ABSTRACT
The objective was to verify the influence of winter crops under management mechanical (roller knife) and chemical (glyphosate), on soil physical properties and yield of soybeans. The experiment was carried out at the field under randomized block design in tracks scheme. The treatments consisted of four different winter crops (oats IPR 126, wheat BRS Tarumãt crambe FMS Bright and forage radish cultivar common) in tracks A and management different (chemical and mechanical) in bands B. The soil properties (macroporosity, microporosity, total porosity and density) were determined by collecting soil core in layers 0-10 and 10-20 cm depth, penetration resistance was determined with the aid of a penetrometer impact to a depth of 30 cm. The soybean harvest was held on 03/12/13, collecting two lines of the floor area of each plot. The evaluations were carried out after the winter crop management and post-harvest of soybeans. There was no significant difference in the interaction of the factors to the values of the porosity in the layer 0-10 cm of soil. As to the values obtained for the penetration resistance of the soil, it was found that the oat (0.91 MPa) and crambe (1.43 MPa) provided significant differences in the layer 0-5 cm depth, after the cycle of winter crops. Winter crops and different managements not affect soybean yield.
Key words: Plantation direct, compaction, conservation systems, soil structure.
The adoption of technologies based on conservationists foundations as the tillage and the use of winter crops are alternatives to increase the sustainability of agricultural systems (Torres et al., 2014; Boer et al., 2007).
The success of the system lies in the fact that the straws accumulated by cover crops and crop residues
from commercial fields create favorable environments for the recovery and the maintenance of the quality of soil and water (Kliemann et al., 2006), beyond allowing favorable conditions for crop development and effective erosion control (Brancalião and Moraes, 2008) Because of the enormous benefits for soil biodiversity, this technology has expanded to various regions of the world, especially in countries such as Argentina, Brazil, Paraguay and Uruguay, which adopt this system in about 70% of the total cultivated area (Derpsch et al., 2010).
In general, the soil when in its natural state, under vegetation present physical characteristics as permeability, structure, soil density and pore space, agronomically desirable. However, as the soils are being worked (Andreolla et al., 2000) and the continuous adoption of soil management systems conventional, considerable physical changes are occurring (Silva et al., 2008).
The structure of the soil is one of the most important properties for the adaptation of the species, and it is by means of physical properties that can be done their monitoring, such as soil bulk density, microporosity, aggregate stability, resistance of soil, permeability, among others. These properties can indicate overgrowth, crusting, susceptibility to productivity loss, environmental degradation and mainly compression (Laurindo et al., 2009).
The process of soil compaction, to increase its density and its mechanical resistance to penetration (PR), as well as to reduce the volume of macropores, the capacity of water infiltration, the aeration and hydraulic conductivity affects the root development, resulting in reduction of crop productivity (Beutler et al., 2005).
For decompressing the ground the use of species of winter crops, especially with the use of crop rotation in species with root system quite aggressive, it is necessary, since this practice protects the soil against erosion, brings benefits to fertility and soil structure due to the elevation of the organic matter content, and improves the thermal amplitude of soil maintaining its moisture, enabling better performance of succeeding crops (Amossé et al., 2013).
According to Campiglia et al. (2010), the benefits of winter crops may still be supplemented, as the maintenance of high rates of infiltration of water through the combined effect of the root system and vegetation cover and promote large and continuous inflow of vegetal mass on the ground.
Among the winter crops that deliver these benefits may be indicated the crambe (Crambe abyssinica Hochst) considered a rustic plant widely used as fodder in crop rotation and soil cover (Varisco and Simonetti, 2012), the radish (Raphanus sativus L.) that in addition to favoring the inflow of organic matter to the soil has adverse allelochemicals reducing the infestation of weeds (Martins et al., 2016) and oats can also be indicated how to plant cover crops, all these cultures have great development in the southern region of Brazil.
Although there are already research related to direct planting in Paraná State is important to test this factor associated with winter cover and handlings checking and monitoring the physical properties of the soil (macroporosity, microporosity, total porosity and density) under the effects of white oat cultivation IPR 126, crambe, oilseed radish and wheat double purpose BRS Tarumã, in function of mechanical and chemical handlings succeeded by the soybean crop.
