- Email: [email protected]
N ratio
Soil & Tillage Research 111 (2011) 231–235
Contents lists available at ScienceDirect
Soil & Tillage Research journal homepage: www.elsevier.com/locate/still
Short communication
Soil organic matter humification under different tillage managements evaluated by Laser Induced Fluorescence (LIF) and C/N ratio T. Martins a, S.C. Saab b,*, D.M.B.P. Milori c, A.M. Brinatti b, J.A. Rosa d, F.A.M. Cassaro b, L.F. Pires b a
State University of Ponta Grossa (UEPG), Av. Carlos Cavalcanti 4748, 84030-900, Ponta Grossa, PR, Brazil Laboratory of Soil Physics and Environmental Sciences, Department of Physics, State University of Ponta Grossa (UEPG), Av. Carlos Cavalcanti 4748, 84030-900, Ponta Grossa, PR, Brazil c Embrapa Agricultural Instrumentation Center (CNPDIA/EMBRAPA), CP 741, 13560-970, Sa˜o Carlos, SP, Brazil d Agricultural Research Institute of Parana´ (IAPAR), BR 376, Km 496, 84001-970, Ponta Grossa, PR, Brazil b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 March 2010 Received in revised form 13 October 2010 Accepted 14 October 2010
In this work is presented the use of the C/N ratio and the Laser Induced Fluorescence (LIF) spectroscopy for determining the humification of soil organic matter (SOM) in an Oxisol under three different longterm tillage managements (no-tillage (NT), reduced tillage (RT) and conventional tillage (CT)). Humification of SOM was evaluated in the soil and its fractions (clay < 2 mm, silt 2–20 mm, sand 20– 1000 mm). The obtained results show that lower SOM humification was observed in soil under NT, mainly at the surface (0–5 cm). In CT, SOM humification values maintained constant for all investigated depths (0–5, 5–10, 10–15 and 15–20 cm). Also, clay was the soil fraction that exhibited the lesser humification of SOM. Based on the obtained results it can be said that NT favors the accumulation of SOM on its surface, increasing aggregate stability and presenting samples with lower humification indexes. These results indicate a larger availability of nutrients for the plants in this management. ß 2010 Elsevier B.V. All rights reserved.
Keywords: Degree of humification Soil fractions No-tillage management system
1. Introduction Soil granulometric fractioning consists of separating a soil sample into its four constituent fractions: clay (<2 mm), silt (2–20 mm), fine sand (20–53 mm) and coarse sand (53–1000 mm). The quantification begins with humid sieving followed by sedimentation process. Different from chemical fractioning, granulometric fractioning does not employ strong acids and bases for the separation process. Then, the possibility of altering the soil organic matter (SOM) components is diminished, representing a less destructive method (Christensen, 1992; Saab and Martin-Neto, 2003, 2008). SOM study interpretation conducted in soil fractions is also simplified when it is performed in conjunction with spectroscopic techniques. This simplification contributes significantly to studies related to SOM physical protection in tropical and subtropical soils (Costa et al., 2004). The Laser Induced Fluorescence (LIF) is a very promising technique of analysis, which is based on the fluorescence emission of aromatic components present in the soil. This methodology uses a laser beam tuned in the blue region of the spectra to excite the samples. Higher fluorescence intensities are related to greater SOM
* Corresponding author. E-mail addresses: scsaab@fisica.uepg.br, [email protected] (S.C. Saab). 0167-1987/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2010.10.009
humification degrees. Simplicity, sensitivity and speediness are advantages of using the LIF technique. Also, it can be used in combination with other analytical techniques, such as electron paramagnetic resonance (EPR) (Saab and Martin-Neto, 2008) and nuclear magnetic resonance (NMR) (Saab and Martin-Neto, 2007). As compared to Fe3+ technique, LIF can be used to determine the degree humification in Oxisols without the need for humic acids extractions (Milori et al., 2006). According to some authors (Milori et al., 2006; Gonza´lez-Pe´rez et al., 2007; Favoretto et al., 2008), LIF is considered a non-destructive and fast technique for SOM analysis as the soil samples to be investigated do not need previous chemical treatment. Milori et al. (2006) investigating Red Latosol samples subject to different tillage managements, concluded that the conventional system (that involves intense soil revolving) presented a higher degree of humification mainly at the surface (to the first 10 cm of depth) in comparison to the conservationist management and the native cerrado (considered as a reference). In the samples of cerrado, the degree of humification was lower due to higher concentration of light SOM or SOM at initial stages of the decomposition process. In this paper some samples were calcined and treated with hydrogen peroxide to eliminate organic matter and assure that the signal in the LIF spectra referred to the humified SOM. Gonza´lez-Pe´rez et al. (2007) found high correlation among results of SOM evaluation obtained using LIF, NMR and EPR
T. Martins et al. / Soil & Tillage Research 111 (2011) 231–235
232
measurements, for soils prepared in different manners. Bayer et al. (2002a) showed that humic acid samples extracted from soils under no-tillage (NT) management had lower degrees of humification than those from soil subjected to CT management. It was concluded based on lower concentrations of stable semiquinonetype free radicals and total fluorescence exhibited by soils under NT. Differences between tillage systems increased along the years demonstrating the continuous effect of management systems on soil humic acid characteristics. Bayer et al. (2003) evaluated the concentration of semiquinone free radicals (SFR) of organic matter from the surface soil layer (0– 25 mm) of a humic soil under years long CT, reduced tillage (RT) and NT. These authors showed that NT presented a lesser degree of humification of SOM as compared to soils under RT and CT. It was related to a less oxidative environment in NT as compared to the other managements. They also demonstrated that the fraction related to clay (2–20 mm) presented the highest concentration of SFR and the smallest line width of the EPR signal. These two results are an indicative of highest degree of SOM humification or of a large organic matter interaction with the mineral fraction of the soil. The objective of this work is to determine the humification of SOM in different depths of an Oxisol (FAO, 1998) submitted to different tillage management systems, using whole soil samples (samples without any previous treatment) and its fractions (clay, silt and sand) using C/N ratio and Laser Induced Fluorescence.
