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ARTICLE IN PRESSAAE-50808; No. of Pages 9
Basic and Applied Ecology xxx (2014) xxx–xxx
lant-available silicon in paddy soils as a key factor forustainable rice production in Southeast Asia
himo Klotzbüchera,∗, Anika Marxenb, Doris Vetterleinb, Janina Schneikerc,anfred Türkec, Nguyen van Sinhd, Nguyen Hung Manhd, Ho van Chiene,
eonardo Marquezf, Sylvia Villarealg, Jesus Victor Bustamanteh,einhold Jahna
Institute of Agricultural and Nutritional Sciences – Soil Science, University of Halle, Von-Seckendorff-Platz 3,6120 Halle (Saale), GermanyDepartment of Soil Physics, Helmholtz Centre for Environmental Research UFZ, Theodor-Lieser-Straße 4, 06120alle (Saale), Germany
Department of Ecology and Ecosystem Management, Terrestrial Ecology Research Group, Technische Universitätünchen, Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising, Germany
Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet,ghia Do, Cau Giay, Ha Noi, Viet Nam
Southern Regional Plant Protection Center, MARD, Long Dinh, Tien Giang, Viet NamCrop Protection Division, Philippine Rice Research Institute, Maligaya, Munoz, Nueva Ecija, PhilippinesInternational Rice Research Institute – IRRI, Los Banos, PhilippinesLas Vegas Restaurant, Banaue, Ifugao 3601, Philippines
eceived 15 November 2013; accepted 1 August 2014
bstract
Rice is among the most important crops for human nutrition. The need to increase yields is commonly achieved by agriculturalntensification that often comes along with negative impacts on the environment. In 2011, the interdisciplinary LEGATO projectas launched with the aim to advance sustainable rice production. A key feature for sustainable rice production is silicon
Si) availability. Si can e.g. improve rice crop resistance against pathogens and prevent the uptake of toxic metals. Herein,e introduce the characteristics of the seven LEGATO study regions in Vietnam and the Philippines (i.e., climate, geology,
oils, agricultural practices) ranging from lowlands with intensive production to mountain regions with extensive and traditional
roduction systems. Secondly, we show data on concentrations of plant-available Si (Sipa) in topsoils of paddy fields (Ap + Arporizons) and of sites with an alternative land-use (forest, upland crops), and discuss factors determining spatial differences ini concentrations. Results show that Si concentrations in topsoils of paddies (assessed by acetate extraction) greatly differ pa paPlease cite this article in press as: Klotzbücher, T., et al. Plant-available silicon in paddy soils as a key factor for sustainable rice productionin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/10.1016/j.baae.2014.08.002
etween Philippine (141–322 mg Si kg−1) and Vietnamese (20–51 mg Si kg−1) regions. This can be explained by differences ineo-/pedologic conditions between the countries. Large Sipa concentrations in the Philippines are due to recent rock formationy active volcanism, hence, by a large Sipa input due to mineral weathering in recent geologic history. Land-use can alsoffect Sipa in topsoils: in Philippine regions, Sipa concentrations were significantly larger for paddies than for other land-use
∗Corresponding author. Tel.: +49 345 5522535; fax: +49 345 5527116.E-mail addresses: [email protected], [email protected] (T. Klotzbücher).
ttp://dx.doi.org/10.1016/j.baae.2014.08.002439-1791/© 2014 Gesellschaft für Ökologie. Published by Elsevier GmbH. All rights reserved.
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ARTICLE IN PRESSAAE-50808; No. of Pages 9
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ypes. In some of the Vietnamese paddies, Sipa concentrations are below critical values, thus might limit plant growth. Manyietnamese farmers export Si from fields by removing straw residues with the harvest. Our subsequent research thus aims to
est whether changes in harvest residue management can improve the Si supply to plants in Vietnamese regions.
