Plant Performance Tests

Evaluate and predict growth promoting or limiting properties of soil amendments.

Hypothesis: for each compost / growing media, there are multiple potential impacts on plant-growth that can be partly isolated and evaluated by selection of test species ...

I - Plant Biomass Tests for composted products

LEFT- Control in Pro-Mix / RIGHT COMPOST All plants below grown on same compost at identical use rate (25% v/v in limed peat).	Test Species and Official Use:
	CRESS TEST *(Lepidium sativa)* (Swiss Compost Assocation & German Compost Association, Woods End Laboratory & Rodale Quality Seal ) Most widely recognized plant species for compost bioassays, also OECD listed; moderately sensitive to salinity; insensitive to auxinic herbicides; fast growing and ideal for lab phytotrons. Biomass measurements required.
	Cucumber Test (USCC TMECC) Incorrectly considered a compost maturity indicator, cucumbers react to multiple factors such as fungal pathogens (useful for pytopathology tests!) and soluble nitrogen (ammonia + nitrate). As moderately fast growers they yield excellent biomass but develop crowding effects rapidly, which confounds stem-length (elongation) tests customarily used to record results.
	Tomato Test *(UK Compost Assocation under revision Jan '05)* Moderately sensitive to maturity factors, somewhat insensitive to salts; responds mostly to soluble nitrogen & potash levels, slow grower and cold-sensitive. Biomass measured after 6 weeks. Useful plant to test ocmposts sold as seedling starters and potting mixes.
Summary: Plant Biomass tests, if performed carefully, will reveal quality differences between composts and can indicate potential plant stress induced by the compost at the given level used in the test.

II - TOPS + ROOTS POT STUDIES

Growth Series: 0 - 25 - 50 - 100% MSW Compost with Sorghum-Sudangrass

This type of plant growth trial employs efficient C4-photosynthesis type plants with vigorous rooting properties. Generally performed for about 21 days. Results indicate any one or more feature of compost that limits rapidly growing high-yield potential plants. In the above image, the compost was moderately immature (high VFA content!) and elevated in salt so a limiting effect is seen with root inhibition beginning after 25%.

Growth Series: 0 - 20 - 40 - 80 - 100% Manure Compost with Soybeans

Soybeans, field peas, and bush beans are insensitive to nitrogen supply but react to salinity stress, trace element toxicity and auxinic herbicides. They are excellent test plants for ag utilization of composts, manures and other wastes. The above manure compost had 8 dS/M conductivity so its use would be limited to a max of 15-20% addition over which yields decline precipitously.

III - Exised/Washed Rootlet Bioassays

These root studies reveal the potential effect of oxygen deprivation from immature compost; on the left, incompletely composted biosolids induces root inhibition through day-97 composting

Washed Root Studies from 60-day Container Studies

OXYGEN STRESS: The major effect of immature compost on plant development

Existed Rootlet form Container Study

Biosolids Compost Aging Series -above

Day 21- 97 - 250 - Control

Rootlet Detail:
LEFT = Control
RIGHT = oxygen stressed rootlet

III. Herbicide Residue Bioassays


Woods End has developed some of the most accurate bioassays for revealing herbicide residue effects. Especially our Trifolium pratense assay combined with dilution to standard conductivity (DSC) is effective to the lowest levels attainable and protects from misinterpretation of other harmful effects.
	Detail: Red clover will display distinct leaf curl at low herbicide residue levels. It is sensitive in the range 3 - 50 ppb, but must be carefully protected from salinity stress induced by many composts. Wood End will publish a paper in 2005 showing superiority of the Woods End red clover to the WDOE herbicide bioassays test using peas, and showing the needed control of salt intereference in toxicity studies for composts.

IV. LEMNA BIOASSAYS


Lemna (Duckweed) have been extensively used for eco-toxicology studies, reacting non-specifically to a number of xenobiotics. Woods End has completed trials with Lemna species and have developed an evaluation system to objectively assess potentially toxic parameters in soils and composts. The growth trials above are digitized (below) and image analysis software interprets area and color density.

Lemna in standard toxicant (Glyphosate @ 9.2 ppm). HIGHLYTOXIC	Control, Non-Toxic Compost extract