Farmers are wasting serious dollars by put the wrong amount of fertilizer on their fields, according to Wade Barnes of Farmers Edge Consulting.
“In one-third of the field you’re over-fertilizing, one-third you’re under-fertilizing and on one-third you’re about right,” Barnes told the Seedmaster’s Master Seeder Conference at Regina in November, citing a University of Utah study that evaluated standard fertilizing practices.
Barnes believes the best way for farmers to maximize their return on fertilizer investment is to look at variable rate technology (VRT). Having an accurate prescription map ready to use at seeding is the only way to ensure enough fertilizer gets to where its needed.
“One thing we’ve noticed if we’re shy of fertilizer on a very productive area, we can’t go back in time and correct that,” he adds. “Eighty per cent of your yield comes from 50 per cent of your land,” so not getting enough on those highly-productive areas can really affect yield.
Yeld variability often comes from the field’s topography.
“There’s variability everywhere; slope, topography and microclimate all play a part in it. A slight change in elevation makes a huge difference in the production potential of a field,” Barnes says.
Using a VRT prescription map to create zones that account for those and other differences across a field is the best way to stretch fertilizer dollars, he says. “I believe it’s a very simple concept. The phrase ‘the right rate at the right time’ really hits it.”
But topographical differences are only one factor.
“The other part of field variability is man-made,” notes Barnes. “What we’ve found through remote sensing is there are huge differences in a field you might not be able to explain (without knowing the field’s use history). What’s happened in the past has a huge impact.
“The primary tool we use is satellite imagery. The second tool, which is probably more valuable than anything, is knowledge of the field. That comes from the grower, the agronomist or the person you rent your land from.”
MERGING SMALLER FIELDS INTO ONE
Without evaluating past history, either through archived maps or through a farmer’s knowledge of past practises, Barnes says it’s easy to misinterpret data from current satellite images.
“What we found was these dynamics were playing themselves out on all the fields we were dealing with. Those agronomic issues that happened 20 to 50 years ago still have an impact today. This happens on every field across Western Canada.”
As farms evolved and grew over the years, collections of smaller fields have been merged together and are now being farmed as one, even though they had very different, localized uses in the past.
“These (previously smaller) fields have all turned into half section fields today,” says Barnes. “(Because of that) putting the same rate of fertilizer across every field on your farm doesn’t make a lot of sense.
“The main reason we use satellite imagery is that we think it shows the crop’s greatest potential and greatest weaknesses. We try and do it (get images) during strategic times during the growing season. We find we can go back up to 10 or 15 years and see the changes in the field.
“Some people go out and buy imagery; they’ll use one year and build (VRT) zones from that. If you pick the perfect year, that’s fine. But if you’re working with someone who doesn’t know your land and all the history behind it, you could have problems.”
Barnes says farmers who try to develop zones for VRT without satellite images are making a mistake.
“Some people believe you can use yield maps to build zones. The problem we’ve found is very few farmers have good yield maps for each field. A lot of times you have holes in your data (often caused by equipment failures).”
But while yield maps may not be the best option for building prescription maps, they are useful in evaluating the results of VRT use.
“We want every single grower to get a yield map,” says Barnes. “It’s a report card to whether the work we’ve done actually makes you money or not.”
It is also important to combine soil testing with the other data in order to fine tune VRT maps for accuracy.
“We test every zone,” he says.
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