fine sand (20–53 mm) was obtained after this process (Saab and Martin-Neto, 2003). 2.2. Elemental analysis (C/N ratio) To perform the C/N ratio analysis approximately 150 mg of whole samples and their fractions were dried (in oven at 60 8C) and homogenized. To calibrate the system, a sample with well known content of C and N (considered as a standard sample) was used. The equipment used in the measurements was a C and N elemental determinator, TRUS PEC CN LECO, which investigates dry samples in powder form. In the measurement, samples are combusted at 950 8C and the gas resulting from the combustion (CO2) is purified and analyzed by an IV detector. 2.3. Laser Induced Fluorescence (LIF) For LIF analysis (whole soil), two pellets of each sample were analyzed in replicate. Each soil fraction was analyzed in three replicates. LIF operation parameters were: (1) lock-in 100 mV, (2) photomultiplier 850 V, (3) 457 nm argon wavelength and (4) 300 mW laser power. The humification index was determined from the equation proposed by Milori et al. (2006), HFIL = ACF/CT, i.e. the humification index is equal to the ratio between the fluorescence curve area and the total C presented in the samples. 2.4. Statistical analysis
2. Materials and methods Soil samples were collected in an Experimental Station of the Agricultural Research Institute of Parana´ (IAPAR) located in Ponta Grossa, PR, Brazil (258130 S; 508010 W; 875 m a.s.l). According to the Brazilian System of Soil Classification (Embrapa, 1999) and FAO (FAO, 1998), the soil studied is classified as a Distrofic Red Latosol and Oxisol, respectively. Twelve soil samples were collected in depths 0–5, 5–10, 10–15 and 15–20 cm at three different points in each tillage management (NT, RT and CT). These managements have been conducted in these areas for 27 years, and information about crop rotations are given in Table 1. 2.1. Particle size fractioning As it was said, physical fractioning consists in separating a soil sample to its fractions: (1) coarse sand (53–1000 mm), (2) fine sand (20–53 mm), (3) silt (2–20 mm) and (4) clay (<2 mm). Coarse sand (fractions above 53 mm) was obtained by humid sieving; silt and clay (particles with diameters below 20 mm) were obtained by natural sedimentation (using the Stokes Law of sedimentation); and
Analysis of statistical significance of tillage and cropping system effects on total fluorescence of soil was performed using mean standard deviation. Relation between fluorescence spectroscopy (HFIL) and C/N ratio results was evaluated by the significance of correlation coefficient (r) at P < 0.05. 3. Results and discussion 3.1. Whole soil Laser Induced Fluorescence In Fig. 1 is shown the fluorescence curve graph for the sample CT0–5. According to Milori et al. (2006), the fluorescence curve is directly related to the C concentration. However, this C concentration is only referent to C in rigid structures such as aromatic rings and quinone groups. In Fig. 1 it can be noticed a wide band with a maximum wavelength of 520 nm. Other samples presented very similar spectra. Differences among the tillage managements and depths, in relation to the degree of SOM humification, indicated by the HFIL index, are shown in Fig. 2. Higher the HFIL index more humified is
Table 1 Culture rotations per year in each tillage system. Year
Culture rotation conventional tillage and reduced tillage
Culture rotation: no-tillage
1981–1990
Wheat and soybean
1990–1995 1995–2000 2000–2005 2005–2007 2007–2008
Black oat/soybean/black oat/sweet corn/wheat/soybean/black oat/soybean/lupine/sweet corn Blackoat/soybean/wheat/soybean/oat + vetch/sweet corn/black oat/soybean/wheat/sweet corn Oat + vetch/sweet corn/oat/soybean/oat/soybean/oat + vetch/sweet corn/oat/soybean/oat + vetch Oat/sweet corn/oat/soybean/oat Oat/sweet corn
Sweetcorn/oat/soybean/ wheat/soybean/lupine/ sweetcorn/oat/soybean/ wheat/soybean/lupine/ sweetcorn/oat/soybean/ wheat/soybean The same as in CT and RT The same as in CT and RT The same as in CT and RT The same as in CT and RT The same as in CT and RT
[(Fig._1)TD$IG]
T. Martins et al. / Soil & Tillage Research 111 (2011) 231–235
6
Table 2 C content for the whole soil.
5
Emission (a.u)
233
4
3
2
Samples (depth in cm)
C content (g/kg) in whole soil
NT0–5 NT5–10 NT10–15 NT15–20
74.70 46.60 37.50 34.60
CT0–5 CT5–10 CT10–15 CT15–20
31.70 31.90 33.60 33.10
RT0–5 RT5–10 RT10–15 RT15–20
42.40 38.70 32.10 28.50
1 480
500
520
540
560
580
600
620
640
Results related to the humification index were coherent with C results. Is this regard, it is expected that lower indexes of humification were being related to higher C contents and viceversa. This was here observed for NT and CT management systems, in a comparison between them. CT was the treatment higher humified. Bayer et al. (2002b) also found higher degree of humification in CT samples, as well as lower C content compared to the same soil under NT. These authors observed that the humification was characterized from semiquinone free radicals concentration, which appearance in the samples is related to the presence of aromatic C or C in a more stable state of decomposition. This result was attributed to the increase and accumulation of vegetal residue on the NT soil surface. Also, it was mentioned that SOM quality increases according to the type of soil preparation. NT management promotes SOM accumulation, mainly at the surface, which increases aggregates stability, decreases erosion processes and increases the amount of nutrients available to the plants. Higher amounts of light SOM causes more humified SOM dilution and by the aggregation physical protection, more labile structures are preserved (Mendes et al., 2003; Favoretto et al., 2008). So it is evident that the type of adopted tillage management influences some properties of the soil, increasing or decreasing its quality.
