Effect of sowing depth and mulch application on emergence and growth of shea butter tree seedlings (Vitellaria paradoxa C. F. Gaertn.)
Shea butter tree seeds from three sources (Makurdi, Akwanga and Kano), were sown at five depths (2, 4, 6, 8 and 10 cm) under mulch and no-mulch conditions at Makurdi in 2006. The aim was to determine the effect of seed source, sowing depth and mulching status on seedling emergence and growth. Factorial combinations of the treatments were arranged in randomized complete block design (RCBD) replicated three times. Analysis of variance (ANOVA) showed significant main effects of treatment on seedling emergence and growth parameters. Similarly, both first and second order interactions were significant. The Akwanga seed source gave significantly higher percentage seedling emergence and growth than all other seed sources. While seeds obtained from Makurdi emerged better at 2 - 8 cm depth, those from Kano did so when sown at 2 - 4 cm. On the other hand, the Akwanga accession showed better emergence at 4 - 8 cm depth, giving poorer E% values at 2 and 10 cm depths. Generally, sowing depths giving better emergence also variously showed better seedling growth in one or two characters at various monitoring intervals. The superior seedling emergence of no-mulch treated plots across most depths was more apparent with the Makurdi and Akwanga seed sources. However, seedling growth was generally more vigorous in plots that did not receive any mulch, although with the Kano seed source, this became more apparent at the final seedling growth stage (50 WAS). It has been inferred that the better emergence and growth of the Akwanga provenance could be due to their larger seed size. Also, while smaller seeds could be planted at 2 - 8 cm depths, larger ones may do better at 4 - 8 cm depth. The study could not establish any positive effect of mulching on shea seedling emergence and growth.