Tuesday, May 13, 1997
University of California Workshop on Compost Use for Pest Management in Agriculture
Assessing Compost Maturity And Suitability For Agricultural Uses
T.K. Hartz
Department of Vegetable Crops
University of California
Davis, CA 95616
The composting of yard and landscape wastes is widely seen as an integral part of the municipal solid waste recycling programs; numerous compost facilities have begun operation throughout the state. Agriculture is projected as the end user of much of this composted green waste. However, there is considerable variation in composting technique, and duration, among commercial composting operations; there can also be seasonal and/or geographical variability in the original feedstocks used. This project was conducted to characterize the physiochemical and biological properties of CGW as affected by composting technique and duration. Specific objectives were:
Materials and Methods
Four composting facilities in central and southern California were studied; these operations differed substantially in their management practices, but all were using municipal yard and landscape waste as the main feedstock. At each site, two windrows were sampled at approximately 3 week intervals over a 11-15 week composting period. At each site one element of windrow management (turning, watering, temperature control, or feedstock blending) was manipulated differently between the two windrows studied.
The four composting facilities sampled were:
Each windrow was instrumented with continuously recording thermisters placed 45-60 cm (18-24 inches) from the outside of the windrow. At the end of the composting period the temperature data were analyzed to determine the cumulative exposure above 40, 50, 60 or 70° C (104, 122, 140 or 158° F). At each sampling date, composite samples of 15-20 liters of compost were collected from each windrow. Extracts (in 2N KCl) of these fresh samples were prepared for determination of ammonium (NH4) and nitrate (NO3) nitrogen concentration. The remainder of the samples were air-dried and stored for later determination of all other parameters.
After the collection of all compost samples from all sources was completed, the samples were screened through 12 mm (0.5 inch) mesh before a battery of evaluations was performed. Mineral N (NH4+ and NO3-) concentration was determined in 2N KCl extracts of dried compost. Electrical conductivity (EC) and pH were measured in 2:1 (deionized water:dry compost) extracts. Total N was determined by the combustion method of Sweeney (1989), total C by combustion and subsequent measurement by thermal electric conductivity. Total P was determined by a colorometric technique following microwave acid digestion (Kingston and Jassie, 1986), total K by atomic emission spectroscopy following 2% acetic acid extraction.
The presence of phytotoxic compounds was examined through a tomato seed bioassay. Air-dried compost (20g) and 100 ml deionized water were mixed and shaken for 2 hr. The solution was filtered, then diluted 2:1 (deionized water:compost extract). Three ml of diluted extract were used to wet filter papers in a petri dish; 10 seed of '3155' tomato were placed on the wetted paper. Three replicate dishes were prepared for each CGW sample. The dishes were incubated at 22° C (72° F) for 3 days, then rated for percent germination and length of radicle. These parameters were used to calculate a germination index, which compared the performance of seeds incubated in CGW extracts to those incubated in deionized water. The calculation was:
(% germ. in compost/% germ. in water)*(mean length in compost/mean length in water).
Weed seed survival in CGW was determined by a 6 week assay. CGW (2 liter volume/sample) was placed 2.5 cm (1 inch) deep in trays in a greenhouse at 25± 5° C (77± 9° F). The samples were kept moist throughout the period; germinating weeds were counted and identified by species.
Nitrogen mineralization/immobilization behavior was measured by controlled-environment aerobic incubation. Blends of 10% CGW/90% soil mix (50% silt loam/50% coarse sand) were moisture equilibrated under 25 centibar pressure, then incubated at constant moisture for 14 days at 30°C (86°F). The change in mineral N concentration (as measured in 2N KCl extracts) over the incubation period represented net mineralization/immobilization. There were 3 replicate samples per CGW sample. An N mineralization index was calculated, relating the change in mineral N concentration to that in unamended soil mix.
The suitability of CGW as a constituent of a potting medium was evaluated in a 6 week greenhouse experiment. Plugs of vinca (Vinca minor cv. 'Pink cooler') were planted in 5 cm (2 inch) diameter pots filled with a 1:1 blend (by volume) of CGW and perlite. There were 12 pots per CGW sample. The plants were fertilized once per week with a 100 PPM N solution (as 20-20-20 plus minor elements). After 6 weeks of growth in a greenhouse at 23± 3° C (73± 5° F) the plants were harvested and total top fresh and dry weights were determined. To help determine whether differences in plant growth were related to physical properties of the blend, air-filled porosity, bulk density and water-holding capacity were measured on triplicate samples by the method of Bragg and Chalmers (1988).
