The Effects of Different Soil Amendments on Fertility and Productivity in Organic
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The Effects of Different Soil Amendments on Fertility and Productivity in Organic Farming Systems A thesis presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Science Scott E. Fisher November 2011 © 2011 Scott E. Fisher. All Rights Reserved. 2 This thesis titled The Effects of Different Soil Amendments on Fertility and Productivity in Organic Farming Systems by SCOTT E. FISHER has been approved for the Program of Environmental Studies and the College of Arts and Sciences by Jared L. DeForest Assistant Professor of Environmental and Plant Biology Howard Dewald Interim Dean, College of Arts and Sciences 3 ABSTRACT FISHER, SCOTT E, M.S., November 2011, Environmental Studies The Effects of Different Soil Amendments on Fertility and Productivity in Organic Farming Systems Director of Thesis: Jared L. DeForest Productivity and soil fertility are two of the most important factors in farming. Many organic farmers fertilize their crops with composted plant or animal waste. Some organic farmers who do not have access to large amounts of compost utilize processed fertilizers that are acceptable under certified organic standards. I hypothesized that soils fertilized with composted organic matter would be more fertile and productive than soils fertilized with processed organic fertilizer. To test the hypotheses, I measured nutrient content and availability at three organic farms, each of which uses a different type of fertilizer (animal manure, composted mushroom growing medium, and processed fertilizer). I also grew beans (Phaseolus vulgaris) in soil from each of the farms to measure bean weight as an estimate of productivity. The soil amended with animal manure was the only treatment that resulted in increases in nutrients, nutrient holding capacity, and bean weight. Soils amended with processed fertilizer showed little difference from controls. Approved: _____________________________________________________________ Jared L. DeForest Assistant Professor of Environmental and Plant Biology 4 ACKNOWLEDGMENTS I would like to sincerely thank my advisor, Dr. Jared L. DeForest, for providing the guidance I needed to complete this project; the Department of Plant Biology for providing me with funding for the entire duration of my time in graduate school; Green Edge Gardens, Shade River Organic Farm, and Sassafras Farm, for providing me with valuable information and significant quantities of organic farm soil; Art Trese and Harold Blazier, who assisted in the design and implementation of the garden experiment; my committee members for their time and input; and my family, for supporting me throughout this process. 5 TABLE OF CONTENTS Page Abstract ............................................................................................................................... 3 Acknowledgments............................................................................................................... 4 List of Tables ...................................................................................................................... 6 List of Figures ..................................................................................................................... 7 Chapter 1: Introduction ....................................................................................................... 8 Chapter 2: Materials and Methods .................................................................................... 20 Chapter 3: Results ............................................................................................................. 29 Chapter 4: Discussion ....................................................................................................... 46 Chapter 5: Sustainability and the Organic Philosophy ..................................................... 52 Chapter 6: Future Research ............................................................................................... 54 Chapter 7: Conclusion....................................................................................................... 55 Works Cited ...................................................................................................................... 58 6 LIST OF TABLES Page Table 1: Percent Differences for Bean Measurements ………………………………. 31 Table 2: Raw Means for Bean Measurements ……………………………………….. 33 Table 3: Percent Differences for Soil Fertility Measurements ………………………. 35 Table 4: Raw Means for Soil Fertility Measurements ……………………………….. 36 Table 5: Basic Properties of Native Farm Soils …………………………………….... 40 Table 6: Nutrient Content of Organic Fertilizers …………………………………….. 40 Table 7: Percent Differences for Microbial Measurements ………………………….. 44 Table 8: Raw Means for Microbial Measurements …………………………………... 45 7 LIST OF FIGURES Page Figure 1: Location of Farms ...........................................................................................21 Figure 2: Layout of Common Garden Experiment .........................................................23 Figure 3: Photograph of Common Garden Experiment .................................................24 Figure 4: Dry Bean Weight ............................................................................................29 Figure 5: Average Number of Beans per Plant ..............................................................30 Figure 6: Plant Dry Weight ............................................................................................30 Figure 7: Measurements of Bean Growth .......................................................................32 Figure 8: Total Soil Carbon ............................................................................................34 Figure 9: Nutrient Holding Capacity .............................................................................34 Figure 10: Nitrogen, Phosphorus, and Potassium Content .............................................37 Figure 11: Calcium, Magnesium, and Sulfur Content ...................................................38 Figure 12: pH, Electrical Conductivity, and Carbon/Nitrogen Ratios ...........................39 Figure 13: Bacterial/Fungal Ratios ................................................................................41 Figure 14: Measurements for Soil Microbes .................................................................42 Figure 15: Nitrogen Mineralization and Nitrification ....................................................43 8 CHAPTER 1: INTRODUCTION Persistent public concern over the potential danger of chemicals in the environment and in the food supply has considerably increased the demand for organically produced commodities over the last decade (USDA, 2010). The implementation of national standards for organic certification in 2002 played a major role in establishing a market for commodities produced without synthetic chemicals. The soaring demand for organic products is evident when examining the recent growth rate of the organic foods market; retail sales have increased from $3.6 billion in 1997 to $21.1 billion in 2008 (USDA, 2010), and the number of certified organic acres has increased from less than one million acres in 1992, to nearly five million in 2008, and yet supply still falls short of demand (USDA, 2010). Accordingly, crop productivity on organic farms is an issue that is important to organic farmers and consumers alike. Consumers are motivated to choose organically grown commodities over conventional products for a variety of reasons. A 2001 survey showed that the public perceives certified organic produce as safer (containing less pesticide residue) than conventionally grown produce (Williams & Hammitt, 2001). Research conducted by the USDA indicated that organic produce typically contains significantly fewer pesticides than conventional produce, and is less likely to contain residues from multiple pesticides (Gold, 2008). Additionally, data collected by the USDA and the Food and Drug Administration (FDA) from samples of conventional produce confirmed 13 different pesticides on a single fruit or vegetable, an average of two to four different pesticides on 9 a single fruit or vegetable, and a total of 52 different pesticides were detected on all commodities tested, some of which were unapproved by the Environmental Protection Agency (EWG, 2010). Another popular assumption is that organically grown crops are more nutritious than crops grown conventionally (Williams & Hammitt, 2001). This is largely based on the basic ideology that organic farming practices are more „natural‟, and therefore produce healthier foods. There are, however, scientific facts that support this theory (comparisons of nutritional values in this paper are based on concentrations of protein, fiber, vitamins, minerals, or polyphenolic antioxidants; Reganold et al., 2010). Because most OM contains a much broader spectrum of nutrients than most synthetic fertilizers (which primarily contain N, P, and K), it is reasonable to assume that organically grown crops would contain a wider variety of nutrients than conventional crops. In order to determine scientifically whether organically grown foods are truly more nutritious than crops grown conventionally, numerous experiments have been conducted comparing nutritional values of crops grown in each system. In the past decade, eight of the ten reviews of literature comparing the nutrition of organic and conventional produce found some evidence that organic foods