Weathering soil depth

A continuous, dynamic, one-dlmenslonal model called the Pesticide Root Zone Model or PRZM, has been developed recently by EPA/ORD In Athens, Georgia (110). PRZM allows for varying hydrologic and chemical properties by soil horizon. Weather data for water flow modeling Is obtained from dally precipitation records of the National Weather Service. It has been successfully validated with atrazlne field data from Watklns-vllle, Georgia and aldlcarb data from Long Island, New York for depths less than 3 meters. 

Soils are loessial sandy loams in most areas, with some alluvial deposits. It is not uncommon to find hard calcarious layers at depths of ten to forty inches. These require fracturing before planting for both water and root penetration. In many places, the soil is underlaid with basalt. Many areas show basaltic outcroppings. Yet, because of the nature of the weather, these are not degraded sufficiently to produce volcanic soils in any significant amount. Soil depths vary from less than twenty inches in some vineyards to more than ten feet in others. 

Figure 7.13 Contributions of different minerals to the total weathering rate as a function of soil depth in four soil layers (horizons) at the Gardsjon site. Reprinted from Applied Geochemistry, 8, H. Sverdrup and R Warfvinge, Calculating field weathering rates with a mechanistic geochemical model PROFILE, 273-83, with permission from Elsevier Science Ltd.,...

The silica release rate and flow-rate mass ratio of Figure 18 depend on estimations of the wetted surface area of reacting minerals and the mass of wetted soil. As discussed by Paces (1983), there is much uncertainty in estimating wetted surface areas of reacting minerals. In Figure 18 and Table 3, it was assumed that 40% of the surface area of soil was weatherable minerals the soil surface area was 0.5 m2 g 1 (except at Coweeta, where Velbel s (1985) procedure was used), the bulk density of the soil was 1.5 kg L-1, and the equivalent saturated water depth was 0.5 m (except at Coweeta and Cristallina, where it was taken to be 0.1 m). All of these parameters were measured at Bear Brook Watershed and applied to the other sites. 

The soils on which western pine grows in the interior portion of the range are also diverse and predominantly Spodosols that have developed from weathered granite, schist, quartzite, argillite, sandstone, and shale. Soil depths range from 25 to over 230 cm. The upper soil layer is often composed of loess or loess-like material (Cooper et al., 1987). In British Columbia, soils have developed from base-rich glacial materials (till, fluvial, or lacustrine deposits) (Wellner, 1965). 

The mechanical rototilling method involves turning over soils to a depth of about 0.30 m (1 ft) below the surface to increase the rate of volatilization. Following treatment, the topsoil is moved to a nearby pile and rototilling is performed on the next 0.30 m (1 ft) of soil. The effectiveness of this mechanical rototilling method is highly dependent on weather conditions. High-speed rototillers and soil shredders can enhance the rate of volatilization. 

Performance data Two moisture monitoring systems were installed, one at Disposal Area A and one at Disposal Area AB plus in May and November 1999, respectively. Each monitoring system has two stacks of time domain reflectometry probes that measure soil moisture at 24-in. intervals to a maximum depth of 78 in., and a station for collecting weather data. Based on nearly 3 years of data, there is generally <5% change in the relative volumetric... 

Based on predicted weathering and erosion rates of the region, we estimate the profile to be several million years old. Because the soil has developed in situ, the topmost grains have reacted with water for the greatest extent of time. With depth, the total "lifetime" of the particles as soil decreases. This implies that the topmost quartz surfaces should be "reactively mature" (all fines removed, deep grown-together etch pits) and the bottom-most quartz surfaces should be "reactively young" (plentiful fines, fresh surfaces). ... 

This application was made between 0700 and 0830 a.m. in cool (air temp., 10 0 clear and windless weather. Both granular and emulsion formulations were incorporated to the 7.5cm depth with a disc cultivator within 15 minutes of application. A second cultivation to the same depth, but at right angles to the first, was completed within 2-3 hours. On May 20th both plots were spring-tooth harrowed for seed-bed preparation for soybean planting on the same day. The only subsequent soil disturbance was a row cultivation in late June to control a severe infestation of quack-grass control of broadleaf weeds was essentially complete with the trifluralin. 

The simulated weather changes that produced the variations in surface vapor flux rate shown in Figure 4.11 began with a soil sample with about 50% pore moisture saturation in a chamber under an artificial atmosphere. A quantity of DNT was introduced beneath the surface, at a depth typical of a landmine, about 3.5 cm. The atmosphere in the chamber was controlled to 50% relative... 

Geodynamic Condition Melioration caused swamping and clay soil settlement procedures are present here. Intensive physical weathering and depth erosion is present here Physical weathering is intensive, with landslides, talus and other gravitational developments Intensive weathering. With landslides, erosion and other developments can be observed here. 

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