Table S1
Pre-screening of feasible parameters to characterise compost quality based on the score points (1 or 2 or 3) relevant to the agronomic value, cost and complexity of the compost.
Parameters / Compost Analyses / Reference / Instrument / Cost of analysis (MYR/sample) / Score Points / Total Score
Agronomic / Cost / Complexity
1 / Temperature / In situ / (Abdullah et al. 2013) / digital thermometer / 0 / Ma (2) / L (3) / L (3) / 8
2 / pH / 1 g sample 5 ml distilled water / (Shyamala and Belagali 2012) / pH meter / 0 / Ha (3) / L (3) / L (3) / 9
3 / Moisture content / Heating 105oC, 24 h / (Kutsanedzie et al. 2012) / oven / 0 / La(1) / L (3) / L (3) / 7
4 / Electric conductivity (EC) / 1 g sample 5 ml distilled water / (Pan and Sen 2013) / EC meter / 0 / Ha (3) / L (3) / L (3) / 9
5 / Cation exchange capacity / Displacement, titration / (Erhart and Burian 1997) / - / 0 / Ha (3) / L (3) / M (2) / 8
Displacement / (Brewer and Sullivan 2003) / AAS / 25 (outsource) / Ha (3) / M (2) / L (3) / 8
6 / Colour / Visual / (Pan and Sen 2013) / - / 0 / Ma (2) / L (3) / L (3) / 8
7 / Odour / Smelling / (Pan and Sen 2013) / - / 0 / Ma (2) / L (3) / L (3) / 8
8 / Organic matter (OM)/ volatile solid (VS) / Heating 550 oC, 5 h / (Saha et al. 2010) / furnace / 0 / Ha (3) / L (3) / L (3) / 9
9 / Self-heating test / Dewar/ insulated flask self heating / (Brewer and Sullivan 2003) / thermometer / 0 / Ma (2) / L (3) / L (3) / 8
10 / O2 uptake rate / SOUR (incubate, measure, calculate related with VS) / (CCQC 2001) / oxygen sensor / 15 (outsource) / Ma (2) / M (2) / M (2) / 6
11 / CO2 evolution / Alkali trap / (Brewer and Sullivan 2003) / - / 0 / Ma (2) / L (3) / M (2) / 7
Solvita CO2 / (Brewer and Sullivan 2003) / Solvita probe and digital colour reader / 30 (outsource) / Ma (2) / M (2) / L (3) / 7
12 / C: N ratio / Dried, grinded, Analyse / (Saad et al. 2013) / CHNS/O elemental analyser / 35 (outsource) / Ha (3) / M (2) / L (3) / 8
Heating & Kjeldahl / (Sharifi and Renella 2015) / - / 0 / Ha (3) / L (3) / H (1) / 7
13 / Humic substances (Humic acid, Fulvic acid) / Extraction, analyze / (Satisha and Devarajan 2011) / chromatography/ elemental analyser/ spectrometer / 100-150 (outsource) / Ha (3) / H (1) / H (1) / 5
14 / Microbial count (3 types: Nutrient, MRS, DRBC agar) / Agar plate count / (Ismail et al. 2013) / - / 20-35 (chemical/ materials/ reagents) / La(1) / M (2) / M (2) / 5
15 / Nutrient Content (3 types: N,P,K) / Merck test kits / - / spectrophotometer / 68 (test kits) / Ha (3) / M (2) / M (2) / 7
16 / Pathogen test (2 types: Salmonella, E.coli) / FDA-BAM / - / outsource-lab / 50 (outsource) / Ma (2) / M (2) / M (2) / 6
17 / Germination index / Extract compost with distilled water (1:10), 10 raddish seeds / (Selim et al. 2012) / - / 3-5 (chemical/ materials/ reagents) / Ha (3) / L (3) / L (3) / 9
18 / Enzymatic activity (cellulose) / React with substrate / (Raut et al. 2007) / spectrophotometer / 10-20 (chemical/ materials/ reagents) / La(1) / M (2) / M (2) / 5
19 / Impurities (metal, glass & synthesis polymer) / 2 mm in size, % of oven dry mass / (Sharifi and Renella 2015) / oven / 0 / Ha (3) / L (3) / L (3) / 9
20 / Particle size / Screen / (Sharifi and Renella 2015) / - / 0 / Ha (3) / L (3) / L (3) / 9
21 / Heavy metals content (7 types: Cd, Cr, Cu, Hg, Ni, Pb, Zn) / Digestion, analysis / (Irshad et al. 2013; Saha et al. 2010) / AAS/ ICP-OES / 210-350 (outsource) / Ma (2) / H (1) / M (2) / 5
22 / VOA or VFAs (any 2 types) / Extraction, analysis / (CCQC 2001) / gas chromatograph / 80-150 (outsource) / Ma (2) / H (1) / H (1) / 4
Ha= Highly related to agronomic value; Ma= Moderadely related to agronomic value; La=Less related to agronomic value
H= High score (3); M=Medium score (2); L=Low score (1)
Table S2
Justification for the quality parameters for compost graded as Ha, Ma and La(Ha= Highly related to agronomic value; Ma= Moderately related to agronomic value; La=Less related to agronomic value).
