Rick Cruse & Mike Castellano- Iowa State University
Healthy soil is the foundation for life. Soil is the world’s largest water purifier, nutrient recycler, and food-producing resource. The capacity of soils to meet these needs varies across the landscape. All soil is not the same. Some soils have low capacity for filtering water, recycling waste and producing food while others are very effective at one, two or all three of these services.
However, with few exceptions the most effective and efficient part of soil for supporting these processes is the surface layer, or what soil scientists call topsoil. Topsoil is critical for human survival but exceptionally vulnerable to degradation from natural and especially anthropogenic influences.
Erosion is the most threatening soil degradation process. Thinning of topsoil negatively impacts a range of ecosystem services including food production. Global studies suggest soil loss rates must generally be limited to about 0.1 mm per year if current food production potential is to be sustained. Limiting loss to this level while maintaining agricultural operations is not an easy task.
Observation of such low levels of erosion can be an even more difficult task. Yet, the first step towards implementation of conservation practices is awareness of a problem. And the combined effects of awareness and self-interest can lead to rapid adoption of soil conservation practices.
To create awareness of soil erosion, Iowa State University created the Daily Erosion Project: (https://www.dailyerosion.org/ ). The Daily Erosion Project uses remote sensing technology and proven soil erosion modeling science, the Water Erosion Prediction Project model (WEPP), to make more than 220,000 daily soil erosion estimates across Iowa with comparable measurement density in large sections of four other states. Soil erosion estimates are driven by soil type, hill slope characteristics, land management and rainfall estimates every two minutes.
Figure 1. Daily Erosion Project (DEP) estimated hill slope soil loss in mm across Iowa for January 1, 2018 – December 22, 2018, which was a year of particularly high rainfall rates and intensities.
Estimating soil erosion rates across large regions is quite challenging but necessary for identifying soil damage and targeting remedial measures and future conservation practices. Factors affecting soil erosion are dynamic in time and space. Every hillslope is unique with specific slope steepness, shape and slope lengths; soil types and properties vary continuously across the landscape; farmers use different crop and soil management practices in different fields; and rainfall is highly variable in both space and time. As one might expect, soil loss across a region (e.g., Iowa, USA in Figure 1) is highly variable.
As farmers and natural resource managers use the Daily Erosion Project to visualize erosion across space and time, the urgency of soil conservation is brought to focus. Rendering the soil surface bare and unprotected from raindrop impact is the single most problematic practice driving accelerated soil erosion rates. One meter of rainfall, an annual amount increasingly observed in the US Corn Belt for example, impacting 10 hectares of soil surface can have as much energy as 1.1 tonnes of the explosive, TNT. Crop residues and living plant covers can reduce soil loss to levels much closer to natural conditions. Quantifying rates of soil loss rates in time and space is a major step in targeting and implementing practices that are effective at conserving soil while producing crops.