Comparison of controlled release and soluble granular fertilizers on cranberry growth, yield, and soil nutrients

Cranberry growers are looking for ways to reduce off-site movement of nitrogen (N) and phosphorus (P). Controlled-release fertilizers (CRF) may increase nutrient uptake efficiency in cranberry and decrease potential for nutrient leaching or lateral movement into drainage. Data regarding N and P in cranberry soil water beyond the root zone in the months following CRF application were lacking. Further, if CRF is more efficiently supplying N and P to the root zone, application rates of those elements might effectively be reduced with CRF compared to other materials. This had not been tested in cranberry. Four CRF were compared to an all soluble forms protocol on a new cranberry planting and N and P concentrations in lysimeter water and in tile drains within the experimental units were measured. All treatments with the exception of one CRF had similar plant growth but rate of N release into the soil water varied. One CRF formulation gave good plant growth and had the least lateral and vertical movement of nutrients in the soil. In the subsequent two years, that formulation, with a low P ratio, was tested against a moderate-P CRF and an all soluble protocol on a producing bed. In the first year, N rate in the CRF treatments was reduced by 8% compared to the soluble treatment (grower practice); the next year the N rate in the CRF treatments was reduced by 24%. Crop yield was not statistically different (p=0.05) among the treatments. The two CRF treatments had more new growth per unit weight of old tissue compared to the soluble (grower practice) treatment, but the differences were not significant. At this site, CRF applied at a reduced N rate was as effective as the grower-practice soluble fertilizer in supporting crop yield and plant growth.