usammenfassung
Reis stellt für einen Großteil der Menschen die Hauptnahrungsgrundlage dar. Der in den letzten Jahrzehnten gestiegeneeisbedarf konnte durch eine Intensivierung des Reisanbaus gedeckt werden, was aber oft zu erheblichen Umweltschäden
ührte. Das seit 2011 laufende interdisziplinäre LEGATO-Projekt hat eine Verbesserung der Nachhaltigkeit beim Reisanbauum Ziel. Ein wichtiger Aspekt hierbei ist ein nachhaltiges Management des Silizium (Si)-Kreislaufs. Si erhöht die Resistenz dereispflanze gegen Krankheitserreger, steigert die Effizienz von NPK-Düngern und kann die Aufnahme von toxischen Metallenerringern. In diesem Artikel stellen wir die Untersuchungsregionen des LEGATO-Projekts vor (Klima, Geologie, Böden,andwirtschaftliche Praxis), zeigen Konzentrationen von pflanzenverfügbarem Si (Sipa) in den Reisböden (Ap + Arp-Horizonte)nd diskutieren Faktoren, welche Unterschiede der Konzentrationen zwischen den Regionen steuern. Das Sipa wurde mittelsxtraktion mit Natrium-Acetat-Lösung bestimmt. Die Ergebnisse zeigen, dass die Sipa-Konzentrationen in philippinischenöden deutlich höher liegen als in vietnamesischen Böden (141–322 vs. 20–51 mg Si kg−1). Dies ist durch Unterschiede der geo-
pedologischen Bedingungen zu erklären. Die hohen Konzentrationen in philippinischen Böden entstehen durch die Freisetzungroßer Mengen an mobilem Si während der Verwitterung vulkanischer Gesteine, die in der geologisch jüngeren Geschichteebildet wurden. Auch die Landnutzung kann die Sipa-Konzentrationen in Oberböden beeinflussen. Die Konzentrationen inhilippinischen Reisböden sind höher als die in Böden unter anderer Landnutzung (z.B. Wald, Gemüseanbau). In einigenietnamesischen Reisfeldern könnte ein Si-Mangel den Reisertrag limitieren. Viele vietnamesische Bauern exportieren Reisstrohach der Ernte und entziehen dem Kreislauf dadurch eine möglicherweise wichtige Quelle von Sipa. Wir werden deshalb alsächstes untersuchen, ob man durch eine Änderung dieser Praxis die Si-Versorgung der Reispflanzen verbessern kann.
2014 Gesellschaft für Ökologie. Published by Elsevier GmbH. All rights reserved.
erable
DtisbwCu(t2ttGcS
tWHsticoncentrations in topsoils between rice fields and adjacent
eywords: Rice production; Silicon cycling; Sustainability; Weath
ntroduction
Rice is among the most important crops for human nutri-ion. With the intensification of rice production in the lastecades, the use of pesticides and chemical fertilizer (NPK)ncreased (e.g., Tilman, Cassman, Matson, Naylor, & Polasky002). Leaching losses of nutrients and pesticides threaten thenvironment and human health, thus questioning the sustaina-ility of current agricultural practices (Tilman et al. 2002).he interdisciplinary LEGATO project (LEGATO stands for:
Land-use intensity and Ecological Engineering – Assess-ent Tools for risks and Opportunities in irrigated rice based
roduction systems’) investigates opportunities to enhancehe sustainability of rice production in contrasting regionsf Vietnam and the Philippines (Settele et al. in this issue).n important element of LEGATO is research on silicon (Si)
ycling. Si is a beneficial element for rice plants (Ma, Miyake, Takahashi 2001; Guntzer, Keller, & Meunier 2012). It can
or example improve the plants’ resistance to fungal diseasesnd insect pests, alleviate the toxicity of metals, or increasehe efficiency of NPK fertilizers (Savant, Datnoff, & Snyder997; Guntzer et al. 2012). Si fertilization can enhance riceields (Ma & Takahashi 1990), but it is not practiced in mostice growing regions (including the LEGATO regions). Si fer-ilization using natural minerals or organic materials might be
Please cite this article in press as: Klotzbücher, T., et al. Plant-available siin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/1
strategy to reduce NPK and pesticide applications (Guntzert al. 2012).