Results
Temperature profiles and windrow management:
A wide range of temperature profiles were encountered in the various windrows studied. Source 2 had by far the lowest temperatures (Table 1), by design; the Luebke method of composting emphasizes temperature control, achieved by manipulating the windrows through watering, turning, the addition of less active material (eg. straw), etc. At Source 2, windrow A (100% yardwaste) was dramatically hotter than windrow B, which contained only 40% yardwaste and 60% less easily degraded materials (aged manure, straw and soil).
Windrows from all other sources developed substantially higher temperatures, for more prolonged periods. Neither windrow turning frequency (Source 3) nor water management (Source 4) substantially affected windrow temperature. Manipulation of aeration within the compost bags (Source 1) did result in differential temperature profiles between bags; in bag 1 temperature >60°C (140°F) was limited to the first 20 days of composting while bag 2 continued to experience >60°C until day 70.
Physiochemical characteristics:
Initial physiochemical characteristics, and their change over time, were similar in compost from all sources (Table 2). Total N concentration ranged from 1.1 to 1.5% in the original feedstocks, and remained quite constant over the composting period. Rapid oxidation of carbon in the initial 3-9 weeks of composting resulted in rapidly decreasing C/N ratios over that period, the ratio stabilizing thereafter. Final C/N ratios varied from 12 to 16. Initial P and K concentration varied from 0.16 to 0.27 and 0.5% to 1.2%, respectively. K concentration was quite stable over the compost period, while P increased marginally.
The initially rapid oxidation of carbon was reflected in a substantial increase in % ash over the first 3-9 weeks of composting. Final ash content varied from 55-67% for compost containing 100% green waste; the higher ash content (76%) of Source 2, windrow B reflected the inclusion of soil in the initial feedstock. EC varied widely among sources, reflecting differences in windrow management, evaporative potential at each site, and salt content of the original feedstock (particularly evident with the inclusion of aged manure to windrow B at site 2). A consistent trend in pH was evident. All windrows began the composting period at or below pH 7.0, and rose steadily until pH neared or exceeded 8.0.
Mineral N concentration was highly variable, but an overall pattern was evident (Table 3). Extracts of fresh compost showed high NH4-N and very low NO3-N concentration during the early stages of composting. As composting proceeded, NH4-N levels generally declined, with NO3-N increasing substantially in a few late samples. Air-drying samples before extraction yielded quite different values, with NH4-N decreasing dramatically and NO3-N generally increasing.
N mineralization index also showed a clear trend. A high level of N immobilization was observed in samples from all sources collected early in the composting period. The degree of immobilization generally decreased over time, but nearly all samples continued to show some level of immobilization, even after more than 100 days of composting.
Few viable weed seeds survived the initial weeks of composting. In the greenhouse assay less than one germinating weed per 2 liter sample was observed in compost from Sources 1, 3 and 4. Approximately 3 weeds per sample were observed in compost from Source 2. A total of fourteen weed species were observed, but only California burclover (Medicago hispida Gaertn.), which accounted for more than 50% of all germinating weeds, occurred with any regularity.
Clear trends were apparent in the degree of phytotoxicity of compost extracts, as measured by the tomato seed germination index (Table 4). Although a statistically significant reduction in germination index was found only in composts from Sources 2 and 4, compost from all sources showed a trend toward increasing seedling vigor (decreasing phytotoxicity) with increased duration of composting; a germination index of 100 represented seedling vigor equal to those germinated in deionized water. Despite the 15:1 dilution employed, EC may have been a confounding factor in this assay, so an adjusted germination index was also calculated, based on the influence of osmotic potential on tomato seed germination reported by Dahal and Bradford (1990). The relative rank of compost samples using this adjusted index did not differ substantially from the original data.
The growth of vinca plants in compost:perlite potting medium showed a similar trend, with plant growth over the 6 week period increasing with increased duration of composting (Table 4). The physical properties of the media (air-filled porosity, water holding capacity, bulk density) were not strongly correlated with vinca growth. Thorough leaching to remove salts precluded EC as a factor. The influence of CGW on nitrogen nutrition was apparently not a significant factor in plant growth, given the similarity in tissue N concentration across CGW samples.
A correlation matrix of physiochemical characteristics of CGW samples and the corresponding biological parameters is presented in Table 5. In general, days of composting was more closely related to biological characteristics than cumulative hours above any threshold temperature. NH4-N concentration, whether extracted fresh or dry, was negatively correlated with phytotoxicity and N mineralization index, whereas NO3-N concentration was positively correlated with mineralization index and vinca growth. C/N ratio, although statistically correlated with N mineralization index, was a less effective predictor than mineral N variables or length of composting.
