Applying lime to soil neutralizes acidity and subsequently increases pH, a major driver in nutrient availability. Managing pH in muck or organic soils (>20% organic matter) in Ohio differs from mineral soils, with a long-standing recommendation to keep organic soils at a target pH of 5.3 to minimize the risk of micronutrient deficiencies (Culman et al. 2020). For vegetable crops on organic soils in this region, university recommendations state that the optimal pH range of muck soils should be between 5.3 and 5.8, depending on the crop (Warncke, Dahl, and Zandstra 2004). Farmers are also interested in using gypsum as a soil conditioner and a readily available source of calcium and sulfur. The purpose of this study is to evaluate the effects of lime and gypsum application on organic soils and vegetable crop productivity.
The trial was conducted from 2017–2021 at The Ohio State University Muck Crops Research Station in Willard, Ohio. An integrated experiment for lime and gypsum was conducted but is reported as two studies here.
The lime study had three treatments, including these annual fall applications:
- 1 ton of lime per acre
- 2 tons of lime per acre
- a control with no lime addition
The gypsum study had three treatments, including these annual fall applications:
- 1 ton of gypsum per acre
- 2 tons of gypsum per acre
- a control with no gypsum addition
A randomized complete block design with four replications was established in the fall of 2017 with plot dimensions of 18 feet by 20 feet. Baseline soil samples were taken (0–8-inch depth) in the fall before application of lime, and then sampled each fall after harvest and before the annual lime application. Vegetable crops following common grower practices were planted and harvested annually, and consisted of the crop rotation zucchini (2018), sweet corn (2019), radish (2020), and two successive crops, radish and then beets, in the final year (2021). In the last year of the trial, tissue samples of the entire aboveground biomass of radishes and beets were taken and analyzed for nutrient concentrations when the crops were harvested.
Results and Discussion
Study 1: Effects of Liming on Soil and Vegetable Crops
Annual application of lime significantly increased soil pH in the final year, as pH ranged from 5.5 (control) to 6.1 (2 tons of lime per acre as shown in Table 1). Baseline soil pH was 5.8, and dropped to 5.5 over the four years of the experiment, still slightly above the recommended 5.3 target pH. The application of lime had no effect on soil test phosphorus (P) or potassium (K) values, but the lime increased both Mehlich-3 extractable Calcium (Ca) and Magnesium (Mg ), as shown in Table 1. Lime application also increased Mehlich-3 extractable micronutrients such as copper, manganese, and zinc (Table 1).
|Variable||Baseline||Control||1 Ton Lime||2 Tons Lime|
|Soil pH||5.8||5.5 c||5.8 b||6.1 a|
|Calcium (M3-ppm)||5405||5086 b||5467 a||5745 a|
|Magnesium (M3-ppm)||834||631 c||834 b||946 a|
|Copper (M3-ppm)||1.1||1.7 b||1.9 ab||2.0 a|
|Manganese (M3-ppm)||24||20.8 b||24.5 a||25.3 a|
|Zinc (M3-ppm)||4||5.6 b||5.9 ab||6.1 a|
Application of lime had a negative effect on crop yields in the second year, with corn in the control treatment out-yielding a lime treatment in 2019 (Table 2). Subsequent years of liming did not significantly increase radish or beet yields, but radish crop yields in 2020 and 2021 ranked: control >1 ton lime per acre >2 tons lime per acre (Table 2).
