Potential of Adapted Mushroom Compost as a Growing Medium in Horticulture

Potential of Adapted Mushroom Compost as a Growing Medium in Horticulture G. Wever and A.M.M. van der Burg Wageningen UR, Applied Plant Research Glasshouse horticulture PO-box 8, NL 2670 AA Naaldwijk The Netherlands G. Straatsma Wageningen UR, Applied Plant Research Mushrooms PO-box 6042, 5960 AA Horst The Netherlands Keywords: Straw, Wood fiber, Peat-free, Compost Abstract Durable use of materials is promoted in horticulture. Especially in countries like the United Kingdom and Switzerland the use of peat is discouraged. In the Netherlands approximately 3.4 million m 3 of peat is used per year. An alternative should have a good quality and should be available in large quantities. Spent mushroom compost is a potential alternative for peat. It is available in large quantities, approximately 2.1 million m 3 per year in the Netherlands only. Spent mushroom compost is a steamed mixture of compost and casing soil, could be used as an alternative for peat, but has a high EC (salt content). The aim of this study was to lower the salt content by changing the recipe of the mushroom compost. Mushroom compost is made from horse manure, straw, chicken manure and gypsum. Both the organic manure and the gypsum increase the salt content. In an experiment the manure was replaced by urea, ammonium nitrate or ammonium sulphate and the gypsum was replaced by lime. To compensate for a lower nitrogen content the compost was supplemented with a product based on soy beans later on in the mushroom cultivation stage. After growing white button mushrooms, Agaricus bisporus, mixtures of spent compost were made with peat and compared with the growth on peat substrates with different EC-levels and mixtures of peat with wood fiber, composted straw, casing soil or compost. Also the compost products were washed to lower the salt content. As a test crop Kohlrabi, Brassica oleracea var. gongylodes was used. The mushroom yield was low if urea was used as a nitrogen source. The combinations of ammonium nitrate or sulphate with additional supplementation seem to have a prospective although the physical circumstances and additional supplementation will have to be optimized. The addition of lime instead of gypsum seems to lower the mushroom yield. The adapted mushroom composts had a salt content of 25 % of the commercial spent mushroom compost. However the level is still too high for high dosages in e.g. peat based growing media. The high level is caused by potassium from the straw and additions of calcium nitrate or sulphate. It is therefore impossible to balance the nutrient levels in the mixtures for growing plants, especially if a high percentage is added to the peat. Based on the nutrient content it is however tried to fertilize the mixtures to an optimum nutrient level using NH 4 H 2 PO 4, Ca(NO 3 ) 2, KH 2 PO 4, NH 4 NO 3, K 2 S0 4, KNO 3, MgSO 4, Mg(NO 3 ) 2 and micronutrients at different levels. Compared to the other tested materials all spent mushroom composts showed growth reduction, especially at higher concentrations of the spent mushroom compost in the growing medium. This was mainly caused by a high salt content (EC). Washing the spent mushroom compost reduced most of the problems concerning nutrient content and growth reduction. The spent casing soil apart from the spent compost seems however to be suitable. This spent casing soil represents however only 30 % of the dry weight of the spent mushroom compost. Next to the salt content, nitrogen fixation by microorganisms was one of the factors in the growth reduction. Only if NH 4 NO 3 was used as a nitrogen source, the level of available nitrogen in the spent mushroom remained at a sufficient level. All the other spent mushroom types showed very low available nitrogen at the end of the trial. This was also found for Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS 2005 171