Discussion
Despite the very different techniques employed by the cooperating composters, compost from all windrows studied showed similar trends over time in both physiochemical and biological characteristics. Relatively rapid changes were evident through the first 6-9 weeks of composting, with subtle yet significant changes continuing throughout the period studied. At the end of the sampling period none of the windrows of 100% yard and landscape waste were 'mature' (biologically stable), as evidenced by their continued high temperature and immobilization of nitrogen. In current practice few commercial operations compost longer than the 3-4 month period monitored in this study; it is likely that the sale and utilization of biologically immature compost is common. There are no easily performed laboratory procedures that can document CGW maturity, but these are several good indicators of immaturity:
The significance of the degree of compost maturity varies with the intended end use:
Compost applied as a non-incorporated surface mulch is usually intended primarily to suppress weeds and conserve moisture. As such, the most significant requirement is that the material has gone through a thermophyllic phase sufficient for control of weed seeds or pathogenic fungi. In this study, acceptable weed control was accomplished in 3-6 weeks, with several hundred hours of exposure above 50° C (120° F). Based on exhaustive studies of soil solarization (passive solar heating), control of common plant pathogens would also be expected with that degree of heating (Katan and DeVay, 1991). It has been suggested that surface application of compost may, over time, suppress the activity of common soil-borne root pathogens such as Phytophthora spp. There is solid evidence of pathogen suppression in nursery media by 'mature' compost (Hoitink et al, 1993), but compelling evidence is lacking for a similar level of suppressive activity in typical field situations, particularly when the compost is not incorporated. It is also questionable whether very young, immature compost (which supports a radically different microbial community than stable, mature compost) would have significant disease suppressive potential.
Compost amendment of field soil is done for one or more of the following reasons: nutrient value, improved soil physical properties, and enhanced microbial activity. This study, and previous work (Hartz and Schrader, 1996), document that short-term release of N is unpredictable, with immature compost typically immobilizing N rather than releasing it. At normal application rates (<10 tons/acre) the degree of N immobilization would be modest, but at higher rates short-term effects on N availability could be substantial. When using CGW of uncertain maturity a substantial period (a month or more) between compost application and planting would be prudent. This would also allow any phytotoxic effects to be minimized, although at normal application rates phytotoxicity is unlikely to be a significant issue; incorporating 10 tons/acre in the top six inches represents an addition of only 1% by weight. In the long term, a program of repeated CGW applications will enhance soil fertility, but quantifying the economic value of this approach vis-à-vis traditional fertilization is problematic.
Improved soil structure and reduced surface crusting with application of organic amendments has been well documented, and could be expected with a program of CGW amendment, regardless of compost maturity stage. Overall microbial activity would be enhanced, even with immature compost (Hartz, unpublished data). The economic value of these changes in the soil environment would vary greatly, depending on original soil conditions and the crops to be produced. Substantially modifying soil moisture holding capacity or cation exchange capacity would require massive amendment and would be unlikely to be of economic benefit.
This is by far the highest value use of CGW, with the most exacting requirements. This study and others (Hartz and Burger, unpublished data) show significant differences in the performance of CGW samples of varying levels of maturity. Variable plant response appeared to be affected less by physical than biochemical properties. More mature compost has less NH4-N and phytotoxic organic compounds, and is less likely to immobilize significant amounts of N. Also, material that is still actively composting (>50° C, 120° F) is unlikely to have substantial disease suppressive ability (Hoitink et al, 1993). Production of woody plant material appears to be less sensitive to variability in CGW samples than bedding plant production. Following these steps will minimize the risks inherent in utilizing CGW in potting mix:
Acknowledgments: This project was supported by the Carlsbad Agricultural Grant Program of the Resource Conservation District of Greater San Diego County, and Davis Street Station for Material Recycling and Transfer.
Literature Cited
Bragg, N.C. and B.J. Chalmers. 1988. Interpretation and advisory applications of compost air-filled porosity (AFP) measurements. Acta Horticulturae 221:35-45.
Dahal, P. and K.J. Bradford. 1990. Effects of priming and endosperm integrity on seed germination rates of tomato genotypes. J. Experimental Botany 41:1441-1453.
Hartz, T.K. and W.L. Schrader. 1996. Suitability of municipal green waste compost for horticultural uses. HortScience 31 (in press).
