Gerald R. Haszler

The effects of organic matter and tillage on maximum compactability of soils using the Proctor test

With the practice of continuous no-tillage, the question arises of whether, after a period of time, some sort of mechanical tillage will be required to alleviate compaction. Studies of maximum compaction using the Proctor test on a total of 36 samples from four Kentucky soils revealed that compactab

Nitrogen Fertilization Suppresses Soil Phenol Oxidase Enzyme Activity In No-tillage Systems

Phenol oxidase is associated with the carbon cycle and its presence in soil environments is important to the formation of humic substances. Little effort has been made to integrate the response of phenol oxidases with soil management. We investigated phenol oxidase activity on a Maury silt loam (fine, mixed, mesic Typic Paleudalfs) soil after 33 years of imposed tillage and N fertilization treatments. Particle size fractions were investigated independently to help identify the location of the enzyme. Phenol oxidase activity was 1.7 times greater (P < 0.01) in no-tillage (NT) compared with moldboard plow (MP) in the control treatment (0 kg N ha−1), consistent with the known effects of tillage. The phenol oxidase was located primarily in the silt fraction, followed by the clay and sand in the NT. In NT, N fertilization (336 kg N ha−1) had a marked negative effect on soil phenol oxidase activity, showing a 38% decrease (P < 0.01) despite the increase in soil organic carbon (SOC). In contrast, MP plots were relatively insensitive to applied N rate. Phenol oxidase activity was related negatively to dissolved inorganic nitrogen (DIN) (r = −0.49, P < 0.1), SOC (r = −0.49, P < 0.1) and dissolved organic carbon (r = −0.51, P < 0.1) in NT. This research provides new information about the response of phenol oxidase enzymes to long-term N fertilization in NT and MP systems. These findings suggest that manipulating the application rates of fertilizer N in soils under NT will make it possible to impact phenol oxidase activity.

Solute and Bacterial Transport through Partially-Saturated Intact Soil Blocks

Steady-state transport of water, chloride and bacteria was measured through intact blocks of Maury and Cecil soils, under partially saturated conditions. Major objectives were to determine if transport occurs uniformly or via preferential flow paths, and if soil physical properties could be used to predict breakthrough. The blocks were instrumented with TDR probes and mounted on a vacuum chamber containing 100 cells that collected eflluent. After each experiment the blocks were sampled for soil physical properties. The fluxes showed no spatial autocorrelation and the eflluent variance was not statistically different between soils. Less than 3% of the influent bacteria appeared in the effluent. Maximum bacterial breakthrough occurred after 0.25 water-filled pore volumes had been leached, and was greater for Cecil soil than for Maury soil. The chloride breakthrough curves were fitted to the convection dispersion equation. The best predictor of dispersivity was volumetric water content (R 2 = 0.28, P<0.01 ), with dispersivity increasing with decreasing water content. Lower water contents lead to more tortuous flow paths and thus, a broadening of the velocity distribution. Soil structural controls on solute dispersion under partially saturated conditions are likely to be indirect, and related to differences in water content at given flux produced by differences in pore-size distribution. Focus Categories: ST, NPP, AG