The effect of duration of composting on compost density and the yield of mushrooms

Scientia Horticulturae, 27 (1985) 21--31

21

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

THE EFFECT OF DURATION OF COMPOSTING ON COMPOST DENSITY AND THE YIELD OF MUSHROOMS

PHYLLIS E. RANDLE and P.B. FLEGG

Glasshouse Crops Research Institute, Littlehampton, West Sussex BN1 7 6LP (Gt. Britain) (Accepted for publication 15 May 1985)

ABSTRACT Randle, P.E. and Flegg, P.B., 1985. The effect of duration of composting on compost density and the yield of mushrooms. Scientia Hortic., 27 : 21--31. When straw was chopped at the start of composting, the bulk density of straw-based mushroom compost increased and there was a corresponding reduction in volume compared with normal (unchopped) straw. Prolonging the duration of composting also increased bulk density and reduced the weight of compost produced per tonne of straw. Mushroom yields per compost volume increased with increasing bulk density and production efficiency, i.e. the weight of mushrooms per unit compost dry matter was not significantly different between composts. Bulk density and porosity of mushroom composts and the relative effects of bulk density and depth of compost on mushroom yields are discussed.

Keywords: bulk-density; compost; mushroom; yield.

INTRODUCTION

Experiments on the effect of the duration of composting on the yield of compost per tonne of straw and the yield of mushrooms (Flegg and Randle, 1980) and on the optimum initial nitrogen content of compost stacks (Flegg and Randle, 1981a) led to the development of a unifying concept of mushroom compost preparation (Flegg and Randle, 1981b). Through the concept, a wide range of mushroom composting methods can be related on the basis of the duration of Stage I (in the stack) and Stage II (in a controlled environment). With increasing duration of the total composting period, there is increasing loss of dry matter and water, and a higher initial nitrogen content can be tolerated in the mixture of materials to be composted. Another factor which our concept suggests will increase with longer duration of composting is the bulk density. This paper describes a series of experiments to examine the relationship between duration of composting and compost bulk density, and their effects on mushroom yields.

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© 1985 Elsevier Science Publishers B.V.

22 MATERIALS AND METHODS

The composting facilities for these experiments were the same as those described by Flegg and Randle (1980) in a previous series, and the synthetic compost was similar. The formulation used throughout was: kg Wheat straw Deep litter chicken manure "Sporavite" Gypsum Water (approx.)

1000 300 150 60 5000

The deep-litter chicken manure was a mixture of w o o d shavings, faeces and feathers. Sporative, (supplied by R u m e n c o Ltd. of Burton-on-Trent) is a fibrous meal containing 25% molasses. The theoretical nitrogen content of this formulation was about 1.5% of the dry matter. The volume of water was adjusted to give about 75% moisture, on a fresh weight basis, at filling. In addition to the "normal" composting procedure for GCRI F2 Synthetic Compost (Randle, 1974), some of the straw was chopped with a forage harvester, which reduced individual straws to less than 10 cm in length. After preliminary trials (Experiments 1 and 2) in which only 33 or 66% of the total straw requirement was chopped, it was decided to proceed in the main series of experiments by comparing stacks of 100% chopped straw and stacks of unchopped {normal) straw. Stage I of composting was terminated at 3, 13 or 23 days, as described for previous c o m p o s t experiments (Flegg and Randle, 1981a), and the use of normal or chopped straw gave 6 treatments which were replicated 4 times to give a total of 24 compost stacks. The compost from each stack was filled into a separate peak-heat room for Stage II. Because of the limitations of the composting area and the peak-heat facilities, there were 2 normal and 2 chopped-straw stacks in each experiment. Six successive experiments formed 3 pairs, with either 3- and 13-, 3- and 23- or 13- and 23-day composts, to give the total 4 replicates. This was treated as a replicated balanced incomplete block design with the factorial treatment structure shown in Table I. According to the duration of Stage I and whether the straw was chopped, or not, between 0.5 and 1.0 tonne of straw was required for each stack. The total weight of materials used in each stack was recorded. The volumes of the stacks were measured daily during Stage I. Composting schedules were planned so that the four c o m p o s t stacks in each experiment were transferred for Stage II in the peak-heat chambers within 4 days of each other after 7, 9 or 11 turns for 3-, 13- or 23-day composts, respectively. Stage II of composting followed previous practice (Flegg and Randle, 1980}. There were 32 trays of compost, stacked 4 high, in each chamber.