nr
minerals; Straw residue management; LEGATO project
Si cycling in rice production systems is poorly studied.esplanques et al. (2006) estimated for a rice field in France
hat about 44% of the Si taken up by rice plants is supplied byrrigation, while the other 56% must be supplied by soil con-tituents. On the long-term, supply of plant-available Si (Sipa)y soils presumably is determined by the relatively sloweathering of parent material (Opfergelt, Delvaux, André, &ardinal 2008; Melzer et al. 2012). On shorter timescales, Siptake by plants and recycling of litter may also be importantDerry, Kurtz, Ziegler, & Chadwick 2005). Silicon precipi-ates in plant tissues, forming so-called phytoliths (Ma et al.006). Phytoliths are amorphous Si bodies that dissolve fasterhan primary and secondary minerals at pH values relevanto most soils (Fraysse, Pokrovsky, Schott, & Meunier 2009;untzer et al. 2012), thus may be a main Sipa source. Agri-
ultural practices such as rice straw export thus may affectipa in soils (Savant et al. 1997).Research in LEGATO is conducted in regions of con-
rasting geology, soils, climate and agricultural practices.e therefore expected differences in Sipa between regions.erein, we first introduce characteristics of the LEGATO
tudy regions. Second, we show data on Sipa concentrations inopsoils of paddy fields and discuss potential factors explain-ng differences in Sipa between regions. We compare Sipa
licon in paddy soils as a key factor for sustainable rice production0.1016/j.baae.2014.08.002
on-rice sites (orchards, vegetable fields, forest) to test howelevant land-use might be for Sipa. The results presented
ARTICLE IN PRESSBAAE-50808; No. of Pages 9
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T. Klotzbücher et al. / Basic and
erein provide the basis for further investigations withinEGATO on an adequate management of the Si cycle in riceroduction, including e.g. experiments on Si fertilization andole of crop residues as Sipa source.
haracterization of LEGATO study regions,andscapes and sites
Research of the LEGATO project focuses on sevenregions’ of 15 × 15 km (Fig. 1). The three regions in Luzonsland (Philippines) are denoted as PH 1 to PH 3, the fouregions in Vietnam as VN 1 to VN 4 (Fig. 1). VN 3 andH 3 are located in mountain areas, where rice is grown on
erraces. Two regions are located in the lowland of Luzonsland (Philippines), two regions are located in the Red Riverrea (Northern Vietnam) and one is located in the Mekongelta (Southern Vietnam).Within each region, five core study ‘landscapes’, consist-
ng of a pair of rice fields (or ‘core sites’), were selected. Theistance between the two rice fields of a pair is ∼150–1000 mach pair consists of one rice field situated in a homogeneousurrounding (i.e., other rice fields dominate the surroundingf 100 m radius) and one rice field in a more heterogeneousurrounding (i.e., the surrounding of 100 m radius is charac-erized by a dominance of non-rice land use such as gardens ororests). Structural heterogeneity will be an important aspector LEGATO researchers focusing on links between biodi-ersity and crop production. We do not consider it as a factorn the present publication because we focus on factors forarger-scale differences in Sipa levels between regions.
limate
Annual temperatures and precipitation of our study areasre given in Fig. 2. The climate in the lowlands of Luzonsland and Southern Vietnam was classified as monsoonalropical (=Am according to Köppen–Geiger classification;eel, Finlayson, & McMahon 2007). Temperatures show noeasonality (Fig. 2). The climate for the lowlands in North-rn Vietnam was classified as warm humid subtropical (=Cwaccording to Köppen–Geiger classification; Peel et al. 2007).t is characterized by hot summers and cool winters. Annualrecipitation is higher, and temperatures are lower in theountains than in the lowland regions.
opography, geology and soils
Information on geology and soil types was drawn fromxisting maps. Furthermore, we examined soil profiles forome of the examined paddies and adjacent forest sites to
Please cite this article in press as: Klotzbücher, T., et al. Plant-available siin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/1
erify information from these existing sources; informationn possible small-scale variability in geology and soil typeithin the study regions is, however, not available. In general,
he soils of the paddy fields belong to the units of Hydragric
Mua9
d Ecology xxx (2014) xxx–xxx 3
r Irragric Anthrosols (according to IUSS Working GroupRB 2006) but have developed from a wide range of other
oil units.Luzon Island is characterized by high volcanic activity
Liu, Zhao, Colin, Siringan, & Wu 2009). The basementf the island consists of mafic volcanic rocks of Late Cre-aceous to Eocene age (Knittel, Defant, & Raczek 1988).he surface geology is dominated by Cretaceous to Quater-ary sedimentary and extrusive rocks (Liu et al. 2009). Theedimentary rocks contain andesitic–basaltic lavas and pyro-lastics. Southern Luzon, i.e. the area of our study regionH 1, is dominated by Plio-Quaternary volcanic rocks,ostly andesites and basalts in association with dacites and
hyodacites. Undifferentiated Cretaceous–Paleogene vol-anic rocks are distributed in the mountains of Luzon. RegionH 1 is hilly, the study landscapes are located at 5–290 mbove sea level (asl). Dominant soil types are Gleyic Cam-isols, Orthic Luvisols and Eutric Nitosols (FAO 1979).egion PH 2 is plain and the study landscapes are locatedt 45–60 m asl. Dominant soil types are Gleyic Cambisols,ystric Nitosols and Pellic Vertisols (FAO 1979). RegionH 3 is mountainous and the study landscapes are locatedt 780–1300 m asl. Dominant soil types are Dystric Nitosolsnd Orthic Acrisols (FAO 1979) as well as Leptosols andmbrisols (steeper landscapes) and Cambisols. Dominant
exture classes of the Philippine topsoils are silty clay loam,ilt loam and clay loam.
