With the increased commercial production of compost in large scales in India, it is not unusual that one can frequently encounter with the poor quality of commercial compost or even that produced at small/marginal levels by individual farmers. The quality may have many different perceptions depending on the product nature, the usefulness and users themselves. But the presence of desirable traits and absence of undesirable traits arc the two prime signatures of compost quality. Common users take positive response in productivity as the best index of compost quality, which does not necessarily, encompasses all the desirable/undesirable trait factors.
Quality Control of Biological Inputs in India
Till recently there was no regulatory body or legislation exists in India to control the quality of biological inputs like compost, vermicompost, biogas slurry/sludge, biofertilizers etc. but now biofertilizer and organic manure are covered under FCO 1985 (Amendment 2006). Moreover BIS has specified nonobligatory standards for four types of biofertilizers. However the biopesticides, also an important component among biological inputs comes under the purview of 'pesticide control act', which is an exception, and occupies a very small portion of the total biological inputs produced in India. In this situation it is difficult to ascertain whether the commercial producers of compost/vermicompost have the urge to maintain their product's quality, even when the market competition is not strong enough.
Effects of Immature Compost
1. Biological blockage of available nitrogen by microbial population.
2. Decrease of Oxygen concentration (anaerobic) and soil Eh (reducing) at root zone (Eh - 15O, increased heavy nletal solubility, increased absorption up to phytotoxic level). (Eh- Reduction potential, 1Eh= 1mV)
3. Presence of even small quantity of ammonia is toxic to the root and normal development of plant.
4. Ethylene oxide: (synthesized during decomposition) is also phytotoxic reportedly inhibiting seed germination.
5. Presence of organic acids is also the cause of phytotoxicity. (propionic, n-butyric, acetic acids> 3000 ppm).
Different Physical, Chemical and Biochemical tests for Maturity Assessment of Compost
A. Physical Tests:
The physical methods are of general importance and can be used by the farmers themselves to judge compost maturity. These include temperature, odour and colour. Mature compost should have constant temperature, should not have any unpleasant odour. However, a characteristic odour similar to that of damp forest may be noted due to the predominance of mesophillic actinomycetes during cooling phase of bio-oxidative period and maturation phase and excretion of secondary metabolite geosmine. After maturation colour will be dark brown or almost dark.
B. Biochemical tests: The enzymatic activity can be a good indicator of compost maturity. Hydrolysable polysaccharide content should be in the range of 30-50 mg of hydrolysable polysaccharide per gram of dry matter. Similarly the C/N ratio below 20 is indicative of compost maturity and a ratio less than 15 is preferable. pH is also considered as good indicator of mature compost. Initially pH increases gradually and finally stabilizes between 7~8 as the compost mature. Conductivity of the final compost should not be more than 4.0 dsm-1 .
C. Biological Test: The compost should be free from phytotoxic compounds and plant test should be done to ensure the efficacy of compost for a specific usage and should generally not be extrapolated to other different conditions. Normally, cress seeds (Lepidium sativum L.) are used to test the phytotoxicity of compost.
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