Management of nitrogen fertilizers for corn in 2020 - farmdoc (2023)

As a year ago, since last fall, the possibilities of nitrogen fertilization are limited. Illinois had average to above average precipitation in the first three weeks of March, with temperatures several degrees above normal. The ground remains wet and current weather patterns do not give much indication of impending drought. However, with higher temperatures potentially accelerating drying, we would like precipitation to remain at or below normal to dry the soil in April.

N feet

Despite challenging conditions in 2019, IFCA's Dan Schaefer and John Pike of Southern Illinois, with funding from the Illinois Nutrition Research and Education Council (NREC), were able to conduct an on-farm N rate trial that showed most regions responded even and on planted plants. later, also similar to those found in recent years. Yields were generally not as high as in 2018, but the fact that in central and northern Illinois the responses were similar to those already in the database meant that adding data from the 2019 survey for this purpose would provide that portion.

However, the 2019 data for southern Illinois continued the trend seen in 2017 and 2018, where higher yields required higher rates of nitrogen fertilizers to achieve those yields. This correlation between optimum nitrogen rates and experimental yields was absent in soils with higher organic matter in central and northern Illinois. We believe this is because the weather conditions (warmer temperatures and high humidity) leading to high yields (and high N uptake) also increased the amount of N provided by soil organic matter mineralization, while the amount provided by fertilizers remained constant at least on average . In contrast, southern Illinois soils have less mineralizable organic nitrogen, so high yield levels make crops more dependent on fertilizer nitrogen.

This correlation between nitrogen rate and yield in southern Illinois supports our idea of ​​adding more nitrogen fertilizers to corn grown in southern Illinois on low organic matter (<2% OM) soils.If the crop has high yield potential.I recommend using MRTN for yields as high as 190-200 bushels per acre and potentially more (based on growing conditions when the corn is 2 to 4 feet tall) to get the total expected benefit of using 1 lb of nitrogen per bushel. This can often mean applying nitrogen using high diameter equipment, as a urea spread or as a near-row UAN drop. Sown nitrogen tends to be more evenly distributed and leaving UAN on the surface near the rows will bring it closer to the root system and possibly improve absorption.

useN Rate CalculatorCalculation of the optimal (MRTN) N ratio for Illinois corn. We updated the database in early March, adding data for 2019 and removing some older data. With a corn price of $3.50 per bushel and current ammonia prices of approximately $500 per ton ($0.30 per pound of nitrogen), the resulting MRTN values ​​and ranges are shown in Table 1 below. The low and high limits of the range are where N returns $1.00 less per acre than MRTN. Also shown are MRTN values ​​for N prices of $0.40 and $0.50 per pound, while corn remains at $3.50 per bushel. Nitrogen prices for UAN and urea are currently around $0.43 per pound of nitrogen.

Note that the MRTN rates (and ranges) generated by the N rate calculator include all N applied to the field, not just primary use. This means adding nitrogen applied with MAP or DAP in the late fall or spring, any nitrogen applied by herbicides or seeders to the total. If you are using N from multiple different sources, calculate the rate for the last application (plus any previous amounts) based on the price of the N fertilizer from the last application.

Management of nitrogen fertilizers for corn in 2020 - farmdoc (1)

N time

In approximately 90% of farm trials comparing fall (using N-Serve) and spring nitrogen applications with ammonia applications, fall and spring nitrogen applications responded almost identically to nitrogen applications and yield levels were the same. , including several that did better with spring nitrogen applications and those that did slightly better with fall nitrogen applications, the optimal nitrogen application averaged about 12 lbs higher - 181 lbs/acre compared to 169 lbs/acre - Yield was reduced by 1 bushel in the optimal fall nitrogen application compared to spring nitrogen application - 235 bushels per acre compared to 236 bushels per acre. This equates to a benefit of $9 per acre for a spring nitrogen application, but this benefit is difficult to realize because the additional benefit must be knowing when and by how much to reduce the amount of spring nitrogen application. Average optimum N for fall N application was almost the same as for MRTN in central Illinois (Table 1): MRTN use would mean using more than optimal N rates. In the experiment, the advantage of spring N application was small.

One of the main lessons we have learned from studying nitrogen timing and nitrogen speciation in recent years is that to maximize yield potential, post-emergence corn plants need a large amount of soil-available nitrogen near the rows at their nodes (mostly) before root development. In the 2019 study, plants were sown in late April, but fertilization could not be applied until early June due to rainy weather in May. As a result, the nitrogen response increased up to the maximum applied nitrogen rate (250 pounds of N), but not to a maximum. We also saw some examples of uncontrolled early intercropping of rye, possibly because rye roots deplete nitrogen from topsoil, which can affect corn yields even with high rates of nitrogen applied after emergence.

