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Innovative management practices are required to increase the efficiency of N fertilizer usage and to reduce nitrous oxide ([N.sub.2]O) and carbon dioxide (C[O.sub.2]) emissions from agricultural soils. The objectives of this study were to evaluate the feasibility of using conservation tillage and N fertilizer placement depth to reduce [N.sub.2]O and C[O.sub.2] emissions associated with corn (Zea mays L.) production on clay loam soils in Eastern Canada. A 3-yr field study was established on a wheat (Triticum aestivum L.)-corn--soybean [Glycine max (L.) Merr.] rotation with each phase of the rotation present every year. Investigations were focused on the corn phase of the rotation. The tillage treatments following winter wheat included fall moldboard plow tillage (15 cm depth), fall zone-tillage (21 cm width, 15 cm depth), and no-tillage. The N placement treatments were 'shallow' placement of sidedress N (2-cm depth) and 'deep' placement of sidedress N (10-cm depth). Nitrous oxide emissions were measured 53 times and C[O.sub.2] emissions were measured 43 times over three growing seasons using field-based sampling chambers. There was a significant tillage and N placement interaction on [N.sub.2]O emissions. Averaged over all three tillage systems and site-years, [N.sub.2]O emissions from shallow N placement (2.83 kg N [ha.sup.-1] [yr.sup.-1]) were 26% lower than deep N placement (3.83 kg N [ha.sup.-1] [yr.sup.-1]). The [N.sub.2]O emissions were similar among the tillage treatments when N was placed in the soil at a shallow depth. However, when N was placed deeper in the soil (10 cm), the 3-yr average [N.sub.2]O emissions from zone-tillage (2.98 kg N [ha.sup.-1] [yr.sup.-1]) were 20% lower than from no-tillage (3.71 kg N [ha.sup.-1] [yr.sup.-1]) and 38% lower than those from moldboard plow tillage (4.81 kg N [ha.sup.-1] [yr.sup.-1]). Tillage type and N placement depth did not affect C[O.sub.2] emissions (overall average = 5.80 Mg C [ha.sup.-] [yr.sup.-1]). Hence, zone-tillage and shallow N placement depth reduced [N.sub.2]O emissions without affecting C[O.sub.2] emissions.

Despite extensive research, reduced corn (Zea mays L.) performance is still encountered using conservation tillage on fine-textured soils in cool humid temperate climates. These problems are intensified when corn is planted into residue from a previous crop such as winter wheat (Triticum aestivum L.). The objective of this 4-yr study was to determine the influence of fall zone tillage (ZT), no tillage (NT), and conventional moldboard plow tillage (CT) (fall plowing) on corn performance and soil physical quality under a winter wheats-corn-soybean (Glycine max L. Merr.) rotation with and without red clover (Trifolium pratense L.) (RC) underseeded in the wheat phase of the rotation. A randomized complete block design (3 x 2 factorial, 4 replicates) was established on three adjacent fields in the fall of 1996 on a Brookston clay loam soil (fine loamy, mixed, mesic, Typic Argiaquoll) at Woodslee, ON Canada, and measurements were collected during 1997 to 2000. Over both wet and dry growing seasons from 1998-2000, zone tillage following underseeded RC produced average corn grain yields (7.23 Mg [ha.sup.-1]) that were within 1% of those obtained using conventional tillage (7.33 Mg [ha.sup.-1]), and 36% higher than those obtained using no tillage and RC (5.33 Mg [ha.sup.-1]). Zone tillage also improved soil quality as evidenced by generally lower soil strength than no tillage, and near--surface soil physical quality parameters that were equivalent to, or more favorable than, those of the other treatments. It was concluded that corn production using zone tillage and RC underseeding is a viable option in Brookston clay loam soil, as it retains much of the soil quality benefit of conventional tillage but still achieves most of the yield benefit of conventional moldboard plow tillage.

Infiltration, drainage, and chemical leaching are strongly influenced by the magnitude and spatial distribution of the field-saturated soil hydraulic conductivity ([K.sub.fs]). The Guelph permeameter (GP) method shows promise as an effective means for field measurement of [K.sub.fs] and its spatial distribution, but its accuracy in medium- and fine-textured soils is not well established. To further assess its accuracy and effectiveness, the GP method was compared with the auger hole (AH) method at the 0.5-m depth at 68 grid locations in a texturally uniform silty clay soil that had stable but spatially variable structure. The two methods yielded similar geometric mean [K.sub.fs] values (P < 0.001), as well as similar semivariograms. The two methods were also positively correlated (r = + 0.6565, P < 0.0001). We therefore concluded that the two methods gave equivalent estimates of [K.sub.fs] at this field site, and that the GP method is capable of providing valid estimates of [K.sub.fs] in at least some fine-textured soils. The [K.sub.fs] values were not correlated with soil texture, organic C content, or soil surface topography, but were negatively correlated (r = - 0.7240 for GP method, r = -0.6070 for AH method, P < 0.0001) with antecedent volumetric water content ([[Theta].sub.a]) measured in situ prior to the GP measurements using a down-hole time domain reflectometry probe. The semivariogram for [[Theta].sub.a] was similar to those for [K.sub.fs]. These results suggest that the magnitude, range, and pattern of variability of the [K.sub.fs] measurements were controlled primarily by the well-developed and stable soil structure at the field site, rather than by texture, organic C content, or surface topography.

The constant head wellpermeameter is an instrument used for measuring hydraulic properties of soil inthe vadose zone. The steady state flow rate of the permeameter is a function offield saturated hydraulic conductivity, K (sub fs) and the matric flux potential (phi sub m) as posited in Glovers Solution. However, the Richards Solution or Simultaneous Equations approach provides a more adequate evaluationof permeameter data if two single-height analyses can be performed together with the simultaneous equations analyses. Sample calculations are presented.