Particulate organic matter in soil under different management systems in the Brazilian Cerrado.
The Cerrado is the second largest Brazilian biome, exhibiting complex dynamics that are strongly affected by seasonal fluctuation and anthropogenic activity (Bolliger et al. 2006; Sano et al. 2007). Many Cerrado areas are currently occupied by agriculture, making it one of the major cropping areas in the world (Siqueira Neto et al. 2009; Pacheco et al. 2012). Crops, however, replace natural Cerrado vegetation, which is cut down and burned, diminishing soil organic matter (SOM) and fertility and increasing erosion (Fearnside 2000; Bernoux et al. 2004). Furthermore, an ultimate consequence of this inadequate land management is an increase in production costs. To counteract this situation, different soil management systems can be adopted, according to their specific effects on SOM, in order to directly or indirectly affect the chemical and physical properties of soil. For instance, management systems that raise carbon content in soil also increase its cation exchange capacity (CEC), as well as nutrient availability for crops (Sa et al. 2009; Siqueira Neto et al. 2009; Turbe et al. 2010; Paterson and Hoyle 2011).
Recently, a growing number of studies have investigated carbon accumulation in Cerrado soils under different management systems, such as conventional, no-till (NTS), and pasture (Beruoux et al. 2004; Blanchart et al. 2007; Siqueira Neto et al. 2009; Carvalho et al. 2010; Pereira et al. 2010; Briedis et al. 2012; Corsi et al. 2012; Loss et al. 2012a). These studies have focussed mainly on determining total organic carbon (TOC) stocks, which is inadequate for determining better land use and management policies. Further research is needed to provide information on the profile of different TOC fractions, including carbon content in the granulometric fractions of SOM.
The NTS, also known as direct seeding or planting, is efficient in reducing erosion and increasing carbon and nutrient load in soil, especially when combined with annual crop rotation (Marchao et al. 2009; Sa et al. 2009; Silva et al. 2009; Boddey et al. 2010; Pereira et al. 2010; Costa Junior et al. 2011; Fernandez et al. 2011; Soane et al. 2012). Moreover, the combination of crop and livestock in NTS can increase the physical and chemical SOM fractions, enhancing carbon and nutrient stocks (Loss et al. 2012a; Uprety et al. 2012). This type of management, interspersing herbage growth with annual crops and livestock production, is known as crop-livestock integration (CLI), an excellent alternative to recover areas degraded by modern agriculture. CLI is highly beneficial to soil, improving biota, fertility, and physical properties such as soil aggregation (Kluthcouski and Yokoyama 2003; Clark 2004; Landers 2007; Franzluebbers and Stuedemann 2008; Carvalho et al. 2010; Souza et al. 2010; Loss et al. 2011; Pacheco et al. 2012).
The carbon content of tropical soils is mostly concentrated in the top layer and can be affected by rainfall distribution, maintenance of soil coverage, and soil management (Brancaliao and Moraes 2008; Loss et al. 2012a). Nevertheless, TOC estimation in cropped areas may not be sensitive enough to detect the short-term effects of land management on the chemical features of SOM (Conceicao et al. 2005; Mirsky et al. 2008; Loss et al. 2009; Souza et al. 2010; Ciampitti et al. 2011; Zinn et al. 2011). Therefore, complementary analyses such as evaluation of carbon flow and changes in SOM fractions should be carried out to assess this response (Lee et al. 2009; Loss et al. 2009; Bouajila and Gallali 2010; Pereira et al. 2012).
Some SOM fractions are reliable in expressing alterations in soil quality as a function of the management system applied. For example, chemical and physical SOM fractions can be used to discriminate between soil samples from NTS and CLI, since these systems promote different biomass inputs. Therefore, the evaluation of granulometric SOM fractions (Cambardella and Elliott 1992; Six et al. 1999; Mirsky et al. 2008; Loss et al. 2009; Ciampitti et al. 2011) is a valuable tool not only for assessing soil changes due to land use but also for quantifying carbon levels in each fraction.
