CURRENT REGULATORY APPROACHES to minimizing nutrient risks associated with livestock operations focus on (i) improving on-farm manure nutrient management practices, (ii) reducing erosion and runoff of land application sites, and (iii) measuring performance by the degree of implementation of required best management practices (BMPs). All CAFOs, regardless of size, are required to develop and implement an NMP in accordance with the nine elements summarized in Table 1. The permitting authority evaluates compliance by reviews of annual reports and on-site inspections checking an individual operation's current management practices against those specified in the NMP (USEPA, 2004).
For large CAFOs, the USEPA (2003) has established effluent limitation guidelines specific to the NMP that require:
- Development and implementation of a site-specific nutrient management plan.
- Determination of application rates.
- Collection and analysis of nutrient content of manure, litter, and process wastewaters.
- Collection and analysis of representative soil samples for P content at least once every 5 yr.
- Maintenance of a no manure application setback of 30 m of cropland or 11 m of vegetated buffer from any down-gradient surface waters and potential connections to surface waters.
- Periodic leak inspections of equipment used for land application.
- Maintenance of on-site records for 5 yr.
The level of adoption of BMPs is commonly associated with improved water quality. However, the value of BMPs is site- and situation-specific. An understanding of the level of BMP implementation provides an indication of potential environmental benefits achieved. However, it provides an imprecise measure of the degree of effectiveness of individual strategies. For example, how can the benefit of a site-specific nutrient plan focused on cropping systems be compared with a nutrient plan targeting a modified feeding program that reduces nutrient excretion? Quantitative measures of performance of individual practices are needed for prioritizing the wide range of potential BMPs and for identifying when a desired environmental goal has been achieved.
Previous authors have used nutrient balance approaches to provide a measurement of environmental performance (Frink, 1969; Aarts et al., 1992; Lanyon and Beegle, 1993; Klausner, 1995; Watts et al., 1994). An integrated whole-farm approach allows comparison of both animal and crop nutrient management options (Dou et al., 1998) as well as a means of evaluating environmental performance resulting from alternative nutrient management strategies (Koelsch and Lesoing, 1999). The imbalance between total N inputs and managed outputs was observed to be 84% for a Pennsylvania dairy (Lanyon and Beegle, 1989), between 59 and 79% for 17 New York dairies (Klausner, 1995), and 86% on a typical Dutch dairy farm (Aarts et al., 1992). (Percentage is an indication of the portion of nutrients in the inputs that is not accounted for in the managed outputs.) A mass N balance by Smolen et al. (1994) for Texas (large beef population) and Adair (large poultry population) counties in Oklahoma suggested an annual N imbalance within these counties of 51% (12400 Mg) and 53% (2400 Mg) of all imported N, respectively. Watts et al. (1994) observed an imbalance ranging from 36 and 66% of all imported P within two Australian beef feedlots and supporting cropland representing 39 and 161 Mg (43 and 177 U.S. tons), respectively, of P added to the farms annually.
Several factors contribute to the large nutrient imbalance characteristics of many modern livestock operations. Yearling cattle retain only 11 and 16% of the N and P fed, respectively (Erickson et al., 1998), whereas swine retain only 40 to 55% of N and 20 to 50% of P (Korenegay and Harper, 1997), leaving most fed nutrients in the manure. Kohn et al. (1997) observed that the differences between a low and improved dairy herd efficiency resulting from feeding program changes produced greater overall reductions in N losses than efforts to reduce N losses from manure storage and land application. Dou et al. (1998) observed that fertilizer inputs accounted for only a small portion of the total N inputs to dairies, limiting the potential environmental benefits associated with improved manure nutrient management, which substitutes manure nutrients for purchased commercial fertilizer. The authors concluded that systems analysis, including analysis of feeding program and animal performance, identified potential management points for improvement in N efficiency not commonly addressed by conventional agronomic studies (Dou et al., 1998).
As livestock operations become more concentrated, more feeds are purchased from off-farm sources. Purchased feed has become the primary nutrient input to many modern livestock farms (Klausner, 1995; Lanyon and Beegle, 1989; Smolen et al., 1994). An upper limit to imported feeds is likely to exist for recycling manure nutrients within the available land base accessible to the livestock operation. Kohn et al. (1997) estimated this limit to be 70% of feed N from purchased feeds or legumes produced on-farm for dairy farms. Klausner (1995) further observed that as the land base decreases relative to animal numbers, the nutrient imbalance appears to be a larger fraction of the total N and P inputs to those farms. A review of nutrient balance for 33 Nebraska livestock operations noted that farm size and ratio of animals to land base provided little explanation of variation in N and P balances observed (Koelsch and Lesoing, 1999). Feed program and manure export practices were more significant indicators of nutrient balance variation.