Optimizing Phosphorus Use in Cranberry Production

Commodities

Practices

Title: Optimizing Phosphorus Use in Cranberry Production. Compared to most crops, cranberry production requires very large inputs of water for irrigation, harvesting, and crop protection, raising concerns about impacts of nutrients from cranberry drainage on downstream water quality. In particular, Upper Midwest cranberry growers have faced increasing scrutiny about potential exports of phosphorus (P) to downstream waters, and the rate of P application needed to balance crop production and water quality concerns remains poorly understood. Surprisingly few data underpin the current Extension recommendations for P application to cranberry. Furthermore, these guidelines were developed using legacy cranberry varieties, which have much lower productivity than the modern varieties currently favored by growers, and studies were conducted in regions with soils that differ from most current commercial cranberry farms (known as marshes) in the Upper Midwest. In these systems, native topsoil is removed and the perennial cranberry
plants are established on layers of fresh sand, with additional sand applied periodically to promote
growth. Thus, organic matter accumulates in the new soil (known as a “bed”), providing a potentially important source of nutrients as the bed ages. Here, we will test the relationship between P application rate and cranberry yield across beds of varying ages, across three different commercial cranberry farms. We will also measure changes in the stocks and forms of P, as well as carbon and nitrogen, to test whether increases in plant-available soil P fractions in older beds can decrease fertilizer requirements, while also assessing potential for P solubilization and loss. Finally, we will calculate P mass balances in these cranberry production systems to quantify water quality risks under different fertility management scenarios. Overall, the project will enable Upper Midwest cranberry growers to assess and improve their P management practices, thereby benefiting the long-term economic and social sustainability of the industry as well as the environment. Project Coordinators (Hall and Atucha) are Extension-funded faculty at UW-Madison and will engage closely with members of the Wisconsin State Cranberry Growers Association through field days, webinars, and extension publications, in addition to producing a peer-reviewed scientific article. Findings will also support development of a module in the cranberry nutrient management training offered by the Wisconsin Department of Agriculture, Trade and Consumer Protection.

Objective 1: Evaluate the relationship between P fertilization and yield components in a high-
yielding cranberry variety (Mullica Queen) across production beds of varying ages.

Objective 2: Quantify soil P stocks and forms and assess their relationships with bed age and
cranberry yield.

Objective 3: Quantify P mass balance in cranberry production systems to estimate potential
impacts on water quality.

Objective 4: Develop extension resources and programming on P management and its implications
for water quality in the cranberry industry.

Learning and action outcomes: Cranberry stakeholders will learn about best practices for P
management in modern commercial cranberry production. This will inform potential changes in
nutrient inputs and water management, improving surface water quality. Outcomes will be
evaluated using pre- and post-project surveys.