Management systems that affect SOM accumulation also affect particulate organic carbon (POM) content in soil. Thus, high POM content in soil indicates storage of carbon and other nutrients in an intermediary pool, protected from losses and available when needed (Carter et al. 2003; Zhang and He 2004; Fronning et al. 2008; USDA 2011; Bhattacharyya et al. 2012). Land use systems such as NTS and CL1, which use crop rotation together with cover crops and pasture, can increase POM levels (Liebig et al. 2004; Bolliger et al. 2006; Komatsuzaki and Ohta 2007; Njaimwe 2010; Miller 2012).
Crop conversion from NTS to CLI can significantly increase soil nutrient levels, since it raises SOM content. On the other hand, intensive cropping with CLI can promote soil nutrient extraction. The benefits of CLI are still a matter of discussion because only a few conclusive studies have investigated changes in SOM fractions after implementation of this system (Franzluebbers and Stuedemann 2008; Carvalho et al. 2010; Loss et al. 2011, 2012a, 2012b).
Against this backdrop, the present study tested the hypothesis that CLI is superior to NTS in increasing soil carbon stocks. To that end, TOC and granulometric fractions of SOM were evaluated in soil samples from areas managed under these systems in a Cerrado area in Goias.
Material and methods
The study was conducted at 'Vargem Grande' farm, owned by Agropecuaria Peeters S.A. and located in Montividiu, Goias (17[degrees]21'S, 51[degrees]28'W). Climate in the area exhibits well-defined dry (May-September) and rainy (October-April) seasons. Annual rainfall is 1500mm, and maximum and minimum temperatures are 30.1 and 17.8[degrees]C, respectively. Soil in the study area was Oxisol (Soil Survey Staff 2006) with clayey texture (Latossolo Vermelho Distrofico; EMBRAPA 2006).
Mineral composition was predominantly gibbsite, kaolinite, and hematite, with 0.81 Ki index (1.70Si[O.sub.2]/[Al.sub.2][O.sub.3]) and Feo/Fed ratio of 0.041 for the A Horizon and 0.77 Ki and 0.063 Feo/Fed for the B Horizon. Treatment with sulfuric acid showed that the soil contained less Si[O.sub.2] than [Al.sub.2][O.sub.3], indicating that this soil is richer in oxides than silicate clays. The [Fe.sub.2][O.sub.3] content was 67 and 71 g [kg.sup.-1] in horizons A and B, respectively (Loss 2011). Chemical characterisation of the soil is described by Loss (2011).
Land-use history and soil sampling
Land-use history in the study area is illustrated in Fig. 1. In 1975, the natural Cerradao vegetation in the study area was replaced by brachiaria grass (Urochloa decumbens, syn. Brachiaria) for a period of 10 years. In 1985, management of the area began applying conventional tillage soil with ploughing and harrowing for growing grain crops (corn, bean, soybean, and sunflower); NTS with crop rotation (corn/bean/soybean/cotton) was introduced in 1991; and from 1999 onwards, part of the areas managed with the NTS began to use CLI. As such, both cropped areas evaluated were subject to NTS management for 17 years, one with rotation of the same crops from 1991 to 2008 and the other with CLI from 1999 to 2008.
The area managed exclusively with NTS (17[degrees]21.1US, 51[degrees]29.461'W; 859 m altitude) rotated sunflower/pearl millet/soybean/corn crops, and the CLI area (17[degrees]21.854'S, 51[degrees]28.599'W; 859m altitude) contained brachiaria grass (U. ruziziensis) intercropped with off-season corn crops to enhance straw production during the dry season, producing a rotation system of corn/brachiaria grass/bean/cotton/soybean. Off-season crops consisted of a short-term culture grown after the annual crop and under less suitable climate conditions. The third area studied was the natural Cerradao (17[degrees]26.64'S, 51[degrees]22.522'W; 951m altitude), adjacent to the cropped site and representing original soil conditions.
The CLI system was employed in the area cropped with corn/brachiaria grass/bean/cotton/soybean. Corn was sown simultaneously with grass (grass was planted between corn rows). Cattle were allowed to graze in the area at a density of 2 animals per ha for 90 days (July-September) after corn harvesting. Animals were then removed and only grass clumps remained in the field. Following the first rainfall events, the grass received 200kg [ha.sup.-1] of NPK topdressing (20:00:20) in the first 2 weeks of September. After sprouting, when grass covered the entire area, it was desiccated using glyphosate and the field was planted with bean.
