Growers face continuous struggles with crop nutrients

Bob Steinacher is vigilant to monitor the nitrogen available to the trees in the organic blocks among the 175 acres of fresh-market figs he grows outside Corning in Tehama County.

Because he is organic, if the crop develops a nutrient deficiency Steinacher does not have available to him any of the quick fixes used by conventional growers.

"I constantly analyze the leaves and soil, because it's easy to get behind and hard to catch up," he said as researchers discussed the challenge of nitrogen management in organic production during a California Association of Pest Control Advisers seminar in Chico.

"We've been growing organic since 1990, and taken more of our figs to organic over the years," Steinacher said. "Over the years, we've fine-tuned our fertilization program. We apply composted manure in the fall, and fertigate through the season."

Although organic growers may never be able to quantify the amount of nitrogen available to their crops with the certainty possible in conventional production, researchers have useful tips on calculating the nutrients coming from compost.

"The only way you're going to know how much nitrogen you are applying is to test your compost," said Dani Lightle, University of California Cooperative Extension farm advisor in Glenn County. "Your supplier should have these tests done, and if you're making your own compost from say, walnut hulls, you should have it tested."

Once lab tests establish the amount of nitrogen in compost, however, there is still an art to deciphering the complex question of how much will be available to the crop the first year.

"Unfortunately, the mineralization rate of compost is something of an art," Lightle said. "We do know some things that influence it. High temperature and moisture make it happen faster, as does incorporation."

The ratio of carbon to nitrogen is also tremendously important in calculating the rate at which the nutrients become available, and this number should also be on the compost label and included in lab tests.

"Lower than 10-to-1, you get about half the nitrogen available in the first year," Lightle said. "At 30-to-1, none is available. Most compost is between 8 and 14, and that should be on the label."

The challenge in providing enough nitrogen to last the entire season varies depending on the organic crop.

"We use a lot of chicken litter, some pellets, and that seems to sustain the row crops through the season," said Ben Carter, who farms about 3,000 acres of diverse crops north of Colusa, about a third of it organic.

He said he finds it more difficult, however, to keep nitrogen levels high enough through the end of the season in his organic rice.

"On the rice side, the fertility is a challenge, and we've been doing a lot of experiments," Carter said. "It runs out of gas late in the season. We're learning something every year. One strategy is to apply compost numerous times over the course of the year, in order to maintain fertility."

Lightle said it is a good practice to apply compost twice a year, in April and October, to keep nitrogen available in the soil.

A good share of the nitrogen, other nutrients and biomass needed to build productive organic soil can come from keeping crop residue on the farm.

"We never bale anything; everything goes into the soil," said Scott Park, who grows more than 30 organic crops on 1,700 acres in the Sacramento Valley. "You couldn't pay me enough to bale. Through time, I've learned the most important thing is your soil health. If you can get your soil health in balance in terms of minerals and microbes, it will do the work for you. By the time we get to planting, we feel we've laid the foundation for a good crop."

This approach, which has helped Park earn a reputation among produce buyers for producing high-quality crops, still leaves a level of uncertainty and mystery about soil building.

"I've been farming for 43 years and I could write a book on what not to do, but I'm not sure what to do," Park said. "I don't blame nature. When something goes wrong, I usually did something wrong."

(Bob Johnson is a reporter in Davis. He may be contacted at bjohn11135@aol.com.)