Evaluation of Supplemental N Source and Timing of Application for Organic Field Corn Production Following a Vetch Cover Crop.

Sustainable N fertility management in organic cropping systems depends on an integrated strategy using crop rotations that include annual and/or perennial legumes, and using manure and other quick-release N sources. Synchronizing N availability with crop N demand in organic systems, however, can be especially challenging.  Since the amount of plant available N provided by green-manures varies considerably by year, corn N needs must often be supplemented by other N sources such as animal manure and byproducts. Excessive reliance on animal manures or byproducts, however, can be cost prohibitive and/or provide excessive P. We conducted research on poultry litter, hydrolyzed feather meal, and two blended organic fertilizers applied pre-plant or at sidedress to supplement N from a hairy vetch cover crop in 2009 and 2010. We quantified available N equivalence, estimated N mineralization kinetics, and compared the synchrony of N release with corn N uptake using laboratory incubations and field plot research. We found that when hairy vetch produced adequate biomass it was capable of satisfying nearly all corn N needs. All of the supplemental organic N materials we investigated feather meal had the highest available N content, fastest mineralization rate, and lowest ratio of N:P. In 2009 sidedress application of all supplemental N materials resulted in increased N use efficiency and increased  corn yield by 12%, N uptake by 20% and harvest index by 6%. In 2010 there was no difference in grain yield or N uptake between pre-plant vs. sidedress treatments but harvest index was again 6% higher with sidedress treatments. Yield of organic corn can be optimized using sustainable rates of supplemental N materials used in conjunction with legume cover crops. Applying these materials at sidedress has the potential to significantly increase N use efficiency by increasing synchrony between N availability and crop N demand.