Guanglong Feng

Evaluating Aeration Criteria By Simultaneous Measurement Of Oxygen Diffusion Rate And Soil-water Regime

Adequate aeration is important for plant root growth. The purpose of this paper was to evaluate aeration criteria by examining the relationships between oxygen diffusion coefficient (ODR) and soil-water potential, soil-water content, air-filled porosity, and gas diffusion rate. In this study we used undisturbed columns and cores of four soils representing different textures (Delhi loamy sand, Arlington sandy loam, Sorrento clay loam, and Imperial silty clay). The ODR was measured under variable soil-water potential conditions. Other aeration parameters, such as oxygen diffusion coefficient (Dp) and air-filled porosity, were calculated based on soil-water content, bulk density, and particle density. Soilwater potential, soil-water content, air-filled porosity, and gas diffusion coefficient at the threshold ODR value of 0.2 μg cm−2 min−1 that provided satisfactory aeration status were evaluated in the four different soils. The threshold ODR value occurred at different soil matric potentials, volumetric water contents, air-filled porosities, and relative gas diffusion coefficients (Dp/Do) for the four test soils, depending on their texture and bulk density. The relationships between ODR and soil-water potential, soil-water content, air-filled porosity, and gas diffusion coefficient were found to be different for the four test soils. All of these results indicate that comparing air-filled porosity and diffusion coefficients at the field capacity for different soils offers little information about the soil aeration capability that influences plant growth directly. We concluded that ODR, a measure that mimics the oxygen supply to root surface, should be used instead for evaluating soil aeration capability.

Influence of long-term tillage and crop rotations on soil hydraulic properties in the US Pacific Northwest

In the low precipitation zone (<0.3 m [11.8 in] annual precipitation) of the Inland Pacific Northwest, no-tillage continuous spring cereal and no-tillage spring cereal-chemical fallow rotations are being examined as alternatives to the traditional winter wheat–summer fallow rotation for soil conservation. There is limited information, however, regarding the long-term effects of no-tillage cropping systems on soil hydraulic properties in this semiarid region. The objective of this study was therefore to characterize infiltration, water retention, saturated hydraulic conductivity and bulk density of a silt loam that had been subject to various tillage and crop rotations in east-central Washington. Treatments examined included no-tillage spring barley–spring wheat (NTSB–SW), no-tillage spring wheat–chemical fallow (NTSW–ChF), and traditional winter wheat–summer fallow (WW–SF). Soil properties were measured in spring and late summer 2006 due to the vulnerability of the soil to rapidly dry and erode during these seasons. Saturated hydraulic conductivity was determined by the falling-head method, infiltration was measured using a double-ring infiltrometer, and water retention characteristics was assessed by examining the temporal variation of in situ soil water content. NTSB–SW resulted in higher infiltration and saturated hydraulic conductivity, lower bulk density, and larger and/or more continuous pores in the upper soil profile (<0.1 m [<3.9 in] depth) than WW–SF and NTSW–ChF. Infiltration and saturated hydraulic conductivity were lower for chemical fallow than for traditional fallow in spring whereas hydraulic conductivity was lower for summer fallow than chemical fallow in late summer. Soil hydrologic properties appeared more favorable for no-tillage continuous spring cereal rotations. These results are useful for soil and water management and conservation planning in the low precipitation zone of the Inland Pacific Northwest.

A multiscale database of soil properties for regional environmental quality modeling in the western United States

The USDA Natural Resources Conservation Service State Soil Geographic (STATSGO) database contains general soils information, but data available in STATSGO cannot be readily extracted nor parameterized to support regional environmental quality modeling. As such, each user must individually and repeatedly process data in STATSGO to obtain necessary soil properties. The objective of this study was to develop a comprehensive database, the Western States Soil Database (WSSD) (http://www.lar.wsu.edu/nw-airquest/soils_database.html), for use in modeling regional soil and water resources and environmental quality across eight western states (Washington, Oregon, California, Idaho, Nevada, Utah, Montana, and Wyoming). We aggregated existing soil properties in STATSGO from 19,681 map units of the eight states and estimated soil properties based upon quantitative relationships among existing soil properties. The WSSD comprises 3,910 map units, with each map unit defined by 10 soil layers and each layer characterized by 31 soil properties. The WSSD was gridded to 1 and 12 km (0.62 and 7.44 mi) resolution cells for application to grid-based environmental models. Data from WSSD was tested against USDA Natural Resources Conservation Service field data and indicated satisfactory agreement; for example, the Root Mean Square Error (RMSE) for sand and clay content varied between 4% and 7%. The RMSE appeared to be greatest for organic matter and was as large as 106% of the measured value. The WSSD provides information on soil properties useful for regional-scale modeling.