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Soil quality assessed by carbon management index in a subtropical Acrisol subjected to tillage systems and irrigation.

Introduction

In order to minimise risks of crop failures due to droughts and improve crop yields, Brazilian farmers have been increasing the sprinkler-irrigated land area at a rate of 85 000 ha per year (1990-2004), so that about 1.37 Mha of Brazil's cropland area was under sprinkler irrigation in 2004 (132 Mha in southern subtropical Brazil) (Christofidis 2006). No-till is another technology being widely adopted by Brazilian farmers, in a current area of about 25.5 Mha (Febrapdp 2007). Despite this wide adoption of irrigation and no-till, little is known yet about the combined influence of these 2 technologies on soil organic C stocks, soil organic C fractions, and soil quality, especially in tropical and subtropical soils. For North American conditions, Lal et al. (1998) estimated that irrigation can increase soil C stocks at rates of 50-150 kg C/ha.year, a range classified by Follett (2001) as conservative under the perspective that improved management technologies related to cropping systems can increase these rates considerably.

Soil quality in croplands, including irrigated lands, can be evaluated through the establishment of a minimum dataset (MDS) that includes soil properties such as bulk density, infiltration rate, total C and N content, pH, electric conductivity, etc. (Doran and Parkin 1994). Gregorich et al. (1994), however, emphasised the importance of including soil organic matter in MDS, not only as a single parameter, but as an integrative attribute related to several other soil properties included in MDS. In agreement with the concept of Gregorich et al. (1994), we believe that the carbon management index (CMI) originally proposed by Blair et al. (1995) can be used to assess soil quality based on information related to soil organic C dynamics. This index expresses the soil quality in terms of increments in the total C content and in the proportion of labile C fraction compared to a reference soil, generally that under native vegetation, which arbitrarily has a CMI of 100. In the proposal of Blair et al. (1995), the labile C fraction was considered as that oxidised with 333 mM KMn[O.sub.4] treatment, but recent studies have proposed the particulate organic matter isolated through physical fractionation based either on density (Diekow et al. 2005; Vieira et al. 2007) or granulometric (Skjemstad et al. 2006) approaches as the labile fraction to estimate the CMI.

The light fraction of soil organic matter is basically constituted by partially decomposed plant, animal, and fungal residues (Gregorich et al. 1994) and therefore it is referred to as being a labile fraction more sensitive to changes in soil management regime than the whole soil organic matter pool (Gregorich et al. 1994; Freixo et al. 2002a). Dalai and Mayer (1986) observed that C losses were 11 times greater in the light fraction (density <2.0 Mg/[m.sup.3]) than the heavy fraction (density >2.4 Mg/[m.sup.3]) after cultivation of virgin land. The light fraction relates to soil quality because it plays a role to stabilise macroaggregates (Six et al. 1999), determines the soil microbial activity (Gregorich et al. 1994), and indicates that physical protection of organic matter in stable aggregates is functioning and therefore decreasing soil organic matter mineralisation rates (Balesdent et al. 2000).

Several studies have shown the significant influence of soil tillage system on particulate organic matter (Cambardella and Elliott 1992; Bayer et al. 2002; Freixo et al. 2002a), so that higher stocks and concentrations of this fraction were found in no-till than in conventionally tilled soils, because of the lower soil disturbance and decomposition rate due to no-till management (Balesdent et al. 2000). Irrigation, on the other hand, by increasing the water availability in soil, may possibly stimulate soil microbial activity and thus increase decomposition of the labile organic matter fraction. However, this is only a hypothesis and the relationship between irrigation and light organic matter dynamics, not being sufficiently covered by literature, is still to be better clarified, particularly for tropical and subtropical soils subjected to different tillage systems.

This study aimed at evaluating the influence of sprinkler irrigation on the soil quality of a southern Brazilian sandy loam Acrisol subjected to conventional tillage and no-till management systems. The soil quality indicator was the CMI, estimated after considering the C in the light fraction as labile.

