The use of irrigation systems to apply swine effluent and liquids from storage and holding ponds is a popular application method due to the labor savings, large volumes of liquid, and when applied close to when the crop needs the nutrients, the improved crop utilization of the nutrients in the manure. Anecdotal reports from producers using center pivot and other irrigation systems to apply swine wastes have reported incidents of crop damage. There are very few written recommendations in the extension literature on how to apply swine manure directly to crops without damaging the plants. Most recommendations are based on salt effects. However, the literature on the salt effects on crop growth is on long term reduction in crop growth from both soil salt concentration and irrigation water effects. These effects were determined by continual irrigation with known salt concentrations and the salt effects accumulating overtime. Usually salt in irrigation water is measured in electrical conductivity (EC). Aerial application of swine manure is a different situation than flood or furrow irrigation with salty water. Swine manure applications to a particular field may be done annually but not at every irrigation. In the areas of Nebraska where sprinkler applied swine wastes is practiced 30-year normal annual precipitation varies from 15 to 27 in. When salt is applied at moderate levels this is enough rainfall to flush salts below the root zone. Hence, long-term salt buildup is usually not a problem. The salt in manure is a consequence of the diet fed to swine and the natural internal metabolic processes. It can’t be reduced to zero. Swine manure contains more chemical compounds than salt and so there may be non-salt related phytotoxic effects. The concern by producers is the immediate damage to growing crops. Producers want to know how much effluent can be applied with the irrigation system at one time without damaging the crops. Application by center pivot may include the renting of an agitator to mix the manure liquids and solids. This means that dilution of swine wastes increases the cost of application due to the need for either multiple applications or longer application times to empty the storage facility. The objectives of this study were to determine the maximum EC of swine effluent that can be irrigated on corn and soybeans without immediate crop damage at several crop stages. Swine manure was applied in early July and toward the end of July. Corn growth stage was at V8 and V14. Soybean growth stage was at V3 and beginning flowering (R1). Therefore the results are most applicable to this period. Concern about May applications also exists, but there are no results to provide answers for early season application. The Electrical Conductivity of the manure is reported in units called mmhos/cm. Underbarn storage facilities may have manure in the 20 EC range, whereas an anaerobic lagoon may have an EC of up to 7 or 8. The research conducted here used manure diluted to achieve 0, 6, 12, and 20 EC. The application technique in the study kept the foliage wet for a minimum of 15 minutes and applied about 0.5 in. Duration of exposure is probably an important factor. The results reported here need to be interpreted in the context of the application system used. With that understood, manure in the range below 6 EC is probably safe for both soybeans and corn when applied in July. Dilution to that level would be preferred to higher EC values, although both soybeans and corn will tolerated the 12 EC manure with only minor yield losses. Corn yields were actually increased with all manure rates at the V14 application. Early season application should be avoided since plants are very sensitive and ponding or other concentration of liquids can cause damage to the roots as well as foliage. It would be prudent to try the application on a small area before applying to the whole field when making the initial application. Soybean leaf damage was evident a day after application. If the leaves are not severely browned, and the plant survives, the crop will recover and produce sufficient yield.
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