Rock and Roll Agronomy
The Pros and Cons of Split-Applied N
Take into account one of your most precious resources during the growing season -- time
By Jason Hanson,
Certified Crop Advisor
As we turn attention to the next growing season, there are two things to note
on the fertilizer front: 1) The price of nitrogen is consistently high in all its forms no matter where you reside. 2) There is more interest in post-applied or
split applications of nitrogen on certain crops, mainly winter wheat and spring wheat.
Actually, there are other crops that have potential for this to work as well, namely canola and corn. But as with all things relating to crop production, there are
many factors that go into determining if post-applied N is beneficial, both agronomically and economically.
The first place to start with all of this is a current soil test from this past fall. Planning to put on a 30 gallon shot of 28% N is a guess if you donít know
what your background nitrogen levels are. What good would an additional 90 units of N do if the field already has a high or very high background
nitrogen reading? If you donít have a test from last fall, try to get one taken this spring.
In my opinion, this past year was a great example of conditions appropriate for using post-applied nitrogen on certain crops. In most areas, there were
quite a few early spring rains that came frequent enough to keep the ground wetter and cooler than in 2002. It made for great stands of small grains.
Rain also gives you the chance to get those N applications incorporated without loss due to volitization. Follow this up with a cool June and that spelled out some good small grain yield potential for 2003.
But even if production conditions were perfect for using post-applied nitrogen, did it pay off economically?
It did if you got the nitrogen on early enough, and had adequate moisture. This past year saw plants that were very efficient in obtaining N either from
organic or inorganic sources. Fertilizer put on pre-plant in the fall of 2002 or spring of 2003 yielded as well as split nitrogen in dryland situations or drier
conditions. Split rates were better when there was more moisture present during the early growing season.
See related data by Joel Ransom, NDSU extension agronomist (Table 3, effect of N timing on wheat yield, page 35). This data can also be found online at www.ag.ndsu.nodak. edu/aginfo/smgrains/IntensW04.htm.
With corn, the case can be made for splits if the ground is of a lighter texture or sandy type of soil. Denitrification or leaching can occur on light as well as
heavy ground. Corn only uses about 15% of its total nitrogen before the rapid leaf growth occurs, which is about at the V10 (tenth leaf stage) or
approximately 35-40 days after emergence. Maximum nitrogen use rate occurs just prior to pollination.
Wheat and barley plants will start to use nitrogen heavily by the 5-6 leaf stage, and so it becomes critical to get it on in a timely manner, before the 5
-6 leaf stage. Be sure to evaluate stand and yield potential before applying a second N application.
In trying to find a way to reduce some of the input costs that have made profitable canola production possible, split nitrogen rates have shown great
promise in increasing yields. There is huge return for canola if nitrogen is put on by the 4-5 leaf stage, provided it rains. That is the biggest part of the
equation. As with other crops, the decision to split apply isnít cut and dried. A person needs to evaluate factors like moisture situation, crop stand and
pest damage (like flea beetles in canola) to determine if using a post-applied nitrogen application may be worthwhile.
A dry year adds another dynamic to the decision of whether to use split-applied N. If the cropís nutrient needs are all put on pre-plant and the
yield potential is low, why spend any more money, when you might even lose what you have invested in nutrients you already put in the ground?
Good question. It just goes to show that the advantage of split applications can vary with each yearís growing conditions, and with each growerís farm situation.
The biggest drawback I see is the effect this may have on one of the crop producerís most precious resources during the growing season, and thatís
time. It may be a challenge getting splits done on a timely basis, and one must also consider the time to do it over a large number of acres or fields over a wide area, with weather always the wild card.
Some guys have a heck of a time getting their post-emergent spraying done the way it is. Knifing on anhydrous or dribbling on 28% N and covering
with a cultivator takes time to do too, and if youíre in a post-emergence weed control program it means youíre going across each acre again. On the other hand, maybe you have the conditions, the resources, and the
manpower where splits are worth the time and effort.
So itís no wonder the issue of split N applications is debatable, because there are pros and cons on both sides of it. If youíre interested in split
applications, you may wish to try it on a limited number of acres first to evaluate the impact on your yields and your time.
Hanson is a certified crop advisor near Devils Lake, N.D.