Purdue University Department of Agronomy

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Updated Jan 2014
URL: http://www.kingcorn.org/news/timeless/NitrogenMgmt.html

Nitrogen Management Guidelines for Corn in Indiana

Jim Camberato, R.L. (Bob) Nielsen, & Brad Joern
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
 

8-YEAR SUMMARY OF CORN RESPONSE TO NITROGEN FERTILIZER

This report summarizes the yield response of rotation corn to fertilizer nitrogen (N) rate in field-scale trials conducted around the state of Indiana since 2006. These results are applicable to situations that implement efficient methods and timings of N fertilizer application. The average Agronomic Optimum N Rate (AONR) for 37 trials conducted on medium- and fine-textured soils in westcentral, southwest, and southcentral Indiana was approximately 182 lbs N / ac. The AONR for 33 trials conducted on medium- and fine-textured soils in northwest, northcentral, and southeast Indiana was approximately 194 lbs N / ac. The AONR for 54 trials conducted on medium- and fine-textured soils in medium- and fine-textured soils in northeast, eastcentral, and central Indiana was approximately 217 lbs N / ac. The average AONR for 10 rotation corn trials around Indiana conducted on non-irrigated sandy soils was 184 lbs N / ac. At the five Purdue locations where we conducted paired trials of corn/soy and corn following corn (corn/corn) in 2007-2010, the average AONR for corn/corn was 44 lbs greater than for corn/soy while average corn/corn yields were 18 bu/ac less than the corn/soy yields.

Economic Optimum N Rates (EONR) for various combinations of N cost and grain price are listed in Tables 1-3 for regions of the state. If you want to determine EONR for other N and grain prices, use the on-line N calculator for Indiana at this web site: http://extension.agron.iastate.edu/soilfertility/nrate.aspx.

N

itrogen fertilizer costs continue to be one of the most expensive variable production costs for corn. Applying “more than enough N” is no longer cheap “insurance” as it once was many years ago. Applying “more than enough N” is also not environmentally friendly. High N fertilizer costs and environmental impacts should encourage growers to critically evaluate their N fertility program, including application rate, fertilizer material, and timing.

Nitrogen rate recommendations for a given field were traditionally linked to its historical yield levels (Camberato, 2012). For corn/soybean, the traditional rule of thumb was an N rate equal to about 1 lb of N per bushel of expected yield. For corn following either corn or wheat, the recommendation was equal to about 1.2 lbs. of N per bushel.

Typical yield response to N ratesThese rules of thumb implied there was a straight-line relationship between yield and N rate; such that the more N you apply, the more grain you harvest. In reality, the relationship is curvilinear; meaning that the first pounds of applied N typically return the greatest number of bushels and the last pounds of applied N typically return the fewest number of bushels (figure to right). At some level of N, grain yield stops increasing with more N. Consequently, applying more N than the crop requires is dollar wasteful and environmentally distasteful.

Throughout the Midwest, most land-grant universities have moved away from yield-based N rate recommendations toward data-driven recommendations that are sensitive to N and grain prices (Sawyer et al., 2006). This approach to N rate recommendations links documented yield responses to N with the relative economics of grain price and N cost.

A couple of new terms or acronyms have developed from this approach. The term “Agronomic Optimum N Rate” or AONR defines the N rate that will produce maximum grain yield, regardless of cost. The term “Economic Optimum N Rate” or EONR defines the N rate that will result in the maximum dollar return to N. The EONR is usually less than the AONR, will usually decrease as N prices increase, will usually increase as grain prices increase, or may remain the same if the ratio between nitrogen cost and grain price (N:G) remains the same.

The “new” approach requires yield data from numerous field trials documenting corn yield responses to N fertilizer rates across a range of growing conditions. We began our current N rate trials in 2006. To date, 214 field-scale trials have been conducted around the state. About 74% of them have been with rotation corn and the rest primarily continuous corn. About 60% of the trials have been conducted on farmers’ fields and the remainder has been trials at Purdue research centers around the state .

The N rate treatments have ranged from nothing but starter N to as much as 286 lbs/ac applied N. Most of the trials used sidedress liquid 28% UAN simply to facilitate trial logistics. Similar results would be expected from late pre-plant or sidedress anhydrous, but not necessarily from early pre-plant anhydrous or early pre-plant 28% or fall anhydrous. Most of the trials were conducted on medium- and fine-textured soils: silt loams, silty clay loams, and the like. All of the trials have been field-scale; meaning that the individual N rate “plots” are usually field length by some multiple of the combine header width. Most of the trials have been harvested with the aid of GPS-enabled yield monitors.

