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Use of high tunnel crop production is expected to increase to meet the growing demand for locally produced fresh market vegetables. These structures have the potential to offer many production benefits; however, managing soil quality in these structures is challenging and work in the area is limited. In this 3-year study, we compared the impacts of organic and inorganic fertility amendments on soil quality, nutrient availability, and the productivity of chard (Beta vulgaris L.) and sweet peppers (Capsicum annuum L.) produced in high tunnel and open field systems. Fertility amendments included a green manure treatment [hairy vetch (Vicia villosa Roth) and dehydrated alfalfa meal], partially composted and pelletized chicken litter, urea, and an unfertilized control. Chard was grown in 2011, and peppers were grown in 2012 and 2013. Soil nutrients, microbial activity, active carbon, pH, electrical conductivity (EC), total soil organic matter, and yield were quantified. Chard yield was lower in the high tunnel compared with the open field in 2011, but pepper yield was greater in the high tunnel in 2012 and 2013. Productivity of chard was lower in the green manure compared with urea in 2011 across high tunnel and open field production systems, but no difference in pepper yield was observed between plants receiving fertility inputs in either 2012 or 2013. Repeated application of green manure and chicken litter resulted in soils with increased microbial activity and active carbon, but the green manure was the only treatment successful at accruing carbon in the high tunnel over time. High tunnel production resulted in greater EC compared with the open field, but levels were not considered inhibitory for chard or peppers. High tunnels can increase vegetable crop productivity in themidwest United States, and organic fertility amendments can improve soil quality as measured by soil microbial activity and active carbon in high tunnel and open field production systems. Demand for fresh, locally sourced vegetables that are marketed directly to consumers is increasing across the United States (Timmons andWang, 2010). Onemajor trend among growers targeting these markets is the use of high tunnels to extend the growing season for increased crop productivity. High tunnels, or polytunnels, are structures covered by a single or double layer of polyethylene and are usually passively ventilated. They create a more controlled growing environment by offering protection from weather extremes, control of water and fertility management, and greater control of some plant pathogens leading to increased yield and quality of produce (Lamont, 2009; O’Connell et al., 2012; Pottorff and Panter, 2009). However, growers using high tunnels must overcome production challenges including balancing increased nutrient needs and soil degradation resulting from intensive production practices (Knewtson et al., 2010a; O’Connell et al., 2012; Reeve and Drost, 2012). In light of the fact that federally funded assistance programs through the USDA-NRCS have supported construction of more than 10,000 high tunnels since 2010 (G. Gilbert, personal communication), the best approaches tomeeting these challenges is a critical question. Soil quality is broadly defined as the ability of a soil to function in terms of sustaining plant productivity and moderating water and air quality, all while allowing for improvement in human health and habitation (USDA, 2014). Managing soil quality is difficult in intensively managed vegetable systems where regular tillage and substantial inputs are required to attain a desired level of crop productivity. Managing soil quality is likely to be evenmore challenging for vegetable growers using high tunnel structures as a result of longer, more intensive cultivation and modification of the soil system. As the use of these structures continues to increase, there is a critical need for research that will identify management practices that maintain or improve soil quality within these systems. Organic fertility amendments have potential to improve soil quality while meeting nutrient needs in high tunnel systems. However, timing nutrient availability with periods of critical nutrient uptake with organic amendments can be difficult because the amendments must mineralize before they are available for plant uptake. Animal manures are commonly applied in high tunnel production systems and they have previously been shown to meet crop nutrient requirements (Knewtson et al., 2010a, 2010b). Amending soil with animal manures can benefit the soil system by inputting carbon (C) and organic nutrients, although repeated use can result in phosphorus (P) accumulation because plants need more nitrogen (N) relative to P, and P accumulation can lead to negative environmental impacts (Edmeades, 2003). Furthermore, soluble salts have been shown to accumulate with prolonged use of animal manures (Yao et al., 2007). Excessive levels of soluble salts can negatively impact crop productivity (Maas and