PHYSICAL ATTRIBUTES, TOTAL CARBON AND 13C NATURAL ABUNDANCE IN FERRALSOL UNDER DIFFERENT AGRICULTURAL SYSTEMS

Article Citation: Marcos Gervasio Pereira, Arcangelo Loss, Roni Fernandes Guareschi, Fabiana da Costa Barros, Marisa de Cássia Piccolo, Adriano Perin, Francirose Shigaki, and Otavio Augusto Queiroz dos Santos. (2020). PHYSICAL ATTRIBUTES, TOTAL CARBON AND 13C NATURAL ABUNDANCE IN FERRALSOL UNDER DIFFERENT AGRICULTURAL SYSTEMS. International Journal of Research -GRANTHAALAYAH, 8(5), 266276s. https://doi.org/10.29121/granthaalaya h.v8.i5.2020.205


INTRODUCTION
The no-tillage system (NTS), with its three basic principles -maintenance of vegetal residues on the surface, crop rotation (CR), and minimum soil turning -was proposed for the Cerrado as an alternative to conventional methods to minimize the impacts on the soil owing to different forms of use (Carvalho et al., 2010;Loss et al., 2016).
However, in the Brazilian Cerrado region, one of the basic principles of NTS, has been replaced by crop succession (CS), mainly due to the limited number of economic crops for the autumn/winter season (Carneiro et al., 2013;Fidelis et al., 2003).
Some previous studies have indicated that NTS with second crop "safrinha" soybean-corn succession (SCS), in some situations, provides inadequate and insufficient soil coverage (Carneiro et al., 2013;Ceccon et al., 2013;Maria and Gomes, 2012), with lower soil organic matter (SOM) content and consequently, higher bulk density and resistance to penetration when compared to NTS with Cerrado region (Franchini et al., 2011).
However, the soybean-millet succession (SMS) under NTS has yielded dry mass (straw) yields above the minimum required amount ( Previous studies have shown that crop-livestock integration (CLI) allied to NTS tends to increase organic matter and carbon stocks in the soil, sometimes even to match and/or exceed the values found in areas of native vegetation of the Cerrado and NTS without grazing (Gazolla et  There is a shortage of studies on the joint evaluation of areas with different types of NTS in the consolidation phase. More research is needed so that the efficiency of these management strategies in the long term can be verified, both in the carbon stock, as well as in the chemical and physical attributes of the soil. Thus, the objective of this study was to evaluate the bulk density (Bd), total pore volume (TPV), carbon stock (Csto) and natural abundance of 13 C in a Rhodic Ferralsol in NTS areas under different succession and rotation of cultures in the Cerrado of Goiás State, Brazil.

MATERIALS AND METHODS
Samples of soil were collected from two rural properties in the municipality of Montividiu, Goiás (17°27′5.2″S; 51°10′33.1″W; altitude 890 m). According to the classification of Köppen, the climate in the region is tropical wetdry (Aw), with two defined seasons, the rainy season (October to April) and the dry season (May to September). The average temperature is 22°C and average annual rainfall is 1740 mm. In the study area, the soils were classified as Rhodic Ferralsol according WRB (2014) and Latossolo Vermelho Distroférrico according Santos et al. (2013).
The PA of Urochloa decumbens had been cultivated with an approximate stocking rate of 1.5 animal units per hectare. The SCS area (17°08′59.8″S; 51°11′23.4″W; altitude 885 m) is located at Estreito Ponte de Pedra Farm, and was opened in 1981, with the removal of the native Cerrado, and for 16-years old it has been cultivated under NTS with soybean in the summer crop and "safrinha" corn. The SMS area (17°18′28.6″S; 51°15′21.8″W; altitude 853 m), is also located at the same farm and has a history of 33-years old of cultivation, with NTS adopted in 1998 after a conventional system (plowing and harrowing of soil) of soybean planting in the summer. This area was cultivated with NTS soybean in the summer and "safrinha" corn up to 2004, and since then has been cultivated with SMS.
The SCBS and SCMBCR areas are in Vargem Grande Farm, belonging to the Agropecuária Peeters (17°21′85.4″S; 51°28′59.9″W; altitude 859 m). The NTS area with SCBS was cultivated with soybean in the summer and "safrinha" corn interspersed with brachiaria for cattle. Finally, the SCMBCR area started to be used from 1975, with the removal of the native Cerrado and cultivation of pasture for 10 years. Subsequently, the conventional cultivation with soybean and corn was carried out for 10 years, and for 19 years it has been cultivated under NTS with SCMBCR. The sequence of this Brazilian Cerrado region showed small variations over the years, according to the financial viability for the adoption of each culture.
In view of the above, it is emphasized that all NTS areas evaluated are in the implantation phase considered as consolidation (10 to 20 years old).
The NTS areas with SCS, SMS, SCBS received liming in the years 2014, 2014, 2013, respectively, with surface application to the soil in the following amounts: 1300 to 2800 kg ha -1 (application with varied rate), 2000 kg ha -1 , 4000 kg ha -1 .
In each area, a representative plot of 2.25 ha (150 × 150 m) was demarcated, and five trenches of approximately 1 × 1 m at the surface and a depth of 0.60 m were randomly positioned in each of them. Undisturbed and disturbed samples soil were collected of each area (treatment), with five replicates per treatment. As this is not an experimental design experiment, sampling was performed according to statistical procedures for experimental design with randomization constraints ( The C contents were quantified by dry combustion by CHNS analyzer (Elementar Analysensysteme GmbH, Hanau, Germany). Based on the C contents and Bd, the Csto were calculated by the equivalent mass method (Sisti et al., 2004), as described below: Were: = total stock (Mg ha -1 ); = sum of carbon from the most superficial to the deepest layer of the soil profile evaluated in a specific experimental area (Mg ha -1 ); = sum of soil mass from the most superficial to the deepest layer of the soil profile investigated in a specific experimental area (Mg ha -1 ); = sum of soil mass from the most superficial to the deepest layer of the soil profile sampled as a reference treatment (Mg ha -1 ); = soil mass in the deepest layer of the soil profile assessed in a specific experimental area (Mg ha -1 ); = cqrbon level at the deepest layer of the soil profile studied in a specific experimental area (Mg C Mg -1 de solo).
The δ 13 C (‰) isotope analysis was done with the aid of the Finnigan Delta Plus mass spectrometer, at the Laboratory of Isotope Ecology (CENA-USP), Piracicaba, São Paulo. The results were expressed as delta 13 C (‰), in relation to the international standard PDB (Belemnitella Americana from the Pee Dee formation), were used to evaluate the contribution of the remaining carbon of the cerrado (C3 plants) and that introduced by pasture (plants C4) in each of the areas.
The areas (land use systems) evaluated were under the same topographic and edaphoclimatic conditions (relief, soil class and texture, temperature, and precipitation), differing only in vegetation cover, and land use. Thus, the results were evaluated as a completely randomized design with five replicates for each area and depth. The data normality and homogeneity were analyzed through the Lilliefors and Bartlet tests, respectively. Subsequently, the results were submitted to analysis of variance by the F test, and significant means were compared using the t-test at 5% probability, using the Assistat statistical software.

