Saturday, 15 July 2006
170-10

Nutrient Movement below Concentrated Animal Feeding Operations.

Gary Pierzynski1, Thomas M. DeSutter2, Grace Vaillant1, and J. Ham1. (1) Kansas State Univ, 2004 Throckmorton PSC, Dept of Agronomy, Manhattan, KS 66506-5501, (2) USDA-ARS National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011

Significant amounts of N and P are used in animal production and the fate of those nutrients in manure is of environmental concern. In concentrated animal feeding operations, manure can be handled in a number of ways. This paper will focus on nutrient movement below animal waste storage lagoons (swine and cattle) and open-air cattle feedlots. Separate studies evaluated seepage rates in lagoons and, even with relatively small seepage losses (< 1mm/day), a significant amount of nutrients can pass through the bottom of the lagoon. In the case of cattle pens, deposition of manure by the animals provides a relatively constant source of nutrients. Population density, precipitation, and frequency of pen cleaning determine the total nutrient load and potential downward movement. Soil cores were collected from beneath a number of animal waste lagoons and cattle pens in feedlots. Soil samples were analyzed for total C and N; extractable ammonium, nitrate, and P; and pH. Evidence of N movement was found up to 2 m below waste lagoons and the majority of the N was in the ammonium and organic forms, as would be expected with the anaerobic conditions (Figure 1A). Evidence of N movement was also found to a depth of 2 m below cattle pens and high nitrate concentrations indicated that a substantial amount of nitrification had occurred (Figure 1B). The soil pH profiles indicated a high (7.5 to 8.5) and uniform pH with depth for lagoons and a strong zone of acidification corresponding to the zone of nitrate accumulation for the cattle pens. The pH at the surface of the pens ranged from 7.5 to 8.5 and decreased to as low as 5.5 at a depth of approximately 75 cm before returning to the high values at greater depths. The high pH values at the surface reflect the use of calcium carbonate in the animal diets. Extractable P concentrations were elevated to depths of up to 2 m beneath the lagoons but only up to 50 cm beneath the cattle pens. Little evidence of C translocation was found beneath the waste lagoons.


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