Moist-soil management refers to management of land to provide moist soil conditions during the growing season to promote the natural production of beneficial plants. Seeds produced by these plants often attract and concentrate waterfowl and other wetland wildlife species.
Encourage the growth of moist-soil plants in wetland basins by drawing the water from the fields during the growing season. This replicates the seasonal drying effect that would have occurred in natural wetlands through the summer or in drought years. Wetlands typically have diverse seed banks in the soil that are viable and will germinate if given the right conditions. Areas that have experienced large inputs of sediment may need to be excavated or disturbed to expose or mix up the seed bank.
Timing and Rate of Water Drawdown
The timing and rate of the drawdown are important for good plant growth. Wetland drawdown times should vary from year to year to stay productive.
- Early drawdowns (March through early April) promote the germination of broadleaf plants like smartweed.
- Mid-season drawdowns (mid-April to mid-May) will result in some smartweeds and more sedges and grasses like wild millet.
- Late drawdowns (late May to June) favor more of the grasses and sedges, like wild millet and chufa (flat sedge).
- Every three to five years, it is good to leave the water on the wetland to evaporate on its own.
Drawdown and Re-flooding
- Begin the drawdown by opening the water-control structure a small amount. The rate of the drawdown should be slow enough to prevent rapid drying of the soil, usually about 1 inch per day. This will discourage undesirable species like cockleburs from germinating while stimulating desirable moist-soil plants.
- Following germination of desired plants, manipulate water levels throughout the summer as necessary to keep soil moist.
- A slow, progressive second flooding of the marsh is best, starting around September 1 for teal or October 1 for many other waterfowl species.
During long summer dry periods, shallow re-flooding (irrigation) will stimulate moist-soil plants and can even kill or set back undesirable plant species, such as cocklebur and morning glory. Moist-soil plants are not adversely affected by summer flooding, as long as one-third of the growing plant is out of the water.
Disking in late summer or early fall is another tool to enhance a moist-soil wetland’s productivity. By breaking the soil and churning up the standing vegetation, conditions are set to give the aquatic insects a jump-start once water is added. These open patches show water earlier as flooding occurs that may not be visible from the air under the thick summer growth of plants.
Although units vary, most marshes should be disked once every three to five years to set back plant succession. This disking will also help control woody plant invasion and can be used to control undesirable plants like cocklebur. When possible disking should be rotated over a unit so that all parts have been disked in a three- to five-year period. A late summer disking followed by a shallow flooding is especially attractive to shorebirds and early migrant waterfowl.