Division of Agriculture and Natural Resources
Division of Agriculture and Natural Resources
Division of Agriculture and Natural Resources
University of California
Division of Agriculture and Natural Resources

Research on nutrient and fertilizer management

Quick nitrate test guides fertilizer management
Michael Cahn and Richard Smith, UC Cooperative Extension advisors in Monterey County, and Tim Hartz, UCCE specialist in the department of Plant Sciences at UC Davis, have developed a quick test to measure soil nitrate in the field so growers can match fertilizer rates with plant needs. The test has reduced nitrogen-loading rates by an average of 70 pounds per acre in lettuce. On-farm demonstration trials have shown that by testing the soil, growers can reduce their fertilizer use by about 30 percent. Major growers in Monterey County, who manage a significant number of vegetable acres in the Salinas Valley, have begun using the quick nitrate test in their operations. For more information read the summary article on p. 5 and fine tuning article on p. 12 of Crop Notes and “Details on the Nitrate Quick Test” on the Salinas Valley Agriculture blog.

Farming practices developed for improving nitrogen use efficiency
Best management practices to minimize nitrate leaching in irrigated crop production have been compiled by UC Cooperative Extension scientists based in the San Joaquin and Salinas valleys and at UC Davis. The project—led by Stuart Pettygrove, UCCE specialist in the department of Land, Air and Water Resources, UC Davis—identifies a wide range of potential techniques for maximizing nitrogen use by vegetables, tree fruits, nuts, vines, field crops, grain, hay, and forage and silage crops, while limiting leaching losses. Many of these practices are already in use by farmers in California, representing a change for the better from historical practices that have contributed to current groundwater nitrate levels.

Nitrogen uptake by crops measured
Aziz Baameur, UC Cooperative Extension advisor in Santa Clara County, and UCCE advisors Mark Bolda and Richard Smith in Santa Cruz County, have been studying the nitrogen use efficiency of lettuce, spinach, broccoli, cabbage, cauliflower, strawberries, raspberries, jalapeños and bell peppers. By identifying the point at which crop quality and yields no longer significantly rise with additional nitrogen, growers can apply fertilizer with more precision to reduce the amount of nitrogen left in the soil. The advisors also show growers how to factor in the nitrogen available in soil and irrigation water. For more information read Fertilizer Management in Strawberry Production.

Assessing plant nutrient status
Leaf sampling is a common method of determining when a nut tree has a nutrient deficiency. Patrick H. Brown, professor in the department of Plant Sciences at UC Davis and Agricultural Experiment Station pomologist, and his colleagues are studying other ways of assessing plant nutrient status to help almond and pistachio growers manage fertilizer applications with more precision. For more information, see Crop Nutrient Status and Demand.

NBOT aids in dairy nutrient planning
The Nitrogen Budget Optimization Tool (NBOT) is a dairy nutrient planning tool being developed by David Crohn, UC Cooperative Extension specialist in the department of Environmental Sciences at UC Riverside. NBOT is an algorithm that uses a daily time step to represent crop nitrogen demand, nitrogen mineralization and losses from leaching, denitrification and ammonia volatilization. Typical nitrogen application charts tell how much nitrogen a crop needs during the growing season, but they do not say when the crop will need it. With NBOT, dairy operators input information about what crop they are growing, how much they expect to harvest and when they can apply manures. NBOT’s output gives an idealized management strategy that helps dairy operators decide what they should do all year round.

Cover crops help trap nitrates
Mark Bolda, UC Cooperative Extension advisor in Santa Cruz County, and Michael Cahn and Richard Smith, UCCE advisors in Monterey County, are studying the ability of cover crops to prevent nitrates from moving out of strawberry and vegetable fields into groundwater. Cover crops can trap mobile nutrients such as nitrate before they can leach below the root zone. Studies in the Salinas Valley have documented that fall-planted non-legume cover crops can take up more than 100 pounds of nitrogen per acre. For more information, read Nitrogen management and water quality protection .

UC helps dairy operators understand and comply with regulations
In 2007, the California Regional Water Quality Control Board–Central Valley Region adopted waste discharge requirements that impose stringent nutrient management and monitoring practices on dairies. In the ensuing years, UC Cooperative Extension advisors and specialists, under the leadership of Deanne Meyer, UCCE specialist in the department of Animal Science at UC Davis, have worked with state and local agencies to develop information and resources that enable dairy operators to comply with the regulations. For example, the Water Discharge Requirements General Order Reference Binder is a comprehensive online resource that provides step-by-step instructions written by UC authors for sampling supply wells and subsurface drainage systems, solid manure, liquid manure and soil. Dairy operators can use the resources to create required maps, complete form templates and review an exhaustive list of reference guides. For more information, see the California Dairy Quality Assurance Program.

N-Ledger software addresses nitrogen management
A software program under development by a team headed by Marsha Campbell Mathews, UC Cooperative Extension advisor in Stanislaus County, will help dairy operators and other farmers improve nitrogen management by calculating when nitrogen applied in manure is expected to be released from organic form into a form that the crops can use. Nitrogen applications are tracked, release rates are estimated and adjusted for expected losses, and the calculated total is compared to the expected daily crop need for nitrogen. The program helps the user choose an application strategy that will meet the crop’s needs and result in the least possible amount of nitrate in the soil during periods when it is vulnerable to leaching or other losses. For more information, see the Stanislaus County UC Cooperative Extension Manure Nutrient Management website.

Gene-to-landscape analysis to improve nutrient cycling on organic farms
Organically farmed crops are uniquely susceptible to nitrogen limitations, as well as to pulses of nitrogen into the environment. At 13 field sites, Louise Jackson, UC Cooperative Extension specialist in the department of Land, Air and Water Resources at UC Davis, is examining the potential for a new test—based on plant gene expression—that more accurately reflects the availability of soil nitrogen for particular crops. In addition, researchers are conducting a landscape survey to assess other diagnostic variables that could serve as new plant- and soil-testing approaches for nitrogen management in organic agriculture. In conjunction with this, they are working with farmers and other decision makers on improving nitrogen cycling in organic farming, utilizing participatory stakeholder activities to demonstrate needs, obstacles and time frames for implementation.

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