Arboriculture & Urban Forestry 37(6): November 2011 Arboriculture & Urban Forestry 2011. 37(6): 269–277 269 Laboratory Assays on the Effects of Aerated Compost Tea and Fertilization on Biochemical Properties and Denitrification in A Silt Loam and Bt Clay Loam Soils Bryant C. Scharenbroch, William Treasurer, Michelle Catania, and Vincent Brand among treatments. No differences between dilute ACT (ACTd at 224 kL ha-1 compared to 30-10-7 fertilizer at 195 kg N ha-1 pared to water in A soils. Soil P (A soils only), NO3 Abstract. Aerated compost tea (ACT) is gaining interest as a nutrient amendment for urban trees. This study examined the effects of ACT, synthetic fertil- izer, and deionized water on 15 biochemical properties with two soil types. Significant effects for pH, Mg2+ ) at 22.4 kL ha-1 , Na+ with A horizon soils. Soil K+ greater increases were observed with fertilizer at hours 48 and 96 (+65 to +127 mg N2 fertilization. Minor improvements in soil fertility were observed with ACTc tilizer compared to ACT. Increases in denitrification were seen with ACTc Urban Trees. Appropriate nutrient management of urban trees is important for tree and environmental health. Traditionally, supplemental nutrients to urban trees have been supplied primarily by inor- ganic fertilizers. When misapplied to urban landscapes, fertil- izers represent threats to the environment. Phosphorus (P) in fertilizer applied to urban landscapes has been identified as a significant contributor to P loads to lakes, potentially leading to algae blooms, reduced oxygen, and fish kills (Corsi et al. 1997; Soldat and Petrovic 2008). Nitrogen (N) applied in excess of plant demands contributes to the acidification of surface waters, eutrophication of coastal water, and groundwater contamination (Vitousek et al. 1997; Mitsch et al. 2001; Driscoll et al. 2003). Traditionally it has been thought that fertilizers increase pri- mary productivity, and thus increase soil carbon (C) through greater plant residue returned to the soil (Halvorson et al. 1999). However, recent findings have shown long-term fertilization to decrease soil C storage via N stimulation of soil microbes and associated increase in CO2 efflux (Khan et al. 2007; Mulvaney the absence of oxygen) in the process of carrying sugars through the respiration-glycolysis process in their cells. Under such conditions nitrate is converted to gaseous N (NO, N2 climate change dilemma (Vitousek et al. 1997). In denitrification, bacteria use the N atom in NO3 Continual use of synthetic fertilizers may also reduce soil qual- ity through salt accumulation (Follett et al. 1981; Finck 1982). O, or N2 ). et al. 2009). Greenhouse gases are produced during fertilizer synthesis by burning fossil fuels (Jenssen and Kongshaug 2003) and following fertilizer applications (e.g., denitrification). Deni- trification losses from the soil are important since soil N is lost and resulting NO and N2 O are gases contributing to the global - as a terminal electron acceptor (in Organic fertilizers contain organic matter and include a diverse group of materials that are often classified as either organic farm manures (e.g., animal or green manure) or organic commercial fer- tilizers (e.g., peat, bone meal, biosolids, compost) (Finck 1982). The majority of the nutrients in organic fertilizers are organically bound and slowly mineralized, so the potential for exceeding plant nutrient demands and associated environmental contamina- tion is reduced relative to synthetic fertilization (Stratton et al. 1995). Because organic fertilizers have lower quantities of imme- diately available N compared to synthetic fertilizers, they may be less likely to speed up CO2 release from soil via N-stimulation of microbial respiration (Follett et al. 1981; Triberti et al. 2008). The use of organic materials as fertilizer promotes useful recycling and removes potentially noxious waste products (Finck 1982). Many studies demonstrate the positive impacts of mulch and compost on soil quality and urban tree health (see reviews by Chalker-Scott 2007; Scharenbroch 2009). However, clients and circumstances often dictate that turfgrass remain under urban trees in lieu of mulch. Furthermore, mulch rings rarely cover the full extent of the rooting area, which recently has been esti- mated to be 38 times the tree diameter (Day et al. 2010). Com- post top-dressing applications on turfgrass show promise for improving soil quality and treating a greater extent of the root- ing area (e.g., Watson 1988). However, liquid-based amend- ments are still a very popular nutrient delivery system for urban trees. Aerated compost teas (ACT) are one such liquid product that is rapidly gaining interest as an arboricultural amendment with the hopes of improving soil quality and managing tree nutrition. A relatively easy transition from synthetic fertiliza- tion to ACT may be feasible because much of the existing tech- ©2011 International Society of Arboriculture - (Bt soils only), dissolved organic N, microbial biomass N, and N mineralization were greater with fer- compared to fertilizer and water in the first 24 hours (+4 to +12 mg N2 and water were detected. Soil K+ , NH4 O kg-1 +, and microbial respiration were greater with ACTc O kg-1 Key Words. Compost Extract; Microbial Activity; Microbial Biomass; Nitrous Oxide; Nutrient Availability; Organic Fertilizer; Synthetic Fertilizer; , and denitrification losses were lower with ACTc , C, N, and C/N ratio were not observed was greater with ACT concentrate (ACTc ) com- ), but ). Greatest improvements in soil fertility were observed with compared to the fertilizer.
November 2011
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