Cranberry Nutrient Management in Southeastern Massachusetts: Balancing Crop Production Needs and Water Quality

Cranberry (Vaccinium marcrocarpon), native to North America, is a low growing plant that produces stolons that cover the soil, root at intervals along their length, and produce upright shoots that bear the crop. The plant is acid-loving and adapted to sandy, nutrient-poor soils and thus, like blueberry, its nutritional requirements are low compared to many other perennial crops. Research conducted over the past 30 years has defined the annual requirements for N (20-60 kg^.ha^-1), P (<20 kg^.ha^-1), and K (40-120 kg^.ha^-1) based on tissue testing, plant growth demands, potential for remobilization, and determination of removal in the crop. However, much of this work was conducted on native cultivars and there is an expectation that requirements of newer hybrid cultivars are greater. In Massachusetts, cranberries are grown in coastal watersheds and often depend on small lakes as their water source for irrigation and harvest and winter flooding.  As a result, cranberry farmers are faced with regulatory demands including TMDL (total maximum daily load) limits as mandated in the Federal Clean Water Act. Since cranberry production is heavily dependent on water use, the interaction of nutrient management, particularly for N and P, and water management has become a primary focus area for research and extension.  A study of N output from a single cranberry farm identified annual output in the range of 20 kg^.ha^-1. That number has since been used in models of watershed-wide N contributions to coastal estuaries in Southeastern Massachusetts. However, the farm in that study was a 'flow-through' style cranberry system with a constantly flowing stream running through the beds. That configuration represents >15% of cranberry farms in the region. Recent preliminary research examining cranberry farms with other configurations has indicated that the cranberry bogs may act as either source or sink for N depending on configuration and management activities. In a study of cranberry farms where P use was reduced to an average of <10 kg^.ha^-1,  P concentration in harvest flood water declined by as much as 85% while crop production was sustained. However, results were variable leading to the need for further research to define how soil types and site hydrology interact with P loss in harvest floods.