Posts tagged ‘potassium fertilizer’

Tips for Fall Application of Phosphorus and Potassium

University of Illinois’ the Bulletin published an excellent article on September 4, 2009 regarding phosphorus and potassium recommendations. I’ll distill that article into key points for you here.  The past three years have seen incredible price jumps in phosphorus and potassium, and even though prices have retreated there is still very high interest in phosphorus and potassium fertilization. In fact, I cannot recall a time when farmers and agronomists have placed so much interest in phosphorus (P) and potassium (K) fertilization.

Over the past few years, there are some familiar questions that I hear over and over;

Do I need to apply P and K?

How much P and K should I be applying?

Which is better, one application every two years or should I apply every year?

Is it better to apply P and K in fall or spring?

The Tri-State Fertilizer Guide tells us that the absolute first place to begin with regards to answering these questions is with a soil test. A soil test is the only tool currently available to let us know the P and K status of our soils as it relates to a crop.

When soil tests are below the critical level (Figure 1), the soil is not able to supply the P and K requirements of the crop. Soil tests below the critical level should be considered as indicating a soil that is nutrient deficient for crop growth and recommended rates of fertilizer should be applied annually. Placement techniques to enhance nutrient availability, such as fall strip tilling, may also be beneficial on nutrient-deficient soils.

Above the critical soil test level, the soil is capable of supplying the nutrients required by the crop and no response to fertilizer would be expected. Recommendations for soil test values on the maintenance plateau are designed to replace the nutrients lost each year through crop removal. Because the purpose of fertilizer applications in the maintenance plateau range is to maintain fertility, no response to fertilizer in the year of application would be expected. Therefore, farmers may choose to make multiple year applications.

When soil test levels exceed the maintenance plateau level, the objective of the fertilizer recommendation is to utilize residual soil nutrients. Fertilizer recommendations are rapidly reduced from maintenance levels to zero. There is no agronomic reason to apply fertilizer when soil tests are above the maintenance plateau level.

Full podcast here:


September 9, 2009 at 8:15 am

Starter Fertilizer in Corn: Current Research and Recommendations

Even with softening of some fertilizer prices, fertilizer use in 2009 remains a very hot topic. And one of the most discussed areas is the use of starter fertilizer. First, let me preface the conversation by stating up front that there is no proven difference between liquid and dry starter fertilizers when considering equivalent fertilizer rate and placement. In fact, research conducted at Farm Focus in 2008 evaluated the use of liquid and granular starter fertilizers and found no differences with respect to corn yield in Hoytville soils.

Next, you’ll need your most recent soil test results in front of you to answer the question of whether or not to include phosphorus and potassium in your starter. Research from Ohio State University and at our own Farm Focus plots clearly indicates that soils that have a history of adequate phosphorus and potassium fertilization and resulting in soil test above the critical levels are unlikely to see a yield benefit from the inclusion of phosphorus and potassium in the starter. Soils that are below the critical level for phosphorus and potassium can benefit from starter, especially if broadcast applications were not made the previous fall. Soils that have been in continuous no-till may benefit from starter phosphorus, regardless of soil test level. Also, keep in mind that the efficiency of phosphorus will be the same if applied broadcast in the fall (or even now), as compared to applying that phosphorus as a starter.

Below are two starter fertilizer trials conducted at Farm Focus in Van Wert County:

2007– Four liquid starter fertilizers compared to untreated check.  Fertilizers included 2-20-18, 6-24-6, 8-19-3, and 10-34-0.  These four liquid starter fertilizers were applied in-furrow directly behind the seed at 5.0 gallons per acre. Results did not show any statistically significant yield differences among the treatments.  Soil test taken from this research field in 2005 show phosphorus at 69 ppm and potassium at 160 ppm (CEC = 12 meq/100g).  Full research report is available at

2008– Three liquid starter fertilizers and one dry starter fertilizer were compared to an untreated check.  The liquid starter fertilizers included 2-20-18, 2-20-18 with Avail (blended to 0.5%), and 2-20-18 with organic additives; the liquid starter fertilizers were applied in-furrow directly behind the seed at a rate of 5.5 gallons per acre. The dry starter consisted of 32-9-8 2×2 banded at 136 lb/acre.   Results did not show any statistically significant yield differences among the treatments.  Soil test taken from this research field in 2007 show phosphorus at 40 ppm and potassium at 182 ppm (CEC = 19 meq/100g).  Full research report is available at

In summary, for starter applications Ohio State University recommends a 2×2 placement for optimum application of nitrogen, which is normally the most limiting nutrient for corn production. Inclusion of phosphorus and potassium in a starter blend is necessary if soil test levels for those two nutrients are at or below the established critical values based on the Tri-State Fertilizer Recommendations.

ADDENDUM: Larger planting equipment may not be able to support 2×2 attachments; as such, pop-up or in-seed furrow applications of fertilizers might be used. The same rule of determining whether to include potassium and phosphorus still applies. That is, you should look at your soil test to determine whether you are near or above the critical level.

January 21, 2009 at 7:00 am 1 comment

Reducing Fertilizer Costs in 2009

It is clear by the number of comments, questions and discussions I overhear that fertilizer costs dominate much of the concern for 2009 crops. Prices of crop fertilizers had increased substantially over the last two years and have only recently begun to soften. Unfortunately the bottom has fallen out of commodity prices which makes fertilizer inputs cost the dominate factor in determining crop profit.

The first and absolutely most important step you can take in determining fertilizer need and use for your crop is to take a soil sample. If there was ever a year to use the reserves of phosphorus and potassium in the soil – this is it! A soil sample can be a ‘do-it-yourself’ project, or contact any one of the local agribusinesses.

The results from your soil test will give you a baseline where you stand on phosphorus and potassium. If you soil test phosphorus and potassium levels reach a certain level, no additional fertilizer is required for that crop that year. If the soil test phosphorus and potassium aren’t at this level they may be at the level that only requires they be used at a maintenance rate.

In addition to phosphorus and potassium levels, a soil test can give you insight to soil pH. Phosphorus can be as much as 20-25% more available in this pH range as opposed to a pH in the 5’s.

Finally, consider using manure on your farm to supplement or offset commercial fertilizer. Manures are an excellent source of fertilizers and can be less expensive than purchased commercial fertilizers. Good distribution and nutrient testing are the keys to the use of manures as fertilizers. They will usually build phosphorus levels and maintain potassium levels when used. The nitrogen availability is somewhat unpredictable but good estimates can be made for the conditions under which the manure was used.

Listen to the full podcast here:

December 23, 2008 at 7:00 am 4 comments

Determining Need for Phosphorus and Potassium Fertilizer

There are a couple of agronomic newsletters I read regularly: Ohio State University’s CORN and Purdue’s Chat ‘n Chew. In a recent edition of Chat ‘ n Chew, Camberato and Joern wrote an excellent article on reducing phosphorus and potassium fertilizer use to save money. The article discusses the differences between critical level, maintenance range and drawdown.

The very first place to start is with a good set of soil samples from your farm(s). Once you have your fields sampled or grid-sampled, you can make decisions based on science and not guessing. Full article here:

Listen to the full podcast here:

September 24, 2008 at 7:00 am 1 comment


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