Nutrient Management

Nutrient elements are required by cranberry plants for the production of vegetation (new leaves and stems), roots, and fruit (crop). Cranberry plants get these nutrients from the soil, from water, or from fertilizers added to the bog. While cranberries require the same nutrients as other plants, they are unique in that the amounts required are much smaller than for most crop plants. The reason for this is that cranberries have adapted through evolution for growth on acid, sandy soils. These soils have little nutrient content, and the plants in the family Ericaceae such as cranberries and blueberries that evolved on them have correspondingly low nutrient needs. Further, cranberries are perennial plants with the capacity to store and reuse nutrients in old leaves, wood, and roots. A unique and important feature of cranberries is that they maintain their leaves over the winter. These leaves also serve as a nutrient source when the plants resume growth in the spring. Commercially, cranberries are grown in either organic soils modified by surface application of sand, or in mineral soils. The rooting zone typically contains about 95% sand. Average organic matter in the surface horizon of Massachusetts cranberry soils is less than 3.5% and silt and clay make up less than 3% of the soil. Therefore, cranberry soil has low cation exchange capacity - little ability to hold positively charged nutrients such as ammonium, potassium, magnesium, and calcium. However, downward leaching of nutrients is minimized by the layered structure of cranberry bog soil. Layers of sand are added to the bogs every 2-5 years leading to alternating sandy and organic layers. The organic layers are comprised of decaying roots and leaves. Nutrient leaching is also minimized in peat based soils by the high organic matter content of the subsoil. Why cranberries need fertilizer: Each season nutrients are removed from the bog during harvest and detrashing (removal of fallen leaves from the bog floor). When the fruit is harvested, the elements removed in the largest quantities are nitrogen, potassium, and calcium, at \u3e20 lb/A (nitrogen) or \u3e15 lb/A (potassium and calcium) in an average (150 bbl/A) crop. The amount of nutrient removal increases with increasing crop load and is less when crops are small. It is to compensate for nutrient removal that cranberry growers add fertilizer to their bogs. Most fertilizer added to producing cranberry bogs contains nitrogen, phosphorus, and potassium (N-P-K fertilizer). Phosphorus is included in the mixture to maintain nutrient balance and because much of the phosphorus in cranberry bog soil is not available to the plants at crucial growth stages. Fertilizer is applied to cranberry bogs using ground rigs (spreaders and seeders), helicopters (aerial application), and the sprinkler system (fertigation)