The CLI area was limed in July 2005 with 3.60 Mg [ha.sup.-1] of dolomitic limestone with total neutralising power of 70%, to enhance base saturation to 70%. The NTS area was also limed at this time with 3.90Mg [ha.sup.-1] of dolomitic limestone with total neutralising power of 70%, in order to enhance base saturation to 60%. Fertilisation and cropping sequences from 2002 to 2008 for both areas are displayed in Table 1. Average productivity of crops and cover crops between 1999 and 2008 is shown in Table 2 for both systems.
For soil sampling in March 2008, the NTS area was cropped with sunflower, and the CLI region with corn + brachiaria grass. A 600-[m.sup.2] section was demarcated at each location and four trenches measuring 40 by 40 by 40 cm were opened crosswise to crop rows for soil sampling at depths of 0-5, 5-10, 10 20, and 20-40 cm. Three single samples were collected in each trench to form a composite sample, totalling four replications for each management system. Samples were air-dried and sieved through a 2-mm mesh sieve to obtain air-dried ground soil. At the same depths, bulk density values (Table 3) were used to calculate the equivalent soil mass and analyse carbon stocks in SOM fractions.
Total organic carbon
The TOC was quantified as described by Yeomans and Bremner (1988).
Granulometric (physical) partitioning of SOM and fraction stocks
Approximately 20g of air-dried ground soil was mixed with 60 mL sodium hexametaphosphate solution (5 g [L.sup.-1]) and stirred for 15 h in a horizontal stirrer (Cambardella and Elliott 1992). The suspension was passed through a 53-[micro]m sieve forced by water jet. The material retained by the sieve, consisting of particulate organic carbon (POC) associated with a sand fraction, was oven-dried at 60[degrees]C for relative weight quantification. Dried samples were ground in a ceramic mortar and the TOC level was determined according to Yeomans and Bremner (1988). Particles that passed through the 53-[micro]m sieve corresponded to the mineral-associated organic carbon (MOC) obtained from silt and clay fractions. MOC was calculated using the difference between TOC and POC.
Carbon stocks in each granulometric fraction were analysed by the equivalent mass method (Ellert and Bettany 1995; Sisti et al. 2004), as described below:
[C.sub.s] = [n-1.summation over(i=1)][C.sub.Ti] + [[M.sub.Tn] - ([n.summation over (i=1)][M.sub.Ti] - [n.summation over (i=1)][M.sub.Si])][C.sub.Tn]
where: [C.sub.s] is total stock (Mg [ha.sup.-1]); [[summation].sup.n-1.sub.i=1] [C.sub.Ti] is sum of nutrients from the most superficial to the deepest layer of the soil profile evaluated in a specific experimental area (Mg [ha.sup.-1]); [[summation].sup.n.sub.i=1] [M.sub.Ti] is sum of soil mass from the most superficial to the deepest layer of the soil profile investigated in a specific experimental area (Mg [ha.sup.-1]); [[summation].sup.n.sub.i-1] [M.sub.Si] is sum of soil mass from the most superficial to the deepest layer of the soil profile sampled as a reference treatment (Mg [ha.sup.-1]); [M.sub.Tn] is soil mass in the deepest layer of the soil profile assessed in a specific experimental area (Mg [ha.sup.-1]); [C.sub.Tn] is nutrient level in the deepest layer of the soil profile studied in a specific experimental area (Mg nutrient Mg [soil.sup.-1]).
The homogeneity of soil characteristics was verified before selecting the study areas, in order to ensure they had similar source material, soil texture and class, and topographic and climate conditions, differing only in the type of management they received. Considering that the areas were under similar environmental conditions, the experimental units were identified as homogeneous before receiving the treatments.
The study was arranged in a completely randomised design comprising three soil management systems (NTS, CLI, and Cerradao) (treatments) with four pseudo repetitions. This completely randomised design is applicable because it is considered the simplest statistical design, which uses a random distribution of experimental units, and equal or unequal repetitions per treatment. The use of completely randomised design requires uniform action of environmental over experimental units and easy identification of these units and the respective treatments (Hurlbert 1984).
Data were checked for normality using the Lilliefors test and for homoscedasticity by the Bartlett and Cochran test. Data underwent analysis of variance with the F-test, and differences detected were compared using the Student test and 1.s.d. at a significance level set at P = 0.05.
