Please cite this article in press as: Mailapalli, D.R., et al., Effects of field length and management practices on dissolved organic carbon export in furrow irrigation. Agric. Water Manage. (2010), doi:10.1016/j.agwat.2010.07.009 ARTICLE IN PRESS G Model AGWAT-3084; No. of Pages 9 Agricultural Water Management xxx (2010) xxx–xxx Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Effects of field length and management practices on dissolved organic carbon export in furrow irrigation Damodhara R. Mailapalli a , Wesley W. Wallender a,b,∗ , Martin Burger a , William R. Horwath a a Department of Land Air and Water Resources, University of California, Davis, CA 95616, USA b Department of Biological and Agricultural Engineering, University of California, Davis, CA 95616, USA article info Article history: Received 23 January 2010 Received in revised form 8 July 2010 Accepted 16 July 2010 Available online xxx Keywords: Furrow irrigation Dissolved organic carbon No till Field length Cover crop Volume balance abstract Farming practices, including tillage, cover cropping and residue management can have profound effects on the efficiency of irrigation practices. The effects of three field management practices (FMPs) standard tillage and winter-fallow (ST), standard tillage and winter-cover crop (STCC), and no-till and winter-fallow (NT) and two field lengths (122 and 366 m) on runoff and export of dissolved organic carbon (DOC) were investigated in a furrow-irrigated cropping system over two years. The residue cover was 40, 32 and 11% in 2007, and 58, 61 and 11% in 2008 for STCC, NT and ST, respectively. Furrow irrigation experiments were conducted prior to crop planting following the cover crop. The inflow was kept constant across all treatments, and infiltration and runoff were estimated using a volume balance model (VBM). The DOC concentration tended to increase with increasing field length, but did not differ among the FMPs. A threefold increase in field length increased infiltration by 40%, and decreased runoff by 60–90% and DOC export by 65–83%. In both years, infiltration was highest in STCC. In NT, infiltration was lowest in 2007, which was likely due to soil sealing, and intermediate among the three FMPs in 2008 perhaps due to the increase in residue cover in the second year. The DOC budget analysis showed that fields and FMPs acted as DOC sinks exporting less DOC than was applied in the irrigation water. The results suggest that longer furrows and STCC were greater DOC sinks compared to ST and shorter field practices. The VBM, as applied in this study to estimate infiltration and runoff, could be used to predict optimal field length to minimize runoff and promote DOC adsorption to soil within the constraints of water quality and availability and soil conditions. Published by Elsevier B.V. 1. Introduction In the arid western US, dissolved organic carbon (DOC) export from irrigation runoff is receiving increasing scrutiny. Furrow irri- gation systems are common in the region and are known to have low water application efficiency and high rates of water outflow that can affect the quality of surface water supplies. The export of DOC in runoff return water can potentially impact drinking water quality by degrading taste, smell and color of water. A more serious concern involving DOC is its reaction with chlorine during drink- ing water treatment, producing disinfection byproducts that are potentially carcinogenic and a major health concern (Volk et al., 2002). Mitigation of DOC in agricultural runoff, which can nega- tively affect the quality of drinking water has been recognized as an important part of agronomic management (Ruark et al., 2009). ∗ Corresponding author at: Department of Land Air and Water Resources (Hydrol- ogy), University of California, 221 Veihmeyer Hall, One Shields Avenue, Davis, CA 95616-8628, USA. Tel.: +1 5307520688; fax: +1 5307525262. E-mail address: wwwallender@ucdavis.edu (W.W. Wallender). Hence, understanding of the field scale contribution of DOC from furrow-irrigated fields is necessary to adopt suitable management practices for DOC control. Management practices such as conservation tillage (CT), no till (NT) and the use of winter-cover crops can reduce runoff and increase infiltration and soil water holding capacity (Blevins and Frye, 1993; Gulick et al., 1994; Folorunso et al., 1992; Gilley, 1995; Potter et al., 1995; Colla et al., 2000; Joyce et al., 2002; Horwath et al., 2006; Mitchell et al., 2007). The CT and NT sys- tems have been reported to conserve soil moisture, replenish soil organic matter and improve irrigation uniformity and crop yields (Triplett et al., 1996; Reeves, 1997; Nyakatawa et al., 2001; Reddy et al., 2004). Cover crops increase water permeability by reducing surface strength and sealing, improving macroaggregate stability, and increasing macroporosity and saturated hydraulic conductivity. Cover crop roots improve soil structure by impart- ing structure through binding and organizing soil particles into aggregates (Tisdall and Oades, 1982). In addition, roots and their exudates provide substrates for microbial activity to enhance aggregation and increase soil aggregate stability (Wuest, 2007). In contrast, tillage operations tend to disrupt surface-vented pores 0378-3774/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.agwat.2010.07.009