- - Soil Science

How Farmers Should Cope with Heavy Rain: Save the Soil

Soaking wet soil is a farmers’ worst nightmare. When heavy rain pours down on soil, it can be detrimental to crops after a long season of planting and growing.

In recent years, heavy precipitation, flooding, and droughts have become increasingly more common due to climate change. The midwestern region known as the Corn Belt, where the majority of the nation’s corn and soybeans grow, is flood-prone. Once heavy rain starts, it does not stop.

In late February, in just less than 48 hours, a month’s worth of rain poured vertically down the Midwest. The major flooding hit states like Indiana, Illinois, and Oklahoma—all the way down to Texas.

The heavy rain in Illinois, part of the Corn Belt, started to aggravate flooding. One agricultural economist who runs the farmdoc project at University of Illinois tweeted: “The #OhioRiver...is nearly 4.9 feet above flood stage and at its highest level since March 1997.”

Farmers in the Midwest hadn’t seen such high water levels in more than a decade. Just south of the Ohio River, Derek Wood, a farmer at Cherry Valley Farm in Arkansas, also experienced the same severe flash flooding.

“We usually start [farming] in the fields Mid-March. The flooding that we’ve received this time—we always have flooding every year—this seems much more than what we’ve had in the past. It’ll stay here for three weeks,” Wood said.

Three weeks is a setback in the spring farming season. Usually after a rainstorm, water will evaporate or infiltrate into the soil. But this time around, for many states in the region, water stayed still. Besides being an economic loss for farmers (floods can cost hundreds of thousands of dollars in damage) there are major environmental factors. When flash floods like this occur, farmers encounter a few big risks: waterlogging, soil erosion, and nitrate leaching.

Physical and Chemical Effects of Rain

Waterlogging happens when soil becomes saturated with water. After it rains, the top layer of soil is usually the most compact. When soil is soaked, clay can clog the soil pores near the top, especially in fields with weak soil structure. This prevents oxygen from diffusing to the lower depths, and that lack of oxygen in the soil can harm plants’ roots. Depending on how deep the roots are, they can start to dry up like prunes and eventually decompose. Just two years ago, farmers in the Corn Belt suffered waterlogging that left soil and cornfields bone-dry. In extreme water logging conditions like theirs, crops rot and die. But if the soil just becomes moist, crops generally can adapt to overcome waterlogging by relying on older roots closer to the surface to survive.

Soil erosion happens slowly, but at a continuous rate over a period of time. After a heavy rainfall, soil starts to spread out; soil structure is lost. Erosion depletes nutrient supplies or macronutrients like nitrogen, potassium, calcium, magnesium, and sulfur. This changes the soil content, soil texture at the surface, water-holding capacity, and pH levels. As the nutrients leave the soil, the soil becomes less fertile. As a result, both soil productivity and crop productivity decrease, because they lack the water, oxygen, and essential nutrients they need.

Nitrate leaching is a side effect of high rainfall. Nitrate is one of the most critical nutrients in soil, and when heavy rain is actively pouring down and flooding the soil, the nitrate sinks deep down into the ground, otherwise called leaching.

Salvaging the Soil

After a heavy rainfall or flash flood, farmers need to react in a timely manner. According to the Soil Society of America and American Society of Agronomy, soil can still be salvaged.

Farmers should begin by removing any debris around the affected area, such as rocks, branches, or sand. If the soil has eroded, tillage can help.

The goal of tillage in this case is to move soil downslope. The soil is lifted in areas where the slope is on an incline and deposited in areas where it is on a decline. This balances the soil levels out. Tillage can be enacted with several mechanic devices such as plows or air/grass seeders. If tillage does not work and help re-disperse the soil, the worst case scenario is that soil has to be physically removed.

The soil needs to replenish its nutrients. Soil microbes (bacteria and fungi) regenerate soil. One example are the fungi-growing arbuscular mycorrhizae. They penetrate the roots of crops. When the fungal biomass is consumed by other microbes, the nutrients are then released into the soil.t This is important so that when crops do eventually grow in the fields, good fungi is present.

Proactive Steps Farmers Can Take Before Flooding

While the weather is out of farmers’ control, there are steps that can help mitigate the risk to soil in the case of heavy rains.

  • Plant cover crops such as legumes (beans) or small grains that cover and protect the soil from erosion. A cover crop provides good ground cover and adds organic matter to soil while also stimulating microbial and fungal activity.
  • Contour plow, which means to plow or plant across a slope using perpendicular contour lines. This way, when rain storms happen, there are rills and gullies to help disperse the water and carefully settle into the soil.
  • Keep field drains clear to drain water after a flood, and make sure they’re kept in good condition.
  • Improve water infiltration to maintain the rate which water gets into soil. This also helps crops have more access to water, but also prevents soil erosion from stealing the nutrients. Organic matter addition and gypsum can help here.

“Maintaining a good soil structure is very important,” says Sarah Kerr from Farming for a Better Climate. Adding, “soil should have good drainage for surface water run off and root growth of the plants should be optimised which will help them.”

Although flooding is a major setback and problem for farmers in rainy regions across the country, there are some plants/crops that love lots of water and even thrive in wet soil, like asparagus, highbush cranberries, mint, and strawberries.