With all the political confusion presently surrounding agriculture, domestically and globally, there’s at least one ray of common sense that shines through – the fact that the ag lime price in the U.S. has increased very little, and its availability has remained very constant.
Being an almost exclusively home-sourced American commodity certainly helps lime. Such closeness to end markets minimizes transportation costs. Lime prices have only increased about 25% in the last 10 years.
The costs of the “big three” fertilizer components – nitrogen (N), phosphate (P2O5) and potash (K) – have basically doubled globally. N peaks spiked worse early in the Russian assault on Ukraine. During the first winter of that conflict, as Russia tried to freeze out Ukraine by curtailing its natural gas supply, commercial N costs went crazy. Natural gas is a key ingredient for synthesizing ammonia and urea.
The fertilizer scene these days, compared to just a few decades ago, is increasingly global. In 1961, the U.S. applied 25% of the planet’s fertilizer. In 2021, that figure had dropped to just 10%. While U.S. crop food usage has increased tremendously in these six decades, crop food demand elsewhere on Earth has increased astronomically.
Prudent use of lime, particularly these days, can take a lot of the sting out of the fertilizer ingredient price wound. Most crop growers agree that fertilizer utilization efficiency is best when soil pH is optimized for the intended crop. pH is defined as “the negative logarithm of the hydrogen ion concentration.”
For corn, clovers and most grasses, we get the best return on plant food investment by raising pH to 6.2. Alfalfa, more demanding in its combat against acidity, wants pH in the 6.8 – 7.0 range. When soil test results indicate that certain lime tonnages should be applied for alfalfa, subtract one ton from that figure to get a recommendation for clover, corn and most other crops.
Remember, the lime recommendations are on a basis of 100% estimated neutralizing value (ENV). Most ground limestones are only about 70% ENV. When we undershoot the pH required for a given crop, the fertilizer utilization efficiency often drops by 30% – 50% (or more).
All of the big three nutrients are 100% available at pH 7.0. But when pH drops to 5.5, N and K availabilities drop to 77%. At that low pH, P2O5 is only 48% available. USDA research shows that at pH of 5.0 – 5.2, that nutrient is only 10% available.
Often, I recommend that with most crops – potatoes and blueberries excluded – growers shouldn’t bother applying the big three unless pH has been dragged up into the 6s. With so much phosphate ore being mined outside the U.S. and the push and shove tariff game being played globally, it makes long-term cost projections for this critical nutrient quite unpredictable.
Before tariffs even became a major global economic factor, the CEO of one mineral company that I work with told me that sales of dical (mono-calcium/dicalcium phosphate) would be limited to historic use patterns for existing customers. Lest we forget, the classic phosphorus deficiency symptom is that signature purple leaf-tip die-back, most visible in corn.
As hinted at strongly before, it’s best not to apply P2O5 if soil pH is 5.9 or less. A deficiency due to the absence or unavailability of this nutrient will most definitely limit crop performance. Again, too low pHs also erode the bioavailability of N and K, but not nearly as much as what P2O5 suffers.
Wanting to experiment with how badly too low soil pHs impair P2O5 availability – and thus corn silage yields – I designed a small field trial. This took place during my career as an agronomy Cooperative Extension agent in Otsego County during the 1970s. Working with a cooperating dairy farmer, under the guidance of Cornell soil scientist W. Shaw Reid, Ph.D., we divided a nine-acre field into three parts. The farmer provided labor and equipment as well as the seed corn. The local farmer-owned cooperative donated fertilizer (300 lbs./acre of 15-15-15) and the ag lime.
A simple pH test called for four tons of lime/acre. With farmers usually so concerned about applying lime on rented ground – as was the case with my experiment – I asked Dr. Reid what the benefit of would be applying just half a dose of this soil amendment.
He said if we applied half the recommended lime, we should realize 80% of the yield increase that we would expect, had we applied the full recommended tonnage. This little-known input vs. benefit relationship proved particularly meaningful for farmers renting fields one year at a time. Dr. Reid did stress that at some point the rest of the lime would have to be applied.
We divided the field into three long rectangles, each three acres. All three plots received the same corn seed rate and band-applied fertilizer. One plot received zero lime, the second plot received two tons/acre and the third plot received four tons/acre.
I randomly sampled whole plant weight from each corn plot. The zero-lime plot calculated out to yield 11 tons/acre. The plot receiving two tons of lime/acre yielded 18 tons of silage/acre. The plot limed at four tons/acre yielded 20 tons/acre. Reid’s prediction was spot on.
Let’s leave behind an actual field trial for a theoretical situation. The hypothetical corn growers in question need 1,000 tons of corn silage and their fields need four tons of lime/acre. If they apply zero lime, they will need to grow 91 acres of corn (1,000/11). A two ton/acre application lowers the land requirement to 55.5 acres (1,000/18). And a four ton/acre application lowers the land requirement to 50 acres (1,000/20).
Generally, each additional piece of rental ground needed to compensate for not liming other corn fields is farther away from the owner’s farmstead than the last piece of rental ground acquired.