Materials and methods

Experimental field

The study was based on a long-term experiment (8 years) located at the Agronomic Experimental Station of the Federal University of Rio Grande do Sul, near the town of Eldorado do Sul, Rio Grande do Sul State, Brazil. The geographic coordinates are 30[degrees]05'S and 51[degrees]40'W, the altitude is 40m, and the local topography is fiat. The soil is a sandy clay loam Acrisol, according to the FAO classification system (Argissolo Vermelho by Brazilian System and Paleudult by Soil Taxonomy), derived from granite and containing 543, 271, and 186g/kg of sand, silt, and clay, respectively. The clay mineralogy is mostly composed of kaolinite (720 g/kg) and iron oxides (109g/kg) (Bayer 1996). The climate is subtropical humid (Cfa, Koppen), with an average annual rainfall of 1446 mm, uniformly distributed over the year (Bergamaschi 2003), but risks of drought especially in summer make irrigation necessary in order to secure maize and soybean yields in the region. The experiment was established in 1995 and prior to the experiment installation, lime was applied at a rate of 4.0 Mg/ha and soil was conventionally tilled to a depth of 200mm, both to incorporate lime and to remove some terrain irregularities. At the beginning of the experiment, after liming, soil presented the following chemical characteristics in the 0-200 mm layer: 2.1% organic matter, pH 5.9 (soil:water 1:1), 0.1 [cmol.sub.c]/kg of [Al.sup.3+], 2.4 [cmol.sub.c]/kg of [Ca.sup.2+], 0.7 [cmol.sub.c]/kg of [Mg.sup.2+], 0.3 [cmol.sub.c]/kg of [K.sup.+], 8.5 mg/kg of P (Mehlich 1), CEC 6.4 cmolc/kg, and base saturation 53%.

The experiment was arranged in a randomised complete block design, with 5 blocks. Two tillage systems (conventional tillage and no-till) were applied in 2 parallel strips of dimensions 22.5 by 75m (mains plots). Sprinklers located between these 2 strips irrigate the half-portion of each strip (~11.5 m), so that irrigated and non-irrigated treatments were obtained for each tillage system (subplots).

The adopted cropping system was oat (Avena strigosa Schreb.) intercropped with common vetch (Vicia sativa L.) as winter cover crops, and maize (Zea mays L.) in summer as cash crop. Conventional tillage was performed through 1 disk-ploughing (170-200 mm depth) and 2 discing operations in September or October each year, before maize planting. In the no-till treatment, the winter cover crops (oat and common vetch) were desiccated with glyphosate (N-phosphonomethylglycine) herbicide, also in September or October, previous to maize planting.

Soil moisture was monitored through a set of tensiometers with cups placed up to 700 mm deep, and the water layer to be applied in irrigation was defined according to evapotranspiration data collected in a lysimeter close to the experimental plots. Only the maize crop was irrigated, with about 6 to 8 irrigation events (~25 mm each) per cropping season (December to February) to bring soil moisture to field capacity. Further details about the experimental procedure are described by Dalmago (2004).

Soil sampling and C analysis

Soil samples from the 0-25, 25-50, 50-100, and 100-200mm depth of each plot in the 5 replicates were collected in a sampling area of 0.20 by 0.50 m, in October 2003, when the experiment was still under winter cover crops. The soil of the adjacent native grassland was also sampled, at 5 sampling points.

Soil samples were air-dried, ground in a ball-mill to pass a 2-mm mesh, and stored in plastic pots. An aliquot was further ground in mortar to pass 0.5-mm mesh and afterwards analysed for total organic C determination in a Shimadzu TOC-VCSH analyser. Since the C of this soil is only in the organic form (Tedesco et al. 1995), the total organic C will be referred only as total C.

The stocks of total C, labile C, and non-labile C were calculated by using the equivalent mass of soil approach (Sisti et al. 2004). The soil mass in each treatment was corrected to the mass of the native grassland soil, taken as reference, so that the effect of soil compaction and differences in soil bulk densities across treatments were isolated. To calculate the mass of soil we used the soil bulk density values presented in Table 1. Soil bulk density was determined throughout the core method, in the 0-50, 50-100, and 100-200 mm layers.

Separation of the organic matter light fraction

The light fraction of the organic matter was obtained by physical fractionation of soil samples that were composited from the 5 experimental blocks (treatment replications). Twenty g of composited soil sample and 80 mL NaI solution with density of 1.8 Mg/[m.sup.3] were added into 100-mL centrifuge tubes and sonicated at an energy level of 350 J/mL. This energy was determined in a previous test as being sufficient to disperse all sand- and silt-size microaggregates. After sonication, the suspension was centrifuged during 30 min at 2000G. The supernatant containing the light fraction was vacuum-filtered through a previously weighed fibre-glass filter (Whatman GF/C, 47-mm diameter). The collected light fraction of the organic matter, together with the filter, was washed, dried at 60[degrees]C for 18 h, ground in mortar, and analysed for C determination in the same Shimadzu TOC analyser to give the labile C concentration. The C concentration in the heavy fraction, the non-labile C, was estimated from the difference between the C concentration in the whole soil and the C concentration in the light fraction, the labile C. The physical fractionation and C determination were performed in duplicate.

