Fertilizer, drought, impact pasture decisions

By Mike Rankin

“Last year we were complaining about the increasing cost of fertilizer, and it was only about half the cost it is now,” notes Paul Beck in a recent Oklahoma State University Extension Cow-Calf Newsletter.

The beef cattle nutrition specialist says that fertilization enhances water-use efficiency, which may be important under the current dry conditions, but fertilizer costs will likely make applications prohibitive for some producers.

In evaluating the economics of fertilizer use in 2022, Beck writes that each pound of applied nitrogen results in 30 to 40 pounds of additional forage production per acre in bermudagrass and old world bluestem pastures and hayfields. This added production comes at a cost of about 3 to 4 cents per pound, or $60 to $80 per ton of additional hay production per acre.

Beck asserts that stocker steers can realize an extra 1.5 to 2 pounds of gain for each pound of nitrogen applied, so the cost of that added gain would be around 55 to 75 cents per pound.

In cow-calf operations, a calf value to nitrogen cost ratio of 2.5 indicates that fertilization is potentially profitable. A weaned calf needs to bring $2.87 per pound for fertilization to be beneficial.

For those who don’t normally fertilize pastures or hayfields, Beck points out that there is little consequence of not fertilizing since the stocking rate is already aligned to the natural productivity of the land.

Conversely, if a producer has been fertilizing pastures, reducing or eliminating fertilizer applications will require grazing decision changes to improve forage utilization and ensure enough rest between grazing cycles for the grass to remain healthy. “Applied fertilizer should be targeted to times of the year and rates that match livestock need to prevent excess forage growth, which wastes the fertilizer’s value,” Beck notes.

The beef nutritionist states that for each ton of hay harvested from a field, about 30 to 40 pounds of nitrogen, 14 pounds of phosphorus, and 45 to 50 pounds of potassium are being removed. “When cattle graze or are fed hay on pasture, most of the nitrogen, phosphorus, and potassium are returned in the excreta,” Beck explains. “So, improved distribution of grazing and hay feeding will improve the distribution of recycled nutrients.”

Pasture weed control improves forage production. Beck notes that for each pound of broadleaf weed production, there is a corresponding decline in desired grass productivity. “Controlling weeds is therefore even more impactful during a drought and when fertilizer prices are high,” he asserts.

With high fertilizer prices, enhanced forage management is needed. At a minimum, Beck recommends culling the cow herd to reduce stocking rates, controlling pasture weeds, and seeding legumes in the fall to improve pastures for next spring.