The Red River Delta in Northern Vietnam is a basin filledith Quaternary sediments that are mainly composed of
ands and gravels with subordinate lenses of silt and clayLi et al. 2006). Our study landscapes are composed of siltyo loamy sediments. The geology of the upland areas in theicinity of the delta is complex. In Vietnamese areas upstreamf the Red River, granites, gneisses, schists, sandstonesnd limestones dominate (Proterozoic, Paleozoic, Mesozoic;romaget & Saurin 1971; Lan et al. 2000). In the uplandsorth of the delta, which are close to our study regions,esozoic sandstones dominate. Region VN 1 is located in
he tide-dominated area of the Red River Delta (Hori et al.004) at ∼50 km distance to the shore (2–6 m asl). RegionN 2 is located at the Northern edge of the Red River Delta
djacent to a hilly region. The study landscapes are located in0–45 m asl. Dominant soil types in the Hai Duong region areutric Gleysols and in the Vinh Phuc region Orthic, Gleyicnd Ferric Acrisols (FAO 1979). Acrisols also dominate theplands in the vicinity of the Red River Delta. Region VN 3 isocated in the mountains of Northern Vietnam, at 730–1295 msl. The region is dominated by orthogneiss and crystallinechists (Fromaget & Saurin 1971). Dominant soils are Orthiccrisols (FAO 1979).The Mekong Delta in Southern Vietnam is filled with qua-
ernary sediments of complex composition. Paleozoic and
licon in paddy soils as a key factor for sustainable rice production0.1016/j.baae.2014.08.002
esozoic sedimentary rocks dominate the geology in areaspstream of the delta (Gupta 2009). Regionally, granitic rocksnd Neogene basalts occur. Region VN 4 is situated at about0 km to the coast of the East Sea. The landscapes are located
Please cite this article in press as: Klotzbücher, T., et al. Plant-available silicon in paddy soils as a key factor for sustainable rice productionin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/10.1016/j.baae.2014.08.002
ARTICLE IN PRESSBAAE-50808; No. of Pages 9
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Fig. 1. Geographic location of the seven LEGATO research regions (15 × 15 km areas; PH = study regions in the Philippines; VN = studyregions in Vietnam).
Ho Chi Minh City
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Fig. 2. Mean monthly temperatures and precipitation rates in the study areas (PH = study regions in the Philippines; VN = study regions inVietnam). Los Banos is located in the Laguna region, close to PH 1 and in ∼170 km distance to PH 2. Banaue is located within PH 3. Hanoi isin ∼60 km distance to VN 1 and ∼40 km distance to VN 2. Sa Pa is located in VN 3. Ho Chi Minh City is in ∼70 km distance to VN 4. Data forBanaue are taken from Settele and Martin (1998). Data for the other areas were drawn from internet resources, retrieved on 11/15/2012. Datafor Hanoi and Ho Chi Minh City are from the website of the World Meteorological Organization: www.worldweather.wmo.int. Data for LosBanos are from the webpage of the International Rice Research Institute: www.beta.irri.org. Data for Sa Pa are from www.vietnamonline.com.
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Table 1. Number of crops per year, crop rotation and straw residue management at the ten paddy fields per study region (PH = study regionsin the Philippines; VN = study regions in Vietnam).
Study region Number of crops per year Crop residue management
PH 1 2× rice (9 fields)2× rice + 1× vegetables (1 field)
The straw is scattered or burned on the fields.
PH 2 2× rice (4 fields)2× rice + 1× vegetables/watermelon (4 fields)1× rice + 1× vegetables (2 fields)
The straw is scattered or burned on the fields. On one field,part of the straw is removed from the fields and used asanimal fodder.
PH 3 1× rice (9 fields)1× rice, sometimes 2× rice (1 field)
The straw is scattered or burned on the fields.
