Maintaining Ground Cover

The US Environmental Protection Agency (EPA) in part defines a confined animal feeding operation (CAFO) as a site that has animal density so high that vegetation can not grow for a period of 45 days or more per year.  Thus, if vegetation is completely gone on a given site,  even if the animals are outdoors, the site is a CAFO and subject to regulation as an intensive production site.  Therefore, for a well-managed outdoor unit, the ground cover should be maintained.  

The US EPA rules do not say how much ground cover is sufficient.  Would 75% ground cover be sufficient?  How about 50 or 25%, would those constitute ground cover?  How would the regulators view animal densities when native grasses is the normal vegetative cover but at only 10% ground cover (in a desert or near-desert, for example)?  These questions have not been answered, but rather than deal with regulatory requirements, it would be better to have a different standard. 

Our proposed standard for outdoor units is that they do not allow nutrients to leave the site either through run-off or seepage into the ground.   To protect from run-off, a border strip can be used around the site.  We found that a 100 foot (~30 meter) vegetative border will catch run-off on a relatively flat site.  Maintaining ground cover at 50% on average on a site, depending upon many factors, will collect nutrients that seep into the ground, leaving the area 24 inches (~61 cm) free from pig nutrients.

To maintain ground cover requires four primary inputs:  soil, water, nutrients and vegetation.  In dry climates, one has better control over the water application by use of irrigation.  Here is a picture of a center pivot over an outdoor pig site. 

  Note the gestation hut on the right side of the center pivot water sprinkler.

Roads also have to be considered.  Here is an outdoor pig breeding area (on the left) that has a road between adjacent pastures on the right.  A lack of ground cover on the roads is less of a problem because (a) roads take up a small area of the total site and (b) animals should not be there depositing nutrients.

We found it much easier to maintain ground cover on the farrowing paddocks than the breeding or gestation paddocks.  On farrowing paddocks, sows are full fed and therefore they remove less ground cover.  At 7 sows per acre and using the paddocks 4 weeks on 2 weeks off,  farrowing paddocks actually had greater ground cover after a year than at the  start of the period. 

Below is a gestation pasture with zero ground cover.  The feeding strip within the pen is the first area to lose ground cover and the region within the paddock with the greatest nutrient build-up.

The paddock below has considerable ground cover (~90%).  Note the center pivot sprinkler in the back.

The paddocks below radiate out from a center hub area.  Note the center paddock contained 7 gestating sows per acre.  The pasture to the right had 14 sows per acre.  Note the rapid loss of ground cover on the pasture on the right. 

Note from the pictures taken from an airplane, that pastures with 14 sows per acre have lost considerable ground cover compared with pastures with 7 sows per acre.

Areas in the paddock that lose ground cover include the feeding area, the hut area, the wallow area and paths that pigs walk.  The wallow area loses all of the ground cover, but we have found less nutrient build-up there than in the feeding area.  Sows apparently urinate and defecate in and near the wallow, but not too frequently compared with other pen regions (such as the feeding area). 

When sows first enter a paddock, the feeding area is not damaged.

Note the road to the left and the feeding area along the road.  

A model of a pasture with a border to catch nutrients that might run off.  The border is shown in green.

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