Results and discussion
Total organic carbon
Cerradao had the highest TOC levels in the most superficial layer (5 cm), owing to high plant residue deposits, which promote elevated organic matter deposition, and to the lack of anthropogenic activity. At depths of 5-10 and 10-20cm, TOC levels were greater under CL1 than NTS or the Cerradao (Fig. 2).
Intercropping of brachiaria grass and off-season crops in the CLI system produced a crop residue mulch of slow degradation, favouring TOC accumulation due to the high C/N ratio. Similar results were described by Passos et al. (2007) in areas of dystrophic Red Latosol (Oxisol) in Minas Gerais state. Those authors reported that TOC distribution along soil layers was more homogeneous in areas cropped with corn for 30 years than in a reference Cerradao region.
The TOC levels at 5-10 and 10 20cm depth were higher under CLI than in the Cerradao or NTS sites (without brachiaria grass). This pattern shows that soil management using CLI is more efficient than NTS (without brachiaria grass) or the natural Cerradao in achieving high TOC levels in subsurface layers.
At the deepest layer evaluated (20-40 cm), the similarity of TOC levels between CLI and NTS may be a result of land-use history. Although these areas received both annual and off-season crops, planting of off-season crops in the NTS area began only 5 years before the experiment. Before this period, the NTS region had no tillage after the soybean harvest, and invading plants such as Guinea grass (Panicum maximum) and brachiaria grass (U. decumbens), both [C.sub.4] plants, occupied the area. In addition to brachiaria grass, pearl millet straw contributed to carbon incorporation in the soil owing to its root system. This explains the similarity between TOC levels in the cropped areas.
The NTS and CLI areas were cropped for 17 years using notill, direct planting. According to Anghinoni (2007), a period of 10 20 years of direct planting can be considered a consolidation stage. During this phase, there is substantial accumulation of organic matter and straw in the soil, increasing CEC, water storage, and nutrient recycling. These factors probably account for the higher TOC levels recorded under CLI (5-20 cm depth) than in NTS and Cerradao areas, which were similar (Fig. 2).
Results obtained indicate the efficiency of NTS in accumulating carbon within soil over cropping years. Moreover, they demonstrate that intercropping of brachiaria grass with off-season corn in CL1 is more efficient than NTS without brachiaria grass. The lack of soil turning in direct planting combined with crop rotation and accumulation of crop residues (Conceicao et al. 2005) favours soil aggregation, protecting it from mineralisation and enhancing SOM content (Sa et al. 2001; Loss et al. 2011).
In the Cerradao, TOC declined drastically with depth, by almost 55% from the 0 5cm depth to 5 10cm and 61% from 0-5 cm to 10 20cm. At the NTS location, TOC decrease in these same layers was 14% and 15%, and under CLI, only 1.2% and 8.3%, respectively (Fig. 2). Therefore, NTS and CLI provided a better distribution of TOC levels than that found in the natural Cerradao area. Consequently, both NTS and CLI improve soil fertility (Loss 2011), as reported by Jantalia et al. (2007) and Siqueira Neto et al. (2009) in other investigations conducted in the Cerrado with the same soil type evaluated here.
Carbon levels and stocks in the granulometric SOM fractions
Levels of POC were greater in the Cerradao and CLI areas to 10cm depth. At depths of 10-0 and 20-0 cm, the Cerradao displayed lower POC levels than the cropped areas (Table 4). Levels of POC are directly related to the input of plant residues in soil. Therefore, although the highest TOC levels observed were in the Cerradao at 0 5cm (Fig. 2), POC in this region was similar to that at the CLI site. This indicates that using brachiaria grass, along with off-season corn crops and legumes (soybean and bean), promotes straw (dry mass) production (Table 4) and biological N-fixation owing to the brachiaria root system. These are higher quality plant inputs that, in contrast to Cerradao, promote higher levels of C (195.75 and 155.1l g [kg.sup.-1] in CLI and Cerradao, respectively) and N (19.45 and 14.41 g [kg.sup.-1] in CLI and Cerradao, respectively) in the free light fraction of SOM (Loss et al. 2012b).