VN 1 2× rice (7 fields)2× rice + sometimes 1 vegetable (1 field)2× rice + 1 vegetable (2 fields)
The straw is scattered or burned on the fields. On six of theten fields, part of the straw is removed from the field.
VN 2 2× rice (5 fields)2× rice + 1 vegetable (5 fields)
Part of the straw is removed from the fields. The other partis burnt or scattered on the field.
VN 3 1× rice (9 fields)1× rice + sometimes 1 vegetable (1 field)
Straw is scattered or burned on the fields. On seven of theten fields, part of the straw is removed from the field.
VN 4 3× rice (10 fields) Straw is burned on the fields. On three of the ten fields, partof the straw is removed from the field.
iD&Nldd
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n 1–3 m asl. Soils are dominated by Eutric Gleysols, andystric and Thionic Fluvisols (Gröger, Proske, Hanebuth,
Hamer 2011). In the regions situated in the lowlands oforthern Vietnam, the dominant texture classes are silty clay
oam, silt loam and clay loam, while loam and clay loam areominant in the mountains (VN 3) and almost heavy clay isominant in the Mekong delta.
gricultural practice
Information on agricultural practice was collected by inter-iewing farmers of the 70 LEGATO rice fields. The numberf rice crops per year range between one in the mountainsPH 3, VN 3) to three in the Mekong Delta (VN 4; Table 1).
ost of the farmers in the other regions grow two rice cropser year. A part of the farmers grow one alternative crop perear on the fields (a variety of vegetables or water melon).he crop rotation is most widely practiced in PH 2 (6 of 10elds) and VN 2 (5 of 10 fields); in the other regions, cropotation is not practiced (VN 4) or only practiced by 1–3 ofhe 10 farmers (Table 1).
The straw residue management differs between the fieldsTable 1). Farmers burn the straw and leave the ash on theelds, leave the straw untreated on the fields, or bring it back
o the fields as compost. Some of the farmers in the Viet-amese regions and in PH 2 remove part of the rice strawrom the fields. It is used as animal fodder, for cooking or asrganic fertilizer for vegetable fields.
The regions are characterized by an intensive use of pes-
Please cite this article in press as: Klotzbücher, T., et al. Plant-available siin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/1
icides and chemical NPK fertilizers with the exception ofH 3 where no chemical fertilizers are used and six of the ten
nterviewed farmers seem not to apply pesticides (Table 2).
ms2A
torage of plant-available Si in paddy soils
opsoil sampling
We sampled soils from all of the 10 paddy fields in eachf the 7 regions. Topsoil samples (Ap + Arp horizons withhicknesses between ∼10 and ∼30 cm) were taken with alastic corer of 7.5 cm diameter (n = 9 cores per field). Foromparison we sampled topsoil (top 20 cm of the mineraloil) from five non-rice sites that were situated close-by theaddy fields using a metal corer (n = 5 or 6 cores per site).n PH 1, fields with different fruit trees and/or vegetablesere sampled. In PH 3 and VN 3, forest sites were sampled.
n VN 2, fields with vegetables, fruit trees or forest wereampled. In the other regions we could not find sites of anlternative land-use type. All soil core samples were air-driednd then shipped to the soil laboratories of the Martin-Luther-niversity in Halle (export and import permits were obtainedefore transfer), where they were oven-dried (40 ◦C), pooledo obtain one sample per paddy field (same dry mass of soilas taken from all of the cores per field) and sieved (< 2 mm)
or laboratory analysis.
oil analysis
We used sodium acetate solutions to extract dissolved andome of the exchangeable Si from soils (Sauer, Saccone,onley, Herrmann, & Sommer 2006). This method is com-
licon in paddy soils as a key factor for sustainable rice production0.1016/j.baae.2014.08.002
only applied to estimate the concentrations of Sipa in riceoils (Dobermann & Fairhurst 2000; Korndörfer & Lepsch001; Snyder 2001; Narayanaswamy & Prakash 2010).cetate-extractable Si was shown to correlate with Si uptake
ARTICLE IN PRESSBAAE-50808; No. of Pages 9
6 Applied Ecology xxx (2014) xxx–xxx
btbcrc0ewL
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osfi
Table 2. Number of fields with application of chemical NPK fertil-izer and pesticides in each study region. The total number of fieldsis 10 in each study region (PH = study regions in the Philippines;VN = study regions in Vietnam).
