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Should you apply an in-furrow or starter fertilizer to corn?

• By Josh Copes, Rasel Parvej, Syam Dodla and Dan Fromme •

cornPhone calls have been coming in regarding applying an in-furrow starter fertilizer at corn planting. An in-furrow starter is commonly called a “pop-up” fertilizer and is applied in the seed furrow (in-furrow).

This allows for ease of application and placing the nutrients close to the germinating seed which allows the seedling to have easy access to nutrients.

A good in-furrow fertilizer will contain a high percentage of phosphorus along with some nitrogen, but could also contain sulfur, potassium, or micro-nutrients. In Louisiana, ammonium polyphosphate fertilizers, 10-34-0 and 11-37-0, are commonly used in-furrow.

When applied in-furrow, there is potential for salt and ammonia injury from fertilizers with high salt indexes or contain urea- or ammonium-nitrogen. Urea is, therefore, not recommended to be applied in-furrow.

Adequate soil moisture at planting, however, decreases the likelihood of potential salt injury. Another starter fertilizer placement strategy is applying in a 2 X 2 band (2 inches to the side of the seed furrow and 2 inches below the seed depth).

This method of application requires additional planter attachments, but allows for use of higher rates of fertilizer at planting and avoid salt and ammonia injury. In-furrow application rates in excess of 5 gallons per acre of ammonium polyphosphate in corn are not advised. If you would like to know more about salt index for fertilizers visit this web site: http://www.spectrumanalytic.com/support/library/ff/salt_index_calculation.htm.

Research into starter fertilizers

In Louisiana, considerable research has been conducted on the use of starter fertilizers in corn, either with 10-34-0 or 11-37-0. In five out of 15 trials (conducted from 1991 to 2005), corn grain yield was significantly increased by the use of an in-furrow starter fertilizer.

It should be noted that in each year soil-test-based phosphorus levels were considered high in the test area. Therefore, corn yield increase could still occur even though soil test phosphorus levels are high. Phosphorus deficiency symptoms and yield responses to the in-furrow fertilizer were most common in light textured soils (e.g. sandy loam and silt loam soils).

Mascagni et al. (2006) also documented that nitrogen only fertilizers had little effect on early season plant growth whereas, in-furrow fertilizers containing phosphorus increased early season plant growth in all trials. This demonstrates that it is the phosphorus component that improved early season plant growth.

The enhanced plant growth from the phosphorus containing fertilizers, also, resulted in hastened maturity of the corn crop. Mid-silk occurred four days earlier where yield responses were observed and three days earlier when no yield response occurred.

With low commodity prices and high input costs, producers are concerned whether or not they should spend the money on applying an in-furrow starter. Situations where a positive yield response will likely occur from the use of in-furrow phosphorus containing fertilizers are:

1) Planting earlier than recommended,

2) Planting in high residue/no-till situations,

3) When there is a need to apply phosphorus fertilizer based on soil test results,

4) Years with poor early season growing conditions (low temperature and excessive rainfall).

Effect of cool soils

Soils, especially, sandy and silt loam soils are slow to warm in the spring. Cool soils can often result in reduced phosphorus uptake by the plant resulting in temporary phosphorus deficiency, even though soil test phosphorus levels are adequate.

Therefore, when planting earlier than Feb. 25 in south and central Louisiana and March 10 in north Louisiana, an in-furrow starter may be beneficial. High residue situations typically result in cooler and wetter soils that can result in poor early growth and phosphorus deficiencies.

Also, early season nitrogen deficiencies may occur in high residue/no-till situations. When soil test levels calls for the addition of phosphorus, using an in-furrow starter would be recommended. As mentioned earlier, in-furrow application of the fertilizer allows easy access of the nutrients since it is applied in a concentrated band with the seed.

Unfortunately, we cannot predict early season growing conditions, an in-furrow starter can be cheap insurance against detrimental cool and wet weather conditions often experienced in Louisiana in March.

In summary, if you are equipped to apply a fertilizer in-furrow and plan on planting as early as possible or into high residue/no-till situations then applying an in-furrow starter may be beneficial. If soil test reports call for the addition of phosphorus then an in-furrow starter would be a good method to place the phosphorus in close proximity to the developing roots.

Also nutrient use efficiency may be greater compared to a broadcast application of phosphorus, especially if the broadcast application occurred in the fall. This is due in part to time, since an in-furrow application is applied at planting, there is less time for soil reactions to “tie” up phosphorus from being available for plant uptake.

Soil pH should also be considered for the decision of when to apply phosphorus. Phosphorus is most plant available from 6.5 to 7.5 pH range. If outside this range phosphorus should be applied closer to planting. If you have any questions please contact your local county agent, Drs. Dan Fromme, Rasel Parvej, Syam Dodla or myself.

Dr. Josh Copes is an assistant professor of agronomy at the LSU AgCenter Northeast Research Station. He may be reached at jcopes@agcenter.lsu.edu

Dr. Syam Dodla is an assistant professor of soil fertility and irrigation at the LSU AgCenter Red River Research Station. He may be reached at sdodla@agcenter.lsu.edu

Dr. Rasel Parvej is an assistant professor of soil fertility at the LSU AgCenter Scott Research and Extension Center. He may be reached at mrparvej@agcenter.lsu.edu

Dr. Dan Fromme is a professor and state corn, cotton and grain sorghum specialist at the LSU AgCenter Dean lee Research Station. He may be reached at dfromme@agcenter.lsu.edu