We don't know how much nitrogen must be present early in corn growth, but we believe that nitrogen must be present in the soil near the plant when nodal roots begin to emerge - around the V2 growth stage. Having 40 to 50 ppm of nitrogen available in the top layer of V2 soil means adding 40-50 pounds of nitrogen to the top 3.5 inches of soil, with most of the nitrogen staying there. If we include N in a 7.5" wide by 3.5" deep behaviorally focused area, just 10 to 12 pounds of N per acre will produce 40 to 50 ppm (300 GDD) when planted. This amount (but no more) can be applied in the furrow, but any downward movement of this N will remove it from the rooting zone of small plants. Applying 30 to 50 pounds of nitrogen in 2 x 2 spots, or dripping liquid or dry fertilizer into the rows to deliver 30 or 40 pounds of nitrogen per acre, better ensures that the time to apply nitrogen is as early as possible if needed. Using 10-12 pounds of N as UAN in the furrow is better than nothing. Seedling damage as a result of such applications is rare, but placing tubes in seed trays better prevents such situations.

Even if sowing is delayed and takes priority over nitrogen, it is necessary to introduce some nitrogen into the row or at the top of the row before emergence: the risk of waiting a week for the first application of nitrogen is too great, especially if N is not applied near the row. If the weather stays rainy this spring, some growers and retailers will need a little creativity to get the job done. Delayed planting means warmer soil at planting time, and warmer soil means more mineralization. This will increase the availability of nitrogen in the soil, but still may not be enough to increase yield potential, especially if rainwater carries some of the mineralized nitrogen downstream.

Split N

In a set of results of applying 150 lbs of nitrogen per acre in different forms and at different times, we found that a split of 100 lbs at planting and 50 lbs per season generally produced slightly higher yields than applying all of the inter-row nitrogen at planting. Applying 50 lbs of UAN as a UAN broadcast at planting (simulating the use of UAN as a herbicide carrier during or after planting) and then 100 lbs of UAN at the V5 stage also had no effect, probably because there was not enough before nitrogen supplement around the roots as needed. Most treatments where 100 pounds of nitrogen was injected at planting followed by 50 pounds as a side application had about the same effect. Waiting to apply all the N until side application is not an efficient way to apply N, and applying UAN to the soil surface also produced lower yields, even when urease inhibitors were taken into account. All of this points to the need to add enough nitrogen to the soil as early as possible to maximize yield potential in the early growing season and apply all nitrogen in a way that minimizes losses.

In these studies, we also found that the distribution of nitrogen (some during or before planting, and the rest as a catch crop) generally did not yield more than previous applications in the same ratio (properly distributed). This does not mean that we should not use N separately, but we should do so more for logistical purposes than as a way to get higher yields for the same (or lower) ratio of N, at least on fertile soils. We found no benefit from reserving 50 pounds of N for inside rim dribbles, nor did we find any benefit from using N (spoon feeding) multiple times during the season. The very rainy June we experienced in 2015 meant in some casesadditionalN. However, it is not easy to apply N under these conditions, and any application of N will incur additional application costs and the risk that N will not reach the roots in time for the plant to respond.


Although inhibitors sold as nitrogen fertilizer additives have been around for decades, there are still many misconceptions about these products, including what they do, when and how to use them.nitrification inhibitorIt slows down the activity of soil bacteria that convert ammonium into nitrate. Both ammonium and nitrate can be taken up by plants, but the ammonium form attracts the negative charge of clay and organic matter and remains in the soil, while nitrate is negatively charged and easily follows water as it moves down the soil. Therefore, slowing down the conversion of ammonium to nitrate (nitrification) is a way to keep more nitrogen in the soil and make it available to crops in (wet) conditions with high losses. Chemicals marketed as nitrification inhibitors include nipyrin (products include N-Serve®Japanese instinct II®Cortiva); pronitridin, a new product developed and marketed as Centuro®Koch AG, and dicyandiamide (DCD), a nitrification inhibitor sold by many companies under different trade names.

Nitrification inhibitors are usually added in the fall using anhydrous ammonia. The later in the spring we apply ammonia, the less likely we will need nitrification inhibitors to protect N. As a biological process, nitrification is slow when soil temperatures are around 50 degrees (until early, mid, and late April in southern, central, and northern Illinois). and begins to accelerate when the soil temperature reaches 60 degrees and above. late April in southern Illinois and mid-May in northern Illinois. If we add to that the effect of NH3Ammonia, which by itself inhibited microbial activity, when applied in southern Illinois after mid-April or in northern Illinois after early April, is unlikely to require further nitrification delays provided by nitrification inhibitors. There are exceptions: it can be warm and wet, with rapid conversion to nitrates, in which case a nitrification inhibitor can help. But if the crop is sown early and grows rapidly in May, absorption will begin earlier. If the weather is relatively dry, nitrogen is less likely to move through the soil, even if it is high in nitrates. That is why it is difficult to know at the time of application whether we should add nitrification inhibitors, we should play with the current conditions and the expected planting time to make an easier decision.

