Cranberry testing
The question often arises among cranberry growers: to sand or not to sand? Dr. Rebecca Harbut of the Sustainable Agriculture and Food Systems Department at Kwantlen Polytechnic University (KPU) finds that while the practice of sanding may be commonplace, the unique growing conditions of BC bogs leaves the question open for research.
“The reality is, we have a very different bog here, than in other regions,” Harbut notes. “Some of the management practices we employ should reflect that.”
‘Sanding’ is exactly what it sounds like: A layer of sand from one-half inch to two inches thick is applied to the surface of the cranberry bogs every few years, and during the winter, growers may actually apply sand on top of ice and snow.
The sand filters down to the vines, covering the stems, encouraging better rooting, and reducing insect populations, weeds and fungi.
Harbut’s point is that since the growing conditions in BC are different, the management practices should reflect that difference. Standard practices from other regions shouldn’t simply be adopted because they are familiar or known. She’d spent time in Ontario and the U.S., so when she returned to BC, the question of sanding came up from BC growers again.
“But it’s not the only question,” Harbut says.
In this vein, in 2016 she began two sanding trials in two different fields to look at the practice of sanding and whether it made sense for BC cranberry growers. One field was healthy, with a dense canopy, upright growth and even signs of overgrowth. The other field appeared to be stressed with patchy sections in the canopy and a lower upright density.
To these fields, she applied three depths of sanding: no sand, 1/2 inch and one inch. Each depth was replicated eight times in each field, and plant growth characteristics were measured in 2017.
When Harbut measured the results, she noticed the yield and canopy depth had not changed significantly when looking at the amount of sand that had been applied to the different replications in each field.
“Statistically, there’s no difference,” she says. “What was interesting is what we saw in the pull test.”
The pull test is a way to measure root health, or the actual power of a root system. By pulling up on the canopy and measuring the non-rooted volume, growers can see how well rooted their plants are. Anything more than an inch in a pull test is often an indication of a plant in stress, under disease or having other issues that contribute to poor root health.
In the pull test, the first field – the healthy field – showed no difference. It already had good rooting ability. The second field gained Harbut’s attention. In this field, while the canopy and yield hadn’t yet changed, there was a non-statistical difference in the rooting capacity and number of uprights.
“On the more stressed bed, sanding had an impact on the number of uprights,” she notes.
There was a growing improvement in rooting capacity that correlated to the increased amount of sand applied. Thus, the plots with one inch applied showed an improvement in rooting capacity and greater rooting capacity than the plots with ½ inch of sand or no sand. The amount of upright growth in the stressed beds also increased.
“It may help to maintain productivity and prevent the bed from becoming stressed,” Harbut suggested.
If sand improves rooting capacity, more may need to be applied depending upon a grower’s results from root tests. When comparing the amount of sand in the trials to other regions, Harbut notes, “Our canopies are deeper, so this amount of sand is minimal compared to the canopy.”
Sanding may be a viable option for stressed fields that show poor root capacity in a pull test, it may also help prevent poor root health. Testing will continue to help determine if canopies and yields show any change.