Less seems to be best
Composting experiments point to reduced use of fertilizer, and lower costs for growers.
By Judie Steeves
ometimes you have to kill a few blueberry plants in order to learn something. It’s just the nature of
And, that is exactly what Tom Forge did, as part of his research into the fertilization of blueberries, and the leaching of nitrogen into groundwater sources in both raspberry and blueberry fields.
Forge is a scientist at the Pacific Agri-food Research Centre at Agassiz who has found that compost is not a high enough pH for blueberry plants— and he killed a few in the process of discovering how sensitive they are. But he is using a different source of compost now, and no more plants have died. In fact, they are doing extremely well.
Forge is experimenting with composted yard waste, comparing berry production to plants in a regular plot, those using compost alone as a mulch, a mix of fertilizer and compost, compost supplemented with half the fertilizer, and a mix of sulphur and compost.
So far, the best yield has come from the use of compost with half the usual amount of fertilizer, he notes. It is also less expensive if a grower can reduce the amount of fertilizer needed, he adds, and compost is more reasonable than sawdust as a mulch. “I’m excited about this,” Forge admits, and he is now getting some funding from growers and from organic growers to continue the work. He also tried composted manure so less fertilizer would be needed, but blueberries are extremely sensitive to too much nitrogen.
It began as research into the leaching of nitrates into the aquifer, but “we also want to know about the long-term sustainability and soil health and quality; about root diseases and about growth and yield,” he explained.
Dr. Tom Forge has found that compost is superior to sawdust as a mulch.
When raspberry growers renovate, they fumigate the soil in the fall before putting in new plants.
Forge wonders whether a rush of nutrients results from the lack of microbes left in the soil after the fumigation, and they leach out. There is more leaching from plots fumigated than from non-fumigated ones.
In another area, Forge is
experimenting with alternatives to the application of manure to raspberries. For instance, between the rows, instead of leaving the soil bare, he is trying different cover crops between the rows, a perennial and an annual one.
“We tried planting a barley cover crop in the fall to take up the nitrates, and tilled it in in the spring,” he explained.
18 British Columbia Berry Grower • Summer 2010
There is a control plot where the standard amount of fertilizer is broadcast, then experimental plots where half the normal amount is used, and where fertigation is used. A variety of irrigation rates are being tried too. “We found we used half the usual amount of irrigation and there was no obvious reduction in crop and yield. It’s astounding,” he commented. In addition, one of the main issues with raspberries, root rot, which favours wet conditions in the root zone, could be eased with the use of less water.
Last year was the first full summer with these experiments, so some of the data must still be analyzed, including the leachate collected from 32 chambers buried throughout the raspberry patch before the plants were put in.
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