Soil cores

Davidson, E., Hart, S.C., Shanks, C.A. and Firestone, M.K. 1991 Measuring gross nitrogen mineralization, immobilization, and nitrification by isotopic pool dilution in intact soil cores. Journal of Soil Science 42 335—349. 

Twelve, 36-inch soil cores of the Lakeland sand were selected for chemical analyses in December 1970. Twenty-five gram samples of 6-inch increments were acidified and extracted with 1 1 hexane acetone. Each sample was extracted with IN KOH, and the aqueous phase was saved for 2,4-D and 2,4,5-T analysis. The hexane phase was extracted repeatedly with concentrated H2SO4 until the acid was clear. The H0SO4 was removed, and the extract was drained through NaHCOs and anhydrous... 

A-C. Hansson, E. Steen, and O. Andren, Root growth of daily irrigated and fertilised barley investigated with ingrowth cores, soil cores and minirhizotrons, Swed-hh J. Agric Re.s. 22 141 (1992). 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

Another approach to improving agrochemical detection is to apply more of the active ingredient to increase the initial soil concentration. As mentioned previously, however, one must be careful not to exceed greatly the labeled application rate of the compound as questions may arise as to concentration effects on the observed dissipation. A more common and acceptable approach is to section the upper soil core into smaller depth increments, yielding increased residue concentrations as the total amount of soil mixed with the residues decreases in each processed sample (Table 1). 

Table 1 Anticipated zero-time concentrations (mg kg ) as a function of soil core length...

Total soil weight per given depth per hectare assumes a bulk density of 1500 kg soil m. Calculations are based on a nominal application rate of 0.168kga.i.ha . Soil core sectioning techniques are discussed in Section 3. 

Regardless of how the upper core is ultimately sectioned, the 15-120-cm depth cores are typically sectioned in 10-15-cm lengths for analysis. Techniques used to section soil cores are presented in Section 3.3.6. 

The need for additional samples to compensate for soil heterogeneity must be reconciled with labor, storage, transportation, analytical, and other constraints that add significantly to study costs. Satisfactory results have been obtained from numerous field studies using three or four treated replications with 5-10 soil cores collected from each replication per sampling period. These replication/repetition numbers strike a reasonable balance between the need for samples sufficient in number to characterize agrochemical dissipation versus financial and logistical constraints associated with sample collection and analysis. 

Influence of soil core diameter on study results... 

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... 

Proper sample collection and handling are the key to acceptable agrochemical recovery at zero time. The zero-time sample interval is defined as the first sample collected after application. Zero-time soil samples should be collected within 3h after application. Zero-time soil core concentrations, such as those given in Table 3,... 

In Table 7, a comparison of actual measurements, and also two well-known pedo-transfer functions, can be found by depth. It is important to note that there is a large difference in water content between the disturbed soil core samples and the undisturbed samples. Additionally, the two pedo-transfer functions also exhibit a large difference in predicted water content. Therefore, when doing calculations or trying... 

Intact soil core measured Disturbed soil core measured Pedo-transfer function I estimated Pedo-transfer function II estimated Intact soil core measured Disturbed soil core measured Pedo-transfer function I estimated Pedo-transfer function II estimated... 

To investigate a vertical distribution of a chemical, a sediment column is divided into sections with appropriate thickness. The sediment column taken in a pipe should be refrigerated in an ice-cooled container, transported to the laboratory, and removed carefully on to a clean tray so that there is as little disturbance as possible to the soil core structure. In the case of a column in which there is little soil moisture and it tends to collapse, the soil should be pushed out to each required thickness and carved off. It is also possible to take a sediment column up to a 30-cm depth using a pipe that is connected to cylinders (5-cm height) with sealing tape. In this case, the sample in each 5-cm fraction can be obtained as it is, after removing the tape. 

Soils were sampled on November 4, 2002. At each sampling point, a 10m circle in diameter was set, and 6 soil cores were randomly taken from 0-5.1 cm layer by a core sampler (5 cm in diameter). Each core contained... 

To determine Paraquat in soil Payne et al. [180] separate the sediment from the sample (2L) by adding calcium chloride to aid flocculation, leaving the mixture overnight in a refrigerator for the sediment to settle, then decanting and filtering through a Whatman No. 42 paper under suction on a Buchner funnel. The wet sediment and soil core samples, are mixed for 4h... 

Kimura and Miller [29] demonstrated (Table 13.7) that mercury in several organic forms can be digested and aerated from unfiltered soil digests. For samples of lOg of soil cores containing 5pg mercury or less, the standard deviations of a single determination were 0.12, 0.15 and 0.23pg, respectively, using 2cm cylindrical optical cells. 

Figge and Schoberl [33] reported on the degradation and fate of 14C-LAS after introduction of digested sludge into the topsoils collected from two agricultural ecosystems. The first of the soil cores transferred into the laboratory test apparatus was a heavy, clay-like soil, while the second was classified as a loose, sandy soil. The initial concentrations of LAS in the top layer of the soils were 27.2 and 16.2 mg kg-1,... 

Two soil sampling tubes were removed from each tank 2, 5, 9, 15, 27, 30, 43, and 58, and 72 days after the start of the experiment, then frozen and stored for later analyses. For analyses, the frozen soil cores were removed from the glass tubes (by brief immersion in hot water), then sectioned into four 1-cm cylinders representing 0-1, 1-2, 2-3, and 3-4 cm soil depths. Samples from each depth were shake-extracted with 100 ml ethyl acetate hexane overnight, and again with 100 ml methanol overnight. Extracts were filtered, concentrated to 20 ml and analyzed by LS and TLC as described below. 

Figure 4.15 indicates the range of rates of O2 consumption in different soils. Oxygen is consumed in oxidation of inorganic reductants, such as Fe(II), as well as in oxidation of organic matter by microbes. Bouldin (1968) and Howeler and Bouldin (1971) compared measured rates of O2 movement into anaerobic soil cores with the predictions of various models, and obtained the best fits with a model allowing for both microbial respiration and abiotic oxidation of mobile and immobile reductants abiotic oxidation accounted for about half the O2 consumed. The kinetics of the abiotic reactions are complicated. They often depend on the adsorption of the reductant on solid surfaces as, for example, in... 

Figure 5.6 shows profiles of NO3 concentration measured with microsensors in soil cores taken from ricefields by Revsbech and co-workers (Liesack et al., 2000). During illumination of the cores, O2 generated in the floodwater penetrated to a depth of 2-3 mm and a clear peak of was apparent, produced in... 

Figure 5.6 Concentration profiles of NO3 in soil cores from a ricefield, illuminated and not illuminated (Liesack et al., 2000). Reproduced with permission from Elsevier Science...

---