Hoitink, H.A.J., M.J. Boehn and Y. Hadar. 1993. Mechanisms of suppression of soilborne plant pathogens in compost-amended substrates. p. 601-621. In: H.J. Hoitink and H.M. Keener (eds.). Science and engineering of compost: Design, environmental, microbiological and utilization aspects. The Ohio State University, Columbus, Ohio.
Katan, J. and J.E. DeVay. 1991. Soil solarization. CRC Press, Boca Raton, Florida.
Kingston, H.M. and L.B. Jassie. 1986. Microwave energy for acid decomposition at elevated temperatures and pressures using biological and botanical samples. Anal. Chem. 58:2534-2541.
Sweeney, R.A. 1989. Generic combustion method for determination of crude protein in feeds: collaborative study. J. Assoc. Off. Anal. Chem. 72:770-774.
Table 1. Cumulative hours of exposure above various threshold temperature during composting.
|
|
|
Cumulative hours above (°C) | |||
Source |
Windrow |
Days of composting |
40° |
50° |
60° |
70° |
1 |
A (moderate temperature) |
20 |
482 |
406 |
274 |
0 |
|
|
49 |
1174 |
773 |
274 |
0 |
|
|
84 |
1909 |
926 |
274 |
0 |
|
|
111 |
2550 |
1115 |
274 |
0 |
1 |
B (high temperature) |
26 |
526 |
430 |
214 |
17 |
|
|
43 |
895 |
804 |
418 |
17 |
|
|
64 |
1399 |
1192 |
647 |
17 |
|
|
96 |
2168 |
1696 |
661 |
17 |
2 |
A (100% green waste) |
10 |
216 |
180 |
130 |
0 |
|
|
33 |
590 |
452 |
197 |
0 |
|
|
54 |
773 |
526 |
197 |
0 |
|
|
74 |
976 |
526 |
197 |
0 |
|
|
82 |
1051 |
598 |
197 |
0 |
2 |
B (green waste/soil/ manure/straw blend) |
10 |
216 |
180 |
30 |
0 |
|
|
33 |
707 |
383 |
130 |
0 |
|
|
54 |
707 |
383 |
130 |
0 |
|
|
74 |
707 |
383 |
130 |
0 |
|
|
82 |
707 |
383 |
130 |
0 |
3 |
A (2 week turning interval) |
22 |
508 |
461 |
313 |
0 |
|
|
48 |
1129 |
1080 |
436 |
0 |
|
|
69 |
1595 |
1283 |
449 |
0 |
|
|
89 |
1828 |
1283 |
449 |
0 |
|
|
109 |
2070 |
1283 |
449 |
0 |
3 |
B (4 week turning interval) |
22 |
509 |
504 |
360 |
8 |
|
|
48 |
1132 |
1055 |
617 |
15 |
|
|
69 |
1550 |
1153 |
617 |
15 |
|
|
89 |
1776 |
1153 |
617 |
15 |
|
|
109 |
2012 |
1153 |
617 |
15 |
4 |
A (normal watering) |
21 |
493 |
452 |
353 |
88 |
|
|
42 |
973 |
898 |
536 |
101 |
|
|
63 |
1453 |
1282 |
685 |
104 |
|
|
84 |
1837 |
1446 |
691 |
104 |
|
|
105 |
2309 |
1699 |
722 |
104 |
4 |
B (extra watering) |
21 |
455 |
442 |
370 |
54 |
|
|
42 |
959 |
934 |
696 |
96 |
|
|
63 |
1410 |
1318 |
834 |
96 |
|
|
84 |
1742 |
1318 |
834 |
96 |
|
|
105 |
2174 |
1520 |
834 |
96 |
Table 2. Physiochemical characteristics of compost throughout the composting period.
