Stratification ratio of organic matter pools influenced by management systems in a weathered Oxisol from a tropical agro-ecoregion in Brazil.
The Cerrado is the second largest biome in Brazil, situated in the central region of the country. During the past few decades, it has been subjected to large-scale expansion of farming, resulting in the loss of soil organic matter (SOM). This SOM loss has negative effects on the emission of greenhouse gases (Lal 2006), the capacity to exchange cations (Resck et al. 2008), and soil aggregation (Ashagrie et al. 2007), thereby altering the natural physical properties of soil, especially macro-aggregation, porosity, and water infiltrability (Resck et al. 2008).
Carbon (C) stocks in Cerrado soil, as found by Bustamante et al. (2006), ranged from 87 to 210 Mg [ha.sup.-1] The C stock in the Cerrado is estimated to average 29 Mg [ha.sup.-1] in vegetation and 117 Mg [ha.sup.-1] in the soil at a depth of 1 m (Lal 2006). However, these estimates may vary greatly from locality to locality because of the large diversity in classes of soils, textures, vegetation, and local conditions.
Data on the alterations of C stocks caused by Cerrado management systems are variable. On average, C stocks were 53.1 Mg [ha.sup.-1] in conventional plantings and 63.5 Mg [ha.sup.-1] for notill, whereas the stock was 68.4 Mg [ha.sup.-1] at a depth of 30 cm in the native Cerrado (Jantalia et al. 2007). Those authors reported that although there was a strong interaction of total organic C (TOC) with the mineral fraction of the soil (Roscoe and Buurman 2003), no-till systems presented larger TOC stocks with systems with 1- or 2-yearly crop rotations. However, Marchao et al. (2009) did not find significant differences in C stocks with soil under native Cerrado vegetation and soil management systems (conventional and no-till). Changes in C stock may be attributed to differences in the amount of residues produced in the various management systems (Dou et al. 2007), as well as the interaction/protection mechanisms between organic matter and soil minerals (Roscoe and Buurman 2003). Additionally, the methods used to determine TOC content may underestimate values in soils from the Cerrado compared with other soils due to the large amount of inert carbon in these soils (Jantalia et al. 2007; Marchao et al. 2009). This inert carbon is not totally recovered by the dichromate oxidation method utilising sulfuric acid with no external heating. According to Tan et al. (2007), the soil organic matter (SOM) loss resulting from conversion of forests to farmland may be attributed to the reduction of light and heavy fractions, whereas consequent gains from conversion of the conventional planting system to no-till could be attributed to an increase in C in the light fraction.
Cerrado Latosol represents ~46% of the total area of the biome, and it is highly used for fanning activities in the region. In these soils, there is a strong textural control of carbon content resulting from SOM associations with clay minerals (Zinn et al. 2005). Such textural control associated with a high rate of crop residue breakdown influences the distribution of SOM fractions as a function of depth. Consequently, short-term differences between conservation and conventional systems cannot be verified in the Cerrado as can be done in temperate climatic conditions. For example, only 3 years were sufficient to observe differences in soil organic carbon fractions from no-tillage and conventional tillage in Georgia, United States (Franzluebbers and Stuedemann 2008).
The study of organic matter fractions with different cycling times and protection methods has been used to improve the detection of organic matter dynamics in soils under different management systems (Cambardella and Elliott 1992; Sa and Lal 2009; Salvo et al. 2010). Changes in these fractions may occur even when the TOC content in the soil is not altered (Roscoe and Buurman 2003).
The permanence of the soil surface and the ability of the SOM to decompose are functions of the quality of crop residues involved in rotation and management systems (Dou et al. 2007). Forestry residues below the soil surface may increase C sequestration potential because they have lower decomposition rates below the surface than at the surface (Lorenz and Lal 2005).
The presence of C-carbohydrates, rather than C-polyphenol, in larger fractions (2000-50[micro]m) indicates the highly labile characteristic of such fractions (Rovira et al. 2010). When compared with the TOC and associated minerals, particulate organic matter C (POC) proved more sensitive for detecting changes promoted by soil management (Salvo et al. 2010).
Microbial biomass and basal respiration are used as soil quality indicators and appear to provide sensitivity for observing the differences between natural ecosystems (Goberna et al. 2006) and farming systems (Wright et al. 2005). Furthermore, microbial respiration may be limited by lack of substrate and oxygen, which normally occurs in the subsurface of managed or natural soils (Rovira et al. 2010), thereby creating a gradient or stratification of microbial activity at that depth.
