Soils biological activity tests

These tests demonstrate that rhizomes of johnsongrass have biological activity and that the activity is residual. The allelochemic usually associated with Sorghum species in general, and with johnsongrass in particular, is the cyanogenic glucoside dhurrin (3) or its decomposition product (p-hydroxybenzaldehyde). Whether these compounds act as allelochemics in field situations is unknown and somewhat suspect, since they would surely be immobilized or altered in most soil situations, as was shown for... 

The allelopathic potential of plants has often been evaluated from tests of the biological activity of volatiles, leachates, and root exudates, or from aqueous extracts of the tissue. Alternatively, assessment of inhibitors in the soil associated with a suspected... 

Limitations It has to be considered that dissipation of volatile substances and degradation due to biological activity during the exposure time influence the result of the toxicity test. The selection of an appropriate reference (control) soil is crucial for obtaining correct results, since the effect measured in contaminated soils is in general related to the reference. 

Soil is a highly variable entity in terms of its composition and biological activity, both varying with location, season, pretreatment, and storage. To date it is impossible to standardize soil as a biodegradation test medium. Most test protocols use these soils with different texture characteristics namely sandy, loam and clay textured soil, and under near optimal conditions of moisture, aeration, temperature and pH [115]. 

Although different nutrients cycle at characteristically different rates in the same ecosystem, the amounts of biologically active M and P will be in balance in an ecosystem in a steady state conditionA ratio of 8 1 for the levels of biologically active N (24 g N m ) to P (3 g P m " ) was estimated for the top 20 cm of a semi-arid grassland soil. This hypothesis now needs further testing in a range of different ecosystems. 

Instiximental neutron activation analysis (INAA) is considered the most informative and highly sensitive. Being applied, it allows detecting and determination of 30-40 elements with the sensitivity of 10 -10 g/g in one sample. The evident advantage of INAA is the ability to analyze samples of different nature (filters, soils, plants, biological tests, etc.) without any complex schemes of preliminai y prepai ation. 

Toxicology and environmental health studies often lack a firm foundation of baseline data, and the NASGLP is a perfect starting point for a baseline data survey. During the field component of the survey, the crews collected two composite samples. One represented the top 5 cm of the soil directly below the litter layer (which will include a lot of the airborne components if they are present), and a second came from the 0-30-cm interval, independent of which soil horizon this may represent. Within this interval (the active layer), most of the interactions between biota and the non-living soil components take place, and thus is the important interval for this type if study. Environment Canada s Biological Methods Division selected one of the northern New Brunswick sites to collect a bulk sample in an attempt to create reference sites across Canada for standardized toxicity test methods. 

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