Loss et al. (2012b) found that in the surface layer (0-5 cm), light organic matter (LOM) levels were higher in a Cerradao area (15.12 g [kg.sup.-1]) than at a CL1 site (7.14 g [kg.sup.-1]). At depths of 5-10cm, no differences were observed between these areas (3.88 g [kg.sup.-1] LOM in Cerradao and 3.44g [kg.sup.-1] in CLI). In terms of total volume, the highest LOM levels were recorded in the Cerradao at 0-5 cm. However, the Cerradao region had only [C.sub.3] plants, whereas the CL1 area had both C4 (corn + brachiaria grass) and [C.sub.3] (soybean + bean) plants. Thus, POC content found at the CLI location is related to the nature of the plant matter in this system, which may correspond to LOM content in the Cerradao area. This pattern can also be observed for POC stocks, i.e. they were similar between CL1 and Cerradao areas at 0-5 cm, but at 5-10 cm depth, POC stocks were higher in the CL1 area and LOM levels were similar between the areas. It is remarkable that at 5-10 cm depth, the highest POC levels and stocks in the CL1 area are also associated with the highest C-LOM levels (Loss et al. 2012b).
For cropped sites, CLI showed higher POC levels than NTS to a depth of 20 cm and similar values at 20-40 cm. With regard to the 040 cm layer, the CLI site had the greatest POC stocks among the three areas evaluated. These results indicate that corn intercropping with brachiaria grass in the CLI area promotes higher input of plant matter (corn root system + brachiaria grass) into soil than in the NTS (to 20 cm) and Cerradao areas. Similar results for both management systems at 20-40 cm depth were also observed for TOC levels and stocks, owing to the use of pearl millet in NTS and corn+ brachiaria grass in the CLI system.
When analysing SOM dynamics to 20 cm for NTS in a Cerrado area in Goias, Rossi et al. (2012) found that soybean fields cropped over brachiaria grass straws had higher POC levels than when cropped over sorghum straws. Corroborating these findings, the present study shows that variations in POC levels depend on plant residue incorporated into the soil. That is, compared with NTS alone, CLI provides higher residue input to the soil surface as a result of high straw production and the root system of grasses reaching deeper soil layers (up to 20 cm). This process increases light SOM fractions (free light fraction and LOM) (Loss et al. 2012b) and, consequently, POC levels.
The current study revealed the same pattern for TOC (Fig. 2) and POC (Table 4) levels in cropped areas, with higher values for CLI than for NTS at 1 0-20 cm and similar values at 2040 cm. Because of the long management period in the areas studied, cropped for 17 years under NTS, both TOC and POC showed the same response to different systems (NTS and CLI). These parameters can therefore be considered good indicators of soil quality.
Levels of MOC were higher in the Cerradao at depths of 0-5 and 20-40 cm, and similar between treatments in the 10-20 cm layer. No differences were detected between cropped areas for MOC levels at the depths evaluated (Table 4). The high MOC stocks in Cerradao can be associated with TOC stocks, which in topsoil (0-5 cm) are greater than in the other systems (Loss 2011). However, in the cropped areas, similarity in MOC stocks likely reflects a minor effect of management systems on the rapture and formation of microaggregates (<53 [micro]m) in Latosol soils (oxidic Red Latosol), whose main cementing agents are poorly crystalline iron oxides (Pinheiro-Dick and Schwertmann 1996; Muggier et al. 1999).
At 5-10 cm depth, CLI and NTS demonstrated higher MOC levels than the Cerradao. All areas had a very clayey texture (Loss 2011), and MOC differences recorded were imposed by the management system used. Therefore, in cropped areas, using crop rotation with [C.sub.3] and [C.sub.4] plants, particularly [C.sub.4] species such as pearl millet under NTS and brachiaria grass in CLI, combined with the action of Fe and Al oxides may promote microaggregate (<53 [micro]m) formation to a greater extent than occurs in the Cerradao. The increased proportion of microaggregates also enhances the levels of MOC contained therein.
