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Selection of manure storage type has a significant influence on the Whole Farm Nutrient Balance (WFNB). This decision also is a controlling factor in a farm’s level of “accessible” nutrients over the life of the storage. Thus selection of storage type will have a long term impact on the manure nutrient value. In addition, nitrogen not accessible from a storage system is likely lost into the environment, adding to the environmental risk. Less accessible phosphorus from an anaerobic lagoon generally presents less of an environmental risk but can be a significant lost opportunity for reducing farm fertilizer costs.

Figure 1. Whole Farm N Balance vs. Type of Storage.

Nitrogen Whole Farm Balance

Farms with a below barn pit storage demonstrated the lowest nitrogen imbalance (1.4 to 1 average). Slightly higher average nitrogen imbalances (1.5 to 1) were observed for exterior manure storage (earthen basins and formed manure storages). Anaerobic lagoons (combined treatment and storage functions) exhibited the largest average imbalance (1.8 to 1). Statistically, none of the differences were significantly different primarily due to the few anaerobic lagoon data points and the substantial variation in values observed for anaerobic lagoons.

The differences in means suggest that additional nitrogen may be lost from uncovered anaerobic lagoons to the atmosphere (assumed, not measured). The potential also exists for some leaching of nitrogen from soil lined earthen structures. High nitrogen losses are commonly associated with anaerobic lagoons. In fact many lagoons have been installed for the purpose of “disposing” of nitrogen at a time when air emissions were less of a concern.

Phosphorus Whole Farm Balance

The average phosphorus balance is reasonably similar for below barn pit (1.4 to 1) and exterior storages (1.2 to 1). With reasonable agitation equipment, most phosphorus is removed annually from these storage types for land application. Anaerobic lagoons exhibit a higher average phosphorus imbalance (2.3 to 1). Statistically, none of the differences were significantly different primarily due to the few anaerobic lagoon data points and the substantial variation in values observed for anaerobic lagoons.

The possible difference is likely a result of phosphorus settling to the bottom of the lagoon where it is not recovered during routine pumping. This unrecovered phosphorus represents a lost opportunity for the farm, and creates a need to purchase more commercial fertilizer phosphorus for crop production. Significant amounts of the settled phosphorus may be recovered if occasional dredging or pumping operations are used to remove sludge accumulations. However, utilization of multiple years of P accumulation in a single year when sludge is harvested can present a challenge.

Results of On-Farm Measurement of WFNB

2006 Results - Appendix A

2007 Results - Appendix B

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Authors: Rick Koelsch, University of Nebraska; Alan Sutton, Purdue University; and Joe Lally, Iowa State University.

This project was funded by The National Pork Board Project

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