Soil profiles

Water leaves the field either as surface mnoff, carrying pesticides dissolved in the water or sorbed to soil particles suspended in water, or as water draining through the soil profile, carrying dissolved pesticides to deeper depths. The distribution of water between drainage and mnoff is dependent on the amount of water appHed to the field, the physical and chemical properties of the soil, and the cultural practices imposed on the field. These factors also impact the retention and transformation processes affecting the pesticide. 

Annual Probability of Exceeding Maximum Acceleration p, =0.002 Maximum Horizontal Ground Acceleration A =0.25 g Soil Profile S2... 

Mention should be made of the soil profile (section through soil showing various layers) because it is important to recognise that the soil s surface... 

Movement of carbonates and salts can also occur in a similar fashion. As these minerals are weathered in the upper soil profile, their component ions go into solution and are moved down through the soil by rainfall entering the soil. As the water moves down the soil there may not be enough water to move the ions out of the soil, so they precipitate in a lower horizon where they accumulate. Such accumulations are common in arid environments with limited rainfall. In high rainfall areas, carbonates and salts are usually completely removed from the soil through leaching. 

For soil profiles that are less than the optimum thickness, there is a destabilizing feedback between soil thickness and weathering rate. Assume that a thin soil is in a dynamic equilibrium such that weathering inputs balance transport losses (A in Fig. 9-3). Weathering rate... 

Scott, G. A. J. (1975b). Soil profile changes resulting from the conversion of forest to grassland in the montaha of Peru. Great Plains-Rocky Mount. Geogr. J. 4,124-130. 

There was a discrepancy between water salinity limits for the three locations, which may be attributed to factors related to difference in soil texture and stmcture. This affects soil infiltration capacity and water retention. These soil hydrologic characteristics influence salt development in the soil profile, which affects plant... 

Plant uptake is one of several routes by which an organic contaminant can enter man s food chain. The amount of uptake depends on plant species, concentration, depth of placement, soil type, temperature, moisture, and many other parameters. Translocation of the absorbed material into various plant parts will determine the degree of man s exposure—i.e., whether the material moves to an edible portion of the plant. Past experience with nonpolar chlorinated pesticides suggested optimal uptake conditions are achieved when the chemical is placed in a soil with low adsorptive capacity e.g., a sand), evenly distributed throughout the soil profile, and with oil producing plants. Plant experiments were conducted with one set of parameters that would be optimal for uptake and translocation. The uptake of two dioxins and one phenol (2,4-dichlorophenol (DCP)) from one soil was measured in soybean and oats (7). The application rates were DCP = 0.07 ppm, DCDD 0.10 ppm, and TCDD = 0.06 ppm. The specific activity of the com-... 

Several facts have emerged from our studies with 2,7-DCDD and 2,3,7,8-TCDD. They are not biosynthesized by condensation of chloro-phenols in soils, and they are not photoproducts of 2,4-dichlorophenol. They do not leach into the soil profile and consequently pose no threat to groundwater, and they are not taken up by plants from minute residues likely to occur in soils. Photodecomposition is insignificant on dry soil surfaces but is probably important in water. Dichlorodibenzo-p-dioxin is lost by volatilization, but TCDD is probably involatile. These compounds are not translocated within the plant from foliar application, and they are degraded in the soil. 

If we assume that the TCDD is contained in the surface 6 inches of the soil profile since it is relatively immobile (5), then the 2,4,5-T at the 947 lbs of active ingredient/acre treatment would have had to contain 2.1 ppm TCDD to be observed. At the lower application rates of 584 and 160 lbs/acre, the 2,4,5-T would have had to contain 3.5 and 12.5 ppm TCDD in the technical materials to have 1 ppb in the top 6 inches of soil. Since the soil is sandy and high rainfall occurred in the area, maximum movement of materials in soil may occur causing TCDD to be present deeper in the profile. If the TCDD moved uniformly throughout the 36 inch soil profile, then six times more TCDD would have had to be present in the original 2,4,5-T for detection. This would have required the presence of 12.6, 21.0, and 75.0 ppm TCDD in the 2,4,5-T applied in the three treatments. These calculations are based on the assumption that no degradation occurred in or on the soil. 

Blanco-Canqui, H. and Lai, R. (2008). No-tillage and soil-profile carbon sequestration An on-farm assessment Soil Sci. Soc. Am. J. 72, 693-701. 

E. Bosatta and G. 1. Agren, Theoretical analyses of carbon and nutrient dynamics in soil profiles. Soil Biol. Biochem. 2S 1523 (1996). 

Soil properties A Soil texture (sand, silt, clay), organic matter/carbon content, and pH Stones, roots, and hardpans must be largely absent to allow representative sampling of soil profile Soil properties should appear uniform over test site Soil texture data should be available at time of site selection. Soil properties must match study purpose. This can be realistic use conditions, realistic worst-case or worst-case in terms of agrochemical mobility and persistence Must ensure that the majority of samples can be taken from the deepest sampling horizon. Information about sub-soils can be obtained from soil maps, test coring and on-site interviews... 

Step 1. Soil probe with outer retainer sleeve (A), Inner probe (B), and probe liner (C) is inserted into soil profile. 

The inner probe (with liner) is removed, leaving the outer retainer sleeve in the soil profile. While the liner Is still in the inner probe, a red cap is carefully placed on the top of the liner. Next, the probe is inverted, the A liner removed from the inner probe, and the bottom of the liner... 

Upper soil profile sample in liner with end caps... 

Outer retainer sleeve (A) remains in soil to prevent drag down of surface residues to lower soil profile... 

Once the soil cores have been collected, all boreholes must be backfilled with untreated soil (with frequent tamping) to prevent bypass flow that could transport residues into the lower soil profile. After backfilling, flags or stakes should be placed at the boreholes. This serves as an additional check to ensure that sub-plots are not sampled more than one time during the study. (Note that these boreholes should... 

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