A Holistic Approach to Use the CIELAB Color Space for the Stability Evaluation of Green tea waste – Rice bran Compost

A simple, rapid and eco-friendly method has long been needed for evaluating the compost stability because application of unstable compost in agricultural field causes phytotoxicity. Thus, the CIELAB variables L*, a*, b*, a* x b*, a* / b*, 2000a* / (L* x b*), 1000a* / (L* + b*), chroma (C*ab), hue (hab) and color difference (∆E00) in dried (70oC) and ground composting materials (particle size ≤ 850 μm), originated from green tea waste and rice bran were studied during composting for stability evaluation using Minolta Colour Reader (CR-13). Most of the measured CIELAB variables were reached roughly in a plateau form from day 84 on. The increase tendency of L* from day 126 of composting may be due to the appearance of white color actinomycetes in that stages. The relationship between CIELAB variables and the popular compost stability evaluation indices (total organic carbon, C/N ratio, NO3-N concentration, humification index and phytotoxicity) was calculated using Pearson’s correlation co-efficient. Most of the CIELAB variables showed strong relationships with the compost stability indices except a* x b*. In this study, L* provided the best relationship with phytotoxicity (r = -0.853), b* with C/N ratio (r = 0.977), 2000a* / (L* x b*) with organic carbon (r = -0.967) and NO3-N concentration (r = 0.764) and hue with humification index (r = 0.945). The CIELAB color space offers a quick, easy, nondestructive, eco-friendly and inexpensive means of determining the compost stability by characterizing the compost properties in different ways. Further investigations need to be done in testing this procedure on different compost products under differing conditions. Media summary Efficient use of CIELAB color space in compost science may lead to develop an easy, quick, inexpensive, nondestructive and eco-friendly way of compost stability evaluation.