By Dan Zinkand
(Editor's note: When Victor Leforestier of the European Union asked about fertilizer strategies for strip-tillers in the U.S., Thurston Manufacturing Co. chief marketing officer Nick Jensen shared his perspectives, which appear below.)
Fertilizer strategies are varied in the U.S. based on climate (application opportunities in the fall vs. the spring), weather, availability on types of fertilizer (largely based on region) and the farmer’s preferences on what he likes to use.
A common fertilizer program for strip-till that seems to work well for a majority of farmers is to apply a dry form of phosphorus and potassium 6 to 8 inches deep in the strip at the time of the strip-till operation. The rate will be based on crop requirements vs. the amount and availability of the nutrients already in the soil.
Some will vary the rate of these nutrients based on soil samples and/or yield data from previous crops. Often, starter nitrogen is applied in a 2-by-2-inch deep band during planting. The rest of the nitrogen needed is injected in a sidedress operation starting around two-leaf stage, splitting the middle of the rows on 30-inch spacings.
The sidedress nitrogen application allows the grower to fine-tune his nitrogen requirements based on adjusted yield expectations, while keeping growing conditions up to that point in the plant’s life cycle in mind. Often, the nitrogen is delivered in a liquid form at 28% or 32%.
When a grower asks me which fertilizer program he should use, this is typically what I recommend to reduce the possibility of nitrogen loss.
Some growers also choose to apply nitrogen at the time of the strip-till operation, normally in the form of anhydrous ammonia gas if applied in the fall. Of these growers, some will choose to do only the nitrogen and leave the phosphorus and potassium as a separate application. Others will apply all three nutrients at once.
Again, this is in a band 6 to 8 inches deep. Rates of application vary greatly among producers, but it would be safe to say it would be common to place around 70% to 80% of the nitrogen needed during the growing season in the strip-till application. The rest would then be applied as starter fertilizer with the planter as described above.
When using anhydrous ammonia after harvest, the grower must wait until the soil temperature is at or below 50 degrees F to reduce the risk of nitrogen loss. Once anhydrous is applied, it quickly converts to NH4 when it encounters water molecules within the soil.
Once converted to NH4, the microbial conversion to nitrate will happen considerably slower (nearly suspended) if the soil temperature is below this level. This allows the nutrient to remain in the soil through winter as NH4, so it can be converted to readily available nitrate in the spring for use after planting.
If strip-tilling in the spring, the same could be done with a liquid form of nitrogen. Using a dry form of nitrogen can also be done in the spring or fall.
When applying nitrogen, phosphorus and potassium, it’s difficult to vary the rate adequately unless you have a dry fertilizer cart with three compartments that can blend them on the go.