|
|
|
% |
| ||||||
Compost source |
Windrow |
Days of composting |
N |
P |
K |
Ash |
C/N ratio |
EC |
pH | |
1 |
A (moderate temperature) |
0 |
1.1 |
0.16 |
0.8 |
37 |
28 |
6.9 |
6.5 | |
|
|
20 |
1.6 |
0.2 |
0.9 |
51 |
16 |
7.2 |
7.3 | |
|
|
49 |
1.5 |
0.22 |
0.8 |
56 |
14 |
6.3 |
7.4 | |
|
|
84 |
1.6 |
0.24 |
0.8 |
51 |
15 |
5.5 |
7.6 | |
|
|
111 |
1.6 |
0.25 |
0.7 |
56 |
14 |
4.5 |
7.5 | |
|
|
118 |
1.6 |
0.19 |
0.9 |
67 |
14 |
10.7 |
7.8 | |
1 |
B (high temperature) |
0 |
1.3 |
0.16 |
0.9 |
33 |
26 |
7 |
6.6 | |
|
|
26 |
1.5 |
0.22 |
1.0 |
49 |
18 |
7.4 |
7.1 | |
|
|
43 |
1.7 |
0.24 |
1.0 |
46 |
15 |
6.6 |
7.4 | |
|
|
64 |
1.6 |
0.22 |
0.9 |
54 |
14 |
6.3 |
7.4 | |
|
|
96 |
1.9 |
0.25 |
0.9 |
55 |
13 |
6.5 |
7.3 | |
|
|
103 |
1.7 |
0.24 |
0.7 |
59 |
15 |
4.1 |
7.6 | |
2 |
A (100% green waste) |
0 |
1.6 |
0.21 |
1.0 |
26 |
23 |
10.2 |
5.8 | |
|
|
10 |
1.4 |
0.23 |
1.1 |
37 |
21 |
6.8 |
7.3 | |
|
|
33 |
1.6 |
0.27 |
1.2 |
51 |
15 |
9.1 |
8.3 | |
|
|
54 |
1.5 |
0.25 |
1.1 |
54 |
16 |
9.8 |
8.4 | |
|
|
74 |
1.5 |
0.3 |
1.2 |
58 |
14 |
11.2 |
8.3 | |
|
|
82 |
1.5 |
0.24 |
1.1 |
55 |
16 |
11.1 |
8.3 | |
2 |
B (green waste/soil/ manure/straw blend) |
0 |
1.1 |
0.17 |
0.9 |
45 |
21 |
40 |
6.5 | |
|
|
10 |
0.9 |
0.28 |
1.3 |
66 |
17 |
18.4 |
8 | |
|
|
33 |
1.0 |
0.26 |
1.2 |
71 |
13 |
24.2 |
8.2 | |
|
|
54 |
1.1 |
0.3 |
1.3 |
74 |
11 |
25.1 |
8.3 | |
|
|
74 |
1.1 |
0.26 |
1.2 |
76 |
12 |
23.2 |
8.3 | |
|
|
82 |
1.0 |
0.25 |
1.4 |
76 |
12 |
25 |
8.2 | |
3 |
A (2 week turning interval) |
0 |
1.1 |
0.18 |
0.5 |
53 |
24 |
5.4 |
6.6 | |
|
|
22 |
1.3 |
0.19 |
0.6 |
52 |
19 |
5 |
6.9 | |
|
|
48 |
1.2 |
0.18 |
0.6 |
53 |
20 |
5 |
7.1 | |
|
|
69 |
1.3 |
0.22 |
0.5 |
57 |
17 |
4 |
7.5 | |
|
|
89 |
1.2 |
0.19 |
0.5 |
61 |
17 |
3.6 |
7.7 | |
|
|
109 |
1.4 |
0.2 |
0.5 |
56 |
16 |
3.6 |
7.8 | |
3 |
B (4 week turning interval) |
0 |
1.1 |
0.18 |
0.5 |
53 |
24 |
5.4 |
6.6 | |
|
|
22 |
1.1 |
0.18 |
0.5 |
49 |
21 |
4.4 |
7 | |
|
|
48 |
1.3 |
0.17 |
0.6 |
47 |
22 |
4.3 |
7 | |
|
|
69 |
1.1 |
0.21 |
0.6 |
59 |
18 |
4.2 |
7.4 | |
|
|
89 |
1.3 |
0.2 |
0.6 |
57 |
15 |
4.9 |
7.7 | |
|
|
109 |
1.3 |
0.2 |
0.6 |
61 |
16 |
4.9 |
7.8 | |
4 |
A (normal watering) |
0 |
1.5 |
0.27 |
1.2 |
41 |
20 |
11 |
6.9 | |
|
|
21 |
1.4 |
0.24 |
1.1 |
47 |
18 |
12.9 |
7 | |
|
|
42 |
1.5 |
0.28 |
1.2 |
53 |
16 |
14.7 |
7.3 | |
|
|
63 |
1.4 |
0.26 |
0.9 |
66 |
13 |
14.5 |
7.7 | |
|
|
84 |
1.6 |
0.29 |
1.0 |
62 |
12 |
14.7 |
8 | |
|
|
105 |
1.6 |
0.28 |
1.1 |
62 |
13 |
16 |
7.9 | |
4 |
B (extra watering) |
0 |
1.5 |
0.24 |
1.2 |
37 |
22 |
11 |
7 | |
|
|
21 |
1.7 |
0.29 |
1.3 |
39 |
18 |
13.1 |
7.3 | |
|
|
42 |
1.5 |
0.26 |
1.0 |
48 |
18 |
12.3 |
6.8 | |
|
|
63 |
1.5 |
0.28 |
0.9 |
63 |
12 |
14 |
8 | |
|
|
84 |
1.4 |
0.29 |
1.0 |
61 |
13 |
15.4 |
8 | |
|
|
105 |
1.3 |
0.28 |
1.1 |
64 |
12 |
16.9 |
8 |
Table 3. Effects of source, management, and duration of composting on compost mineral N concentration (PPM)
and N mineralization index.
