Too much nitrogen in the soil

Asked June 23, 2016, 6:45 PM EDT

I believe I applied too much manure into my garden last Fall and now my crops are curling and shriveling up. What can I do to correct too much nitrogen in the soil? I will certainly not put any more manure in this Fall, but I hope my soil can recover for next Spring's planting. I have been told to use barn lime, mulch, or plant heavy feeding crops. I grow organically. The photos show tomato and bush bean.

Le Sueur County Minnesota

1 Response

Even though the manure is the cause of the problem, it’s not because too much was added. Instead, it’s due to herbicide carryover in the manure or other composted organic materials used in or on the soil. Unfortunately, this has been a widespread problem across the country for a number of years.

The underlying situation is that one of several agricultural herbicides against broadleaf weeds in such crops as a pasture and grain fields. (Such contamination has also occurred in commercially packaged composts and potting mixes.) When livestock feed on the grass or grain, these herbicides survive the trip through the animals’ guts and are excreted in the manure which is then composted. In order for the chemicals to be inactivated, the manure must be hot composted for a year before use in gardens.

Here are several helpful resources which describe how the damage occurred; how to verify the contamination via a simple bio-assay; and what you can do to remedy the situation.

- Page 3 of “Herbicide carryover in hay, manure, compost, and grass clippings” describes an easy bio-assay you can do: http://content.ces.ncsu.edu/herbicide-carryover

- Numerous images of various affected plants as well as informative text (via the menu at left of the page) including a bio-assay: (http://whatcom.wsu.edu/ag/aminopyralid/)

As a safety measure, I now suggest gardeners do a bio-assay prior to using any composted materials from other sources.