Regional and Soil Differences for Optimum N Rate

Nitrogen used by the corn crop originates from soil organic matter and crop residues as well as from applied fertilizer. Some soils provide as little as 25% of the crop N requirement, the remainder coming from fertilizer N. Other soils provide in excess of 50% of the crop N demand, with a lesser amount needed from applied N. The N supply and N loss potential of a soil are related to soil properties and, of course, soils vary geographically around the state. In general, soils with higher organic matter and better drainage provide more N to the crop and retain more fertilizer N than lower organic matter, more poorly drained soils. As we conduct more and more trials, we are identifying regional differences in AONR that make sense as we consider the soils in those regions. It is important to note that most of our trials employed efficient fertilizer application methods and timings. Less efficient N management would likely require higher fertilizer N rates in response to the greater risk of N loss.

For now, we have grouped the N guidelines according to Indiana Crop Reporting Districts (Fig. 1). The average Agronomic Optimum N Rate (AONR) for 37 trials conducted on medium- and fine-textured soils in westcentral, southwest, and southcentral Indiana was approximately 182 lbs N / ac (Fig. 2). The AONR for 33 trials conducted on medium- and fine-textured soils in northwest, northcentral, and southeast Indiana was approximately 194 lbs N / ac. The AONR for 54 trials conducted on medium- and fine-textured soils in northeast, eastcentral, and central Indiana was approximately 217 lbs N / ac. The average AONR for 10 rotation corn trials around Indiana conducted on non-irrigated sandy soils was 184 lbs N / ac. We do not have enough field trials on irrigated sandy soils to provide any guidelines. The EONR is less than the AONR, based on the relative cost of N and value of grain. Economically optimum N rates can be found in Tables 1 - 3.

More field research is needed in several areas of Indiana and on sandy soils to determine whether other regional and soil specific recommendations are warranted. Please consider collaborating with us in conducting on-farm research N rate trials.

More Discussion on N Management

Although we report a single AONR for a region, specific AONR values often vary from field to field and from year to year for a single field. For example, the average AONR for rotation corn at our research site near West Lafayette is 184 lbs N / ac, but the AONR for individual years (2006 - 2012) has ranged from 130 to 221 lbs N / ac. This variation in optimum N rate is not particularly surprising since we’ve always known the difficulty of predicting soil N supply, fertilizer N loss, and growing season weather. Weather influences both soil N supply and fertilizer N efficiency. Crop health, N uptake, and N use efficiency are also weather- and soil-dependent.

Soil or fertilizer N lost to leaching, denitrification, or volatilization is N no longer available to the plant (Nielsen, 2006). The most effective N application method and timing for minimizing N loss is to inject N prior to the beginning of rapid crop N uptake at roughly growth stage V6 (six leaves with visible leaf collars, approximately 18 inches tall). If making fall or early-spring applications, anhydrous ammonia is the least risky of the N sources because it is the slowest to convert to the nitrate form that is susceptible to leaching or denitrification losses. Urea-containing fertilizers should be incorporated to eliminate volatilization losses or a urease inhibitor can be used to delay the initial conversion of urea to ammonia (reducing the risk of volatilization loss). Nitrification inhibitors can be used with anhydrous, urea, or liquid N to delay the conversion of ammonium to nitrate. NOTE: Practices such as fall-applied or early-spring applied N or surface-applied urea provide a larger “window of opportunity” for N loss and therefore would require higher N rates than our results would suggest to achieve optimum yield.

Even if you take steps to minimize the risk of N loss, predicting the optimum N rate for a particular field in a particular year remains a challenge. Several tools exist that may improve N management. These include: the Pre-Sidedress Nitrate Test (Brouder & Mengel, 2003b) which can be used to estimate soil N supply in manured fields or soils with very high organic matter content, a chlorophyll meter (Brouder & Mengel, 2003a) or active sensor in conjunction with a high-N reference strip which can be utilized during the growing season to evaluate crop N status, and the end-of-season stalk nitrate test (Brouder, 2003) which can serve as a “report card” to determine whether N was over- or under-applied.

The bottom line on N use in corn is that we’re dealing with a biological system that interacts with everything under the sun, including the sun. We cannot accurately predict the weather. We cannot accurately predict soil N supply throughout the year. Yet, we cannot afford (financially or environmentally) to simply apply “more than enough” N. We can minimize the risk of fertilizer N loss by understanding the processes and matching N source with placement and timing. We can develop average N rate recommendations that will work in “average” years. We can attempt to fine-tune those recommendations with tests, models, optical sensors, or simply educated guesses.

