One way to keep nitrates out of the groundwater is to avoid leaching, said Larry Schwankl, irrigation management specialist with the University of California Kearney Research and Extension Center.

“Nitrates won’t be leached if there is not water to move them,” he said.

The water to move any contaminants downward comes from rainfall or irrigation. Schwankl said applying nitrogen at the correct time and in the correct amounts is key.

“You don’t want excess nitrate in the soil going into the winter rains since it could be leached by rainfall,” he said.

Schwankl pointed out that some compounds of nitrogen other than nitrates — notably ammonium or organic forms — do not readily leach.

“From a production issue and from a pollution issue, it is important not to have leaching,” he said, pointing out that it’s most productive to have nutrients remain in the root zone.

Determining water needs and application rates is important to avoid the over-watering that leads to leaching, Schwankl said. Clogging of lines and variability in applying irrigation water can lead to over-watering as a grower seeks to assure that under-watered areas get enough moisture.

Richard Snyder, a biometeorology specialist with UC Davis, talked of how water and wind machines can be used on citrus to prevent cold weather damage. He referred participants in the meeting to the website http://biomet.ucdavis.edu/ that offers a wealth of information on frost protection, including videos in Spanish and English.

He explained damage caused to the fruit by formation of ice outside cells that draws water out, resulting in dehydration.

One of the best ways to protect against frost is site selection, Snyder said. Avoiding low spots where cold air will collect is critical for citrus and for vineyards, he said, recalling how winemaker Joseph Gallo sought advice on where to plant grapes.

Snyder said it can be helpful to remove “cold air dams” that keep the air from drifting out of an area. Likewise, he said, it may help to add hay bales, plastic fences or other impediments to divert cold air away from a grove.

Ground cover in citrus is not helpful when it comes to keeping the floor of the grove warm, Snyder said. It reflects sunlight and results in some energy loss. “It doesn’t store as much heat,” he said.

Water from sprinklers under trees is most effective when it is allowed to freeze, Snyder said. The water should not be sprayed into trees. But for furrow irrigation, he said, the water should not be allowed to freeze, and furrows should be on the edge of trees, not directly below them.

Covers and wraps can help for younger citrus, but they should be waterproof, Snyder said.

“The enemy is evaporation,” Snyder said, pointing out that it is necessary to cool and freeze six times as much water as is lost to evaporation, and evaporation depends on the dew point and wind speed.

Carol Lovatt, professor of botany and plant sciences, at UC Riverside, is studying alternate bearing in citrus. She said that holding an “on” crop on the tree for harvest exacerbates the problem of alternate bearing.

Early harvest of the on crop in November or December will increase spring bud break and yield the next year, Lovatt said. She adds that fruit thinning in early July of an on crop will increase the number of shoots without fruit and thus increase vegetative shoot growth and return bloom and should mean a higher yield and increased fruit size.

To limit the number of fruit without thinning, Lovatt is exploring the use of plant growth regulators.

She said it is important to fertilize for the current crop load, not to replace what the previous crop used.