Soil erosion and water quality

The impact of soil erosion can be very significant not only in reducing soil productivity but also in deteriorating water quality. Sediment resulting from soil erosion is a major water quality pollutant in Iowa’s surface water bodies. Increased levels of nitrogen (N) and phosphorus (P) in surface waters are also leading contributors to reduced water quality.



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Water erosion on conventionally tilled field.

The N, and particularly P, can move from fields into lakes and streams when sediments are transported through surface water runoff and soil erosion. One of the many problems that is commonly associated with soil erosion and sediment is the impact of P- and N-rich sediment in causing eutrophication, or a significant growth of algae and other aquatic plants in nutrient-enriched waters that lowers dissolved oxygen levels. As these algae and other plants die and decompose, the result is fish kills, increased turbidity, and shifts in aquatic flora and fauna populations.

Improving Iowa’s surface water quality

One way producers can help improve surface water quality is by reducing soil erosion through adoption of conservation practices such as conservation tillage, no-till, buffer strips, terracing, and other management practices. Conservation tillage starts with an effective residue management program that protects the soil’s surface during the nongrowing season and minimizes water erosion. In no-till or conservation tillage, leave crop residue evenly distributed across the field behind the combine to provide a protective blanket of residue on the soil. Minimum crop residue cover left on the soil surface after planting in the spring must be at least 30 percent or more to effectively reduce rain-splash erosion.

Best management practices

In addition to implementing effective soil erosion practices, best management practices for nutrient management (manure and commercial fertilizers) are essential. Eliminate costly overapplication of crop nutrients when applying fertilizers and use a regimen of soil sampling, manure analyses, fertilizer and manure calibration equipment, plant testing, and proper timing of fertilizer application.

Other best management practices include using extended crop rotations and cover crops and setting realistic and profitable yield expectations. It is also important that producers learn more about using in-season fertility management techniques to monitor crop progress and nutrient requirements. In-season nitrogen application using the late-spring nitrogen test (ISU Extension publication PM 1714, Nitrogen Fertilizer Recommendations for Corn in Iowa) and cornstalk testing after kernel black layer (PM 1584, Cornstalk Testing to Evaluate Nitrogen Management) are two ways to evaluate season-long nitrogen management.

Summary

Controlling soil erosion and managing nutrients are the most effective ways of improving surface water quality, being effective environmental stewards, and preserving inherent fertility and an increased profitability.

This article originally appeared on pages 176-177 of the IC-488(21) -- September 23, 2002 issue.

Updated 09/22/2002 - 1:00pm