Abstract:
Despite the increased recognition of the nutritional value of the Oyster mushroom,
coupled with its ability to tolerate a wide range of climatic conditions, its production
is still at infancy stage with low adoption rate in Kenya. The low uptake could be
attributed to lack of skills for substrates and spawns preparations, cost of buying
substrates and spawns coupled with poor knowledge on its production and
consumption benefits. The objective of this study was to optimize Pleurotus ostreatus
(Oyster mushroom) production through response surface methodology and simplex
centroid mixture designs. The specific objectives were to optimize the spawns
production, screen the local suitable substrates for the oyster mushroom cultivation,
establish yield as a function of proportions of mixture components and then conduct
the economic return analysis for the oyster mushroom farming in Machakos County.
To achieve the objectives the spawns propagation was optimized by varying the
temperature level, sterilization time and culture media concentration in order to
establish the feasible levels which minimized the days of mycelium full development
using central composite designs. One factor at a time approach was used to determine
the local suitable substrate among them, the star grass, euphorbia, cattle manure,
sugarcane bagasse and sawdust. Simplex-centroid mixture design was used to
determine the substrates mixture that maximized the yield and lastly the contribution
margin formula was used to determine the economic returns on the oyster mushroom
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production. Based on the study findings 26.30 C, 17.40 minutes and and 60.89g/L of
temperature level, sterilization time and culture media concentration level respectively
minimized the days to full coverage of mycelium in a petri dish. There was no pinning
on the cattle manure and the euphorbia substrates hence they were eliminated at the
screening stage. The results showed significant variability on the different substrate
compositions used under the study. Sawdust yielded the most under the pure blend at
1.1 kg per experimental unit while on the mixed blend sugarcane bagasse and sawdust
produced the highest yield at 1.3 kg per experimental unit (1kg of dry substrate),
giving 10% and 30% biological efficiency respectively. The economic returns
analysis indicated that, the break-even point was at 54 kilograms of the oyster
mushroom production, beyond that point each succeeding kilogram was produced at a
diverging profit. Therefore oyster mushroom production was economically viable
against the continued arable land decrease in Machakos County coupled with the
rainfall unreliability. Central Composite Designs in controlling the temperature level,
sterilization time and culture media were recommended for spawns maximum
production. Since the mixture response was found to be more valuable than the pure
blend responses then simplex- centroid mixture design for rightly proportioned
substrates was recommended for improved oyster mushroom production. A further
research on determining suitability of alternative locally found substrates which may
be more cost effective and multiple response optimizations aimed at achieving
maximal nutritional value and yield against minimal cost of spawns and substrates are
recommended.