Carbon management index

The CMI was calculated for the whole 0-200mm layer, considering the weighed average concentration of the total, labile, and non-labile C fractions in the 0-25, 25-50, 50-100, and 100-200mm layers. The CMI consists of the carbon pool index (CPI) and the lability index (LI):

CMI = CPI x LI x 100 (1)

The CPI is the ratio between the total C concentration of the treatment ([C.sub.treatment]) and the total C concentration of the reference system ([C.sub.reference]), in this ease of the native grassland:

CPI = [C.sub.treatment]/[C.sub.reference] (2)

The LI is the ratio between the carbon lability in the treatment ([L.sub.treatment] and the C lability in the reference system ([L.sub.treatment]):

LI= [L.sub.treatment]/[L.sub.reference] (3)

The C lability is the ratio between the concentration of labile ([C.sub.labile]) and non-labile ([C.sub.non-labile]) C:

L = [C.sub.labile]/[C.sub.non-labile] (4)

Statistical analysis

The soil C results were submitted to analysis of variance using the SAS package, and the difference between means evaluated by Tukey test at P = 0.05. For comparison of light fraction results, that was fractionated from composite soil samples, and the standard mean error was calculated. A similar procedure was used for L, LI, and CMI indexes derived from labile C of the light fraction.

Results and discussions

Total carbon stock and carbon pool index

In both irrigated and non-irrigated plots, the no-till soil showed significantly higher C concentration in the upper layers of 0-25 and 25-50 mm than the conventional tillage soil, but in the 100-200 mm layer the opposite was observed, with conventional tillage showing higher C concentrations than no-fill (Table 1). Because crop residues are buried and mixed during the inversion of the arable layer (170 or 200 mm depth) in disc-ploughing operations of conventional tillage systems, there is a nearly uniform distribution pattern for C Concentration with depth, which is not observed in no-till soil where most of crop residues are not incorporated and are left to decompose at the surface, creating a kind of negative gradient for C concentration in depth. Haynes and Beare (1996) reported that crop roots can be more abundant in top surface layers of no-till than conventional tillage soil, further enhancing the gradient in no-till. The higher concentration of C in the lower part of the arable layer, at about 100-200-mm depth, in conventional tillage soil in comparison to the same layer in no-fill soil was also reported by Freixo et al. (2002b), under cerrado conditions of Brazil.

Because the incorporation of C into the 100-200 mm layer of conventional tillage counterbalanced the effect of C deposition in the top layers of no-till, the total C stock in the whole 0-200 mm layer of both irrigated and in non-irrigated plots did not differ significantly between the 2 tillage systems (Fig. 1), even though 8 years have passed since the establishment of the experiment. However, we still believe that the total C stock of no-fill soil will significantly surpass that of conventionally tilled soil, as observed in studies of a nearby experiment that has been carried out for 22 years under the same soil and climatic conditions (Bayer et al. 2000; Zanatta et al. 2007).

Regarding the effect of irrigation, the total C concentration was lower in the irrigated than non-irrigated system in the 0-25 mm layer and was similar in deeper layers (Table l), so that total C stocks in the 0-200 mm layers did not differ (Fig. 1), although irrigation increased the C addition of crop residues by 19% (1.6 MgC/ha.year) compared with the non-irrigated system, as shown in a previous work of De Bona et al. (2006). This suggests that the higher C addition due to irrigation was counterbalanced by a higher organic matter mineralisation rate associated with a greater microbial activity stimulated by the higher soil water availability. In temperate conditions of Nebraska, USA, Verma et al. (2005) showed that although irrigation increased the gross primary productivity of a no-till, maize-soybean field after 3 years, the simultaneous increase in the ecosystem respiration, including soil (Mollisol) respiration, did not allow an increase in the net ecosystem productivity and the soil C stocks for irrigated compared with rainfed fields. On the other hand, Gillabel et al. (2007), also in Nebraska, observed C stocks 25% higher under irrigated than non-irrigated Mollisols subjected to conservation tillage. As observed in other studies, Gillabel and collaborators have found higher C turnover rates (higher mineralisation rates) in irrigated fields, but not enough to neutralise the positive effect of the much higher C input (2.5 times) obtained with irrigation. It seems therefore that there is no clear effect of irrigation on C stocks, and results may change considerably under different situations of soil, region, management, and climate.

