Consideration for Corn N Management under Dry Soil Conditions

Source: C.O.R.N. Newsletter

Sidedress applications of nitrogen have begun and many more fields will receive applications in the upcoming week.  The information below from the C.O.R.N. Newsletter maybe of some interest.

When considering adjusting your corn nitrogen program for dry weather conditions, consider how N gets to the root system for uptake. Mass flow is the primary mechanism for nitrogen (also sulfur, magnesium, and calcium). Mass flow is where nutrients in soil solution move toward the root as the plant takes up and transpires water through the crop canopy. Also, consider how dry weather affects the plant root system. Root growth will slow in dry soils, the situation we are now experiencing in the upper soil depths. Fortunately, root growth will re-establish, and the mass flow of nitrogen will quickly improve with rainfall. Here are a few considerations for managing N applications.

Nitrogen placement is one area to consider changes within the limitation of equipment available. The nodal root system originating from the lowermost nodes will take up nearly all N. Normally we discourage surface applications of nitrogen due to potential volatilization losses of N in urea form found in UAN or urea. Under dry weather conditions, we have limited opportunities for rainfall to move N into position for uptake. The goal should be to have nitrogen close to the root system and close to roots actively taking up water. So, moving UAN placement closer to the row and a little deeper will improve plant access. Anhydrous application is already deep enough and moving closer to the row increases root injury potential, so no adjustment is needed.

Nitrogen rate is another consideration. Looking at our N yield response data from 1998-2022 does not show that lower yields usually require less fertilizer N than higher yields. We think that’s because the causes of lower yields, which are typically stress from having less available water at critical times, often affect root growth, and so may make it harder for plants to take up the N that is in the soil. If your plan was to apply a rate based on the Corn Nitrogen Rate Calculator (https://www.cornnratecalc.org) which is for corn after soybean and a N:Corn Price between 0.1 and 0.15, the rate is 160 to 181 pounds of N per acre then stay with that amount. If the plan was to apply more than that, then cutting back would be reasonable.

A final consideration is timing. Application systems that make late-season applications possible have become more common. Putting down a reasonable side-dress rate and then basing a later application on rainfall could be a reasonable strategy.

Cover crops would also be something to start looking at now. We know if the yield falls short of normal, we will have excess soil nitrogen left after the growing season. The edge of field studies conducted by USDA-ARS has shown we can recover a substantial amount of this residual N through a cover crop. Exploring available cost-share programs with NRCS and SWCD would be a reasonable way to retain that valuable N on your field for a future crop.

When and How Much Nitrogen to Apply to Wheat

Wheat has already reached green-up across the state so spring N may be applied anytime fields are fit. Keep in mind that research has shown no yield benefit to early N applications as long as the application was made by Feekes – 6 (one visible node).  If you need a reminder on how to assess if wheat is at Feekes GS 6, see this video: https://www.youtube.com/watch?v=D_f3VrqzV5c.  Nitrogen applied early has the potential to be lost since wheat will use little N until after jointing. Urea-ammonium nitrate (UAN) or 28% has the greatest potential for loss and ammonium sulfate the least. Urea will have little potential for loss as long as it does not volatize. No stabilizer will protect the nitrate component of UAN, which is roughly 25% of the total N in UAN at application time.

Ohio State University recommends the Tri-State Fertilizer Recommendation Bulletin for N rates in wheat. This system relies on yield potential. As a producer, you can increase or reduce your N rate by changing the value for yield potential. Thus, a realistic yield potential is needed to determine the optimum N rate.  To select a realistic yield potential, look at wheat yield from the past five years.  Throw out the highest and lowest wheat yield, and average the remaining three wheat yields.  This three-year average should reflect the realistic yield potential.

Table 10 in the Tri-State Fertilizer Bulletin recommends 120 lb N for yield goals of 100 bu/A, 110 for 90 bu/A crop, 90 lb for 80 bu/A crop, and  80 lb for a 70 bu/A crops. These recommendations are for total N. If you prefer to be more specific, the following equation may be used for mineral soils, which have both 1 to 5% organic matter and adequate drainage:

N Rate = (1.33 x Yield potential) – 13.

No credit is given for previous soybean or cover crops, since it is not known if that organic N source will be released soon enough for the wheat crop. The Tri-State Fertilizers Bulletin recommends that you subtract from the total (spring N) any fall applied N. I would take no more than a 20 lb/A credit even if you applied a larger amount. Whether you deduct fall N depends how much risk you are willing to take and your anticipated return of investment from additional N. Based on the equation above and deducting 20 lb from a fall application, a spring application of 100 lb N per acre would be recommended for a yield potential of 100 bu, 90 for 90 bu potential; and 70 for a 80 bu potential.  Nitrogen rate studies at the Northwest Agricultural Research Station over the past 20 years have shown the optimum rate varies depending on the year. However, averaged over years, yield data from these studies correspond well with the recommendation equation given above. These studies have also shown apart from one year, yields did not increase above a spring rate of 120 lb N per acre.

