Concepts for Application and Utilization of CAFO Effluents with Subsurface Drip Irrigation.

Subsurface drip irrigation (SDI) can be successfully used for application of confined animal feeding operation (CAFO) effluents to agricultural fields with careful consideration of design and operational issues.  Primary advantages are that exposure of the effluent to volatilization, leaching, runoff into streams, and humans can be reduced while the primary disadvantages are related to system cost and longevity, and the fixed location of the SDI system.  The use of livestock effluent through agricultural irrigation systems can have positive or negative impacts on the environment, depending on the method and intensity of use.  The effluent can also be an inexpensive fertilizer resource for crop producers, providing nutrients in a timely fashion to the crop.  Lagoon-based livestock effluent as used through most irrigation systems is approximately 98% water and 2% solids. Historically, clogging of the emitters leading to reduced and nonuniform discharge has been the primary reason for microirrigation system failure, so it may seem ironic that this paper discusses using a particle-rich water source through SDI.  However, as it is with all microirrigation systems, the problem is attacked through the standard design and operational considerations: (1) Selecting and installing the proper system components; (2) Filtering the effluent effectively; (3) Suppressing biological growth and chemical precipitation; (4) Flushing materials that may accumulate in the distribution systems, and (5) Monitoring system performance to assure that partial clogging is treated before it becomes catastrophic.  In addition to the conceptual discussion, the results from two research studies will be briefly discussed. An engineering study with beef feedlot effluent has indicated that driplines with discharge of 1.5 to 2.3 L/hr-emitter can be used successfully with little clogging.  SDI tended to have greater corn yields and better nutrient utilization than low-energy precision application (LEPA) center pivot sprinklers when using swine effluent in a two-year agronomic field study.