There is a need to assess changes in soil quality resulting from introduction of conservation practices. This study tested for an effect of tillage practice and crop rotation on activity of six soil enzymes (dehydrogenase, urease, glutaminase, phosphatase, arylsulfatase, and β‐glucosidase). Samples of the Ap horizon were collected from adjacent no‐till and tilled fields. At one site, fields were located on a simple, single slope averaging 4%, and differed in previous cropping history. The second site included coarse‐ and fine‐textured soils at lower and upper slope positions, respectively. Enzyme activities of field‐moist samples were measured during two growing seasons, and maximum reaction velocity (Vmax) values were estimated for three enzymes on a subset of air‐dry samples. At the first site, implementation of no‐till and previous cropping to forages increased activity of all enzymes. At the second site, there was no consistent response of enzyme activities to tillage practice in the coarse‐textured soils, which had relatively large total C content. In the fine‐textured soil, activity of phosphatase and arylsulfatase, and dehydrogenase in the surface (0–8 cm) layer, was greater in the no‐till field. At this location, these enzyme activities were more sensitive than total C (TC) concentration to tillage practice. Slope position and time and depth of sampling influenced enzyme activities and affected management comparisons.

This study measured the spatial dependence of soil enzyme activities and other properties of the Ap horizon in a Gray Brown Luvisol (Hapludalf). Soil samples were collected at 74 positions along a slope following harvest of soybean [Glycine max (L.) Merr.] and fall tillage. Parameters measured were activity of dehydrogenase, urease, glutaminase, phosphatase, arylsulfatase, and β‐glucosidase; water, organic carbon (OC), mineral N, and inorganic P contents; the light fraction of soil organic matter; and depth of the Ap horizon. Rank correlation indicated significant relationships between water and dehydrogenase, urease, glutaminase, phosphatase, and arylsulfatase activities, and between water and OC content. Depth of the Ap horizon, water content, and arylsulfatase activity were strongly spatially dependent; OC and inorganic P contents and phosphatase activity were moderately spatially dependent. Other properties showed little or no spatial dependence. The ranges of spatial dependence were similar for depth of the Ap horizon, inorganic P content, and phosphatase activity (≈20 m). The range for arylsulfatase activity was 16 m, while that of OC content was 32 m. The relatively long range estimate for water content (98 m) was influenced by a trend along the slope. Maps of water and OC contents and phosphatase and arylsulfatase activities indicated similar spatial patterns along the slope. The magnitude of these soil properties was minimal in the middle or upper portion of the slope, and maximal at the footslope. Similarity in spatial patterns along the slope was interpreted as evidence for influence of water or OC content on amounts of phosphatase and arylsulfatase at that scale.

Denitrification and nitrous oxide production rates were determined in a field/laboratory study following application of N fertilizer (255 kg N ha−1 as NH4NO3) and liquid (450 kg N ha−1) and solid (600 kg N ha−1) cattle manures. We measured the three proximal regulators, O2 supply (water content, air‐filled porosity), NO−3 concentration and C supply (CO2 production, extractable‐C content) along with denitrifying enzyme activity (DEA) and NH+3 concentration, using a soil core technique. Part 1 of the study involved measurements with soil cores collected from the 10‐, 20‐, and 40‐cm depths following N‐fertilizer and manure applications in the fall 1991 and spring 1992. At the 40‐cm depth, denitrification rates and DEA were very low, indicating that little soluble C was leached from the manured soil. Air‐filled porosity, CO2 production and NH+3 concentration were most closely related to denitrification rates at the 10‐ and 20‐cm depths with the manure treatments. Denitrification rate with different manures depended on time (season) of application and was influenced by soil water content. Solid manure promoted denitrification for a longer period than liquid manure. In Part 2 of the study, denitrification and nitrous oxide production rates in the tilled (0–15 cm) layer were measured over a 49‐d period. Both were most closely related to soil water content, but neither was related to NO−3 content. Peak rates of denitrification and N2O production occurred early in the sampling period with liquid manure but later with solid manure. Cumulative production of N gases was greater with solid than liquid manure, which, in turn, produced more N gases than with the fertilizer or control treatments.