New OMAFRA General Recommended Nitrogen Rates for Corn:
The Ontario Corn N Worksheet

Explanation of Worksheet Factors

Introduction: In 2005, the Ontario Soil Management Research and Services Committee approved the revision of the OMAFRA General Nitrogen Recommendations for Corn, based on a review of N response research. The goal behind these general recommendations is to achieve the highest economic return for nitrogen fertilizer. Yield increases from applying higher N rates than recommended are not likely to be large enough to pay for the extra fertilizer.

1. Base N Requirement: In most of the province, the medium textured soils (silt loams and loams) have the lowest "Base N Requirement" (Table A). In both coarser and finer textured soils, the nitrogen requirements are higher. Fields in the counties of Frontenac, Renfrew, and all the counties to the east of them, have significantly lower N requirement than fields with similar soils in the rest of the province.
2. Yield Adjustment: Multiply the proven yield for the field by 0.77 lb N per bushel of yield (13.6 kg/tonne of yield). Use average yields for the previous five years to estimate the productive capacity of the field. Entering an inflated yield goal into this adjustment will not increase the productivity of the field, will cost money for wasted N, and may result in environmental harm.
3. Heat Unit Adjustment: The data shows that corn in the long season areas of the province require more nitrogen than the short season areas. The adjustment is approximately 4 pounds per 100 CHU above or below the base value of 2650.
4. Previous Crop Adjustment: The crop that was grown immediately prior to planting corn has a significant impact on the nitrogen requirements. The N recommendations in this table have been stated relative to the preceding crop with the highest N requirement (grain corn), so all of the adjustments for previous crop are in the form of a credit.
5. Price Ratio Adjustment: As the cost of nitrogen fertilizer goes up, or the value of the corn crop goes down, the amount of yield required to pay for a pound of nitrogen increases. This means that the nitrogen rate that provides the maximum return to added fertilizer is reduced. The amount of reduction in N rates for various combinations of corn and nitrogen price is found in Table E.
6. Total N Recommendation: This figure, calculated by summing values A through E, represents the total N requirements for the crop. This is normally supplied by a combination of starter fertilizer, broadcast or side-dressed fertilizer, and manure.
7. Deduct Starter N: Any N that is supplied at planting should be included here.
8. Deduct Manure N Credits: Available nitrogen from manure (or biosolids) should be included on this line. The more accurate the estimate of available N from manure, based on accurate application rates and manure analysis, the more confidence you will have in the manure N credits.
9. Preplant Additional N: The difference between the Total N recommendation, and the credits for starter N and manure N, is the amount of nitrogen that will need to be included in a pre-plant broadcast application. This value would also apply to N applications that occur at or shortly after planting (i.e. broadcast UAN with herbicide).
10. Sidedress Additional N: Nitrogen that is applied just before the crop needs it is utilized more efficiently than N applied pre-plant, because there is less opportunity for loss through denitrification or leaching. This difference is most pronounced in the heavier textured soils. Sandy soils do not normally show a benefit to side-dress N applications. NOTE: This adjustment does not apply in Eastern Ontario, where the N recommendations are already relatively low.

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General Recommended Nitrogen Rates for Corn: Corn N Worksheet (Metric)

A. Base N Requirement (choose from Table A)	=_____________A
B. Yield Adjust (Yield (T/ha)_____X 13.6) =	+_____________B
C. Heat unit Adjustment Your CHU's = _________Less - 2650 Total =_____________ x 0.041 =_______________à	+/-___________C
D. Previous Crop Adjustment (Choose from Table D)	-_____________D
E. Price Tartio (PR) Adjustment (for nitrogen price relative to corn price; choose from Table E)	-_____________E
F. Total N Recommendation (F=A+B+C-D-E)	-_____________F (kg N/ha)
G. Deduct Starter N (kg N/ha)	-____________G
H. Deduct Manure N Credits 1 (kg N/ha)	-___________H
I. Preplant Additional N (I=F-G-H)	=___________I (kg N/ha)
or
J. If apply N as Sidedress
J=_________(I) x_________adjustment value from Table J.	=____________J (kg N/ha)

¹ Manure N Credits can be found in the Soil Management Section of Publication 811, or the Nutrient Management Workbook

Table A: Base N Requirement

Soil Texture	Base N Requirement South Western and Central Ontario	Base N Requirement Eastern Ontario*
Clay, Heavy Clay	53	1
Clay Loam	40	1
Loam	32	1
Loamy Sand	46	19
Sand	52	19
Sandy Clay, Sandy Clay Loam	43	19
Sandy Loam	38	19
Silt Loam	20	1
Silty Clay Loam	36	1
Silty Clay	49	1

*Eastern Ontario includes Frontenac, Renfrew and counties to the east of them.

