Plant Nutrition - Research Highlights

Dr. Carolyn DeMoranville

Effects of road salt on cranberry growth and soil chemistry
Funding: MA Highway Cooperators: Dr. Joan Davenport (WSU), Dr. Teryl Roper (U-WI),
Bog Hollow Farm
This project was initiated to determine the critical concentration of sodium chloride (road salt) that will induce negative growth effects in cranberries. In addition, we studied how road salt accumulates in cranberry soil and how such soil may be decontaminated. To date we have determined that the critical concentration is below 250 ppm, and likely at or below 100 ppm. Chronic salt exposure led to red spotting of leaves, abnormal runner growth, ‘brittleness’ of shoots, yellowing, and at exposures to 250 ppm or greater, reduced shoot growth. Chloride exposure may also negatively impact flowering at these rates. In fact, flowering and fruiting was depressed (compared to control) at Cl levels as low as 50 ppm.

We have identified mitigation treatments in the lab treatments in the lab and began field testing them in 2003. Data from this experiment will be used to set standards for monitoring cranberry water supplies impacted by road salt runoff. We are also examining the salt alternative calcium-magnesium acetate and calcium chloride, also used in road management. Additional funding is pending for continued research into impacts on fruit production.

Phosphorus movement in cranberry systems-impact on water quality
Funding: MA DEP Cooperators: Dr. Brian Howes (UMass Dartmouth), Eagle Holt Cranberry,
Benson’s Pond Cranberry
Working with Dr. Brian Howes of SMAST (UM-D), we will develop information regarding critical activities with potential for P discharge from bogs and develop methods and practices to minimize P movement. One of our test sites is adjacent to Blackmore Pond, where a homeowners association has expressed concerns regarding the impact of cranberry bogs on the ‘health’ of their pond. A teamwork approach has led to cooperation among all interested parties in regard to data gathering and to an increased understanding among the homeowners regarding normal farming practices and steps growers take to preserve water quality. This project will result in information for the Clean Water Act mandated TMDL program and best management practices for cranberry growers to use to preserve water quality.

Beginning in 2001, we collected soil and water samples, monitored water flow, and studied water quality. The pond has low chlorophyll values and is well oxygenated to the bottom. Inorganic P was low in both surface and bottom waters of pond. This is consistent with good oxygenation, preventing large releases of P from sediments. Total P was moderate but below the threshold for eutrophic conditions. Quality of the water taken from the pond to flood the bog was compared to that of the water returned to the pond. Inorganic P was 8x greater and Total P was 5x greater in return samples compared to water from the pond. Inorganic nitrogen was roughly equivalent in incoming and outgoing water. We attempted to improve release water quality by impounding the 2002 harvest flood, then releasing it slowly using a barricade and gravity flow. After about 10 days of impoundment, water quality began to deteriorate. Gravity release with the barricade did appear to ‘scrub’ some of the P from the bog water, but the last water to leave was quite P-laden. To complete the picture regarding water moving between pond and bog, we estimated water volumes using staff gauges in the bog and a water level monitor in the pond along with bog mapping data and pond bathymetry to estimate volumes of water moving in flood events. We have also used the pond level monitor to calculate refill of the pond by groundwater recharge during floods (while the water is on the bog). Between of 9 and 13 million gal of water move onto the bog from the pond in a harvest flood (<15% of pond capacity). Depending on the season, 75%-90% of water was returned to the pond after harvest via surface discharge. As much as 2 million gal of water entered the pond through ground water during the time that the bog was flooded for harvest.

To summarize: Cycling water in and out of the pond may help to keep the bottom oxygenated, preventing sediment discharge of P; not all water withdrawn is returned; lengthy impounding can be counterproductive but gravity release and filtering appear to be beneficial.