Warm weather conditions in some parts of the country this past week have resulted in farmers being able to complete “fall” tillage and even address soil nutrient needs.
In this week’s edition of the Boots in the Field Report, Farm Journal Field Agronomist Ken Ferrie addresses nutrient removal rates. As low commodity prices have increasingly taken their toll on farmers’ profitability that, in turn, has resulted in some growers cutting corners with fertility especially on rented ground. That’s resulted in more land leases that contain the stipulation that fertilizer applications must account for crop removal rates, at a minimum.
“Landlords and farm managers are trying to protect the farm’s base fertility to make sure it is as good when the tenant leaves as it was when they started,” Ferrie says. “I understand this thinking, as we've seen a number of new farms come through Crop-Tech here in the last two years that were really trashed, indicating nobody was managing the fertility.”
Ferrie notes that applying nutrients based on crop removal rates is an easy way to address this issue, but it's not the best.
Many people who employ this tactic assume that the soil test values are hard numbers that you can work with. For instance, Ferrie says if a soil test has a value of 46 pounds, or 23 parts per million, of phosphate and a 200-bu. corn crop removes 70 lbs., you only have to apply 24 lbs. for replacement because the soil gives 46 lbs. If this were true at the end of the year, your soil test would be 0 for the next crop.
“Or, another common thought is that if you apply 70 pounds, then your soil test will stay the same 46 pounds that we had at the beginning of the year, because I replaced everything I removed. This, too, doesn't pan out in real field conditions,” Ferrie notes.
He explains that if you want to raise soil phosphorus levels, it takes about 9 lbs. of P2O5 to raise the soil test 1 pound or 18 pounds to raise it 1 part per million. “So, if this was true in this case, if a soil had 65 parts per million of P2O5, and we raised the 200-bu. corn crop that removes 70 pounds of P2O5 and we didn't apply any P2O5 to our field, our soil test would come down basically about 4 parts per million, and it'd be 61 parts per million.
“I can tell you 30 years in the business, it doesn't work that way either,” Ferrie says.
He explains that there are a number of different extractions and methods used with soil testing, depending on where you farm and what laboratory you use to provide results. That means you could see a wide range of test values.
“A reading that is in the optimum range with one soil-testing technique, may be in the low range on another,” he says. “The soil test does not tell us the total amount that is in your soil, it's only a predictor of how much will become available for the crop in a specific season.”
Listen here for more insights from Ferrie on the information various soil testing methods provide and how to ensure your soils have adequate nutrients going into the 2019 season.