Parameters / Justifications
Graded as Ha
/ GI offers a relatively high degree of reliability and repeatability in measuring phytotoxicity based on well-understood principles (Huang et al. 2003). GI value can indicate the toxicity level that will influence seed germination and root growth to a different degree depending on the tolerance of the crops.
/ OM is a measure of carbon-based materials in compost and a basic indicator for soil health (Ryals et al. 2014). OM relates closely to various soil-enhancing characteristics such as relaxing soil aggregation, enhancing water-holding capacity as well as promoting soil biological activity (Ryals et al. 2014). In the study by Saha et al. (2010), the highest weighing factor was assigned to organic carbon content to indicate the fertilising index of compost from municipal solid waste. It was useful in estimating the physical properties, age of composts and the application area.
- Carbon to nitrogen ratio (C: N)
/ C: N ratio is often used by researchers to evaluate the degree of completion of a composting process. It describes the characteristic or compost quality in the similar way like OM. In several regions, a product cannot be deemed as compost unless the C: N is less than 25: 1 as application of compost with high C: N will lead to increase oxygen consumption and reducing oxygen available to plant root (Woods End Research Laboratory 2005). It is a must pass test in CCQC (2001)for compost maturity index to be rated as acceptable prior to further testing.
- Cation exchange capacity (CEC)
/ CEC expresses the quantity of negative charges in the compost to hold cations. It is important in retaining nutrients against leaching and to increase the availability of N (Mu’minah and Baharuddin 2014). Iqbal et al. (2012) stated that compost with CEC larger or near to 60 cmol kg-1 is suitable for cropland application.
- Electric conductivity (EC)
/ EC is an estimated measurement of soluble salts concentration in the compost due to the presence of nitrate, potassium, calcium and also some undesirable soluble salts like sodium. Excessive soluble salts may affect the crop growth and yield therefore EC determination is essential especially as different plant species has different level of tolerance against salts. Compost with EC lower than 10 dSm-1 is advised for most end use; compost with EC lower than 2 dSm-1 can be used directly but dilution is recommended when the range is within 3-10 dS/m (Wood End Research Laboratory 2005).
/ pH of compost must be analysed as compost application may alter the soil pH subsequently affecting the nutrient available to plant. The ideal pH of compost should be close to neutral (Pan and Sen 2013).
/ The declaration of nutrients in compost is indispensable especially for nitrogen (N), phosphorus (P) and potassium (K), the three nutrients that are greatly required in soil.
/ Compost with excessive impurities will influence its agronomic values because they offer no benefit to the soil and are usually aesthetically offensive. By analysing the impurities the quality of compost can be ensured and the entry of inerts (glass, plastic, metal object, stone, rock) to the agriculture land can be minimised.
/ Particle size is often included in most of the standards and is recommended for compost specification. Distribution of particle size will greatly affect the potential application (Brown et al. 2008). For instance, compost with small particle size is not suitable as mulch product or product to prevent erosion while large particle size is undesirable for application where rapid drainage is required (Kuo et al. 2004).
/ Compost quality depends significantly on humic substances as they have the beneficial effect to improve the properties of soil ecology, fertility and structure (Iqbal et al. 2012). The degree of humification is closely relevant to the formation of humic acids with increased aromatic structure, functional group as well as oxygen and nitrogen concentration (Bernal et al. 2009). The content of humic substances is an indicator for compost maturity and agronomic value. The use of humificationindex, humification rate, humification ratio, percent of humic acid, polymerisation index and different molecular weights of humic acid (Zhou et al. 2014) have been considered as indicator for compost maturity.
Graded as Ma
- Temperature
- Self heating
- O2 uptake rate
- CO2respirometry
- Odour
- Colour
- Volatile organic/ fatty acids content
- Pathogen test
- Heavy metals content
/ Temperature, self heating test, CO2respirometery, O2 uptake rate are responsible for indicating the stability of compost rather than maturity (Oviedo-Ocaña et al. 2015). Although application of unstable compost will affect the biological activity of soil leading to nutrient tie up and lacking of available oxygen, the values fail to give distinct idea on the suitable end use similar to the parameters graded as highly relevant to agronomic value. Odour and colour are the easiest way to determine the quality of compost however as the sensory test is not a sensitive indicator. Volatile organic acids or fatty acids (VOA/VOF) content can be used to determine the odorous smell and the stability of compost (Kuo et al. 2004) but it is relatively time consuming and expensive. Heavy metal content and pathogen content are important in term of compost safety however they are not highly related to the agronomic value of the compost. Moderately relevant to the agronomic value is still granted in spite of agronomic value as the threshold values for heavy metal content and pathogen content are well established and informative to the end user.
Graded as La
- Microbial count
- Enzymatic activity
- Moisture content
/ Microbial count and enzymatic activity reflect the stability of the compost yet they are highly dependence on the process design and type of input materials, up to date there are no threshold values suggested for the stability level unless they are monitored throughout the composting process. Both parameters could not provide a clear insight on the agronomic value of the compost. The moisture content of compost greatly affectingits handling and transportation (Ng and Yusoff 2015) however is less relevant to its agronomic value (Kuo et al. 2004).