λ (nm) Fig. 1. Emission spectra of whole soil sample (conventional tillage 0–5 cm depth, CT0–5).
the whole soil sample (Milori et al., 2002, 2006). It was found that the most humified sample was the RT15–20 and the least humified was the NT 0–5. When 0–5 cm depth samples from different managements are compared, the most humified is the CT sample, followed by the RT and NT. For the NT and RT treatments there was a gradual decrease in the degree of humification as deeper depths are compared. Nevertheless, the same behavior was not observed for the CT samples, in which a uniform degree of humification was observed for samples from different depths. Remarkable differences between the humification of superficial (0–5 cm) and the deep (15–20 cm) samples from both NT and RT treatments were observed. Results found here are consistent with others presented in the literature (Milori et al., 2006; Gonza´lez-Pe´rez et al., 2007) where NT samples presented a higher C content (Table 2) and lower humification index. This is an indicative that C in the soil is available as a nutrient for the crop. The results of the samples at 0– 20 cm are also in agreement with those of Favoretto et al. (2008) who determined the degree of humification of the same whole Oxisol samples and their fractions using LIF. For the NT and RT, increase in the degree of humification occurred gradually as deeper depths were investigated, while in the CT there was no change in [(Fig._2)TD$IG]the degree of humification.
[(Fig._3)TD$IG]
3.2. LIF—particle size fractioning Fig. 3 shows the LIF spectrum obtained for sand samples (20– 1000 mm) of CT form (0–5 cm depth). As presented to the whole
whole soil humification
4,0
3,5
Emission (a.u)
HFIL(a.u)
16
8
3,0
2,5
2,0
1,5 0 0-5
5-10 10-15 15-20
NT
--
0-5
5-10 10-15 15-20
CT
--
0-5
5-10 10-15 15-20
(cm)
RT
Fig. 2. Difference among tillage systems and depths in relation to the SOM humification degree indicated by the HFIL index. The error bar (standard deviation) of the measurements is shown.
1,0 480
500
520
540
560
580
600
620
640
λ (nm) Fig. 3. Emission spectrum of the sand fraction (20–1000 mm) in the CT.
[(Fig._4)TD$IG]
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234
Table 3 C/N ratio of whole soil and fractions.
clay fraction (<2 μm) humification
18
C/N ratio Samples (depth in cm)
Whole soil
Clay
Silt
Sand
NT0–5 NT5–10 NT10–15 NT15–20
11.00 8.24 7.79 6.70
7.97 7.34 7.13 6.37
9.13 7.74 5.97 6.16
6.34 4.19 3.90 3.28
6
CT0–5 CT5–10 CT10–15 CT15–20
6.40 6.57 6.90 7.22
5.92 6.34 5.82 6.02
6.46 6.20 5.58 5.84
3.95 3.81 4.93 4.10
0
RT0–5 RT5–10 RT10–15 RT15–20
7.92 7.45 6.92 5.85
6.76 7.00 6.17 5.72
7.38 6.70 5.58 5.13
6.70 4.13 2.80 2.14
HFIL(a.u)
12
0-5
5-10 10-15 15-20
--
0-5
NT
5-10 10-15 15-20
--
0-5
5-10 10-15 15-20
--
(cm)
RT
CT
24
silt fraction (2-20 μm) humification
HFIL(a.u)
16
8
0 0-5
5-10 10-15 15-20
--
0-5
5-10 10-15 15-20
--
0-5
5-10 10-15 15-20
CT
NT
--
(cm)
RT
sand fraction (20-1000 μm) humification
HFIL(a.u)
60
30
0 0-5
5-10 10-15 15-20
NT
--
0-5
5-10 10-15 15-20
CT
--
0-5
5-10 10-15 15-20
--
(cm)
RT
Fig. 4. Humification index for the granulometric fractions of Oxisol. (a) <2 mm fraction; (b) 2–20 mm fraction; (c) 20–1000 mm fraction. The error bar (standard deviation) of the measurements is shown.
soil samples, a broad band peak with average maximum at 520 nm was also identified in this soil fractions. The behavior of the fluorescence curve indicates the presence of molecular structures, rich in complex structures of fluorophores such as, condensed and/ or substituted aromatic rings, quinone groups and cyclic systems (Milori et al., 2006; Favoretto et al., 2008). Fig. 4 shows the humification index of soil fractions, which were determined in the same way as described for the whole soil. In the fraction >2 mm the highest humification was observed to the sample CT10–15 and the lowest for the sample NT0–5. As for the
whole soil, fraction >2 mm of CT also presented uniform values along different depths. Nevertheless, were observed differences between 0–5 cm and 15–20 cm layers of NT and RT. For the fraction 2–20 mm, the most humified sample was the RT15–20 and the least humified was the NT0–5. The same behavior was also observed to the 20–1000 mm fraction. NT and RT fractions 2–20 mm and 20–1000 mm, have gradually increased their humification with depth. On the other hand, CT samples presented a uniform humification along different depths. Probably it results from intense soil revolving, which disrupts soil aggregates promoting SOM homogenization among depths, i.e. from 0– 5 cm to 15–20 cm (Favoretto et al., 2008). The results obtained here show the fraction that presented the highest degree of humification was the 20–1000 mm, followed by the 2–20 mm and then by the <2 mm. The NT in all cases presented the lowest index of humification, mainly at the 0–5 cm layer. The fraction that exhibited the highest index of humification was the sand (20–1000 mm). These results are in accordance with Favoretto et al. (2008) who found higher humification indexes in fine sand samples (20– 53 mm) and lower indexes in the clay fraction (<2 mm). In relation to the tillage management and depths, it was also observed lower degree of humification in superficial samples of soils under NT. Gonza´lez-Pe´rez et al. (2006) working with latosols treated with sewage sludge, found higher humification of the silt fraction (2– 20 mm), and also a higher C content in this fraction. Saab and Martin-Neto (2003), studying Gleysols by the EPR technique, found that the silt fraction (2–20 mm) is more stable than the others. According to these authors this higher stability is related to higher SOM recalcitrance or due to its linkage to the organic-mineral fraction. Favoretto et al. (2008) attribute the SOM stability in the clay fraction (<2 mm) by its physical protection by the organicmineral instead of the humification. Table 3 shows the C/N ratio of whole soil samples and fractions. The C/N ratio provides additional information regarding the SOM degree of humification. C/N smaller ratios are related to higher degrees of humification and it is related to decreases in C rates in the decomposition process. Results obtained by the C/N ratio are coherent with the HFIL results. In both cases there were verified a uniformity of humification in NT samples. For the whole soil the most humified sample is the RT15–20 in both analyses, being the sand fraction the most humified fraction. It was observed that larger HFIL indexes are related to lower C/N ratios. This behavior can be clearly observed in Fig. 5 for the whole soil and its fraction. Thus, as the C/N ratio decreases for higher humification, the HFIL index increases proportionally.
