Soil storage conditions

Modification of the soil storage conditions, use of purified enzymes and... 

A solution to this dilemma is to place soil samples immediately in a freezer located in the field, the temperature of which is continuously monitored, as described previously. Laboratory-prepared storage study samples can then be used to determine test substance stability under freezer storage conditions that match those used in the field and during transportation and final storage. If a valid laboratory storage stability... 

The samples must be stored in good conditions pending analysis. The storage conditions that are appropriate will depend upon the type of sample and the determinations required. Most soil analysis, for example, is done on air-dried soil, but the nitrate content can be altered by drying, so nitrate studies are usually done on fresh soil. If the soil has to be stored, this should be at <4 °C and for no more than 48 hours. Similarly samples in which analysis of the volatile components is required, such as silage, urine and faeces, are usually kept frozen until immediately before the analysis. 

All scientific studies involve some aspect of practical work. It is therefore essential to be able to observe and to record information accurately. In the context of environmental analyses, it should be borne in mind that not all practical work is carried out in the laboratory. Indeed it could be argued that the most important aspects of the whole practical programme are done outside the laboratory in the field, as this is the place where the actual sampling of environmental matrices (air, water, soil, etc.) takes place. It is still common practice, however, to transport the acquired sample back to the laboratory for analysis, so knowledge and implementation of the storage conditions and containers to be used are important. Both sampling and sample storage are covered in Chapters 3 and 4, respectively. 

In the laboratory, some of the diphenamid-treated soils lost their activity after 1 or 2 years, but the enhanced degradation could be restored in these soils much faster than it took to develop enhanced degradation in the first place in the previously non-treated soil. Handling and storage conditions of the soil in the laboratory are critical for preserving the activity. 

Stable under normal, dry storage conditions. Slowly decomposed by heat and moisture. Rapidly degrades in the environment by hydrolysis, oxidation, photolysis, and metabolism, tm (water 25°C) 20 days (pH 5) and 34 h (pH 9). ti/2 (soil) 6 to 15 days... 

Stable for more than 2 years under normat storage conditions. Hydrotyzed by boiUng with strong acids and atkalis. Aqueous solutions are unstable to UV light. ti/2 (water 20°C) < 1 day (pH 5, 7 or 9). ty2 (soil) 7 to 234 days, depending on soil type... 

Rapidly degraded in soils under both aerobic and anaerobic conditions, by hydrolysis and by photolysis. ty2 (soil) 3 to 8 days Stable under normal storage conditions. Relatively stable to hydrolysis at pH 5 to 9 (under 30°C). Decomposed by strong acids and alkalis. In soil, the methylthio group is rapidly oxidized to the sulfoxide and, further, to the sulfone Decomposed in acid media. Some deterioration on prolonged exposure to heat, air or moisture. ty2 (water 22°C) 128 days (pH 4), 18 days (pH 7), 9 h (pH 9). t 2 (sandy soil pH 6.7) 12 h... 

Stable under normal storage conditions. Hydrolyzed by strong acids and alkalis. Stable to light. Decomposition temperature >200°C. Main loss from soil via microbial degradation. ty2 (soil heavy clay) 10 to 12 weeks, (soil loam) 8 to 10 weeks... 

In devising assays for soil enzymes it is necessary to ensure that the reaction catalysed is biochemically mediated, and that the rates of reaction, whether based on substrate disappearance or product formation, are not influenced by their participation in other reactions, biological or physico-chemical. Enzyme activities may also be influenced by the time and conditions of soil storage between sampling from the field and assay. The basic requirements for establishing soil enzyme assays, the advantages and disadvantages of selected assay conditions, and the responses of different enzymes to soil pretreatments have been reviewed in detail elsewhere 19 > 113 j i 2 / > 128 > 149 ... 

Physical appearance, as well as flavor quaUty and strength, can be iafluenced by soil conditions, rainfall, storms, blights, iasects, growing and harvesting methods, storage, etc. AH of these must be considered to evaluate a particular lot and to harvest, seH, or buy the lot and use it ia a food product. 

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