“A New Era of N Management”

By Tracy Sayler

Dave Franzen recalls that when he started in the fertilizer business in 1976, the price of anhydrous ammonia was about $125/ton. Now, it’s about $500/ton or 30 cents/lb N, with the price of urea ranging about $276-368/ton and UAN about $168-224/ton. And the NDSU extension soils specialist doesn’t see the price falling much from this plateau over the long-term.

He says that while ammonia and urea are being imported into the U.S. in record quantities, the infrastructure hasn’t been able to keep up with the increased need, stressed further by the lingering effects of last year’s Hurricane Katrina which disrupted barge traffic. But it’s the increased cost of energy which is the real lynch pin to the trend in higher N costs – more than 90% of the cost of making anhydrous ammonia now is the cost of natural gas.

 “We are entering a new era in N management,” he says. This means more attention must be given to soil testing to accurately account for residual N – Franzen estimates that now, only about 25% of N.D. farmers use soil testing to guide N rates.

Franzen also sees more interest in site-specific or variable rate fertilizer applications, and zone soil sampling.  Instead of a composite soil testing approach, where 20-30 soil cores are combined, mixed, and then a subsample is obtained from the bucket to represent the entire field, the field is broken up into logical zones, guided by topography (landscape) yield maps, soil electrical conductivity, EC sensors, aerial photography (hired plane, or FSA aerial photos) and satellite imagery (usually NDVI- normalized digital vegetative index which is based on an infrared/red ratio of reflectance from crop canopy).

Three to five zones are usually sufficient to improve the grower’s understanding of the nitrate patterns in fields, and provide more confidence in the soil analysis numbers for use in N rate determination (More information on zone sampling online at www.ext.nodak.edu/extpubs/soilfert.htm - see the site-specific publications).

Fertility recommendations in the past were developed in a time when N was cheaper, and crop prices were higher from an inflationary perspective. But with $500+/ton ammonia fertilizer, more attention is also being given to economic optimum N rates.  “Should N rates be the same regardless of the price of N and the crop? Probably not,” he says.

NDSU, for example, is exploring adjustments to its recommended N rates for a number of crops grown in the state to reflect increased costs – generally, as crop prices decline and N costs increase, N rates may be adjusted, albeit slightly. Certainly, cutting back on fertilizer N too much will affect yield and quality of most crops.  But generally, yield response to N, and economic return compared to the cost of N, tends to level off at high N rates (see corn tables).

Franzen recommends crop producers know their existing soil N in fields through soil sampling analysis, and establish reasonable yield goals based on past experiences and historical average yield. Use the historical yield average for a field and current fertilization recommendations to arrive at a base N rate. Then from the recommended total N rate, consider decreasing the rate by about 10% for 30-cent N, and 15% for 40-cent N. 

Adjusting fertility rates with wheat is more complex, given the consideration of how it can impact both yield and protein. Generally, however, as wheat prices are reduced by 50 cents, Franzen says optimum economic return rates decline by about 10 lb N/acre.   And as N prices increase by 5 cents/lb N, optimum economic N rates decline by about 10 lb N/acre.

Growers should take a look at historical yields on the farm and consider that for at least wheat, the possibility of growing greater than 10% of the average yield happens less than 20% of the time,” Franzen says.  “Using this historical average as a basis for N rate decisions is not a bad decision.”

Use the historical average yield for a field and current recommendations to come up with a base N rate (NDSU’s crop fertility recommendations can be found online at www.ext.nodak.edu/extpubs/soilfert.htm). Then increase or decrease rate based on the current wheat price and N prices, compared with about a $4 historical wheat price and 20 cent N rate of about 15 years ago. If the decision is made to reduce rates, choose a higher protein variety that has a tendency to make grade no matter the conditions, Franzen advises, taking other traits into consideration as well, including disease resistance, lodging, and yield consistency.

Growers are encouraged to consult with their local agronomists or extension experts for more information on managing N rates.