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A reliable laboratory index of N availability would be useful for making N recommendations, but no single approach has received broad acceptance across a wide range of soils. We compared several indices over a range of soil conditions to test the possibility of combining indices for predicting potentially mineralizable N ([N.sub.0]). Soils (0-5 and 5-15 cm) from nine tillage studies across the southern USA were used in the evaluations. Long-term incubation data were fit to a first-order exponential equation to determine [N.sub.0], k (mineralization rate), and [N.sub.0.sup.*] ([N.sub.0] estimated with a fixed k equal to 0.054 [wk.sup.-1]). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KC1 (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to NO (r > 0.85) and had linear regressions with [r.sup.2] > 0.60. None of the indices were good predictors of k. Correlations between indices and [N.sub.0.sup.*] improved compared with [N.sub.0], ranging from r = 0.90 to 0.95. Total N and flush of C[O.sub.2] determined after 3 d (Fl_C[O.sub.2]) produced the best multiple regression for predicting [N.sub.0] ([R.sup.2] = 0.85) while the best combination for predicting [N.sub.0.sup.*] ([R.sup.2] = 0.94) included TN, Fl_CO2 Cold_N, and NaOH_N. Combining indices appears promising for predicting potentially mineralizable N, and because TN and Fl_CO2 are rapid and simple, this approach could be easily adopted by soil testing laboratories. Abbreviations: Ana_N, anaerobic N mineralization; TC, total carbon; Ca_hypcl, calcium hypochlorite; Cold_N, KCl extractable N[O.sub.3]--N; CT, conventional tillage; Fl_CO2, flush of C[O.sub.2] during 3 d; Hot_N, hot KCl extractable N[H.sub.4]- -N; Hyd_N, hydrolyzable N; k, mineralization rate constant; TN, total nitrogen; NaOH_N, sodium hydroxide distillable N; [N.sub.0], potentially mineralizable N; [N.sub.0.sup.*], value of [N.sub.0] determined using a fixed value for k, Nmin_24, N mineralization during 24 d; NP, not plowed (prairie soil); NT, no-Tillage; NT+SS, no-tillage with non-inversion subsurface deep tillage; PB_N, phosphate- berate distillable N; POMC, particulate organic matter C; POMN, particulate organic matter N; SM, stubble mulch tillage (sweeps to undercut weeds); ST, strip tillage (in-row subsoil for disruption of subsurface pan and coulters for preparation of narrow strip of tilled soil).

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2009.02.003 Byline: Michael B. Jenkins (a), Dinku M. Endale (a), Harry H. Schomberg (a), Peter G. Hartel (b), Miguel L. Cabrera (b) Abbreviations: NT, no-till; CT, conventional-till; PL, poultry litter; CF, conventional fertilizer Abstract: Thirteen metric tons of poultry litter are produced annually by poultry producers in the U.S. Poultry litter contains the sex hormones estradiol and testosterone, endocrine disruptors that have been detected in surface waters. The objective of this study was to evaluate the potential impact of poultry litter applications on estradiol and testosterone concentrations in subsurface drainage and surface runoff in irrigated crop land under no-till and conventional-till management. We conducted an irrigation study in fall of 2001 and spring of 2002. Four treatments, no-till plus poultry litter, conventional-till plus poultry litter, no-till plus conventional fertilizer, and conventional-till plus conventional fertilizer, were evaluated. Flow-weighted concentration and load ha.sup.-1 of the two hormones were measured in drainage and runoff. Soil concentrations of estradiol and testosterone were measured. Based on comparisons to the conventional fertilizer (and control) treatments, poultry litter did not add to the flow-weighted concentration or load ha.sup.-1 of either estradiol or testosterone in subsurface drainage or surface runoff. Significant differences were, however, observed between tillage treatments: flow-weighted concentrations of estradiol were greater for no-till than conventional-till plots of the June irrigation; and runoff loads of both estradiol and testosterone were less from no-till than conventional-till plots for the November irrigation. Although the differences between no-till and conventional-tillage appeared to affect the hydrologic transport of both hormones, the differences appeared to have inconsequential environmental impact. Author Affiliation: (a) Southern Piedmont Conservation Research Unit, USDA-ARS, J. Phil Campbell, Sr., Natural Resource Conservation Center, 1420 Experiment Station Road, Watkinsville, GA 30677, USA (b) University of Georgia, Athens, GA 30605, USA Article History: Received 19 June 2008; Revised 8 January 2009; Accepted 8 February 2009