RESULTS AND DISCUSSIONS
In the PA, the lowest levels of C content (0.0-0.40 m) and Csto (0.0-0.20 m; 0.20-0.40 m) were verified in comparison to the other areas evaluated ( Figure 1 and Table 2). Such results occurred due to a set of factors, such as low productivity, absence of management (mainly maintenance fertilization) and intensive grazing. The history of the PA shows that it doesn't receive annual maintenance fertilization. Similar results were also reported by Guareschi   Means followed by the same lowercase letter between areas, in each depth, do not differ by t-test (p<0.05). PA = pasture area, SCS = soybean-corn succession, SMS = soybean-millet succession, SCBS = soybean-corn-brachiaria succession, SCMBCR = soybean-corn-millet-beans-cotton rotation According Loss et al. (2019), the higher contribution of plant residues recorded in NTS than in the pasture area can be related to better soil fertility conditions in the NTS (Table 1), which favors plant growth and subsequent input and surface accumulation. These authors too reported that high production of plant litter in the Cerrado area is attributed to greater climatic stability under the tree canopy and the absence of anthropogenic intervention. .58 a *Means followed by the same letter in the columns and in each depth do not differ significantly between the systems evaluated, by the t-test at 5% probability. PA = pasture area, SCS = soybean-corn succession, SMS = soybean-millet succession, SCBS = soybean-corn-brachiaria succession, SCMBCR = soybean-corn-millet-beans-cotton rotation The SCMBCR showed higher levels of C and Csto (0.0-0.05 m; 0.10-0.20 m) compared to the other cultivated areas (SCS, SMS, and SCBS) ( Figure 1 and Table 2). According to Franchini In general, the content of C (0.0-0.40 m) and Csto (0.0-0.20 m) was higher in the SCMBCR area than in the SCS and SMS areas ( Figure 1 and Table 2). Similar patterns were observed for the SCBS area in relation to SCS and SMS areas with respect to C content (0.05-0.10, 0.20-0.40 m) and Csto (0.05-0.20 m) ( Figure 1 and Table 2). This is thought to be owing to the larger number and variety of species cultivated in the SCMBCR and SCBS in relation to the successions evaluated. According to Campos et al. (2011) the entry of C into soil increases with the diversification of the cultivation system. Thus, the inclusion of species with an aggressive root system and the long-term entry of different types of crop residues into soils managed under NTS associated with native Cerrado increase the reserves of C with greater lability ( It is also worth mentioning the superiority, in some cases, of C contents (0.05-0.20 m) and Csto (0.05-0.40 m) of SCMBCR and SCBS areas compared to PA (Figure 1 and Table 2). This pattern indicates that such soil management practices are promoting a positive impact on soil quality, recovering soil C levels to the original growing conditions. Evaluated the total organic carbon (TOC) content in soil cultivated with onions in succession or rotation with other species (e.g., grasses, and, legumes) in NTS, Comin et al. (2018) reported that winter grasses in rotation with maize preceding onion crops in NTS increases TOC, and, higher TOC is found in areas with more soil cover plant species in rotation. The results found by Comin et al. (2018) indicated that the adopting soil management systems with conservationist bases that use permanent soil coverage and crop rotation can maintain or improve the SOM content, as well as observed in this study (Figure 1).
The density of particles (Pd) did not present statistical difference between the areas and depths analyzed (Table 3). This result is due to the areas presenting the same soil class and mineralogical composition of sand and clay fraction, constituted mainly by quartz and kaolinite, respectively (Gazolla et al., 2013).
In the 0.0-0.05 m layer, the area with SCMBCR presented a lower Bd value and higher TPV in relation to the other areas evaluated (Table 3). It can be affirmed that this result is due to the higher levels of C contents of SCMBCR compared to the other cultivated areas. This pattern occurs because NTS areas with native Cerrado present a continuous supply of organic material by the vegetal residues and/or root exudates, whose subproducts are constituted by organic molecules in several phases of decomposition, acting as an agent of formation and stabilization of the aggregates, providing better soil structuring, which can promote reduction in Bd and increase TPV or TP (Franchini et al., 2011;Laurindo, 2009).
