Sweet potato (Ipomoea batatas) growth and tuber yield as influenced by plant spacing on sandy loam in humid tropical environment

The choice of appropriate plant spacing that gives optimum  density of sweet potato (Ipomoea batatas (L.) Lam) is crucial for its productivity, considering that plant density of cover crops affects above-ground access to sunlight, degree of soil surface cover, and below-ground tuberization. The influence of plant planting and the ensuing plant density on growth and tuber yield of sweet potato in a sandy-loam soil in southern Nigeria was assessed in the 2012 and 2013 growing seasons. The field trials involved five plant spacings namely 90 × 90, 60 × 90, 60 × 60, 30 × 90, and 30 cm × 60 cm; corresponding to plant densities of 1.23, 1.85, 2.78, 3.70 and 5.56 plants m–2, respectively. Data were collected on vine girth, number of leaves, leaf area, tuber weight plant–1 and tuber yield, as well as on weed dry matter. Closer plant spacings resulted in higher number of leaves m–2 and leaf area index (LAI). However, tuber weight plant–1 was highest with the second widest spacing (60 cm × 90 cm) and decreased with spacing. By contrast, tuber yield increased with spacing; the closest spacing (30 cm × 60 cm) gave the highest value (12.95 t ha–1) which, however, was similar to 10.55 t ha–1 due to the second closest spacing (30 cm × 90 cm) which, in turn, was similar to 60 cm × 60 cm (9.55 t ha–1) and 60 cm × 90 cm (8.89 t ha–1). Tuber yield correlated with number of leaves (r = 0.57*) and LAI (r = 0.54*), suggesting that the increases in these growth variables due to denser plant population translated into greater photosynthetic activity and translocation of assimilates to the tubers, which manifested as increased tuber yield. Spacing had no influence on weed dry matter. Sweet potato growers on well-drained sandy loam and similar soils in the humid tropics should consider adopting 60 cm × 90 cm with ‘intercropping’ to maximize space and resource use. Alternatively, they should space sweet potato 30 cm × 90 cm in sole production to achieve the desired density (3.70 plants m–2) for optimizing resource use and tuber yield.Key words: leaf area index, number of leaves, tuber weight per plant, optimum tuber yield, sweet potat

Diversity and spatial distribution of epiphytic flora associated with four tree species of partially disturbed ecosystem in tropical rainforest zone

As components of forest communities, epiphytes influence litter and nutrient cycling while providing shelter, nesting materials and food for arboreal animals, thereby promoting diversity. Their preference for certain tree species (phorophytes) influences biodiversity and distribution, but this association is poorly understood in the tropics. We assessed the diversity and spatial distribution of epiphytes associated with four phorophytes (Alstonia booneii, Peltophorum pterocarpum, Mangifera indica and Terminalia catappa) in southern Nigeria, with number of trees sampled as 4, 29, 32 and 44, respectively. The epiphytes were delineated, sampled and identified. Soil samples were collected from tree pockets for textural and pH analyses. On the four phorophytes, 265 epiphytes under seven species (Platycerium elephantotis, Microgamma owariensis, Nephrolepis biserrata, Funaria hygrometrica, Axonopus compressus, Commelina benghalensis and Ficus spp.) and five families (Polypoidaceae, Funariaceae, Poaceae, Commelinaceae and Moraceae) were recorded. The three most abundant were Funaria hygrometrica (109), Platycerium elephantotis (102) and Microgamma owariensis (44), being present on all four phorophytes. Funaria hygrometrica and Platycerium elephantotis were the most abundant on M. indica (32 each) and T. catappa (44 and 39, respectively). Nephrolepis biserrata appeared only once on T. catappa; so too did Axonopus compressus and Commelina benghalensis on P. pterocarpum. Altogether, A. booneii, P. pterocarpum, M. indica and T. catappa had 11, 62, 89 and 103 epiphytes, respectively. Funaria hygrometrica traversed three tree strata, while others were restricted to two or even one stratum. Canopy layer, middle stratum and lower portion hosted four, five and three epiphytic species, respectively out of the seven recorded, pointing to the relative importance of light, spaciousness and moisture, respectively in epiphyte abundance on trees. Epiphytes distribution on phorophytes was not influenced by texture of the arboreal soils, but was inversely related to their pH. This study has provided useful information on epiphyte-phorophyte association in tropical environments and deserves repetition with more tree species in more natural forests.Keywords: forest tree species, tree spatial strata, epiphyte distribution, species abundance, Nigeri