Use of the hot water percolation (HWP) method for compost analysis
There was a need for a simple, fast and cheep method in compost quality asurance system, to follow the composting process and measuring the quality of compost. Hot water percolation (HWP) method was used first in soil analysis (Füleky – Czinkota, 1993).
Later it was introduced into the compost analysis, too. The extraction was carried out in a coffee percolator like instrument. The water percolated through the compost sample are collected in 100 cm3 aliquots and analysed for C, NO3–N, NH4–N, P and K. For analysis the compost samples of grape pomace and horse manure were used. Also two compost samples were prepared from animal and plant residues, respectively as well as some commercial compost samples were analysed. Not only the quantity of nutrient elements but also the rate of element supply is reflected with the HWP method. The hot water extractable C, NO3–N, NH4–N, P and K content of compost samples, when the percolation time is long enough, could be described with the equation of the zero, first, and second order kinetic reatictions, respectively or by the combination of theese equations. The cummulated amounts of NO3-N and K reach a maximum in the percolation time, but the cummulated amounts of C and P increase also out of the measuring time (700 cm3 percolated solution or 600 sec percolation time). There was a very close relationship between the hot water soluble C content and the absorbance measured at different wavelengths. The highest absorbance was measured always in the first fraction followed by exponentially decreasing values in the later extractions. We can conclude that the close relationship between hot water soluble carbon content and absorbance could be applied for controlling the composting process. The measurements show a tendency where the less mature compost samples contain more hot water soluble C than the mature samples. The E4/E6 values used for the humus quality evaluation in soils, also reflect the proceeding of composting process and the number of hot water extraction steps. In grape pomace compost samples the E4/E6 values show a slight decrease in composting time, explaining it with the increase of the ratio of humic acids. At the same time with the increasing number of extractions the decreasing absorbance of solutions show that the fulvo acids coming to the fore.
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© Lexxion Verlagsgesellschaft mbH (8/2024)
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