Farm advisors from UC Cooperative Extension convering the entire San Joaquin Valley, where most of California dairies are located, are collaborating with a UC Davis nutrient specialist to research faster ways to measure how much nitrogen (N) is in dairy lagoon water. The project is supported by the California Dairy Research Foundation and local dairy producers,

Why Lagoon Water Matters
Dairy farmers often irrigate their forage crops with fresh water blended with lagoon water. Lagoons are storage ponds on dairies that hold dairy process wastewater and contain water used for cleaning and cooling cows as well as flushing barns where the animals excrete urine and manure. Irrigating with lagoon water is like fertilizing because many plant nutrients are found in lagoon water, and N is abundant. This is good because N is the most limiting plant growth and development nutrient. However, there are challenges with using lagoon water as a crop nutrient source.

Understanding Nitrogen Availability
• Not all nitrogen in lagoon water is immediately available for plant uptake. Typically one=third to two-thirds of the nitrogen is in
organic form, while the remainder is ammonium, a mineral form plants can absorb right away. Organic nitrogen must first be decom- posed by soil microbes and converted to ammonium before plants can use it.  

• Electrical conductivity (EC)
• Turbidity
• Specific gravity
• Solids content
• Ammonium concentrationThe Challenge of Measurement

Currently, there are no known direct measurements of N in lagoon water beyond what a laboratory can measure. Despite local ag labs providing highly accurate analyses with a relatively short turnaround, samples of lagoon blended irrigation water analyzed at a lab only allow the farmer to know how much N was applied to their crop a few days after it was applied. It may have been too little, just the right amount, or more than planned. We think this can be improved.

Toward Real-Time Nitrogen Estimates
Farmers need to know how much nitrogen is being applied as irrigation occurs. Real-time data would allow them to adjust lagoon blends to meet target nitrogen applications.

Preliminary results show electrical conductivity strongly correlates with total nitrogen in lagoons.

For more information about this project contact the author, Nick Clark, by email: neclark@ucanr.edu .