The final installment in the 4 Rs series

Fertilizer placement can be discussed at two levels. The macro level involves placement based on in-field geographical locations. The micro level is based upon placement within the soil profile and in proximity to the growing crop.

There is no doubt that placing plant nutrients in the Right place on the landscape is one of the most cost effective management strategies. We have been variably applying nutrients across fields for over 15 years. The success of these programs has been tremendous, and I highly recommend the technology across most farming operations.

In terms of micro placement, there is no universal most efficient location. Agronomically, there are multiple factors when considering where to place crop nutrients.

The crop grown has a tremendous effect on plant food placement. With perennial crops like alfalfa and tall fescue, it is impractical to incorporate plant foods, so surface broadcast is appropriate. The one exception is immediately before crop establishment. Whenever possible, lime and fertilizer applications designed to raise soils to optimum levels should be followed by an incorporating tillage immediately prior to planting.

In row crops, there is tremendous diversity in terms of the most effective nutrient placement. We generally recommend completely different fertilizer nutrient placement strategies between corn and soybeans.

Corn has a fibrous root system that extracts nutrients differently than soybeans, which have a taproot system. Corn also tends to be planted earlier than soybeans, a time when cool/wet conditions slow soil nutrient release via mineralization or dissolution, and also slow root growth and subsequent interception of soil derived nutrients. For these reasons, corn responds more consistently to banded fertilizer than do soybeans.

Fertilizer bands tend to be more efficient than broadcast applications in no-till situations. Surface bands concentrate nutrients, thus leading to less potential tie-up on crop residues. Subsurface bands place nutrients deeper in the soil profile where it may be more accessible to plant roots, especially when dry conditions lead to restricted root activity near the surface.

Another practical reason for banding in corn compared to soybeans is the row widths involved. A general rule is that the bands can be spaced no more than two row widths apart. Corn is generally planted in wider rows than soybeans, thus making the equipment set-up, cost and application efficiencies for banding more economical.

Banded fertilizer is generally more efficient in low-testing compared to high-testing soils. This is because the higher concentration of fertilizer in the banded area slows the rate of fixation (tie-up) the soil has for the applied nutrients. Whereas, when soils already contain optimum nutrient levels, our fertilizer recommendations are based upon current crop removal replacement rates and the current season nutrient use efficiencies are not as crucial. It should be noted that banding fertilizer to improve efficiencies in low testing soils is almost always less effective and less economical than maintaining optimum soil nutrient test levels throughout the root zone.

Starter fertilizers are usually placed near the planted seed. This is because under cool-wet early growing season conditions, root growth to intercept banded nutrients and availability of soil nutrients is inhibited.

There are limits to the amount of fertilizer that can be placed near newly planted seed. Fertilizer salts and ammonia injury can occur in pop-up or in-furrow starter fertilizer systems. Therefore, the rule of thumb is no more than ten pounds of combined nitrogen, sulfur and potassium can be applied in-furrow.

I prefer that starter fertilizers be placed at least 2 inches beside and 2 inches below the planted seed. This safely allows much higher rates of nutrients and a more dependable rate for stimulating early season crop growth.

One placement system that is gaining attention is to apply anhydrous ammonia, phosphorus, potassium and desired micronutrients in a band sometime between the fall and early spring. Using RTK guidance, the planted row can be placed directly over the band, therefore obtaining a “starter effect.” These systems have worked well in reduced tillage, strip-tillage or intensive tillage systems.

This ends the series on the 4Rs of crop nutrient management. For more information on the 4Rs, visit the International Plant Nutrient Institute website at http://www.ipni.net.

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