At the conference, participants heard from speakers including:
Tim Hartz, University of California extension specialist, addressing nitrogen budgeting for annual crops and the issues of nitrogen released into groundwater or the air.

“The basic principle of nitrogen management is that any nitrogen applied to a production field but not removed from the field in a harvested product is at risk of eventually being released in the environment, either in gaseous emission to the atmosphere or lost through runoff or leaching,” Hartz said.

How much is removed with harvested material varies greatly by crop, from less than 30 percent for broccoli to nearly 100 percent for forages. “That means some crops and some production systems will get more scrutiny than others,” he said.

Hartz said he has heard more about the idea of “nitrogen budgeting” by growers “in the past 12 months than in the previous 20 years.”

He said leaching of nitrates accounts for the highest loss of nitrogen. Ammonia volatilization from animal manure, anhydrous ammonia or urea fertilizer can mean a loss of 30 percent. Denitrification, reduction of nitrates to nitrous oxide and nitrogen can be a problem when soils are at or near saturation.

Katherine Pope, with UC Davis, who talked of optimizing fertilizer management in almonds, another nitrates issue.

She reiterated something Giclas said, referring to the “4-R’s” of nitrogen management, applying it at the right time, at the right rate, from the right source and in the right place.

“Trees take up nutrients when they are needed,” Pope said. “If you throw them on in May, the trees are not going to suck all that up.”

For walnuts, she said, the most demand is in June, July and August. As for the right place to deliver nutrients, she said, that would be the root zone which is about 2 feet deep.

She said fertilizer application should be planned at the beginning of the year and leaf monitoring should be done.

Marsha Campbell Mathews, with UC Cooperative Extension in Stanislaus County, talked of a new software tool for nitrogen budgeting for agronomic crops. She emphasized the strategic timing of irrigation and pointed out that the software takes into account different forms of agriculture applied, including lagoon water and irrigation water.

Mathews said the software is easy to use and has pull-down menus for accessing data in various forms, including pounds, gallons and loads per acre.
It can be used to manage nitrogen applications while minimizing leaching. The software currently supports winter cereal forage, silo corn and single cut sudangrass.

Jim Ayers, agricultural engineer with the Agricultural Research Service in Parlier, discussed water and nitrogen requirements for developing pomegranates. He said demand for water will increase as California’s population grows, and much still remains to be learned about the ancient crop that is thought to be both drought and salt tolerant.

Ayers said research in Parlier indicated trees grown with subsurface drip had higher yields that those grown with surface drip irrigation. Subsurface drip, he said, eliminates runoff and deep drainage and minimizes surface soil and plant evaporation.

Ayers said it is still too early to develop conclusions regarding the required levels of nitrogen for a pomegranate orchard, and initial results show little effects on yield when nitrogen levels are increased.


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