct is approved for use in certified-organic agriculture, and it’s a good source of potassium. The byproduct that results after extraction cannot be used on certified-organic farms but is a good source of lime, which is particularly useful for soils in the Northeast.

Carpenter said some organic matter sources, such as seaweed byproducts, are simpler and more cost-effective to find recycling programs for, which means there are more of those programs out there. On the other hand, there are not as many existing paper mill residuals recycling programs available because there is not as much know-how behind the process. There is also generally less financial savings in diverting paper mill residuals from landfills, he said.

He said using organic waste sources as soil amendments can be more complicated and costly than using chemical fertilizers, depending on the type of organic matter source used, the equipment required and the location and size of the farmer’s operations.

Ned Beecher, executive director of the New Hampshire-based North East Biosolids and Residuals Association (for which Carpenter is a board member), said he has seen growth in the use of organic matter-based by-products in general.

“It’s been slowly increasing at a somewhat higher rate over the last decade,” Beecher said. “I think the pace of understanding is increasing now. … All of these kinds of materials have really just become part of the normal (soil amendment) market.”

Choosing the Right Organic Matter Source

Carpenter has advice for farmers looking to tap into organic waste—not all organic matter sources are the same.

“If you’re a farmer that’s not familiar with using manure or compost, you really need to look into the source of compost or manure that you’re getting and be able to make a good determination on what it’s actually going to provide to you,” he said.

For example, horse manure is similar to leaf and yard waste in that it is very high in carbon and low in nitrogen and phosphorus, Carpenter said. Chicken manure is on the other extreme—very rich in nitrogen and phosphorus. Farmers can recruit certified crop advisers and other agricultural consultants to help determine the best match for their crops.

Carpenter said farmers using organic waste recycling plans must also keep close watch over their practices.

“It’s very important to monitor what you’re doing to see how it’s working… for instance, taking soil samples and tracking trends in your soil fertilization over time,” he said. “I would also recommend when doing soil sampling to spend a little extra money—usually very little per sample, maybe $5 per sample—to look at micronutrients and make sure they’re in good balance.”


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