the composted straw and to a lesser extent for the tested wood fibers. If spent mushroom compost is to be used in the future as a growing medium on a large scale not only the recipe of the compost has to be changed but also washing the material before use in horticulture seems necessary. Research concerning the impact of washing techniques on environmental impact is important and should be compared with the profits of enlarging the life cycle of the spent mushroom compost. INTRODUCTION The use of renewable raw materials rather then non-renewable materials is a global concern. In Horticulture for growing media 3.4 million m 3 of peat is used in the Netherlands (Wever et al., 2002). The worldwide use is about 35 million m 3. As the society is becoming more aware of the environmental effects of peat excavation consumers in e.g. the United Kingdom and Switzerland are demanding peat free growing media (Holmes et al., 2000). For this purpose in the Netherlands a project is set up in which the possibilities of peat replacement are examined (Vegter, 2004). It appears there are good horticultural alternatives for peat but the major concerns are the availability of large quantities and economical aspects. Possible alternatives are organic fibers like grass and woodfiber, urea formaldehyde and some compost types (Wever et al., 2002). SMS (Spent Mushroom Substrate) could be an alternative as this waste is available for a low price in large quantities. In the Netherlands about 2.1 million m 3 is available annually. Experiments have been performed to test the suitability of spent mushroom compost for horticultural purposes (Lemaire et al., 1985, Li et al., 1998, Chong and Rinker, 1994, Chong et al., 1994). The main conclusion of all this research is that the SMS can only be used in minor additions as the salt content is far too high. There are possibilities of lowering the salt content by lowering the salt content of the input materials. Mushrooms need fertilization but the input materials contain an overload of the minerals needed for growing. In this experiment compost recipes with less nutrients are made to see whether in this way the waste material SMS could be used for growing plants in horticulture. The aim of this study was to lower the salt content by changing the recipe of the mushroom compost. MATERIALS AND METHODS Standard SMS is a finished mixture of compost and casing soil. Compost is made of horse manure, straw, chicken manure and gypsum. After composting and inoculating with Agaricus bisporus, the material is covered with casing soil. Casing soil is a mixture of black peat and lime. Following to the mushroom growing the mixture of compost and casing soil is steamed and used as e.g. soil improver. In the experiment manure was replaced by: urea (3.8 kg/ton), ammonium nitrate (19.9 kg/ton)or ammonium sulphate (8.7 kg/ton). aiming at an N contents of 1.4 % (w/w, dry) well below a traditional value of 2.2 % N. Traditionally gypsum is applied at (25 kg/ton), now it was applied at 5 kg/ton or was replaced by lime (3 kg/ton). To compensate for the lower nitrogen the mushroom substrate was supplemented with a product based on soy beans (Miilichamp 6000). The recipes can be found in Table 1. From the different spent mushroom substrates the most promising were selected for the growing trial with kohlrabi. The selection was based on the yield and the expected salt content. The champost SMS materials D, F, H, J and N were tested without the casing soil. The casing soil from treatment o and p were tested separately. As reference materials also Peat, Composted straw, Woodfibre (2 brands), Composted greenwaste and a commercial champost (mixture champost with casing soil) were tested. The materials with a high salt (Table 2) content were thoroughly grinded by hand and washed (rinsed) with rain water at a ratio of a minimum of 3/1 (water volume/substrate volume). If the salt content was acceptable the materials were mixed with peat in the ratio 1:2 and 2:1. It was tried to fertilize to an optimum by linear programming for the major nutrients. Based on the nutrient content NH 4 H 2 PO 4, Ca(NO 3 ) 2, KH 2 PO 4, NH 4 NO 3, K 2 S0 4, 172

