Another Look at Improving Soil pH

Another Look at Improving Soil pHOne definition of “logistics” reads “the detailed coordination of a complex operation involving many people, facilities or supplies.” Though farm-related logistics are better now than they were this past winter and spring, input suppliers still strive to keep product inventories as low as possible. Thus, many goods must still be ordered from central locations. Waiting till the last minute to order stuff is still not a good idea. Freight costs have gone up due to such logistical problems, which have been further complicated by the geopolitical military mess in Ukraine. Beyond transportation costs, most farm inputs have experienced major price increases. Let’s compare some cost figures from the good old days to some modern sticker shocks.

I’ll mentally flash back to 1966 and our Catskills foothills family farm, where my dad bought a new tractor. He was told he should expect to pay $100/horsepower. He bought a green 70-hp diesel tractor for about $7,000, and a 250-gallon fuel tank, which he filled up with 20-cent “green” diesel. Good hybrid seed corn cost about $15/bag although we didn’t plant any corn on our higher altitude hillside farm. He had ag lime delivered and spread for $10/ton.

Returning to the present, two growers told me that these days new tractors typically cost about $1,000/horsepower. Current sticker shock includes diesel priced at over $5/gallon and non-GMO seed corn at $200/bag; also, glyphosate-tolerant GMO seed corn runs about $300/bag. Ag lime increased to $30/ton and to $35 – $40/ton for small growers just ordering one trailer-load. While price increases for machinery and seed corn plus many other inputs have far exceeded the general rate of inflation, ag lime has lagged way behind consumer price increases.

Higher yields per acre can minimize the acreage a grower must harvest in order to achieve a certain targeted tonnage. It’s obvious that improving yield per acre reduces tractor and worker hours. It will take a lot more equipment time and human time to harvest 200 acres yielding three tons dry matter (DM) per acre than to harvest 100 acres, each yielding six tons/acre DM. Yet the total harvest is the same in both cases. I stress the yield-enhancing benefits of applying ag lime. The shocking costs of these non-lime inputs causes deep-thinking growers, and their crop advisors, to capitalize on the cheapest input in order to optimize the performance of more expensive ones.

Classic land grant institution research shows that when soil pH is 6.8 – 7.0, phosphorus (P) is essentially 100% available to plant roots. But at pH 5.0 – 5.2, P is only 10% available. So for all field crops, it’s best not to apply P if pH is 5.9 or less. A P deficiency due to absence or unavailability of this nutrient will limit crop performance. Lower pH also undermines the availability of nitrogen (N) and potash, but not nearly as much as is the case with P.

Wanting to demonstrate just how badly lower pH reduces soil P availability and thus silage yields, I designed a small field trial during my agronomy Cooperative Extension career. This took place during the 1970s in Otsego County, when I worked with a cooperating dairy farmer under the guidance of Cornell field crops specialist Professor Shaw Reid. We divided a nine-acre field into three equal parts. The farmer provided the labor, equipment and seed corn. The local farmer-owned cooperative donated the fertilizer at 300 lbs./acre of “triple 15” as well as the ag lime. Simple pH testing called for four tons of lime/acre. With farmers concerned about applying lime on rented corn ground, I asked Dr. Reid what the benefit would be of applying just half the recommended dose of lime.

He said if we applied half the recommended lime, we should realize 80% of the yield increase that we would expect if the full recommended amount had been applied. This little known input vs. benefit relationship proved particularly significant for farmers renting fields one year at a time. The professor did stress that at some point the rest of the lime would have to be applied. We divided the field up into three long rectangles, each three acres. All three plots received the same corn variety, seed rate and band-applied fertilizer. One plot received zero lime; the second plot received two tons/acre; the third plot received four tons/acre. I randomly sampled whole-plant weights from each corn plot. The zero lime plot’s yield calculated out to be 11 tons of silage/acre; the plot receiving two tons lime/acre yielded 18 tons silage; the plot limed at four tons/acre yielded 20 tons silage/acre.

Let’s take a theoretical situation, in which hypothetical corn growers need 1,000 tons of silage and their fields need four tons of lime/acre. Using the math from the real example above back in the 1970s, if they apply no lime, they will need to grow 91 acres of corn. A two ton/acre lime application lowers the land requirement to 55.5 acres. And a four ton/acre lime application reduces the land requirement to 50 acres. Generally, each additional piece of rental ground is farther away from the farmstead than the last piece of rental ground. Those farther away parcels usually involve more travel time and more highway travel.

Here are some examples of fertilizer cost comparisons, compliments of the online Argus North American Fertilizer newsletter, dated Aug. 18 of this year. They’re FOB Cincinnati, the nearest freighter ship depot to the Northeast: urea prices averaged $633/ton, up $170/ton from a year earlier; diammonium phosphate prices averaged $800/ton, up $159/ton from a year earlier; and mono-ammonium phosphate averaged $823/ton, up $145/ton from a year earlier. Looks like applying lime properly last year was a good idea; this year it was and still is a great idea.

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