|
|
|
NH4-N |
|
NO3-N |
| ||
Source |
Windrow |
Days of composting |
Fresh |
Dry |
|
Fresh |
Dry |
N mineralization indexz |
1 |
A (moderate temperature) |
20 |
110 |
18 |
|
5 |
12 |
-20 |
|
|
49 |
13 |
6 |
|
4 |
2 |
-23 |
|
|
84 |
107 |
14 |
|
16 |
35 |
-23 |
|
|
111 |
67 |
20 |
|
42 |
77 |
-5 |
|
|
118 |
46 |
8 |
|
152 |
161 |
-4 |
1 |
B (high temperature) |
26 |
328 |
48 |
|
4 |
12 |
-25 |
|
|
43 |
181 |
377 |
|
3 |
40 |
-24 |
|
|
64 |
72 |
13 |
|
164 |
38 |
-10 |
|
|
96 |
74 |
14 |
|
162 |
209 |
5 |
|
|
103 |
18 |
11 |
|
21 |
12 |
-5 |
2 |
A (100% green waste) |
10 |
|
27 |
|
|
2 |
-18 |
|
|
33 |
|
8 |
|
|
5 |
-20 |
|
|
54 |
|
8 |
|
|
12 |
-20 |
|
|
74 |
|
7 |
|
|
15 |
-10 |
|
|
82 |
|
7 |
|
|
15 |
|
2 |
B (green waste/soil/ manure/straw blend) |
10 |
|
15 |
|
|
2 |
-17 |
|
|
33 |
|
7 |
|
|
30 |
-15 |
|
|
54 |
|
5 |
|
|
10 |
-13 |
|
|
74 |
|
6 |
|
|
20 |
-8 |
|
|
82 |
|
15 |
|
|
28 |
|
3 |
A (2 week turning interval) |
|
441 |
121 |
|
8 |
1 |
-26 |
|
|
22 |
126 |
12 |
|
2 |
42 |
-19 |
|
|
48 |
34 |
13 |
|
2 |
61 |
-20 |
|
|
69 |
158 |
10 |
|
9 |
18 |
-16 |
|
|
89 |
96 |
11 |
|
4 |
13 |
-17 |
|
|
109 |
|
|
|
|
|
|
3 |
B (4 week turning interval) |
22 |
226 |
18 |
|
2 |
1 |
-17 |
|
|
48 |
100 |
11 |
|
4 |
93 |
-18 |
|
|
69 |
47 |
14 |
|
4 |
18 |
-20 |
|
|
89 |
153 |
9 |
|
7 |
35 |
-14 |
|
|
109 |
108 |
8 |
|
4 |
55 |
-17 |
4 |
A (normal watering) |
21 |
245 |
49 |
|
5 |
20 |
-29 |
|
|
42 |
265 |
147 |
|
4 |
1 |
-49 |
|
|
63 |
102 |
32 |
|
2 |
7 |
-23 |
|
|
84 |
117 |
10 |
|
14 |
19 |
-13 |
|
|
105 |
602 |
15 |
|
7 |
89 |
-12 |
4 |
B (extra watering) |
21 |
170 |
48 |
|
7 |
28 |
-27 |
|
|
42 |
511 |
377 |
|
15 |
1 |
-49 |
|
|
63 |
76 |
13 |
|
6 |
21 |
-21 |
|
|
84 |
268 |
14 |
|
9 |
25 |
-18 |
|
|
105 |
182 |
11 |
|
55 |
121 |
-14 |
z
change in mineral N concentration (PPM) during a 14-day incubation of a 10% compost/90% soil blend relative tounamended soil; negative numbers indicate net N immobilization.
