|Authors: ||C. DeMoranville, B. Howes, D. Schlezinger, D. White|
|Keywords: ||Vaccinium macrocarpon Ait., phosphorus, water quality, flood management, fertilizer practice|
Cranberries (Vaccinium macrocarpon Ait.) are grown in wetland settings.
Environmental concerns have led to a need for nutrient management planning by cranberry farmers.
In particular, phosphorus (P) has been identified as a potential environmental pollutant discharging from cranberry systems to inland water bodies.
Most growers apply fertilizers that are a complete blend of N-P-K, basing the application rate on the amount of N required.
Depending on the N:P ratio of the chosen fertilizer, P rates may be in excess of plant needs.
The recommended rate for P in cranberries with tissue tests above the critical value (0.1% P) should be ~22 kg•ha-1 P per season (~50 kg P2O5). As part of a water quality study, growers reduced P inputs in bogs paired with standard practice bogs (generally 22-35 kg•ha-1 P). Substantially reduced P fertilizer inputs did not suppress yield and were associated with marked reduction in P concentration in flood discharges.
A 40% reduction in P over a 3-year period at one study site resulted in a decrease in average total P concentration in flood discharge from 0.377 to 0.097 mg•L-1. During that same period, yield increased while net P discharge from this bog system was reduced by more than half.
Based on these studies, growers have begun to use fertilizers with lower N:P ratios.
An additional outcome of this research has been the identification of the interaction of fertilizer P applied and P movement into flood water and improved management practices for the handling of flood discharges.
Use of >22 kg•ha-1 P was associated with higher levels of P discharge into harvest flood waters when compared to bogs receiving reduced P fertilizer.
Retention of floods for extended periods was associated with increased P in the discharge.
Best management practices should incorporate reduced P fertilizers and minimal retention times of harvest floods.
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