According to the results for C content in our study, the CPI between no-till (mean of 1.02) and conventional tillage (mean of 0.95) and between irrigated (mean of 0.99) and non-irrigated (mean of 0.98) systems remained unaltered (Table 2), indicating that, with respect to the total C pool, in this eighth year of study, the soil quality was similar among the management systems and also similar to the reference native grassland (CPI=1.00) (Table 2). We believe, however, that solely quantitative parameters of C are not enough to serve as a soil quality index and that parameters related to C lability, being more sensitive to management changes, must also be considered.

Light fraction carbon

The concentration of labile C in the light fraction of the organic matter varied from 190 to 370 kg C/Mg (Table 1), comparable to other reported results (Cambardella and Elliott 1992; Diekow et al. 2005). Along the profile, there was a clear tendency for the concentration of labile C in the light fraction to diminish with depth (Table 1), possibly because the amount of C was proportionally lower relative to the amount of clay particle contaminants that commonly remain in this light fraction (dilution effect).

The light fraction C concentration in the whole soil varied from 0.28 kg C/Mg to 4.26 kg C/Mg (Table 1), representing about 4-19% of the total C content. In the 2 top layers, no-till soils contained higher light fraction C concentrations than conventionally tilled soils, but the opposite trend was observed in deeper layers (Table 1), following observations of the distribution of total C content within the soil layers. The pattern of the light fraction C distribution in no-till soil, either in irrigated or non-irrigated systems, was similar to that observed in native grassland soil and reflected a light C accumulation in the 2 top layers (Table 1).

[FIGURE 2 OMITTED]

Accordingly, the stock of light fraction C in the 0-200 mm layer of the non-irrigated soil was 27% higher in the no-till (3.08 Mg C/ha) than the conventional tillage treatment (2.42 Mg C/ha) but with irrigation, no-till was only 7% higher (2.31 Mg C/ha) than conventional tillage (2.16 Mg C/ha) (Fig. 1). Irrigation decreased the labile C concentrations mainly in the 2 top layers, in no-till and conventional tillage soils (Table 1), so that the labile C stock in the whole 0-200 mm layer was on average 33% and 12% lower when irrigation was adopted in no-till and conventional tillage soils, respectively (Fig. 1). The proportionally higher labile C loss due to irrigation in no-till compared with conventional tillage could be attributed to a combination of residue accumulation and higher water availability on the soil surface, which provided suitable conditions to increase the microbial mineralisation activity (De Bona et al. 2006).

Carbon lability and lability index

The C lability of all management systems, except no-till without irrigation, were lower than that of native grassland soil (Table 2, Fig. 2), which was also reflected in the lability index (LI) (Table 2) and expresses the lower capacity of these management systems to preserve the labile organic matter in comparison to the original native grassland. In non-irrigated systems, the LI of no-till soil (0.95) was 32% higher than the LI of the conventionally tilled soil (0.72), a trend not observed in the irrigated system, where the LI was similar for both no-till (0.67) and conventional tillage (0.64) (Table 2). These results are related to the favourable conditions for microbial mineralisation of the light organic matter in the top layers of irrigated no-till soil, as previously discussed.

At depth, C lability followed the same trend as the labile C concentration, with higher values for no-till than conventional tillage in the top layers, and the opposite in deeper layers (Fig. 2a, b). Non-irrigated soils also showed higher C lability than irrigated soils, in almost all assessed layers (Fig. 2c, d). In other words, with respect to C lability, the quality of the soils subjected to conventional tillage or irrigated no-till is lower than that of native grassland soil. However, no-till without irrigation, with regard to the C lability, could improve soil quality to the level of native grassland, and expectations are that it may even surpass it. It is important to consider, however, that the lower C lability does not necessarily mean a lower total C stock in irrigated systems (Fig. 2). Gillabel et al. (2007) observed that total C stocks increased by 25% with irrigation and they attributed this result to C accumulation inside microaggregates and not to the supposedly labile C associated with macroaggregates.

Carbon management index

Of the 2 indices that comprise the CMI, LI was more sensitive than CPI in reflecting the influence of management systems on soil organic matter dynamics in the short- to mid-term (Diekow et al. 2005). This could be observed in the broad variation between the maximum and minimum values for LI (56%) in comparison to the same variation for CPI (8%) (Table 2), and this is what makes the CMI a more sensitive indicator than considering only variations in the total C content.