Because cold soil dries slowly, ammonia is usually applied in early spring (before planting) when the soil is wetter than ideal. Applying ammonia to wet soil means more soil compaction, the diameter of the ammonia band is small when applied to wet soil, and the concentration of ammonia in the band is high. If the soil dries out significantly after application (rarely if moist until April), NH3It can start where the tape is melted and work its way through the soil through the knife mark where it can damage the seed or roots. Using RTK to apply a strip 6 to 8 inches from where the plant row is located can eliminate this type of damage. Tillage after ammonia application also helps disperse the filaments, often reducing or eliminating the risk of ammonia damage to seedlings. Deeper placement also helps prevent damage, but moves N away from the roots.

Another inhibitor that is used to add to nitrogen fertilizers isInhibitorni ureazyInhibitors that do this include NBPT (sold under various brand names) and NBPT with Duramine (ANVOL®z Koch Ag)i NPPT (Limus®from BASF). Thiosulfate is also used as a sulfur source and is believed by some to inhibit urease, although laboratory studies show it to be less effective. As the name suggests, urease inhibitors are only effective when added to urea or other urea-containing fertilizers such as UAN solutions. They do not slow down the conversion from ammonia to nitrate; they simply slow down the rate at which urea is broken down into ammonia and carbon dioxide. If this decomposition occurs at or near the soil surface, ammonia can be released into the air as ammonia gas.

Ammonia is very soluble in water, so if urea is decomposed in moist soil, the released ammonia immediately dissolves and is difficult to get out of the air. Urease, which accelerates this decomposition, is a common occurrence in the soil, so if you spray the soil with urea or urea and it hasn't rained for a week or more, a lot of ammonia can escape into the air. UAN seeding, which thinly disperses nitrogen over the soil surface, exposes more urea to urease. But only half of the nitrogen in UAN is in the form of urea - the other half is nitrate and ammonium, which are not affected by urease. Urea and ammonium nitrate solutions contain some free ammonia, some of which may evaporate as the solution dries. Dry urea, when dissolved in soil water, is susceptible to the action of urease, but urea particles that fall into cracks on the soil surface can receive some protection.

Rain transports urea into the soil, which simultaneously moistens the soil and dissolves ammonia, which significantly reduces ammonia loss. This means that it is uncertain whether a urease inhibitor should be used. If urea or urea is incorporated into the soil during or immediately after planting or as a supplemental application, there is no need to add urease inhibitors because ammonia rarely leaches out of the soil. Droplet or surface UAN were slightly less affected by urease and transported some of the urease a short distance into the soil. UAN that drips onto the surface near the rows is less exposed to sunlight and wind, and water from light rain or dew that runs down plant stems helps transport nitrogen into the soil. Even so, surface-applied UAN can never be considered completely immune to evaporation loss, so if the forecast calls for warm, rain-free conditions for a week or more after surface-applied near the rows, inhibitors may be useful.

At warm soil surface temperatures, nitrification will begin shortly after urea dissolves and enters the soil (as ammonia). super perfect®(Koch), containing both urease and nitrification inhibitors, performed well in surface application tests and gave a higher urea yield than application with the urease inhibitor Agrotain (NBPT). Assuming that both products inhibit urease equally, the difference must be due to the faster conversion of ammonium to nitrate and the removal of part of the nitrogen from the root zone.

A new product for sale that increases nitrogen fixation by microorganisms

Advertisements and products purporting to deliver microbes or stimulate existing soil microbes to fix atmospheric nitrogen and deliver it to corn crops have increased recently. Microbial nitrogen fixation is how soybeans get most of the nitrogen they need, but this legume nitrogen fixation involves plant nodules that attach to roots below the soil surface where anaerobic (low-oxygen) conditions exist to aid the fixation process. We have long known that there are some "free-living" (non-nodular) bacteria in the soil that fix atmospheric nitrogen, but the measured rate of nitrogen fixation by these microbes is usually low—on the order of several pounds per acre of nitrogen applied. This is partly because it takes a lot of energy to fix atmospheric nitrogen, and the soybean plant pumps sugar into the nodules much faster than it can leak out of the roots (corn) to ensure life around the roots. Microbes provide food. It was once hoped that corn plants could be genetically engineered to produce nodules and host bacteria that could fix most of their own nitrogen, but the machinery needed by plants to form nodules and transport the fixed nitrogen through the plant is so complex that it seems unlikely. or at least there is still a long way to go.