Franzluebbers (2002) suggested that C stock alone is a poor indicator of soil quality, whereas SOM stratification has been successfully used as an indicator of soil quality (Franzluebbers 2002; Sa and Lal 2009). The SOM stratification ratio (SR) is defined as the relationship between TOC content at 0-5 cm and deeper soil layers (Franzluebbers 2002). According to studies performed by Franzluebbers (2002) and Franzluebbcrs and Stuedemann (2008) for temperate climate regions and by Sa and Lal (2009) for subtropical regions, the stratification ratio of SOM is more pronounced in conservation management systems such as no-till, and shows a stronger relationship with crop residue breakdown on the soil surface. Among other factors, SOM stratification depends on the intensity of crop rotation (Dou et al. 2007). An increase in the POC SR is an explanation for the increase in surface soil quality (Sa and Lal 2009). These results of organic matter pool stratification presented for temperate (Franzluebbers 2002; Franzluebbers and Stuedemann 2008) and subtropical regions (Sfi and Lal 2009) must be evaluated for soils of tropical regions with high rates of residue decomposition, as in the Brazilian Cerrado.
For Cerrado soils under different management systems and natural forests, little research has been performed on organic matter stratification and its pools as an index that may influence soil quality and C sequestration. The objective of this study was to evaluate the impact of management systems on soil C stocks and SRs of various SOM pools: TOC, POC, mineral-associated organic C (MAOC), microbial biomass C and nitrogen (MBC and MBN), basal respiration (BR), and the particulate organic matter N (PON).
Materials and methods
Location and characteristics of the study area
This long-term experiment on soil management systems was conducted at the Embrapa Cerrados experimental field, in Planaltina-DF, Brazil (15[degrees]35'30"S, 47[degrees]42'0"W; altitude 1014m). The climate in this region is rainy tropical, according to the Krppen classification, with dry winters and rainy summers, and a rainless period during the rainy season, known as the Indian summer. Mean annual temperature is 26[degrees]C, and mean annual rainfall ~1500mm, with >80% of rainfall normally occurring from November to April. Maximum and minimum monthly temperature and precipitation during the experiment are shown in Fig. 1.
All treatments were installed in a clayey Oxisol (Typic Haplustox) (Soil Survey Staff 1998), Latossolo Vermelho according to the Brazilian Soil Classification (Embrapa 2006) or Gibbsic Ferralsol (IUSS Working Group WRB 2006). Chemical and physical attributes of the soil are displayed in Table 1.
Experimental design and description of treatments
The experimental design consisted of randomised blocks with three repetitions. Six treatments were selected from an experiment installed in 1996 consisting of 16 treatments and an additional control with native Cerrado plots (Table 2). The experiment was designed to study the dynamics of soil preparation and crop rotation systems with alternations in time and space. Each experimental plot consisted of an area 22 m long by 18 m wide. The sequence of management practices used during the experiment (1996-008) is presented in Table 3.
Soil sampling time and depth and crop cultivation
In each plot, five random subsamples were collected using an 8-cm-diameter auger to form a composite sample. Soil samples were collected in February 2008 during the soybean (Glycine max L.) flowering period, at five soil layers: 0 5, 5-10, 10-20, 20-30, and 30-40 cm.
With exception of the pasture, all systems were cultivated with soybeans under the same planting conditions. The soybean variety Conquista was planted on 28 November 2007. Rows were spaced at 45 cm and there were 15 plants [m.sup.-1] in the row. Seeds were inoculated with Bradyrhizobium at a concentration of 0.5 kg of inoculant for each 40 kg of seeds treated with fungicides. Crop fertilisation was performed at a rate of 400 kg [ha.sup.-1] using 0-20-20 NPK plus 50 kg [ha.sup.-1] of FTE (flitted trace elements) BR 12(R) with the following composition: 1.8% boron, 0.8% copper, 3% iron, 2% manganese, 0.1% molybdenum, and 9% zinc. Harvest was conducted on 18 April 2008.
The pasture used in the PAST treatment was Urochloa brizantha planted in rows spaced at 45 cm space and at a rate of 25 kg seeds [ha.sup.-1.] The amount of fertiliser used annually was 60 kg [ha.sup.-1] of [P.sub.205], 60 kg [ha.sup.-1] of [K.sub.20,] and 60 kg [ha.sup.-1] of N (as ammonium sulfate, 20% N). Two manual cuts were conducted each year, one in February-March and the other in July-August.