KNO 3, MgSO 4, Mg(NO 3 ) 2 and micronutrients were added to the best possible level. As certain materials still will have a rather high salt content the peat reference is fertilized with different amounts of PG-mix 0.5, 1.0, 1,5 and 2.0 kg/m 3 to have a good reference with a high salt content. The quality of the substrates was evaluated by chemical analyses and a growing trial. For the chemical analyses of the media EN 13037 (1999), EN 13038, (1999), EN 13040 (1999) and EN 13652 (2001) are used. A growing trial for 2 weeks with Kohlrabi (Brassica oleracea var. gongylodes) was performed in a greenhouse. An additional factor was included in the growing trial to be sure that the physical circumstances during germination are optimal. The seeds were therefore partly sawn in the substrate as tested and partly in a layer of peat substrate. In 10 cm (diameter) pots 12 seeds were sown. After a week the number of plants has been brought back to 8. The pots were irrigated frequently with a nutrient solution. After two weeks the plants were weighed and the EC and nutrient content of the substrates were measured according to the 1:1.5 volume extract (Sonneveld et al., 1974). Statistical analysis was performed using regression analysis and ANOVA of Genstat 5 Release 4.1 developed by Lawes Agricultural Trust (Rothamsted Experimental Station). The least significant differences (LSD) were determined at the 5% level. RESULTS AND DISCUSSION The mushroom yields (Table 1) are based on small scale trials but give an indication concerning the potential of certain composts. Urea as a nitrogen source gives low productions. Probably the nitrogen is not available for the mushroom mycelium. However Noble et al. (2002) found better results with urea as a nitrogen source. Combinations of ammonium nitrate or ammonium sulphate with additional supplementation seems to have perspective. The substrates had low ash contents, therefore the amount of moisture expressed per amount of organic material was low. In some cases composts were quite dry, had a high ph and had quite high NH 4 -N contents, all suboptimal for a good yield. The physical circumstances like moisture contents and additional supplementation will have to be optimized. The addition of lime instead of gypsum seems to lower the mushroom yield. Although a small effect concerning the ph is to be expected it is not clear what the reason is of the difference found. Based on the yield of mushrooms, used composts were selected for testing for horticultural purposes. The selected mushroom composts in Table 2 have still a very high nutrient content although the level is only a quart of the level of commercial champost (13). The maximum levels according to Kipp et al. (2000) for tolerant crops if used unmixed can be used to validate the results (Table 2). If a substrate is only used in a lower concentration the maximum levels can be higher, e.g. if only 20% is mixed through the maximum level can be a factor 5 higher. The high level of electrical conductivity of the composts is caused by potassium from the straw and additions of calcium nitrate or sulphate. It is therefore impossible to balance the nutrient levels in the mixtures, especially if a high percentage is added to the peat. For composted straw (2) the same results can be found. Casing soil (11 and 12) and woodfibre (3 and 4) can be used in high concentrations. Care should be taken with the ph as the manganese contents are high. Based on the nutrient content it is however tried to fertilize the mixtures to an optimum nutrient levels using NH 4 H 2 PO 4, Ca(NO 3 ) 2, KH 2 PO 4, NH 4 NO 3, K 2 S0 4, KNO 3, MgSO 4, Mg(NO 3 ) 2 and micronutrients at different levels. Compared to the other materials tested all spent mushroom composts showed growth reduction, especially at higher concentrations of the spent mushroom compost in the growing medium (Table 3). In statistical analyses the electrical conductivity (EC) was strongly correlated with growth reduction.. Washing the spent mushroom compost solved in most cases the problems concerning nutrient content and growth reduction. The results of the spent casing soil apart from the spent compost are comparable to pure peat. This spent casing soil represents however only 30 % of the dry weight of the spent mushroom compost. 173