There are two types of these products, which are mainly developed and sold by start-ups. One category is microbial (bacterial) N-fixing agents; these are usually used in furrows, the idea being that they multiply and grow near the roots, eventually getting enough sugar from the roots to fix nitrogen that the plants can take up. The idea is that the corn plant and the bacteria form a mutually beneficial (symbiotic) relationship, with the corn providing sugar and other materials for growth, and the bacteria returning the nitrogen. It is not entirely clear whether bacteria can act as "nitrogen pumps" in this way, and if so, how this symbiosis would benefit plants or microbes.

Another product sold is a chemical said to promote the growth and activity of nitrogen-fixing bacteria on corn plants. Some of these appear to be suitable as foliar sprays, possibly because they can be released into the soil through the roots or they stimulate the plant itself to release something, which in turn promotes the growth of immobilized N bacteria.

Claims on websites about these products may state that they accelerate plant (and root) growth, and often include pictures of this effect. Some have mentioned how much nitrogen can be tied up with the product. I haven't researched this, but I have noticed that at low N fixation rates (25 pounds of N per acre per season seems to be a typical amount) it is really difficult to determine microbial N fixation rates and any of these numbers should be treated with caution. One way to do some of these studies in the past was to use a relatively high rate like 200 pounds of nitrogen per acre and then use a lower rate like 160 or 175 pounds of nitrogen per acre and produce if yields were about the same. Draw conclusions about the differences in the product offering.

I recommend a wait and see approach to such products. Some companies ask producers to do on-farm trials, and if it is possible to make a set of paired strips, randomly assigned to each pair with or without treatment, this could be instructive. Split-field trials are less satisfactory because the two halves of the field never produce exactly the same yield, and field variability can be greater than any treatment effect. But most companies control the data from such tests and in most cases the product "wins" when such results are published on the website.

Manage the N this spring

One of the lessons we learned from the 2019 growing season is that we can apply nitrogen even when conditions are not good. This does not mean that N is used to the maximum in every domain: there are examples of domains that do not use N early enough to maximize performance. But with due care in applying the right rate at the right time, using a form that can prevent losses, Illinois farmers have the ability and flexibility to properly manage N, even when spring conditions are difficult.

While most of Illinois is currently wet, and the forecast is unlikely to warm and dry anytime soon, we can begin to plan our nitrogen management strategies based on the above principles. I won't go into detail about what might happen this spring and how to deal with it, but here are some things to keep in mind as you move forward:

  • useN Rate CalculatorTo begin with, when determining how much N to use. Note the extended "profitable range" on both sides of the MRTN. For most fields, the total N rate should be in this range, and the results of hundreds of tests conducted in Illinois over the years tell us that we can expect a return on N (increase in production and total revenue minus N costs) in the underground.
  • While we've said in the past that we might consider moving the N index outside (above) the range provided by the calculator, we've found consistent benefits from doing so only in very wet Junes. In this case, root damage due to excessive soil moisture and/or nitrogen loss may mean that the crop may benefit from additional nitrogen, but only if the soil dries out a bit to improve root function, and if possible before pollination or nitrogen application .
  • In southern Illinois, apply rates in the MRTN range and wait for V5 or V6 to decide if yield potential is greater than 190 to 200 bushels per acre; if so, consider adding some nitrogen in late vegetative growth to get the expected bushel. the amount of N used for crop production was 1 pound of N.
  • From October 1 to March 23, precipitation in northern Illinois ranged from slightly below normal to normal, while the southern part of the state reported 3 to 6 inches above normal. There have been spikes in temperature and precipitation over the winter, but we're not seeing more than normal fall-applied nitrogen loss; we can count on it to appear in the crops of 2020.
  • If the weather permits ammonia before the end of April, we should use it. Ammonia is currently cheaper and safer to use than any other form of nitrogen. Care must be taken not to use the planter in such a way that it can fall into the application, otherwise there is little chance that the ammonia will damage the seedlings.
  • If wet soil delays planting and nitrogen application, it pays to find a way to get some nitrogen (at least 40 to 50 pounds per acre; more may be better if not concentrated near the rows) so that nodal roots are available when they begin to develop around V2 degree.
  • If there is rye in the field where the corn will be planted, try spraying it a few weeks before planting to kill it. The more rye is killed, the faster it is killed, the more important it is. If the rye grows large (over 8 inches) before it is killed, be especially careful to plant N close to the rows so that it is regenerated as the rye is removed from the soil.
  • If you planted corn where there was no crop in 2019 and weeds are controlled by plowing or herbicides, the 2020 crop could benefit from a planter application of phosphorus to prevent "fallow syndrome." If spring weeds are strong or if MAP or DAP is sown this spring, there will be less (or no need) to apply P near the rows.
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