Oil palm water use: calibration of a sap flux method and a field measurement scheme

Abstract

Oil palm (Elaeis guineensis Jacq.) water use was assessed by sap flux density measurements with the aim to establish the method and derive water-use characteristics. Thermal dissipation probes were inserted into leaf petioles of mature oil palms. In the laboratory, we tested our set-up against gravimetric measurements and derived new parameters for the original calibration equation that are specific to oil palm petioles. In the lowlands of Jambi, Indonesia, in a 12-year-old monoculture plantation, 56 leaves on 10 palms were equipped with one sensor per leaf. A 10-fold variation in individual leaf water use among leaves was observed, but we did not find significant correlations to the variables trunk height and diameter, leaf azimuthal orientation, leaf inclination or estimated horizontal leaf shading. We thus took an un-stratified approach to determine an appropriate sampling design to estimate stand transpiration (Es, mm day(-1)) rates of oil palm. We used the relative standard error of the mean (SEn, %) as a measure for the potential estimation error of Es associated with sample size. It was 14% for a sample size of 13 leaves to determine the average leaf water use and four palms to determine the average number of leaves per palm. Increasing these sample sizes only led to minor further decreases of the SEn of Es. The observed 90-day average of Es was 1.1 mm day(-1) (error margin ± 0.2 mm day(-1)), which seems relatively low, but does not contradict Penman-Monteith-derived estimates of evapotranspiration. Examining the environmental drivers of Es on an intra-daily scale indicates an early, pre-noon maximum of Es rates (11 am) due to a very sensitive reaction of Es to increasing vapor pressure deficit in the morning. This early peak is followed by a steady decline of Es rates for the rest of the day, despite further rising levels of vapor pressure deficit and radiation; this results in pronounced hysteresis, particularly between Es and vapor pressure deficit.

Oil Palm and Rubber Tree Water Use Patterns: Effects of Topography and Flooding

“…For oil palm, we followed the sampling and data processing procedure as described in Niu et al (2015). Four oil palms, each with four sensors inserted into individual leaf petioles, were equipped with TDPs.…”

“…Four oil palms, each with four sensors inserted into individual leaf petioles, were equipped with TDPs. Specific calibration parameters were applied to calculate J s (Niu et al, 2015) and leaf conductive areas (cm 2 ) were determined from a linear regression with petiole baseline length (Niu et al, 2015). To calculate palm water use rates (WU, kg day -1 ), respective sap flux densities were multiplied by average leaf conductive areas and by the average number of leaves per palm.…”

“…Multiplying the resulting average palm water use by the number of palms per unit of land yielded stand transpiration rates ( T ; mm day -1 ). All 16 TDP sensors of a certain oil palm plot running simultaneously would result in an error margin of estimated stand transpiration of oil palms of about 10% (Niu et al, 2015). This error is due to a limited sample size for both, establishing the average water conductive area per palm (by counting leaves and measuring petiole baseline length on a limited number of palms) and establishing average J s (with a limited number of TDP sensors running simultaneously).…”

“…Results are presented both as daily values and as diurnal hourly means; as a measure of the spatial, within-plot variability of J s and stand transpiration, standard errors (SE) of these values are provided; they were derived among all trees or palms within a certain plot (i.e., from 16 sensors on four oil palms or 12 sensors on six rubber trees, in analogy to Niu et al, 2015). Maximum J s values ( J smax ) were derived from the 90-percentile of hourly J s observations of the selected sunny days.…”

Modeling Potential Impacts of Planting Palms or Tree in Small Holder Fruit Plantations on Ecohydrological Processes in the Central Amazon

“…Most of the existing literature is focused on "cosmopolitan" palms, such as coconut, date and oil palms [15], whereas publications on the water use characteristics of palm species currently restricted to a small geographic area are almost completely missing. To our knowledge, the only existing study on the water relations of palms in the Amazon attributes only a minor contribution of palm trees to overall stand transpiration in a mixed forest canopy; however, it outlines the relatively high individual water consumption of these plants [1,16].…”