ABSTRACT
Soil moisture stress is a major abiotic factor limiting oil palm (Elaeis guineensis Jacq.) production in Nigeria especially in the dry season. Two greenhouse experiments were conducted at the Nigerian Institute for Oil palm Research, (NIFOR), near Benin City, Edo State Nigeria. The first experiment was carried out from October 2018 – March 2020 to determine the effects of soil moisture stress on growth, leaf relative water content and nutrient uptake by oil palm seedlings. To obtain more information on how growth of oil palm seedling is affected by progressive soil moisture stress, a second experiment was carried out from October 2019 to March 2020. In these trials, plants were grown under greenhouse conditions in 35 x 40 cm polyethylene pot containing sandy loam soil under well - watered and moisture stress conditions. In the control (CT), plants were kept near field capacity (FC) 95 - 100 % FC. In the stressed treatment, the soil moisture was reduced gradually by withholding water, watering was resumed when soil moisture dropped to 70 - 75, 60 - 65, 50 - 55, 40 - 45 and 30 - 35 % of FC. Each moisture level was maintained by weighing pot with the seedling daily and then compensating the water loss thorough evapo – transpiration by adding equivalent amount of water.
Results showed that plant height, leaf area, number of leaves, collar girth and total dry weight of oil palm seedling were highest in the control treatment (95 – 100 % FC). Above mentioned growth parameters did not significantly differ between (95 – 100 % FC) and 70 – 75 % FC. However, when soil moisture stress increased from 60 – 65 to 30 – 35 % FC vegetative growth and total dry weight were negatively affected. Relative leaf water content of oil palm seedling decreased with increasing levels of soil moisture stress. Relative leaf water content in the control (95 – 100) and moisture stress at 70 – 75 % FC were significantly similar. When soil moisture stress increased from 60 – 65 to 30 – 35 % FC relative leaf water content was significantly reduced as compared with 95 – 100 % FC. Nitrogen (N), Phosphorus (P), Potassium (K) and Magnesium (Mg) uptake by oil palm seedling also decreased with increasing levels of soil moisture stress in the following order 95 - 100 > 70 - 75 > 60 - 65 > 50 - 55 > 40 - 45 > 30 - 35 % of FC. However, total N, K and Mg uptake by plants did not significantly differ between the control (95 - 100 %) and soil moisture stress at 70 - 75 % of FC. In addition, treatments 95 - 100, 70 - 75 and 60 - 65 % of FC produced statistically the same total Mg uptake. When soil moisture stress increased from 60 - 65 to 30 - 35 of FC, total N, P and K uptake by oil palm seedling were significantly reduced as compared with the well - watered control (95 - 100 % FC). Moreover, there was significant reduction in increased total P uptake when moisture stress increased from 50 – 55 to 30 - 35 % of FC as compared with 95 - 100 % FC. The current study showed that soil moisture stress beyond 70 – 75 % FC should be avoided especially in the dry season to minimize reductions in nutrient uptake, leaf water status and growth of oil palm seedling grown on sandy loam of Orlu series in the area.