Table 4. Effect of source, management and duration of composting on compost phytotoxicity and suitability as a nursery medium.
|
|
|
Phytotoxicityz |
|
Vinca growth (g/plant) |
|
Media physical characteristics | |||||||||||||||
Compost source |
Windrow |
Days of composting |
Raw |
Adjusted |
|
Fresh wt. |
Dry wt. |
Vinca tissue % N |
Porosity (% volume) |
Water holding (% volume) |
Bulk density (g/ml) | |||||||||||
1 |
A (moderate temperature) |
0 |
82 |
89 |
|
|
|
|
|
|
| |||||||||||
|
|
20 |
75 |
82 |
|
2.0 |
0.27 |
4.6 |
0.15 |
0.48 |
0.19 | |||||||||||
|
|
49 |
93 |
99 |
|
2.3 |
0.32 |
4.4 |
0.15 |
0.51 |
0.21 | |||||||||||
|
|
84 |
109 |
115 |
|
1.8 |
0.30 |
4.4 |
0.14 |
0.46 |
0.21 | |||||||||||
|
|
111 |
106 |
111 |
|
2.1 |
0.29 |
4.5 |
0.13 |
0.46 |
0.23 | |||||||||||
|
|
118 |
93 |
104 |
|
2.6 |
0.38 |
4.3 |
0.13 |
0.46 |
0.26 | |||||||||||
1 |
B (high temperature) |
0 |
67 |
74 |
|
|
|
|
|
|
| |||||||||||
|
|
26 |
75 |
82 |
|
1.9 |
0.27 |
4.5 |
0.15 |
0.49 |
0.19 | |||||||||||
|
|
43 |
80 |
87 |
|
2.0 |
0.26 |
4.6 |
0.14 |
0.49 |
0.21 | |||||||||||
|
|
64 |
87 |
93 |
|
2.4 |
0.33 |
4.4 |
0.11 |
0.52 |
0.22 | |||||||||||
|
|
96 |
107 |
114 |
|
2.8 |
0.37 |
4.6 |
0.10 |
0.52 |
0.23 | |||||||||||
|
|
103 |
108 |
112 |
|
2.4 |
0.38 |
4.5 |
0.13 |
0.46 |
0.22 | |||||||||||
2 |
A (100% green waste) |
0 |
13 |
23 |
|
|
|
|
|
|
| |||||||||||
|
|
10 |
57 |
64 |
|
0.9 |
0.15 |
4.0 |
0.24 |
0.35 |
0.2 | |||||||||||
|
|
33 |
51 |
60 |
|
1.4 |
0.20 |
4.2 |
0.18 |
0.45 |
0.23 | |||||||||||
|
|
54 |
49 |
59 |
|
1.3 |
0.16 |
4.3 |
0.15 |
0.47 |
0.28 | |||||||||||
|
|
74 |
82 |
93 |
|
1.6 |
0.21 |
4.2 |
0.10 |
0.5 |
0.33 | |||||||||||
|
|
82 |
89 |
100 |
|
1.7 |
0.22 |
4.2 |
0.09 |
0.53 |
0.34 | |||||||||||
2 |
B (green waste/soil/ manure/straw blend) |
0 |
36 |
76 |
|
|
|
|
|
|
| |||||||||||
|
|
10 |
55 |
73 |
|
1.5 |
0.19 |
4.4 |
0.13 |
0.47 |
0.28 | |||||||||||
|
|
33 |
81 |
105 |
|
1.2 |
0.16 |
4.3 |
0.09 |
0.45 |
0.33 | |||||||||||
|
|
54 |
25 |
50 |
|
1.4 |
0.17 |
4.2 |
0.14 |
0.49 |
0.39 | |||||||||||
|
|
74 |
76 |
100 |
|
1.5 |
0.20 |
4.2 |
0.13 |
0.53 |
0.46 | |||||||||||
|
|
82 |
90 |
115 |
|
1.4 |
0.17 |
4.4 |
0.14 |
0.54 |
0.47 | |||||||||||
3 |
A (2 week turning interval) |
0 |
|
|
|
|
|
|
|
|
| |||||||||||
|
|
22 |
78 |
83 |
|
1.9 |
0.26 |
4.5 |
0.13 |
0.49 |
0.19 | |||||||||||
|
|
48 |
87 |
92 |
|
2.0 |
0.29 |
4.6 |
0.09 |
0.53 |
0.23 | |||||||||||
|
|
69 |
90 |
94 |
|
2.6 |
0.37 |
4.5 |
0.14 |
0.46 |
0.26 | |||||||||||
|
|
89 |
123 |
126 |
|
2.8 |
0.38 |
4.5 |
0.13 |
0.43 |
0.27 | |||||||||||
|
|
109 |
116 |
120 |
|
2.7 |
0.39 |
4.3 |
0.14 |
0.49 |
0.28 | |||||||||||
3 |