Wheat generally does not benefit from a nitrification inhibitor since temperatures are relatively cool at application time and the application is made to a growing crop, this is especially true as the crop approaches Feekes – 6. However urea may benefit from a urease inhibitor (products containing NBPT) if conditions for volatilization exist for several days after application. These conditions would include an extended dry period with warm drying temperatures (risk increases with temperatures above 70°F) and evaporating winds. Urea applications need at least a half inch rain within 48 hours to minimize volatilization losses unless temperatures remain relatively cool. The urease inhibitor will prevent volatilization for 10 to 14 days with the anticipation of a significant rainfall event during this time.

ESN or polymer coated urea will reduce the potential for N loss from leaching, denitrification, and volatilization. Since these conditions are unlikely to occur in most years, it may not be economical to use this product. Cool weather may prevent the timely release of N from ESN, so if ESN is applied, it should be mixed with urea or ammonium sulfate and be no more than 60% ESN.

A split application of N may be used to spread the risk of N loss and to improve N use efficiency. However, Ohio State University research has not shown a yield increase from this practice compared to a single application after green-up. In a split system, the first application should be applied no sooner than green-up. A smaller rate should be applied with the first application since little is needed by the crop at that time and the larger rate applied closer to Feekes – 6.

Wheat Growth Stages

OK, Mother Nature is not cooperating which means we can’t talk about corn and bean planting so let’s talk about the crop we do have growing – Wheat

Source: K-State University

Knowing what growth stage your wheat crop is at is essential for nitrogen, herbicide and possibly fungicide applications.  Most of the wheat I have seen in the county so far is between Feekes 5 and Feekes 6.

Feekes 5 is the time to be making your last nitrogen applications and applying herbicides as needed for weed control.  However at Feekes 6 you should cutoff for nitrogen applications to avoid leaf injury.  Additionally some growth regulator herbicides, like 2, 4-D and dicamba should not be applied.

Updated Tri-State Fertilizer Recommendations Now Available

After 25 years, the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa has been comprehensively updated and is now available. The full version can be downloaded as a free pdf, or a printed copy can be purchased: https://extensionpubs.osu.edu/search.php?search_query=974&section=product

A summarized version of findings can be found here: go.osu.edu/fert-recs

The recommendations are based on more than a decade of field trials evaluating N, P, K, S and micronutrients, including over 300 on-farm trials across 41 Ohio counties. This work confirms that the original Tri-State recommendations provided sound guidelines for nutrient management. However, some changes in the recommendations have been made to keep pace with contemporary practices in Ohio’s field crops. This new guide provides an objective framework for farmers to manage nutrients as judiciously and profitably as possible.

Red counties reflect the Ohio counties where fertilizer trials were conducted (2014 – 2018).

Corn of Many Colors

Source: Alexander Lindsey, Steve Culman, Peter Thomison, OSU Extension

As corn is emerging and beginning to grow, we are again seeing many colors present. In any given field, corn can appear dark green in sections, while other sections are yellow and occasionally purple. Yellowing (due to low nitrogen or sulfur uptake and/or limited chlorophyll synthesis) or purpling (reduced root development and/or increased anthocyanin production) of corn plants at this stage of development generally has little or no effect on later crop performance or yield potential. If it’s induced by environmental conditions, the yellow or purple appearance should change to a healthy green after a few sunny days with temperatures above 70 degrees F (and as soils dry). If plants remain yellow then closer inspection and assessment is needed to determine if the yellowing is caused by nutrient deficiency or some other factor. Cooler wet conditions often increase the appearance of these different colors. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool.

 

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Ponding and Saturated Soils: Results of Recent Ohio Corn Research

Source: Alexander Lindsey, Peter Thomison

Persistent rains during May and early June have resulted in ponding and saturated soils in many Ohio corn fields and led to questions concerning what impact these conditions will have on corn performance.

The extent to which ponding injures corn is determined by several factors including (1) plant stage of development when ponding occurs, (2) duration of ponding and (3) air/soil temperatures. Corn is affected most by flooding at the early stages of growth (see https://agcrops.osu.edu/newsletter/corn-newsletter/2018-15/young-corn-wet-feet-what-can-we-expect). Under certain conditions, saturated soils can result in yield losses. Saturated soil conditions can result in losses of nitrogen through denitrification and leaching. Additionally, root uptake of nutrients may be seriously reduced even if plants are not killed outright by the oxygen deficiency and the carbon dioxide toxicity that result from saturated soil conditions. Root growth and plant respiration slow down while root permeability to water and nutrient uptake decreases. Impaired nutrient uptake may result in deficiencies of nitrogen and other nutrients during the grain filling stage. Once the corn has reached the late vegetative stages, saturated soil conditions will usually not cause significant damage. Moreover, moderate temperatures should help minimize the level of stress.