According to the results of CPI and LI, higher CMI was always related to no-till or non-irrigated systems than to their conventionally tilled or irrigated counterparts (Table 2). The no-till management without irrigation showed the highest CMI (95) among agricultural systems, being able to recover the original soil quality of the native grassland soil (CMI = 100) during these 8 years (Table 2). Further, expectations are that non-irrigated no-till may even surpass the soil quality of native grassland with regard to the CMI.

Important to emphasise however that the CMI should be considered only as a soil quality indicator and not a as general soil quality index, because several other aspects associated to the capacity of soil to function must also be considered when assessing soil quality. In a whole assessment of soil quality or sustainability of the agro-ecosystem it would be reasonable to consider, for example, that irrigation increased biomass production (De Bona et al. 2006), including food production. It would also be reasonable to consider the C equivalent costs related to irrigation practices which contribute to C emissions, especially when the main source of energy to run pumps derives from fossil fuels (Lal 2004).

Conclusions

The labile C fraction is more sensitive to the influence of tillage system and irrigation system than the total C stock, so that conventional tillage and irrigation reduced significantly the labile C stock in comparison to the no-till and non-irrigated systems.

The soil quality based on the carbon management index was improved with adoption of no-till in substitution to conventional tillage, but not with adoption of irrigation, possibly due to increase in the decomposition rate of labile organic matter. Thus no-till soils subjected to irrigation require a higher phytomass addition than non-irrigated soils.

Manuscript received 22 January 2008, accepted 3 July 2008

References

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F. D. De Bona (A), C. Bayer (A,B,E), J. Dieckow (C), and H. Bergamaschi (D)

(A) programa de Pos-Graduacao em Ciencia do Solo, Universidade Federal do Rio Grande do Sul, PO Box 15100, 90001-970 Porto Alegre/RS, Brazil.

(B) Departamento de Solos, Universidade Federal do Rio Grande do Sul, PO Box 15100, 90001-970 Porto Alegre/RS, Brazil.

(C) Departamento de Solos e Engenharia Agricola, Universidade Federal do Parana 80035-050 Curitiba/PR, Brazil.

(D) Departamento de Plantas Forrageiras e Agrometeorologia, Universidade Federal do Rio Grande do Sul, PO Box 15100, 90001-970 Porto Alegre/RS, Brazil.

(E) Corresponding author. Email: cimelio.bayer@ufrgs.br
Table 1. Soil bulk density, concentration of total C, labile C
(light fraction C), and non-labile C as affected by tillage
systems and irrigation

Lower case letters compare irrigated and non-irrigated treatments,
within the same tillage system; upper case letters compare
conventional tillage and no-till, within the same irrigation
treatment (Tukey's test, P < 0.05); values in parentheses refer
to the standard mean error

Layer Soil density (A) Total C conc.
(mm) (Mg/[m.sup.3]) (kg/Mg soil)

Conventional tillage, non-irrigated

0-25 1.74 11.5a (B)
25-50 1.74 10.4a (B)
50-100 1.60 9.3a (A)
100-200 1.58 8.7a (A)
0-200 1.63 9.4a (A)

Conventional tillage, irrigated

0-25 1.74 10.5b (B)
25-50 1.74 9.8a (B)
50-100 1.60 9.5a (A)
100-200 1.58 8.9a (A)
0-200 1.63 9.4a (A)

No-till, non-irrigated

0-25 1.63 22.2a (A)
25-50 1.63 14.0a (A)
50-100 1.61 8.8a (A)
100-200 1.65 6.3a (B)
0-200 1.64 9.9a (A)

No-till, irrigated

0-25 1.63 19.6b (A)
25-50 1.63 12.8a (A)
50-100 1.61 9.0a (A)
100-200 1.65 7.6a (B)
0-200 1.64 10.10a (A)

Native grassland

0-25 1.47 19.3
25-50 1.47 12.0
50-100 1.69 9.2
100-200 1.75 7.4
0-200 1.67 9.9

 Labile C conc.:

Layer In LF (B) In soil Non-labile C conc.
(mm) (kg/Mg LF) (kg/Mg soil) (kg/Mg soil)

