MARTIN NETO, L.

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UNIVERSiTÀ DEGLI STUD! Di CATANIADipartimento di Scienze Agronomiche, Aqrochirniche e delle Produziorii Animal!SEZ!ONE DI SCIENZE AGROCHfr\~ICHEINTERNATlor~AL HUMIC SUBSTANCES SOCIETVSEZIONE lTAL(ANAVIt CONVEGNO NAZIONALEATT!CATAN~A3i rnaggio - 1 giugno 2007a cura di Cristina AbbateRole of humic substances in sustainable agriculture andenvironment: field and molecular scale resultsLadislau Martin Neto, Brazilian Corporation for Agricultural Research(Embrapa), National Center of Agricultural Instrumentation, Rua XV deNovembro, 1452, 13561-970 São Carlos/SP, Brazil.martin@cnpdia.embrapa.br1. INTRODUCTIONQuestions associated to natural orqaruc matter (NOM) and their rnarnconstituents, the humic substances, are of immense importance due to severalfunctions of NOM in different terrestria!, aquatic and aerial environments.Nowadays, this importance has been extraordinarily intensified by associationwith C cyc1e that has a direct relationship with increase of greenhouse effectand c1imate changes in the Planet. Besides food and fiber productions fromagriculture, the Brazil is engaged in biofuels program to substitute oilderivatives, as ethanol, from sugar-cane (Iast year Brazil produced 17 G liters ofethanol used mainly as car fuel, using just 3 M ha of a 100 M ha yet available tobe cultivated), and started a biodiesel program with a huge potential of 300 Gliters of biodiesel just in savanna region of country, without cut any tree inAmazonian rainforest. So agribusiness plays a very important role in theeconomy, society and environment. Specifically soil characteristics of Brazilgives to organic matter a fundamental role regarding questions associated tosoil fertility (importance increased due to predominant kaolinite c1ay soil with lowcation exchange capacity), aggregation of soil partic1es, reduction of erosion(generally very strong ih tropical regions due to intense rainfall), and othersnaturally important. aspects as interactions with pesticides and rnetallic ions,'. . contribution to 1rihalomethane formation and water quality. AIso due to some ofthese c1imate chatacteristics Brazil have increased strongly adoption of soilconservative practices, indude no-till or direct drilling. Nowadays Brazil hasaround 22 M ha under no-till, more than 40% of total grains cultivated area.Besides contributions to soil fertility, local and regional environment, no-till haveproven to be successful in promoting soil carbon sequestration in Brazil (Bayeret al., 2006). In this work will be described some important field studies onareas under soil carbon sequestration, inc1uding areas under no-til! with grainsand pastureland grass in Brazil, with an estimative of potential of these activitiesto mitigate greenhouse effects. To follow dynamic and reactivity of humicsubstances and SOM in these areas some spectroscopic tools, as ElectronSpin Resonance (ESR), UV-Vis fluorescence and laser induced fluorescence,were applied helping to explain several reactions in the soil and environment2. MATERIALS ANO METHOOSExperiments of tillage effectsThe study was based 011 two long-term experiments, one established in 1992near the town of Luziânia in the Brazilian state of Goiás, the second setup in1994 near the town of Costa Rica in the Brazilian state of Mato Grosso do Sul,both at Central region of country. The experimental treatments were threetillage systems (conventional tillage (CT), reduced tiIIage (RT), and no-till (NT))arranged in a complete randomized block design with three replicates. The soilwas left fallow during the dry season and cultivated with soybean, maize, orcotton in the summer. No-til! causes rninirnal soil disturbance, with crops beingdirectly sown in summer on the residues of the .weeds that grew up during thefallow period. Adjacent native Cerrado areas at each site were included in thisstudy to represent the original soil conditions.Experiments on pasturelandThis study refes