We Are Looking for On-Farm Trial Cooperators

Our long-term objective is to develop more region- or soil-specific N rate guidelines. Conducting N rate trials on farmer’s fields is the best way for us to expand our efforts and increase the database for making regional recommendations. The general protocol for such trials is to sidedress-apply strips of five or six N rates (for example: 70, 110, 150, 190, and 230 lbs N per acre), repeated at least three times across a field. Size of individual plots (a single N rate strip) can be length of field by some multiple of combine header width. If you use a variable rate controller that accepts prescription N rate files, we can create and provide a prescription file that essentially eliminates the logistics of implementing the replicated N rate treatments. Use of combine yield monitors is strongly encouraged primarily because they greatly reduce the harvesting logistics of such a trial.

The general protocol for our N rate trials can be downloaded from the Web at http://www.agry.purdue.edu/ext/ofr/protocols/PurdueNTrialProtocol.pdf.

If you are interested in conducting on-farm N rate trials, contact Jim Camberato (765-496-9338 or jcambera@purdue.edu) or Bob Nielsen (765-494-4802 or rnielsen@purdue.edu). We will work with you to come up with the best compromise between our desires for statistical soundness and your desire for logistical simplicity.

Cited references

Brouder, Sylvie. 2003. Cornstalk Testing to Evaluate the Nitrogen Status of Mature Corn. Purdue Extension publication AY-322-W. Online at http://www.agry.purdue.edu/ext/pubs/AY-322-W.pdf. [URL accessed Jan 2014].

Brouder, Sylvie and David Mengel. 2003a. Determining Nitrogen Fertilizer Sidedress Application Needs in Corn Using a Chlorophyll Meter. Purdue Extension publication AY-317-W. Online at http://www.agry.purdue.edu/ext/pubs/AY-317-W.pdf [URL accessed Jan 2014].

Brouder, Sylvie and David Mengel. 2003b. The Presidedress Soil Nitrate Test for Improving N Management in Corn. Purdue Extension publication AY-314-W. Online at http://www.agry.purdue.edu/ext/pubs/AY-314-W.pdf. . [URL accessed Jan 2014]

Camberato, Jim. 2012. A Historical Perspective on Nitrogen Fertilizer Rate Recommendations for Corn in Indiana (1953-2011). Purdue Extension. On-line at http://www.extension.purdue.edu/extmedia/AY/AY-335-W.pdf [URL accessed Jan 2014].

Nielsen, RL (Bob). 2006. N Loss Mechanisms and Nitrogen Use Efficiency. Handout for 2006 Purdue Nitrogen Management Workshops. Purdue Extension. Online at http://www.agry.purdue.edu/ext/pubs/2006NLossMechanisms.pdf. [URL accessed Jan 2014].

Sawyer, John & multiple co-authors. 2006. Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn (PM-2015). Iowa State Univ. Extension. On-line at http://www.extension.iastate.edu/Publications/PM2015.pdf [URL accessed Jan 2014].


Indiana Crop Reporting Districts
Fig. 1. Indiana crop reporting districts as identified by USDA-NASS.

AONR for regions of the state
Fig. 2. Average agronomic optimum N rates (AONR) for non-irrigated sandy soils (10 trials statewide) and medium- and fine-textured soils in three geographic regions in Indiana (127 trials statewide) with corn following soybean to date since 2006.

Table 1. Range of economic optimum N rate (EONR) values (lbs/ac applied N) for corn following soybean as influenced by nitrogen cost per lb. N (Table 4) and grain price per bushel based on yield response data summarized over westcentral, southwest, and southcentral Indiana on fine-textured soils. The average agronomic optimum N rate for these regions of Indiana is estimated to be 182 lbs N/ac.
Table 1

Table 2. Range of economic optimum N rate (EONR) values (lbs/ac applied N) for corn following soybean as influenced by nitrogen cost per lb. N (Table 4) and grain price per bushel based on yield response data summarized over northwest, northcentral, and southeast Indiana on fine-textured soils. The average agronomic optimum N rate for these regions of Indiana is estimated to be 194 lbs N/ac.
Table 2

Table 3. Range of economic optimum N rate (EONR) values (lbs/ac applied N) for corn following soybean as influenced by nitrogen cost per lb. N (Table 4) and grain price per bushel based on yield response data summarized over northeast, eastcentral, and central Indiana on fine-textured soils. The average agronomic optimum N rate for these regions of Indiana is estimated to be 217 lbs N/ac.
Table 3

Table 4. Cost per lb. N for four common fertilizer sources of N at varying costs per ton of product.
Table 4


End of document.