When corn (Zea mays L.) was grown, the variety 1001 BRS was planted during October. The spacing used was 0.90 cm between rows, with and six seeds [m.sup.-1]. The amount of fertiliser used yearly was 350 kg [ha.sup.-1] of 4-30-16 NPK. Two foliar applications of 38 kg [ha.sup.-1] of N (as ammonium sulfate, 20% N) were applied when the plants had 4-5 leaves and 10-12 leaves, respectively. Also applied was 50 kg [ha.sup.-1] of FTE as above.
Fractionation of organic matter
Physical fractionation of the organic matter was conducted according to the study by Cambardella and Elliott (1992), with some adaptations of the sample mass (Bongiovanni and Lobattini 2006). After air-drying, subsamples were sieved through a 2-mm sieve. Then 20-g samples were put in 250-mL plastic bottles, to which 70 mL of a sodium hexametaphosphate solution (5.0 g [L.sup.-1]) was added. The mixture was shaken for 15h in a horizontal shaker at 130 rpm. Afterwards, the contents of the bottle were sieved through a 53-[micro]m sieve and washed with a weak jet of soft water. The material retained in the sieve, defined as particulate organic matter (>53[micro]m), was dried in an oven at 50[degrees]C. After drying, the sample was ground in a porcelain mortar and sieved again through a 0.149-mm sieve. The samples were then weighed and subjected to total C and N content analysis to determine POC and PON.
A portion of the original subsample was ground in a porcelain mortar and sieved though a 0.149-mm sieve. This material was then used for the TOC analysis of the bulk sample. The MAOC was calculated as the difference between TOC and the POC contents.
Microbial biomass (carbon and nitrogen) and soil basal respiration
The soil microbial biomass was estimated using the fumigation-extraction method (Vance et al. 1987). The MBC and MBN were determined using the same soil sample and maintaining a 1:2.5 ratio between the soil and the extractor.
Six 20-g soil subsamples were weighed for each field sample (in triplicate) with an adjusted water content so as to be in equilibrium with a tension of 0.03 MPa (~80% of the soil field capacity). These samples were pre-incubated at room temperature (26[+ or -]2[degrees]C) for 7 days in capped 600-mL containers kept in the dark. Then, the three subsamples were fumigated (F) for 24 h in a drier containing a Petri dish with 25 mL of chloroform without ethanol ([C.sub.HC13]). The other, non fumigated (NF), subsamples were kept at room temperature. After fumigation, the F and NF subsamples were subjected to horizontal shaking (150rpm) for 30min with 50 mL of the extraction solution (0.5 M [K.sub.2SO4]). Subsequently, the subsamples were filtered through a qualitative filter paper.
The MBC was determined according to the study of Vance et al. (1987) using an 8-mL aliquot of the filtered extract. The MBC was determined as the difference between the C extracted from F and NF soil samples using a correction factor ([k.sub.c]) of 0.35 (Joergensen 1996).
The MBN was determined according to the study of Brookes et al. (1985) using a 20-mL aliquot of the filtered extract. The MBN was calculated as the difference between the amount of N recovered in the extract from the F sample and that recovered from the NF sample using a correction factor ([k.sub.N]) of 0.54.
Soil respiration was determined in the laboratory via the incubation method for 7 days according to the study performed by Alef and Nannipieri (1995). Crop residues were carefully removed from soil samples before being passed through an 8mm mesh sieve. Soil (20 g, field-moist) was incubated in the dark, the water content was maintained at 60% of field capacity, and the temperature at 26[degrees]C. The CO2 liberated after the incubation period was determined by titration with 0.1 M HCI in a 0.3 M KOH solution saturated with [B.sub.aC12].
Total organic carbon and total nitrogen analysis
The determination of TOC and total N of both the particulate fractions and the integral sample was conducted via dry combustion in a CHNS elemental analyser (model PE 2400, 11 series CHNS/O, PerkinElmer, Norwalk, CT, USA).
Carbon stock, stratification ratio, and statistical analyses
Total C stock and its fractions were calculated by multiplying the TOC contents with the soil density and the layer thickness. The total stock (0-40 cm) was obtained as the sum of stocks from the different layers. The SOM SR was calculated by dividing the C or N concentration in each SOM compartment in the 0-5 cm layer by that in the 10-20 and 30-40 cm layers (Franzluebbers 2002). Data were submitted to analysis of variance (ANOVA). For comparison of the averages the Tukey test (P<0.05) was used. Analyses were conducted using SAS (SAS 2001).
