Doctor of Philosophy, The Ohio State University, 2022, Horticulture and Crop Science

Many Midwestern organic farmers in their focus on improving soil quality for crop production attempt to balance their soil's calcium (Ca) and magnesium (Mg) saturation levels by applying calcium-rich amendments. For most soils, this practice based on the base cation saturation ratio (BCSR) hypothesis, requires repeated applications of calcitic limestone and or gypsum to increase Ca to approximately 65% of a soil's saturation capacity and reduce Mg saturation to less than 20%. Expected and claimed benefits of this practice of soil balancing include improved soil structure, decreases in weed pressure, and increases in crop yield. We applied various Ca and Mg rich minerals in a corn-soybean-small grain rotation in two Ohio soils over several years. Our treatments were designed to contrast the effects of different Ca to Mg ratios on the weed community and on soil properties. Our research is the first to provide evidence that Ca:Mg ratios in the soil can reduce density of weed seeds found in the soil. At the silt loam soil, broadleaf and grass seedbank densities were on average about 25% and 40% lower after the second year of gypsum applications, respectively, across crops. Weed emergence for the same soil showed a similar response. At the clay loam soil, grass seedbank densities were on average about 40% higher after the third year of epsom application across crops. Our experimental design enabled us to also investigate the claim of soil balancing proponents and farmers that the increases in crop yield they experienced were due to higher Ca:Mg ratios rather than pH correction. We examined crop yield in response to both pH and Ca and Mg saturation levels over 6 years and concluded that balancing the soil Ca and Mg levels did not impact corn or soybean yields but managing soil acidity did. Our results confirm that correcting excess acidity remains the fundamental reason to apply limestone as a tool to improve crop yields. Previously reported research from our project had (open full item for complete abstract)

Committee: Douglas Doohan (Advisor); Christine Sprunger (Committee Member); John Cardina (Committee Member); Steve Culman (Committee Member) Subjects: Agriculture; Agronomy; Soil Sciences

Master of Science, The Ohio State University, 2018, Horticulture and Crop Science

In Ohio, many organic farmers use the term `balancing' to express the rationale of using a wide variety of soil amendments to improve soil quality and plant health. Soil balancing or the base cation saturation ratio (BCSR) approach is a method first proposed more than 100 years ago that aims to achieve the `ideal soil'. William Albrecht in the 1970's concluded that if saturation of the major exchangeable cations is 65-85% for Ca, 6-12% for Mg, and 2-5% for K, plant nutrition will be balanced. Research conducted by Zwickle et al. (2011) indicated that many organic farmers believe balanced soils produce higher quality crops and have diminished weed infestations compared to unbalanced soils. For many farmers, soil balancing includes using amendments thought to enhance soil biology and increase the soil's capacity to store and release minerals needed by plants. Combined mineral and these organic/bio-active soil products can be very costly, as much as US $1000-1250/ha in the first year. While farmers believe they are benefiting from these expenditures, there is no objective evidence to confirm their belief. I conducted on-farm studies at six locations in Northeast Ohio, with the overall goal of determining the effect of gypsum, with or without “biological stimulants”, on the soil microbial community, crop quality, weed populations, and soil chemical characteristics. Soil seed bank and soil health/biological properties were measured, including soil respiration, active carbon, protein content, microbial biomass, and complete mineral analysis. Crop foliage for nutrient analysis, and crop quality was determined after harvest. Differences in final soil nutrient levels, base saturation, crop and weed community effects were influenced more by the farm than by the treatments applied. After two years, soil sulfur levels were significantly higher in plots amended with gypsum. Failure to detect treatment response by other mineral amendments suggests the relatively narrow difference (open full item for complete abstract)

Committee: Douglas Doohan (Advisor); Warren DIck (Committee Member); Kleinhenz Matthew (Committee Member); Steve Culman (Committee Member) Subjects: Agriculture; Horticulture; Soil Sciences

Master of Science, The Ohio State University, 2015, Horticulture and Crop Science

Organic farmers rely on many methods for weed control. While cultural practices are considered to be important, tillage, cultivation and hand weeding are paramount. Soil balancing is a cultural approach to weed management that is frequently discussed but poorly understood. Likewise organic-approved herbicides are of great interest to some farmers but of uncertain efficacy. Soil balancing is an approach to soil management based upon the “Basic Cation Saturation Ratio” (BCSR) hypothesis, which postulates that an ideal soil has a base saturation ratio of ~70% Ca, ~10% Mg, and ~5% K. The effects of soil balancing and the efficacy of approved natural-product herbicides on weeds have not been adequately investigated. A long-term field experiment was initiated to determine the effects of various soil balancing amendments, gypsum plus limestone, limestone only, and an amendment obtained from a local company (Green Field Farms Cooperative) on crop, weed, and soil parameters. Respecting organic herbicides, a greenhouse experiment was initiated to determine the efficacy of cinnamon oil, manuka oil, lemongrass oil, clove oil, citric acid, acetic acid, and a mixture of citric acid and garlic oil on three broadleaf weeds and two grasses. In the soil balancing experiment, balanced levels of Ca, Mg, and K base saturation were not achieved following two years of amendment application, although changes in soil pH, Ca, Mg, P, and S were measured over the course of the experiment with the specific amendments applied. Soil amendment led to higher levels of K, Ca, S, Mo, Cu, and Mn in corn and soybean foliage in 2014, and S in 2015, there were no treatment effects on grain yield or quality. Conclusions about the effect of soil balancing on weed communities could not be made because balance was not achieved; moreover, there were not clear treatment effects on weeds. However, a rotational effect was observed. Clover plots had the fewest weeds in 2015 because fewer weed seedlings emerged (open full item for complete abstract)

Committee: Doug Doohan (Advisor); Laura Lindsey (Committee Member); Warren Dick (Committee Member); Steve Culman (Committee Member) Subjects: Agriculture; Agronomy; Soil Sciences