Thanks for answering!
Although I coudln't find an MSDS for the brand of fertilizer you gave me, I did find one for a very, very similar product, so according to the MSDS (material safety data sheet) for Milogranite Organic Nitrogen Fertilizer which can be found here: http://www.milorganite.com/about/material_safety_data_sheet.cfm
"Some coprophagic canines (fecal eating dogs) may transfer their fecal attraction to Organic Nitrogen fertilizer, rip open bags in storage and over eat. A dog may be sick for 24-38 hours, beginning with vomiting that can lead to dehydration, incontinence, atrophy, depression and black stools. Liquids, bland diet, analgesics and stomach coatings such as Pepto Bismol to soothe irritation to the stomach lining and inflammation provide comfort. Full recovery is expected by the third day after ingestion."
It goes on to say that you should treat symptomatically, and since your dogs are only showing the vomiting, I'd say that is a good way to handle this ingestion.
If this were my dog, I'd fast him for 24 hours (providing he doesn't have any underlying diseases such as diabetes that require he eat every few hours). No treats, no food, nothing. You can leave a small amount of water available, but don't allow him to drink too much at one time (placing ice cubes in his bowl so that he can't gulp water will help).
After the 24 hours, I'd offer a bland diet of boiled rice and boiled hamburger (3 parts rice to 1 part burger) in VERY small amounts (perhaps 1/4 c every hour or so) for the next 24 hours. Once you start feeding the rice mixture, monitor the dog for recurring vomiting. If the vomiting doesn't start again, you can begin slowly mix in his kibble over the next few days until you're back to just kibble.
If the vomiting persists for more than another day or so, or if your dog becomes lethargic, begins to have diarrhea or shows other 'unusual' signs, you should have him seen by a vet, just tto be on the safe side..
I hope this helps!!