ABSTRACT

Three field experiments were conducted between 2018 and 2020 cropping seasons at the Forestry Research Institute of Nigeria (RFIN), Humid Forest Research Station farm Umuahia, and at Itu Ngwa, Obingwa in Abia, south eastern Nigeria. The studies were designed to: determine the effect of spent mushroom substrate (SMS) and NPK fertilizer on field performance of white and orange-fleshed sweetpotato in south eastern Nigeria; effect of interactions on orange-fleshed sweetpotato and maize productivity under different rates of spent mushroom waste and NPK fertilizer and effect of location and NPK fertilizer on three sweetpotato varieties raised in Triple S system. The three experiments were laid out as split-split plot in a randomized complete block design (RCBD) with three replications. Results showed that spent mushroom substrate significantly increased leaf area index, shoot biomass and storage root yield. Application of NPK increased leaf area index and top yield in both years and storage root yield in 2019. The white-fleshed TIS 87/0087 had higher root yield than Umuspo 3 in 2018, but in 2019, Umuspo 3 out yielded TIS87/0087. Three-way interactions were significant for shoot biomass in 2018 and for storage root yield in both years. The highest top yield (28.70-30.0t/ha) in 2018 was obtained from TIS 87/0087 at moderate rates of 2t/ha SMS and 300kg/ha NPK fertilizer. The highest storage root yield was obtained from TIS 87/0087  at 4t/ha spent mushroom substrate alone in 2018 and yield from Umuspo 3 at 4t/ha spent mushroom substrate only in 2019. Intercropping reduced significantly sweetpotato vine length, number of branches per plant, leaf area index, number of storage roots per plant, root weight per plant and storage roots yield in both cropping seasons. Intercropping also reduced maize leaf area index, 100-seed weight, seed yield and shelling percentage in 2019 relative to sole cropping. On the basis of mean land equivalent ratio, land equivalent coefficient and area time equivalent ratio, yield advantage accrued when both crops were intercropped under any fertilizer regime but highest economic returns was obtained from orange-fleshed sweetpotato sole cropping at 400kg/ha NPK + 2t spent mushroom substrate, followed by sole sweetpotato at 4t spent mushroom substrate only. Leaf area index in 2019 and shoot biomass, root weight and storage root yield in both cropping seasons (2019 and 2020) were significantly higher in Obingwa than in Umuahia location. There was a linear increase in number of branches, leaf area index, shoot biomass and storage root yield with increase in NPK fertilizer application up to 400kg/ha. White-fleshed TIS87/0087 and orange-fleshed Umuspo 1 varieties had higher values for number of branches, leaf area index, above ground biomass than orange-fleshed Umuspo 3, but the latter had significantly higher storage root yield, followed by Umuspo