Making optimum use of fertilizer often depends on its location within the soil profile. With the increased use of no-till and conservation tillage practices, the potential for stratification of nutrients like potassium and phosphorus develops.

"These nutrients are practically immobile in the soil, and unless they are physically mixed by tillage, they can develop concentrated layers near the soil surface," says Bruce Due, District Agronomist, Mycogen Seeds. "To accurately detect a nutrient stratification problem in no-till systems, a soil sample should be taken from the zero to 2-inch depth as well as the zero to 7-inch depth. If a large portion of the available nutrients are in the zero to 2-inch zone, then this indicates nutrient stratification in the upper soil surface."

Limited field research indicates that plants develop more roots near the soil surface in conservation tillage due to improved moisture conditions, a result of the in-the-surface mulch. Shallow-rooted crops cause management challenges, especially during periods of extreme drought where surface-level moisture is limited, or under the strain of high winds.

"With continued use of reduced tillage practices, the levels of fertility at deeper soil depths may be depleted and future soil fertilization methods may need to be adapted," Due says.

Soil tests are an important tool for proper phosphorus, potassium and pH management in any tillage system. Make sure to sample soil from the full 7-inch depth. If nitrogen (which lowers pH) is applied to the surface and is not thoroughly incorporated with tillage, pH tests of the upper 2 inches of soil are needed to aid in the management of some herbicides.

"Once the field is sampled and the lab results are received, carefully evaluate with the input supplier, agronomist or crop consultant to determine the best method of bringing soil fertility levels back to the desired level," Due explains.

Some possible application styles are:

  • Broadcast – Best used in higher fertility environments where tillage includes deep primary tillage. Broadcast every few years to thoroughly distribute nutrients.
  • Row – On soils low in fertility, placement of fertilizer in a concentrated band below and to the side of the seed. Traditionally, a short-term fix when buildup levels of fertilizers won't be applied.
  • Deep Placement – Also referred to as root-zone banding. Generally, a mixture of nitrogen, phosphorus and potassium is placed at a depth of 4 to 8 inches on 15- to 30-inch spacing depending on the crop to be grown. This method may be a good choice to rebuild fertility at deeper soil depths.
  • Site-Specific – Use of specifically designed applicators that vary the rate of fertilizer application as they move across the field. Offers the potential to improve yields while minimizing the possibility for over-fertilizing less productive acres.

For further information, please contact Bruce Due, District Agronomist, with Mycogen Seeds at (701) 642-6007 or via e-mail at bfdue@dow.com.