Iowa’s farmers use a variety of conservation practices to ensure the best use of soil and water resources to reduce nutrients in water and ensure their long-term ability to farm. What is best for a particular farm depends on many factors, so a variety of practices are used to maximize results.
Some practices are considered every year and take place in the field. Others provide long-term water quality benefits and only require maintenance to keep working. These practices may be installed within the cropped area of the field or at the edge of the field, depending on the practice.
Cover crops have been identified as a best management practice to improve water quality by retaining nutrients on farm that may otherwise leave the field via erosion, runoff or leaching.
Cover crops can be defined as non-commodity crops planted into standing cash crops or bare fields following harvest, with the intent of increasing farm profitability through increased yields, reduced fertilizer costs and reduced weed management costs.
There are so many! Based on several years of research among the agronomist community, the following list equates to the many reasons cover crops are great:
Improves soil quality
Retains soil nutrients
Breaks up soil compaction
Increases organic matter
Cover crops need to be planted early enough in the fall to allow for germination and growth before frost (aerial seeding can help with this), and they need to be terminated in the spring to prevent interference with the next crop. However, this can easily be accomplished through grazing, haying, tilling, spraying or a combination of these methods.
No-till farming greatly reduces soil disturbance, which in turn reduces soil erosion, builds soil organic matter and helps reduce phosphorus entering waterways. Soil and crop residues are left undisturbed between harvest and planting, other than nutrient injection.
Strip-till is a modified form of no-till where tillage is limited to a narrow zone in which next year’s crop will be planted. Soil disturbance is greatly reduced compared to conventional tillage. Strip-till reduces soil erosion, builds soil organic matter and helps reduce phosphorus entering waterways.
Extended crop rotation is a planting cycle of different crops, such as grasses, legumes, small grains, corn and soybeans, to help improve soil health and decrease insect and disease pressure. The increased number of months that soil is covered with actively growing plants is the benefit to water quality and soil health.
The fertilizer rate, timing, placement and the form of nutrients applied are managed to maximize the nutrients that are taken up by the crop while minimizing the loss of nutrients – particularly nitrogen and phosphorus – to surface water, groundwater or to the atmosphere.
Drainage water management or controlled drainage is the use of a control structure to manage drainage of water from fields throughout the year. The practice reduces the loss of nitrates and can increase crop yields in some years.
Bioreactors redirect tile water to an underground bed of woodchips where nitrate is removed naturally by microorganisms. Bioreactors can reduce nitrates by an average of 43 percent. Vegetation on top of the bioreactor can provide other benefits, such as wildlife habitat.
A water level control structure that is installed near the outlet of a tile line, but within or immediately adjacent to an existing stream buffer, is a saturated buffer. A portion of the water is diverted into a tile line parallel to the stream and within the buffer. Excess nitrate in the tile flow is converted to harmless nitrogen gas in the soil of the stream buffer due to organic matter and low oxygen.
Buffer strips of native prairie grasses are placed on the contour in crop fields, combined with filter strips of prairie grass strategically placed where runoff leaves the field. This practice results in large improvements in runoff water quality with only a small (~10 percent) portion of the field taken out of row crop production.
Stream buffers are grassy or native vegetation adjacent to streams that trap sediment from surface runoff. This reduces phosphorus entering a waterway, filters nitrogen as it moves in groundwater through the soil, stabilizes stream banks and provides habitat for wildlife.
Constructed wetlands are shallow vegetated pools that help filter nutrients, especially nitrates, control flooding and provide wildlife habitat. They have been shown to improve water quality by reducing nitrogen by an average of 52 percent. Actual nitrate removal depends on rainfall, with greater removal in drier years and lesser removal in wetter years. In addition to removing nutrients, wetlands provide habitat, recharge groundwater, reduce flooding downstream by storing runoff and can provide recreational opportunities.
Grassed waterways are areas within fields that are maintained in grass to address areas of concentrated water flow. Grass waterways prevent soil erosion and associated phosphorus loss.
Terraces are earthen embankments, ridges or ridges-and-channel built across a slop to slow water runoff, therefore reducing soil erosion and phosphorus loss.
This practice is very similar to a terrace, but water and sediment control basins are generally short and straight, are placed at the lower end of slopes and do little to reduce slope length. They may be used to help control gully erosion and/or to prevent sediment accumulations farther downstream.