Soil carbon, nitrogen, pH, and earthworm density as influenced by cropping practices in the Inland Pacific Northwest Karl J. Umiker *, Jodi L. Johnson-Maynard, Timothy D. Hatten, Sanford D. Eigenbrode, Nilsa A. Bosque-Pe ´ rez University of Idaho, Department of Plant, Soil and Entomological Sciences, P.O. Box 442339, Moscow, ID 83844-2339, USA 1. Introduction ThePalouseregionofnorthernIdahoandeasternWashington,USA is characterized by deep, silt loam-textured soils that are formed in loessandarewellsuitedforcerealandlegumeproduction.ThePalouse region is approximately 800,000 ha in size and is one of the most productive wheat(TriticumaestivumL.)growingregionsintheUnited States (Hall et al., 1999); however, with slopes of up to 30% or more, tillage-related erosion threatens the region’s productivity (Busacca etal.,1985,1993;Mulla,1986).Directseed(DS)management,atoolin many conservation tillage (ConsT) systems, limits soil erosion by reducingsoildisturbance andconserving surface residue (Veseth and Karow,1999).AdoptionofConsTpracticesinpreviouslyplowedfields has been shown to increase soil carbon levels with an average rate of 570 kg C ha 1 year 1 (West and Post, 2002). Results of some studies, however, show that ConsT practices promote greater carbon levels at thesoilsurfacebutdepletecarbonwithdepth(Etanaetal.,1999;Yang and Wander, 1999; Baker et al., 2007; Ga ´l et al., 2007) potentially resulting in no net change in soil carbon storage compared to conventionally tilled systems. In addition to influencing soil organic carbon (SOC), reduced tillage has also been shown to stratify pH (LimousinandTessier,2007)andalterothersoilproperties(Grantand Lanfond, 1993; Franzluebbers et al., 1995) that may ultimately influence plant productivity and therefore, SOC levels. Direct seed management directly influences soil properties through lack of disturbance, but also has indirect effects that arise from its influence on soil organisms such as earthworms. Although earthworms are considered to be biological indicators of soil quality (Doran and Zeiss, 2000), little information is available concerning tillage- or crop-related effects on earthworm populations within the Palouse region. The surveys of Fender (1985) and James (2000) covered portions of the Palouse region but focused on non- agricultural lands. Fauci and Bezdicek (2002) surveyed agricultural fields on the Palouse, and found four exotic earthworm species with Aporrectodea trapezoides being the most common, but earthworm density and soil properties were not measured. In a replicated research station plot experiment, the density of earthworms was significantly greater under no-till (NT) (150 individuals m 2 ) vs. conventional tillage (CT) (38 individuals m 2 )(Johnson-Maynard Soil & Tillage Research 105 (2009) 184–191 ARTICLE INFO Article history: Received 21 November 2008 Received in revised form 18 August 2009 Accepted 1 September 2009 Keywords: Tillage Conservation tillage Carbon Nitrogen pH Earthworms ABSTRACT Farmers within the Inland Pacific Northwest are gradually transitioning to direct seed (DS) practices that reduce soil disturbance and increase surface residue compared to conventional tillage (CT). Despite this transition the impacts of DS practices on soil properties and fauna in commercial fields has been little studied in the region. During the spring and summer of 2002 and 2003 we compared soil organic carbon (SOC), total nitrogen (TN), pH, and earthworm and cocoon densities in CT and DS fields planted to either spring wheat or pea in the Palouse region of northern Idaho. In 2002 mean SOC within the 0–10-cm depth was greater in DS fields (2.05%) than at the same depth in CT fields (1.79%), however SOC within the 30–40-cm depth was lower under DS compared to CT. Mean soil pH within the 0–10-cm depth was 5.35 under DS and 5.61 under CT indicating that pH stratification can occur when tillage is reduced. Tillage effects on SOC, TN, and pH were not found in 2003. Tillage also did not significantly influence earthworm densities, which averaged 39 individuals m 2 in 2002 and 57 individuals m 2 in 2003. Correlations were detected in 2003 DS fields between soil properties (SOC and TN) and earthworm and cocoon densities at depths above 30 cm while in 2002 correlations in DS fields occurred with cocoon density, but not with earthworm density. Direct seed management can increase near-surface SOC and TN concentrations compared to CT practices, however, SOC concentrations deeper in the soil appear to remain the same or possibly decrease. Higher SOC and TN near the soil surface, as found in DS fields, appear to promote greater earthworm densities, which may improve long-term soil productivity. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author at: University of Idaho, Ag. Sci. Bldg. Rm 242, Moscow, ID 83844-2339, USA. Tel.: +1 208 885 7505; fax: +1 208 885 7760. E-mail address: kumiker@uidaho.edu (K.J. Umiker). Contents lists available at ScienceDirect Soil & Tillage Research journal homepage: www.elsevier.com/locate/still 0167-1987/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2009.09.001