Little work has been done to establish the rate and timing of nitrogen fertilizer applications to optimize return from fertilizer expenditures and minimize potential for ground and surface water pollution in Oregon cranberries (Vaccinium macrocarpon Ait.). Predicting cranberry N requirements is difficult because cranberries require little N and soil tests for N are not helpful for perennial crops, especially when grown in shallow sandy soils. We used 15N-labeled ammonium sulfate to measure both plant uptake and movement of fertilizer N in a south coastal Oregon cranberry bed. A bed planted to the Stevens variety was fertilized with 15N-labelled ammonium sulfate at two rates (18 kg/ha and 36 kg/ha) applied at five phonological stages: popcorn, hook, flowering, early bud, and late bud. Plant N uptake and translocation were measured throughout the growing season in uprights, flowers, berries, and roots, Initial results indicate that when N was applied at popcorn stage approximately 12% of the N was present in the above-ground vegetative biomass at harvest. Incorporation of fertilizer N into the duff and mineral soil was measured. An estimate of fertilizer N leaching was made by trapping inorganic N below the root zone using ion exchange resin bags.
Kris L. Wilder, J. M. Hart, Arthur Poole and David D. Myrold
Jennifer Moore-Kucera, Anita Nina Azarenko, Lisa Brutcher, Annie Chozinski, David D. Myrold and Russell Ingham
Organic growers are required to maintain or improve soil chemical, biological, and physical properties and thus need to integrate biological processes into fertility management. However, few guidelines exist for satisfying tree nutrient demands ecologically. Sound nitrogen (N) management is a key component for overall orchard productivity whereas poor N management may result in multiple environmental impacts, including runoff to surface or leaching to groundwater sources. Many growers substitute synthetic inputs with rapid-release, approved N fertilizers that have little effect on long-term soil health and fertility. The authors seek an alternative approach for synchronizing nutrient availability with tree demand that relies on managing soil biological communities to attain their maximum potential functionality and thus meet tree nutrient demand. This paper outlines a new conceptual framework with which to evaluate a variety of soil functions that are quantified using biological, microbial, and biochemical properties in relation to overall orchard performance. By combining information gathered from soil faunal indices (nematode community structure and diversity analyses) with data obtained by biochemical and microbial analyses of the soil samples, a new, in-depth view of soil communities and their response to management practices will be obtained. As a result, a better understanding of the effects of differing management practices on soil fertility and community structure will be gained. This approach is currently being investigated by our group in organic and integrative sweet cherry orchards. Our goal is to determine which soil parameters may be used to help orchardists optimize soil health while maintaining orchard productivity. Furthermore, we wish to validate a number of assumptions that are commonly made regarding each soil parameter tested across multiple management, soil, and climate types.