to a long-term experiment located in São Carlos city, state ofSão Paulo, Brazil, at experimental farm of Brazilian Corporation for AgriculturalResearch (Embrapa), at Southeast Cattle Center, on a 8rachiaria decumbenspastureland, established 27 years ago, following a corn field. Soil was a loyvfertility, acid Óxisok, with 25% clay content. Treatmente were: TOO - 27 years'-junder Brachiari decumbens pasture, without lime and fertilizer additions; tO-without surface liming, but.with 400 kg y-1 N- ammonium sulfate and K20; t2r:rk2 t ha-1. surface limestone with same tO NK fertilizeruse and 1 t ha'reinforcement of limestone; t4sa- 4 t ha' of surface limestone without NKfertilizer use; CV- dense cerrado vegetation in transition to a native mesophylesemideciduous tropical forest and tilled soil- pasture area changed to crop, with0-20 cm depth till.Organic Carbon and Elemental Analysis MeasurementsTotal carbon analysis were performer in soil and humic acids (HA) samplesusing a total carbon analyzer (LECO model CI~ 412) and CHN (Perkin Elmermodel), respectively, and also usrnq the Walkley-Black wet combustionmethod. Soil bulk density was assessed and used to calculate the soil C stocksHumic Acids Extraction and PurificationHA samples were extracted from soil samples and purified according to theInternational Humic Substances Society (IHSS) method. HA samples analyzedwere extracted from two depths: 0-10 cm and 10-20 cm, in ali treatmentsreported before.Spectroscopic AnalysesElectron Spin Resonance (ESR). The ESR measurements of HA wereperformed in a Bruker EMX spectrometer operating at 9 GHz (X- band) at roomtemperature. The relative concentrations for semiquinone-type free radicaiswere obtained using Singer's method (Martin-Neto et al., 2001) using as asecondary standard a ruby crystal calibrated with strong piteh reference of knowfree radical content, provided by Bruker.Ultraviolet-Visible light fluorescence. Fluorescenee spectra in the emissionand synchronous-sean excitation modes were aequired in a Perkin Elmer LS-50B luminescence spectrometer. Each HA sarnple was dissolved in 0.05 moi L·1NaHC03 with 20 mg L ·1 concentration, and pH 8 (Milori et al., 2002).Laser Induced Fluoreseenee (LlF). Sai I samples of approximately 0.5 9 aspellet of 1 em diameter and 2 mm thickness, were prepared and inserted ito ahome assembled apparatus to run L1F measurements (Milori et al., 2006).Samples were exeited with 458 nm radiation emitted by an argon laserequipment (Coherent Innnova 90-6), with 300 mW exit power.3.. RESULTS ANO OISCUSSION .' 1., ..•, .;;'Iin Figure 'l Jspossible to observe variations rn total earbon content Jn areas;~ • under different tiIIage practiees. As ean be seenthere is an increase in carboneontent in area managed under no-till in cornparison to native··Cerrado or underconventional tillage area. Based in these two experimental areas and severalother data from literature it was estimated that savanna region of Brazil has apotential to accumulate 0.35 Mg C/ha/year (Bayer et al., 2006). Considering thelarge potential area to eultivation in savanna region (Cerrado) of Brazil a 100 Mha under no-till could remove from atmosphere a 0.126 Pg C02/year, around10% of total Planet emission due to defores!ing and land use (Lal et al., 2004).Analysis of fluorescence induced by laser (LlF) of whole soil samples fromthese areas under different tillage practices demonstred a clear possibility ofidentify humification degree of soil organic matter, confirming potential of thesenew tool to work on samples without any chemical or physical extractionprocedures of SOM (Milori et al., 2006). In soil samples from areas under no-tillin 0-5 cm it was identified a decrease in humification degree compared withconventional tillage practice (data not shown), in agreement with previousobservations made using humic acids (Milori et ai., 2002).The work with pastureland was undertaken to measure the carbon storagepotential of a 25% clay content Oxisol under