[(Fig._5)TD$IG]
T. Martins et al. / Soil & Tillage Research 111 (2011) 231–235
235
16
12
2
a
Whole soil
Clay 14
8
12
6
10
C/N
10
6
b
R = 0,82
2
R = 0,85
12
6
18
7
8
8 24
c
2
R =0,92
2
R =0,77 6
Silt
d
Sand
C/N
18
4
12 2
4
6
8
HFIL(u.a)
10
30
60
HFIL(u.a)
Fig. 5. Correlation between C/N ratio and Laser Induced Fluorescence (LIF). (a) Whole soil sample; (b) clay fraction; (c) silt fraction; and (d) sand fraction.
4. Conclusion The sample no-tillage at 0–5 cm that contains the highest C content, presented higher stability of aggregates and lower degree of humification. This conclusion was based on HFIL indexes and C/N ratio results. Among fractions, the 20–1000 mm was the most humified and the <2 mm least humified one. The C/N ratio and the humification index HFIL were inversely related, i.e. lower C/N ratios are related to higher humidified samples and vice-versa. On the other hand, HFIL and humification are directly related, i.e. larger values of HFIL are related to more humidified samples. In general, it can be said that NT favors the accumulation of organic matter on its surface, increasing aggregates stability and presenting samples with lower humification indexes which determines the larger availability of nutrients for the crop. Acknowledgements Authors acknowledge Capes and CNPq, Brazilian Agencies, for financial support. References Bayer, C., Martin-Neto, L., Mielniczuk, J., Saab, S.C., Milori, D.M.B.P., Bagnato, V., 2002a. Tillage and cropping system effects on soil humic acid characteristics as determined by electron spin resonance and fluorescence spectroscopies. Geoderma 105, 81–92. Bayer, C., Martin-Neto, L., Saab, S.C., 2003. Humification decrease of soil organic matter under no-tillage. Rev. Bras. Cienc. Solo 27, 537–544.
Bayer, C., Mielniczuk, J., Martin-Neto, L., Ernani, P.R., 2002b. Stocks and humification degree of organic matter fractions as affected by no-tillage on a subtropical soil. Plant Soil 238, 133–140. Christensen, B.T., 1992. Physical fractionation of soil and organic matter in primary particle size and density separates. Adv. Soil Sci. 20, 1–19. Costa, F.S., Bayer, C., Albuquerque, J.A., Fontoura, S.M.V., 2004. No-tillage Increases Soil Organic Matter in a South Brazilian Oxisol, vol. 34. Cieˆncia Rural, pp. 587– 589. Embrapa, 1999. Sistema Brasileiro de Classificac¸a˜o de Solos, 1st ed. Embrapa Solos, Rio de Janeiro, 412 pp. FAO, 1998. World reference base for soil resources. In: World Soil Resources Report 84, Food and Agriculture Organisation of the United Nations, Rome, 88 pp. Favoretto, C.M., Gonc¸alves, D., Milori, D.M.B.P., Rosa, J.A., Leite, W.C., Brinatti, A.M., Saab, S.C., 2008. Determination of humification degree of organic matter of an oxisol and of its organo-mineral fractions. Quim. Nova 31, 1994–1996. Gonza´lez-Pe´rez, M., Milori, D.M.B.P., Colnago, L.A., Martin-Neto, L., Melo, W.J.A., 2007. Laser-induced fluorescence spectroscopic study of organic matter in a Brazilian Oxisol under different tillage systems. Geoderma 138, 20–24. Gonza´lez-Pe´rez, M., Milori, D.M.B.P., Martin-Neto, L., Colnago, L.A., Camargo, O.A., Berton, R., BettioL, W., 2006. Laser-induced fluorescence of organic matter from a Brazilian oxisol under sewage-sludge applications. Sci. Agric. 63, 269–275. Mendes, I.C., Souza, L.V., Resck, D.V.S., Gomes, A.C., 2003. Biological properties of aggregates from a Cerrado oxisol under conventional and no-till Management systems. Rev. Bras. Cienc. Solo 27, 435–443. Milori, D.M.B.P., Galeti, H.V.A., Martin-Neto, L., Dieckow, J., Gonza´lez-Pe´rez, M., Bayer, C., Salton, J., 2006. Organic matter study of whole soil samples using laser-induced fluorescence spectroscopy. Soil Sci. Soc. Am. J. 70, 57–63. Milori, D.M.B.P., Martin-Neto, L., Bayer, C., Mielniczuk, J., Bagnato, V.S., 2002. Humification degree of soil humic acids determined by fluorescence spectroscopy. Soil Sci. 167, 739–749. Saab, S.C., Martin-Neto, L., 2008. Characterization by electron paramagnetic resonance of organic matter in whole soil (Gleysoil) and organic-mineral fractions. J. Braz. Chem. Soc. 19, 413–417. Saab, S.C., Martin-Neto, L., 2003. Use of the EPR technique to determine thermal stability of some humified organic substances found in soil organic-mineral fractions. Quim. Nova 26, 497–498. Saab, S.C., Martin-Neto, L., 2007. Condensed aromatic rings and E4/E6 ratio: humic acids in gleysoils studied by nmr cp/mas 13C, and dipolar dephasing. Quim. Nova 30, 260–263.