Study region Chemical fertilizer Pesticides
N P K
PH 1 10 6 6 10PH 2 10 10 7 10PH 3 10 10 10 4VN 1 10 10 10 9VN 2 10 10 10 10VN 3 10 10 9 10VN 4 10 10 10 10
Ace
tate
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ract
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[mg
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]
0
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PH_1 PH_2 PH_3 VN_1 VN_2 VN_3 VN_4
a
cb
d e
dff
Fig. 3. Boxplots of concentrations of acetate-extractable Si (Sipa)in Ap + Arp horizons of paddy fields of the study regions (n = 10 ricefields per region; PH = study regions in the Philippines; VN = studyrb
aPp
D
iiaiBrB
T. Klotzbücher et al. / Basic and
y rice plants (Snyder 2001). We used the widely applied pro-ocol of Imaizumi and Yoshida (1958) as cited in the reviewy Sauer et al. (2006). Note that modifications of this proto-ol were used in some studies cited herein (e.g. soil:solutionatios, concentration of the extractant and/or extraction timesan differ). Briefly, 10 g of dry soil was incubated with 100 ml.18 M NaOAc, adjusted to pH = 4, for 5 h at 40 ◦C (Sauert al. 2006). The extracts were filtered (0.45 �m) before Sias measured by ICP-OES (Ultima 2, Horiba Jobin-Yvon,ongjumeau, France).We additionally determined basic soil properties (Table 3).
oil pH was measured using a 1 mol KCl solutionsoil:solution ratio of 1:2.5). Organic carbon (Corg) contentsere determined using a CNS analyzer (Vario EL, Elemen-
ar Analysensysteme, Hanau, Germany). Total contents of SiSitot), Al (Altot), Fe (Fetot), Ca (Catot), Mg (Mgtot), K (Ktot),ere determined by X-ray fluorescence analysis (S4 PIO-EER, Bruker-AXS). The total reserve of bases (TRB) wasetermined as the sum of the total contents of alkaline andlkaline earth elements. Particle size distribution was deter-ined according to Deutsches Institut für Normung (2002).article size distribution was determined for five fields peregion (i.e., one field of the 5 core landscapes), the otherroperties were determined for all ten fields.
ata analysis
We used the Kruskal–Wallis one-way analysis of variancend the Wilcoxon–Mann–Whitney test in order to test forignificance of differences in soil properties. Non-parametricethods were chosen because the data were not normally
istributed. Differences are reported as being significant if p0.05. The Statistica 99 software (Statsoft, Hamburg, Ger-any) was used for all calculations.
esults
Concentrations of Sipa in Ap + Arp horizons of paddyelds were significantly larger for Philippine than for Viet-amese regions (mean values of 141–322 vs. 20–51 mgi kg−1; Kruskal–Wallis-ANOVA, p < 0.0001; Fig. 3). Fur-
hermore, they significantly differed between the Philippineegions, with PH 1 > PH 3 > PH 2 (mean values of 322,03 and 141 mg Si kg−1; Wilcoxon–Mann–Whitney test;
< 0.001 for PH 1 vs. PH 2; p = 0.005 for PH 1 vs. PH 3; = 0.002 for PH 2 vs. PH 3). In Vietnam, Sipa concentra-ions were significantly smaller in VN 2 than in the otheregions (Wilcoxon–Mann–Whitney test; p values of 0.005 ormaller), furthermore they were significantly larger in VN 4han in VN 1 (p = 0.003).
Please cite this article in press as: Klotzbücher, T., et al. Plant-available siin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/1
Mean values of Sipa concentrations in the top 20 cmf the mineral soil from sites of alternative land-use weremaller than mean values of Ap + Arp horizons of paddyelds (Fig. 4). Significant differences between paddies
2ews
egions in Vietnam). Different letters indicate significant differencesetween regions (p < 0.05 Wilcoxon–Mann–Whitney test).
nd alternative land-use were, however, only found for thehilippine regions PH 1 (Wilcoxon–Mann–Whitney test;
= 0.002) and PH 3 (p = 0.03).