Results and discussion
Effect of management systems on the total, particulate, and mineral-associated organic carbon stocks
The TOC stocks varied from 78.1 to 85.9 Mg [ha.sup.-t] in the conventional tillage (CT) and pasture (PAST) systems, respectively, in the 0-40 cm layer. While the CT system reduced TOC stocks, no-till (NT) planting did not show significant differences when compared with soil under native vegetation (CER) (Table 4). These results demonstrated that for the climatic conditions of the Cerrado, as hypothesised, pasture and conservation systems are excellent options for increasing the stocks of soil organic carbon. Increase in TOC stocks promoted by no-till planting in the Cerrado region (0-20 cm deep) was also found by Bayer et al. (2006), whereas Marchao et al. (2009) found no differences between the CER and CT or NT systems. The PAST system showed a higher TOC stock (040 cm) than the CT and NT3 systems (Table 4), and it did not differ significantly from the other treatments. The increase in C stock promoted by PAST differed from the results found by Marchao, et al. (2009), who encountered a decrease in TOC stocks when a single or companion/rotation forage species was introduced along with the annual crops.
When the layers were studied separately, differences were found in TOC stocks only for the 0 10 cm layer. In this layer, the differences among systems showed the same patterns as those observed for the whole 040 cm layer, except that in the 0-10 cm layer there was a difference among NT systems, where the NT1 system showed a higher TOC stock than the NT3 system. The biannual NT1 corn-soybean rotation favoured a TOC increase in the superficial soil layer. These results i agree with those of Salvo et al. (2010), who found differences in TOC stocks between management systems in superficial layers (0-3 cm).
With the exception of PAST, all systems had lower POC stocks than the natural vegetation system (Table 4). This was observed in all of the separately studied layers and in the overall 0-40cm layer. The PAST system promoted a high POC stock, which was 47%, 46%, 53%, and 59% higher, respectively, than those resulting from the CT, NT1, NT2, and NT3 systems. These results show a higher potential for correctly managed pastures to increase soil C stocks, mainly in the form of particulate organic matter. Bayer et al. (2004) concluded that POC stocks were more sensitive to management than was TOC. The stocks of light fractions were higher under no-till planting than conventional planting even when the weighed fractions were not altered (Tan et al. 2007). When considering the 0-20 cm layer among different crop rotations, a rotation of forage turnip with corn and soybean showed higher POC stocks under no-till than under conventional tillage in the Cerrado region (Bayer et al. 2004). In subtropical conditions in Uruguay, the POC stocks varied in layers to 18 cm between management systems (conventional and no-till), and always exhibited higher values in no-till systems (Salvo et al. 2010).
When considering the 0-40 cm layer, the percentage of POC in the TOC stock ranged from 20% in NT3 to 46% in the PAST system. These results indicate that C stocking in soils under pasture occurs through particulate organic matter.
The CT, NT1, NT2, and NT3 systems showed higher MAOC stocks than PAST and CER in the whole 0-10 cm layer. These results indicated a rapid transformation of the organic matter into stable forms imposed by tropical conditions in the region. In the case of PAST, a high POC intake explained the low MAOC contribution to the TOC. Bayer et al. (2004) did not find significant differences in MAOC stocks between no-till and conventional systems. Those authors attributed the lack of difference between MAOC stocks to the short adaptation time of no-till planting and the high protection of organic matter inside micro-aggregates.
Different systems under no-till planting did not show differences in the total (0-40 cm) TOC, POC, and MAOC stocks (Table 4); and these results are in agreement with those found by Bayer et al. (2004). Total stocks in the 0-40cm layer were not sensitive in detecting differences between the different systems under no-till.
Stratification ratio of soil organic carbon and nitrogen fractions and biological pools affected by soil management systems
The SR of the TOC ranged from 0.93 to 1.28, a range of 0.35. The SR range was 1.76 for POC, 0.52 for MAOC, 1.62 for PON, and 1.29 for the POC:PON ratio (Table 5). These values indicate that the labile SOM pools were more sensitive than those more stable (MAOC) to the SR in soils under different uses. Different SR sensitivities among SOM pools have also been found by other researchers (Franzluebbers 2002; Franzluebbers and Stuedemann 2008; Sfi and Lal 2009).
There was a difference between the managed systems with respect to TOC stratification. However, when comparing the CT and the NT systems, only NT1 had a higher SR than CT. In a subtropical region, Sa and Lal (2009) observed a higher TOC SR in systems under no-till planting than in the conventional systems.
