Roots nourish microbes by providing a food source or by releasing nutritious compounds into the soil. It is estimated that plants release from 10-40 percent of the carbon fixed by photosynthesis through the roots. This carbon increases soil organic matter.

 

Five different types of organic compounds released through roots are:

 

1. Cells are continually falling off root tips as roots grow;

2. Root tips produce an insoluble lubricating gel that helps the root penetrate small pores and provides the root tip protection against drying, helps gather nutrients, and binds soil particles together into aggregates that allow for better soil aeration and water percolation;

3. Soluble compounds called exudates are produced and leach from the root surface. These leacheates include organic acids, amino acids, proteins, sugars, phenolics, and other substances easily decomposed by microorganisms. The exudates have many functions; for example, they can solubilize plant nutrients such as phosphate from the soil particles, change the redox state on the root surface making iron more available, desorb nutrients from clay surfaces, or chelate zinc;

4. Sugars are fed directly by roots to fungi and bacteria that live in symbiosis with roots. Most well-known examples are rhizobia that fix atmospheric nitrogen in legume roots, and abuscular mycorrhizal fungi that form bushy structures inside root cells connected to hyphae that extend the reach of the root into surrounding soil (See the figure to the right).

5. Dead cells are being lost from the root surface continuously as the roots develop. Subsequently, decomposer fungi and bacteria feed upon these dead cells located away from root tips. Our perennial grasslands consist of cool season grasses, warm season grasses, and flowering forbs. Consequently, adaptable plants are able to grow during the cool spring and fall weather, as well as the summer heat. Allowing for a continual live plant feeding carbon exudates to the soil food web during the entire growing season. 

 

Winter crops such as wheat can provide a living root during traditionally fallow periods of a cropping season. Fall-seeded “cool season” cover crops or summer seeded “warm season” cover crops can also fill in during dormant periods period and provide the missing live root exudates. Cover crops may be incorporated into a cropping system as annuals, biennials, or perennials. Starting on a small acre scale will allow farmers and ranchers to find the best fit for their operation.

 

Cover crops can address a number of resource concerns:

• Harvest CO2 and sunlight, providing the carbon exudates to the soil food web.

• Building soil aggregates and pore spaces, which improves soil infiltration.

• Cover the soil, controlling wind and water erosion, soil temperature, and rainfall compaction.

• Catch and release of inorganic nutrients, improving water quality.

• Salinity management.

• Pollinator food and habitat.

• Weed suppression.

• Wildlife food, habitat and space.

• Livestock integration.

• Adding crop diversity

• Adjusting the cover crop combination’s carbon/nitrogen ratio, to either accelerate or slow decomposition.

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Tools

• Midwest Cover Crops Council