Abstract
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 potato
Highlights
Among the tuber crops of the world, sweet potato (Ipomoea batatas (L.) Lam) ranks third in importance after Iris potato and cassava (Ikeorgu, 2003)
Both variables showed lowest values in plots where the plants were spaced 90 cm × 90 cm which was the widest spacing and lowest density. They showed highest values in plots where the plants were spaced 30 cm × 90 cm which was the second closest spacing and highest density. These two variables tended to progressively increase as plant spacing became closer and plant density higher up till the second closest spacing and highest density; thereafter, they showed a drop in values in plots with the closest spacing and highest density
The results of this study show that plant spacing and the ensuing plant density influenced the growth and yield of sweet potato on a well-drained sandy loam belonging to the soil order of Ultisols in Benin, located in the rainforest belt in southern Nigeria typifying a humid tropical environment
Summary
Among the tuber crops of the world, sweet potato (Ipomoea batatas (L.) Lam) ranks third in importance after Iris potato and cassava (Ikeorgu, 2003). The only tuber crop with a positive per capita annual rate of production in sub-Saharan Africa (Tewe et al, 2003). This rests on its high yield potential that may be realized within a fairly short growing season. Sweet potato tuber is a major source of carbohydrate and can be eaten without processing. The leaves and tubers may be processed into starch, noodles, candy, flour, desserts and alcohol for human consumption. There is advocacy for the cultivar known as orange-fleshed sweet potato for being rich in -carotene (precursor for vitamin A) (Anderson et al, 2007)
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