Effect of substrate additives on oyster mushroom growth (Pleurotus sp.): cultivation timeline and reuse of the spent substrate for radish germination.

Abstract

Oyster mushrooms (Pleurotus spp.) convert agricultural residues into food, but the
value of low-cost additives to paddy straw and the fate of the spent substrate are rarely
examined together. This study compared three locally available additives — seaweed
extract (20 mL of a 2 g L⁻¹ solution injected after mycelium set), egg shell powder (2
g per bag) and coir pith (20 g dry weight per bag) — with a paddy straw control in a
completely randomised design with two bags per treatment. The spent substrate of
each treatment was then tested as a component of a vermicompost–soil medium for
radish (Raphanus sativus) germination. Egg shell powder gave the earliest pinning
(17.5 ± 0.7 days vs. 23.5 ± 3.5 days in the control; −25.5%, Dunnett P = 0.068). Coir
pith significantly delayed pinning (32.0 days, +36.2%, P = 0.022); only one of its two
bags fruited, and it gave the fewest harvest cycles (0.5 ± 0.7 vs. 3.0 ± 0.0 per bag; P
= 0.098). Seaweed extract did not differ from the control in any timeline measure. In
the reuse trial (200 seeds per tray), germination ranged from 69.5% (coir pith) to
81.0% (seaweed extract) against 73.0% in the untreated medium. No pairwise
difference reached significance (seaweed extract vs. baseline, P = 0.057; overall χ²(4)
= 7.99, P = 0.092), and 74.6% of all 1,000 seeds germinated. Egg shell powder is a
promising low-cost additive for earlier fruiting, coir pith is unsuitable as a bulk
amendment at this rate, and spent Pleurotus substrate is a usable component of a
diluted growing medium.