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Christine M. Worthington and Chad M. Hutchinson

The St. Johns River has been identified by the state of Florida as a priority water body in need of restoration. Best Management Practices were evaluated for potato (Solanum tuberosum L. `Atlantic') production in the Tri-County Agricultural Area to reduce nitrate run-off from about 9,300 ha in production. Objectives of this study were 1) determine the influence of soluble and controlled release fertilizer (CRF) and timing of leaching irrigation on nitrate leaching and 2) compare yield and quality of the potato crop fertilized with either a soluble or controlled release nitrogen fertilizer in a seepage irrigated production system. The experiment was a split-split plot with four replications. Main plots were irrigation events (0, 2, 4, 8, and 12 weeks after planting, (WAP)), nitrogen source and rates included (ammonium nitrate (AN) 224 kg·ha–1 or controlled release fertilizer (CRF) 196 kg·ha–1). About 7.6 cm of water was applied at each irrigation event and surface water runoff collected. CRF decreased NO3-N loading by an average of 35%, 28%, and 32% compared to AN fertilizer during the 2, 8, and 12 WAP irrigation events, respectively, compared to AN. Plants in CRF treatments had significantly higher total and marketable tuber yields (30 and 25 t·ha–1) compared to plants in AN treatments (27 and 23 t·ha–1), respectively. Plants in the CRF treatments also had significantly higher total and marketable yields in 2005 (28 and 23 t·ha–1) compared to plants in AN treatments (25 and 21 t·ha–1), respectively. CRF was an effective alternative to conventional soluble forms of fertilizer maintaining yields and protecting natural resources from nonpoint source pollution.

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Ian A. Merwin, John A. Ray, Tammo S. Steenhuis and Jan Boll

Commercial apple (Malus domestica Borkh.) orchards in the northeastern United States receive heavy pesticide inputs and are often located on well-drained soils near surface and groundwater resources. Nonpoint-source water pollution by agrichemicals has been monitored in agronomic crop systems and simulated using computer models and laboratory soil columns, but inadequately studied at field scale in orchards. We monitored the concentrations of agrichemical tracers, nitrate-N, and benomyl fungicide in water samples from two apple orchards under mowed sodgrass (Mowed-Sod), shredded bark mulch (Bark-Mulch), preemergence residual herbicides (Resid-Herb), and postemergence herbicide (Post-Herb) groundcover management systems (GMSs). In one orchard, we evaluated subsurface spatial patterns and flow rates of a weakly adsorbed blue dye (pesticide analog) and potassium bromide (nitrate analog) under trees after six years of Post-Herb and Mowed-Sod treatments. Nitrate and pesticide tracers leached more rapidly and in higher concentrations under Post-Herb treatments, apparently via preferential macropore flowpaths such as root channels, soil cracks, and macrofauna burrows. At another orchard, we monitored subsurface leaching and surface runoff of benomyl and nitrate-N on a whole-field scale. Peak concentrations of benomyl (up to 29 mg·liter-1) and nitrates (up to 20 mg·liter-1) were observed in subsoil leachate under Resid-Herb plots during 1993. In 1994, nitrate concentrations were greater in leachate from all GMSs, with upper ranges from 48 to 66 mg·liter-1, while benomyl concentrations were lower in all GMSs compared with the previous summer. In surface water runoff during 1993, the highest benomyl concentrations (387 mg·liter-1) and most frequent outflows occurred in Resid-Herb plots. During 1994, benomyl runoff was more frequent in both herbicide GMSs, with concentrations up to 61 mg·liter-1 observed in the Post-Herb plots. Weather patterns, irrigation intensity, differing soil conditions under each GMS, and the turfgrass/clover drive lanes affected the relative frequency and concentrations of benomyl and nitrate leaching and runoff. Preferential bypass flow appeared to be a major subsurface leaching pathway, and erosion sediment an important factor in surface movement of these agrichemicals. Our studies suggest that nitrate-N and benomyl fungicide may be more prone to leaching or runoff from orchard soils under some herbicide GMSs in comparison with mowed sodgrass or biomass mulch systems.