Next to the salt content, nitrogen fixation by microorganisms was one of the factors in the growth reduction. Only if NH 4 NO 3 (compost 7 and 8) was used as a nitrogen source, the level of available nitrogen in the spent mushroom remained at a sufficient level. All the other spent mushroom types showed very low available nitrogen at the end of the trial. This was also found for the composted straw and to a lesser extent for the tested wood fibers. CONCLUSION Promising mushroom yields are found for compost made from straw and ammonium nitrate and ammonium sulphate as a nitrogen source instead of chicken manure. For horticultural purposes the salt content in the spent mushroom compost with alternative nitrogen sources is still rather high. Although the salt content of the used composts is brought back by factor 4. Compared to peat the growth in mixes with the used composts show growth reductions, especially in the higher concentrations. Rinsing lowered the electrical conductivity and solved the problems concerning growth reduction. Compost made from straw and ammonium nitrate will have lesser problems concerning growth reduction by nitrogen deficiency. If spent mushroom compost is to be used in the future as a growing medium on a large scale changing the recipe of the compost by using less manure in combination with rinsing the material for use seems the solution. Research concerning the impact of washing techniques on the environment is important and should be compared with the profits of enlarging the life cycle of the spent mushroom compost. Literature Cited Chong, C., Cline, R.A. and Rinker, D.L.1994. Bark- and peat-amended spent mushroom compost for containerized culture of shrubs. HortScience 29(7):781-784. Chong, C. and Rinker, D.L. 1994. Use of spent mushroom substrate for growing containerized woody ornamentals: an overview. Compost Science and Utilization. 3, 45-53. EN 13037. 1999. Soil improvers and growing media - Determination of ph. EN 13038. 1999. Soil improvers and growing media - Determination of electrical conductivity. EN 13040. 1999. Soil improvers and growing media - Sample preparation for chemical and physical tests, determination of dry matter content, moisture content and laboratory compacted bulk density. EN 13652. 2001. Soil improvers and growing media - Extraction of water soluble elements. Holmes, S., Lightfoot-Brown, S. and Bragg, N. 2000. Peat Alternatives, A review of performance, future availability and sustainability for commercial plant production in the UK. Report ADAS Horticulture & DEFRA, Horticulture & Potatoes Division, http://www.adas.co.uk/horticulture/. Kipp, J.A., Wever, G. and de Kreij, C. 2000. International Substrate Guide. Elsevier. Lemaire, F., Dartigues, A. and Riviere, L.M. 1985. Properties of substrate made with spent mushroom compost. Acta Hort. 172, 13-29. Li, P.P., Mao, H.P. and Wang, D.H. 1998. Effect of medium residue from mushroom culture as a soilless culture medium for vegetable crops. China Vegetables (5), 12-15. Noble, R., Hobbs, P.J., Mead A. and Dobrovin-Pennington, A. 2002. Influence of straw types and nitrogen sources on mushroom composting emissions and compost productivity. Journal of Industrial Microbiology & Biotechnology 29, 99-110. Sonneveld, C., van den Ende, J. and van Dijk, P.A. 1974. Analysis of growing media by means of 1:1.5 volume extract. Comm. Soil Sci. Plant Anal. 25: 3199-3208. Vegter, B. 2004. Veen gaat in de ban. Vakblad voor de Bloemisterij 32, 38-39. Wever, G., de Kreij, C., van Woerden, S., Straatsma, G. and Olijnsma, T. 2002. Orientation towards durable use of growing media for horticulture and mushroom 174

