Go With The Flow

New regulations force California dairies to rethink nutrient management

by Catherine Merlo

Recently enacted regulations in California mandate a nearly impossible requirement for the state’s dairies: Nutrients from manure cannot be applied to fields in amounts of more than 140% to 165% of crop uptake.

While no other state has set that specific target, others could someday face similar restrictions, particularly Arizona, Idaho and Florida where groundwater leaching has raised concerns. Meanwhile, producers in other states should take heed of the environmental demands being placed on California dairies, says Marsha Campbell Mathews, a University of California Cooperative Extension farm adviser in the Stanislaus County office.

“California’s new regulations will require a complete rethinking and revamping of infrastructure” for the state’s dairies, Mathews says.

New waste discharge requirements (WDRs) were handed down to the Central Valley’s 1,600 dairies in May. The goal of the order is to prevent groundwater degradation. To comply, dairies must monitor their manure storage and distribution systems, as well as manage nutrient application.

While producers look for ways to contain their compliance costs—estimated at $45,000 to $60,000 per dairy in the first year—it’s not likely they will stop applying manure-based nutrients to their fields. The nitrogen, potassium and phosphorus found in dairy lagoon water can supply everything that crops need to grow, Mathews says. But there’s a downside, too.

“Where groundwater contamination occurs, it is mostly a result of improper land application of manure,” Mathews says.

To minimize groundwater degradation, California dairies need a comprehensive nutrient management plan to successfully use dairy lagoon water as the primary nutrient source for their crops.

The starting point of any nutrient-management strategy is making sure a dairy has enough land to accommodate the nutrients it generates, Mathews says. To protect groundwater, the total amount of nitrogen has to be considered.

“Having a balance isn’t enough,” she says. “The nutrient management plan is what will allow these nutrients to be appropriately applied to minimize excess applications while maintaining crop yields.”

This involves setting up a system to measure and apply appropriate amounts of nutrients. “In practice this can be an enormously complex undertaking that involves nearly every aspect of a facility,” she says.

In California, a dairy’s functional nutrient management system requires three major components. “They are equally important,” Mathews says. “If any of the parts are deficient, the entire system will not function. They are also interdependent, and each cannot be designed without consideration of the other parts.” They are:

1. Facility and land application infrastructure. These are the dairy’s physical facilities that collect, separate, transport and store manure. They include sufficient crop acreage and lagoon storage, a source of fresh water for dilution, and correctly sized pumps and pipelines.

California lagoons are being built or upgraded to hold 120 to 180 days of liquid storage. One approach to minimize the buildup of fine solids in storage lagoons is to construct and operate two storage lagoons in series. One lagoon is sized for about one-third of the storage requirement; the other holds the balance.

A dairy’s nutrient-management system must also include a solids removal system to prevent solids from building up, help keep pipelines clear and provide a more uniform product for nutrient application, Mathews says. A solids removal system also makes it easier to manage the organic nitrogen fraction of lagoon nutrients, and allows more nitrogen and phosphorus to be moved off site, if necessary.

Two separation systems that are increasingly showing up on California dairies are settling basins and screen separators.

Settling basins allow large amounts of suspended solids to be removed from lagoon water.

Screen separators are stainless steel, inclined wedge, wire units that come in a variety of configurations and slot-opening sizes. Screened solids can be an excellent source of bedding material for dairies using manure for bedding.

2. Applying nutrients to cropland. This nutrient-management component involves the actual procedure of deciding when and how much manure and fertilizer to apply to the crops, and the process of working out that plan.

The trick to nutrient management balance under high leaching conditions, Mathews says, is synchronizing when and in what quantity nutrient-filled irrigation water is applied.

The best way to measure application is by installing a flow meter on the pond outlet. The device is essential for matching application with uptake, Mathews says.

A flow meter, when installed with a control valve, allows specific amounts of water to be applied to each field. It measures the total gallons at the same time. Flow meters that work in high-solids water can cost $1,000 to $4,000. “In many cases, the cost of the flow meter can quickly be recovered in savings on commercial fertilizer,” Mathews says.

Mathews urges producers to learn when crops need nutrients. “Most plants will have periods during the season when their need for nutrients is greater,” she says.

Timing nutrient applications to coincide with crop uptake will ensure the highest yields. Applying crop nutrients at times when the crop doesn’t need them can result in losses, especially of nutrients like nitrogen that have the potential of leaching into groundwater.

3. Record-keeping. All other nutrient-management components may be in place, but without a practical means of keeping track of applications and crop uptake, it will still be impossible to determine if nutrients are being appropriately applied.

Because computerized record-keeping is a must under California’s new WDR, Mathews has developed Aptrak, a record-keeping and nitrogen-application program for dairy nutrient management. The Excel-based program incorporates crop uptake and mineralization models into a spreadsheet designed for fast data entry. Download the spreadsheet at http://manure.ucdavis.edu. DT