Applying N? You May Be Wasting Your Time and Money
There is an old saying: The definition of insanity is doing the same thing over and over expecting different results. Today, current and ongoing research seeks to better identify the right balance between application of nutrients -- namely nitrogen -- to row-crop fields in an effort to ultimately end the trend of farmers resorting to those applications whether needed or not.
Nutrient application research isn't new. Farm groups, universities, and companies have been researching nitrogen use and uptake by all crops for decades. While that research has yielded frequent nutrient recommendations, they're taken as just that -- recommendations many farmers may use as a baseline, but from which they ultimately diverge in the nutrients they apply to their fields. The logic is sound: Apply more nitrogen and raise a bigger, more vigorous crop. Often, that's not the case, though. Farmers should take a second look at what they're applying -- even if it's based on pretty precise measurements in the field -- and reconsider how much they're putting down.
How much N you put down depends first on your attitude, researchers say. Think you're headed for a bin-buster? You're likely to apply more nitrogen, says Keri L. Jacobs, Iowa State University ag economist. Some of that has to do with the inherent optimism that comes with being a farmer, she says, though some of it can come back to bite you.
"Studies by psychologists and behavioral economists almost invariably find that people are overconfident. A form of overconfidence relevant to agricultural production is unrealistic optimism -- the belief that really good outcomes will occur despite objective evidence to the contrary. Our survey does not indicate overconfidence is prevalent among the central Iowa farmers surveyed," Jacobs says. "However, we do find some evidence of unrealistic optimism regarding yield expectations among a subset of the farmers. A roughly equal-size group of respondents is pessimistic about yield expectations, that is, they expect lower yields than those estimated by independent data sources. On average, the farmers we surveyed expect to harvest only slightly more bushels per acre than is predicted by historical data."
Next, it matters how much you think that nitrogen is worth to your crop. Jacobs says many farmers she and her colleagues at ISU's Center for Agricultural and Rural Development surveyed recently say they don't lack in confidence when it comes to the benefit of nitrogen in their fields.
"Preliminary analysis suggests that farmers overstate the impact nitrogen has on corn yields. Our survey asked farmers their perceptions about the yield response to added nitrogen on the fields that they managed, and the results show farmers believe that the decline in expected yield due to a nitrogen reduction is generally larger than the rise in expected yield due to a similar increase in nitrogen applied," Jacobs says. "A crucial question we seek to answer is, do farmers’ subjective beliefs about nitrogen-corn yield relationships match the objective data or the agronomic models and advice that they receive? Our preliminary findings suggest the answer to this question is no. For approximately 30% of the farmers in our survey, the expected incremental increase in yield from an increase in nitrogen applied exceeds the objective estimate that was attained from the research farm data."
What about soybeans?
You can get higher soybean yields from applying supplemental nitrogen. How much higher and whether those increases happen with any regularity are huge question marks and typically make applying extra N a wash at best and, at worst, a total waste of money when soybeans are expected to raise average yields, says University of Illinois Extension agronomist and corn expert Emerson Nafziger. His most recent research shows a range of nitrogen applied in different formats does influence yield, but in nowhere near the predictable manner to yield a recommendation.
"Yields ranged from 39 to 87 bushels per acre, with an average of 66. We saw significant (statistically likely to have been due to treatment, not just to chance) yield increases in two of the 33 trials, both about 6 bushels above the untreated check, and a significant decrease (of a little less than 5 bushels) in one trial. The average response to using N fertilizer over all 33 trials was .5 bushel (increase) per acre. There was no tendency for the response to be higher in higher-yielding trial; the 10 lowest-yielding sites showed an average response of about 1 bushel while the 10 highest-yielding sites showed an average response of only .25 bushel," Nafziger says of the most recent five years of soybean nutrient research trials. "These results show that adding N fertilizer can increase soybean yield, but also that a consistent yield increase is not likely. Getting a yield increase high enough to pay for the practice is also unlikely. The cost of the fertilizer (100 pounds of urea is about $23 at the current price of about $460 per ton) plus application means that yields need to increase by 3 to 4 bushels per acre just to break even. Ignoring statistical significance, we saw a yield increase of 3 bushels or more in five of the 33 trials and of 4 bushels or more only three times."
In circumstances when higher soybean yields are expected, nitrogen efficacy does increase, though there remain questions as to whether -- in situations where yields as high as 90 bushels per acre are expected -- applying additional N is worth it.
"The inconsistency of N response in scientific studies is likely because most soybean yields were restricted to below 60 bushels per acre by diseases, nematodes, drought stress, or other factors. It is only when these and other production limitations are removed that N becomes yield limiting. As higher soybean yields become more common due to improvements in genetics and management practices, N additions may be needed to maximize potential yields. Nitrogen needs that are unmet by the combination of N mineralization by the soil and N fixation by the plant can be supplied by other sources such as N fertilizer or manure. These supplemental N needs to meet crop demands are shown below for various soybean yield levels," says John P. Schmidt, DuPont Pioneer research scientist. "Even when soybean needs for supplemental N have been identified, a critical question remains - will N additions be cost-effective? That question will only be answered over time with broad-based research studies and side-by-side comparisons in growers' fields. With that in mind, the best approach to determine if supplemental N is required for your soybean field may be to simply try a low rate of N in alternate strips on a few acres. If a cost-effective yield increase is observed with 20 to 30 pounds of N per acre, then consider testing an even higher rate. With the availability of precision farming technologies, many growers can directly evaluate the merits of an N fertilizer application to soybean on a field-by-field basis. Knowledge of which soybean fields respond to additional N fertilizer is valuable information for future soybean crops."
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