Contents lists available at ScienceDirect
Soil & Tillage Research journal homepage: www.elsevier.com/locate/still
Short communication
Soil organic matter humification under different tillage managements evaluated by Laser Induced Fluorescence (LIF) and C/N ratio T. Martins a, S.C. Saab b,*, D.M.B.P. Milori c, A.M. Brinatti b, J.A. Rosa d, F.A.M. Cassaro b, L.F. Pires b a
State University of Ponta Grossa (UEPG), Av. Carlos Cavalcanti 4748, 84030-900, Ponta Grossa, PR, Brazil Laboratory of Soil Physics and Environmental Sciences, Department of Physics, State University of Ponta Grossa (UEPG), Av. Carlos Cavalcanti 4748, 84030-900, Ponta Grossa, PR, Brazil c Embrapa Agricultural Instrumentation Center (CNPDIA/EMBRAPA), CP 741, 13560-970, Sa˜o Carlos, SP, Brazil d Agricultural Research Institute of Parana´ (IAPAR), BR 376, Km 496, 84001-970, Ponta Grossa, PR, Brazil b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 March 2010 Received in revised form 13 October 2010 Accepted 14 October 2010
In this work is presented the use of the C/N ratio and the Laser Induced Fluorescence (LIF) spectroscopy for determining the humification of soil organic matter (SOM) in an Oxisol under three different longterm tillage managements (no-tillage (NT), reduced tillage (RT) and conventional tillage (CT)). Humification of SOM was evaluated in the soil and its fractions (clay < 2 mm, silt 2–20 mm, sand 20– 1000 mm). The obtained results show that lower SOM humification was observed in soil under NT, mainly at the surface (0–5 cm). In CT, SOM humification values maintained constant for all investigated depths (0–5, 5–10, 10–15 and 15–20 cm). Also, clay was the soil fraction that exhibited the lesser humification of SOM. Based on the obtained results it can be said that NT favors the accumulation of SOM on its surface, increasing aggregate stability and presenting samples with lower humification indexes. These results indicate a larger availability of nutrients for the plants in this management. ß 2010 Elsevier B.V. All rights reserved.
Keywords: Degree of humification Soil fractions No-tillage management system
1. Introduction Soil granulometric fractioning consists of separating a soil sample into its four constituent fractions: clay (<2 mm), silt (2–20 mm), fine sand (20–53 mm) and coarse sand (53–1000 mm). The quantification begins with humid sieving followed by sedimentation process. Different from chemical fractioning, granulometric fractioning does not employ strong acids and bases for the separation process. Then, the possibility of altering the soil organic matter (SOM) components is diminished, representing a less destructive method (Christensen, 1992; Saab and Martin-Neto, 2003, 2008). SOM study interpretation conducted in soil fractions is also simplified when it is performed in conjunction with spectroscopic techniques. This simplification contributes significantly to studies related to SOM physical protection in tropical and subtropical soils (Costa et al., 2004). The Laser Induced Fluorescence (LIF) is a very promising technique of analysis, which is based on the fluorescence emission of aromatic components present in the soil. This methodology uses a laser beam tuned in the blue region of the spectra to excite the samples. Higher fluorescence intensities are related to greater SOM
* Corresponding author. E-mail addresses: scsaab@fisica.uepg.br, [email protected] (S.C. Saab). 0167-1987/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2010.10.009
humification degrees. Simplicity, sensitivity and speediness are advantages of using the LIF technique. Also, it can be used in combination with other analytical techniques, such as electron paramagnetic resonance (EPR) (Saab and Martin-Neto, 2008) and nuclear magnetic resonance (NMR) (Saab and Martin-Neto, 2007). As compared to Fe3+ technique, LIF can be used to determine the degree humification in Oxisols without the need for humic acids extractions (Milori et al., 2006). According to some authors (Milori et al., 2006; Gonza´lez-Pe´rez et al., 2007; Favoretto et al., 2008), LIF is considered a non-destructive and fast technique for SOM analysis as the soil samples to be investigated do not need previous chemical treatment. Milori et al. (2006) investigating Red Latosol samples subject to different tillage managements, concluded that the conventional system (that involves intense soil revolving) presented a higher degree of humification mainly at the surface (to the first 10 cm of depth) in comparison to the conservationist management and the native cerrado (considered as a reference). In the samples of cerrado, the degree of humification was lower due to higher concentration of light SOM or SOM at initial stages of the decomposition process. In this paper some samples were calcined and treated with hydrogen peroxide to eliminate organic matter and assure that the signal in the LIF spectra referred to the humified SOM. Gonza´lez-Pe´rez et al. (2007) found high correlation among results of SOM evaluation obtained using LIF, NMR and EPR
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measurements, for soils prepared in different manners. Bayer et al. (2002a) showed that humic acid samples extracted from soils under no-tillage (NT) management had lower degrees of humification than those from soil subjected to CT management. It was concluded based on lower concentrations of stable semiquinonetype free radicals and total fluorescence exhibited by soils under NT. Differences between tillage systems increased along the years demonstrating the continuous effect of management systems on soil humic acid characteristics. Bayer et al. (2003) evaluated the concentration of semiquinone free radicals (SFR) of organic matter from the surface soil layer (0– 25 mm) of a humic soil under years long CT, reduced tillage (RT) and NT. These authors showed that NT presented a lesser degree of humification of SOM as compared to soils under RT and CT. It was related to a less oxidative environment in NT as compared to the other managements. They also demonstrated that the fraction related to clay (2–20 mm) presented the highest concentration of SFR and the smallest line width of the EPR signal. These two results are an indicative of highest degree of SOM humification or of a large organic matter interaction with the mineral fraction of the soil. The objective of this work is to determine the humification of SOM in different depths of an Oxisol (FAO, 1998) submitted to different tillage management systems, using whole soil samples (samples without any previous treatment) and its fractions (clay, silt and sand) using C/N ratio and Laser Induced Fluorescence.