iscussion
The main result of this study is that Sipa concentrationsn topsoils are considerably larger in the Philippine thann the Vietnamese regions. Weathering of primary miner-ls is the primary source of all ‘reactive’ Si that is cyclingn the plant–soil system (Sommer, Kaczorek, Kuzyakov, &reuer 2006). Recent studies showed that plant Si uptake is
elated to storage of weatherable minerals in soils (Henriet,odarwé, Dorel, Draye, & Delvaux 2008; Opfergelt et al.008; Tavakkoli, Lyons, English, & Guppy 2011; Melzer
licon in paddy soils as a key factor for sustainable rice production0.1016/j.baae.2014.08.002
t al. 2012). Two processes might explain these findings: first,eathering of primary minerals directly provides Si to plants;
econd, soils containing larger resources of weatherable
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Alternat ive land-use
Pad
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s
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est
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and
crop
s/fo
rest
not sign .
notsign.
p=0.002
p=0.03
Fig. 4. Comparison of concentrations of acetate-extractable Si(Sipa) in topsoils of paddy fields (n = 10) and in topsoils of sites ofalternative land-use (n = 5). PH indicates study regions in the Philip-pines; VN indicates study regions in Vietnam. Error bars indicatethe standard error. Shown are p values of Wilcoxon–Mann–Whitneytt
mt(spateb(iprHl
Tyhiosowacep3
(todttpPtaVfto
frtftePl(p
T
R
PPPVVVV
CP
ests (pair-wise comparison of paddy fields and alternative sites forhe individual regions).
inerals accumulate larger amounts of phytoliths in the long-erm, and these phytoliths are a main Si source for plantsOpfergelt et al. 2008). Type and age of parent material andoils should play a role for the release of reactive Si fromrimary minerals. Extrusive rocks (e.g. basalt, andesite) usu-lly contain smaller total amounts of Si but weather fasterhan intrusive rocks (e.g., granite). Hence, weathering ofxtrusive rocks should release reactive Si at a higher rate,ut intrusive rocks are the larger source in the long-termMelzer et al. 2012). The surface geology in the Philippiness dominated by extrusive rocks of a relative young age (i.e.yroclasts and lavas in Quaternary and Neogene sedimentary
Please cite this article in press as: Klotzbücher, T., et al. Plant-available siin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/1
ocks and Plio-Quaternary extrusive rocks; Liu et al. 2009).ence, weathering of parent material presumably caused a
arge production of reactive Si in recent geologic history.
mse
able 3. Properties of topsoils of paddy fields (Ap + Arp horizons) studie
egion pHKCl Corg (g kg−1) Sitot (g kg−1) Fetot (g kg−1) Altot
H 1 4.8 (0.2) 27 (2) 261 (3) 50 (5) 89H 2 4.7 (0.2) 14 (1) 292 (9) 52 (2) 76H 3 4.1 (0.1) 29 (4) 234 (5) 54 (3) 103N 1 4.6 (0.1) 15 (1) 323 (9) 32 (3) 68N 2 4.3 (0.0) 16 (1) 375 (15) 18 (4) 43N 3 4.3 (0.1) 17 (1) 288 (13) 39 (5) 86N 4 3.6 (0.1) 30 (3) 278 (15) 30 (4) 99 (
org = organic C content; Sitot, Fetot, Altot = total contents of Si, Fe, Al; TRB = totaH = study regions in the Philippines; VN = study regions in Vietnam.
d Ecology xxx (2014) xxx–xxx 7
his can explain the high Sipa concentrations in topsoils. Theoungest rocks can be found in PH 1, the region with theighest Sipa concentrations (Figs. 3 and 4). In contrast, rocksn the upstream areas of the Red River and Mekong delta arelder than those in the Philippines. The dominant soils aretrongly weathered Acrisols (FAO 1979). Hence, sedimentsf the Vietnamese river deltas derive from old and stronglyeathered land surfaces and presumably contain only small
mounts of easily weatherable minerals. In line, the TRB, aommonly used measure of weatherable minerals (Opfergeltt al. 2008), is larger in Philippine than in Vietnameseaddy soils (average of regions of 167–176 cmol kg−1 vs.1–94 cmol kg−1; Table 3).The influence of climate on Si cycling is poorly studied
Struyf & Conley 2012). Climate may indirectly affect the Siransport by water, dissolution of phytoliths and weatheringf soil minerals (Struyf & Conley 2012). The climatic con-itions differ between our regions, but we found no evidencehat the differences showed an overall effect on Sipa concen-rations. For instance, mean annual temperatures (MAT) andrecipitation (MAP) are comparable in the lowlands of thehilippines and in Southern Vietnam (Fig. 2) but Sipa concen-
rations largely differ between the regions. In contrast, MATnd MAP are lower in Northern Vietnam than in Southernietnam but Sipa concentrations are similar. Furthermore, we
ound no evidence that lower MAT and higher MAP in moun-ainous than in the lowland regions of Northern Vietnam andf the Philippines affected Sipa concentrations.Sipa concentrations in topsoils of the non-rice sites (i.e.,
orest, orchards or upland crops) also differed betweenegions and these differences were similar to those betweenhe paddy fields (Fig. 4). These data support the view that dif-erences in litho-/pedologic conditions between regions arehe main control for Sipa concentrations in topsoils. How-ver, land-use can also be a factor as suggested by data forH 1 and PH 3, where Sipa concentrations were significantly
arger for paddy fields than for sites with alternative land-useFig. 4). An explanation therefore might be large Si inputs toaddy fields with the irrigation water, which presumably is a
licon in paddy soils as a key factor for sustainable rice production0.1016/j.baae.2014.08.002
ajor source of Sipa (Desplanques et al. 2006). More detailedtudies, however, are necessary to test why rice cultivationnhances Sipa in topsoils.