In the CT system, the soil presented the lowest POC SR. In soils from different locations in North America, the most significant differences between no-till and conventional planting were observed in the SR of particulate organic matter (Franzluebbers 2002). The conversion of areas of natural vegetation into farming ecosystems via ploughing degrades soil quality, causing mixing of the topsoil with the subsurface to decrease organic matter stratification (Sa and Lal 2009). With exception of the NT1, all systems had lower POC SRs than CER. The systems could be divided into three general groups: CER with the highest ratios, the NT systems with intermediate values, and the CT system with the lowest SR. Because the POC in the 0-5 cm layer is linked to the deposit and maintenance of crop residues on the soil surface, the use of a heavy disc harrow enabled the incorporation of organic matter. This incorporation promoted the transformation to stable organic matter as was observed with MAOC. Among the planting systems, only NT1 showed the same POC SR value compared with CER. This decrease in the labile reservoirs of organic matter in the subsurface of the NT1 system may come from the transformation of abundant litter material and the gradient created on the soil profile (Sa and Lal 2009).
In the CT system, the SR of MAOC, unlike POC, was higher than in the other systems, with the exception of NT1. These results show that stratification of the stable compartment of organic matter in the soil is aided by turning the soil over annually, probably as a consequence of aeration. Carbon sequestration in the soil is higher in intense crop rotation and minimal in soil disturbance systems (Dou et al. 2007).
The PON SR did not present the large variation among systems that was visible with POC. These results differ from those of Franzluebbers (2002), who observed differences in the stratification of PON among management systems. All systems showed PON SRs >1.00. This indicates that the particulate organic matter present in the deep layers has a lower N concentration than that entering through the soil surface.
The CER system had a higher SR for POC : PON than any of the managed systems, showing that there are differences in the quality of particulate organic matter in the soil profile in the transition from native to cultivated areas.
Soil use management systems decreased the MBC SR. The results showed that for Cerrado climatic conditions, which favour rapid decomposition of crop residues, the transformation of natural vegetation into agro-ecosystems promotes a reduction in SOM stratification. The PAST system presented the lowest SR of MBC with values <1.00, indicating a more favourable environment for microbial development directly below the soil surface, perhaps as a consequence of higher POC stocks at depths of 10-20 cm (Table 4). In the Cerrado region, well-managed pasture had high MBC levels at depths of 0-20 cm (Oliveira et al. 2001). Carbon increase through rhizodeposition by forage species encouraged microbial growth along the soil profile. When subjected to certain management systems and crops, the entrance of organic matter beneath the surface by roots may be an important path for C sequestration in the soil (Dou et al. 2007).
The MBC SR values ranged from 0.98 to 2.62 in the different systems, indicating that it is a sensitive indicator of differences imposed by soil management systems. These values are similar to those encountered in temperate climates by Franzluebbers and Stuedemann (2008). In the study by Sa and Lal (2009), the range was 1.33-2.68, with higher values in the cases of implementing no-till planting for 22 years and for soil under natural vegetation. Differences in the range of MBC SR between these studies may be explained by the climatic differences of the regions under study and the soil conditioning systems before establishment of no-till planting. Figueiredo et al. (2007) observed differences in the stratification of MBC among conservation systems in the Cerrado 22 years after the preparation of soil with different ploughing systems that were used before the establishment of no-till planting.
The SR of BR ranged from 0.71 to 2.18 (Table 4). In subtropical conditions in Brazil, the SR of BR ranged from 1.29 to 7.52 (Sa and Lal 2009). Basal respiration, also an indicator of soil quality, showed a positive correlation with POC, which represents the main C source for soil microorganisms (Rovira et al. 2010). The fact that systems under NT planting showed lower BR SRs compared with other regions may be due to the incorporation of crop residues in the subsurface as a C source for the microbial activity that occurred in the stage before the establishment of no-till planting.
Figure 2 shows the SR variations (0-5 : 30-40 cm) in different C pools in the management systems compared with natural Cerrado soil vegetation. In general, all management systems promoted a decrease in SR for TOC, POC, and MBC, as well as an increase in SR for MAOC. Among the C pools, those most labile (POC and MBC) showed the highest variations in S R of the different management systems compared with native Cerrado. The CT system resulted in the greatest reductions to POC SR. This reduction may explain the reduction in C stocks promoted by the CT system. The NT planting system NT2 yielded a smaller reduction of SR for TOC, POC, and MBC compared with the NT3 system. This difference may be explained by the second crop planting, which, despite the low yields due to the lack of rain, increased the entrance of organic matter, mainly in the form of POC, as observed in Table 4.
