Erosion can be a very gradual process. Naturally, erosion occurs everywhere. Energy in rain drops or wind detaches particles at the soil surface, then moves these mineral and carbon particles downslope or down-wind to another location.   In the Great Plains and further west, this energy is most often provided by the wind. But in the east, including Kentucky, the energy is provided in the form of raindrops.  

When a raindrop hits the soil surface, weakly bound soil aggregates break into smaller particles, and some particles are dislodged. These smaller separate particles are then suspended in the surface runoff and will move across the surface with water once the precipitation rate exceeds the soil’s ability to infiltrate the rainfall. When this occurs, agricultural runoff (moving surface water plus dislodged soil particles) is produced. Importantly this runoff contains soil organic matter and valuable nutrients.

Accelerated soil erosion remains a serious problem around the world. Indiscernible soil losses in row crop fields can occur after even a small rainstorm. On fields with steeper slopes, soil losses due to erosion will increase. These losses can add up, with time, to tons of soil. One inch of soil loss represents approximately 167 tons of topsoil per acre and will require at least 30 years to replace. 

An acceptable soil loss rate has been developed by the USDA NRCS and can be calculated for different geologic settings. For most deep, agriculturally productive soils, an acceptable loss has been estimated to be 2 to 5 tons per acre.   Across the United States, farm fields are losing soil 10 times faster than the rate of natural replenishment from the weathering of soil parent materials. Each year, erosion costs the United States about $40 billion and costs the world about $400 billion. About 60 percent of the soil that is eroded ends up in rivers, streams, and lakes, making waterways more prone to flooding.  

In Kentucky, all drainage ways flow to the Gulf of Mexico, where the agricultural runoff negatively impacts the annual $2.8 billion fishing and $20 billion tourism industries. There are several in-field management practices that have been implemented by many Kentucky farms to reduce erosion. Conservation tillage practices (i.e., no-till) reduce erosion potential by maintaining intact soil aggregates, which improves infiltration. Leaving crop residue on the field after harvests will protect the soil surface from raindrop impacts that can disaggregate soil particles. 

Keeping growing vegetation in the field year-round (i.e., cover crops) can also help hold the soil in place during precipitation events. All these practices have been promoted and been demonstrated by the USDA NRCS to be beneficial across the United States. However, even if these practices are adopted, that does not guarantee that an erosion event will not occur.

In partnership with the University of Kentucky College of Agriculture, Food, and Environment, Kentucky Geological Survey, and USDA NRCS, the Kentucky Soybean Board, several Kentucky farms, and the Kentucky Agricultural Development Board initiated an edge-of-field (EOF) water quality monitoring project to measure the nutrients and soil that are lost during agricultural runoff events. 

 This is part of a national effort by the USDA NRCS as well as other interested conservation organizations to evaluate the effectiveness of agricultural Best Management Practices like reducing tillage and using cover crops. Nationally, we are aware of 15 states that are conducting EOF monitoring, including Alabama, Arkansas, Colorado, Indiana, Iowa, Maryland, Michigan, Minnesota, Missouri, New York, Ohio, Vermont, Washington, and Wisconsin.

Within Kentucky, we have 29 active monitoring stations, including 22 stations on agricultural fields and 7 stations on Agricultural Conservation Easements that have been converted from row crops to wetlands. Collectively, this program is called Blue Water Farms. Our oldest stations have collected data for 5 years, while the most recently established stations just completed the second year of monitoring. Each station monitors a small watershed, 3 to 15 acres, within a row crop field or forested area and has instrumentation installed at the field’s edge - a precipitation gauge, a flume that measures the quantity of agricultural runoff leaving the field, and an automated water sampler that collects agricultural runoff samples to determine how much soil and nutrients are lost. 

These systems are managed by dedicated personnel who work with cooperating land managers to record inputs and cropping management system practices. After each precipitation-driven runoff event, they collect the samples taken by the automated water sampler at each monitoring station.

There was a summer, 7-inch rainfall event on a growing, no-till soybean crop that caused very little erosion (0.2 tons per acre).  However, a winter 2.2-inch rainfall event resulted in a 9-ton per acre soil loss despite the presence of the cover crop. This latter event demonstrates how a significant soil loss can occur, despite conservation efforts.  

Heavy summer rainfalls can result in very little erosion when an actively growing soybean crop is in the field, the soil is relatively dry, and both crop canopy cover and underlying corn residue levels are high. However, in the winter, even when the field has a late-season cover crop on it, a smaller rainfall on already moist soil can lead to gully erosion and much greater soil loss.