Estimating oil-palm Si storage, Si return to soils and Si losses through harvest in smallholder oil-palm plantations of Sumatra, Indonesia
Abstract. Silicon (Si) is known to have multiple beneficial effects on crops. Most plant-available Si in soils is provided through litter decomposition and subsequent phytolith dissolution, especially in strongly desilicated tropical soils. The importance of Si cycling in tropical soil-plant systems raised the question if oil-palm cultivation, the oil palm being a Si-accumulating crop, alters Si cycling. As Si accumulates in plant tissue, we hypothesized that i) Si is stored in the aboveground biomass of oil palms with time, and that ii) the system might lose considerable amounts of Si every year through fruit-bunch harvest. To test these hypotheses, we sampled leaflets, the rachis, fruit-bunch stalk, fruit pulp, kernels and frond bases from mature oil palms planted on well-drained and temporarily flooded riparian smallholder oil-palm plantations (n = 4 each) in lowland Sumatra, Indonesia. We quantified Si concentrations of these oil-palm parts by NaCO3 extraction. We further estimated Si storage in the total above-ground biomass of the oil palms, Si return to soils through decomposing pruned palm fronds, and Si losses from the system through harvest, to assess if Si return to soils via pruned palm fronds sufficed for maintaining Si cycling in the system, or if any measures are needed to compensate for Si export through fruit-bunch harvest. At all sites, leaflets of oil-palm fronds had a significantly higher (p ≤ 0.05) mean Si concentration (≥ 1 wt. %) than the rachis, frond base, fruit-bunch stalk, fruit pulp and kernel (≤ 0.5 wt. %). All analysed oil-palm parts had a Si/Ca weight ratio ≥ 1, except for the rachis. At well-drained sites, mean Si concentrations in leaflets increased with palm-frond age (R² = 0.98). Estimates of Si storage in the total above-ground biomass of oil palms, Si return to soils through decomposing pruned palm fronds, and Si losses through harvest were similar at well-drained and riparian sites: a single palm tree could store about 4–5 kg of Si in its total above-ground biomass, a smallholder oil-palm plantation of 1 hectare could store about 550 kg of Si in the palm trees’ above-ground biomass. Pruned palm fronds were estimated to return 110–131 kg of Si per hectare to topsoils each year. Fruit-bunch harvest corresponded to an annual Si export of 32–72 kg Si per hectare in 2015 and 2018. Thus, on smallholder plantations in our study area, more Si can be returned to soils through pruned palm fronds than is lost through fruit-bunch harvest. Greater Si losses would occur if oil-palm stems were removed from plantations prior to replanting. Therefore, it is advisable to leave oil-palm stems on the plantations e.g., by distributing chipped stem parts across the plantation at the end of a plantation cycle (~25 years). This would return about 550 kg ha-1 Si stored in the palm trees’ above-ground biomass to the soils.
Britta Greenshields et al.
Britta Greenshields et al.
Britta Greenshields et al.
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It is my great pleasure to review the manuscript (egusphere-2022-905) entitled by ‘Estimating oil-palm Si storage, Si return to soils and Si losses through harvest in smallholder oil-palm plantations of Sumatra, Indonesia’.
The authors present a manuscript that provides interesting data supporting some hypotheses raised during the last years: first, that the contribution of crop in soil Si bioavailability and Si uptake of crop; second, that authors point at some interesting findings regarding their Si flux via driving various Si distribution in plant. The experimental work has been well performed. It consisted of experimental analysis that yielded some interesting data. It is in general nicely documented by the authors, but some parts are not well introduced and discussed. It is a bit strange on missing the data from soils, while it may be improved by introducing recent findings from soils. Overall, I support publication of this work. Yet I have some comments to be considered before further publication.
at line 15, to revise ‘raised’ to ‘raise’; to revise ‘if’ to ‘as’; in fact, high Si concentrations
Oil-palm has been by Munevar and Romero (2015), suggesting a high Si accumulator.
At line 20, Revise ‘by NaCO3 extraction’ to ‘using NaCO3 extraction’; to revise ‘are needed’ to ‘were’;
At line 35, [more Si can be returned to soils through pruned palm fronds than is lost
35 through fruit-bunch harvest….] is not right as it is hard to understand. Should be rephased.
In addition, Abstract should be shortened and precise a bit to highlight the key significance and findings;
In introduction session, I encourage that authors carefully consider the previous studies on straw return regarding its silicon recycling and silicon uptake; what have it done? what should be considered on the Si status under the management of their return in cropland; next step to point at What is its existing gap in oil cultivation? Indeed, it is true that it is not well-investigated on the Si flux of oil palm. This is a key challenge, especially that their respective return on Si biological cycle is largely active in the highly weathered soil where oil palm grows. This needs to a better estimate on Si distribution in oil palm, bettering predicating their management in future. Indeed, crop straw return has gained increasing attention in recent years due to its importance as an approach to supply soil biogenic and plant available silicon (Si) for mitigating agricultural desilication due to its importance as nutrient for many plants. Recent research, for instance, has demonstrated that biological processes, such as plant-Si-uptake, phytolith production and recycling of phytoliths in soil, are important regulators of the Si cycle in the soil-plant ecosystems (Li et al., 2020, Geoderma 368, 114308; Puppe, et al., Geoderma 403 (2021): 115187, and so on). Returning their phytoliths into soil thus boosts the biological recycling of Si in agroecosystem, sustaining its health development, especially in highly weathered soils (Li and Delvaux 2019, GCB Bioenergy 11 (11), 1264-1282). But this effect is less studied in oil-palm plantations, as it is limited on a better understanding of Si distribution in oil palm.
At line 145, ‘The procedure was conducted on two replicate samples’ , did each sample have two replicates? Why not three replicates? DeMaster technique using 1% Na2CO3 can underestimate amorphous silica (i.e., phytogenic silicon, phytolith; Meunier et al., 2014; Li et al., 2019; Puppe, et al.,2019). Author should refer this issue, as this directly impact the Si content in the analyzed plant tissue and then its budget.; Also a bit strange is that soil data is missing in this section.
At line 260-265, these sentence look much more discussion than results.
To add ‘that’ before ‘mean Si concentration increases with leaf age’; what do you mean ‘In fact, Si availability
could suffice for a second generation of oil-palm plantations’? is it soil Si availability? If yes, could authors offer these data referring soil analysis?
I am not native English speaker but still found some grammatic errors in this manuscript, but I feel that it will be better to improve its English a bit. Personally, it also needs to enhance its readily for reader, to concentrate its key finding and significance to be highlighted.