23 TABLE I

Experimental design: replicated balanced incomplete b l o c k w i t h factorial treatment s t r u c t u r e : 3 c o m p o s t s , 2 straw t y p e s ( n o r m a l (N) or c h o p p e d (C)) a n d 4 replicates Experiment

Duration of Stage I (days)

No.

3

3 4 5 6 7 8

13

N

C

N N N

C C C

N

C

N

N N N N

23 C

C C C C

N

C

N N

C C

N N

C C

The trays, 90 × 60 cm and 18 cm deep, were filled manually and the compost was piled to 30 cm. When free ammonia in the compost was less than 20 mg 1-1, the compost was cooled to 25°C and spawned with 'Darlington 649' strain. At spawning, the identity of the compost from each tray was maintained by re-filling tray-for-tray on the spawning-line as the compost was delivered from the spinner. The depth of compost was measured in each tray after pressing for 5 s at a maximum pressure of 0.84 kg cm-2. The trays were re-stacked for spawn-running in the same relative positions within a stack of 4 trays as during Stage II of the composting. Because of staggered filling dates and differing durations of Stage II, the composts were not necessarily spawned on the same day, but after about 2 weeks of spawn-running at 25°C, all the trays were cased on the same day with a mixture of moist sphagnum peat and lump chalk. To obtain comparable yields from all the composts, it was necessary to adjust the depth of compost to 18 cm before the casing was added. Allowance was made for any compost removed when the yields of mushrooms were calculated. After casing, the trays were transferred to a cropping room and arranged in 4 randomised blocks of 32 trays each. The water content of the c o m p o s t was determined in samples taken during Stage I and at both filling and spawning. During a cropping period of 4 weeks, the weights of mushrooms were recorded from each tray. Compost and mushroom weights and measurements made during the experiments provided data to determine: (1) changes in fresh weight during Stage I and Stage II of composting; (2) change in c o m p o s t volume during Stage I; (3) bulk density (kg m -3) of the c o m p o s t at filling and spawning; (4) yield of mushrooms per unit fresh weight and per unit volume of spawned compost; (5) production efficiency (PE), i.e. fresh weight of mushrooms per 100 g c o m p o s t dry matter.

24 TABLE II Weight of compost at filling and spawning as % materials in the original stacks for normal and chopped straw after composting for 3, 13 or 23 days in Stage I. Means of 4 experiments are shown: N = normal, C = chopped straw Stage I (days)

At filling

At spawning

N

C

Means

N

C

Means

3 13 23

84.5 49.0 47.6

80.4 54.9 48.5

82.4 51.9 48.0

56.2 34.6 36.8

56.4 41.1 38.0

56.3 37.8 37.4

Means

60.4

61.3

42.5

45.2

Standard error of differences between means (SED)

Reps. SED

Duration

Duration

8 3.5***

8 5.1"**

The data were statistically analysed to test for significant differences between c o m p o s t treatments. RESULTS

Y i e l d o f c o m p o s t . - - Table II shows the weight of c o m p o s t remaining as a percentage of the original raw materials for the six composts, that is 3-, 13- or 23-days for Stage I with normal or chopped straw. Chopping the straw did n o t affect the weight of compost produced from the raw materials. The respective amounts remaining for normal and chopped straw were 60.4 and 61.3% at filling and 42.5 and 45.2% at spawning. There were some significant effects of the duration of Stage I. After 3 days 82% remained, and at 13 days the original materials were reduced to 52%, but further loss was comparatively small and 48% remained even after composting for 23 days. The average times taken to complete Stage II were 9, 10 and 12 days for 3-, 13- and 23-day composts, respectively, and Table II shows the final yield of compost to spawn. The 3-day composts yielded 56% of the weight of the original materials, which was significantly more than that obtained from the 13- and 23-day composts. The actual yields of compost to spawn per tonne of straw for 3-, 13- and 23-day composts were 3.2, 2.0 and 1.9 tonnes, respectively. V o l u m e o f c o m p o s t . - - Figure 1 illustrates the change in the volume of c o m p o s t which occurred during 23 days in Experiment 6 in stacks with

25

30

-

•

Normal straw

o

Chopped straw Stack turned

Oo

20

--

°°

0•

00 o

E=

0

>

10 --

0

• 0 O•

000 • OOo •

o o

OO

OOoooooo OO o,o,o. 0

fftt

~

I

o o

5

t

I

10

I

f

15

if 20

I 25

Day number

Fig. 1. Volume (m 3) of 23-day compost stacks in Experiment 6, with either normal or chopped straw, measured daily and after each turn during Stage I.