fine sand (20–53 mm) was obtained after this process (Saab and Martin-Neto, 2003). 2.2. Elemental analysis (C/N ratio) To perform the C/N ratio analysis approximately 150 mg of whole samples and their fractions were dried (in oven at 60 8C) and homogenized. To calibrate the system, a sample with well known content of C and N (considered as a standard sample) was used. The equipment used in the measurements was a C and N elemental determinator, TRUS PEC CN LECO, which investigates dry samples in powder form. In the measurement, samples are combusted at 950 8C and the gas resulting from the combustion (CO2) is purified and analyzed by an IV detector. 2.3. Laser Induced Fluorescence (LIF) For LIF analysis (whole soil), two pellets of each sample were analyzed in replicate. Each soil fraction was analyzed in three replicates. LIF operation parameters were: (1) lock-in 100 mV, (2) photomultiplier 850 V, (3) 457 nm argon wavelength and (4) 300 mW laser power. The humification index was determined from the equation proposed by Milori et al. (2006), HFIL = ACF/CT, i.e. the humification index is equal to the ratio between the fluorescence curve area and the total C presented in the samples. 2.4. Statistical analysis
2. Materials and methods Soil samples were collected in an Experimental Station of the Agricultural Research Institute of Parana´ (IAPAR) located in Ponta Grossa, PR, Brazil (258130 S; 508010 W; 875 m a.s.l). According to the Brazilian System of Soil Classification (Embrapa, 1999) and FAO (FAO, 1998), the soil studied is classified as a Distrofic Red Latosol and Oxisol, respectively. Twelve soil samples were collected in depths 0–5, 5–10, 10–15 and 15–20 cm at three different points in each tillage management (NT, RT and CT). These managements have been conducted in these areas for 27 years, and information about crop rotations are given in Table 1. 2.1. Particle size fractioning As it was said, physical fractioning consists in separating a soil sample to its fractions: (1) coarse sand (53–1000 mm), (2) fine sand (20–53 mm), (3) silt (2–20 mm) and (4) clay (<2 mm). Coarse sand (fractions above 53 mm) was obtained by humid sieving; silt and clay (particles with diameters below 20 mm) were obtained by natural sedimentation (using the Stokes Law of sedimentation); and
Analysis of statistical significance of tillage and cropping system effects on total fluorescence of soil was performed using mean standard deviation. Relation between fluorescence spectroscopy (HFIL) and C/N ratio results was evaluated by the significance of correlation coefficient (r) at P < 0.05. 3. Results and discussion 3.1. Whole soil Laser Induced Fluorescence In Fig. 1 is shown the fluorescence curve graph for the sample CT0–5. According to Milori et al. (2006), the fluorescence curve is directly related to the C concentration. However, this C concentration is only referent to C in rigid structures such as aromatic rings and quinone groups. In Fig. 1 it can be noticed a wide band with a maximum wavelength of 520 nm. Other samples presented very similar spectra. Differences among the tillage managements and depths, in relation to the degree of SOM humification, indicated by the HFIL index, are shown in Fig. 2. Higher the HFIL index more humified is
Table 1 Culture rotations per year in each tillage system. Year
Culture rotation conventional tillage and reduced tillage
Culture rotation: no-tillage
1981–1990
Wheat and soybean
1990–1995 1995–2000 2000–2005 2005–2007 2007–2008
Black oat/soybean/black oat/sweet corn/wheat/soybean/black oat/soybean/lupine/sweet corn Blackoat/soybean/wheat/soybean/oat + vetch/sweet corn/black oat/soybean/wheat/sweet corn Oat + vetch/sweet corn/oat/soybean/oat/soybean/oat + vetch/sweet corn/oat/soybean/oat + vetch Oat/sweet corn/oat/soybean/oat Oat/sweet corn
Sweetcorn/oat/soybean/ wheat/soybean/lupine/ sweetcorn/oat/soybean/ wheat/soybean/lupine/ sweetcorn/oat/soybean/ wheat/soybean The same as in CT and RT The same as in CT and RT The same as in CT and RT The same as in CT and RT The same as in CT and RT
[(Fig._1)TD$IG]
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Table 2 C content for the whole soil.
5
Emission (a.u)
233
4
3
2
Samples (depth in cm)
C content (g/kg) in whole soil
NT0–5 NT5–10 NT10–15 NT15–20
74.70 46.60 37.50 34.60
CT0–5 CT5–10 CT10–15 CT15–20
31.70 31.90 33.60 33.10
RT0–5 RT5–10 RT10–15 RT15–20
42.40 38.70 32.10 28.50
1 480
500
520
540
560
580
600
620
640
Results related to the humification index were coherent with C results. Is this regard, it is expected that lower indexes of humification were being related to higher C contents and viceversa. This was here observed for NT and CT management systems, in a comparison between them. CT was the treatment higher humified. Bayer et al. (2002b) also found higher degree of humification in CT samples, as well as lower C content compared to the same soil under NT. These authors observed that the humification was characterized from semiquinone free radicals concentration, which appearance in the samples is related to the presence of aromatic C or C in a more stable state of decomposition. This result was attributed to the increase and accumulation of vegetal residue on the NT soil surface. Also, it was mentioned that SOM quality increases according to the type of soil preparation. NT management promotes SOM accumulation, mainly at the surface, which increases aggregates stability, decreases erosion processes and increases the amount of nutrients available to the plants. Higher amounts of light SOM causes more humified SOM dilution and by the aggregation physical protection, more labile structures are preserved (Mendes et al., 2003; Favoretto et al., 2008). So it is evident that the type of adopted tillage management influences some properties of the soil, increasing or decreasing its quality.
