Search

Most plant-available Si in strongly desilicated soils is provided through litter decomposition and subsequent phytolith dissolution. The importance of silicon (Si) cycling in tropical soil–plant systems raised the question of whether oil-palm (Elaeis guineensis Jacq.) cultivation alters Si cycling. As oil palms are considered Si hyper-accumulators, we hypothesized that much Si is stored in the above-ground biomass of oil palms with time. Furthermore, the system might lose considerable amounts of Si every year through fruit-bunch harvest. To test these hypotheses, we analysed Si concentrations in fruit-bunch stalks, fruit pulp and kernels, leaflets, rachises, and frond bases of mature oil palms on eight smallholder oil-palm plantations in Sumatra, Indonesia. We estimated Si storage in the total above-ground biomass of oil palms, Si return to soils through decomposing pruned palm fronds, and Si losses from the system through harvest. Leaflets of oil-palm fronds had a mean Si concentration of > 1 wt %. All other analysed plant parts had < 0.5 wt % Si. According to our estimates, a single palm tree stored about 4–5 kg Si in its total above-ground biomass. A smallholder oil-palm plantation stored at least 550 kg Si ha -1 in the palm trees' above-ground biomass. Pruned palm fronds returned 111–131 kg of Si ha -1 to topsoils each year. Fruit-bunch harvest corresponded to an annual Si export of 32–72 kg Si ha -1 in 2015 and 2018. Greater Si losses (of at least 550 kg Si ha -1) would occur from the system 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). [ABSTRACT FROM AUTHOR]

Effects of oil-palm (Elaeis guineensis Jacq.) management on silicon (Si) cycling under smallholder oil-palm plantations have hardly been investigated. As oil palms are Si accumulators, we hypothesized that management practices and topsoil erosion may cause Si losses and changes in spatial Si concentration patterns in topsoils under oil-palm cultivation. To test this hypothesis, we took topsoil samples under mature oil-palm plantations in well-drained and riparian areas of Jambi Province, Indonesia. The samples were taken from four different management zones within each oil-palm plot: palm circles, oil-palm rows, interrows, and below frond piles. We quantified mobile Si (Si M) and Si in amorphous silica (Si Am) by the extraction of CaCl 2 and NaCO 3 , respectively. Both fractions are important Si pools in soils and are essential for plant–soil Si cycling. We further installed sediment traps on sloping, well-drained oil-palm plantations to estimate the annual loss of soil and Si Am caused by erosion. In well-drained areas, mean topsoil Si Am concentrations were significantly higher below frond piles (3.97 ± 1.54 mg g -1) compared to palm circles (1.71 ± 0.35 mg g -1), oil-palm rows (1.87 ± 0.51 mg g -1), and interrows (1.88 ± 0.39 mg g -1). In riparian areas, the highest mean topsoil Si Am concentrations were also found below frond piles (2.96 ± 0.36 mg g -1) and in grass-covered interrows (2.71 ± 0.13 mg g -1), whereas topsoil Si Am concentrations of palm circles were much lower (1.44 ± 0.55 mg g -1). We attributed the high Si Am concentrations in topsoils under frond piles and in grass-covered interrows to phytolith release from decaying oil-palm fronds, grasses, and sedges. The significantly lower Si Am concentrations in palm circles (in both well-drained and riparian areas), oil-palm rows, and unvegetated interrows (only in well-drained areas) were explained by a lack of litter return to these management zones. Mean topsoil Si M concentrations were in the range of ∼ 10–20 µ g g -1. They tended to be higher in riparian areas, but the differences between well-drained and riparian sites were not statistically significant. Soil-loss calculations based on erosion traps confirmed that topsoil erosion was considerable in oil-palm interrows on slopes. Erosion estimates were in the range of 4–6 Mg ha -1 yr -1 , involving Si Am losses in a range of 5–9 kg -1 ha -1 yr -1. Based on the observed spatial Si patterns, we concluded that smallholders could efficiently reduce erosion and support Si cycling within the system by (1) maintaining a grass cover in oil-palm rows and interrows, (2) incorporating oil-palm litter into plantation management, and (3) preventing soil compaction and surface-crust formation. [ABSTRACT FROM AUTHOR]

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 oilpalm 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' aboveground 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. [ABSTRACT FROM AUTHOR]

