Abstract:
Two major challenges facing arid and semi-arid areas (ASALs) of Kenya today are food insecurity and poverty, occasioned by low agricultural production. Diversification into low input agriculture like mushroom cultivation can help address these challenges. However, commonly used mushroom substrates in Kenya, (rice and wheat straws) are not widely and cheaply available. Several crop residues are found in the ASALs, while Melia volkensii is becoming popular agroforest trees in these areas. Literature suggests that these materials can serve as alternative substrates, but their effectiveness have not been adequately evaluated. This study aimed at evaluating the potential of different agro-waste materials as substrates for cultivation of phoenix oyster mushroom (Pleurotus spp.) in the ASALs of Kenya. Five different agro-waste materials and their combinations were tested, namely: maize stalks, beans straw, maize cobs, rice straw, and Melia volkensii leaves. The study was conducted from March - May 2019, and assessed the effects of these substrates on different mushroom growth parameters. All the substrates were routinely prepared with buffers and supplements and the experiment set in a randomized complete block design (RCBD). Relative humidity was maintained at 80 - 90% and an average room temperature of 23 - 24°C. Mushroom morphological data was collected over a 45-days harvest period and subjected to two-way analysis of variance (ANOVA) using SPSS (version 21 ) to detect differences between treatments. Correlation between mushroom growth parameters (days to first harvest, stipe length, cap diameter, fruit bodies, weight and biological efficiency) were also determined. Results showed that substrates containing Melia volkensii leaves failed to colonize fully, with only the bean straw + Melia volkensii leaves combination (BSMV) yielding little, while all the other substrates yielded mushrooms. Days to first harvest varied significantly, with the mean ranging from 35.1 to 48.1 days for the maize cobs + rice straw (MCRS) and BSMV, respectively. The tallest mushroom was obtained from rice straw (6.8 cm) and was followed closely by maize straw + bean straw combination (MSBS) with 6.7 cm, while the shortest was obtained from BSMV with 4.4 cm. The highest average number of marketable fruit bodies per 1kg of wet substrate bag was 9.5 from MSBS, while the lowest was from BSMV (6.2). The overall average yields per 1kg of wet substrate varied from 136.2 g in BSMV to 434.9 g in rice straw, while the average biological efficiency varied from 37.1% to 130.6% for BSMV and rice straw respectively. BSMV substrate gave the worst performance, taking the longest time to first harvest (48.1 days) and gave the lowest yields, indicating that Melia volkensii leaves are not suitable mushroom substrates. Further result showed positive correlation between cap diameter, fresh weight and biological efficiency. In conclusion, this study showed that combinations of maize stalks, bean straw and maize cobs are suitable alternatives to rice straw. Among the combinations, MSBS produced the highest (403.7 g) after rice (437.9 g), and therefore recommended as a suitable alternative substrate to where rice straw is not readily available or economical to use.