UC researchers evaluate several organic fertilizers

In plots at the University of California, Davis, vegetable test fields, researchers are working to match as closely as possible applied nitrogen and crop needs over the course of the season for organic tomatoes.

This is the second year they have evaluated a dozen or so organic fertilizer products for their ability to supply the popular Brandywine heirloom variety as much nitrogen as the crop needs, when it needs it.

"After these two years, if we can identify some trends, we should be able to tell a story comparing these materials," said Margaret Lloyd, UC Cooperative Extension small farms and organic advisor based in Woodland.

Lloyd is working both in the field and the lab with UC Davis soils and biogechemistry specialist Patricia Lazicki to analyze the differences in organic fertilizers.

"When we are done, we should have two big pieces of information," Lloyd said. "We should know how much nitrogen the plant takes up at different stages; the other information is the release rates of the different materials."

One of the great challenges of organic production is that there are no materials that release all of their nitrogen as quickly as synthetic fertilizer.

"We're looking at release rates from the fertilizers," Lazicki said. "We are also taking whole-plant samples and looking at them for nitrogen content, to get an uptake curve for Brandywine tomatoes. We sample the fruit to see how much nitrogen is removed with the harvest."

In addition to studying how the fertilizers supply nutrients to the plants in the field, the researchers are also examining the materials for their release rates under controlled laboratory conditions.

"We have been evaluating a number of commonly used organic amendments to understand when the nitrogen applied with various amendments actually becomes available for plant use," Lloyd said.

Lazicki has kept more than a dozen materials in organic soil from the Capay Valley at 73 degrees for 12 weeks in an incubator at the Geisseler Lab on the Davis campus.

A pelleted seabird guano with 12-12-2.5 was the fastest acting material, making a majority of the nitrogen available virtually immediately, and more than 95 percent over the first six weeks.

Next in line were a 2-3-0.5 liquid fish emulsion, a 12-0-0 feather meal and a 3-3-2 food-based fertilizer, which all released most of their nitrogen in the first three weeks.

"The amount of nitrogen released is highest in seabird guano, feather meal, food-based liquid fertilizer and liquid fish emulsion," Lloyd said.

The slowest materials were municipal yard trimmings from two different facilities, as they made next to no nitrogen available at first, and then actually served as nitrogen sinks while they decomposed.

Numerous poultry manure composts were relatively slow, but they still released 30 to 35 percent of their nitrogen over the course of three months.

"All the products show a similar nitrogen release curve, except composts," Lloyd said. "The trend is a spike of rapid release in the first 10 days, followed by a steady release between 10 and 40 days, and leveling out to minimal release thereafter."

These results were based on analyzing changes in the materials over time as they were incubated in organic soil at 73 degrees in a lab, and need to be confirmed in the field.

"Although the incubation methods do not necessarily replicate field conditions, they are useful to understand how the amendments behave compared to each other under the same conditions," Lloyd said. "These relationships are likely to play out similarly on-farm."

Unexpected help may be on the way for organic growers, who generally must make do with fertilizers and amendments that are relatively low in nitrogen and release the nutrients slowly.

"Looks like to some extent this problem has been solved by the discovery and development by Brian Ward out of Clemson University of a bacteria-produced organic source of ammonium," said Mark Bolda, UC Cooperative Extension farm advisor based in Watsonville.

Ward, an organic vegetable researcher, has already patented a bacteria-based process for creating ammonium nitrogen, which could be used to produce large amounts of readily available organic nutrients.

He is in the process of gaining Organic Materials Review Institute approval and finding a commercial partner able to produce and merchandise the fertilizer on a large scale.

"Ward is hoping to scale up to commercial by 2021," Bolda said. "This is very important news for organic berry growers, actually all organic crop growers."

In the meantime, Lloyd and Lazicki are looking to see if they have repeatable results in their field study of available nitrogen that could guide decisions on the most economical choices for feeding organic crops.

A major reason for the differences among the products looks to have been the varying ratios in the materials of carbon to nitrogen.

"Generally, the higher the carbon-to-nitrogen ratio, the less readily available plant nitrogen," Lloyd said. "Yard trimmings composts are unlikely to contribute much nitrogen fertility in the year they are applied, though they are useful for building long-term soil fertility. Composts with a high carbon-to-nitrogen ratio may tie up soil nitrogen."

The fast-acting seabird guano, for example, has a low 1-to-2 carbon to nitrogen ratio, while the yard trimmings had 13-to-1 to 20-to-1 carbon to nitrogen ratios.

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