Poultry litter (PL) can supply N, P, K, and other plant nutrients; however, excessive application may cause environmental problems, depending on management and crop nutrient demand. Changes in soil test (ST) nutrient content in a Cecil soil (a fine, kaolinitic, thermic Typic Kanhapludult) during a 10-yr period of PL use was evaluated at the USDA-ARS J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA. During the cotton (Gossypium hirsutum L.) cropping phase (1995-2000), 4.4 Mg PL [ha.sup.-1] [yr.sup.-1] resulted in small changes in ST nutrient content in the surface 15 cm. Differences were observed between tillage treatments, with less accumulation of Ca, Mg, and Mn and greater accumulation of Zn for no-till (NT) than conventional tillage (CT). During the corn (Zea mays L.) cropping phase (2001-2005), average annual PL inputs (11.2 Mg [ha.sup.-1]) increased P and Zn contents, with changes being similar for CT and NT. After 10 yr, ST nutrient contents in the surface 15 cm reflected 25, 4, 45, 26, 17, and 97% of the input from PL for P, K, Ca, Mg, Mn, and Zn, respectively. Changes in soil profile nutrient content (to a depth of 60 cm) from 1997 to 2005 were predominantly at 0 to 15 cm, where P and Zn increased >200%. Accumulation of Ca, K, P, and Zn at lower depths was also observed. Strategies for increasing nutrient removal following repeated long-term application of PL should be considered to avoid excessive levels of nutrients. Abbreviations: CE conventional fertilizer; CT, conventional tillage; FS, fertilizer source; NT, no-till; PL, poultry litter; ST, soil test.

Soil C and N greatly influence long-term sustainability of agricultural systems. We hypothesized that cropping and tillage differentially influence dryland soil C and N characteristics in the Southern High Plains. A Pullman clay loam (fine, mixed, thermic Torrertic Paleustol) cropped to wheat (Triticum aestivum L.)--sorghum [Sorghum bicolor (L.) Moench]--fallow (WSF), continuous wheat (CW) and continuous sorghum (CS) under no-tillage (NT), and stubble mulch (SM) was sampled at three depths to determine soil C and N characteristics. For CW, CS, and WSF phases ([F.sub.WSF], [S.sub.WSF], [W.sub.WSF]), soil organic C (SOC) averaged 10.6 to 13.1 kg [m.sup.-3] and was greatest for CW. Carbon mineralization ([C.sub.MIN]) at 0 to 20 mm was 30 to 40% greater for CW and [F.sub.WSF] than for CS, [S.sub.WSF], or [W.sub.WSF]. Cropping system by depth influenced soil organic N (SON) with greatest SON at 0 to 20 mm in CW (1.5 kg [m.sup.-3]). At 0 to 20 mm for SM and NT, SOC was 9.9 and 12.5 kg [m.sup.-3], soil microbial biomass C (SMBC) was 0.80 and 1.1 kg [m.sup.-3], and soil microbial biomass N (SMBN) was 0.14 and 0.11 kg [m.sup.-3]. Also at 0 to 20 mm, NT had 60% greater [C.sub.MIN], 11% more SMBC as a portion SOC, and 25% more SON compared to SM. Summed for 0 to 80 mm, NT had more SOC (0.98 vs 0.85 kg [m.sup.-2]) and SON (0.10 vs 0.9 kg [m.sup.-2]) than SM, and CW had greater or equal C and N activity as other systems. Negative correlations between yield and SOC, SMBC, [C.sub.MIN], SON, and SMBN indicate N removal in grain negatively affects active and labile C and N pools. Under dryland conditions, C and N conservation is greater with NT and with winter wheat because of less soil disturbance and shorter fallow.