normal and chopped straw. The mean volume changes of all the composts in Stage I are shown in Table III. Because of the rapid early change in volume, the data do n o t fit a normal distribution and were transformed to loge for analysis of variance. It was found that the significant effect on volume between normal and chopped straw on Day 0, when the mean volumes per tonne of straw were 25.2 and 19.8 m 3, respectively, was mainTABLE III Volume of compost (m 3) per tonne of normal or chopped straw at the end of Day 0 and at filling after composting for 3, 13 or 23 days in Stage I. Means of 4 experiments are shown. N = normal, C = chopped straw Stage I (days)

Day 0

At filling

N

C

N

C

Means

3 13 23

27.49 24.41 23.57

20.31 19.98 19.18

15.29 7.99 6.39

11.13 7.69 5.19

13.21 7.84 5.79

Means

25.16

19.82

9.89

8.00

Standard error of difference between means (SED) Straw

Duration

12 8 1.03"** 1.05"**

Interaction 4 1.06" 1.06"

Reps. within expts. between expts.

26 tained until filling, w h e n the m e a n volumes were and 8.0 m 3 for c h o p p e d - s t r a w c o m p o s t . At filling, post stacks were significantly d i f f e r e n t according I, and t h e r e were significant i n t e r a c t i o n s b e t w e e n for t h e 3- and 23-day c o m p o s t s .

9.9 m 3 for normal-straw the volumes o f the comt o the d u r a t i o n o f Stage straw-type and d u r a t i o n

TABLE IV Bulk density (kg m-3) of compost in the stack at filling and after pressing in the trays at spawning prepared with either normal (N) or chopped (C) straw and composted for 3, 13 or 23 days in Stage I. Means of 4 experiments are shown Stage I At filling (days) N C

At spawning Means

N

C

Means

3 13 23

310 411 360 339 385 362 380 485 432

384 442 440 521 542 627

Means

343 427

455

413 480 584

530

Standard errors of differences between means (SED) Straw Reps.

12

SED

16"**

Duration 8

22**

Straw Duration 12

32*

8

45**

- - T h e bulk densities o f t h e c o m p o s t s at filling, s h o w n in Table IV, are values calculated f r o m the m e a s u r e d volumes o f t h e stacks and t h e t o t a l weight o f c o m p o s t at filling. T h e m e a n bulk densities for normal- and c h o p p e d - s t r a w c o m p o s t s were 343 and 427 kg m -3, respectively; a d i f f e r e n c e o f 24% which was significant at 0.1% probability. T h e m e a n bulk density o f t h e 23-day c o m p o s t s was significantly d i f f e r e n t f r o m 3- and 13-day c o m p o s t at 1.0% p r o b a b i l i t y . T h e variation in b u l k density f r o m t o p t o b o t t o m o f the c o m p o s t stacks was n o t d e t e r m i n e d , b u t after spawning, w h e n t h e c o m p o s t had b e e n m i x e d and pressed in t h e trays, t h e b u l k d e n s i t y was assumed t o be u n i f o r m . Bulk density at spawning was derived f r o m t h e m e a s u r e d weight and d e p t h o f c o m p o s t in each tray. Table IV shows t h a t t h e bulk d e n s i t y increased significantly with t h e d u r a t i o n o f c o m p o s t i n g . C h o p p e d - s t r a w c o m p o s t had a higher bulk d e n s i t y (530 kg m -3) t h a n normal-straw compost (455 kg m - 3 ) ; a d i f f e r e n c e (16%) which was significant at 5% probability.

Bulk density of compost.

W a t e r in t h e c o m p o s t . - - T h e r e q u i r e d m o i s t u r e c o n t e n t o f t h e c o m p o s t at filling was 75% o f t h e fresh weight. Table V shows t h a t this was achieved

27 TABLE V Moisture content (as % fresh weight) of compost at filling and spawning prepared with either normal (N) or chopped (C) straw and composted for 3, 13 or 23 days in Stage I. Means of 4 experiments are shown Stage I

