A Reliable Quality Index for Mushroom Cultivation

The aim of this study was to develop a systematic quality index for application in the cultivation of Agaricus bisporus (Lange) Imbach mushrooms, based on the physical, chemical and biological properties (indicators) of the compost and casing layers (factors). The relative importance (weight) of each of the factors and indicators, their normalized scores, the quality index values and the correlation with the mushroom yield were evaluated. Three casings (soil + peat moss, Dutch commercial casing, and peat moss + spent mushroom substrate) and two composts were used. The resulting quality index is reliable and useful for identifying problems and can also serve as a rapid tool for possible intervention when problems occur. There was little difference between the two composts used, both of them showing high factor index values. Although the peat + spent mushroom casing presented certain limitations because of its high electrical conductivity, the other two casings showed satisfactory factor index values.


Introduction
The methodology used to obtain a "quality index" has been applied in agricultural research, especially in the field of soil science (Glover et al., 2000;Doran and Park in, 1994).For example, according to Larson and Pierce (1994), soil quality is a combination of the physical, chemical and biological properties of soil as well as its capacity to promote the growth of vegetables and animals, to regulate the flow of water in the environment and to act as a filter in the degradation and degeneration of environmentally hazardous substances.
However, quality index methodology has never been applied to mushroom production.Here, were study Agaricus bisporus (Lange) Imbach, the most widely cultivated mushroom in the world, for which an abundant literature exists concerning appropriate cultivation technology, especially optimal growth conditions and the factors that affect yield.In this work, were focus on the compost and casing layer.
The development of a quality index for mushroom cultivation is important in that it can help identify problems in the cultivation process, provide realistic yield estimates and avoid potential errors, while enabling government sectors to monitor the sustainability and quality of mushroom production and the changes related with the compost and casing layers used.
Sustainability in mushroom production is a multi-dimensional concept that includes aspects such as the stability of production and profit, the protection and improvement of basic natural resources (biotic and abiotic) and the maintenance of social order (e.g., the maintenance of family farms and industry).
Based on the different aspects and stages of A. bisporus production, four basic steps must be followed for precise quality evaluation and monitoring: 1) select and define the principal factor (or factors) involved in the commercial production of mushrooms that need to be assessed (e.g., compost and/or casing); 2) establish the attributes that are relevant to the quality indicators for the selected factors (e.g., "pH and C/N ratio" for compost); 3) determine the key points of data analysis and specify the evaluation and integration process (analysis method, weight (a and b) and slope at baseline); 4) establish specific criteria for the interpretation of the data to guarantee reliable estimates of the production quality of each attribute (e.g., normalized score).
To be of practical use to professionals (researchers, extension agents, growers, designers and others), quality indicators must meet the following criteria: a) be accessible to users worldwide and facilitate measurement; b) be applicable to any growth condition; c) own criteria for quantification and interpretation of values; d) be flexible in the face of changes (variations in temperature, humidity and CO 2 , irrigation alterations that cause problems with casing layer compaction, etc.); e) allow both short-and long-term assessments of production quality; f) if possible, be components of existing databases.
Based on the above mentioned criteria, compost and casing layers were selected from the many factors involved in mushroom cultivation to be the key factors in our analyses.The following parameters were evaluated and integrated: -Indicators of compost quality: moisture content, C/N ratio, pH, nitrogen and presence of mites, nematodes and competitor moulds.
-Indicators of casing layer quality: water-holding capacity, porosity, pH, electrical conductivity and presence of mites, nematodes and competitor moulds.
Two compost and three casing layers were used in our study.The aim was to develop a systematic quality index of the physical, chemical and biological properties (indicators) of the compost and casing layers (factors).The relative importance (weight) for each of the factors and indicators, their normalized scores, the quality index values and the correlation with the mushroom yield at the end of the harvest period were also evaluated.

Materials and methods
The experiment was carried out at the Centro de Investigación, Experimentación y Servicios del Champiñón (CIES), Quintanar del Rey (Cuenca, Spain) in a controlled room used specifically for mushroom growing.The total research time was 52 days (14 days of spawn run and 38 days of harvest phase).

Mushroom strain
The commercial strain "Gurelan 45" (large off-white hybrid) was used.The spawn is recommended for cultivation in the winter and spring, and the optimal fruiting conditions are 18ºC (although it may bear fruit at 15ºC), a relative humidity of 87% and adequate ventilation to keep CO 2 levels between 1000 and 1500 ppm.

Composts
Two commercial composts from different composting facilities were used.For both composts, Phase I was carried out in bunkers with controlled air flow, and Phase II in a pasteurization tunnel to eliminate pests and diseases.The physical, chemical and biological properties of these composts are summarized in Tables 2, 3 and 4.