d within LEGATO (mean values and standard errors in brackets).
(g kg−1) TRB (cmol kg−1) Clay (%) Silt (%) Sand (%)
(2) 168 (21) 39 (9) 44 (5) 17 (5) (4) 176 (23) 37 (5) 48 (5) 15 (5)
(3) 167 (16) 28 (3) 47 (2) 25 (3) (5) 94 (9) 27 (2) 65 (3) 8 (3) (8) 31 (9) 14 (2) 58 (4) 27 (5) (7) 90 (19) 27 (5) 37 (2) 39 (2)10) 89 (8) 56 (11) 32 (1) 12 (11)
l reserve of bases; Clay, silt, sand = relative contribution of clay, silt, sand;
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Little information on the effects of agricultural practicesn Si cycling in paddy rice is available. Numerous fac-ors such as irrigation, crop variety, number of crops perear or crop residue management might play a role. Thegricultural practice differs in a number of factors betweenur regions and also between individual farmers within theegions. Furthermore, they presumably changed dramaticallyn the last decades due to agricultural intensification. Unfortu-ately, only limited information on the history of agriculturalractices could be gained by farmer interviews. Availablenformation thus is not sufficient for a detailed analysis of theotential relevance of agricultural practice for Sipa. Herein,e would like to draw attention to the aspect of straw man-
gement because it likely is critical. The removal of strawesidues has been hypothesized to decrease Sipa in soilsSavant et al. 1997). Removing rice straw at harvest is aommon practice in Vietnam (i.e., 26 of 40 farmers indi-ated that they removed part of the straw; Table 1), andight be a reason for low Sipa concentrations in Vietnamese
addies.
onclusions and outlook
Differences in Sipa concentrations in topsoils betweenhe regions can be explained by geo-/pedologic conditions.
e assume that the large Sipa concentrations in Philippineoils are mainly due to a large Sipa input due to weather-ng processes in recent geologic history. Potential effects ofifferences in climate between regions are masked by theominant effect of geo-/pedologic conditions. In some of theietnamese paddy fields, Sipa concentrations are below crit-
cal values proposed in literature (Dobermann & Fairhurst000). Si may therefore limit crop production on these fields.any of the Vietnamese farmers remove part of the rice straw
rom the fields. This might cause decreasing Sipa concentra-ions in soils. Hence, an improved straw management mightmprove the Si supply to plants. We plan to test this hypothesisithin LEGATO.
cknowledgements
We thank the German Federal Ministry of Educationnd Research (BMBF; 01LL0917N) for funding within theMBF-Funding Measure “Sustainable Land Management”
http://nachhaltiges-landmanagement.de), PD Dr. Josef Set-ele (Helmholtz Centre for Environmental Research – UFZ)or coordinating the LEGATO project, the farmers of theEGATO paddy fields for their support, Alexandra Boritzki
or the help in the laboratory, and the authorities for the exportnd import permits of the soil samples (General Department
Please cite this article in press as: Klotzbücher, T., et al. Plant-available siin Southeast Asia. Basic and Applied Ecology (2014), http://dx.doi.org/1
f Geology and Mineral of Vietnam; the Philippines’ Depart-ent of Environment and Natural Resources; Landesanstalt
ür Landwirtschaft, Forsten und Gartenbau Sachsen-Anhalt).
d Ecology xxx (2014) xxx–xxx
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