This reduction in SRs of organic matter pools confirms the reduction of the TOC stocks observed, with negative impacts on soil quality and the emission of CO2 to the atmosphere. Furthermore, differences in reduction rates reinforce the need for implementation of conservation systems that enhance the entry of plant biomass and stratification of organic matter.
While no-till systems did not reveal any differences in total stocks (0-40 cm) of soil TOC compared with native vegetation, conventional tillage reduced TOC stocks. The POC stocks were lower in the management systems than in the native Cerrado, proving to be a more sensitive soil quality indicator. Only the pasture retained POC stocks equal to those of native Cerrado. As occurs in temperate and subtropical regions, the SR of labile organic matter (POC, MBC, and MBN) was more sensitive to the differentiation of changes caused by agricultural use in the Cerrado. However, the present study showed that between CT and NT systems, the differences with regard to stratification of weathered soils from the Cerrado are less intense than those of temperate and subtropical regions. Pastures proved to be an excellent option for increasing C content in the soil, which preferentially occurs through particulate organic matter. Reductions in the SR of labile organic matter compartments are related to the reduction of organic C in soil, consequently reducing soil quality and the emission of greenhouse gases caused by intensive agricultural use of Cerrado soils.
Received 20 July 2012, accepted 1 May 2013, published online 16 may 2013
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C.C. Figueiredo (A,E), D.V.S. Resk (B), M.A.C Carneiro (C), M.L.G. Ramos (A), and J.C.M. SA (D)
(A)Faculty of Agronomy and Veterinary Medicine, University of Brasflia, 70910970 Brasflia, DF, Brazil.
(B)Embrapa Cerrados, 73310970 Planaltina, DF, Brazil.
(C)Laboratory of Soil Science, Federal University of Goas, 75800000 Jatai, GO, Brazil.
(D) Department of Soil Science and Agricultural Engineering, University of Ponta Grossa, 84030900 Ponta Grossa, PR, Brazil.
(E)Corresponding author. Email: firstname.lastname@example.org
Table 1. Chemical and physical characterisation of the soil studied Values are means [+ or -] standard deviation of the samples of each depth (n=24) in the treatments considered in this study Property 0-5 cm 5-10 cm Organic carbon 18.8 [+ or -] 3.9 16.4 [+ or -] 2.6 (g [kg.sup.-1]) pH([H.sub.2]O) 5.2 [+ or -] 0.4 4.8 [+ or -] 0.2 [Al.sup.3+] ([cmol.sub.c] 0.6 [+ or -] 0.7 0.8 [+ or -] 0.5 [kg.sup.-1]) [Ca.sup.2+] [Mg.sup.2+] 3.6 [+ or -] 1.4 2.6 [+ or -] 1.3 ([cmol.sub.c] [kg.sup.-1]) [Ca.sup.2+] (cmolc 2.5 [+ or -] 1.1 1.9 [+ or -] 1.0 [kg.sup.-1]) H + Al ([cmol.sub.c] 6.8 [+ or -] 2.5 7.3 [+ or -] 1.3 [kg.sup.-1]) CEC ([cmol.sub.c] 10.93 10.2 [kg.sup.-1]) Base saturation (%) 38 28 Nitrogen (g [kg.sup.1]) 1.8 [+ or -] 0.3 1.7 [+ or -] 0.2 Phosphorus (mg 9.2 [+ or -] 1.9 11.8 [+ or -] 5.3 [kg.sup.-1]) Potassium (mg [kg.sup.-1]) 211 [+ or -] 71.7 113.1 [+ or -] 18.9 Bulk density (kg 1.09 [+ or -] 0.08 1.06 [+ or -] 0.07 [dm.sup.3]) Clay (g [kg.sup.-1]) 508 [+ or -] 27 505 [+ or -] 26 Silt (g [kg.sup.