In recent years, many in the Midwest U.S. have experienced wetter-than-normal conditions, causing headaches for many area farmers. Flood conditions bring more issues than just moisture; saturated situations can cause contaminants, alterations to the physical soil profile and a severe loss of nutrients.

Contaminants

Depending on location and where floodwaters are rising from, soil contamination can be a serious condition. Contaminants to be concerned about are not only any waste or chemical scenarios but weeds as well. Stagnant waters can carry weed seeds and deposit them onto clear sites. This creates a lingering issue not only the season after flooding but for multiple seasons afterwards as well. Many weeds may germinate after a weed assessment has been completed during the flood, so it is imperative to continue to assess the weed population on a regular basis.

Waste and chemical contaminants are typically easy to identify, as many instances can be spotted clearly. Being familiar with your area can also provide a firsthand knowledge of what contaminants may be close enough to pose an issue if there ever is a floodwater scenario. Fuel and chemical storage would be the biggest issues facing most producers today, depending upon their site locations.

While not classified as a chemical contaminant, floodwaters can leave behind many different types of sediments. These different debris create not only a difference in the physical profile of soil but can create a difference in pH as well. Deep-sediment deposits should be spread across the field and worked into the soil to distribute as evenly as possible. Only after soil is worked should soil tests be performed to evaluate nutrient and pH levels to determine a fertilization strategy moving forward.

Nutrient loss

The first concern many think of when a saturation event occurs is the nutrient loss in the soil profile. Nutrient leaching is of great concern, but there are several ways nutrients are lost during wet conditions. Soil microbes will go through denitrification when underwater and devoid of oxygen for an extended period. This converts nitrate in the soil to gas, where it is lost as an available nutrient. This scenario also drastically decreases the microbe activity in the soil, leaving nutrient cycling and plant uptake to take the hit; when the microbe population decreases, the symbiotic relationship between them, and the crop planted, becomes depressed. This leaves the crops unable to absorb the nutrients left in the soil, causing delayed growth and often times stunting productivity.

Fallow syndrome

One of the biggest worries for producers is wondering when they will physically be able to get into their fields post-flood. If they cannot get in to evaluate and alleviate the situation, then the field can lay fallow. This creates a new host of issues to face once the field is habitable. Fallow syndrome can be characterized by uneven crop growth and phosphorus deficiency symptoms.

By leaving fields empty for a season, the arbuscular mycorrhizal fungi (AMF) population is affected. AMF form a cooperative relationship with 70%-80% of plant species. This fungal specimen grows throughout the different levels of the soil matrix, sharing water and essential nutrients with the host plant – in this case cash crops. These fungi also produce glomalin, a key binding agent providing adequate pore space to allow root growth, water access and air exchange. The relationship between AMF and crops is essential to maintaining a healthy soil profile; therefore, the fallow state can create a large deficit that can take years to renew.

Physical effects of fallow syndrome can be highly detrimental as well. Without a cover or cash crop to protect soil from the elements, the condition can go downhill rapidly. Erosion, compaction, crusting and sedimentation are physical difficulties that without a planted crop can become larger issues. Erosion can destroy the integrity of a soil profile quickly, which in turn can take years to replenish. Compaction and crusting make it difficult for root and upward growth to occur, causing delay in growth in the ever-important early stage of growing season.

Restoring the soil profile

The priority post-flood is to establish a starting point. Once all physical sediments have been distributed and mixed in, evaluations can begin. Soil is to be tested for pH and nutrient levels so an appropriate fertilization plan can be implemented. It is at this point that a crop plan can also be established and planted. Whether it be a cover crop or cash crop, it is imperative to get roots in the ground. These crop systems aid in nutrient cycling, soil aggregation and plant-microbe relationships, establishing continued improvement in the soil profile.

Choosing which type of crop to plant is driven by multiple factors. The largest of these is cost: seed cost, maintenance cost and potential income. Planting date and desired goals also point producers in specific directions on post-flood planting. When evaluating all points, it can become overwhelming to make a decision on which plan is best for each situation. Consulting an extension source can help guide producers in the correct direction.

When choosing legumes to be planted post-flood, know they will require a slightly different approach than others. Particularly when the flood situation is extended for several days at a time, the bacteria population that process nitrogen fixation becomes increasingly depressed. In turn, it becomes necessary to apply inoculants to provide the nitrogen fixation required by legume crops. To ensure legume crops fulfill their growing period, applying inoculants becomes essential.

Looking ahead

Coming off a record-setting wet year in 2019, many are looking for answers to get the most out of their acres in 2020. Many acres in the Midwest were left fallow last year, because producers were physically unable to get into the fields without the risk of severe damage. Looking forward to a new growing season, recovery and re-establishment of soil nutrients and soil integrity are the main concerns that will keep producers trending in a positive growing pattern.

While there are alarms that this year will be an exceptionally wet year as well, having an established plan and using resources available can aid in negating the stress of dealing with flood situations.