Field moist soil

Potentially mineralizable C and N are often measured by incubating a sample of field-moist soil at a known temperature in a sealed chamber containing an alkali trap. The C02-C accumulated in the trap is measured by acid titration and this represents the quantity of C mineralized. Alternatively, C02 in the headspace of the incubation chamber can be measured using a C02 analyser. The amount of N mineralized during incubation is calculated as the difference in extractable NH4+ - andNCV-N measured in the soil before and after incubation. Mineralizable N can also be measured in an open incubation system where the soil is leached periodically and NH4+- andNCV-N in leachates is measured (Stanford 1982). 

Rochette and Koskinen (1996) developed a system that uses supercritical C02 to remove pesticides from the aqueous phase of an unsaturated soil without first requiring the separation of the solution from soil. Using this technique, sorption coefficients were found to increase with increasing organic carbon and clay contents for three field-moist soils. Moreover, sorption significantly increased in sand as gravimetric moisture content increased from 4% to 16%, and in a silt loam as moisture increased from 9.6% to 27%. 

A variety of studies have shown that as temperature increases, sorption may increase, decrease, or remain the same, with isosteric heats of sorption being very low (Table 21.7). These studies have used the batch slurry technique, so the impact of temperature on water-triazine interactions may mask surface-triazine interactions. In contrast, at 10% soil moisture isosteric heats of atrazine sorption ranged from -10 to -12kcal/mol determined with the SF technique (Koskinen and Rochette, 1996). Sorption coefficients in field-moist soils were much greater than are typically obtained with the batch slurry system, while heats of sorption were much more negative, indicating greater sorption at low moisture contents. 

Koskinen, W.C. and E.A. Rochette (1996). Atrazine sorption-desorption in field-moist soils. Intern. J. Environ. Anal. Chem., 65 223-230. 

Rochette, E.A. and W.C. Koskinen (1996). Supercritical carbon dioxide for determining atrazine sorption by field-moist soils. Soil Sci. Soc. Am. J., 60 453 160. 

In practice, and in most soil laboratories, drying the soil is, in general, the only option. Where drying the soil would entail a loss of essential information it may be preferable to make use of the soil solution itself obtained, for example, by centrifugation or displacement (Sanders, 1983 Linehan et al., 1985) rather than trying to use field-moist soils. 

Very few determinations are usually conducted on field-moist soils, although the practice is essential for the determination of extractable ammonium-N and nitrate-N.7,8 These two species may change very rapidly in biologically active soils, especially if the soils are dried and rewetted. However, these determinants are not measured by flame spectrometry. Speciation studies are best performed... 

Large Continuous Cu, Cr,Ni, Field-moist soil from a FAAS/ Off-line 500 mL Artificial rainwater at Anderson... 

Procedures based on extraction with deionised water, dilute calcium chloride (0.01 M CaCl2) potassium chloride (1M KC1), saturated sodium fluoride (NaF) and hydrogen peroxide (H202) have been described. All procedures (except for H202 which ideally uses field-moist soil) are based on the use of air-dry soil of <2 mm particle size. No correction for water content is made when reporting pH results. The soil/solution ratio and the temperature of measurement should be noted on the report, as other soil/solution ratios are often used. These include saturation extracts and soil/solution ratios of 1 1 and 1 2.5. 

This method, adapted from Ford and Calvert (1970) and Rayment and Higginson (1992) is mostly used on as received (field moist) soil to obtain an indication of the presence of oxidisable sulfide ions (S2-). It can also be used on soils dried rapidly at 80-85°C to stabilise pyritic soils for later analysis. 

Samples requiring analysis for VOCs should be taken from an untreated field-moist-soil sample wherever possible. 

ISO/PRF TS 14256-1 Soil quality - Determination of nitrate, nitrite and ammonium in field-moist soils by extraction with potassium chloride solution - Part 1 Manual method. 

The sewage sludge-amended soil was collected from Great Billings Sewage farm (Northampton, UK). Some 300 kg of field-moist soil was collected by multiple sampling to a depth of 10 cm and bulked into polyethylene bags for transport... 

Note Field moist soils incubated at 60% water-holding capacity. Source Blackmer and Bremner (1981). 

To determine the PMP, field moist soils are incubated under anaerobic conditions at 30°C for a period of 15 days. This method is similar to the one described for potentially mineralizable nitrogen... 

In one method, removal of labile by anion exchange resin from air dried, ground soil provided for a precise estimate of microbial P on small soil samples, and the change in resin-extractable P during extraction indicated microbial P uptake. Larger samples (10 g) of field moist soils were needed to compensate for greater soil heterogeneity in the other method, but microbial P contents were believed to relate more closely to field soils. 

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