Hurricane Ida: A Good Reminder to Keep Soils Covered

By Sjoerd Willem Duiker

Ida wreaked widespread havoc in the northeastern U.S., with reports of up to 11 inches dropped in southeastern PA on September 1^st. It is another wake up call to manage our soils so that they are protected and can take in high volumes of water. Most runoff and erosion happens during few events such as these so if your soil would sit bare at that time there would be large potential for runoff and erosion to happen. Because you never know when this event will occur, it is important to be always prepared and never let your soil sit naked, exposed, and hungry. If our farmland is managed well it can take in large amounts of water, even if it comes down fast and furious. On one dairy farm in Franklin County that is managed judiciously with continuous no-till, diverse crop rotations, and cover crops, we measured 27"/hr infiltration rate with an automated single-ring infiltrometer in a diverse cover crop mix planted after small grain, and no runoff in 1-hr long, 3"/hr simulated rain events. This kind of infiltration rate may not be achievable on every soil type (this was a well-drained shaly Berks silt loam), but just gives you an indication of what the possibilities are. Keys to maximizing infiltration and minimizing soil erosion are: 

1. Reduce soil disturbance. Loose soil is much easier dislodged than firm soil, and tillage also reduces aggregate stability while it destroys continuous macropores. It reduces the high-organic matter layer that accumulates in the soil surface over time in long-term no-till, and it breaks fungal hyphae and decomposing roots that favor soil aggregation. It also destroys the habitat of earthworms that live in vertical burrows that can channel water down quickly into the subsoil.
2. Keep soil covered. Raindrops from high-intensity storms are large and carry high impact energy. By keeping the soil surface protected with mulch or living plant cover we avoid soil sealing that leads to infiltration reduction.
3. Maintain the living root 24/7/365. Always try to have the drill in the field at harvest time. Soil biological activity is concentrated in the rhizosphere – a thin area around roots. This is where the microbes congregate, and the soil food web is most active. The roots do their own work by enmeshing soil and therefore improving soil aggregation, but the microbes and those feeding on them also help improve soil porosity and aggregation as well.
4. Vary crop types in the rotation or in mixtures. By using crop types thoughtfully, we can also help improve infiltration capacity and soil health over time. For example, perennial sod crops, especially mixtures of grasses and legumes, are a great way to improve soil aggregation and soil health in the rotation. Cover crop mixtures of tap- and fibrous-rooted crops do the same. Some crops such as corn add much crop residue to the soil, while others, such as soybeans don’t. Using this knowledge allows us to design a crop rotation to maximize soil health and infiltration capacity.
5. Avoid soil compaction. This year will be another test case for farmers’ ability to avoid compacting their soils during harvest season because of the wet soil conditions. As you can see in the picture accompanying this article, soil erosion and runoff is greater from compacted areas. I discussed strategies to avoid soil compaction in last week’s Field Crop News.

The impressive thing with sustainable soil management is that the farmer is benefiting both him/herself as well as the community at large. Our soil can absorb large amounts of water in a short time if managed properly, and then release it slowly to groundwater. This recharges soil water to carry crops through dry periods, but it also reduces flash flooding.