Goats Can Be Too Much of a Good Thing for Pastures

Dale Ritchey, a retired soil scientist, and Doug Boyer, a hydrologist at the Agricultural Research Service's Appalachian Farming Systems Research Center in Beaver, W. Va., and colleagues showed this in an experiment that also confirmed that–up to a point–liming the soil ameliorates the nitrogen “burn” from the urine, as well as the plant scorching effects of the urine's concentrated salts and organic acids.

They found that one or two urinations supplied enough nitrogen to actually help fescue grass growth: yields were up three to four-and-a-half times those from the soil cores with no urine added. Liming increased the yields even more. But the third application of urine was deadly. And the lime only made it worse.

The scientists collected 32 sample soil cores, complete with vegetation left in place, from an abandoned pasture typical of those farmers use goats to clear. Soils in these pastures in the Appalachian Region are usually acidic, infertile soils.

In a greenhouse, the scientists treated 16 soil cores with lime. Then 18 weeks later, they added one urine sample to most cores. Two weeks after that, they added a second urine treatment to 16 cores. Two weeks after that, they added a third urine sample to 8 of those cores. They left some cores without urine for comparison.

“Drainage water from the cores that had three urine applications had nitrate-nitrogen concentrations much higher than the safe limit for drinking water,” Boyer says.

“In soils not pretreated with lime, urine lowered soil calcium and magnesium levels and further raised the soil's acidity. And it raised levels of aluminum, which is toxic to plant roots. Soils pretreated with lime prevented these damaging changes, in a matter of months.” Boyer says. “This was especially true for the highest urine level. It seems that liming works more quickly as urine levels rise in soils. This adds useful information to the little we've known about the combined effects of liming and heavy urine levels in marginal soils. We had found earlier that liming can take several years to lower toxic levels of aluminum, for example. But in this study we found that urine-soaked soil can shrink that time span to 27 weeks.”

The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://soil.scijournals.org/cgi/content/abstract/72/3/626.

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