At filling

At spawning

(days) N

C

Means

N

C

Means

3 13 23

78.3 74.6 74.4

77.8 74.5 74.7

78.0 74.5 74.5

73.2 69.5 67.9

73.6 69.6 69.2

73.4 69.5 68.8

Means

75.8

75.7

70.2

70.8

except in the 3-day composts, where the shorter composting time did not allow the usual adjustment through the water loss which occurs in a longer duration of Stage I. However, the mean moisture contents were similar for normal- and chopped-straw compost, about 76% at filling and 70% at spawning, and although the mean moisture contents at spawning decreased as the duration of composting increased, the differences between the means were not significant. A comparison of moisture content and bulk density at spawning showed that there was not a significant correlation, so that although it is a contributing factor to bulk density, other physical properties appeared to over-ride the moisture content of compost alone. Y i e l d o f m u s h r o o m s . - - The yields of mushrooms are shown in Table VI. When expressed as kg mushrooms per tonne of spawned compost, there was no difference between the mean yields from normal- and choppedstraw composts, but the yield from 13-day composts (152 kg tonne -1) was significantly greater, at 1.0% probability, than from the 3- and 23-day composts, which yielded 119 and 114 kg tonne -1, respectively. The yields of mushrooms were also calculated per litre of compost. This volume can be visualised as a 10-cm cube, although in practice the depth of compost would be 15--30 cm. Table VI shows that the 3-day c o m p o s t yielded significantly fewer g 1-' than 13- and 23-day composts. Yields of mushrooms calculated in g 1-1 of compost gave a direct comparison with bulk density (g 1-1) of the compost. Figure 2 shows a significant correlation between compost bulk density and weight of mushrooms produced per litre of compost. There was a difference of 18% in weight of mushrooms per litre of c o m p o s t between normal- and chopped-straw compost, the m e a n s being 57 and 68 g 1-1 , respectively. This result is consistent with the higher bulk density of the chopped-straw compost at spawning shown in Table IV. Production efficiency (PE), i.e. yield of mushrooms per unit dry weight

28 T A B L E VI Yield o f m u s h r o o m s , kg t o n n e -~ of spawned c o m p o s t , g 1-1 of spawned c o m p o s t , and g per 100 g of c o m p o s t dry m a t t e r ( p r o d u c t i o n efficiency, PE) in 4 weeks from compost prepared with normal (N) or chopped (C) straw and c o m p o s t e d for 3, 13 or 23 days in Stage I. Means of 4 experiments are shown Stage I (days)

kg tonne-~

PE

g 1-'

N

C

Means

N

C

Means

N

C

Means

3 13 23

125 149 110

114 155 118

119 152 114

47 67 58

49 79 76

48 73 67

47 48 36

43 50 41

45 49 38

Means

128

129

57

68

44

45

Standard errors of differences b e t w e e n means (SED)

Reps. SED

100

Duration

Duration

8 11"**

8 8.3*

-

0 0 0 o

0

0

80

E 0 0

o

~. 6o E 0

0

~

0

0 0

0

0

0

E 4O

~ o

°

I

l

I

I

l

I

200

300

400

500

600

700

Bulk density, g compost/litre

Fig. 2. Bulk density (g c o m p o s t per litre of the m u s h r o o m bed) and yield (g of mushr o o m s per litre of c o m p o s t ) after 4 weeks cropping, r = 0.62; significant w h e n P = 1.0%. y = 12.61 + 0.10x.

29 of compost, is an assessment of the nutritional value of the dry matter of the substrate. In these trials, there were no significant differences between the production efficiencies of the compost, which suggests that differences in mushroom yields, when expressed in other ways, were related to physical differences between the composts. DISCUSSION A given volume of compost contains water, dry matter and air. The bulk density depends partly on the physical structure of the organic material and its moisture content, and is inversely related to porosity -- or the volume of air -- which can be calculated from the formula

WI W2) p

1 - ra

rl

r2

where p = porosity, r a bulk density, rl = specific gravity of water, r~ = specific gravity of dry matter, W, -- parts by weight of water, W2 = parts by weight of dry matter. By definition, the specific gravity of water is 1.0 and, depending on the proportion of non-combustible material, that of the dry matter is about 1.5. In these experiments, the mean values of bulk density and moisture content of the compost at spawning were 0.5 and 70%, respectively, giving a mean porosity of 0.55, or 55% air in the compost. However, compost bulk density is not an absolute value, it depends not only on the physical state of the organic material but also on the compression applied, for example, when mushroom beds are prepared. Therefore, if the bulk density of the compost were to be increased from 0.5 to 0.6 without loss of water, the volumes of water and dry matter in a litre of compost would be increased to 0.42 and 0.12, respectively, and the volume of air in the compost would be reduced to 46%. Mushroom compost can be reduced by compression, but it is not permanently deformed and the original volume is partly restored when the pressure is released; i.e. compost exhibits both plastic and elastic properties. High water content and well degraded or physically short material increases plasticity, and conversely lower moisture content and less degraded or physically longer material increases the elasticity of compost. Therefore, although the bulk density of any one compost could be increased with increasing pressure, the higher the elasticity the less susceptible the compost would be to permanent change in bulk density. In these experiments, the same pressure was applied to all the composts when the mushroom beds were prepared after spawning, and differences in bulk density between composts resulted from the straw treatments and composting time alone. Short-duration and normal-straw composts had ~he lowest bulk densities, being less permanently reduced in volume =

