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Soil Building-- Apprenticing With Mother Nature

In organic agriculture we speak of using nature as a model. Yet as we get into the push and pull of the economics of agriculture, it is easy to forget about the quiet, long-term perspective of nature. Yet we cannot escape nature's laws. If we look at nature as a a model for soil building we see a diversity of plants interspersed on a piece of ground. It does tend to move to a predominance of one type of crop as the organic matter increases the health and biological activity of the soil. However, it is never a monocrop.

A key aspect of nature's soil building is that the majority of plant growth is returned to the soil every year. Farmers need to maximize the organic matter fed to the soil year in and year out as one of the very basic premises of organic and sustainable agriculture.

Soil building is a fundamental principle of organic farming closely linked to crop rotation. NPSAS is publishing a series of two articles which were written to challenge farmers to think about soil building as a key part of their farm's survival and as part of their stewardship of the land. First we take care of it, then it can take care of us and our children after us.

Soil Building and Soil Quality (Part I)
by Terry Jacobson

Soil building is an essential part of sustainable organic crop production. In a systems approach to farm management, a farmer strives to use the resources of the farm, the creativity of the farmer, and solar energy to enhance the health and productivity of the soil. An effective soil building program can minimize the need for purchased fertility inputs.

Soil building is easiest on a farm that has both livestock and crops because livestock manure or compost is so valuable in recycling nutrients and increasing soil biological life. Farmers are aware of the NFK benefits of manure or compost but overlook the added benefit of the bacterial inoculation of the soil resulting from compost or manure applications.

Increasing soil biological activity helps recycle organic material such as straw or weeds. It also increases the soil's ability to break down the mineralized or rock portion of the soil.

Compost is the preferred method of manure application to the soil since it has already gone through some breakdown. The heating process of composting substantially decreases the viability of weed seeds in the manure. When uncomposted manure is used, care must be taken to apply it at least 60 days prior to harvest so as not to overstimulate a crop with nitrogen. Both manure and compost should be incorporated into the soil as quickly as possible to minimize volatilization of the nitrogen. FVO standards require that manure brought in from conventional sources must be composted before it is used on an organic farm.

For effective soil building and minimal nutrient loss, it is important to have plenty of high carbon trash on the fields that receive raw manure. This allows soil bacteria to have the key nutrients they need to break down organic material, feed themselves, and build stable soil particles.

Many farms do not have enough livestock to make a significant impact on soil building. For these farms it is absolutely essential to have an effective green manure soil building program. Farmers without livestock manure should have a green manure crop worked in to feed the soil at least every third year. The more often you can work a green manure or cover crop into the soil, the more you feed and stimulate soil biological life. As farmers are stressed economically, it is tempting to stretch the time between green manure crops in favor of cash crops. This is counter productive because it reduces yields and increases weed populations, making the farm more dependent on expensive off farm inputs to supplement for declining soil health.

There is a great variety of ways in which green manure crops can be raised in a crop rotation. For instance, where the growing season is long enough, an effective green manure crop can be grown in the fall following a low plant residue crop such as soybeans. It works particularly well if a late seeded crop is grown the next year giving the green manure crop of clover or rye time to grow more in the spring creating greater biomass to feed the soil microbiology.

In a book on sustainable agriculture written for Moldovan farmers by Walter Goldstein and Boris Boinchan, Walter points out that in order for a green manure crop to have long lasting soil building effects it must grow long enough to begin forming lignin. This is a compound more common in mature plants. Lush green plants have very little lignin and break down very rapidly in the soil. Thus the stable humus that improves the long-term soil structure is not built up when the green manure crop is worked down too early.

Soybeans are often cited as a soil building legume crop. While it is a legume crop, it really does not meet the criteria to be called a soil building crop. FVO standards do not permit more than three consecutive row crops because the extra tillage practiced in row crops actually results in breakdown of soil structure. The relatively low amount of crop residue with soybeans also provides little to feed soil biological life. There is nitrogen

fixation with soybeans, but much of that nitrogen is used to supply the needs of the high protein soybean crop.

Legumes such as alfalfa, clover, and vetch send down deep roots that help loosen soil. They also produce more lignin for building humus. They not only are famous for nitrogen fixation but also produce substantial biomass for feeding soil microbus.

In areas with shorter growing seasons or insufficient moisture for double cropping planting a legume under a nurse crop is a common practice. The following year, the legume is worked down as a green manure. This allows time for greater biomass to be produced and consequently more lignin. This can be very important for dry regions because lignin changed to humus increases the soil's ability to absorb and hold badly needed moisture. It is part of the art and science of farming to figure out that right balance of lignin and rapidly recycling organic matter. Raising more biomass takes more moisture out of the soil, but working the green manure crops early produces less

lignin. The farmer must adapt this system to the particular needs of your farm. Experimentation on a small scale is recommended for trying to perfect your understanding of this balance.

Another rotation plan that is popular involves three or more years of alfalfa in a rotation followed by three or four years of annual crops. Even though the alfalfa is harvested for hay, it is deemed a soil building crop. Soil building is enhanced if grass is planted with the alfalfa. In the earlier mentioned book, Walter Goldstein explains that grasses are the best plants for building stable humus because of their extensive fibrous roots and the way the roots are sloughed off when the grass is cut or grazed.

This system is further enhanced if the final hay crop is grazed or has manure applied and is worked down with the standing alfalfa as green manure crop. The positive effects of that combination of practices will be seen for many years. Care must be taken following alfalfa to be sure phosphate levels in the soil are not depleted.

If the phosphate is in the soil but chemically tied up and unavailable, increasing soil biological activity helps release more phosphate. Clover seems to have the ability to access tied up phosphate that many other crops cannot release. In nature, clover is a plant that is among the first plants to grow on bare soil. It seems to heal the soil and create a soil environment suitable for grasses and other plants. Buckwheat, either as a crop or as a green manure crop, is noted for its ability to release tied up phosphate.

Increasing soil health and biological activity has the obvious benefit of increasing the soil fertility. It also improves a soilís ability to absorb and hold water. As mentioned earlier, a biologically active soil slowly breaks down the rock fraction (mineral component) of soil, releasing new minerals and trace elements for plants. Research has also documented that a biologically active soil accelerates soil breakdown of disease pathogens by beneficial bacteria. Effective recycling of crop residues is also a benefit.

Unless we pay attention to soil building, we are not adequately taking care of the land we farm. We are more like parasites that destroy their host than stewards. Economic stresses push us to exploit the land by neglecting this basic part of organic farm management. Failing to properly manage soil building may jeopardize your organic certification, but more importantly, it may threaten the health and productivity of your farm.*

The articles in this two part series first appeared in the December '99 issue of In Contact, a quarterly publication of International Certification Services/Farm Verified Organic. Authors Terry Jacobson and David Podoll are members of the FVO Certification Committee.

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