well managed tropical grasspasture, Brachiaria decumbens, established 27 years ago after corn crop, incomparison to native dense Cerrado vegetation, in São Carlos, SP, Brazil..Greatest SOM content occurred under pastureland in the 10 cm surface soillayer (data not shown). Compared to native Cerrado, the C stocks in pastureincreased from 1.7 to 3.5 Mg C ha" y-1 for the 0-100 cm layer, depending onnitrogen availability. Changing the soil management from Cerrado vegetation togood managed grass pasture will result in an anriual sequestration rate rangingfrom 6.1 to 12.8 Mg CO2 ha' v', which corresponds to 8.3 to 17.3% of the totalemissions from deforestation and land use change worldwide.ESR studies (Figure 2) demonstrated that HA from pasture soil had highersemiquinone-type free radicais than from Cerrado soil under native vegetationand tilled soil. Higher semiquinone-type free radical content occurred in t2m andt4sa treatments, more probably due to lime presence. Lime use is known to'increase soil pH, stimulating soil microbial activity and generating more humifiedhumic acids. Alternatively or simultaneously the Ca-HS bond could also!( contribute to generate more humified humic acids. These ESR data agreed with" 'Fluorescence Spectroscopy of dissolved HA (data' riot shown). . .4. CONCLUSIONSCompared to conventional tillage, no-till management and pastureland areasincreased the C stock in Cerrado Oxisols. Considering the large Cerrado landarea which is, and could be, used for cropland and pasture (about 200 millionhectares), the adoption of no-till management and well managed pasturelandhas the potential to turn Cerrado soils into a significant atmospheric C sink and----..I.- Ce rra d o-o- CT-<r- RT20 ........,.'-----------------' ---{]---- NT•Organic Carbon Content, kg 111 -3O 10 ] 5 20 25 30 35 40 45°rI---l5r-c()fi 10c..4):::J f---!15Figure 1- Organic C concentration as affected by tillage systems in the CostaRica c1ayey Oxisol. Horizontal bars refer to the LSD obtained by Tukey's test(P ::; 0.05). Cerrado- is native savanna soil; CT- conventional tiIIage; RT-reduced tillage and NT- no-till. (Adapted from Bayer et al., 2006).1.21.0~• -;t:!J 0.8c.õ..r-:Vl 0.6oxÕ OAe::::u,(/)0.2CV till soil TOO tOsoil treatmentst2m 14saFigure 2 - Levei of semiquinone-type free radical [spins g-1 (X1017)] of sai!humic acids determined by Electron Spin Resonance (ESR) under different sai!treatments in the pasture!and Brachiaria Oecumbens areas.· .contribute to mitigating global climate changes in addition to increased food andbiofuel productions.The spectroscopic analysis permitted identify changes in humic substances dueto tiIIage effects, including use of no-till, in areas with qrams, and liming andfertilization of pastureland, generated new insights about structure andreactivity of humic acids. The combination of long-term field experiments,extractions and fractionation of humic substances and spectroscopic analysiswas very fruitful permitting generation of agronomic and environmental interestresults and molecular scale humic acids data.REFERENCES(1) Bayer, C ; Martin-Neto, L. ; Mielniczuck, J ; Pavinato, A ; Oieckow, J . Soil &Tillage Research, v. 86, p. 237-245, 2006.(2) Lal, R. Science, v. 304, p. 1623-1627,2004.(3) Martin-Neto, L.; TragheUa, O.G.;Vaz, C.M.P.; Crestana, S.; Sposito, G.Journal of Environmental Quality, v. 30, p. 5.20-525, 2001.(4) Milori, O.M.B.P; Martin-Neto, L.; Bayer, C.; Mielniczuk, J.;Bagnato. V.S. SoilScience, v. 167, p. 739-749, 2002.(5) Milori, O.M.B.P.; Galeti, H.v.A.;Martin-Neto, L.;Oieckow, J.;González-Pérez,M.;Bayer, C.;Salton, J.C. Soil Science Society of America Journal, v. 70,p. 57-63, 2006.",'.:Õ', .

Role of humic substances in sustainable agriculture and enviroment: field and molecular scale results.

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Role of humic substances in sustainable agriculture and enviroment: field and molecular scale results.

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