production. Proc. Symposium IPS II en V, Peat in Horticulture Quality and Environmental Challengies, p 367-372. Tables Table 1. Results of mushroom production. Treatment N-source Lime/gypsum supplemented MC6000, kg/ton mushroom yield; kg/ton A urea CaCO 3 1 2 B urea CaCO 3 2 0 C urea CaSO 4.2H 2 O 1 29 D urea CaSO 4.2H 2 O 2 46 E NH 4 NO 3 CaCO 3 1 217 F NH 4 NO 3 CaCO 3 2 184 G NH 4 NO 3 CaSO 4.2H 2 O 1 159 H NH 4 NO 3 CaSO 4.2H 2 O 2 157 I (NH 4 ) 2 SO 4 CaCO 3 1 134 J (NH 4 ) 2 SO 4 CaCO 3 2 177 K (NH 4 ) 2 SO 4 CaSO 4.2H 2 O 1 161 L (NH 4 ) 2 SO 4 CaSO 4.2H 2 O 2 150 M chicken manure CaCO 3 1 10 N chicken manure CaCO 3 2 11 O chicken manure CaSO 4.2H 2 O 1 161 P chicken manure CaSO 4.2H 2 O 2 203 175

Table 2. Results of the chemical analyses of the raw materials used. Mn mg/l 0,1 0,6 7,2 5,4 0,4 3,1 3,1 3,4 5,9 4,1 0,1 0,1 3,5 0,8 Zn mg/l 0,0 0,3 1,1 0,9 0,3 0,3 0,4 0,7 1,0 1,2 0,0 0,1 1,2 1,3 B mg/l 0,3 0,0 1,1 0,8 0,4 0,3 0,3 0,3 0,5 0,6 <0.1 <0.1 0,8 0,7 Cu mg/l 0,1 0,2 0,2 0,2 0,1 0,2 0,2 0,1 0,7 0,4 0,1 0,2 0,6 0,4 Mo mg/l <0.05 <0.05 <0.05 <0.05 0,05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 0,19 * after washing NH4 mmol/l 1 1,5 2,2 0,7 0,1 0,4 2,8 1,6 0,8 0,4 0,6 0,6 14,2 K mmol/l 0,42 10,7 1,6 1 8,7 11,38 12,35 11,9 11,4 13,75 2,4 2 60 Na mmol/l 0,4 1,1 0,2 0,4 2,2 0,51 0,56 0,7 0,4 1,17 0,6 0,6 8,7 Ca mmol/l 0,1 1,8 0,5 1,8 0,7 4,38 6,26 7,4 11,5 5,24 1,7 1,5 13,7 Mg mmol/l 0,24 0,6 0,3 0,5 0,5 1,49 1,75 1,6 1,6 2,16 0,5 0,4 7,2 Si mmol/l 0,07 0,4 0,23 0,11 0,17 0,22 0,27 0,53 0,3 0,46 0,42 0,42 0,8 NO3 mmol/l 0,9 7,9 3,4 1,7 1,1 8,9 7,6 2,3 <0.1 0,3 <0.1 <0.1 0 Cl mmol/l 1,2 1,3 0,5 0,5 7,7 0,8 0,9 0,8 0,6 1,5 1,1 1,2 33 SO4 mmol/l 0,6 0,5 0,4 1 1,1 1,1 4,1 7,9 10,8 4,3 1 0,8 33,6 HCO3 mmol/l <0.1 4,769 0,113 0,38 1,41 2,108 3,529 2,004 0,568 3,573 2,643 2,55 13,712 P mmol/l 0,05 <0.01 0,25 0,02 0,1 0,17 0,5 0,08 0,12 0,79 0,14 0,12 0,7 Fe µmol/l 3,24 2,8 5,5 2,2 44,3 5,21 5,69 5,5 5,7 8,14 0,9 1,3 21,4 Mn µmol/l 0,37 2,1 26,2 19,5 1,6 11,32 11,44 12,4 21,4 15,02 0,3 0,2 12,6 Zn µmol/l 0,04 0,9 3,4 2,8 0,8 0,86 1,17 2,1 3,1 3,71 0,1 0,2 3,6 B µmol/l 5,45 0,7 20 14 8 4,7 5,6 6 10 10,25 <1 <1 14,5 Cu µmol/l 0,33 0,7 0,48 0,62 0,47 0,59 0,69 0,45 2,33 1,25 0,26 0,54 2 176

Table 3. Results of the growing trial with Kohlrabi (lsd 5% before EC correction 0.16 g after EC-correction 0.17 g) and EC (1:1.5) of the substrate after the growing trial. Substrate Peat part Rinsed Plant weight (g/plant fresh) EC Results after EC-correction volume ratio test substrate peat test substrate peat ms/cm 1 + 0.5 kg/m 3 PG-mix 1/1-1,07 0,91 1,04 0,88 0,6 1 + 1.0 kg/m 3 PG-mix 1/1-1,05 1,04 1,11 1,10 1,1 1 + 1.5 kg/m 3 PG-mix 1/1-0,90 0,93 0,99 1,03 1,2 1 + 2.0 kg/m 3 PG-mix 1/1-0,85 0,90 1,06 1,11 1,8 2 2/3-1,10 1,04 1,07 1,00 0,6 2 2/3 + 1,15 1,04 1,16 1,05 0,8 2 1/3-0,86 1,02 0,91 1,08 1,0 2 1/3 + 0,85 0,86 0,83 0,84 0,7 3 2/3-0,97 0,98 0,97 0,99 0,8 3 2/3 + 0,98 1,00 1,04 1,05 1,0 3 1/3-0,84 1,04 0,82 1,02 0,7 3 1/3 + 0,97 1,11 0,99 1,13 0,9 4 2/3-1,04 0,96 1,06 0,98 0,8 4 2/3 + 0,97 1,03 1,00 1,07 1,0 4 1/3-0,89 0,96 0,87 0,94 0,7 4 1/3 + 0,99 1,06 0,99 1,06 0,8 5 2/3-0,94 0,95 0,94 0,95 0,8 5 2/3 + 0,99 1,09 1,02 1,12 0,9 6 2/3-1,13 1,06 1,12 1,05 0,7 6 2/3 + 0,93 1,00 0,95 1,01 0,8 6 1/3-0,79 0,84 0,83 0,89 1,0 6 1/3 + 1,05 0,97 1,05 0,97 0,8 7 2/3-0,96 1,05 0,95 1,05 0,8 7 2/3 + 1,04 0,97 1,06 0,98 0,8 7 1/3-0,74 0,75 0,83 0,84 1,2 7 1/3 + 0,92 0,92 0,93 0,94 0,8 8 2/3-0,91 1,07 0,97 1,13 1,0 8 2/3 + 1,08 1,02 1,12 1,05 0,9 8 1/3-0,79 0,83 0,97 1,01 1,6 8 1/3 + 0,95 1,01 0,96 1,02 0,8 9 2/3-0,85 0,92 0,96 1,03 1,3 9 2/3 + 0,88 1,04 0,93 1,09 1,0 9 1/3-0,77 0,84 0,93 1,00 1,6 9 1/3 + 0,89 0,93 0,94 0,99 1,0 10 2/3-1,15 1,12 1,16 1,13 0,8 10 2/3 + 0,89 0,89 0,94 0,94 1,0 10 1/3-0,51 0,57 0,47 0,70 1,4 10 1/3 + 0,90 0,89 0,92 0,90 0,8 11 2/3-1,07 1,09 1,06 1,08 0,7 12 2/3-0,92 1,15 0,91 1,14 0,7 13 9/10-0,91 1,08 1,04 1,20 1,4 13 2/3 + 1,15 1,05 1,22 1,12 1,1 177