λ (nm) Fig. 1. Emission spectra of whole soil sample (conventional tillage 0–5 cm depth, CT0–5).
the whole soil sample (Milori et al., 2002, 2006). It was found that the most humified sample was the RT15–20 and the least humified was the NT 0–5. When 0–5 cm depth samples from different managements are compared, the most humified is the CT sample, followed by the RT and NT. For the NT and RT treatments there was a gradual decrease in the degree of humification as deeper depths are compared. Nevertheless, the same behavior was not observed for the CT samples, in which a uniform degree of humification was observed for samples from different depths. Remarkable differences between the humification of superficial (0–5 cm) and the deep (15–20 cm) samples from both NT and RT treatments were observed. Results found here are consistent with others presented in the literature (Milori et al., 2006; Gonza´lez-Pe´rez et al., 2007) where NT samples presented a higher C content (Table 2) and lower humification index. This is an indicative that C in the soil is available as a nutrient for the crop. The results of the samples at 0– 20 cm are also in agreement with those of Favoretto et al. (2008) who determined the degree of humification of the same whole Oxisol samples and their fractions using LIF. For the NT and RT, increase in the degree of humification occurred gradually as deeper depths were investigated, while in the CT there was no change in [(Fig._2)TD$IG]the degree of humification.
[(Fig._3)TD$IG]
3.2. LIF—particle size fractioning Fig. 3 shows the LIF spectrum obtained for sand samples (20– 1000 mm) of CT form (0–5 cm depth). As presented to the whole
whole soil humification
4,0
3,5
Emission (a.u)
HFIL(a.u)
16
8
3,0
2,5
2,0
1,5 0 0-5
5-10 10-15 15-20
NT
--
0-5
5-10 10-15 15-20
CT
--
0-5
5-10 10-15 15-20
(cm)
RT
Fig. 2. Difference among tillage systems and depths in relation to the SOM humification degree indicated by the HFIL index. The error bar (standard deviation) of the measurements is shown.
1,0 480
500
520
540
560
580
600
620
640
λ (nm) Fig. 3. Emission spectrum of the sand fraction (20–1000 mm) in the CT.
[(Fig._4)TD$IG]
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Table 3 C/N ratio of whole soil and fractions.
clay fraction (<2 μm) humification
18
C/N ratio Samples (depth in cm)
Whole soil
Clay
Silt
Sand
NT0–5 NT5–10 NT10–15 NT15–20
11.00 8.24 7.79 6.70
7.97 7.34 7.13 6.37
9.13 7.74 5.97 6.16
6.34 4.19 3.90 3.28
6
CT0–5 CT5–10 CT10–15 CT15–20
6.40 6.57 6.90 7.22
5.92 6.34 5.82 6.02
6.46 6.20 5.58 5.84
3.95 3.81 4.93 4.10
0
RT0–5 RT5–10 RT10–15 RT15–20
7.92 7.45 6.92 5.85
6.76 7.00 6.17 5.72
7.38 6.70 5.58 5.13
6.70 4.13 2.80 2.14
HFIL(a.u)
12
0-5
5-10 10-15 15-20
--
0-5
NT
5-10 10-15 15-20
--
0-5
5-10 10-15 15-20
--
(cm)
RT
CT
24
silt fraction (2-20 μm) humification
HFIL(a.u)
16
8
0 0-5
5-10 10-15 15-20
--
0-5
5-10 10-15 15-20
--
0-5
5-10 10-15 15-20
CT
NT
--
(cm)
RT
sand fraction (20-1000 μm) humification
HFIL(a.u)
60
30
0 0-5
5-10 10-15 15-20
NT
--
0-5
5-10 10-15 15-20
CT
--
0-5
5-10 10-15 15-20
--
(cm)
RT
Fig. 4. Humification index for the granulometric fractions of Oxisol. (a) <2 mm fraction; (b) 2–20 mm fraction; (c) 20–1000 mm fraction. The error bar (standard deviation) of the measurements is shown.
soil samples, a broad band peak with average maximum at 520 nm was also identified in this soil fractions. The behavior of the fluorescence curve indicates the presence of molecular structures, rich in complex structures of fluorophores such as, condensed and/ or substituted aromatic rings, quinone groups and cyclic systems (Milori et al., 2006; Favoretto et al., 2008). Fig. 4 shows the humification index of soil fractions, which were determined in the same way as described for the whole soil. In the fraction >2 mm the highest humification was observed to the sample CT10–15 and the lowest for the sample NT0–5. As for the
whole soil, fraction >2 mm of CT also presented uniform values along different depths. Nevertheless, were observed differences between 0–5 cm and 15–20 cm layers of NT and RT. For the fraction 2–20 mm, the most humified sample was the RT15–20 and the least humified was the NT0–5. The same behavior was also observed to the 20–1000 mm fraction. NT and RT fractions 2–20 mm and 20–1000 mm, have gradually increased their humification with depth. On the other hand, CT samples presented a uniform humification along different depths. Probably it results from intense soil revolving, which disrupts soil aggregates promoting SOM homogenization among depths, i.e. from 0– 5 cm to 15–20 cm (Favoretto et al., 2008). The results obtained here show the fraction that presented the highest degree of humification was the 20–1000 mm, followed by the 2–20 mm and then by the <2 mm. The NT in all cases presented the lowest index of humification, mainly at the 0–5 cm layer. The fraction that exhibited the highest index of humification was the sand (20–1000 mm). These results are in accordance with Favoretto et al. (2008) who found higher humification indexes in fine sand samples (20– 53 mm) and lower indexes in the clay fraction (<2 mm). In relation to the tillage management and depths, it was also observed lower degree of humification in superficial samples of soils under NT. Gonza´lez-Pe´rez et al. (2006) working with latosols treated with sewage sludge, found higher humification of the silt fraction (2– 20 mm), and also a higher C content in this fraction. Saab and Martin-Neto (2003), studying Gleysols by the EPR technique, found that the silt fraction (2–20 mm) is more stable than the others. According to these authors this higher stability is related to higher SOM recalcitrance or due to its linkage to the organic-mineral fraction. Favoretto et al. (2008) attribute the SOM stability in the clay fraction (<2 mm) by its physical protection by the organicmineral instead of the humification. Table 3 shows the C/N ratio of whole soil samples and fractions. The C/N ratio provides additional information regarding the SOM degree of humification. C/N smaller ratios are related to higher degrees of humification and it is related to decreases in C rates in the decomposition process. Results obtained by the C/N ratio are coherent with the HFIL results. In both cases there were verified a uniformity of humification in NT samples. For the whole soil the most humified sample is the RT15–20 in both analyses, being the sand fraction the most humified fraction. It was observed that larger HFIL indexes are related to lower C/N ratios. This behavior can be clearly observed in Fig. 5 for the whole soil and its fraction. Thus, as the C/N ratio decreases for higher humification, the HFIL index increases proportionally.
