- Fruits: berries (cranberries)
- Crop Production: nutrient cycling
- Education and Training: focus group, workshop
- Pest Management: field monitoring/scouting
- Soil Management: nutrient mineralization, organic matter, soil analysis
This study provides a more comprehensive characterization of nitrogen cycling than has previously been documented for cultivated cranberry beds. Highlights of this study include data from five conventionally cultivated cranberry beds. Our data demonstrate that the amount of nitrogen held in the plants and the soil (average = 82 kg N/ha) exceeds the annual inorganic nitrogen inputs (average = 50 kg N/ha).We considered other potential sources of nitrogen, and for most of the growing season, early May through August, dissolved organic nitrogen (DON) dominates extractable nitrogen pools in the bed (5-25 kg/ha), while amounts of extractable inorganic nitrogen are quite low (0-2 kg/ha). The large pool of DON may represent an additional nitrogen input that helps to settle the discrepancy in the mass balance equation.
Cranberry (Vaccinium macrocarpon), is a low-growing, woody, evergreen vine that is native to Wisconsin. The cranberry industry in Wisconsin has the highest amount of acreage and production in North America (~17,000 acres). Ammonium-based fertilizers are applied at rates of 40 – 50 kg N/ha, much lower than the nitrogen additions for most agronomic crops. Cranberries are also different in that they are very sensitive to large inputs of nitrogen; they cause cranberries to have excess vegetative growth at the expense of yield (Figure 1). Therefore applications of nitrogen fertilizer are carefully regulated by growers.
Although inorganic nitrogen additions from fertilizers are carefully managed, dissolved organic nitrogen is currently not considered a nitrogen source for the plants. Therefore it is not included in growers’ management plans. However, there is evidence that because cranberry roots form an association with ericoid mycorrhizal fungi, they may be able to access dissolved organic nitrogen (Bending and Read 1996). Unlike fertilizer additions, the dissolved organic nitrogen pools are naturally replenished by leaf litter additions and fine root turnover throughout the season. Further research on the cranberry-ericoid mycorrhizal fungi association will provide growers with important information that may help them to take advantage of a naturally existing relationship.
My short-term objectives are to measure extractable soil nitrogen pools. I looked at three different forms of nitrogen: ammonium, nitrate, and dissolved organic nitrogen (DON). I also explore the impacts of a relationship between cranberry roots and mycorrhizal fungi in the field on nutrient management. The intermediate-term objectives are to share the results with the growers. Over the long-term, I hope that the growers may find my research useful and incorporate some of the findings into their nutrient management plans. By 2008, cranberry growers will be required to provide annual nutrient management plans to the Wisconsin Department of Natural Resources, in an attempt to more carefully monitor and regulate surface and groundwater inputs, including additions made by fertilizers. Furthermore, a better understanding of the patterns of nitrogen cycling and use by cranberries may increase production profitability and sustainability.