Nitrogen boosts bermudagrass capacity

It’s often the case that when cattle prices fall, producers look for cost-cutting measures. If you’ve got bermudagrass, cast your eyes somewhere other than nitrogen (N) fertilizer.

That is the recommendation of Myriah Johnson and Eddie Funderburg of the Samuel Roberts Noble Foundation in Ardmore, Okla. Johnson is an agricultural economist, and Funderburg is a senior soils and crops consultant. They discussed the topic in a recent edition of the Noble Foundation’s Ag News and Views newsletter.

To make their point, an example 100-acre bermudagrass pasture is used. It generates 2,500 pounds of dry matter forage per acre with no N fertilizer applied; this is an average amount with normal southern Great Plains rainfall and where phosphorus and potassium aren’t limiting productivity.

Though 2,500 pounds of dry matter are generated, at least 1,000 pounds is left in the pasture over the course of summer to maintain productivity. This effectively equates to a residual plant height of 3 to 4 inches. Hence, the pasture produces 1,500 pounds of grazeable forage dry matter.

The consultants estimate that the average cow will consume about 10,000 pounds of dry matter per year, so 6.67 acres are needed to carry one cow (10,000 divided by 1,500). Looking at this another way, 15 cows can be carried on the 100 acres. This assumes that no additional hay is being purchased from outside sources, which would boost the carrying capacity.

What difference would applying 50 pounds of actual N make?

Though bermudagrass response varies by variety, soil productivity, and precipitation, an average return is 30 pounds of additional dry matter per acre for every 1 pound of actual N applied. This assumes that no N was previously applied to the pasture.

Applying 50 pounds of N (109 pounds of dry urea) will produce an additional 1,500 pounds of dry matter forage (50 pounds N × 30 pounds of dry matter per pound of N). This boosts the pasture dry matter production to 4,000 pounds per acre. Subtracting the 1,000 pounds of residual forage leaves 3,000 pounds of grazeable dry matter forage and the ability to now carry one cow per 3.33 acres. Hence, the 100 acres can now support 30 cows, or double the original carrying capacity. But is there a payback?

With the price of N at about 38 cents per pound ($350 per ton for urea), the cost to make a 50-pound-per-acre application is about $19. Adding an application charge of $5 brings the total cost to $24 per acre, or $2,400 for the entire 100 acres.

Dividing $2,400 total fertilizer cost by 15, the number of additional cows potentially added, results in a cost per cow of $160.

The Noble Foundation’s consultants assumed the calves would be sold in October at 500 pounds for $130 per hundredweight, generating $650 per calf. This then equates to $552 of additional revenue per cow ($650 per calf × 85 percent weaning rate).

If variable out-of-pocket costs are $400 per year per cow, this leaves $152 per cow as a return to fixed costs and management. The per-acre return would then be $22.80 over not fertilizing ($152 x 15 cows / 100 acres).

As is almost always the case, N fertilizer on grass offers some of the best returns possible. In most cases, it will be wise to look somewhere else for input cost savings.