30

after pressing than composts with longer composting time and chopped straw. The depth of compost in mushroom beds can affect productivity. In these experiments only one depth of compost was tested, and the weight of mushrooms per volume of compost increased with increasing bulk density. However, Gerrits (1972) showed that with increased depth, mushroom yield per unit fresh weight of compost decreased, while yield per unit area increased. This confirmed earlier work by Lambert (1962), Rasmussen (1962) and the Lee Valley {Anon., 1969) depth trials. Flegg and Ganney (1973) also obtained higher yields per fresh weight of compost from shallow layers of compost. Apparently, the mushroom yield per weight (or volume) of compost was reduced in deeper beds because the cropping area became limiting compared with the weight {or volume) of compost. Another factor causing a decline in yield per unit weight of compost could be the overheating that can occur in deeper beds as the mycelium colonises the compost. Gerrits (1976) showed that with careful temperaturecontrol during spawn-run and cropping, it is possible to maintain the yield of mushrooms per tonne of compost in beds deeper than 15 cm. In respect of over-heating, increasing the bulk density of a compost could have the same effect as increasing the depth. The former reduces porosity, the latter increases distances for gaseous exchange, and both would increase the heat capcity of the compost. The results of cropping trials can be confounded if the experimental design does not distinguish between the similar effects of bulk density and depth of compost. Mushroom yields can be expressed in different ways, either to show biological efficiency, i.e. conversion of compost (on either a fresh- or dryweight basis) into mushroom tissue, or to show the physical efficiency of the space occupied by the compost. For example, in these experiments the yield of mushrooms per unit volume increased with increasing bulk density, so that more mushrooms were produced per unit bed area. However, the yield of mushrooms per unit fresh weight of compost was greatest from the 13-day composts (with intermediate bulk densities) than from 3- and 23-day composts (with extreme bulk densities). Also, the variation in production efficiency of the compost dry matter was such that there were no significant differences between composts when mushroom yields were expressed in this way. Either the nutrient value of the composts to the mushroom actually varied, or their potentials were not equally realised because of interactions with other environmental factors. In these trials, the effects of physical factors, moisture content and bulk density predominated and gave the differences in mushroom yields between the types of compost. ACKNOWLEDGEMENTS

We thank J.S. Fenlon and Helen ttobinson for help and advice with the statistical analysis, and Margaret Love, J.N. White and C.A. Penn for help with the experiments.

31 REFERENCES Anonymous, 1969. Pressing and casing materials experiment. First Progress Report, 1966 and 1967. Lee Valley Exp. Hortic. Stn. Rep. 1967--68: 157--172. Flegg, P.B. and Ganney, G.W., 1973. Cropping of mushrooms on shallow layers of compost. S c i e n t i a Hortic., 1 : 331--339. Flegg, P.B. and Randle, P.E., 1980. Effect of the duration of composting on the amount of compost produced and the yield of mushrooms. Scientia Hortic., 12: 351--359. Flegg, P.B. and Randle, P.E., 1981a. Relation between the initial nitrogen content of mushroom compost and the duration of composting. Scientia Hortic., 15: 9--15. Flegg, P.B. and Randle, P.E,, 1981b. A unifying concept of compost preparation for the cultivation of the mushroom Agaricus bisporus. Mushroom Sci., 11(1): 341-349. Gerrits, J.P.G., 1972. Hoeveel compost per m ~ is optimaal? De Champignoncultuur, 16: 171--177. Gerrits, J.P.G., 1976. Enkele proeven over de hoeveelheid compost per m: en de invloed van persen van de compost. De Champignoncultuur, 20: 17--25. Lambert, E.B., 1962. Cropping experiments to test the efficiency of nutrient translocation by cultivated mushrooms. Mushroom Sci., 5 : 340--347. Randle, P.E., 1974. Compost. Rep. Glasshouse Crops Res. Inst., 1973: 82--84. Rasmussen, C.R., 1962. Carbon dioxide accumulation in mushroom compost and its influence on cropping yield. Mushroom Sci., 5: 390--414.