Fine-tuning N application for profits,
water quality
by Chad Ingels, nutrient and manure management specialist,
Maquoketa Watershed Project
Three area producers, Jule
Brown, Gary Soules, and Joe Wingert, cooperated with Iowa State University
Extension Maquoketa Watershed Project staff during crop year 2000 with on-farm
demonstrations comparing different nitrogen (N) rates for corn production
following soybeans.
Results from these N
management demonstrations show that N use can be reduced from average watershed
levels while maintaining yield and increasing profit. Reducing commercial N
application may promote more efficient crop use of soil N, therefore decreasing
the chance of N moving into the surface water system.
The six treatments, 0, 30, 60,
90, 120, and 150 pounds of N per acre, were replicated three times at each
site.
Figure 1 shows the three-site
average yield for the six treatments. Without any commercial N applied, the
yield was 120 bushels per acre. An addition of 30 pounds of N per acre provided
15 more bushels per acre than the check. Likewise, the 60 pounds of N per acre
treatment yielded 15 more bushels per acre than just 30 pounds of N per acre.
However, the next two treatments, 90 pounds N and 120 pounds N per acre,
increased yields by only five and three bushels per acre, respectively. The final
treatment of 150 pounds of N per acre actually showed a lower yield than the
120 pounds per acre N rate.
Maximum yield was achieved
with 120 pounds of N per acre, but profitability of N fertilizer was maximized
at 90 pounds of N per acre, as shown in figure 2.
In this evaluation N was given
a value of $0.20 a pound and corn was valued at $2.40 per bushel (black line)
and $2.00 per bushel (gray line). Using $2.40 per bushel corn, $66 per acre is
returned to the producer when investing 90 pounds N per acre. Even though 120
pounds of N per acre yields three bushels per acre better, the return on the
investment was also $66 per acre. Treatments of 60 and 150 pounds N per acre
return $59 and $54 per acre, respectively.
When $2.00 per bushel corn is
assumed, 90 pounds N per acre actually returns one dollar more than 120 pounds
N per acre, $52 to $51 per acre. The 60 pounds of N and 150 pounds of N per
acre treatments follow behind with returns of $47 and $40 per acre
respectively.
Producers may not be comfortable
applying 90 pounds N per acre to soybean stubble for corn production, but
applying more than 120 pounds N per acre may cut into farm profits. Some N rate
in between may provide the best yield and profit scenario for individual farms.
In conclusion, the nitrogen
management demonstrations show that N use can be reduced from current levels
while maintaining corn yields and expanding farm profits. Results from year
2000 produced corn yields with a 158 bushels per acre average where 120 pounds
N per acre was applied to soybean stubble. This yield compares to the January
1999 producer survey which reported a five-year average of 160 bushels per acre
for the watershed. Further demonstrations need to be conducted in the following
crop seasons to confirm these findings and support the goals of the Headwaters
Council and watershed producers.
Water monitoring efforts
within the Maquoketa headwaters have increased community awareness of crop
nutrients in surface water and have producers interested in fine-tuning N
fertilizer inputs.
A January 1999 survey of area
farmers showed an average application rate of 128 pounds of N per acre on
fields going to corn following soybeans. Producer responses ranged from 75-260
pounds of N per acre. Using survey results, the Texas Institute for Applied
Environmental Research (TIAER) developed several computer modeling scenarios of
the Maquoketa headwaters in regards to nitrogen, phosphorus, and sediment.
With the survey information
and modeling results from TIAER the Headwaters Council set a goal of reducing N
loss by 50 percent from current levels. The Council realizes that area farmers
have control over the nitrogen application in the headwaters watershed.
For more details about these
demonstrations, contact the MWP staff in Fayette at (319) 425-3233.
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