Cost Effective Nitrogen Rate Adjustments in 2005
By Greg Stewart, OMAF Corn Specialist & Ken Janovicek, University of Guelph

If, on average, you apply more than 1 lb of N per bushel of expected corn yield there may be some adjustments you can make to improve your nitrogen economics this year.

About five years ago the Ontario Corn Producers' Association decided that it would be a good investment of their research money to gather up all of the corn/nitrogen research that had been done in the province in the past 40 years. This data existed in many places ranging from computer files to dust covered binders of long-since-retired researchers. The aim of this project was to get all of this data compiled into a central database and then re-evaluate the fertilizer nitrogen recommendations for growing corn in Ontario.

As a critical step in this project, we reviewed the key management factors that corn producers should consider in selecting a nitrogen rate for a field or portion of a field. These factors were: 1) Expected Yield, 2) Cost of N:Price of Corn ratio, 3) Crop Heat Unit rating for the field in question, 4) Previous Crop grown on the field 5) Soil Texture, and 6) Timing of N Application, planting time or sidedress. There are some important findings from our analysis of these factors that may help you as a producer to make better N rate decisions.

Expected Yield - there has been some question as to whether yield goal or yield history has any bearing on N rates. This project showed quite clearly that yield expectation should be a component of general recommendations. Adjusting N rates for expected yield still makes sense and 2005 is certainly not the year to apply 130 lbs of N with the hope that the field that rarely breaks 100 dry bushels per acre will surprise you this time.

Cost of N:Price of Corn - fertilizing for maximum yield is particularly ludicrous in a year when N costs are high and corn prices are near record lows. The concept, as unfriendly as some may find it, is to fertilize for maximum return not for maximum yield. This project identified that with all other factors being equal, and if nitrogen stayed at $.38/lb while corn fell from $3.25 to $2.50 per bushel, a grower would be correct in reducing N rates by 10 lb N/acre across the board.

CHU Rating - interestingly, but not totally explainable, is the fact that N rates appear to increase as you move to areas within the province with higher heat unit ratings. So again - all other factors being equal (i.e. expected yield, price ratio, soil type, etc.) it appears that about 20 more lbs of N per acre are required to grow the same corn crop in Essex County (3,300 CHU) as it does in Wellington County (2,650 CHU).

Previous Crop - not surprisingly, previous crop has a significant impact on N rates for corn. The project establishes a soybean credit (compared to growing grain corn after grain corn) of 27 lbs N/acre. We also discovered that credits for uniform stands of red clover underseeded in winter wheat (if you can find one) have a larger credit than we have traditionally applied. 2005 is not a year to ignore previous stands of red clover or alfalfa when it comes to reducing N rates while not sacrificing corn yield!

Soil Texture - we are excited by the fact that soil type can be used as a tool for adjusting N rates for corn. Simply put, the project revealed that silt loam soils were the most productive of any soil texture class when it came to producing corn with lower requirements for fertilizer nitrogen. As soil texture became heavier - towards heavy clay soils - there is an additional requirement of about 30 lbs N/acre. Similarly, as you moved towards lighter sand soils this same additional amount of N (about 30 lbs N/acre) was also shown to be required when compared to silt loam soils. The take home message for growers on productive silt loam soils is that there may be a tendency for over-application of N. We also discovered that the soils of the Ottawa Valley have a tendency to need less fertilizer nitrogen than other similar textured soils in the rest of the province.

Application Timing - current provincial recommendations do present a fairly significant lowering of N rates when sidedressing compared to planting time applications, but only in that area defined as South Western Ontario. Our estimations would indicate that there is a sidedress credit, that it should exist across most of the province, and that the level of this credit is dependent on soil type. We found that on heavy soil textures that there is potential to reduce N rates by 20% if you sidedress rather than apply at planting. So if you came up with a recommendation on a clay loam soil for 125 lbs of N as broadcast urea prior to planting the model, would recommend a rate of 100 lbs N/acre if you were going to sidedress. Since we have shown fairly consistently the need for adequate planter N in a sidedress situation this recommendation, in practical terms, would be more like 30 lbs N/acre on the planter and 76 lbs N/acre as sidedress.

Putting It All Together
Some of the aforementioned concepts may have given you ideas as to how to trim N rates in a cost effective manner in 2005. For example, if you are growing corn after soys, on a silt loam soil, and farm in an area less than 2750 CHU you may be feeling that applying your traditional 140 lbs of N on your farm that has averaged 125 bu/acre over the past 5 years is more than you need, especially in 2005. OCPA has commissioned us to put together a worksheet or calculator that puts all of these factors together in an easy to follow format. You can access this calculator by going to and click on the Corn Nitrogen Calculator icon. This will allow you to run or download the calculator. These recommendations are not official OMAF recommendations as of yet. We do not believe this or any other set of general recommendations will consistently predict your N requirements with bulls-eye type accuracy, but they can help you target areas to improve your N management in corn both in 2005 and in the future.

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