Methods to account for tree-scale variability in soil- and plant-related parameters in oil palm plantations

Abstract

Background and aims Lateral tree-scale variability in plantations should be taken into account when scaling up from point samples, but appropriate methods for sampling and calculation have not been defined. Our aim was to define and evaluate such methods. Methods We evaluated several existing and new methods, using data for throughfall, root biomass and soil respiration in mature oil palm plantations with equilateral triangular spacing. Results Three ways of accounting for spatial variation within the repeating tree unit (a hexagon) were deduced. For visible patch patterns, patches can be delineated and sampled separately. For radial patterns, measurements can be made in radial transects or a triangular portion of the tree unit. For any type of pattern, including unknown patterns, a triangular sampling grid is appropriate. In the case studies examined, throughfall was 79 % of rainfall, with 95 % confidence limits being 62 and 96 % of rainfall. Root biomass and soil respiration, measured on a 35-point grid, varied by an order of magnitude. In zones with steep gradients in parameters, sampling density has a large influence on calculated mean values. Conclusions The methods defined here provide a basis for representative sampling and calculation procedures in studies requiring scaling up from point sampling, but more efficient methods are needed. (Résumé d'auteur

Total and heterotrophic soil respiration in a swamp forest and oil palm plantations on peat in Central Kalimantan, Indonesia

“…A higher SRt rate near trunk than in the harvest path is in agreement with observations by Comeau et al (2016) and Dariah et al (2014) in mature plantations established on peat soils and by Nelson et al (2014) in mature plantations on mineral soil. Nelson et al (2014) attributed elevated respiration near trunk to inputs of organic matter in stemflow, root respiration and decomposition of root-derived organic matter since root density was higher there than elsewhere in the studied plantation. Root density in the 6 cm top soil was higher at the CT than at the FT position in the OP2012 but not in the OP2007.…”

“…Root density in the 6 cm top soil was higher at the CT than at the FT position in the OP2012 but not in the OP2007. Oil palm root biomass often exhibits a radial pattern (Dariah et al 2014;Haron et al 1998;Nelson et al 2014) yet this is not always the case (Oktarita et al 2017;Ruer 1967). The difference in spatial allocation of roots between the plantations as well their difference in root density may originate from their development stage.…”

“…The thorough grid approach undertaken by Nelson et al (2014) in a mature plantation on mineral soil showed a patchy distribution of soil respiration with highest rates observed near trunks, in the frond pile and where empty fruit bunches had been placed. These areas all together accounted for about 40% of plot-scale soil respiration.…”

“…Given the existing trade-off between spatial and temporal variability, our design was limited to two spatial positions for assessing SRt. We tested it by computing plot-scale SRt from the respiration rates measured by Nelson et al (2014) near trunks and at mid-distance between palms and the 35:65 ratio we computed for the CT:FT share in the OP2007. We obtained a result of 7.0 lmol CO 2 m -2 s -1 very close to the 7.7 lmol CO 2 m -2 s -1 flux calculated by Nelson et al (2014), which suggests that our design and assumptions can capture reasonably well the spatial variability in SRt inherent to mature plantations.…”

Key unknowns in nitrogen budget for oil palm plantations. A review

“…Empty fruit bunches are usually applied in piles adjacent to the harvest path. Temporal and spatial heterogeneity may both influence N dynamics and may also affect the measurement accuracy of N fluxes and stocks (Nelson et al 2014). Third, internal fluxes of N within the plantation may be important.…”