270 Scharenbroch et al.: Biochemical Properties and Dentrification in A and Bt Soils nology (e.g., spraying equipment) for applying fertilizers can be used to apply ACT to urban trees (pers. comm.: R. Bastian of Davey Tree Experts, and J. Lloyd of Rainbow Tree Care). Aerated compost tea is made by mixing compost with aer- ated water (NOSB 2004). Aeration during the brewing process distinguishes ACT from other compost extracts, and is important considering the goal of increasing aerobic microorganisms. Ac- cording to the National Organic Program (NOP), the predomi- nant ACT production method in the United States involves one part compost in 10-50 parts water, constant aeration for 12–24 hours, and immediate application (NOSB 2004). NOP standards specify that compost used to make ACT must be made from al- lowable feedstock materials and the entire pile must undergo an increase in temperature to at least 55°C for at least three days (NOSB 2002). ACT additives—such as molasses, yeast extract, and algal powders—are used to encourage growth of beneficial microbes, but they can also have nontarget negative effects by supporting the growth of bacterial human pathogens from un- detectable levels in properly made compost to detectable lev- els in ACT. The NOSB (2004) specifies that ACT made with additives can be applied to ornamental plants not intended for human consumption, and it is exempt from EPA standards for bacterial indicators of fecal contamination. No standards exist for application rates of ACT in agriculture or horticulture. Cur- rent ACT application rates for horticultural and arboricultural plants range from 4 to 400 kL ACT ha-1 (pers. comm.: E. Ing- ham of Soil Foodweb, Inc., and R. Bastian of Davey Tree Ex- perts), albeit these rates are not based on scientific evidence. Proponents assert that ACT will transfer desirable micro- organisms, fine particulate organic matter, and soluble nutri- ents to soil surfaces. Specifically, unsubstantiated claims are made that ACT will: 1) help retain nutrients via increased mi- crobial immobilization, 2) increase microbial mineralization and make nutrients available at rates plants require them, 3) build soil structure and decrease the effects of compaction, 4) detoxify soil and water, and 5) suppress disease by inducing competition among disease (anaerobic) and beneficial (aero- bic) organisms (e.g., Ingham 2003a; Ingham 2003b; Ingham 2004; Lowenfels and Lewis 2007). In comparison to the an- ecdotal experiences reported by ACT practitioners, relatively few peer-reviewed, controlled, replicated scientific stud- ies have been performed on the impacts of ACT on plants, soil, and the environment (Duffy et al. 2004; Scheurell and Mahaffee 2004; Scheurell and Mahaffee 2006; Larkin 2008; Segarra et al. 2009). Furthermore, consistent findings among these studies have not been reported for the impacts of ACT on plants, soil, or the environment (see review by Scheurell and Mahaffee 2002). The objective of this research was to evalu- ate ACT, synthetic fertilization, and deionized water control treatments in conjunction with two soil types, for their effects on 15 soil biochemical properties, including denitrification. MATERIALS AND METHODS Making and Monitoring ACT Aerated compost tea was made with a KIS compost tea brewer, 18.9 L (Keep It Simple, Inc., Redmond, Washington, U.S.). Deionized water (18.9 L) was combined with one commer- cially available package of compost (approximately 500 g) ©2011 International Society of Arboriculture containing wood chips, sawdust, rock, minerals, fungal in- gredients, humus, and vermicompost (KIS 5 gal compost tea brewing kit from Keep It Simple, Inc., Redmond, Washington). The compost contained 11,648 µg bacteria g-1 g-1 (mean hyphae diameter of 2.8 µm), 18,883 flagellates g-1 14,596 amoebae g-1, 11,338 ciliates g-1 , 3,547 µg fungi , , and 1.2 nematodes g-1 (analyses performed by Soil Foodweb, Inc., Corvallis, Oregon, U.S.). A package (500 g) of microbial food consisting of 80% organic nutrients, 20% natural minerals derived from feather meal, bone meal, cottonseed meal, sulfate of potash-magne- sia, alfalfa meal, kelp, soymeal, and mycorrhizae was added at the start of brew. Humic acid (25 g) and soluble seaweed powder (25 g) were also added at the start of the brew. Dur- ing the 24-hour brew cycle, dissolved oxygen, temperature, pH, and electrical conductivity were measured every hour. Dis- solved oxygen remained above 6 mg kg-1 , with a mean value of 7.3 mg kg-1 throughout the brew cycle. Mean temperature, pH, , and electrical conductivity were 21°C, 4.9, and 2,169 µS cm-1 respectively. On average (12 brews over 2008 and 2010 un- der similar conditions described), the ACT contained only a fraction of what was in the compost itself: 1,972 µg bac- teria g-1 , 4.9 µg fungi g-1 1,920 flagellates g-1, 1,392 amoebae g-1 , Na+ (DON), microbial biomass N (MBN), potential N mineraliza- tion (PMN), and microbial respiration (RES) (Table 1). The procedures used for these measurements are described below. , total C, N, NH4 +, NO3 Laboratory Assay I Laboratory assay I was a full-factorial experiment with two soil types, four treatments, and six replicates. The four treatments were: deionized water, NPK fertilizer at 195 kg N ha-1 ACT (ACTd) at 22.4 kL ACT ha-1 Na+ were determined with atomic adsorption spectroscopy (Mod- el A5000, Perkin Elmer, Inc., Waltham, Massachusetts, U.S.) (Schollenberger and Simon 1945). Soil phosphorus was deter- fertilizer N source is ureaformaldehyde, P source is monopo- tassium phosphate, and K source is monopotassium phosphate. Throughout this paper, the term “fertilizer” is used to represent the synthetic fertilizer, and “ACT” to represent compost tea. The two soils tested were an A horizon silt loam (0 to 10 cm) and Bt horizon clay loam (10 to 25 cm)—both from a fine, illitic, mesic Oxyaquic Hapludalf, Ozaukee series soil pro- file (Kelsey 2000). The two soil types were collected from a two meter wide by three meter deep pit on the grounds of the Morton Arboretum (Lisle, Illinois). Soil was air-dried in the laboratory, passed through a two-millimeter sieve, and thor- oughly homogenized. One hundred-gram soil samples were placed into 250 mL beakers, and liquid treatments were added to bring soils to 60% water-filled pore space. The treated soils were incubated in the dark at 25°C and sampled after 10 days. After the incubation period, soil sub-samples were extracted with 1 M NH4 O5 ), and 5.8% elemental K or 7% soluble potash (K2 OAc (pH 7.0) and mg kg-1 of Ca2+ , Mg2+ , K+ , and at 224 kL ACT ha-1. The fertilizer contained 30% elemental N , and concentrate ACT (ACTc (20% water insoluble synthesized N and 10% water-soluble syn- thesized N), 4.4% elemental P or 10% available phosphoric acid (P2 O). The , dilute ) (mean hyphae diameter of 2.6 µm), , 7.7 ciliates g-1 ter treatments, and baseline soils were analyzed for pH, Ca2+ Mg2+, K+ , and 0.1 nematodes g-1. Six replicates of the ACT, fertilizer, wa- , -, dissolved organic N
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