-1]) 89 [+ or -] 20 91 [+ or -] 17 Sand (g [kg.sup.-1]) 403 [+ or -] 23 404 [+ or -] 22 Property 10-20 cm 20-30 cm Organic carbon 15.3 [+ or -] xx 12.7 [+ or -] 1.4 (g [kg.sup.-1]) pH([H.sub.2]O) 4.7 [+ or -] 0.2 4.8 [+ or -] 0.1 [Al.sup.3+] ([cmol.sub.c] 0.9 [+ or -] 0.4 0.9 [+ or -] 0.3 [kg.sup.-1]) [Ca.sup.2+] [Mg.sup.2+] 2.1 [+ or -] 1.1 1.4 [+ or -] 0.8 ([cmol.sub.c] [kg.sup.-1]) [Ca.sup.2+] (cmolc 1.4 [+ or -] 0.9 0.9 [+ or -] 0.6 [kg.sup.-1]) H + Al ([cmol.sub.c] 7.0 [+ or -] 1.1 6.5 [+ or -] 0.8 [kg.sup.-1]) CEC ([cmol.sub.c] 9.23 7.98 [kg.sup.-1]) Base saturation (%) 24 18.7 Nitrogen (g [kg.sup.1]) 1.6 [+ or -] 0.2 1.3 [+ or -] 0.2 Phosphorus (mg 8.1 [+ or -] 2.8 3.3 [+ or -] 1.3 [kg.sup.-1]) Potassium (mg [kg.sup.-1]) 50.8 [+ or -] 22.9 34.1 [+ or -] 12.4 Bulk density (kg 1.04 [+ or -] 0.05 1.07 [+ or -] 0.05 [dm.sup.3]) Clay (g [kg.sup.-1]) 509 [+ or -] 25 517 [+ or -] 25 Silt (g [kg.sup.-1]) 87 [+ or -] 13 78 [+ or -] 19 Sand (g [kg.sup.-1]) 403 [+ or -] 21 405 [+ or -] 27 Property 30-40 cm Organic carbon 11.4 [+ or -] 1.2 (g [kg.sup.-1]) pH([H.sub.2]O) 4.8 [+ or -] 0.1 [Al.sup.3+] ([cmol.sub.c] 0.9 [+ or -] 0.2 [kg.sup.-1]) [Ca.sup.2+] [Mg.sup.2+] 1.2 [+ or -] 0.5 ([cmol.sub.c] [kg.sup.-1]) [Ca.sup.2+] (cmolc 0.8 [+ or -] 0.4 [kg.sup.-1]) H + Al ([cmol.sub.c] 6.0 [+ or -] 0.9 [kg.sup.-1]) CEC ([cmol.sub.c] 7.26 [kg.sup.-1]) Base saturation (%) 17.3 Nitrogen (g [kg.sup.1]) 1.3 [+ or -] 0.2 Phosphorus (mg 1.3 [+ or -] 1.2 [kg.sup.-1]) Potassium (mg [kg.sup.-1]) 22.7 [+ or -] 9.7 Bulk density (kg 1.07 [+ or -] 0.06 [dm.sup.3]) Clay (g [kg.sup.-1]) 524 [+ or -] 21 Silt (g [kg.sup.-1]) 77 [+ or -] 19 Sand (g [kg.sup.-1]) 400 [+ or -] 17 Table 2. Description of soil management systems Management system Symbol Description Cerrado CER Natural Cerrado area next to the experimental area, used as a reference environment (soil without anthropic action) Conventional CT Soil preparation with a heavy disc tillage with harrow and cultivation with soybean heavy disc harrow for 13 years No-till planting NTl Soil preparation with a disc plough in with biannual the first 2 years and mouldboard plough rotation in the subsequent 2 years. No-till planting was used from the fifth year onwards with a biannual rotation of com and soybean No-fill planting NT2 Soil preparation with a disc plough with biannual in the first 2 years and mouldboard rotation and a plough in the subsequent 2 years. No- second crop till planting was used from the fifth year onwards with a biannual rotation in the summer of corn and soybean, combined with a second crop of a leguminous plant, guandu beans (Cajanus cajan L.), in the first 2 years with corn No-till planting NT3 Soil preparation with a disc plough in with annual the first 2 years and mouldboard plough rotation in the subsequent 2 years. No-till planting was used from the fifth year onwards with an annual rotation of corn and soybean Pasture PAST Soil preparation with a disc plough and forage crops, rice (Oryza saliva L.), and com in the first 2 years and mouldboard plough with guandu beans in the subsequent 2 years. From the fifth year onwards, Urochloa brizantha pasture was used without animal grazing Table 3. History of management systems and crop