In the 0.05-0.10 m layer, the lowest values of Bd and highest TPV values of the areas SCMBCR and SCBS in relation to the PA (Table 3) stood out. As previously discussed, these results are related to the higher C content in these areas than that in PA, as well as being due to the low productivity of the grass associated with the animal trampling effect evident in the area, which possibly compacted the soil (Gazolla et al., 2013).
At other depths (0.10-0.40 m) the managed systems presented Bd and TPV similar to each other ( Table  3). These areas present, up to 0.40 m depth, Bd below the "critical limit of 1.30 to 1.40 for clayey soil," which is harmful to the development of the roots (Reichert et al., 2003). Thus, it can be inferred that the Bd of the studied soils does not adversely affect the development of cultivated crops in the areas. The results of natural abundance of 13 C (‰) in the soil profile showed that the PA presented greater contribution of plant residues from C4 plants in all depths examined (Figure 2). This result is consistent, considering that this area has received input of plant residues from grazing for many years. Based on the literature, C3 plants have 13   Means followed by the same lowercase letter between areas, in each depth, do not differ by t-test (p<0.05). PA = pasture area, SCS = soybean-corn succession, SMS = soybean-millet succession, SCBS = soybean-corn-brachiaria succession, SCMBCR = soybean-corn-millet-beans-cotton rotation.
Among NTS areas, it is observed that, up to 0.40 m from the soil surface, the 13 C (‰) signal decreases as compared to that in the PA-that is, the signal approaches the average values established for C3 plants (between -33 and -22 ‰), especially in the area with SCMBCR ( Figure 2). This transitory effect may be occurring because, in these areas, organic matter has a greater contribution of vegetal residues derived mainly from C3 plants, such as soybean, beans, and cotton in SCMBCR area and soybean in the other NTS areas evaluated (Guareschi et al., 2014).
In the NTS without native Cerrado (SCS, SMS and SCBS), the isotopic signature of the C3 and C4 vegetation mixture was closer to the C4 (PA) vegetation signal (Figure 2). This is due to the lower supply of C3 plants in these systems when compared to SCMBCR, as well as the greater contribution of grasses (corn, millet and brachiaria) to the maintenance of these values. Siqueira evaluating a chronosequence of NTS areas in the Cerrado, also showed that the isotopic signature was closer to the C4 vegetation signal, presumably due to greater contribution of cereal crop residues. Studies carried out with the 13 C technique in the native Cerrado region in Goias, indicate that the isotopic variation found in the 0.0 to 0.40 m depth was predominantly from C3 plants, with values ranging from -27 to -24 ‰ (Loss et al., 2012a, 2019; Guareschi et al., 2014). Therefore, in areas in NTS, which have been native Cerrado in the past, the isotopic sign found indicates a significant contribution of C derived from C4 plants, such as corn (SCS), millet (SMS), corn + brachiaria (SCBS) and corn + millet (SCMBCR). Thus, part of the carbon content and stocks found ( Figure 1 and Table 2) are derived from the current vegetation.

CONCLUSIONS
The no-tillage system with soybean-corn-millet-beans-cotton crop rotation followed by no-tillage system with soybean-corn-brachiaria succession were those that presented greater potential for carbon stock increase and total soil pore volume, as well as bulk density reduction.
The origin of the soil organic matter in the no-tillage system areas is related to plants employing the C4 photosynthetic cycle; however, for mixed C3 and C4 plant systems, the isotopic signature of 13C is reduced, mainly in areas with crop rotation.

SOURCES OF FUNDING
None.

CONFLICT OF INTEREST
None.

ACKNOWLEDGMENT
To Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) -Finance Code 001.