MAY 2017
CELEBRATING 138 YEARS AS CANADA’S PREMIER HORTICULTURAL PUBLICATION
THEGROWER.ORG
SOIL FERTILITY
Dig deeper for fertilizer prescriptions by plot
By early May, all the inputs are in place for a new crop of asparagus. Like many perennials, asparagus needs long-term planning for soil fertility that will support high yields for a life cycle of 10 to 15 years. Access to variable rate technology to apply fertilizers is changing how growers think about their soils and managing them for more uniform yields. Mike Kungl, St. Williams, Ontario, is one such example. When he scratches down into the earth, he commonly finds earthworms: nature’s tilers. Photos by Glenn Lowson.
KAREN DAVIDSON From a geological perspective, the soils in the sandy plains of southwestern Ontario are young. Mike Kungl plans to make the most of his lucky inheritance after almost 40 years of growing asparagus near St. Williams, Ontario. “The old-timers used to say there was a kilometer of feeder roots if you dug up an asparagus crown,” says Kungl. “Asparagus has a massive root system, when you take the feeder hairs into account.” When planted in rows, four feet apart, asparagus roots can be found stretching across the underground aisle, tangled together. To support that web of life takes long-range planning. In the two to three years before planting asparagus plugs, Kungl soil samples more intensively than most. He takes a soil sample for every acre, and certainly for every different soil zone in the intended field.
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“Growers are taking soil fertility more seriously,” says Kungl. “My soil textures are variable, from sharp sand to sandy loam.” That willingness for a fertilizer prescription by plot comes from the fact that GPS allows growers to manage fields in a more targeted way. The technology allows finetuning of nutrients by zone. Kungl says that soils tend to be acidic, so it’s best to have a neutral pH of 7. One ton of lime per acre achieves this target. Next, potash is important for the rapid cell development that takes place in asparagus stalks. For asparagus growers, there’s only one chance to add phosphorus to make a strong root system, and that’s when planting the plugs for the bed that’s going to produce 6000 - 8000 pounds per acre for the next 10 to 15 years. Phosphorus is a hot topic in agriculture. In general, phosphorus is available in soluble, partially stable and stable forms. Plants have access to the available soluble portion. However, this soluble portion can also be removed from the field whenever there is water
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movement due to rain or snow melting, either on the surface or through tile drainage systems. That’s why cover crops are recommended to keep soil – and water—in place. Not to be forgotten is the touchtone of soil health: organic matter. While manure can be used, Kungl prefers mushroom compost from a Leamington plant. His observation is that the heat-treated compost results in a weed-free and heavy metal-free amendment to the soil. This compost is applied a year or two before planting and can also be applied again at the end of June harvest. This attention to detail, well in advance of planting asparagus, results in more consistent yields over the life cycle of the crop. To stabilize the long-term yield curves of 50 acres of asparagus, Kungl is always taking five or six acres of the older, spent plots out of production and planting new ones. Continued on page 3
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