Building soil organic matter is the key to restoring soils. That is it, plain and simple. There are many tools and combinations of tools to build soil organic matter. The compost and biosolids that we people make are some of the tools. That doesn’t mean that it makes sense to take the compost from Los Angeles and ship it to the cornfields in Kansas. Don’t get me wrong. It would be great for those cornfields. But the farmers in Kansas have their own feedstocks and hopefully the people in LA will realize that they have soils too. Why share your materials when you can use them in your own backyard?
The best approach to building organic matter for your soil depends on where you are, what tools you have, and what you want to do with your soil. Still, certain rules of thumb apply worldwide. This is the universal language for soil:
• Soil does not like to be naked or disturbed
• Soil does not like simple, in reference to both what is growing on top or living down below
• Increasing organic matter in soils lets them support more complex living systems and reduces the chances that they will be caught naked and/or disturbed
• The more organic matter you have in a soil, the less work you will have to do to make it work for you
If you want to build a strong soil (read more organic matter) plants really are key. By that I mean plants in general and multiple kinds of plants. These multiple kinds of plants in turn support multiple types of animals, both above and below ground. A healthy soil is part of a complex system with an incredible diversity of life. This includes life that is visible to the naked eye and the vast jungle of microbes that are both too small to see and whose cities are below the surface of the soil. The goal in making a strong soil is to try to replicate at least a portion of that complexity.
Conventional farms, even in some cases those that are certified organic, do the opposite. They try to simplify. If you go to a lettuce farm in California or a tulip factory in Washington State, you see growing crops and soils defined on an industrial scale and lots and lots of exactly the same type of crop. Don’t laugh about the tulip factory. I have toured one and was astounded to see flowers being grown on conveyer belts in a warehouse.

From Cultivation To Engineering

Much of the science of farming in the 20th century was to move growing things and tending soil from an art to cultivate to a science to engineer. In this process, soil became a growing media rather than a living entity. Soils were tilled to create a uniform planting bed. Prescribed quantities of chemicals were added to the media to supply plant nutrient demand and kill unwanted pests (plant and animal). Now the tide is starting to turn back. In the 21st century, our 20th century farming models are requiring greater and greater chemical inputs to achieve declining yields. The key to restoring soils is to figure out a way to add the complexity (aka the carbon and life) back to the soils while simultaneously being able to grow enough lettuce, tulips and wheat to keep us all happy.
The tools surfacing to restore soils can be summed up simply: try to bring as much of the complex system back while still being able to grow food. These are not necessarily mutually exclusive tasks. We just have to adapt to figure out how they can work together. This means that instead of growing wheat year after year you include different crops over time. Instead of planting only one type of crop per field or farm you sometimes plant multiple types at the same time. It means tilling as little as possible and leaving the surface of the soil untouched and covered with the remnants of the last thing harvested.

Green Manure

A critical component of this is understanding the variety and types of manures, i.e., organics, that we feed back to the soils. This broad definition of manure includes recycled organics that can be from cities far away from farmers’ fields.
Back in the old days manure just meant poop from animals. That is so yesterday. Now farmers can grow their own manure without a cow in sight. Green manure is the term used for cover crops, which are planted to make sure that the soil doesn’t go naked in the off-season. Cover crops are typically allowed to die in place. With no till farming, mechanical planters are able to plant directly through the cover crop.
Cover crops can also be selected to increase soil fertility. Nitrogen fixing crops, when used as cover crops, both provide fertility for the subsequent crop and keep the soil covered. Deep rooted crops can be planted to break up soil clods and bring nutrients in the subsoil to the surface. Cover crops are increasingly planted as mixtures to get multiple benefits.
Examples:
Mixing the Perfect Cover Crop Cocktail
Mix Master | South Dakota Grower Blends Cover-Crop ‘Cocktails’ for Multiple Benefits
In some cases the farmers whom have discovered green manure are rediscovering the benefits of the brown variety. Livestock is reappearing on farms managed to maximize diversity and rebuild soils. Including livestock in agricultural systems that have traditionally focused on crops is another level of complexity and potential benefits. Chewing on grass stresses it and forces it to add more carbon to the root zone. This in turn increases the resilience of the pasture mixtures. Intensive grazing systems where animals stay on a field for only a few days and move on just like the buffalo used to appears to work wonders for the animals, the forage and the soil.
The ideal new farming system has rebuilt the soil into a living system with its associated complexity in crops and animals. The high levels of organic matter provide a well of nutrients. The soil microbial complex works in tandem with the plants that in turn work in tandem with above ground animals to build healthy and sustainable systems.

Recycled Organics

So where do recycled organics fit in? In many cases these composts and biosolids are gateway drugs for farmers who are starting to rebuild their soils. A few columns back I talked about Rockey Farms, potato growers in Colorado who have redefined how to grow potatoes. They use complex mixtures with their potatoes and have increased yields and reduced water use. They are even talking about getting some cows. You can check out their pictures on Facebook. Their soil rebuilding process started with compost. It is a great way to remind soil of what life can be — a wonderful introduction to soil building. But I would argue that it is something that these same farmers can learn to do without.
Most of the organics that I talk about come from green bins, community compost piles or anaerobic digesters. All of which are a long way from that bucolic complex farm field. But most farms are also a long way from that bucolic complex farm field. Composts, biosolids and digestates can play a part in the effort to restore soils. Using these materials instead of synthetic fertilizers adds carbon and micronutrients back to the soil. These are critical to restoring soil carbon concentrations. Multiple studies have shown that regular use of composts and biosolids will result in increased soil organic matter over time. It has also been shown that these amendments can increase yield in comparison with synthetic fertilizers.
Despite this, I think of these tools more as gateway drugs than as a sustainable practice for most agronomic crops. By agronomic crops I mean crops that require a combine to harvest, things like corn, soybeans and wheat. These same farms are in a better position to adopt complex rotations, cover cropping systems and no till than your average home gardener. At least where I live getting to these farms with recycled organics involves well over a 200 mile round trip truck haul, which makes it hard to justify when there are so many soils much closer to home that need them as well.
As urban agriculture continues to grow and as cities come to recognize the value of greenspace for communities and for infrastructure, the need for recycled organics close to home continues to expand. The fact is that even if we use our biosolids and food and yard waste locally it will only be a drop in the bucket for the soils we need to fix within the urban corridor. We can’t afford to waste a peel.
Farmers understand the value of soil as they work with it every day. For those of us in cities, getting someone to put their hand in the dirt is a major step towards environmental awareness and passion. Recycled organics, if made well, are a fabulous way to make that step easier, quicker and better. The same people who make the feedstocks for these amendments are in greater need for the gateway drugs than growers who have access to other options. Call me selfish and greedy, but I want my “waste” to fix my soil first. Once everybody in LA realizes that they have soil too, any talk of sending these materials far away will come to seem silly. Once we realize that there are soils in cities, us city folk will want all the compost we can get.
Sally Brown is a Research Associate Professor at the University of Washington in Seattle and a member of BioCycle’s Editorial Board.