use during the 12 years of the experiment CT, Conventional tillage; NT, no-till (see Table 2 for description of NTl--NT3); PAST, pasture; CER, Cerrado. HDH, Heavy disc harrow; DP, disk plough; MP, mouldboard plough; G, grass; L, legume 1996-97 1997-98 1998-99 1999-2000 CT HDH-L HDH-L HDH-L HDH-L NTl DP-G DP-G MP-L MP-L NT2 DP-G L DP-G L MP-L G MP-L G NT3 DP-G DP-L MP-G MP-L PAST DP-G DP-G MP-L MP-L CER CER CER CER CER 2000-01 2001-02 2002-03 2003-04 CT HDH-L HDH-L HDH-L HDH-L NTl NT-G NT-G NT-L NT-L NT2 NT-G L NT-G L NT-L G NT-L G NT3 NT-G NT-L NT-G NT-L PAST PAST PAST PAST PAST CER CER CER CER CER 200405 2005--06 2006-07 2007-08 CT HDH-L HDH-L HDH-L HDH-L NTl NT-G NT-G NT-L NT-L NT2 NT-G L NT-G L NT-L G NT-L G NT3 NT-G NT-L NT-G NT-L PAST PAST PAST PAST PAST CER CER CER CER CER Table 4. Total (TOC) and particulate (POC) organic carbon stocks, as well as those associated with minerals (MAOC), in clayey Oxisol under various management systems and natural Cerrado vegetation in different layers CT, Conventional tillage; NT, no-till (see Table 2 for description of NTl-NT3); PAST, pasture; CER, Cerrado. Means followed by the same letter are not significantly different by the Tukey test at P=0.05 for comparison among treatments of each carbon pool at the same depth Depth (cm) CER CT NTl TOC, Mg [ha.sup.1] 0-10 25.9a 21.5bc 24.3ab 10-20 20.0a 21.6a 21.4a 2040 38.9a 35.1a 38.8a 110 84.8ab 78.1c 84.6ab POC, Mg [ha.sup.1] 10 13.8a 7.1c 9.8b 10-20 9.2a 7.0b 4.1c 20-40 12.3a 6.7b 7.3b 140 35.4a 20.8b 21.2b MAOC Mg [ha.sup.1] 0-10 12.2bc 14.3ab 14.5ab 10-20 10.7c 14.56 17.3a 20140 26.6bc 28.4abc 31.6a 140 49.4c 47.2b 63.4ab Depth (cm) NT2 NT3 PAST TOC, Mg [ha.sup.1] 0-10 23.0abc 21.2c 24.8a 10-20 21.8a 20.2a 22.5a 2040 36.1a 38.9a 38.8a 110 80.9abc 80.4bc 85.9a POC, Mg [ha.sup.1] 10 7.0c 5.6c 14.5a 10-20 4.4c 4.1c 10.4a 20-40 6.9b 6.36 14.4a 140 18.3b 16.0b 39.4a MAOC Mg [ha.sup.1] 0-10 15.9a 15.6a 10.2c 10-20 17.4a 16.1ab 12.1c 20140 29.2ab 32.6a 24.3c 140 62.6ab 64.3a 46.6c Table 5. Stratification ratio (0-5 cm : 10-20 cm) of total organic carbon (TOC), particulate organic carbon (POC) and nitrogen (PON), mineral-associated organic carbon (MAOC), POC:PON ratio, microbial biomass C (MBC) and N (MBN), and basal respiration (BR) under different management systems and natural Cerrado vegetation CT, Conventional tillage; NT, no-till (see Table 2 for description of NTl-NT3); PAST, pasture; CER, Cerrado. Means followed by the same letter are not significantly different by the Tukey test at P=0.05 for the comparison among treatments of each variable Variable CT NTl NT2 TOC 0.93c 1.17ab 1.066c POC 0.59d 2.02ab 1.88bc MAOC l.l0a 0.96ab 0.87b PON 1.68b 2.00ab 2.67ab POC: PON 0.59c 1.026 0.72c MBC 1.35cd 1.57c 1.28d MBN 0.72c 1.116 1.00bc BR 1.06ab 1.98a 2.10a Variable NT3 PAST CER TOC 1.076c 1.23ab 1.28a POC 1.66c 1.58c 2.35a MAOC 0.926 0.80b 0.58c PON 1.38ab 3.00a 1.92ab POC: PON 1.23b 0.49c 1.78a MBC 1.86b 0.98e 2.62a MBN 0.91bc 1.12b 2.07a BR 0.71b 2.18a 2.03a
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|Author:||Figueiredo, C.C.; Resck, D.V.S.; Carneiro, M.A.C.; Ramos, M.L.G.; Sa, J.C.M.|
|Date:||Mar 1, 2013|
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