The U.S. Department of Agriculture (USDA) defines organic production as “A production system that is managed in accordance with the Act (Organic Foods Production Act of 1990) and regulations … to respond to site-specific conditions by integrating cultural, biological, and mechanical practices that foster cycling of resources, promote ecological balance, and conserve biodiversity” (USDA, 2002). In order for organic producers to accomplish this goal, many focus their production and management practices on soil physical, chemical, and biological properties including organic matter content, bulk density and tilth, microbial biomass, and nutrient levels. The number one production practice used by organic farms is the use of green or animal manures, and organic fertilizer purchases rank fifth in production expenses after feed, labor, supplies and repairs, and cash rent and lease (USDA, 2015). Clearly managing soils and soil quality are a high priority in the organic production of crops.
Many of the changes that are envisioned in organic production can be slow to materialize since one major aim is long-term sustainability of the production system. Small incremental changes in a positive direction, especially in soil physical and chemical properties, are often key to implementation and maintenance of organic production systems. Both the 3-year transition period and a mandate to build soils are therefore a basic requirement. Several long-term organic comparison trials in the United States attest to the need and usefulness of studies that go beyond traditional 2- to 4-year field studies (Delate et al., 2015; Idowu et al., 2009). Most of these long-term studies have been in agronomic crops (Delate et al., 2015). However, some efforts have been made to study long-term effects of organic management in vegetable production (Arthur et al., 2011; Idowu et al., 2009; Mitchell et al., 2007; Ozores-Hampton et al., 2012). Beyond these long-term studies, the effects of soil management on microbial biomass, weed pressure, nutritional content of the crop, and economics have been studied—to name a few (Chang et al., 2007; Darby et al., 2006, Gilman and Langer, 2011; Herenncia et al., 2011; Horneck, 1992; Schmutz et al., 2007; Srivastava et al., 2007). Despite these wide ranging topics, soil management seems to be at the basis of the many studies attempting to gauge long-term sustainability of organic production systems. Soil management can include tillage, compost and manure applications, cover crops and green manures, and crop rotations. In general, limiting tillage, judicious application of compost and green manures, the use of cover crops and green manures, and crop rotations have all shown beneficial effects on a number of soil physical, biological, and chemical properties in vegetable production systems (Delate et al., 2008; Garcia et al., 2008; Gunter, 2010; Ndiaye et al., 2000; Pritchett et al., 2011; Swenson et al., 2004; Waldrip et al., 2012; Wu and Powell, 2007). These studies also allude to the complex interactions between physical, chemical, and biological properties that determine soil productivity.
The potential of soils to support plant growth is the result of both the inherent capacity to sustain crop production and the short- and long-term soil management practices, including tillage and the organic fertilizer applications used on that soil. The complex nature and combination of organic fertilizers together with their even more complex interaction with soils make organic soil management recommendations and decisions difficult (Lee, 2010). This is especially true when considering carry over effects from year to year and longer (Endelman et al., 2010). Soil health, soil potential, soil quality, and soil fertility—more or less defined in the literature—have all been employed to define the long-term carrying capacity of soil and sustainability of agroecosystems (Idowu et al., 2009; Knight et al., 2013). Despite the importance of soil, no one set of parameters has been unequivocally agreed on to measure these complex set of factors (Arthur et al., 2011; Idowu et al., 2009; Pattison et al., 2008).
In 1999, to provide information on the long-term effects of different methods of organic production and soil management on soil health, soil quality, soil fertility, crop yields, weed pressure, disease and insect incidence, and economic returns the Division of Plant and Soil Sciences at WVU established a long-term organic farming systems project with agronomic, animal, and horticulture components. Two organic production systems were initiated. One was a crop-livestock experiment and the other a market garden experiment, data from which are reported here. Our overall goal was to compare the impact of long-term annual animal manure–based applications with green manures and the incorporation of hay mulches. Here we report data from two selected years (2004 and 2014), 1 year after transition (2000–03), and the last year for which we collected yields. Data on soil nutrient concentration, SOM, bulk density, yields, and economic returns immediately after the transition phase (2004) and 15 years (2014) into the project are presented as a means to quantify soil quality and long-term sustainability of the agroecosystems under study.
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