OMAHA (DTN) -- Higher than normal input costs and falling commodity prices will tempt farmers to cut back on expenses in 2009. Many farmers talk about cutting back on fertilizer, particularly phosphorus (P) and potassium (K).

Where soils have medium or high test levels for those nutrients, there often might not be a yield response to a full fertilizer application. Farmers can cut back or even skip a year of applications to save money.

If you plan to skip or cut back in 2009, but you don't want to miss out on a P or K response, then consider adding starter fertilizer.

Nutrients most commonly applied via starter include N (nitrogen), P, K, S (sulfur) and Zn (zinc).

Starter fertilizer's role is particularly important when planting corn early when soils are cool and in high-residue situations such as no-till. Low soil temperatures slow nutrient diffusion; when temperatures drop from 70 to 60 F, corn root growth decreases five-fold, and P uptake decreases four-fold.

Starters might also play a role when you want to cut back on fertilizer application, but want to make sure that what is applied will be used more efficiently.

It's important that starters be placed near the roots to optimize fertilizer availability. Immobile nutrients like P and K primarily move to the roots by diffusion. Diffusion is a slow process where nutrients move from regions of high concentrations among soil particles to areas of low concentrations at root surfaces.

When dry fertilizer is broadcast, 100 percent of it is distributed in the top six inches of soil. When surface banded, the fertilizer occupies 20 percent of the soil volume. When deep banding, fertilizer occupies only one percent of the soil volume.

Banding P and K fertilizers near the seed creates a zone of high concentration near the roots. Nutrients move a very short distance to be absorbed. Phosphorus also can react with calcium and iron in the soil to form an insoluble mineral. Banding increases the concentration of P beyond that fixation capacity of the soil, keeping it available longer.

TIMING OF HIGHEST DEMAND

The highest demand for P is early in the season, when it is least available and roots are smallest, so placement of P near roots is beneficial and particularly on soils that have a low soil-test value.

Potassium benefits are similar to P in no-till corn, and K availability in the spring is affected by the same factors that affect phosphorus availability.

Nutrients such as N, S, Ca (calcium) and Mg (magnesium) are more mobile, and move through the soil with water flow. As the young plant transpires water above ground, it pulls water into the roots bringing along these mobile nutrients via a process referred to as mass flow. That is why N, S, Ca and Mg can be broadcast; mass flow moves these mobile nutrients into the root zone, and banding is less important.

Starter fertilizer can be applied in a number of ways including: with the seed; two inches over from the seed and two inches deep; four inches below the seed; or dribbled on top of the soil along the seed furrow. Any of these methods can work effectively.

It is this concentrated band occupying only about one percent of the soil volume that keeps P and K available to the plant and makes starter fertilizer more effective.

If you cut back on P and K, then using starter will help offset for the reduction in application rates.

Next in the series: Farmers who are using strip-tillage to improve crop emergence, lower equipment needs and get the most efficiency out of nitrogen fertilizer.

For a detailed discussion of fertility ideas for 2009, attend the DTN Web seminar, "Economizing on Nitrogen," February 4 at 3 p.m. To register go to