Effects of oil-palm (Elaeis guineensis Jacq.) management on silicon (Si) cycling under smallholder oilpalm plantations have hardly been investigated. As oil palms are Si accumulators, we hypothesized that management practices and topsoil erosion may cause Si losses and changes in spatial Si concentration pattems in topsoils under oil-palm cultivation. To test this hypothesis, we took topsoil samples under mature oil-palm plantations in well-drained and riparian areas of Jambi Province, Indonesia. The samples were taken from four different management zones within each oil-palm plot: palm circles, oil-palm rows, interrows and below frond piles. We quantified mobile Si (Si,) and Si in amorphous silica (Si) by CaCl and NaCO extraction, respectively. Both fractions are important Si pools in soils and are essential for plant-soil Si cycling. We further installed sediment traps on sloping, well-drained oil-palm plantations to estimate the annual loss of soil and Si caused by erosion. In well-drained areas, mean topsoil SiAm concentrations were significantly higher below frond piles (3.97 ±1.54 mg g') compared to palm circles (1.71± 0.35 mg g'), oil-palm rows (1.87 ± 0.51 mg g') and interrows (1.88 ± 0.39 mg g'). In riparian areas, highest mean topsoil Siconcentrations were also found below frond piles (2.96 ± 0.36 mg g') and in grass-covered interrows (2.71 ± 0.13 mg g'), whereas topsoil Si concentrations of palm circles were much lower (1.44 ± 0.55 mg g'). We attributed the high Siconcentrations in topsoils under frond piles andin grass-covered interrows to phytolith release from decaying oil-palm fronds, grasses, and sedges. The significantly lower SiAm concentrations in palm circles (in both well-drained and riparian areas), oil-palm rows and unvegetated interrows (only in well-drained areas) were explained by a lack of litter return to these management zones. Mean topsoil Si; concentrations were in a range of10 20 g g'. They tended to be higher in riparian areas, but the differences between well-drained and riparian sites were not statistically significant. Soil-loss calculations based on erosion traps confirmed that topsoil erosion was considerable in oil-palm interrows on slopes. Erosion estimates were in a range of 4 6Mg ha' yr', involving Si losses in a range of 5 9 kg' ha' yr'. Based on the observed spatial Si patterns, we concluded that smallholders could efficiently reduce erosion and support Si cycling within the system by (1) maintaining a vegetation cover in oil-palm rows and interrows, (2) incorporating oil-palm litter into farm management and (3) preventing soil compaction and surface-crust formation. [ABSTRACT FROM AUTHOR]

Copyright of Geostandards & Geoanalytical Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the most widely used sample preparation methods for Si isotopic analyses (δ30Si and δ29Si) is based on cationic chromatography, which does not remove anions from samples. Although it was first thought that the presence of anions in natural concentrations does not distort the isotopic analyses, it has recently been shown that the presence of sulfate can induce a significant shift in isotopic ratio measurements above SO42−/Si ratios (wt) of 0.02. Here, we show that dissolved organic matter can also induce a major Si isotopic bias when analysing river waters. To overcome these non-spectral matrix effects we propose fast and reliable ways, tested on natural freshwater and rock digestion solutions. The sulfate matrix effect is solved by adding to both sample and bracketing standard sulfuric acid in large excess compared to the naturally occurring SO42−. The organic matrix is mineralized by the combined action of UV-C and ozone. We also provide the first δ30Si signature measurements of two common geostandards: SGR-1 (δ30Si = +0.03‰) and FeR-1 (δ30Si = −0.20‰). [ABSTRACT FROM AUTHOR]

In Vietnam, approximately 39 million tons of rice (Oryza sativa) residues accrue every year. In this study, we quantified soil nutrient balances of paddy rice fields under different crop-residue management practices in northern Vietnam. On twelve farms, we calculated nutrient balances for the four prevalent rice-residue management practices, i.e., (1) direct incorporation of rice residues into the soil, (2) application of rice-residue compost, (3) burning of rice residues on the field, and (4) the use of rice residues as fodder for livestock. Soils under practices (1) to (3) showed a positive nutrient balance, which indicates that soil fertility can be maintained under these practices and that the amounts of chemical fertilizers can be considerably reduced. If not, there is a risk of eutrophication in the surrounding surface waterbodies. Practice (4), in contrast, resulted in a negative nutrient balance, which indicates the need for returning nutrients to the soils. From our findings we conclude that knowledge about the effects of rice-residue management practices on nutrient cycles may help to optimize the use of fertilizers, resulting in a more sustainable form of agriculture. [ABSTRACT FROM AUTHOR]

A correction to the article on landscape cultivation in terrestrial ecosystems, published in a previous issue is presented.