COLUMN: Nitrogen requirements depend on the production system used | Agriculture / Energy

Wheat and canola planting has already started, with most of it being dusted in the hope of rain not only to germinate it but also to establish it.

Forage and grain yield goals will be highly dependent on timely moisture. Although wheat pastures have already received preplant nitrogen, fields could still benefit from in-season management.

Nitrogen (N) is a mobile nutrient and can be lost or become unavailable to plants. The source or type of nitrogen fertilizer used can also have a big impact. Different production systems will require more or less nitrogen initially than others.

In a dual-purpose wheat or pasture system, more N is needed at the start compared to a cereal-only system. A grain-only system needs about 2 pounds of N per bushel of seed produced, or 80 pounds of N for a grain yield of 40 bushels.

Wheat forage production is strongly influenced by the nitrogen available to the wheat crop, so more nitrogen is needed in a dual purpose system to produce adequate forage.

It takes about 60 pounds of N to produce one ton of wheat forage. Thus, in a dual-purpose system, 60 to 70 pounds of N will be needed at planting, compared to 30 to 40 pounds of N for a grain-only system. The second application of N is generally applied in late fall to early spring.

For grain growers only, the old rule of thumb of 2 lbs N per bushel is a good starting point, but it might be an overstatement. Looking at 15 years of field test data from Oklahoma State University’s North Central Research Station near Lahoma, optimal pounds of N per bushel ranged from 0 to 3.2. The average pounds of N per bushel to achieve an economic optimal N rate was 1.6; however, if 2 pounds per bushel had been applied, grain yield would have been maximized in 13 of those 15 years.

Split application is often a best management practice for canola as well. The canola crop needs enough nitrogen to produce a healthy crop and better withstand winter. Too much N in the fall or at planting can result in excessively large plants that overwinter.

Excessive nitrogen and prolonged hot growing conditions can lead to overwintering issues if the growing point of plants begins to elongate vertically. Canola needs about 2.5 pounds of N per bushel of seed yield, or 100 pounds of N for a 40 bushel yield.

It is almost impossible to determine total N requirements at planting time. Applying N to wheat and canola is a good management practice because it decreases the risk of N losses and benefits from the influence of late season N recommendations based on potential crop yield. Topdress application rates may be influenced by current harvest expectations and weather forecasts. Basically, the estimate of yield potential becomes more accurate as the season progresses.

Use of the tools at hand can significantly influence N recommendations. Applying N-rich strips in early fall, especially in dry years like this, can help estimate N needs. year-round for dual-purpose and grain-only systems.

This management tool can help determine N deficiencies or sufficiency. Farmers applying anhydrous ammonia pre-plant in dry soils could have lost up to half the N if it had been applied correctly. Open furrow slices, shallow placement and lack of moisture for it to bind lead to the highest risk of losses.

N-rich strips can be as simple as hand spreading a few cups of urea (46-0-0) or using custom applicators on UAVs or tractors. The bands can be used to visually determine if there is enough N or not. If the band is not visible, it is not necessary to apply N at this time. If the band is easily visible, then more N is needed.

In addition to using N-Rich strips, all OSU Extension offices have access to a GreenSeeker crop sensor. Handheld sensors estimate crop biomass and greenness inside and outside the N-Rich band. Using sensor data and an online calculator, yield estimates can be calculated.

This tool can help growers determine their crop’s yield potential with and without added N to make economic decisions on how much N to treat.

Based on past farm data, using N-Rich strips with a portable sensor has averaged a net profit of $10 per acre or more.

Contact your local OSU County Extension office for more information.

Bushong is the Northwest Region Agronomy Specialist for the Oklahoma Cooperative Extension Service.