Although standing water is evident in fields with compacted areas, ponding has usually been of limited duration (i.e. the water has drained off quickly within a few hours). In Ohio in 2017-2018, we observed a 10% yield loss when corn was flooded at V4 for 2 days and received 120 lbs N pre-plant + 60 lbs N sidedress (applied post-flood). When flooded for 4 or 6 days, yield loss increased to 15 and 33%, respectively, when receiving the same N regime. If the additional 60 lbs N was not side-dressed post-flood, yield losses increased to 30, 50, or 57% for 2, 4, or 6 days of flooding, respectively. According to Dr. Emerson Nafziger at the University of Illinois (http://bulletin.ipm.illinois.edu/?p=1240) “…At the time the crop reaches stage V13 (about head-high), it still has to take up 110 to 120 lb of N, and in years when June is wet, a common question is whether or not the crop might run out of nitrogen, leaving the crop short. While the need for 20 or more lb of N per week would seem to raise the possibility of a shortage, the production of plant-available N from soil organic matter through the process of mineralization is also at its maximum rate in mid-season. For a crop with a good root system growing in a soil with 3 percent organic matter, mineralization at mid-season likely provides at least half the N needed by the crop on a daily basis. This means that normal amounts of fertilizer N, even if there has been some loss, should be adequate to supply the crop.”

If the rain has been paired with strong winds, root lodging may occur. Yield losses of 4, 10, and 15-25% have been reported for 100% root lodging at V10, V13-15, and V17-R1, respectively in Wisconsin. Results from Ohio in 2018 suggest these values may be greater than previously reported (8, 37, and 58% yield loss when root-lodged at V10, V13-14, and VT-R1, respectively).  This trial will be repeated in 2019 in Ohio.

Disease problems that become greater risks due to ponding and cool temperatures include Pythium, corn smut, and crazy top. Fungicide seed treatments will help reduce stand loss, but the duration of protection is limited to about two weeks. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage from corn smut and crazy top is difficult until later in the growing season. However, the economic impact of these latter two diseases is usually negligible.

Spring Herbicide Applications on Winter Wheat – Part 2 Labeled Herbicides

Source: Purdue University (Edited)

If weed infestations are severe enough to require a herbicide application, the use of liquid nitrogen fertilizer solution as a carrier is a popular option for applying herbicides and topdressing the wheat crop in a single pass over the field.  Caution should be taken when using a liquid fertilizer as a herbicide carrier as moderate to severe crop injury can result, especially in saturated conditions.  Many post applied wheat herbicide labels allow for liquid nitrogen carriers, but require different rates and types of surfactants than if the herbicide was applied with water as the carrier.  Table 1 includes precautions to be taken when applying wheat herbicides using liquid fertilizer as a carrier; further details and directions can be acquired from the herbicide label.

Another consideration growers should take into account when planning early spring herbicide applications is the plant back restrictions to double crop soybeans.  A large percentage of the herbicides listed in Table 1, especially those with activity on Ryegrass and Brome, have soybean plant back restrictions greater than the typical three month time period between spring applications and double crop soybean planting.  The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double crop soybeans after wheat.  Refer to Table 1 for more specific plant back timing restrictions.Click Here For Complete Table

Evaluation of Adapt-N and FieldView Corn N Fertilizer Tools in Ohio

Source:  Dr. Steve Culman, OSU Extension

NutrientStar, an independent evaluator of nutrient management tools, has just released results testing the performance of two web-based tools that provide customized corn nitrogen fertilizer rates: Adapt-N and Climate FieldView. Both tools are available for farmers in Ohio to use for a fee.

NutrientStar conducted 61 trials over 3 years evaluating Adapt-N and 21 trials over 2 years evaluating FieldView in Ohio. A summary of findings is presented below.

Compared to ‘farmer normal practice’ using the tools produced a range of yield differences across trials and years in Ohio. Some trials yielded more grain using the tools (positive values) and some yielded less grain (negative values). When all trials within a year were averaged, both tools resulted in lower yields compared to farmer normal practices (8 – 41 bushels/acre less). Depending on the year, farmers lost on average between $6 – $131/ acre on their return to N fertilizer.

The results varied by state, with some states benefiting from the tools and other states not benefiting from the use of the tools. Unfortunately, these tools have not performed well in Ohio to date.

An alternative approach to deciding corn N fertilizer rates is to use the economic model that Ohio State University Extension endorses. This simple calculator is based on maximizing farmer profitability. It uses 3 inputs to determine at what point will additional N fertilizer not pay for itself with more yield. This free, publicly-available tool was recently updated with extensive on-farm trials in Ohio and can be found here: http://go.osu.edu/corn-n-rate

More information on Adapt-N evaluation: http://nutrientstar.org/tool-finder/adapt-n/

More information on FieldView evaluation: http://nutrientstar.org/tool-finder/climate-fieldview/