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No-tillage (NT), a practice that has been shown to increase carbon sequestration in soils, has resulted in contradictory effects on nitrous oxide (N 2 O) emissions. Moreover, it is not clear how mitigation practices for N 2 O emission reduction, such as applying nitrogen (N) fertilizer according to soil N reserves and matching the time of application to crop uptake, interact with NT practices. N 2 O fluxes from two management systems [conventional (CP), and best management practices: NT 1reduced fertilizer (BMP)] applied to a corn (Zea mays L.), soybean (Glycine max L.), winter-wheat (Triticum aestivum L.) rotation in Ontario, Canada, were measured from January 2000 to April 2005, using a micrometeorological method. The superimposition of interannual variability of weather and management resulted in mean monthly N 2 O fluxes ranging from À1.9 to 61.3 g N ha À1 day À1 . Mean annual N 2 O emissions over the 5-year period decreased significantly by 0.79 from 2.19 kg N ha À1 for CP to 1.41 kg N ha À1 for BMP. Growing season (May-October) N 2 O emissions were reduced on average by 0.16 kg N ha À1 (20% of total reduction), and this decrease only occurred in the corn year of the rotation. Nongrowing season (November-April) emissions, comprised between 30% and 90% of the annual emissions, mostly due to increased N 2 O fluxes during soil thawing. These emissions were well correlated (r 2 5 0.90) to the accumulated degree-hours below 0 1C at 5 cm depth, a measure of duration and intensity of soil freezing. Soil management in BMP (NT) significantly reduced N 2 O emissions during thaw (80% of total reduction) by reducing soil freezing due to the insulating effects of the larger snow cover plus corn and wheat residue during winter. In conclusion, significant reductions in net greenhouse gas emissions can be obtained when NT is combined with a strategy that matches N application rate and timing to crop needs.

Abstract:The spatial variability of soil water content can be measured with the ground wave velocity of ground-penetrating radar (GPR) using short antenna offsets, but picking the correct ground wave arrival time is rather difficult. In applying the GPR ground wave method to soil water content estimation it is also important to know the effective sampling depth of the method. Uniform drainage experiments were conducted with 100 and 450 MHz GPR antennas using 1Ð0 and 2Ð0 m fixed antenna separations on a sandy loam soil to investigate time zero picking methodologies and to estimate the sampling depth of the GPR method. The GPR water content data were compared with time-domain reflectometry (TDR)-measured data using six vertical TDR probes of different lengths. Time zero was calculated from an air calibration at a 2Ð0 m antenna separation and from wide-angle reflection and refraction data, and a difference was found between the two time-zero calibration methods. A method was analysed to determine the arrival time of the leading edge of the direct ground wavelet using the arrival time of the peak amplitude, since the arrival time of the leading edge of the ground wave can be difficult to pick. Regression analysis showed that the GPR (100 MHz) measured water content was not different from the water content measured with TDR at 0-0Ð1 m depth, implying that this may be a reasonable estimate of the GPR ground wave method's sampling depth. A similar analysis based on the differences between the 0-0Ð2 m TDR and the GPR shows that the effective sampling depth of the direct ground wave of the 450 MHz data is less than the sampling depth of the 100 MHz data.

We describe a simple method for the determination of heme protein reduction potentials. We use the method to determine the reduction potentials for the PAS-A domains of the regulatory heme proteins human NPAS2 (Em = −115 mV ± 2 mV, pH 7.0) and human CLOCK (Em = −111 mV ± 2 mV, pH 7.0). We suggest that the method can be easily and routinely applied to the determination of reduction potentials across the family of heme proteins.

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Best management practices are recommended for improving fertilizer and soil N uptake efficiency and reducing N losses to the environment. Few year-round studies quantifying the combined effect of several management practices on environmental N losses have been carried out. This study was designed to assess crop productivity, N uptake from fertilizer and soil sources, and N losses, and to relate these variables to the fate of fertilizer 15N in a corn (Zea mays L.)-soybean (Glycine max L.)-winter wheat (Triticum aestivum L.) rotation managed under Best Management (BM) compared with conventional practices (CONV). The study was conducted from Cumulative NO 3 leaching loss was reduced by 51% from 133 kg N ha À1 in CONV to 68 kg N ha À1 in BM. About 70% of leaching loss occurred in corn years with fertilizer N directly contributing 11-16% to leaching in CONV and <4% in BM. High soil derived N leaching loss in CONV, which occurred mostly (about 80%) during November to April was attributable to 45-69% higher residual soil derived mineral N left at harvest, and on-going N mineralization during the over-winter period. Fertilizer N uptake efficiency (FNUE) was higher in BM (61% of applied) than in CONV (35% of applied) over corn and wheat years. Unaccounted gaseous losses of fertilizer N were reduced from 27% of applied in CONV to 8% of applied in BM. Yields were similar between BM and CONV (for corn: 2000 and 2003, wheat: 2002, soybean: 2004 or higher in BM (soybean: 2001). Results indicated that the use of judicious N rates in synchrony with plant N demand combined with other BMP (no-tillage, legume cover crops) improved FNUE by corn and wheat, while reducing both fertilizer and soil N losses without sacrificing yields.