Hoffman, 1977). Accumulation of salts is of particular concern in high tunnels, where decreased exposure to rainfall and higher temperatures prevents leaching and increases evapotranspiration. One alternative strategy to meet fertility needs and improve soil quality in high tunnels without the negative soil quality impacts that could result from animal manures is the use of green manures. Green manure fertility sources include cover crops that are tilled under before seeding or transplanting or the incorporation of dehydrated plant materials recovered at another location. Legumes (e.g., hairy vetch) are a popular choice as a result of their ability to fix atmospheric N and their narrow C-to-N ratio, which results in rapid mineralization and release of plant-available nutrients for subsequent crops. The benefits of green manures on soil and water quality are well established in exposed agricultural settings (Snapp et al., 2005). For example, incorporating legumes as green manure maintains nutrient poolswith longermean residence times, thus reducing nutrient loss through leaching (Komatsuzaki and Ohta, 2007; Snapp et al., 2005). These C-rich amendments can Received for publication 16 Sept. 2014. Accepted for publication 18 Nov. 2014. This work was supported by Purdue Agriculture Research Programs. We thank Longjie Cheng and the Purdue Statistical Consulting Service for their assistance with statistical analyses. We also thank Nate Linder, Tristand Tucker, and Jay Young for assistance and guidance in plot management. To whom reprint requests should be addressed; e-mail lhoaglan@purdue.edu. HORTSCIENCE VOL. 50(3) MARCH 2015 461 also replenish labile C pools that aid in the biochemical conversion of key plant nutrients (Drinkwater and Snapp, 2007). However, although green manure amendments have been tested for their impacts on crop productivity in high tunnels (Araki et al., 2009; O’Connell et al., 2012), their impact on soil quality has not been conclusively demonstrated. The goal of this study was to determine how soil quality and vegetable productivity are impacted by organic and inorganic fertility amendments in high tunnel and open field production systems. We predicted that animal and green manure amendments could meet crop needs and increase soil quality relative to an inorganic fertility treatment and an untreated control, although green manures may not have some of the potential negative side effects that animal manures can have in high tunnel systems. This trial was conducted side by side in a high tunnel and open field setting to understand how the production systems alter N availability and influence the potential soil quality benefits of these amendments. The experiment was conducted over 3 years and quantified the impacts of repeated application of fertility amendments on soil nutrients, indicators of soil quality, and vegetable crop yield. Materials and Methods Site description and soil treatments. Field trials were conducted at the Meigs Horticulture Research Farm (lat. 40 17#21$ N, long. 86 53#02$W), a subsection of Throckmorton Purdue Agriculture Center, located in Tippecanoe County, IN. The mean annual precipitation at this site is 1008 mm, and summer temperatures typically range from 21.1 to 26.7 C with mean maximum temperatures reaching 29.5 C. Soil at this site is from the Drummer soil series (fine-silty, mixed, mesic Typic Endoaquoll) that typically contains 3.2% organic matter and has a neutral pH. Previousmanagement history at this site (2002– 09) consisted of a conventional corn/soybean [Zea mays L./Glycine max (L.) Merr.] rotation with variable rates of fertilizer depending on the crop that was grown. In 2010, high tunnels (14.6 · 7.9 · 3.7 m, Quonset-frame, 6-mil single-layer polyethylene) were constructed in an east-to-west orientation at this site, and adjacent open field settings of the same size were left uncovered for comparison trials. Our study was conducted in one of the high tunnel and open field pairs from Spring 2011 to Fall 2013. Soil fertility amendments used in this trial included: 1) green manure consisting of fallseeded (broadcast at 33.6 kg·ha) hairy vetch (Vicia villosa; Johnny’s Selected Seeds, Albion, ME) supplemented with dehydrated alfalfa meal [(3.0N–0.2P–0.8K); Fertrell, Bainbridge, PA]; 2) animal manure (partially composted and dehydrated chicken litter, 3.0N–0.9P–2.5K; Fertrell), 3) urea (46N– 0P–0K); and 4) unfertilized control. The animal manure and green manure were supplemented with Phostrell (0N–2.6P–0K; Fertrell) and sulfate of potash (0N–0P–43.2K; Fertrell) and urea was supplemented with triple superphosphate (0N–20.1P–0K) and potassium chloride (KCl; 0N–0P–49.8K) to provide additional P and potassium (K) as needed to meet recommended crop nutrient needs. The annual fertility contribution of the hairy vetch green manure crop was estimated by calculating the amount of dry biomass and determining the N content of

Sustaining Soil Quality in Intensively Managed High Tunnel Vegetable Production Systems: A Role for Green Manures and Chicken Litter