Research weighs soil amendments
Online calculator offers guidance on various offerings
By STEVE BROWN
A new online calculator enables growers to compare soil amendments.
Amendments are chosen for different uses -- fertilizer or mulch -- based on nitrogen availability.
Fertilizers, for instance, have a low carbon-nitrogen ratio, supplying nitrogen for plants. Mulches, on the other hand, have a high carbon-nitrogen ratio, tying up nitrogen.
Washington State University and Oregon State University scientists performed a series of tests with sweet corn, examining results using raw and composted forms of broiler litter, dairy manure, yard trimmings, rabbit manure and specialty products, such as fish fertilizer, canola meal and feather meal.
The majority of nitrogen in all of the amendments is in its organic form, which must be broken down by microbes to become usable ammonium, WSU scientist Craig Cogger said.
"They way I look at it is: 'If you build it, they will come,'" he said. "The microbes that exist in the soil are going to do their job."
In lab tests, broiler litter decomposed rapidly over the first few weeks, making nitrogen abundantly available. Fresh dairy solids showed a similar curve, but not quite as rapid. Composted dairy solids had more humus material and much lower rate of decomposition.
Specialty products decomposed the most rapidly of all, and the other composts performed like the composted dairy solids, with a very stable rate of decomposition.
"The broiler litter would be a good organic fertilizer," Cogger said. "The dairy solids, you would actually have to add a nitrogen source for it to be suitable for application to soil. The compost would be a good soil amendment, soil builder, but not a lot of release of nutrients in the first year, so you would need to supplement it with fertilizer as well."
Cogger said OSU researchers Nick Andrews, Dan Sullivan, Jim Julian and Kristin Pool have incorporated the research data in spreadsheet form -- an organic fertilizer calculator -- to answer such questions as:
* How much of this fertilizer should I apply?
* How do these two fertilizers compare?
* What's the cheapest source of available nitrogen (N), phosphorus (P), and potassium (K)?
* Does this program match my fertilizer recommendation?
"You would find that some materials wouldn't even be feasible," Cogger said. "Some would be feasible at lower rates than others. You can input costs and compare costs as well."
WSU Extension Professional Development: http://ext.wsu.edu/pd
OSU Organic Fertilizer and Cover Crop Calculator: http://smallfarms.oregonstate.edu/calculator