|Crop||Control (1,000 lb. per acre)||1 Ton Lime (1,000 lb. per acre)||2 Tons Lime (1,000 lb. per acre)|
|2019 Sweet corn||40.0 a||35.7 b||36.6 ab|
In the fourth and final year of the study, liming decreased tissue P concentrations in both crops relative to the control, and decreased only tissue K concentrations in radishes (Table 3). Lime increased tissue concentrations of Ca and Mg in radishes. Interestingly, lime application decreased tissue concentrations of the micronutrients Boron (B), Manganese (Mn), and Zinc (Zn) in radish and beet crops relative to the control (Table 3). Collectively, the crop yield and tissue data suggest that the lime applications:
- exceeded what was beneficial for vegetable crops in organic soils
- made essential nutrients less available
- resulted in yields trending lower
|Nutrient||Control||1 Ton Lime||2 Tons Lime||Control||1 Ton Lime||2 Tons Lime|
|Phosphorus (%)||0.6 a||0.5 b||0.5 b||0.5 a||0.4 b||0.4 b|
|Potassium (%)||5.6 a||4.5 b||4.5 b||5.9||5.7||6.4|
|Calcium (%)||2.2 b||2.9 a||2.9 a||1.5||1.5||1.5|
|Magnesium (%)||0.4 b||0.5 a||0.5 a||1.8||1.9||1.7|
|Boron (ppm)||32 a||25 b||21 c||34 a||33 a||28 b|
|Manganese (ppm)||62 a||37 b||34 b||344 a||274 b||201 c|
|Zinc (ppm)||53 a||47 ab||44 b||183 a||140 b||113 b|
Mehlich-3 versus Tissue Concentrations to Assess Micronutrient Availability
Mehlich-3 extractable micronutrients were not a good indicator of crop nutrient availability, as tissue micronutrient concentrations were often negatively related to soil Mehlich-3 concentrations. For both beet and radish crops, as soil Mn levels increased, tissue concentration decreased (Figure 1, left panel). The decrease in Mn availability was likely driven by increasing soil pH (Figure 1, right panel), and was at odds with what the soil Mehlich-3 extraction indicated. With the application of lime to a muck soil, soil pH increases, and subsequently so do the micronutrient Mehlich-3 values (Figure 2).
The application of lime decreased micronutrient tissue concentrations for B, Mn, and Zn (Table 3). Interestingly, lime application increased soil Mehlich-3 levels of Mn and Zn, but had no effect on B (Table 1). This demonstrates the inconsistency of using Mehlich-3 as a diagnostic tool to detect micronutrient deficiency. As discussed previously, the micronutrient recommendations in Ohio were developed based on measuring different soil extractants rather than using Mehlich-3 (0.1 N HCl for Mn and Zn, and 1.0 N HCl for Cu) (Sharma et al. 2018). Mehlich-3 has not been established as a reliable diagnostic of soil micronutrient deficiency in Ohio (Culman et al 2020). This underscores the importance of tissue testing to diagnose micronutrient deficiencies rather than solely relying on soil tests.
Study 2. Effects of Gypsum on Vegetable Crops
Gypsum increased soil Mehlich-3 Ca (data not shown) and increased soil pH from 5.5 (control) to 5.8 (2 tons of lime per acre annually). As a neutral salt, gypsum typically has minimal effects on soil pH, but some pH changes can occur as Ca replaces exchangeable acidic cations (positively charged ions) in the soil. This is especially true with large application rates, as we had in this study. Gypsum application did not improve vegetable yields, as the control plots had the largest yields each year, although not statistically different than plots receiving gypsum treatments (Table 4). Gypsum also decreased P and Zn concentrations in both radishes and beets in 2021, as well as decreased Mn and B concentrations in radishes (data not shown). Despite interest from farmers in using gypsum for soil conditioning, we found no advantage to this approach.
|Crop||Control (1,000 lb. per acre)||1 Ton Gypsum (1,000 lb. per acre)||2 Tons Gypsum (1,000 lb. per acre)|
|2019 Sweet corn||40||38.7||38.6|
This study demonstrated the importance of managing soil acidity in organic soils for vegetable production. Over-application of lime (2 tons per acre each year) resulted in reduced macro- and micro-nutrient availability as measured through tissue tests and also resulted in a general trend of reduced yields. Interestingly, Mehlich-3 extractable Mn and Zn increased as soil pH increased, but total tissue concentrations decreased. This underscores the limitations of using Mehlich-3 micronutrients as an indicator of their availability in muck soil. Our study demonstrated the importance of managing pH and confirms the recommendation of keeping muck soil pH at approximately 5.3 to optimize plant-available macro- and micro-nutrients. There were no observed advantages of applying gypsum to muck soils for vegetable production in this four-year study.
Culman, Steve, Anthony Fulford, James Camberato, Kurt Stienke. 2020. Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa. (Bulletin 974). Columbus: The Ohio State University.
Sharma, Stuti, Steve Culman, Anthony Fulford, Laura Lindsey, Douglas Alt, and Grace Looker. 2018. “Corn, Soybean, and Alfalfa Yield Responses to Micronutrient Fertilization in Ohio.” (AGF-519). Ohioline, The Ohio State University. ohioline.osu.edu/factsheet/agf-519.
Warncke, Darryl, Jon Dahl, and Bernard Zandstra. 2004. “Nutrient Recommendations for Vegetable Crops in Michigan.” (Bulletin E2934). East Lansing: Michigan State University Extension. PDF. canr.msu.edu/fertrec/uploads/E-2934-MSU-Nutrient-recomdns-veg-crops.pdf.