Effect of spent mushroom substrate and NPK fertilizer on sweetpotatoes

Spent mushroom substrate and NPK (15:15:15) fertilizer were assessed under field conditions for their comparative effects on white and orange-fleshed sweetpotato varieties in Umuahia, south eastern Nigeria. The experiment was a split split plot in randomized complete block design with three replicates. The main plot treatments were two sweetpotato varieties (white-fleshed TIS87/0087 and orange-fleshed Umuspo 3). The split plot treatments were five NPK fertilizer rates (0, 100, 200, 300 and 400kg/ha) while the split split plot treatments were three spent mushroom substrate levels (0, 2 and 4t/ha). Averaged across sweetpotato varieties and NPK fertilizer, spent mushroom substrate significantly increased leaf area index, shoot biomass and storage root yield. Application of NPK fertilizer increased leaf area index and shoot biomass in both years and storage root yield in 2019. The white-fleshed TIS87/0087 variety produced significantly higher shoot biomass than Umuspo 3 in both years. TIS87/0087 had higher root yield than Umuspo 3 in 2018, but in 2019, the latter out yielded the former. Three-way interactions were significant for shoot biomass in 2018 and for storage root yield.