Bringing Flooded Fields Back To Life
This spring brought catastrophic flooding to many areas, particularly Nebraska and western Iowa. One of the many negative effects of this flooding was the deposition of several feet of sandy sediment on top of the soil on river bottom fields. There has been a great deal of discussion, questions, and head scratching on how to restore productivity back to these fields. Here are some of our thoughts.
The key to productivity on any soil is humus, which is composed of the microbial byproducts of decayed organic matter. There are two ways to build humus in a soil. One is to import organic materials (such as manure or compost) to a field, spread them, and let them rot. This method works just fine but moving large quantities of manure or compost around and spreading across millions of acres involves a very large expense. The other is to grow as much plant material as possible on the field and allow a high percentage of it cycle back onto the field and decay. Another important new realization is that the most important factor in the production of organic matter is the amount of root exudates, as these root exudates are the perfect food for soil microbes. Current estimates are that 25-50% of the carbon fixed during photosynthesis will end up in the form of root exudates. This is not an unfortunate accident on the part of the plant, the soil microbes fed by these exudates return the favor with an improved availability of plant nutrients, better uptake of water, and reduction in root disease. With these factors in mind, here are some tips for restoring these fields back to productivity.
Get something growing. Never allow the land to be idle. Sunlight falling on bare soil is sunlight that is lost forever. Capture all available sunlight with green growing plants as many days as possible and allow sunlight to get converted into food for man, beast or microbe. Always follow a harvest with a planting, keep the leaf canopy intact for as much photosynthesis as possible for production of plant material and for producing exudates for the soil organisms that do the heavy lifting for organic matter production.
Dig a hole and determine the depth of the deposits. It is useful to know how much sediment you need to deal with. If it is just a few inches, you may not have to do anything. If it is several feet in depth, you may have your work cut out for you. The remediation strategy may be completely different depending on sediment depth. Also be aware that the depth of sediment is likely not uniform across the field. Dig several holes for proper assessment of the situation.
Armor the soil. For an active microbiology to occur, it is important that the soil be neither too hot nor too cold. A layer of residue on top of the soil prevents sunlight from baking it in the summer and prolongs the soil warmth in the fall to delay freeze-up which provides for more days of microbial action. A good mulch will also help reduce evaporation and help retain moisture in the soil. Grow high residue crops and do not remove the residue through tillage, baling or burning. Some high residue crops with persistent residue include rye, oats, triticale, barley, flax, sunn hemp, sorghum-sudan, pearl millet, and okra.
Bring in the organic matter. Whatever is wrong with just about any soil can be remedied with organic matter. Manure or compost can not only bring in much needed mineral nutrients but can also improve the soil water-holding capacity, and perhaps most importantly, help establish valuable microbial populations. Lacking enough manure or compost to completely remediate a soil, establishing microbes can be accomplished over a large acreage with surprisingly little material by applying just a few gallons of compost extract from properly made compost. If the process of creating compost and compost extracts for your own homemade microbe inoculant interests you, please attend our compost workshop June 12 and 13th 2019 in Bladen, NE.
Bring in the livestock. Research now indicates that manure from ruminant livestock can produce more organic matter than would have produced by the decay of the plant material that was eaten by the animals. The rumen is a perfect environment for microbial action; it is warm, moist, and protected from ultraviolet light, and different materials are ground finely and mixed so carbonaceous materials and proteinaceous materials are intimately intermingled for microbial benefit. Grazing produces more soil organic matter than the simple decay of the material on the soil surface. Just be sure to not allow grazing to the point where the soil is no longer covered.
Bring in the feed. Using these flood damaged areas to winter livestock with hay, grain, or silage is a great way to import a great deal of carbon into the system in a short period of time. However, it is also important to have a plan to be able to evacuate livestock to higher ground from these flood prone areas in a rapid manner. The feed should be fed in a manner so that the manure and wasted feed is deposited in a uniform manner, such as by bale grazing or rolling hay out on a new spot each day.
Use deep-rooted crops that can reach down to the underlying good soil to extract water and nutrients. Some examples among annual crops include sorghum-sudan, okra, sunflower, and safflower. Many perennials are also deep-rooted, with chicory, alfalfa, eastern gamagrass, and reed canarygrass being noted for their ability to root deeply, among others.
Consider seeding the land to perennial pasture. Perennials in general tend to be deeper-rooted, have higher root mass, have higher amounts of root exudates, and do not have a seedling stage in which there is little plant material available for capturing sunlight or producing root exudates. Pasturing perennials converts the above ground plant biomass to manure, the perfect soil improving substance. However, perennials are often hard to establish on degraded soil. Using grazed annual cover crops for a year or two to produce a layer of moisture-conserving organic mulch can greatly improve the success of a perennial seeding. Perennials to consider may be cool-season grasses (like friendly endophyte tall fescue, meadow brome, smooth brome, orchardgrass, low alkaloid reed canarygrass, or pubescent wheatgrass) warm-season grasses (like eastern gamagrass, big bluestem, or Indiangrass) legumes (like alfalfa). I believe the best success with a perennial is to plant a compliment to your existing pasture resources. For example, if you live in an area in which warm-season native grasses predominate, such as the Nebraska sandhills, then planting a cool-season mixture might be very useful for lengthening the grazing season, providing pasture earlier in spring than the native grass, and then providing pasture in the fall after cattle are brought home from rangelands. If you live in an area where cool-season grass like brome predominate, a warm-season grass mixture may provide higher quality pasture during the summer than the existing brome, which allows the brome to be stockpiled during the summer for a high quality fall pasturing.
Inoculate with mycorrhizal fungi. Mycorrhizal fungi are a class of fungi that colonize plant roots in a mutually beneficial relationship and send out very fine threadlike structures called hyphae that act like roots to bring water and nutrients back to the plants. This increased ability to access water and nutrients can greatly improve the success of most plants on difficult soils like sand that lack much ability to hold water or nutrients. Mycorrhizal fungi also exude a compound called glomalin that is nature’s most powerful soil aggregating agent, with the ability to dramatically improve the soil structure.
To till, or not to till? That is the question. We at Green Cover Seed are not fans of tillage. Tillage causes a loss of soil organic matter, leaves soil prone to erosion, destroys soil structure, and buries moisture conserving mulch. The vast majority of the effects of tillage are bad. However, if you are dealing with a shallow layer of sand (with no organic matter, no soil structure, and no layer of crop residue) over a layer of rich soil, it may be advantageous to do some form of deep inversion tillage to bring good soil up to the surface where it can be put to good use. Obviously, the soil would need to be buried shallow enough that it can brought up to the surface with the tillage implement, hence the need for digging a hole to determine the sediment depth. Some may also consider using a bulldozer and dump trucks to remove sediment from the field. Both ultra-deep plowing and sediment removal are extremely expensive, and it may just be a better route to use all the other methods described above to attempt to change that sand into soil. Removing the sediment is not only likely prohibitively expensive but will lower the elevation of the field making it more prone to flood damage in the future.
Learn to like sand. There are farmers all over the world raising exceptional crops on very sandy soils, particularly if irrigation is available. Sand certainly has its limitations as a growing medium, notably poor water holding and nutrient holding capacity, but it also has advantages, such as generally good rainfall infiltration, drainage and aeration, that can be valuable for certain high value crops like potatoes and melons, or for livestock pasture during muddy periods when heavier soils tend to become plugged up messes.
In summary, nature has dealt many of us a difficult situation, but it is also a situation that can be largely alleviated by some innovative management.