Stocks of POC were higher in the CLI area at all depths evaluated, including the whole 0-40 cm layer. However, no differences in POC stock were detected between the CLI and Cerradao (0-5 cm) and between CLI and NTS (20-40 cm). Results indicate that, compared with the NTS (without brachiaria grass) and Cerradao at deep layers, applying CLI provides greater plant matter input to soil. Except for topsoil, cropped sites had higher POC stocks than the Cerradao, indicating that the pearl millet used in NTS and the brachiaria grass in CLI (per dry mass production; Table 2), associated with fertilisation (Table 1) and soil exploitation by roots, were efficient in increasing the light fraction of soil (deep organic residues). According to Parihar et al. (2012), since pearl millet is a [C.sub.4] plant (as is brachiaria grass), it is more efficient than [C.sub.3] plants in accumulating carbon and performing photosynthesis. Therefore, pearl millet and brachiaria grass are more efficient than Cerradao [C.sub.3] plants in accumulating carbon, thereby increasing POC stocks.
Stocks of MOC followed the same pattern as observed for MOC levels in the different areas and different layers, except for 10-20cm depth, where the CLI area exhibited higher stocks (Table 4). These results can be associated with TOC stocks, which were higher in the CL1 area (Table 4). In the 0-40 cm layer, the Cerradao displayed higher MOC stocks than cropped sites. However, this pattern was not observed for TOC stocks, which were similar between CLI and Cerradao locations (Loss 2011). Divergences detected are probably a result of proportions of POC and MOC stocks comprising TOC stocks. In the CLI area, the 17-year land use (12 years with NTS and 5 years with CLI) was enough to recover TOC stocks to original (Cerradao) levels. However, TOC stock in the CLI area corresponded to 55% MOC and 45% POC, whereas the Cerradao exhibited 65% MOC and 35% POC.
Figueiredo et al. (2010) studied the dynamics of labile and stable organic matter fractions of soil under different management systems and native Cerrado. Those authors found a negative correlation between POC and MOC, indicating that these fractions have opposing formation processes. As such, a greater decrease in POC by decomposition, with subsequent association to silt- and clay-sized minerals, is needed to produce higher MOC levels in soil. This pattern was observed in the Cerradao area, which had the lowest POC stocks and consequently the highest MOC stocks in the 0-40cm layer (Table 4), suggesting that part of the POC stocks were decomposed and formed MOC stocks.
In general, similarity in MOC levels and stocks between cropped areas and contrasts in POC levels and stocks between areas suggest that direct planting (NTS and CL1) promotes higher stratification rates of POC than of MOC stocks (Sa and Lal 2009). Stratification of plant residues on the surface and subsurface was better in the CLI area due to dry matter production by brachiaria (Table 2), fertilisation (Table 1), and random manure spreading by cattle, which grazed in the area for 3 months. Therefore, CLI produced higher POC levels and stocks than NTS.
An evaluation of mean crop and cover crop productivity from 1999 to 2008 (Table 2) showed that soybean and corn, cropped under both soil management systems, performed better in CLI than in NTS (by 84 kg [ha.sup.-1] for soybean and 732 kg [ha.sup.-1] for corn). Considering that the Vargem Grande farm has nearly 400 ha of arable land, the productivity gap of soybean and corn is significant, as well as the benefits provided by CLI to soil. The CL1 system enhanced productivity by increasing C and N stocks (Loss et al. 2012a, 2012b), soil aggregation (Loss et al. 2011), and C-POM levels. Moreover, land under CLI was more productive due to beef cattle husbandry for 3 months. However, to obtain all of the benefits provided by CLI, a high nutrient export system must be ensured, and more attention must be devoted to soil acidity correction and fertilisation.
Based on the productivity results described, it can be concluded that the CLI system is an efficient solution to counteract the lack of tillage in crop areas in the Cerrado of Goias, where this practice is compromised by unfavourable weather conditions. CLI promotes rapid decomposition of cover crops such as soybean and bean. In addition, it can be applied off-season (March July), when weather conditions are unfavourable, preventing cropland idling.
The CLI system is more efficient in increasing TOC, POC levels, and POC stocks compared with NTS. Compared with areas of natural Cerradao vegetation, those managed for 17 years (1991-1999) with crop rotation and NTS and for 9 years (1999-2008) with CLI had increased TOC (at 5-10 and 10-20cm) and POC stocks (at 5 10, 10 20, 2040, and 0-40cm). The largest POC stocks in CLI (corn/brachiaria grass/bean/cotton/soybean) and NTS (sunflower/pearl millet/ soybean/corn) areas at a depth of 0-40cm indicate that, in addition to the benefits of crop rotation and fertilisation, the use of pearl millet (NTS) and brachiaria grass (CLI) is more efficient in accumulating carbon than is Cerradao because of dry mass production. The CL1 system favours POC stratification in surface and subsurface soil layers through dry matter production by brachiaria, fertilisation, and 3-month cattle grazing with random manure release over the soil surface. POC is more sensitive to modifications imposed by management systems than to TOC.
