A two-year Red River Valley study looking at the usefulness of sidedressing to correct in-season nitrogen deficiency produced mixed results. Its bottom line? The likely payoff — or lack thereof — depends upon the circumstances. Here’s an explanation.
While sidedressing is quite common with certain crops in the Red River Valley, like corn, it is decidedly less so with beets. One reason to look at the practice’s feasibility, Smith suggests, is climate. “Last year (2012) was a little dry; but during the 10 previous years we had a lot of standing water from excess rain — and under the ‘right’ conditions, we can lose large amounts of nitrogen due to denitrification,” he says.
Another reason for this study, its authors note, is that in an excessively wet fall in the Red River Valley, many growers are unable to apply all — sometimes little or none — of the next year’s sugarbeet nitrogen needs prior to freeze-up. If they must put it all on in a spring treatment (e.g., 120-pound rate), unacceptable plant stand loss may occur.
Then there is the N-use efficiency aspect: when does that beet plant really need the nitrogen in order to achieve maximum yield?
And finally, “the other reason to look at [in-season sidedressing] is environmental concerns,” Smith explains. “We’re seeing a lot more tile drainage being installed in the Valley; and if we have nitrogen going through (due to leaching), there’s the threat of it ending up in streams and rivers.”
The objective of the Crookston study was to determine the effects of sidedressing 30 or 60 pounds per acre of nitrogen — at different times and with different soil N levels — on sugarbeet yield, quality and profitability. The 2011 trial was planted around May 7; the 2012 trial went in two and a half weeks earlier, on April 20. “We went in at 30-pound increments and established N rates in the fall at 0, 30, 60, 90, 120, 150 and 180 pounds,” Smith explains. “We also had 45 pounds of residual N.”
The researchers then sidedressed at either 30 or 60 pounds of actual N as UAN (equatable to 10 to 20 gallons of 28%). A fluted disk coulter and tube placed the UAN at a 4- to 5-inch depth. Placement was down the middle between 22-inch rows, so 11 inches from each row of beets.
Two different timings were evaluated: “T1,” which equated to the six-leaf stage; and “T2,” which was at row closure. In 2012 the T1 application was made on May 25 and the T2 treatment on June 15. The trial was harvested on September 24, 2012.
In terms of overall beet yield (regardless of rate and timing of sidedressed N), yields in 2012 peaked at 29.0 tons with the 120-pound rate of total applied N. However, there was no statistical difference between 120, 150 and 180. (Remember, too, the 45 pounds of residual N already in the soil.) Recoverable sugar per acre (RSA) peaked at 90-120 pounds and then dropped off (though again, not significantly). With net sucrose, there was a significant reduction beyond 90 pounds of applied N. “The most important category from the grower’s point of view is gross return per acre,” Smith points out. “There we peaked at the 90- and 120-pound rate. Everything else was significantly less.”
Smith and Nielsen found that sidedressing at all six nitrogen levels (30, 60, 90, 120, 150 and 180) did not appreciably increase sugarbeet yield, quality or profitability. However, they did conclude that sidedressing N may increase gross return if there has been a loss of nitrogen due to environmental conditions. The trial also underscored the importance of timing: the sidedressed N must be applied earlier in the season rather than later (toward row closure) to maximize return.
While Table 1 indicates no advantage to sidedressing part of the crop’s nitrogen needs, Table 2 reflects the potential benefits of sidedressing, assuming 30 pounds of N being lost to denitrification. (All of the sidedressed N treatments would be at the T1 timing.) While adding 30 pounds of sidedressed N under the “120 applied/30 lost” scenario actually ends up costing $106, the opposite is true at the lower rates of applied N with the same 30 pounds lost. Table 3 is even more dramatic. It shows, for example, that if 90 pounds were applied but 60 lost to denitrification, one could gain $213 per acre by sidedressing 60 pounds of N at the T1 stage. The figure is even higher at “60 pounds applied/60 pounds lost”.
As reflected in Table 4, Smith and Nielsen emphasize that sidedressing must be done early in the growing season to maximize returns from the practice. This point correlates with American Crystal Sugar Company grower recommendations regarding sidedressing. Crystal, which has a number of on-farm sidedressing trials, summarizes its guidelines as follows: (1) soil test just ahead of application, (2) apply no later than the six- to eight-leaf stage, and (3) placement below the soil surface for best results.