Farmers have long known that their cows' manure made good fertilizer for the corn or winter-forage crops they raised to feed the animals. But because it hasn't been easy to estimate nitrogen and other plant nutrients in the manure, the farmers typically played it safe and supplemented the manure with commercial fertilizer.
That was expensive for the farmers, and raised the risks of excess nitrogen and salts seeping into the valley's aquifers.
In a three-year research and demonstration project, 11 San Joaquin Valley dairies worked with UC Cooperative Extension farm advisors to develop a system of flow meters and nitrogen "quick tests" for dairy manure water. Knowing the nutrient content of their manure water enabled the farmers to eliminate nitrogen fertilizer applications on the test fields without cutting their crop yields.
"The dairy project addressed a key environmental challenge faced by Central California dairy operators without compromising their economic viability," said Stu Pettygrove, a UC Cooperative Extension specialist in the UC Davis Department of Land, Air and Water Resources. "The new system has helped reduce excess nutrients moving into aquifers of the San Joaquin Valley."
The manure-management system should be transferable to many of California's Central Valley dairies, he said.
The Biologically Integrated Farming Systems dairy project was administered by the UC Sustainable Agriculture Research and Education Program. Heading the project with Pettygrove were UC Cooperative Extension specialists Deanne Meyer and Dan Putnam and project manager Alison Eagle.