Developing a Management Plan for Irrigation Runoff

Water Management Guidelines for Nursery/Floral Producers

Floral and nursery producers rely heavily on fertilizers and pesticides for producing high quality crops. Runoff from rain and irrigation can concentrate these chemicals in small collection points where they can enter surface or ground water.

Injurious effects such as fish kills, reproductive failure in birds and acute illness in humans and animals have been correlated with chemical contamination of water. Since over half the U.S. population relies on underground sources of drinking water, the potential for these chemicals entering surface and ground water poses a serious threat to the environment.

Recently, many growers throughout the United States have had to face the challenge of developing a management plan for handling contaminated irrigation runoff. This is no small task, considering that non-compliance with state and federal water quality standards can result in fines of up to $10,000 per day per discharge site. Unfortunately, few growers take the time required to develop such a plan until their operation has been found in violation. When this situation occurs, time is usually critical, and costly decisions are often made in haste.

A management plan is relatively inexpensive to develop, and implementation costs can be phased in over a period of time. These plans can be extremely flexible, and as simple or as complex as needed. Regardless of how extensive, your plan will be a clear indication that you are working toward managing runoff and will serve as a useful tool in developing control measures.

Monitoring Water Quality

Federal and state standards for irrigation runoff are not always easy to identify or understand. The Environmental Protection Agency has established basic water quality guidelines, and in many areas this agency is responsible for regulating surface and groundwater for the state. In some states, however, water commissions, boards and districts serve as the primary regulatory agencies.

The first step in developing a management plan is to determine what standards apply to your location(s). Direct inquiries through your county Extension office, commodity association or Soil Conservation District.

Once you have this information, it is advisable to submit runoff samples for analysis. A simple test for nitrates, as well as other nutrients, is usually inexpensive. A complete analysis, including pesticides, can be costly.

If you decide to conduct a thorough analysis, first inventory the chemicals used in your operation and then determine the chemicals to include. Be aware that the sampling technique, as well as the analytical methodology, can both affect the results. Consult your state water testing lab or state chemist if in doubt.

After reviewing results from these tests, as well as local water quality standards, it should be apparent if you have a problem or not. Excessive nitrates and phosphorus are the most common problems. Check pesticide concentrations carefully to determine if any are above acceptable limits. Monitor on a regular basis and maintain careful records to track water quality.

Developing Cultural Practices

Many of the production techniques used for floral and nursery crops can be easily modified to reduce the potential for contaminated runoff. Most of these decisions will have to be made on a case-by-case basis, but the following are some general suggestions that may be implemented.

Capturing and recycling runoff can be very expensive and requires careful management. Toxic levels of salts and pesticides can accumulate in surface basins and careful monitoring is essential. Many operations must also be equipped to capture up to the first 2 inches of runoff from rainfall.

Improved irrigation management reduces runoff by reducing the volume of irrigation water used. Therefore, optimizing irrigation frequency is important. Also, drip irrigation is much more effective in reducing the volume of water used than overhead systems.

Optimizing fertility regimes means reducing excessive fertilizer applications, an important means of managing runoff. Carefully evaluate the role of soluble and slow release fertilizers, as well as the sources of raw materials from which they are formulated. Determine the fertilizer concentration that provides optimum plant quality.

Reducing pesticide applications dictates that you apply pesticides as needed and eliminate routine or maintenance programs. Rely on close inspection and scouting to determine when pesticides are to be applied. Be familiar with chemicals before using them (read the label) and stay at the low end of recommended rates when possible. Alternate pest control products to avoid insect resistance and try to use resistant plant varieties if available.

Improving application techniques makes the most of the chemicals you apply. Direct pesticide applications to the target area using as precise of a method as available. Be sure all sprayers are calibrated correctly and that chemicals are mixed accurately. Avoid spills and back siphoning into water supplies. Dispose of empty containers and chemical wastes properly. Many of these activities are probably already a part of your cultural program, but document them carefully in the management plan, along with those changes to be implemented.

Categorizing Pesticides

The Soil Conservation Service has developed a data base that estimates the potential risk of various pesticides to water resources. Although these figures shouldn't be considered as precise, they can be used as a guide for developing a management plan. The following factors were considered in classifying pesticides:

Formulation type The long-term (weeks to months) life of a pesticide is a function of its physical properties and persistence, but its initial life (hours to days) is strictly a function of its formulation. For example, about 30 times more wettable powders than emulsified concentrates will be lost if both are applied and are immediately subjected to rain or irrigation.

The solubility of pesticides in water at room temperature is given in parts per million (mg/1). This is the solubility of pure active ingredient and not the formulated product. Solubility is a fundamental property of a chemical and strongly affects the ease of washoff and leaching through soil. In general, pesticides with solubilities of 1 part per million or less tend to stay at the soil surface and are washed off in the sediment phase of runoff.

Half-life, given in days, is the time required for pesticides in soils to be degraded so that their concentration decreases by one-half. Pesticide degradation can be fairly accurately described by assuming that each successive half-life decreases the pesticide concentration by half. For example, a period of two half-lives reduces a soil concentration to one-fourth of the initial amount. "Persistence times," often reported in scientific literature, are the times required for a pesticide to degrade to the point that it is no longer active.

Soil sorption index is measured by the Koc value. The Koc measures a pesticide's tendency to be strongly attached, by chemical or physical bonds, to soil particle surfaces. Higher Koc values (1,000) indicate a stronger attachment to soil and a lesser tendency for the pesticide to move, except with sediment movement. Conversely, pesticides with lower Koc values tend to move with water and have a potential for deep percolation below the root zone or being carried away in runoff water.

Runoff potential indicates the tendency of a pesticide to move with sediment in runoff. A large rating means the pesticide has a high tendency to move with sediment, while a small rating means the pesticide has a low potential to move with sediment. The leaching potential indicates the tendency of a pesticide to move in solution with water and leach below the root zone into deep percolation. The ratings of large, medium, small and total, shown in table 1, use describe the potential for leaching. A large rating means the chemical has a high potential for leaching. The total use rating means the pesticide shouldn't leach with percolating water.

Unfortunately, little is known about the leaching capacity of most pesticides in soil mixtures or soilless growing media. Since a portion of applied pesticides will first move through these substrates, it is important to consider their interaction.

It is safe, however, to assume that producers should try to reduce the application of pesticides with high surface loss and leaching potentials. This is not to say that these chemicals should be eliminated from the inventory, but that their use be limited to an "as needed" basis. This information, along with the Soil-Pesticide Interaction Ratings Matrix, is available from the Soil Conservation Service and can also be used to determine the overall potential for pesticide loss to surface runoff or leaching.

Common Sense is the Key

Many aspects of dealing with runoff are really nothing more than common sense. But organizing your thoughts in a water management plan can greatly assist in identifying where more than just good judgement may be required.

Water quality is a sensitive, emotional issue that is going to become increasinly importance in the next few months. A proactive approach in developing sound management practices for your operation now may prove to be a much more efficient use of time than responding to a crisis situation later.


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