Therefore, the benefits that the CL1 system provides to soil, i.e. increased C and N stocks (Loss et al. 2012a, 2012b), soil aggregation (Loss et al. 2011), and POC levels, increase productivity. Furthermore, CLI also promotes benefits in terms of beef cattle production. In conclusion, the CLI system is a promising solution to counteract no-till problems caused by poor weather conditions in the Cerrado of Goias, Brazil.
Received 18 July 2012, accepted 22 December 2012, published online 5 February 2013
The study is part of the PhD thesis of A. Loss, and the authors thank the CNPq and FAPERJ for providing A. Loss with a PhD scholarship; the Agrisus Foundation for sponsoring the research project; the Graduate Program in Agronomy Soil Science (CPGA-CS) at the UFRRJ for support provided; and Dr Adriano Perin and collaborators for assisting in soil sampling.
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Arcangelo Loss (A,D,) (1), Marcos Gervasio Pereira (B), Adriano Perin (C), Fernando Silva Coutinho (B), and Lucia Helena Cunha dos Anjos (B)
(A) Department of Rural Engineering, Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC 88034-000, Brazil.
(B) Department of Soils, UFRRJ, Seropedica, RJ 23890-000, Brazil.
(C) Instituto Federal Goiano, Rio Verde, GO 75901-970, Brazil.
(D) Corresponding author. Email: firstname.lastname@example.org
(1) This paper is part of the PhD thesis of A. Loss in Soil Science, Postgraduate Course in Agronomy, CPGA-CS, at the Universidade Federal Rural do Rio de Janeiro (UFRRJ), Seropedica, RJ, 23890-000, Brazil.
Table 1. Fertilisation and cropping sequence in the two areas studied at 'Vargem Grande' farm, Montividiu, Goias, Brazil Year Month Crop CLI area (corn/brachiaria grass/bean/cotton/soybean) 2002 October Soybean 2003 February Com + brachiaria grass 2003 October Soybean 2004 February Com + brachiaria grass 2004 October Soybean 2005 February Com + brachiaria grass 2005 September Bean 2005 December Cotton 2006 October Soybean 2007 February Com + brachiaria grass 2007 October Soybean 2008 February Corn + brachiaria grass 2008 September Bean 2008 December Cotton NTS area (sunflower/pearl millet/soybean/corn)(A) 2002 August Pearl millet 2002 October Soybean 2003 February Com 2003 August Pearl millet 2003 October Soybean 2004 February Com 2004 August Pearl millet 2004 October Soybean 2005 February Com 2005 August Pearl millet 2005 October Soybean 2006 February Sunflower 2006 August Pearl millet 2006 October Soybean 2007 February Corn 2007 August Pearl millet 2007 October Soybean 2008 February Sunflower 2008 August Pearl millet 2008 October Soybean Year Fertilisation NPK Topdressing CLI area (corn/brachiaria grass/bean/cotton/soybean) 2002 580 kg [ha.sup.-1] (2:20:18) -- 2003 500 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2003 580 kg [ha.sup.-1] (2:20:18) -- 2004 450 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2004 500 kg [ha.sup.-1] (2:20:18) -- 2005 490 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2005 400 kg [ha.sup.-1] (5:20:10) Urea 90 kg [ha.sup.-1] 2005 500 kg [ha.sup.-1] (10:30:10) 250 kg [ha.sup.-1] (20:0:20) 2006 500 kg [ha.sup.-1] (2:20:18) -- 2007 450 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2007 450 kg [ha.sup.-1] (2:20:18) -- 2008 450 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2008 400 kg [ha.sup.-1] (5:20:10) Urea 90 kg [ha.sup.-1] 2008 500 kg [ha.sup.