Table D: Previous Crop Adjustments

Previous Crop	Adjustment
Grain Corn	0
Silage Corn	14
Cereals (straw removed)	12
Cereals (straw not removed)	0
Soybeans	30
Edible Beans	30
Clover cover crop (plowed)	82
Clover cover crop (no-till)	67
Perennial Forages
Less than 1/3 legume	0
1/3 to 1/2 legume	55
Over 1/2 legume	110
Crops Not Listed	0

 

Table E: Price Ratio (PR) Adjustment
(Nitrogen Price $/kg N)

Corn Price $/Tonne	0.88 kg N/ha	0.99 kg N/ha	1.10 kg N/ha	1.21 kg N/ha	1.32 kg N/ha
98	27	34	42	49	57
102	24	32	39	46	53
106	22	29	36	43	50
110	20	27	34	40	47
114	18	25	31	38	44
118	16	23	29	35	41
122	15	21	27	33	39
126	13	19	25	31	37
130	12	18	23	29	35
134	11	16	22	27	33

 

Table J: Timing Adjustment (Sound Western and Central Ontario only)

Soil Texture	Adjustment
Clay, Clay Loam, Loam, Silt Loam, Silty Clay, Silty Clay Loam	0.8
Sandy Clay, Sandy Clay Loam, Sandy Loam	0.9
Sand, Loamy Sand	1.0

 

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General Recommended Nitrogen Rates for corn: Corn N Worksheet (Imperial)

A. Base N Requirement (choose from Table A)	=_____________A
B. Yield Adjust (Yield (bu/ac)_____X 0.77) =	+_____________B
C. Heat unit Adjustment Your CHU's = _________Less - 2650 Total =_____________ x 0.037 =_____________à	+/-___________C
D. Previous Crop Adjustment (Choose from Table D)	-_____________D
E. Price Ratio (PR) Adjustment (for nitrogen price relative to corn price; choose from Table E)	-_____________E
F. Total N Recommendation (F=A+B+C-D-E)	-_____________F (lbs N/ac)
G. Deduct Starter N (lbs N/ac)	-_____________G
H. Deduct Manure N Credits 1 (lbs N/ac)	-_____________H
I. Preplant Additional N (I=F-G-H)	=_____________I (lbs N/ac)
or
J. If apply N as Sidedress
J=_________(I) x_________adjustment value from Table J.	=____________J (lbs N/ac)

¹ Manure N Credits can be found in the Soil Management Section of Publication 811, or the Nutrient Management Workbook

Table A: Base N Requirement

Soil Texture	Base N Requirement South Western and Central Ontario	Base N Requirement Eastern Ontario*
Clay, Heavy Clay	47	1
Clay Loam	36	1
Loam	28	1
Loamy Sand	41	17
Sand	46	17
Sandy Clay, Sandy Clay Loam	38	17
Sandy Loam	34	17
Silt Loam	18	1
Silty Clay Loam	32	1
Silty Clay	44	1

*Eastern Ontario includes Frontenac, Renfrew and counties to the east of them.

Table D: Previous Crop Adjustments

Previous Crop	Adjustment
Grain Corn	0
Silage Corn	12
Cereals (straw removed)	11
Cereals (straw not removed)	0
Soybeans	27
Edible Beans	27
Clover cover crop (plowed)	73
Clover cover crop (no-till)	60
Perennial Forages
Less than 1/3 legume	0
1/3 to 1/2 legume	49
Over 1/2 legume	98
Crops Not Listed	0

 

Table E: Price Ratio (PR) Adjustment
Nitrogen Price $/lb N

Corn Price $/bu	0.40 lb N/ac	0.45 lb N/ac	.50 lb N/ac	.55 lb N/ac	.60 lb N/ac
2.50	24	30	37	44	51
2.60	22	28	35	41	48
2.70	20	26	32	38	45
2.80	18	24	30	36	42
2.90	16	22	28	34	40
3.00	15	20	26	32	40
3.10	13	19	24	32	37
3.20	12	17	23	28	33
3.30	11	16	21	26	31
3.40	10	14	19	24	29

 

Table J: Timing Adjustment (Sound Western and Central Ontario only)

Soil Texture	Adjustment
Clay, Clay Loam, Loam, Silt Loam, Silty Clay, Silty Clay Loam	0.8
Sandy Clay, Sandy Clay Loam, Sandy Loam	0.9
Sand, Loamy Sand	1.0

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