B (4 week turning interval) |
0 |
|
|
|
|
|
|
|
|
| |||||||||||
|
|
22 |
105 |
110 |
|
1.9 |
0.25 |
4.7 |
0.13 |
0.49 |
0.21 | |||||||||||
|
|
48 |
90 |
94 |
|
1.9 |
0.26 |
4.6 |
0.17 |
0.41 |
0.22 | |||||||||||
|
|
69 |
83 |
87 |
|
2.7 |
0.35 |
4.5 |
0.12 |
0.49 |
0.25 | |||||||||||
|
|
89 |
96 |
100 |
|
2.3 |
0.30 |
4.5 |
0.14 |
0.47 |
0.27 | |||||||||||
|
|
109 |
106 |
110 |
|
2.8 |
0.39 |
4.5 |
0.10 |
0.52 |
0.26 |
Table 4. Continued | ||||||||||||
|
|
|
Phytotoxicityz |
|
Vinca growth (g/plant) |
|
Media physical characteristics | |||||
Compost source |
Windrow |
Days of composting |
Raw |
Adjusted |
|
Fresh wt. |
Dry wt. |
Vinca tissue % N |
Porosity (% volume) |
Water holding (% volume) |
Bulk density (g/ml) | |
4 |
A (normal watering) |
0 |
51 |
62 |
|
|
|
|
|
|
| |
|
|
21 |
22 |
35 |
|
1.4 |
0.20 |
4.4 |
0.14 |
0.5 |
0.19 | |
|
|
42 |
28 |
43 |
|
1.6 |
0.23 |
4.3 |
0.17 |
0.46 |
0.19 | |
|
|
63 |
59 |
74 |
|
2.4 |
0.32 |
4.5 |
0.11 |
0.52 |
0.23 | |
|
|
84 |
52 |
67 |
|
2.5 |
0.33 |
4.6 |
0.08 |
0.53 |
0.25 | |
|
|
105 |
53 |
69 |
|
2.6 |
0.38 |
4.4 |
0.07 |
0.59 |
0.26 | |
4 |
B (extra watering) |
0 |
48 |
59 |
|
|
|
|
|
|
| |
|
|
21 |
36 |
49 |
|
1.6 |
0.22 |
4.4 |
0.17 |
0.41 |
0.22 | |
|
|
42 |
30 |
42 |
|
1.6 |
0.24 |
4.3 |
0.17 |
0.45 |
0.18 | |
|
|
63 |
33 |
47 |
|
2.1 |
0.29 |
4.4 |
0.11 |
0.53 |
0.24 | |
|
|
84 |
56 |
71 |
|
2.2 |
0.32 |
4.6 |
0.09 |
0.55 |
0.23 | |
|
|
105 |
45 |
62 |
|
2.4 |
0.30 |
4.5 |
0.10 |
0.55 |
0.22 |
z
phytotoxicity expressed as germination index of tomato seed in compost extract; higher numbers represent less phytotoxicity. 'Adjusted' values represent correctionfor EC of compost extract.
Table 5. Correlation matrix of biological and physiochemical compost characteristics.
|
Phytotoxicityz |
Adjusted Phytotoxicityz |
N mineralization index |
Vinca dry wt. |
Length of composting (days) |
.45* |
.48* |
.49* |
.62* |
Hrs > 40°C |
.17 |
.15 |
.15 |
.52* |
Hrs > 50°C |
.26 |
.22 |
.18 |
.85* |
Hrs > 60°C |
-.09 |
-.15 |
-.12 |
.67* |
NH4-N (fresh) |
-.47* |
-.47* |
-.41* |
-.27 |
NH4-N (dry) |
-.37* |
-.41* |
-.72* |
-.12 |
NO3-N (fresh) |
.20 |
.23 |
.51* |
.25 |
NO3-N (dry) |
.25 |
.26 |
.51* |
.41* |
Total N (%) |
-.02 |
-.11 |
-.06* |
.27 |
C/N ratio |
.12 |
-.01 |
-.37* |
-.09 |
Media porosity |
|
|
|
-.29 |
Media water holding capacity |
|
|
|
.36* |
Media bulk density |
|
|
|
-.31 |
*correlation significant at the 5% level of probability (p < .05, n=40)
z
phytotoxicity expressed as germination index of tomato seed in compost extract; higher numbers representless phytotoxicity. 'Adjusted' values represent correction for EC of compost extract.