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CropTalk: Nutrient Removal Rates Revisited

November 2019

Published on Monday, November 04, 2019

What does 13 lb. of diammonium phosphate (DAP) and 27 lb. of potash mean to your operation? Out of context it probably doesn’t mean much, but what if you added it up on ever acre of corn you grow? To illustrate, on 1,000 acres of corn, that’s 6.5 tons of DAP and 13.5 tons of potash. At the time this article was written, DAP was $491/ton and potash was $387/ton. So, to answer my own question, 13 lb. of DAP and 27 lb. of potash across 1,000 acres equals $8,416.00.

Now the question is where did the figures 13 and 27 come from? The Tri-State Fertilizer Recommendations for agronomic crops have changed. Academic soil and fertility scientists have tested modern corn hybrids for several years and concluded that fewer nutrients are needed to make a bushel of corn — about 5% less phosphorous and 26% less potassium, to be exact. I haven’t yet seen the updated Tri-State Fertility Recommendation, but Ohio State University Extension Agronomist, Harold Watters, shared these updated crop removal rates this past January in the Ohio County Journal as shown in Table 1.

Using Table 1., if you take the 0.03 lb. difference in P2O5 and 0.08 lb. difference in K2O across a 200 Bu./A. corn crop, you should come up with an approximate difference of 13 lb. DAP and 27 lb. potash. According to Purdue’s 2019 Crop Cost and Return Guide, corn fertilizer accounted for 31.5% of total input costs for the crop. I am not condoning cutting your fertilizer rate; however, with current commodity prices, it is advantageous to make the most of every dollar. If you can save $8,416.00 (based on 1,000 acres of corn at 200 Bu./A.), then you should.

Another update to Tri-State’s Fertility Guide is that all phosphorous and potassium recommendations will be made based on the Mehlich III extraction method. The previous guide made recommendations based on Bray P1 for phosphorous and ammonium acetate for potassium. This is important to note because the sufficient, deficient, and maintenance ranges will change. Based on Mehlich III extraction, the maintenance range for potassium will be 100 to 150 ppm.

Talk with your local Beck's agronomist or representative to discuss options or scenarios that would work for your operation. For information and updates concerning the Tri-State Fertility Guide, visit SoilFertility.osu.edu.

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Author: Austin Scott

Categories: CropTalk, 2019

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