Improving Manure Nutrient Application in Karst Topography (CIG Summary)

Project Title and Full Report Link

Demonstration of Enhanced Technologies for Land Application of Animal Nutrient Sources in Sensitive Watersheds
Entire Report (PDF file, 1.5 MB)

Project Background

Land application of animal manure has been implicated as a contributing factor of non-point source pollution. The application of these manure nutrient sources are often made without adequate knowledge of its nutrient content, resulting in application rates far in excess of crop removal. In addition, application methods have lead to inefficient use of manure nutrients and are pollution potentials. Consequently, residual fertility has increased, and so have N and P leaching from soil environments.

Illustration of environmentally sensitive features in karst topography

Several pieces of legislation have been enacted to limit non-point source pollution including the Clean Water Act of 1972 (Public Law 92-500) and the Safe Drinking Water Act of 1974 (Public Law 93-523). The result of these legislative acts is that the USDA-NRCS has been tasked with carrying out training for, and implementation of nutrient management plans (NMPs). To develop a NMP, a manure sample must be collected and analyzed for total nitrogen (TN) and total phosphorus (TP) on an annual basis. The justification for requiring manure samples in NMPs is that published manure nutrient characteristics show significant variability as far as actual concentrations (Dou et al., 2001; and Lindley et al., 1988).

Because laboratory analysis of submitted manure samples can require up to two weeks, it has been suggested that on-farm methods for determining TN and TP would allow producers to rapidly assess concentrations of nutrients in manure for calculating application rates. Although rapid methods exist for determining TN and TP (Cheschier, 1985; and Van Kessel et al., 1999), their use has not been widely adopted. A rapid on-farm method for determining TN and TP in swine slurry has been proposed by Higgins et al. (2004a,b), to provide producers with a means of predicting manure TN and TP to calculate application rates to meet crop and NRCS-NMP requirements. However, even if manure samples are collected and nutrient determinations are made, an obstacle for producers is how to alter land application rates, where to vary rates, and how to apply manures effectively.

Previous work suggests that surface application, in contrast to sub-surface injection, may result in elevated odor levels and volatilization of ammonia (Jokela and Côté, 1994). Pain et al. (1991) demonstrated that subsurface manure injection reduces odor emissions by up to 80%. Misselbrook et al. (1996) reported that subsurface injection reduced ammonia volatilization by up to 79% on grasslands when contrasted with surface application. The resulting quantity of nitrogen available for crop growth is significantly reduced (Schmitt et al., 1995). Manure applied to soil in addition to fertilizer N is a significant source of excessive soil NO3-N (Angle et al., 1993; Jokela, 1992). There is evidence that manure increases NO3-N leaching compared to fertilizer N applied at equivalent nitrogen rates (Jemison and Fox, 1994; Roth and Fox, 1990). Because most NMPs are based on plant N requirements, this invariably means that P is over-applied relative to needs. Although many soils have considerable P sorption capacity, residual inorganic and organic P will build up with time, resulting in increasingly greater opportunities for P to leach and/or be carried to sensitive waters by surface runoff. Once soil test P values exceed crop requirements, the potential for P loss far exceeds any agronomic benefits (McDowell et al., 2002).

Recent work suggests that surface application of manure to pasture lands can make grasses less palatable to animals, and may create disease and pathogen problems. Warner and Godwin (1988) have shown that injection prevents the risk of crop contamination and pathogenic activities. Manure injection or incorporation provides more available nutrients to the plant (Schmitt et al., 1995). Injection was determined to cause grass damage as a result of soil disturbance in two investigations (Hann et al., 1987; and Warner and Godwin, 1988). Alternately, Hultgreen and Stock (1999) found a yield increase associated with manure injection and incorporation. Objectives

Goal and Objectives

The major issue with respect to watershed protection is how to manage manure application in ways that are not detrimental to water, soil, and air quality. The goal of this project was to demonstrate state-of-the-art nutrient management technologies and application practices for the purposes of educating producers and custom waste applicators. These techniques enable producers to maintain crop yields while increasing nutrient utilization, and reduce the potential for leaching and off-site movement of nutrients. This project was accomplished by completion of the following objectives:

  • Demonstrate a rapid on-farm model for determining total N and P

contents using historical manure data and solids content.

  • Demonstrate the efficacy of guidance aids and map-based manure

application to reduce the potential for offsite nutrient movement in environmentally sensitive areas when used in conjunction with subsurface and aerated injection application systems.

  • Demonstrate the use of variable-rate manure management and real-time

solids content sensing for injection application systems.

  • Quantify the environmental benefits and costs associated with

producer adoption of one or more of these technologies and management practices.

More Information

Stephen Higgins
Biosystems and Agricultural Engineering
128 C. E. Barnhart Building
University of Kentucky
Lexington, KY. 40546-0276

This research summary was prepared with the assistance of William Reck, USDA NRCS