Farming Ohio's muck soils for vegetables

Northwest Ohio grows vegetables on ground that most of the state would not recognize as soil. The black muck of the old lake plain holds more than 20 percent organic matter, and that single fact changes almost everything about how you feed a crop, how you lime it, and what you expect a pH reading to mean. The university recommendations for these organic soils have long pointed growers toward a target pH of 5.3, well below the neutral mark that mineral-soil growers aim for, because pushing muck soils higher risks locking up the micronutrients a vegetable crop needs. If you farm muck ground, the useful question is not whether to lime but how much, and what the yield response actually looks like.

The details cited in this entry were checked on Ohio State fact sheet.

What makes muck soil behave differently

Organic soils in this region are defined by their organic matter content, above 20 percent, and Ohio State University recommendations place the optimal pH range for vegetable crops on these soils between 5.3 and 5.8, depending on the crop (Warncke, Dahl, and Zandstra 2004). That range sits low on the 0 to 14 scale. A mineral-soil grower chasing 6.5 on a sandy loam is working a different problem from a muck grower trying to hold a muck field at 5.5, and the two should not be given the same advice.

The reason the target is low comes down to micronutrient availability. Let a muck field drift upward and the risk of micronutrient deficiencies rises, which is the long-standing argument for keeping organic soils near 5.3 (Culman et al. 2020). The pH number is not a score to maximize. It is a lever, and on muck ground it has a narrow useful band.

What the Willard trial tested

From 2017 to 2021, a trial ran at The Ohio State University Muck Crops Research Station in Willard, Ohio. It was set up as an integrated experiment for lime and gypsum but reported as two separate studies. The lime study carried three treatments applied each fall: 1 ton of lime per acre, 2 tons of lime per acre, and a control with no lime. The gypsum study used the same three-part structure: 1 ton of gypsum per acre, 2 tons of gypsum per acre, and an untreated control.

The design was a randomized complete block with four replications, established in the fall of 2017, with plots measuring 18 feet by 20 feet. Baseline soil samples were pulled from the 0 to 8 inch depth in the fall before any lime went on, then sampled each fall after harvest and before the next annual application. Crops followed common grower practice and ran as a rotation: zucchini in 2018, sweet corn in 2019, radish in 2020, and two successive crops of radish and then beets in 2021. In that final year, tissue samples of the entire aboveground biomass of the radishes and beets were taken at harvest and analyzed for nutrient concentrations.

What lime did to the soil

Annual lime application significantly raised soil pH by the final year. Across the plots, pH ranged from 5.5 in the control up to 6.1 where 2 tons of lime per acre had gone on each fall. Baseline pH was 5.8 at the start and had dropped to 5.5 over the four years of the experiment, which still left it slightly above the recommended 5.3 target.

Lime moved calcium and magnesium, and it moved some micronutrients too. Soil test phosphorus and potassium were not affected by the lime applications. Mehlich-3 extractable calcium and magnesium both rose with lime, and so did extractable copper, manganese and zinc.

  Variable
  2017 Baseline
  2021 Control
  2021 1 Ton Lime
  2021 2 Tons Lime



Soil pH5.85.5 c5.8 b6.1 a
Phosphorus (M3-ppm)181172171166
Potassium (M3-ppm)288135152165
Calcium (M3-ppm)54055086 b5467 a5745 a
Magnesium (M3-ppm)834631 c834 b946 a
Boron (M3-ppm)0.60.80.80.8
Copper (M3-ppm)1.11.7 b1.9 ab2.0 a
Iron (M3-ppm)219326320312
Manganese (M3-ppm)20.8 b24.5 a25.3 a
Zinc (M3-ppm)5.6 b5.9 ab6.1 a

The potassium figures deserve a second look before you read them as a lime effect. Values fell from a baseline of 288 ppm to somewhere between 135 and 165 ppm by 2021, and the decline tracks with four years of cropping rather than with anything the lime did. Yield removes potassium, and the trial reports no lime effect on soil test K.

Did the crops follow the pH

They did not, and this is the part of the trial that should slow a grower down before ordering a lime spreader. Lime application had a negative effect on crop yields in the second year, with corn in the control treatment out-yielding a lime treatment in 2019. In the years that followed, continued liming did not significantly increase radish or beet yields. The 2020 and 2021 radish crops ranked control first, 1 ton of lime per acre second, and 2 tons of lime per acre last.

Zucchini in 2018 came in at 58.5 thousand pounds per acre in the control, 60.2 under 1 ton of lime, and 60.4 under 2 tons, a spread that does not read as a lime response. The fact sheet carries the 2019 sweet corn row into the table, and the figures beyond that point are not given in the text of the page.

Where does gypsum fit

Growers in the region have shown interest in gypsum as a soil conditioner and as a readily available source of calcium and sulfur, and that interest is what put the second study in the ground. The trial applied 1 ton and 2 tons of gypsum per acre each fall against a control, on the same station and the same rotation, and reported it as a separate study from the lime work. The page presents the lime results in detail and does not carry the gypsum results through in the same way.

What a muck grower should take from four years of lime

The headline result runs against intuition. Four annual lime applications raised pH from 5.5 to 6.1 at the highest rate, and the crop never thanked anyone for it. Radish yields in the last two seasons were best where no lime had been applied at all. On ground that starts near the recommended target, adding lime appears to buy a pH change and very little else.

The study is a single site in Willard over four years, and the fact sheet is explicit that it evaluates lime and gypsum on organic soils and vegetable crop productivity; it does not claim the result transfers to every muck field in the region. A field sitting well below 5.3 is a different case from a field sitting at 5.8, and the trial's starting point was 5.8.

Reading your own soil test

Before you act on any of this, you need a number from your own ground. A standard soil test reports pH along with phosphorus, potassium, calcium and magnesium, and pH is the value that drives the rest of the soil chemistry. Micronutrients, including iron, manganese, zinc, boron and copper, come as an added-cost option at most labs, and on muck ground that option is worth pricing, because the whole argument for holding pH low is micronutrient availability.

Results come back with interpretations and recommended corrective rates, which is what keeps you from guessing at a fertilizer rate. On a field with no history of amendment, an initial look at texture, salinity and micronutrients is recommended; on ground that has been farmed and fertilized for years, a routine macronutrient test usually answers the question unless you are chasing a specific plant problem.

If you want the trial's full treatment list, its plot dimensions and its yield table, the Ohio State fact sheet carries them. Request micronutrient analysis on your next muck field sample and compare the manganese figure against the pH on the same report before you book lime.

About the resource: Ohioline is the fact sheet service of Ohio State University Extension. The ANR-0102 page reports a 2017 to 2021 lime and gypsum trial on organic soils at the Muck Crops Research Station in Willard, listing treatments, plot design, the crop rotation of zucchini, sweet corn, radish and beets, soil test tables and yield tables. The page states no author, no publication date and no cost, and it points to Culman et al. 2020 and Warncke, Dahl, and Zandstra 2004 for the pH recommendations behind the work.