Growing of mushrooms
After applying the casing layer over the composts, the plastic boxes were transferred to the production chamber where disinfectant treatment (formalin, 18 ml m -2 ), insecticide treatment (diflubenzuron 25%, 3.6 g m -2 ) and fungicide treatment (prochloraz 46%, 0.62 g m -2 ) were done on days 1, 3 and 5, respectively.The casing was deeply raked on day 6, and ventilation was carried out 11 d after casing to stimulate primordia formation.The growth cycle after casing lasted 38 d, and three flushes of mushrooms were harvested.

Quality index
Were assessed the quality indexes for the two composts and three casing layers in the cultivation of A. bisporus.

Factors to evaluate
Any proposals to improve or increase A. bisporus yield necessarily involves through two stages of the production process: composting and the selection and preparation of the casing layer.
As regards composts, the different factors that should be considered include changes in raw materials or supplements, the methods used in composting (Phase I and Phase II), the formulations used, and all the other aspects that can directly affect the physical, chemical and biological properties of the composts.For this reason, two different composts from two commercial facilities, each prepared with a particular method, formulation and technique, were selected.Three casing materials were selected for the same reason.These included two organic casings (Dutch commercial casing as a reference, and peat moss + SMS, considered an interesting alternative for growers that reuse spent mushroom compost) and soil + peat moss (widely used worldwide), a mixture with high mineral soil content.

Quality indicators
To establish the best quality indicators for the compost and casing layers that directly affect the yield of mushrooms, were selected the following principal parameters, which can be analyzed by well-defined analytical methods at low cost.

Critical limits for quality indicators
Based on previous data (Gerrits, 1988;Visscher, 1988;Pardo, 1994;Hearne, 1994;Pardo, 1999;Shekhar Sharma and Kilpatrick, 2000), the laboratory records at the Centro de Investigación, Experimentación y Servicios del Champiñón and the practical experience of the author and their collaborators in experimental and industrial cultivation, the critical limits and the optimal values of the indicators were defined, as shown in Table 1.

Weights for each factor (a) and for each quality indicator (b)
Based on their relative importance for yield, the compost factor was given a weight of 0.65 and the casing layer factor a weight of 0.35 (the numerical weights must total 1.0).We also established the weights of the quality indicators (their sum must also be 1).The most influential indicator for the final behavior of the crop was selected according to its importance and the possible consequences due to deviations from optimal values.For example, in addition to being a key element in "Phase I and II" of the composting process, the total N content of the compost is directly linked to other factors that may affect yield.A high N content would favor the presence of contaminants such as Coprinus and Chaetomium in the compost; moreover, if poorly composted, NH 3 becomes toxic to the mushrooms, while a low N content would cause problems with fermentation during Phase I (difficult for the temperature to reach 75-80ºC) lower yield and longer mean spawn-run time, which, jointly, mean a higher risk of compost contamination and a longer growing cycle.
The weight was set for each factor and quality indicator, as shown in Table I.For the different factors, the numerical weights assigned to all the quality indicators must add up to 1.0 at each level.

Normalized scores obtained (c) for the indicators
The normalized score of the indicators ranged from 0 to 1.0, with 0 representing the worst value and 1 representing the best value.The scoring curves were generated using the following equation (1) (Wymore, 1993): where  is the normalized score, B is the critical value or the baseline value of the indicator (a score of 0.5 sets the difference between a bad and good quality indicator), L is the initial value, which can be lower than a property and can be expressed as 0, S is the slope of the tangent to the curve at the critical value of the indicator and x is the indicator value measured in the laboratory.
To apply the above-mentioned equation of Wymore (1993), the slope (S) of the tangent to the curve at the critical value of the indicator ( = 0.5) was first calculated using the following equation ( 2): With the scoring curve equations, three types of normalized scoring functions were generated (Figure 1): (a) "More is better", e.g., water holding capacity and porosity; (b) "Less is better", e.g., electrical conductivity and the presence of mites; (c) "Optimum", e.g., pH and C/N ratio.

Calculation of final quality index
The quality index (Q) for the cultivation of A. bisporus was obtained in two stages.The indexes of each individual factor were first calculated (1st step), and their sum provided the factor index for each compost-casing combination (2nd step): (2 nd step).where Q 1 and Q 2 are the index values of the main factors (compost and casing layer), a 1 and a 2 are the weights of these factors, b i and b j are the weights of the m indicators of factor 1 (compost) and the n indicators of factor 2 (casing layer), c i and c j are the normalized scores of these indicators.Q is the final quality index value.

Test of the feasibility of modeling
To verify the safety and significance of this methodology, a correlation analysis was carried out for the final quality index values obtained for the six compost-casing combinations and the yield values recorded at the end of the growing for the same combinations.SigmaStat 3.5 with the Linear Regression tool was used for data analysis.