The study was conducted at the Experimental Farm "Professor Antonio Carlos dos Santos Person " (latitude 24º 33 ' 22' ' S and longitude 54º 03' 24 ' ' W , with an altitude of approximately 400 m ) at the Universidade Estadual do Oeste do Paraná - Campus Marechal Cândido Rondon in Eutrophic Red Latosol (LVe) (Embrapa, 2013). The intercropping antecedents in the area constituted in no-tillage system. In the Table 1 is described the chemical and physical characteristics of the area before the experiment. Due to the low of V% (percentage of saturation of bases) liming was performed 30 days before sowing at a dosage of 2 Mg ha -1 (large 80 %) to raise it to 70%.
The area of conducting of the experiment has a history in which for a period of four years, traditionally, the winter corn were grown (for silage production) in the off season and soybeans in the summer crop. These crops were always performed under the no-tillage system.
The local climate, classified according to Koppen, is Cfa, subtropical humid mesothermal dry winter with rainfall well distributed throughout the year and hot summers. The average temperatures of the quarter more cold vary between 17 and 18°C, the quarter more hot between 28 and 29°C, in its turn, the annual temperature ranged between 22 and 23°C. The total average annual precipitation normal pluvial for the region vary from 1600 to 1800 mm. with quarter more humid presenting totals between 400 to 500 mm (IAPAR, 2006). The climate data of the experimental period were obtained in automatic climatological station of the University of Paraná, distant approximately 100 m of the experimental area and are presented in Figure 2.
The experiment was started in autumn-winter of 2012 and the area has been desiccated 30 days before sowing, using glyphosate-isopropylamine salt in the dose of 3.0 L ha-1 with a volume of 250 L ha-1.
The experimental design used was randomized blocks in schematic of tracks, with three repetitions. On tracks A (5 x 40 m), four winter crops were allocated (IPR 126 oats, crambe Bright FMS, forage radish cultivate common wheat and BRS Tarumã). In ranges B (20 × 23 m), were allocated the managements of winter crops (chemist with isopropylamine and mechanical glyphosate -salt using knife roll). The plots were formed by a combination of bands A and B (5 × 20 m), each block had an area of ​​920 m² (23 × 40 m). During the development of the cultures was not performed any application of the herbicide. Winter crops were sown in the day 19/04/12, with drill seeder, coupled to the tractor on direct sowing system on maize straw. 60 kg ha-1 of oats` seed, 15 kg ha-1 of crambe` seed, 15 kg ha-1 of radish` seeds of and 90 kg ha-1 of wheat` seeds, with 0.17 m between lines were used. The fertilizer for growing oats, f. radish, fodder wheat and radish, was performed according to CQFS -SC (2004). For the correction of soil fertility 200 kgha-1 a formulated 8-20-20 (N, P2O5 and K2O, respectively) were used. The fertilization in coverage was carried out using 90 kg ha-1 of N as urea.
The values of resistance to penetration in the layer from 0 to 35 cm, before installation of the treatments are presented in Figure 1.
The treatment was performed 90 days after sowing, being the mechanic performed with knife roll and chemical with the application of the herbicide glyphosate-isopropylamine salt 480 g L-1 in the dose of 3.0 L ha-1, with a volume of 250 L ha-1.
After 30 days of culture management, the first collection was held for determination of properties physical properties. The density values (Ds-kg dm-3) were evaluated by the method of volumetric ring (Blake, 1965) and the macroporosity (S-cm3 cm-3), from the relationship S = a - q, where the (cm3 cm-3) is the total porosity, calculated by the ratio a =1-(Ds/Dr), where Dr (kg dm-3) is the real density and q (cm3 cm-3) is the water content in soil volume when subjected to a matric potential of -60 cm water column (Vomocil, 1965).
