May 2000
UC innovation helps dairy farmers better manage wastewater
Typically dairy lagoon water is pumped onto adjacent farmland where farmers grow corn or winter forage for cow feed. To ensure a good crop, commercial fertilizer is commonly added. But the practice can result in more nitrogen being applied than the crop can use. The leftover could seep down into the aquifer and pollute groundwater.
Campbell Mathews has found that, with careful monitoring and application procedures, using the nutrients in the wastewater alone produces a top-yielding crop and reduces the risk of contaminating groundwater. In just four minutes, right on the banks of dairy lagoons, the quick test tells farmers the level of ammonia nitrogen and estimates organic nitrogen in the water. The ammonia nitrogen is chemically the same as the fertilizer purchased by most dairies. The organic nitrogen also contributes to the nutrient needs of the crop.
"The amount of nitrogen in dairy lagoon water varies widely," Campbell Mathews said. "You can't take a sample in spring and use the same number all season long. With the quick test, we've given dairy farmers a way to calculate the amount of nitrogen in the water minutes before it's pumped onto the field."
Campbell Mathews said the reagent used in performing the quick test produces a tiny amount of mercury in about three-quarters of an ounce of water, which must be handled as a hazardous waste. However, in Stanislaus County, disposal is not an obstacle. The waste may be collected in a bottle and dropped off at a hazardous waste disposal site, just like used batteries and leftover paint.
Applying the correct amount of lagoon water is another important component of an ecologically sound disbursement system, Campbell Mathews said. She has tested a system that uses a special clog-resistant valve to adjust the flow of lagoon water and a flow meter to monitor the exact amount of nitrogen being applied.
With funding from the UC Sustainable Agriculture Research and Education Program, the California Dairy Research Foundation and the Environmental Quality Incentives Program, the system was demonstrated at three commercial dairies near Modesto.
"We have grown fantastic corn," Campbell Mathews said. "And we didn't apply any commercial water-run fertilizer. We were able to apply just the amount of ammonia-form nitrogen we intended to. This coming season we plan to account for organic-form nitrogen as well."
The task has not been simple, nor does Campbell Mathews expect it to be for dairy farmers who must reconfigure their lagoon water distribution systems. Particularly in the sandy soils of the northern San Joaquin Valley, timing of lagoon water applications must be coordinated precisely with the crop's nutritional needs. That means there must be sufficient space to store dairy wastewater when it cannot be used.
"A lot of dairy operators didn't have the capacity in a wet winter to hold all the water in their ponds," said Thomas Harter, UC Davis groundwater hydrologist based at the UC Kearney Ag Center near Parlier and a cooperator on some of the projects. "It was standard practice to empty the pond in the fall. But if the soil is sandy, you can't put fertilizer on one part of the year and hope it is there six months later to help plants grow well. In the Modesto area, you have to spoon feed the fertilizer to the crop."
At the dairies where the UCCE demonstrations were conducted, the operators built additional water storage lagoons, modified irrigation systems and/or purchased state-of-the-art pumps and valves to make optimum use of lagoon water.
Campbell Mathews and Tulare County UC Cooperative Extension farm advisor Carol Frate have offered six workshops on the proper use of dairy lagoon water. More than 75 individuals completed the three-part series. Additional classes will be offered in the fall.
"There are going to be quite a few flow meters installed in the coming season," she said. "Using a flow meter is by far the easiest way to implement the system, but it's not the only way. Flow can also be measured by calculating pond drop or pump output."
Campbell Mathews said she is heartened by the interest and enthusiasm of dairy operators in the dairy wastewater management system and is beginning to see a shift in the way they think about the lagoon water.
"Some people are used to thinking of it as waste, but now they realize it can actually be a precious resource," she said. [Prepared by Jeannette Warnert]
Media Contacts:
Lyra Halprin, (530) 752-8664, lhalprin@ucdavis.edu
