Methods online

The United States Environmental Protection Agency (EPA) has a website where physical and chemical test methods for evaluating solid wastes may be downloaded as pdf files:

http://www.epa.gov/sw-846/main.htm We understand here by compost a marketed product of an organic based material derived from a variety of sources. These might be treated municipal waste, spent mushroom compost, a bracken- or seaweed-based compost, agricultural and food processing wastes etc., which might be put to agricultural use. Composts are often very heterogeneous, which makes it difficult to prepare a sufficiently homogeneous sample. The high humus content makes them similar to peat soils, where organic matter can exceed 95%, which can affect not only the analytical method, but also the interpretation of the results in making fertilizer recommendations.

Typical specifications

Typical parameters and nutrient levels for assessment of compost quality are shown in Table 5.2. These are combined values from a variety of sources, including Bertoldi etal. (1987), and are merely intended to help in setting up analytical procedures.

Some typical and preferred heavy and trace element concentrations for soils and municipal composts are shown in Table 5.3. The levels in soils are typical for dilute aqueous extractants such as 0.05 M EDTA, 0.5 M acetic acid, hot water for boron, and, for molybdenum, Tamm's reagent (acid ammonium oxalate; Reisenauer, 1965). Tables in the literature often give total values obtained spectrographically, by XRF, or by extraction with hot

Table 5.2. Typical parameters and nutrient levels for assessment of compost

quality.

Normal

Minimum

range

Maximum

Preferred values

Parameter

Dry matter (DM)

40-60%

lower

Organic matter

20-40% DM

x2 organic C

pH

5.5

6.5-8.0

8.0

7.0-8.0

Salinity (as NaCl)

2.0 g l-1

(conductivity)

1 -2 dS m-1

2.0 dS m-1

^0.5 dS m-1

Nutrient (g kg-1 DM)

Calcium (CaO)

20

35-140

Calcium (Ca)

14

25-100

Magnesium (MgO)

3

4-16

Magnesium (Mg)

1.8

2.4-9.7

Nitrogen (Kjeld.)

6

6-13

High

Organic-N % total

^90%

nh4-n

2-5

0.4

Low

no3-n

50-200

High

NO^N/ nh4-n

X20-80 ratio

^60

CN3 4

X10-20 ratio

22

Phosphorus (P2O5)

5

3.5-14

High

Phosphorus (P)

2.2

1.5-6.0

High

Potassium (K2O)

3

4.5-18

High

Potassium (K)

2.5

3.7-15

High

Table 5.3. Some typical and preferred heavy and trace element concentrations for soils and composts; various local regulations specify different maximum levels.

Typical/

Municipal

Max. in

Heavy

preferred

compost

compost

Preferred

and trace

in soil

(typical)

(var. regs.)/a

values

elements

Symbol

(mg kg-1 DM)

(mg kg-1 DM)

(mg kg-1 DM)

(mg kg-1 DM)

Boron

B

0.01-10/0.5-<3

0.3-11.9

Cadmium

Cd

<0.01-1/0

1 -8

3-20/1.5

0

Cobalt

Co

<0.05-3/<50

15

34-150

<50

Copper

Cu

0.3-20/1-<3

50-475

100-1200/200

<100

Chromium

Cr

0.1-4.0/low

30-200

150-1200/100

<100

Iron

Fe

<10-3000/10-50

18200

Lead

Pb

0.1-10/0

65-900

100-1200/150

0

Manganese

Mn

5-100/3-<50

320

Mercury

Hg

0.02-0.4/0

0.5-4

0.8-5/1

0

Molybdenum

Mo

0.08-0.8/2-7

5-20

Nickel

Ni

0.2-25

15-100

25-200/50

<25

Zinc

Zn

<2-30/1 -8

160-2100

300-3000/400

<300

aUpper limit set by The Composting Association (TCA, 2000).

aUpper limit set by The Composting Association (TCA, 2000).

concentrated acids, and these can be about 2-20 times the values obtained with mild extractants. Examples of surveys of trace elements in soils are given by Archer (1980), Archer and Hodgson (1987) and Berrow and Burridge (1980).

Various local regulations specify different maximum levels, so the appropriate authority must be consulted when formulating composts. For a summary of compost standards in Canada, visit the Composting Council of Canada website at:

http://www.compost.org/standard.html The European Committee for Standardization (CEN) is harmonizing European standards, and it is hoped their draft methods will eventually be introduced as British Standard methods, coded BS EN.

For specifications of a typical commercial compost, visit:

http://www.asiagreen.com.my/chem_ana.htm and /chem_anb.htm Apart from mandatory specifications, there are voluntary specifications, which permit the compost manufacturer to use the validating scheme's symbol. In the UK, The Composting Association (TCA) have drawn up their Standards for Composts covering certification, testing, monitoring and labelling of composts (TCA, 2000). These may be viewed at: http://www.compost.org.uk/standard.htm Specifications for composts for organic farming are seen in the EU Eco-label for Soil Improvers, and The Soil Association Standards for Organic Food and Farming - Certified Products Scheme. Criteria for the award of the EU Eco-label to soil improvers are available at:

http://www.europa.eu.int/comm/environment/ecolabel/soil_improver s/htm

Preparation of sample

Although the cation exchange capacity (CEC) of the compost before application has a poor relationship to its CEC when incorporated into the soil, it provides possibly a better indi cator than the C:N ratio of the maturity of the compost (Estrada et al., 1987). It therefore appears as a diagnostic measure of maturity rather than as a parameter defining the quality of the marketed compost. In this context, Jacas et al. (1987), have shown that the fineness of grind in the preparation stage can markedly affect the measured CEC. They expressed the results as mEq 100 g-1 ash-free sample (CEC/TOM), and the average values using different grinding procedures for four different samples are as follows:

It is evident that for comparability and consistency, the same procedure should be adopted for subsequent batches, and the proposed method suggests pulverizing to 0.75 mm.

Cation exchange capacity

In the review by Mathur et al. (1993) the shortcomings of the CEC method for composts have been highlighted. The CEC of the mineral constituents of compost have been estimated as about 10 mEq 100 g-1 DM (Harada and Inoko, 1980), and that of the whole compost at the start, after 5 weeks, and at maturity, as 40, 70 and 80 mEq 100 g-1 DM (Harada et al., 1981). Others have found that different mature composts can vary from 27 to 83 mEq 100 g-1 DM (for domestic refuse plus sewage sludge, and pine bark plus sewage respectively), and from 72 to 144 for the same samples when expressed as mEq 100 g-1 organic matter (Jacas et al., 1987). The assessment of whether compost maturity has been reached is therefore only possible if the initial CEC has been determined for comparison. Jacas et al. (1987) describe a simplified unpublished method proposed by Inoko and Harada, an outline of which is given below.

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