Sowing of soybean using the soybean cultivar BMX Potencia RR was held on 22/11/12. The area was previously desiccated using glyphosate-isopropylamine salt in the dose of 3.0 L ha-1 with a volume of 250 L ha-1. For the base fertilization was used 347 kg ha-1 of a commercial formulated 2-20-20 (N, P2O5 and K2O), being performed on the basis of chemical analysis of the soil (SFREDO, 2008). The seeds were treated with fungicide Carbendazim (150 g L-1) + Tiran (350 g L-1) 2 ml kg-1 of seed, insecticide Fipronil (250 g L-1) 0.8 ml kg of seed-1 and inoculated with Bradyrhizobium. The spacing, as well as the density of sowing, were carried out in accordance with the recommendation for the cultivar (BRASMAX, 2012).
For the sowing was used a seeder fertilizer coupled to a tractor, with the seeds deposited at a depth of average of 4 cm. During the crop development cycle fungicide applications were performed (triazole) at a dose of 0.65 L ha- 1 with spray volume of 250 L ha- 1 and (estrobilurina + triazol) in the dose of 0.30 L ha-1 with volume of 250 L ha-1 of commercial product. The soybean harvest was performed on 03/12/13, collecting two lines of the useful area of each plot, which totaled 0.90 m² with this were estimated the quantity produced per hectare. For the determination of the weight of one thousand seeds and yield of soybean was realized the trail of the material with trailed crop beater. After the trail was determined the thousand seed weight according to Brazil (1992), and productivity (kg ha-1), with discounts of impurity and moisture.
To 15 days after soybean harvest volumetric rings were collected for the determination of soil physical parameters as well as, performed the determinations of soil resistance to penetration. The determination of resistance to penetration and other physical properties of the soil was performed according to Embrapa (1997). The determination of soil resistance to penetration was performed with the use of an impact penetrometer model Stolf, with needle tip cone thin (60°), at three points in each plot. To minimize differences in soil moisture between treatments and between the depths, evaluation was performed three days after a precipitation, with humidity next of field capacity. The points were taken randomly, up to 30 cm of depth, and the data obtained in the field in the unit of impacts/decimeter processed in MPa, using the equation described by Stolf (1991).
The data obtained were submitted to statistical analysis using the SISVAR program (Ferreira, 2011), and the averages compared by the Tukey test at 5% level of probability.
There was no difference (p>0.05) for average values of macroporosity, total porosity, microporosity and bulk density in the layer of 0 - 10 and 10 - 20 cm, on the basis of the factors studied after the managements of cover plants (Table 2). With regard to the results obtained after the harvesting of the soybean crop was found significance between the factors, for the values of macroporosity in the superficial layer of 0 - 10 cm of soil (Table 3). For the other physical characteristics of the soil (microporosity, total porosity and density) average values obtained were similar, not showing influences suffered by the treatments applied. There being thus possible to differentiate the most effective species, as well as more efficient management systems, improvement of soil physical properties.
It was expected that the different winter crops involve changes in the physical characteristics of the soil, because the root system of crops requires an adequate supply of oxygen to maintain its physiological operation once that, its roots perform gaseous exchanges through a system porous that must also ensure an adequate supply of nutrients and water (Torres and Saraiva, 1999). However the results obtained are similar to those found by Sanchez (2012), that evaluated the influence in the physical properties of the soil by the winter crops observed that the use of these plants, in its first cycle of cultivation, not promoted changes in soil bulk density, microporosity, total porosity, however, in the layer from 0.10 to 0.20 m were verified larger values of macroporosity in treatments of oat and ryegrass.
The values found (Table 3) demonstrate that there was little variation between the results. These results corroborate with the study conducted by Bertol et al. (2004), in which the authors have not observed variation in the physical properties of the soil by the use of different cultivation systems, understood as rotation and succession with cultures of coverage in a production cycle, concluding that it would be necessary to carry out experiments for longer period of time to be able to check the results of the action of the plants on the physical properties of the soil.
Macroporosity
The values of macroporosity values obtained on the Layer 0 - 10 cm after completion of the managements of winter crops showed no significant difference between the treatments and the same occurred in the layer of 10 - 20 cm (Table 4).