Conventional tillage, non-irrigated

0-25 350 (6.93) 1.56 (0.04) 9.94 (0.04)
25-50 310 (19.09) 0.87 (0.02) 9.53 (0.02)
50-100 300 (9.83) 0.69 (0.01) 8.61 (0.01)
100-200 230 (7.85) 0.54 (0.01) 8.16 (0.01)
0-200 0.75 (0.02) 8.67 (0.02)

Conventional tillage, irrigated

0-25 310 (19.37) 1.10 (0.00) 9.40 (0.00)
25-50 280 (2.40) 0.73 (0.02) 9.07 (0.02)
50-100 260 (14.85) 0.63 (0.00) 8.87 (0.00)
100-200 290 (12.94) 0.55 (0.01) 8.35 (0.01)
0-200 0.66 (0.01) 8.70 (0.01)

No-till, non-irrigated

0-25 370 (1.70) 4.26 (0.13) 17.94 (0.13)
25-50 340 (5.37) 1.60 (0.02) 12.40 (0.02)
50-100 280 (2.05) 0.52 (0.02) 8.28 (0.02)
100-200 220 (6.58) 0.28 (0.01) 6.02 (0.01)
0-200 1.00 (0.03) 8.87 (0.03)

No-till, irrigated

0-25 360 (0.21) 2.89 (0.21) 16.71 (0.21)
25-50 320 (7.42) 0.98 (0.03) 11.82 (0.03)
50-100 240 (25.17) 0.43 (0.02) 8.57 (0.02)
100-200 190 (33.38) 0.31 (0.00) 7.29 (0.00)
0-200 0.75 (0.03) 9.35 (0.03)

Native grassland

0-25 360 (9.33) 3.63 (0.05) 15.67 (0.05)
25-50 340 (5.09) 1.47 (0.01) 10.53 (0.01)
50-100 300 (19.94) 0.74 (0.03) 8.46 (0.03)
100-200 270 (6.15) 0.45 (0.00) 6.95 (0.00)
0-200 1.05 (0.02) 8.87 (0.02)

(A) Data obtained by Dalmago (2004) and De Bona et al. (2006).

(B) Concentration of C in the light fraction (LF), density
<1.8 Mg/[m.sup.3].

Table 2. Carbon pool index (CPI), lability (L), lability index (LI),
and carbon management index (CMI) as affected by tillage system and
irrigation

CPI (carbon pool index), Total soil C concentration in the
treatment/total soil C concentration in grassland; L (lability),
labile soil C concentration/non-labile soil C concentration;
LI (lability index), lability in treatment/lability in grassland;
CMI (carbon management index), CPI x LI x 100. Values in parentheses
refer to the standard error

Tillage system Irrigation CPI L

Conventional tillage Non-irrigated 0.95 (0.04) 0.086 (0.004)
 Irrigated 0.95 (0.06) 0.076 (0.005)

No-till Non-irrigated 1.00 (0.09) 0.113 (0.011)
 Irrigated 1.03 (0.12) 0.079 (0.010)

Native grassland Non-irrigated 1.00 0.119 (0.006)

Tillage system Irrigation LI CMI

Conventional tillage Non-irrigated 0.72 (0.03) 68 (4)
 Irrigated 0.64 (0.04) 61 (5)

No-till Non-irrigated 0.95 (0.09) 95 (12)
 Irrigated 0.67 (0.08) 69 (11)

Native grassland Non-irrigated 1.00 100

Fig. 1. Stocks of total C, labile C, and non-labile C as affected by
tillage systems and irrigation. Letters above the bars compare the
effect of management systems, according to Tukey's test (P<0.05).
Values after [+ or -] for labile and non-labile fractions refer to
the standard mean error.

 conventional
 tillage

 Non-irrigated Irrigated

Labile carbon 2.42 2.16
 [+ or -] 0.03 [+ or -] 0.01

Non-labile carbon 28.72 28.91
 [+ or -] 0.03 [+ or -] 0.01

 no-till grassland

 Non-irrigated Irrigated Native

Labile carbon 3.08 2.31 3.30
 [+ or -] 0.02 [+ or -] 0.09 [+ or -] 0.05

Non-labile carbon 28.69 30.50 28.94
 [+ or -] 0.02 [+ or -] 0.09 [+ or -] 0.05

Note: Table made from bar graph.
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Article Details
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Author:De Bona, F.D.; Bayer, C.; Dieckow, J.; Bergamaschi, H.
Publication:Australian Journal of Soil Research
Article Type:Technical report
Geographic Code:3BRAZ
Date:Aug 1, 2008
Words:5543
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