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Use Cover Crops to Reclaim Wet Ground

08/11/2014 @ 3:46pm

When wet soil conditions prevent spring planting in some fields, summer-planted full-season cover crops can reclaim the ground. The alternative of leaving fields bare over summer opens the door to soil degradation and loss of nutrients.

“When living roots are absent from soil, the beneficial organisms in the soil begin to suffer,” says Barry Fisher, state soil health specialist with the Natural Resources Conservation Service in Indiana. “Without the plant roots, the beneficial bacteria and fungi have a hard time surviving in supersaturated soil conditions.”

Because the beneficial bacteria and fungi play important roles in the cycling of nutrients within the soil, their loss can create nutrient-deficient growing conditions for subsequent crops.

Purple corn syndrome, for instance, is a crop condition resulting from soil becoming deficient in beneficial organisms.

“Corn is very reliant on the activity of mycorrhizal fungi in the soil in order for its roots to access phosphorus,” says Fisher. “When the beneficial fungi can’t colonize, the corn turns purple. This indicates a phosphorus deficiency in the crop.”

Soil structure suffers as well when wet ground remains unplanted. “Without living roots in the soil, the stability of soil aggregates starts to break down,” says Fisher.

As a result, pore space shrinks, restricting oxygen. This contributes to a further sealing of the soil, delaying the drying of wet ground.

“These conditions lead to a continuing breakdown of total soil function,” Fisher says. “It’s hard to rebound from that. The first thought is to break up the soil with tillage after the field dries out. This only further diminishes soil structure and destroys soil organic matter. It simply compounds the problem.”

Diversity
An alternative for reclaiming wet ground is the planting of a diverse cover crop as soon as conditions permit. The greater the diversity of the cover, the broader the range of soil services fostered by the diverse colonization of the resulting soil life.

If the cover crop is planted in early to midsummer, warm-season species like cowpeas, soybeans, and sunflowers are good options. Warm-season grass species are also beneficial. Sorghum, sorghum sudan, and millet are particularly effective at promoting mycorrhizal activity.

“Including a clover in the mix is helpful,” says Fisher. “Red or alsike or sweet clover can tolerate a broad range of conditions. Each adapts to both dry and wet soil conditions; sweet clover tolerates salinity. A deep-rooted legume can break through compaction.”
Late-season plantings of a cover crop in wet ground might include cool-season species such as barley, cereal rye, winter peas, crimson clover, and brassica crops like oilseed radishes, rapeseed, and turnips.

“Oats makes a good choice for cool-season planting,” says Fisher. “Oats is a quick starter. It’s a good option for recolonizing populations of good bacteria and the mycorrhizal community as quickly as possible.”

Cover crops lend themselves to aerial seeding. Maximum benefits from cover crops result from letting the plants grow full season. This lets the beneficial community of fungi and bacteria continue growing into winter, maximizing their populations.

In the short term, cover crops reclaim wet ground by the moisture they consume, using as much as 7 inches of soil water in one season.

Longer-term reclamation comes from improved soil health. “The rebuilt soil aggregates and plant roots create channels for moisture to flow through the soil,” says Fisher. “This lets surface soil dry out while adding to the bank account of soil moisture stored at deeper levels.”

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