Too much hype? | Soil on some farms may not vary enough to warrant the cost
CALGARY — Variable rate fertilizer technology can be expensive, says Alberta Agriculture research scientist Ross McKenzie, which is one big reason to approach it with caution.
At $10 to $12 per acre, the technological cost can’t exceed the value of potential benefits, he said.
As a result, producers should walk before they run into full-scale VRF.
“My concern, then, is a clash be-tween scientific knowledge and marketing. Is the marketing promoting VRF technology beyond realistic and scientific capabilities? I want you to think long and hard about that.”
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McKenzie told the Precision Ag 2.0 conference Feb. 23 that many factors influence soil variability, and VRF technology will not allow farmers to control all of them.
In theory, the greater the soil variability, the greater potential for VRF benefits, but that depends on the accuracy and correct interpretation of the data derived from soil maps and other measurements.
He said soil factors that should be considered when developing a VRF strategy include plant-available nutrients, organic matter, texture, water content at time of seeding, pH, profile depths to the C horizon, past erosion, salinity, surface water drainage and topography.
VRF has the best potential in the ground moraine and hummocky moraine soil types of the Northern Great Plains, McKenzie said. Lacustrine and fluvial lacustrine soils are less likely to benefit.
A field’s topography is also crucial. Knolls typically have thin topsoil, lower organic matter, poorer soil structure and lower water infiltration and water holding capacity.
Lower areas generally have the opposite properties.
McKenzie said grid soil sampling in combination with soil mapping would likely provide the best data for creating soil management zones, but grid sampling can be time and cost prohibitive.
He suggested aerial photos combined with farmer knowledge of the field as a starting point, followed by information from topography maps derived from on-board GPS.
Electrical conductivity tests provide data on salinity, while remote sensing imagery during crop growth can identify parts of the field with measurable different productivity.
Yield maps, though poorly correlated to soil type, can also be helpful, McKenzie said.
That data, combined with the results of soil sample tests, should allow the creation of specific soil management zones.
Various companies offer agronomic services to interpret data and help farmers create these zones, but McKenzie advised caution there, too.
“I heard some pretty scary things yesterday about how fertilizer recommendations are developed,” he said about the Feb. 22 conference sessions.
“The biggest concern I have is the variation among agronomists on how they make their recommendations.”
He encouraged producers to consider available soil moisture before developing their fertilizer plan, and to fertilize according to reasonable yield expectations.
Those considering VRF should start on a small scale, use logic to create management zones and consider their own experience and knowledge about that particular field.
“We have great engineering technology for VRF. But are the soils on your farm varied enough to consider VRF? If so, start small. Expand as you develop knowledge and expertise,” McKenzie said.
