EFFECTS OF SHADING, IRRIGATION AND MYCORRHIZAL INOCULATION ON GROWTH AND DEVELOPMENT OF OIL PALM (Elaeis guineensis jacq) SEEDLINGS IN THE NURSERY

Abstract

Experiments were conducted to examine the growth and development of oil palm seedlings subjected to shading, irrigation regimes and mycorrhizal inoculation in the dry season. Treatments were 2 x 2 x 2 factorial scheme consisting of shade and no-shade (open sun), 7 and 14 day irrigation intervals and mycorrhizal inoculation or non-inoculation. Seedlings that were grown under shade and irrigated weekly produced highest number and length of fronds, and shoot, leaf and frond weights in addition to taller plants compared to open sun (unshaded) seedlings. Across irrigation treatments, un-shaded (open sun) seedlings had lower weights of leaf, frond and shoot biomass. Seedlings development pattern was affected by the treatments imposed: the effects of shade treatments were significant (P ≤ 0.05) on plant height and frond length across sampling dates (2, 8, 14 and 20 weeks after planting, WAP). Significant differences were obtained for number of fronds at 2 and 8 WAP between seedlings under shade and unshaded treatments. Though shaded seedlings produced more fronds, this was not significantly different from unshaded (open sun) seedlings at 14 and 20 WAP. Oil palm seedlings that were irrigated weekly were taller than those irrigated fortnightly, although treatment differences were not significant. Non-shaded treatment appeared to have enhanced below ground (root biomass) growth than the above ground (shoot biomass) while the weight and number of roots were not significantly different for seedlings grown under open sun and shaded treatments. The non-shaded seedlings that were irrigated fortnightly produced longer roots in comparison with those unshaded and had weekly irrigation. Root development was enhanced by fortnightly irrigation compare to weekly irrigation as seedling root weight and length of roots were higher in the former. Shade and irrigation regimes affected soil moisture contents and plant water use (water consumption), weekly irrigation produced higher soil moisture contents and water use under shade than for open sun at 2, 8 and 14 WAP. Seedling grown under shade and irrigated weekly used larger amount of water compared to those irrigated fortnightly. Significant interactions were obtained between shade and irrigation regimes for most of the growth parameters (plant height, frond length, root length, shoot weight, leaf weight and frond weight) measured. Mycorrhizal inoculation enhanced growth responses of oil palm seedlings to irrigation (weekly) and shade. The presence of mycorrhizae spores on the roots of oil palm seedlings was examined. Black dots of mycorrhizae fungi (Acaulospora scrobiculatu) were found on roots of oil palm seedlings three months after the application of Arbuscular Mycorrhiza Fungus (AMF). The black dots were more on unshaded seedlings which indicated higher mycorrhizal colonization of roots compared to shaded treatment. The differences were not significant between open sun under fortnight and weekly irrigation. In general, mycorrhizal inoculation enhanced the responses of oil palm to shading and irrigation regimes imposed