Rock and Roll Agronomy

Don’t Base Optimum N Rate on the Cost of N

By Jason Hanson
Certified Crop Advisor
jlhanson@agriliance.com

There have been a lot of questions concerning the economics of applying nitrogen to wheat. Even with the increasing costs of N and uncertainty of wheat prices, it is still a very good investment. Furthermore, there is good research information and guidelines to help producers develop an optimum nitrogen rate, including these recommendations:

1) Base nitrogen levels on a realistic yield goal.

2) Use good soil sampling and testing to determine what residual nitrate is available in 0-24 inch soil depth.

3) Take into account what nitrate may be immobilized by crop residues and what nitrate will be mineralized from soil organic matter or legume residue.

Yield goals should be based on long-term history of each field or sub-field if applicable. There are numerous ways of calculating an average yield; past 6 to 8 years, past 6 years plus 10%, or past 8 years without the highest and lowest years. What really matters is that you’re using a realistic goal that can be obtained.

Soil nitrate levels should be tested to a depth of 24 inches, and soil residual nitrate will then be subtracted from the nitrogen requirement. This is important if soybeans, alfalfa or other legumes are in the rotation. Make sure that soil samples are representative of the field and cropping history.

Again, use realistic yield goals to derive how much N is required to produce a crop. It takes approximately 2.5 pounds of N to produce a bushel of wheat. From this requirement, nitrogen is either added for immobilization or subtracted for mineralization. A 30-60 lb N credit will be subtracted when following a legume crop. Immobilized and mineralized nitrogen values should be adjusted based on local experience.

With the increasing price of N, at what price should a producer cut back? The fact is that neither the cost of N or crop price has little to do with optimum fertilizer rates. Here is an example of some local data that was done out in northeast Montana on dryland wheat. This data was collected from actual fields and real farm numbers from cooperating producers. Land costs, land tax, machinery, seed, chemical, repairs, fuel, labor and all other related expenses were included in this study. The main focus here will be the nitrogen use rates and costs. In this example, the cost of phosphate is $240/ton, urea is $265/ton and anhydrous is $340/ton.

A premium was factored in for wheat over 12% protein. The highlighted results where zero actual N was applied illustrates the truth in the saying “nothing ventured, nothing gained.”  By doing nothing, the cost to the grower is either a large loss per acre or very little money to be made. Yes, a bigger cost of N is more money per acre than last year, but it can still bring a profit to the grower by putting on the needed amount to maximize profits.

From this example it is obvious that the price of N has very little to do with the optimum N rate.  The key is to manage this input as efficiently as possible.  Using best management practices in selecting good quality seed, and planting in a timely manner at an optimum rate will bring greater return than trying to save money in cutting nitrogen rates. Furthermore, it is important to evaluate all aspects of the nitrogen cycle when developing a nitrogen management plan. Shortcutting sampling depth or not giving credits where applicable will result in a poor nitrogen recommendation—which can be every bit as costly as the price of N itself.

N Rate	Starter	Protein	Yield	Net
60 Actual-Urea	50#	12%	47.47 bu	$38.31
90 Actual-Urea	50#	13.3%	54.39 bu	$78.97
60 Actual-NH3	50#	12.5%	42.03 bu	$41.88
0 Actual	0#	11.0%	23.39 bu	$2.45
90 Actual-Urea	60#	13.1%	52.87 bu	$55.08
90 Actual-NH3	60#	13%	52.95 bu	$71.52
120 Actual-NH3	80#	14.2%	64.50 bu	$107.90
120 Actual-Urea	80#	13.9%	60.20 bu	$51.72
0 Actual	0#	10.8%	9.37 bu	($43.11)
150 Actual-NH3	100#	13.8%	51.79 bu	$49.52
60 Actual *	50#	13.4%	55.46 bu	$91.19
Wheat sold for $3.25/ bushel Starter is 11-34-8-5 * Previous crop was fallow

Hanson is a certified crop advisor, near Devils Lake, N.D.