-1] (10:30:10) 250 kg [ha.sup.-1] (20:0:20) NTS area (sunflower/pearl millet/soybean/corn)(A) 2002 -- -- 2002 550 kg [ha.sup.-1] (2:20:18) -- 2003 450 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2003 -- -- 2003 550 kg [ha.sup.-1] (2:20: 18) -- 2004 450 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2004 -- -- 2004 550 kg [ha.sup.-1] (2:20:18) -- 2005 450 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2005 -- -- 2005 550 kg [ha.sup.-1] (2:20:18) -- 2006 300 kg [ha.sup.-1] (2:20:20) Urea 100 kg [ha.sup.-1] 2006 -- -- 2006 500 kg [ha.sup.-1] (2:20:18) -- 2007 400 kg [ha.sup.-1] (7:28:14) Urea 100 kg [ha.sup.-1] 2007 -- -- 2007 500 kg [ha.sup.-1] (2:20:18) -- 2008 300 kg [ha.sup.-1] (2:20:20) Urea 100 kg [ha.sup.-1] 2008 -- -- 2008 500 kg [ha.sup.-1] (2:20:18) -- CLI, Crop-livestock integration; NTS, no till system (A) From 2002 to 2008, pearl millet was annually sowed in the NTS area, always in August, to enhance straw yield for direct planting of soybeans. Before 2002, off-season and pearl millet crops were not planted and the area remained at rest from May to September. During this resting period, grass species such as coloniao (Panicum maximum) and brachiaria grass (U. decumbens) grew spontaneously. Table 2. Mean crop and cover crop productivity (kg [ha.sup.-1]) from 1999 to 2008 in areas under no-till system (NTS) or crop-livestock integration (CLI) on the 'Vargem Grande' farm Management system CLI NTS Soybean 3780 3696 Corn 6282 5550 Cotton 4470 -- Bean 2580 -- Sunflower -- 2340 Dry mass of brachiaria grass 11300 -- Dry mass of pearl millet -- 7800 Table 3. Bulk density (Mg [m.sup.-3]) in natural Cerradao areas and sites under no-till system (NITS) or crop-livestock integration (CLI) on the 'Vargem Grande' farm Bulk density determined by the volumetric ring method (EMBRAPA 1997) (source: Loss 2011) Depth Management system (cm) CLI NTS Cerradao 0-5 0.89 0.94 0.69 5-10 0.97 1.06 0.89 10-20 0.97 1.09 1.09 20-40 0.93 0.89 0.92 Table 4. Granulometric SOM fractions and the respective carbon stocks in soil under different management systems on the 'Vargem Grande' farm NTS, No till system; CLI, crop livestock integration; POC, particulate organic carbon; MOC, mineral-associated organic carbon; CV, coefficient of variation. Within columns and depths, means followed by the same letter are not significantly different (l.s.d. at P=0.05, Student test) Management Granulometric carbon Carbon stock system fraction (g [kg.sup.-1]) (Mg [ha.sup.-1]) POC MOC POC MOC stock stock 0-5 cm NTS 21.19B 6.92B 7.29B 2.37B CLI 23.63A 7.10B 8.13A 2.44B Cerradao 24.88A 30.99A 8.56A 10.64A CV (%) 3.35 10.95 4.55 10.59 5-10 cm NTS 6.90B 17.39A 4.87C 6.42A CLI 13.08A 17.27A 7.91A 6.45A Cerradao 12.20A 13.02B 6.76B 4.48B CV (%) 4.99 8.16 4.47 8.29 10-20 cm NTS 4.81B 18.99A 7.74B 14.34B CLI 8.49A 19.67A 8.58A 17.54A Cerradao 3.55C 18.49A 6.07C 14.43B CV (%) 6.54 11.74 5.30 11.14 20-40cm NTS 7.56A 10.14B 14.37A 20.37B CLI 7.89A 10.02B 14.06A 20.15B Cerradao 3.99B 14.10A 7.3100 25.78A CV (%) 10.57 6.60 12.07 9.59 0-40 cm NTS -- -- 34.27B 43.50B CLI -- -- 38.68A 47.34B Cerradao -- -- 28.70C 55.33A CV (%) 11.07 13.59
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|Author:||Loss, Arcangelo; Pereira, Marcos Gervasio; Perin, Adriano; Coutinho, Fernando Silva; dos Anjos, Luci|
|Date:||Nov 1, 2012|
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