All Things Organic - Understanding glomalin can lead to organic success

By Ian Cushon
February 26, 2004

Soil is the foundation of life on earth, but most soil scientists admit they know little about the many soil organisms that work to provide and protect soil fertility.

Another piece of that complex puzzle is starting to be understood. In 1996, United States Department of Agriculture scientist Sara Wright discovered glomalin. Glomalin is one of the most important parts of healthy soil. It is a sticky protein that holds soil together. It is a glue that binds organic matter to the minerals in silt, sand and clay in aggregates. Glomalin is what adds structure to soil, giving it tilth and stability. It is also an important part of soil that helps prevent soil erosion. Glomalin is not soluble in water. Without adequate supplies, soil will erode easily. It may prove to be a key indicator of soil fertility and health.

Glomalin is a major component of soil organic matter. It is also a large reservoir of soil carbon. In one study glomalin accounted for 27 percent of total soil carbon. Glomalin is produced by arbuscular mycorrhizal fungi, or AMF, which are fungi that form a symbiotic relationship with the roots of most plants. This relationship benefits both organisms. The AMF attach themselves to the roots of plants. The plant roots provide carbon to the fungi and the AMF grow hairlike filaments called hyphae, which extend the reach of the roots. The hyphae supply additional water and nutrients, especially phosphorous. Glomalin is found on the outside of the hyphae acting to seal them so they can carry water and nutrients. As the root systems grow, the hyphae move down the roots and the hyphae on the upper roots stop transporting nutrients. The unused glomalin on these hyphae then attaches to the minerals and organic matter, forming aggregates. Glomalin may also be an important part of successful organic farming. The AMF that produce glomalin may be some of the most important soil organisms that help soil provide nutrients to organically managed crops.

In soil tests, phosphorus is deficient on many organic farms. While there is a lot of phosphorus in most prairie soils, most of it is tied up and unavailable to crops. Under these conditions, long-term organic farmers have often wondered how organic crop yields can still be relatively good if their soil is deficient in phosphorus. AMF may be the answer. If AMF is acting as a supplier of nutrients, then perhaps AMF is making up for the deficiency in phosphorus by making more available than is indicated by the soil tests.

Wright also studied different farming systems and crops and found that different practices affected AMF and glomalin. Wright and her colleagues found that AMF numbers were increased by using less phosphorus fertilizer. Under prairie organic systems that use little off-farm phosphorus, it is likely that farmers are increasing the benefits of AMF. This would help explain the lack of phosphorus deficiencies in yield results.

Farmers can also use other production practices to manage AMF and glomalin. Some of the highest glomalin contents are found on grasslands. Levels of glomalin were also raised or maintained by no-till and cover crops. Many crops of the brassica family do not have AMF on their roots. As a result canola, mustard, cabbage and cauliflower do not help produce glomalin.

Tillage and summerfallow negatively affect AMF and glomalin. AMF need crop roots to grow. Black summerfallow and excessive tillage will result in decreased levels and as a result increase soil erodibility. Using green manure crops on fallow should offset some of the losses caused by tillage. Minimizing the use of summerfallow and increasing the frequency of forages and grasses in rotations will greatly increase AMF and glomalin.

This reaffirms that mixed farming operations that have careful rotations of annual grasses and legume forages may prove to be some of the best management systems for enhancing soil quality.

Ian Cushon
Moose Creek Organic Farm Inc.
P.O. Box 85
Oxbow, Saskatchewan
Canada, S0C 2B0

Tel. 306-483-5034
FAX 306-483-2799
Cell 306-483-8257
E-mail: coldridge@sasktel.net