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Manage soil moisture
Well-managed crop rotations that increase soil organic matter to sufficient levels help to moderate soil moisture, retain moisture in dry conditions and allow excess moisture to drain away in wet seasons.
Shifting crop types also helps vary water demand within the soil profile. Spring-seeded small grains use water in the 2- to 4-foot range and sunflower, safflower, corn and sugar beets pull water from the 5- to 6-foot range. The deeper crops following shallow crops can access moisture reserves as well as capture any nutrients that have leached below the shallower root zones before they reach groundwater. Following with a grass crop allows the field to build its moisture reserve back up.
Mulch effect: Generally speaking, the higher the carbon-to-nitrogen ratio (C:N) of the cover crop residue, the longer the residue will serve to suppress weeds and conserve moisture. Small grain cover crops are well suited for this; most legume residues with higher nitrogen content will decompose more rapidly and be less effective as mulch.
The microbes that decompose crop residues use carbon as an energy source and nitrogen to build tissue. If residues have a carbon-to-nitrogen ratio higher than 20:1, such as mature rye, the microbes will need to gather nitrogen from the surrounding soil to do their work.
This concludes the Practices lesson. By now, you should have an understand of tillage and cultivation practices related to organic agriculture. You should also realize the value in planting cover crops and using crop rotations. In the next and final lesson of this module we'll discuss making and using compost.
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Establishment of a thick stand of rye is needed to suppress weeds in an organic no-till system. Rolling the rye in a direction perpendicular to the row creates a more even mat of residue than is shown here. (Photo: TRI)
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