[(Fig._5)TD$IG]
T. Martins et al. / Soil & Tillage Research 111 (2011) 231–235
235
16
12
2
a
Whole soil
Clay 14
8
12
6
10
C/N
10
6
b
R = 0,82
2
R = 0,85
12
6
18
7
8
8 24
c
2
R =0,92
2
R =0,77 6
Silt
d
Sand
C/N
18
4
12 2
4
6
8
HFIL(u.a)
10
30
60
HFIL(u.a)
Fig. 5. Correlation between C/N ratio and Laser Induced Fluorescence (LIF). (a) Whole soil sample; (b) clay fraction; (c) silt fraction; and (d) sand fraction.
4. Conclusion The sample no-tillage at 0–5 cm that contains the highest C content, presented higher stability of aggregates and lower degree of humification. This conclusion was based on HFIL indexes and C/N ratio results. Among fractions, the 20–1000 mm was the most humified and the <2 mm least humified one. The C/N ratio and the humification index HFIL were inversely related, i.e. lower C/N ratios are related to higher humidified samples and vice-versa. On the other hand, HFIL and humification are directly related, i.e. larger values of HFIL are related to more humidified samples. In general, it can be said that NT favors the accumulation of organic matter on its surface, increasing aggregates stability and presenting samples with lower humification indexes which determines the larger availability of nutrients for the crop. Acknowledgements Authors acknowledge Capes and CNPq, Brazilian Agencies, for financial support. References Bayer, C., Martin-Neto, L., Mielniczuk, J., Saab, S.C., Milori, D.M.B.P., Bagnato, V., 2002a. Tillage and cropping system effects on soil humic acid characteristics as determined by electron spin resonance and fluorescence spectroscopies. Geoderma 105, 81–92. Bayer, C., Martin-Neto, L., Saab, S.C., 2003. Humification decrease of soil organic matter under no-tillage. Rev. Bras. Cienc. Solo 27, 537–544.
Bayer, C., Mielniczuk, J., Martin-Neto, L., Ernani, P.R., 2002b. Stocks and humification degree of organic matter fractions as affected by no-tillage on a subtropical soil. Plant Soil 238, 133–140. Christensen, B.T., 1992. Physical fractionation of soil and organic matter in primary particle size and density separates. Adv. Soil Sci. 20, 1–19. Costa, F.S., Bayer, C., Albuquerque, J.A., Fontoura, S.M.V., 2004. No-tillage Increases Soil Organic Matter in a South Brazilian Oxisol, vol. 34. Cieˆncia Rural, pp. 587– 589. Embrapa, 1999. Sistema Brasileiro de Classificac¸a˜o de Solos, 1st ed. Embrapa Solos, Rio de Janeiro, 412 pp. FAO, 1998. World reference base for soil resources. In: World Soil Resources Report 84, Food and Agriculture Organisation of the United Nations, Rome, 88 pp. Favoretto, C.M., Gonc¸alves, D., Milori, D.M.B.P., Rosa, J.A., Leite, W.C., Brinatti, A.M., Saab, S.C., 2008. Determination of humification degree of organic matter of an oxisol and of its organo-mineral fractions. Quim. Nova 31, 1994–1996. Gonza´lez-Pe´rez, M., Milori, D.M.B.P., Colnago, L.A., Martin-Neto, L., Melo, W.J.A., 2007. Laser-induced fluorescence spectroscopic study of organic matter in a Brazilian Oxisol under different tillage systems. Geoderma 138, 20–24. Gonza´lez-Pe´rez, M., Milori, D.M.B.P., Martin-Neto, L., Colnago, L.A., Camargo, O.A., Berton, R., BettioL, W., 2006. Laser-induced fluorescence of organic matter from a Brazilian oxisol under sewage-sludge applications. Sci. Agric. 63, 269–275. Mendes, I.C., Souza, L.V., Resck, D.V.S., Gomes, A.C., 2003. Biological properties of aggregates from a Cerrado oxisol under conventional and no-till Management systems. Rev. Bras. Cienc. Solo 27, 435–443. Milori, D.M.B.P., Galeti, H.V.A., Martin-Neto, L., Dieckow, J., Gonza´lez-Pe´rez, M., Bayer, C., Salton, J., 2006. Organic matter study of whole soil samples using laser-induced fluorescence spectroscopy. Soil Sci. Soc. Am. J. 70, 57–63. Milori, D.M.B.P., Martin-Neto, L., Bayer, C., Mielniczuk, J., Bagnato, V.S., 2002. Humification degree of soil humic acids determined by fluorescence spectroscopy. Soil Sci. 167, 739–749. Saab, S.C., Martin-Neto, L., 2008. Characterization by electron paramagnetic resonance of organic matter in whole soil (Gleysoil) and organic-mineral fractions. J. Braz. Chem. Soc. 19, 413–417. Saab, S.C., Martin-Neto, L., 2003. Use of the EPR technique to determine thermal stability of some humified organic substances found in soil organic-mineral fractions. Quim. Nova 26, 497–498. Saab, S.C., Martin-Neto, L., 2007. Condensed aromatic rings and E4/E6 ratio: humic acids in gleysoils studied by nmr cp/mas 13C, and dipolar dephasing. Quim. Nova 30, 260–263.