If your purchased-nitrogen budget is limited, you”ll see much better returns by applying some nitrogen to all responsive acres rather than applying all of your nitrogen to some fields and none to others, according to Larry Bundy, a soil scientist at the UW-Madison”s College of Agricultural and Life Sciences.
The biggest yield increases occur with the first pounds of nitrogen applied. The following results from corn-growing trials on high-yield-potential soils in Wisconsin show how yield increases fall off as more nitrogen is applied. They also show how nitrogen price influences profitability at various application rates.
* Applying 40 lb N/acre increased yields by 12.6 bushels/acre, for a gross return of $25.20 and a return of 63 cents per pound of N applied (at $2 per bushel corn).
* Applying 80 lb N/acre increased yields by 10 more bushels/acre, for a gross return of $20 and a return of 50 cents per pound of N applied.
* Applying 120 lb N/acre increased yields by 7.4 more bushels/acre, for a gross return of $14.80 and a return of 37 cents per pound of N applied.
* Applying 160 lb N/acre increased yields by 4.7 more bushels/acre, for a gross return of $9.40 and a return of 24 cents per pound of N applied.
* Applying 190 lb N/acre increased yields by just 1.8 more bushels/acre, for a gross return of $3.60 and a return of just 9 cents per pound of N applied.
You”ve reached the “economic optimum nitrogen rate” when the cost of the last pound of nitrogen you apply equals the value of the yield increase produced, according to Bundy. Based on the above results, if you”re paying 24 cents per pound for nitrogen, you”re losing money at 190 pounds per acre, and breaking even at 160 pounds. But you”re gaining a lot with the first 120 pounds per acre.
Mike Rankin, extension crops and soils agent for Fond du Lac County, has developed a downloadable Excel spreadsheet to calculate economic returns from nitrogen applications. The spreadsheet is based on nitrogen response rates for major Wisconsin soil groups. Users can select nitrogen and corn prices of interest and see their effects on economic return. Go here.
Management can help to minimize nitrogen losses, Bundy notes. Sidedress nitrogen on coarse-textured soils, incorporate or inject manure to conserve nitrogen, and manage urea-containing fertilizers to avoid ammonia losses. Corn following alfalfa usually doesn”t need added nitrogen. And don”t forget to credit manure and legume nitrogen from previous seasons.