By TIM HEARDEN

Capital Press

DAVIS, Calif. -- University scientists here warn that more study is needed about how farmers use nitrogen fertilizers before the state imposes regulations that could be harmful to agriculture.

Researchers at the University of California-Davis report more than 600,000 tons of nitrogen fertilizer is sold in the state each year, but information on fertilizer sales isn't an accurate indicator of how it is used.

For now, there is neither a comprehensive source of information nor current estimates on average applications by crop in California, the new study published in the scholarly journal California Agriculture asserts.

Regulation without supporting data could fail to address the problem while damaging agriculture, said Tom Tomich, co-author of the study and director of the Agricultural Sustainability Institute at UC-Davis.

"There are questions about the data we have," Tomich said in an interview. "They really don't shed much light on the issues of how farmers can increase their nitrogen efficiency.

"One of the other things that's unfortunate about the lack of information is it looks like California farmers have been increasing their nitrogen usage, but if we had better data, farmers would probably look pretty good," he said. "We have a long way to go, just like everyone on the planet. This is one of the biggest challenges facing the 21st century."

The study by Tomich, lead author Todd Rosenstock and others is part of the university's ongoing California Nitrogen Assessment, which aims to draw connections between use, surplus and environmental and human health effects of excess nitrogen, according to a news release.

The effort comes as the state Water Resources Control Board is considering more scrutiny on nitrates in groundwater after a UC-Davis study last spring showed that nitrate contamination in drinking water is a pervasive problem.

Farmers on the Central Coast are already grappling with new application and monitoring rules, and growers in the Central Valley could soon face similar rules.

University experts plan to offer training next year to more than 600 private crop advisors on how to help growers avoid leaching nitrates into groundwater.

To estimate the amount of nitrogen used on different crops, Tomich, Rosenstock and the other researchers aggregated data from existing UC studies, grower surveys and other sources and found information for 33 of the state's major crops, a news release explained.

While fertilizer use has risen over the last three decades, it has leveled off in recent years, Tomich said. While one of the factors is that growers have shifted to more nitrogen-intensive crops such as almonds, that doesn't necessarily mean almond growers are among the biggest polluters, he said.

"Almond growers deserve a lot of credit," he said. "They've made some of the greatest strides in improving nitrogen use. That's another key point. It's not about targeting crops that are nitrogen intensive, it's about targeting practices that leach nitrogen."

The goal is to improve management of fertilizers, which Tomich said would help farmers reduce their production costs while also reducing the impact on the environment. Also, proper management techniques will have to depend on the crop, its location and other factors, he said.

"California agriculture is so complex and so dispersed and so diverse that it's just not the kind of challenge that top-down command and control approaches work on," he said. "The risk of such an approach is you'll actually make things worse.

"I think everyone agrees that the way forward is through a collaborative process with growers to work with them to discover ways to improve nitrogen usage," he said.

Online

Nitrogen fertilizer use in California: Assessing the data, trends and a way forward: http://californiaagriculture.ucanr.edu/landingpage.cfm?article=ca.E.v067n01p68&fulltext=yes