การปรับตัวลักษณะสรีรวิทยาและการเจริญเติบโตของต้นกาแฟโรบัสต้าภายใต้สวนยางพารา

Abstract

Coffee tree can be grown under shaded condition in a mixed cropping system. To evaluate the adaptation of robusta coffee leaf structural traits from the effects of full sunlight and shaded conditions. Also, the association of rubber tree with robusta coffee sapling was investigated to evaluate the effects of the limitation of leaf traits on the vegetative development. The experiment was carried out on the rubber plantation of rubber-based small holders, located at Satun province, in the South of Thailand. There was conducted under three different plots: sole robusta coffee (T1), rubber-robusta coffee intercropping (8-year-old rubber plantation) (T2) and rubber-robusta coffee intercropping (16-year-old rubber plantation) (T3). Also, the effects of chemical and organic fertilizer applications were investigated on coffee seedlings in one rubber plantation. Experiment was conducted with three treatments of 100% standard chemical fertilizer (15-15-15) (T1), 75% standard chemical fertilizer and 50% manure (T2), and 50% standard chemical fertilizer and 50% manure (T3). Results found that the effect of shading on coffee growth was significant in the rainy season, it tended to have a larger growth (height and canopy width) than in summer. Only in the rainy season, shade grown saplings had significantly greater LA (leaf area), leaf fresh weight, leaf dry weight and leaf nitrogen concentration (N) than the full-sun saplings. However, full-sun leaves generally had higher leaf chlorophyll content (Chltotal/LA) and leaf carotenoid content (Car/LA) than shaded leaves which appeared to be significantly affected. Under the rubber plantation, mean percentage of light penetration did not exceed 60% at any point measured beneath the rubber trees, while it was always 100% in full sunlight condition. The soil moisture content rose from the soil (20 cm soil depth) inside the rubber tree plantation. Coffee plants grown under the full sunlight had higher values of height, canopy width, stem diameter and no. of leaves than coffee plants under shaded conditions. Robusta coffee leaves under direct sunlight were also significantly higher in leaf nitrogen content and nitrogen content/leaf area than those under shaded conditions. For the root system, there were significant differences of fine root length in the 20 and 40 cm layers which the highest densities found in coffee plants under direct sun light. However, no significant differences of root diameter were found. In addition, the significantly higher tree height (105.57 cm) was obtained using standard chemical fertilizer than with other manure applications, but there was no effect on canopy width, stem diameter and number of leaves in the Robusta coffee seedlings. Root length at 20 cm and 40 cm soil depths was significantly different according to the level of chemical fertilizer. New leaf flushing at 51.43% showed the highest increase for 75% chemical fertilizer and 50% manure. Chemical and organic fertilizer had no adverse effect on leaf characteristics of Robusta coffee seedlings (leaf area, leaf dry weight, chlorophyll contents and TNC). Leaf nitrogen content and nitrogen content/leaf area (Na) were significantly higher for the 75% chemical fertilizer and 50% manure seedlings. This study indicated that growth potential of coffee saplings was strongly limited by combination of shaded and root competition conditions under rubber plantation. Also, an adequate supply of chemical and organic fertilizers could promote rapid growth development of Robusta coffee saplings grown under shaded condition. Further studies on shaded Robusta coffee are required to focus on light transmission and root distribution for the vegetative development and production of coffee trees, as an intercropping system in immature and mature rubber plantations.