Results and discussion
Tables 2, 3 and 4 summarize the quality indexes obtained for each different casing layer, which include the main factors, the indicators within each factor, the weights of each factor ( a ) and indicator ( b ), the mean observed values, the normalized scores of each indicator ( c ), the factor index and the calculated values of the quality indexes.
The data were grouped according to the casing layers, with each table showing the values obtained for one type of casing layer cultivated with two different composts.The same method was previously used by Karlen and Stott (1994) to define a soil quality index.These authors stated that if the observed values of the indicators were equal to their critical limits, the quality index would be equal to 0.5.Values below 0.5 would represent soils with more limitations, and values above 0.5 soils with fewer limitations.Thus, the maximum possible value for any normalized score ( c ) or factor-quality index is 1.0.The closer the value is to 1.0, the better the result selected for each evaluation.
It follows that compost 1 has a better factor index value than compost 2, and, as regards the casing layers, DCC has the highest factor index value and peat + SMS (3:2, v/v) the lowest.
It is important to emphasize that this method can be used worldwide to study quality indexes for the cultivation of A. bisporus.A database with different types of compost and casing layers used in both situations (past and present) can be built, which will give realistic estimates of the quality indexes expected for each country.
A further examination of the data revealed little differences in the compost index values (0.995 and 0.992 for compost 1 and 2, respectively).The lowest normalized score ( c ) of 0.984 was obtained for pH in compost 2, which can still be considered a high value indicating good quality.
Based on the observed results, we conclude that the composting process was well established and developed in these two facilities, and that the substrates were well suited for our research, especially with regard to their physical, chemical and biological characteristics.
For fungiculture practice, it would be of great interest to periodically sample all existing composting facilities to identify potential problems (such as technical errors in the process, limitations of the constructions and bad materials used) and provide suggestions at critical time points.
Unlike the results obtained for the composts, substantial differences were found between the casing layers, with the factor index values ranging from 0.989 (DCC, Table 3) to 0.876 (peat + SMS, Table 4).Possible actions to improve the quality indicator valued below 1.0 in the peat + SMS casing would include correcting the value of the electrical conductivity (with a normalized score ( c ) of 0.183), increasing the leaching of the SMS by adding more water and extending the maturation period.Another alternative strategy would be to mix small amounts of SMS with peat moss, black peat or mineral soil for use as casing layer.
Rendering to the yield obtained at the end of the harvest phase, this methodology showed high correlation coefficient (R=0.829) between the yields and quality index values (Figure 2) and is therefore reliable.
It should be noted that the factors and indicators proposed in this paper and their critical limits and weights may not necessarily be fixed.Due to the flexibility of the factor selection process, additional indicators can always be included for better adaption to local conditions.Logically, they can also include other factors of production such as the grower's knowledge (training and experience), characteristics of the facilities (construction aspects and degree of automation) or the mycelium used.
To predict precise quality index values, more work needs to be done, and more indexes should be analyzed.With the continuation of our current work (to test other factors-indicators and their respective weights), the proposed quality index method will become more reliable and should eventually become an indispensable tool for mushroom cultivation (A.bisporus and others) worldwide.

Conclusions
This methodology used to obtain the quality index analysis is reliable and practical for identifying problems and can also serve as a rapid tool for possible intervention when problems occur.There was little difference between the two composts, both of which showed high factor index values.Although the peat + SMS based casing layer presented certain limitations as a result of its high electrical conductivity, the other two casings showed satisfactory factor index values.
Table 2. Weight ( a and b ) of factor and indicators, normalized score ( c ) and final quality index values for evaluating soil + peat moss (4:1, v/v) casing ( a ) Function level weight scores are the sums of associated Level 1 indicator values.( b ) For Level 1 indicators that are determined by Level 2 indicators (i.e., moisture), the weight scores are the sums of Level 2 indicator values.Table 3. Weight ( a and b ) of factor and indicators, normalized score ( c ) and final quality index values for evaluating DCC (4:1, v/v) casing ( a ) Function level weight scores are the sums of associated Level 1 indicator values.( b ) For Level 1 indicators that are determined by Level 2 indicators (i.e., moisture), weight scores are the sums of Level 2 indicator values.
Table 4. Weight ( a and b ) of factor and indicators, normalized score ( c ) and final quality index values for evaluating brown peat + spent mushroom substrate (2:3, v/v) casing ( a ) Function level weight scores are the sums of associated Level 1 indicator values.( b ) For Level 1 indicators that are determined by Level 2 indicators (i.e., moisture), weight scores are the sums of Level 2 indicator values.

Figure 1 .
Figure 1.(a) "More is better" normalized score function as applied to water holding capacity.(b) "Less is better" normalized scoring function as applied to the presence of mites.(c) "Optimum" normalized scoring function as applied to C/N ratio