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Brian E. Jackson, Robert D. Wright and Mark M. Alley

The objective of this study was to compare substrate solution nitrogen (N) availability, N immobilization, and nutrient leaching in a pine tree substrate (PTS), peat-lite (PL), and aged pine bark (PB) over time under greenhouse conditions. Pine tree substrate was produced from loblolly pine logs (Pinus taeda L.) that were chipped and hammer-milled to a desired particle size. Substrates used in this study were PTS ground through a 2.38-mm hammer mill screen, PL, and aged PB. A short-term (28-d) N immobilization study was conducted on substrates fertilized with 150 or 300 mg·L−1 NO3-N. Substrates were incubated for 4 days after fertilizing and NO3-N levels were determined initially and at the end of the incubation. A second medium-term study (10-week) was also conducted to evaluate the amount of N immobilized in each substrate when fertilized with 100, 200, 300, or 400 mg·L−1 N. In addition to determining the amounts of N immobilized, substrate carbon dioxide (CO2) efflux (μmol CO2/m−2·s−1) was also measured as an assessment of microbial activity, which can be an indication of N immobilization. A leaching study on all three substrates was also conducted to determine the amount of nitrate nitrogen (NO3-N), phosphorus, and potassium leached over 14 weeks under greenhouse conditions. Nitrogen immobilization was highest in PTS followed by PB and PL in both the short- and medium-term studies. Nitrogen immobilization increased as fertilizer rate increased from 100 mg·L−1 N to 200 mg·L−1 N in PL and from 100 mg·L−1 N to 300 mg·L−1 N for PB and PTS followed by a reduction or no further increase in immobilization when fertilizer rates increased beyond these levels. Nitrogen immobilization was generally highest in all substrates 2 weeks after potting, after which immobilization tended to decrease over the course of several weeks with less of a decrease for PTS compared with PL and PB. Substrate CO2 efflux levels were highest in PTS followed by PB and PL at each measurement in both the short- and medium-term studies. Patterns of substrate CO2 efflux levels (estimate of microbial populations/activity) at both fertilizer rates and over time were positively correlated to N immobilization occurrence during the studies. Nitrate leaching over 14 weeks was lower in PTS than in PB or PL through 14 weeks. This work provides evidence of increased microbial activity and N immobilization in PTS compared with PB and PL. Increased N immobilization in PTS explains the lower nutrient (primarily N) levels observed in PTS during crop production and justifies the additional fertilizer required for comparable plant growth to PL and PB. This work also provides evidence of less NO3-N leaching in PTS compared with PL or PB during greenhouse crop production despite the higher fertilizer rates required for optimal plant growth in PTS.

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Winter-Killed Cover Crops Influence Nitrate Leaching Although cereal grain cover crops can reduce nitrate leaching, few vegetable production fields are planted to winter cover crops in the coastal valleys of California. Most growers leave their

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P. Chris Wilson and Joseph P. Albano

coating and degradation of an exterior coating or nitrate-embedded polymer. Nitrate leaching from either formulation type from containers is enhanced by the low anion-holding capacity of most media used for plant production ( Handreck and Black, 2002

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Eric Simonne, Chad Hutchinson, Jim DeValerio, Robert Hochmuth, Danielle Treadwell, Allan Wright, Bielinski Santos, Alicia Whidden, Gene McAvoy, Xin Zhao, Teresa Olczyk, Aparna Gazula and Monica Ozores-Hampton

Allaire-Leung, S.E. Wu, L. Mitchell, J.P. Sanden, B.L. 2001 Nitrate leaching and soil nitrate content as affected by irrigation uniformity in a carrot field Agr. Water Mgt. 48 37 50 Aparicio, V. Costa, J.L. Zamora, M. 2008 Nitrate leaching assessment in a

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Nikolaos Ntoulas, Panayiotis A. Nektarios, Thomais-Evelina Kapsali, Maria-Pinelopi Kaltsidi, Liebao Han and Shuxia Yin

volume was determined simultaneously for all three lysimeters along with their temperature. Nitrate leaching To simulate a “first flush” event, leaching studies were performed on the final inorganic mixture. The latter was combined with four different

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T.K. Hartz and R.F. Smith

reduces nitrogen fertilizer use and nitrate leaching hazard in lettuce production HortScience 37 1061 1064 Hanson, B.R. 1995 Practical potential irrigation efficiencies Proc. 1st Intl. Conf., Water Resources Eng. Div., Amer. Soc. Civil Eng San Antonio, TX

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Kelly T. Morgan, Kent E. Cushman and Shinjiro Sato

. 35 1 12 Shoji, S. Kanno, H. 1994 Use of polyolefin coated fertilizers for increase fertilizer efficiency and reducing nitrate leaching and nitrous oxide emissions Fert. Res. 39 147 152 Shoji, S. Delgado, J. Mosier, A. Miura, Y. 2001 Use of controlled

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Dale A. Devitt, Lena Wright, Daniel C. Bowman, Robert L. Morris and Michelle Lockett

Bowman, D.C. Devitt, D.A. Engelke, M.C. Rufty, T.W. Jr 1998 Root architecture affects nitrate leaching from bentgrass turf Crop Sci. 38 1633 1639 Bowman, D.C. Devitt, D.A. Miller