Virginia Karst Program - Living on Karst

Living on Karst

A Reference Guide for Landowners in Limestone Regions
Produced by the Cave Conservancy of the Virginias, June 1997

Fertilizers and Nutrients

Nutrients, including nitrogen, phosphorus, phosphate, and sulfur compounds derived from fertilizers and animal wastes, play a vital role in agriculture. Large amounts are used in residential areas as well. Over the years, fertilizers have contributed to increased farm production and more attractive lawns. If not managed carefully, however, commercial fertilizer and livestock manure are potential sources of nitrate/nitrogen in groundwater. Nitrate levels above federal and state drinking water standards have been found in the majority of wells and springs tested in some karst areas.

Excessive nutrients in drinking water can pose a health risk to young children as well as young livestock. Increased levels of nutrients can also add to water pollution by causing an overgrowth of algae and other vegetation, leading to a loss of beneficial oxygen in aquatic habitats and water supplies.

Testing the Soil

The first step before adding nutrients or fertilizer to your lawn, trees, or fields is to have a sample of your soil tested by the Agricultural Extension Service. This test will tell you which nutrients are already in the soil. You also should get an estimate of the soil thickness or depth to bedrock across the site by using a soil probe or similar device. When mowing, cut 1/3 of the height of the grass blade. Leave clippings on the yard as a natural fertilizer and mulch.

Improperly managed fertilizers can release nutrients into groundwater after a leak, spill, or over-application. Both surface waters and groundwater are less likely to be contaminated if appropriate fertilizer management and handling procedures are followed.

BMPs - Best Management Practices should be the basis for determining fertilizer and nutrient practices.

BMPs for Lawns and Gardens

Use yard compost as a natural fertilizer
Use fertilizer only when necessary
Follow the directions on the fertilizer label.
Select the correct fertilizer based on your soil test
Apply the correct amount - too much can damage fragile plant roots and groundwater.
Apply the fertilizer at the proper stage in the plant's life cycle

BMPs for Agricultural Enterprises

Apply fertilizer based on realistic yield or growth expectations of the crop to be grown.
Monitor nutrient levels of soil and plant tissue, as well as irrigation water, and springs or well water.
Determine and credit the contribution of non-commercial fertilizer nutrients from legumes, manure, and compost.
Identify the appropriate timing and application methods for fertilizer to reduce runoff and leaching losses.
Properly calibrate and operate fertilizer application equipment.
Evaluate field limitations based on environmental hazards such as sinkholes, highly erodible soils, shallow aquifers, shallow depth to bedrock, and nearby surface waters.
Consider soil moisture conditions, particularly if applying liquid fertilizer through an irrigation system (fertigation), and closely watch impending weather conditions.

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