The 4 Rs of crop nutrition–the Right time

Written by Dr. Paul Tracy on .

Another installment in the 4 Rs of crop nutrition

Fertilizer timing is critical for economic returns on your farming. I’ll never forget a study conducted by Dr. Dale Blevins at the University of Missouri back in the late 1980s. Dale was able to obtain tremendous yield increases by delivering nutrients directly into soybean plants via medical intravenous setups. Obviously, using an IV to deliver nutrients is not practical, but it does demonstrate the value of a constant nutrient flow throughout the growing season.
Nitrogen receives the most application timing attention. This is because of its soil mobility. In almost all cropping situations, it is agronomically efficient to split nitrogen applications. In many situations, that translates into improved economic efficiencies.

Although many producers do quite well with all of their corn nitrogen applied preplant, I am a supporter of splitting corn nitrogen applications as a key management practice for producing consistently high yields.

Unless your environment allows for fall/winter anhydrous application, I usually recommend some nitrogen (a quarter to a third of the total crop needs) at or near planting, followed by the remaining nitrogen applied sidedress at the three- to six-leaf stage. This strategy provides the seedling adequate nitrogen. It also provides the growing crop with a dependable nitrogen supply immediately prior to the rapid growth that occurs between the six-leaf stage and tasseling. It also allows for mid-season rate adjustments based upon within-season environmental factors.

In wheat, I recommend two or three-way nitrogen splits. Some nitrogen (about a third) is needed at or near planting to stimulate fall tiller production.
The remaining nitrogen should be applied just prior to spring green-up. In planned high yielding programs (greater than 100 bushels per acre), the non-fall nitrogen can be split into two spring applications, with half near green-up and the other half near the boot stage.

Nitrogen use and timing for soybeans is often debated. Some preplant (10 to 20 pounds per acre), usually applied through nitrogen-containing phosphorus materials, can aid the seedling’s development prior to nodulation. Recent work has also shown that, under high yielding conditions (greater than 60 bushels per acre), 10 to 20 pounds of nitrogen per acre applied near pod set can help “finish off” a crop.

Tall fescue benefits from split nitrogen applications. In grazing situations, I prefer the majority of tall fescue’s nitrogen applied in late August to stimulate winter stockpile production. In hay situations, I prefer the majority of the nitrogen applied near spring green-up. In combination situations (hay + stockpile) a 60/40, spring/fall split application works well. When moisture conditions are appropriate, an additional nitrogen application in the early summer after haying or aggressive spring grazing pays great dividends.

Proper fertilizer timings do not only apply to mobile nutrients like nitrogen. Relatively non-mobile nutrients like phosphorus and potassium are commonly applied based upon convenience, and often applied once every other year. Although this timing philosophy works well in many situations, sometimes more frequent applications are beneficial.

High or low pH soils have the ability to fix or tie-up phosphorus. Some types of soil clays have the ability to fix potassium. In most cases, moving from a biennial to an annual fertilization system will help eliminate tie-up issues.
Certain crops (especially forages) have the ability to take up and remove via harvest more phosphorus and potassium than they require—a term referred to as luxury consumption. For this reason, in alfalfa, we generally recommend half of the annual fertilizer after the first cutting and the other half after the third cutting.

Environmental inconsistencies with the timing, release and availability of crop nutrients, along with higher commodity values have increased interest in slow-release materials, fertilizer enhancers, fertilizer protection products and bio-stimulants.
Some of these materials, like Super U, ESN, Agrotain, N-Serve and NFusion for nitrogen, and Avail for phosphorus, have been tested and can reduce the need for multiple applications in some situations. Other lesser-known and less researched materials may or may not help. Some have very little merit and should be avoided. Sorting through all the claims concerning untested products is a difficult task. My advice is to always stick with products that have been evaluated by unbiased, trusted parties.

Dr. Paul Tracy is director of agronomy for MFA Incorporated.