For the found values of macroporosity after soybean harvest, the cultures that stood out were the forage radish in camanda of 0 - 10 cm (0.07 m3m-3) in the mechanical handling and the crambe in this same layer with the use of chemical management (0.07 m3 m-3). These same cultures showed higher values (0.09 m3m-3) also in the layer of 10 - 20 cm (Table 5). It is believed that regarding the macroporosity wheat presented higher results, because it is long cycle and with the mechanical handling may have suffered a stimulus for regrowth and rooting.
Considering the optimal values ​​for the full development of plants, ranging from 0.07 to 0.17 m3 m-3 (Drewry et al., 2003), in all layers, macroporosity values ​​(Tables 4 and 5) found in this study (average of 0.06 m3 dm-3) are considered low which increases the risk of deficit of O2 in the roots and reduces the continuity of pores and the permeability of soil (Lanzanova et al., 2007). The reduction of macroporosity in agricultural production systems tend to reflect negatively, reducing the total porosity and increasing soil density (Reichert et al., 2003).
The lower volume of macropores, with consequent greater volume of pores on the surface of the soil under no-tillage, can reduce the rate of water infiltration in this system of management, in relation to conventional tillage
(Bertol et al., 2004).
Microporosity
With relation to the microporosity, in general there was no significant difference (p>0.05), as well as the different managements also did not influence the results. In the mechanical control values were established with an average of 0.43 m3m-3, and the chemical management with an average of 0.44 m3 m- 3 in the layer 0 - 10 cm in the evaluation performed after the handling of the cultures. The same occurred for the layer of 10 - 20 cm of this same evaluation in which the average remained at 0.42 m3 m-3, for both the mechanical management as for the chemical management, not differentiating among cultures (Table 4). For the evaluation performed after soybean harvest, the layer 0 - 10 and 10 - 20 cm, the values showed no differences. The cultures with larger sized were the crops of oats (0.46 m3 m-3) and wheat (0.46 m3 m-3) in the chemical management in the layer of 0 - 10 cm. In the layer 10 - 20 cm excelled the culture of oats in mechanical handling and cultures of crambe and wheat in chemical management with the average of 0.44 m3 m-3 for each of these cultures (Table 5).
It can be inferred that the ideal soil is the one with values of 0.10 to 0.16 m3m-3 for macroporosity, up to 0.33 m3m-3 for microporosity and approximately 0.50 m3m-3 for total soil porosity (Kieh, 1979). Thus, the values of microporosity in this work, in practically all layers studied, are above the ideal conditions. The volume of micropores that are relatively high, present in all the treatments studied indicates the possibility of occurrence of capillarity in soil (Bertol et al., 2004). The microporosity is related to the water storage in the soil, influencing the development of plants especially in critical water availability times (Veiga, 2005). This factor has acted as a supply in the early establishment of winter crops, since this development time of the occurrence of precipitation was reduced over the subsequent months, as can be seen in Figure 2. Bertol et al. (2004) found a greater microporosity under no-tillage compared to conventional soil pre-paration, at layer 0 to 10 cm.
For Albuquerque, Ender and Sangoi (2001), the increase of the microporosity can be considered a reflection of the reduction of structure and assigned to the reduction in the volume of macropore, that makes harmful to the development of the plants. Similar results were obtained by Silva et al. (2008), evaluating soil management systems in crop succession and its influence on soil physical properties, they found that microporosity was not affected, regardless of the studied layer.
Total porosity
As there was no difference in the values of macroporosity and microporosity, total porosity was not affected (Table 4). Changes in soil porosity limit nutrient absorption, infiltration and redistribution of water, gas exchange and root development (Bicki and Siemens, 1991).
Whereas the ideal soil should be roughly 0.50 m3m-3 for total soil porosity (Kiehl, 1979), the results found for this factor are considered ideal or very close to the ideal. In the evaluation performed after the management, the average of the different cultures in the layer 0 - 10 cm consisted of 0.51 m3m-3 for mechanical handling and chemical management obtained an average of 0.52 m3m-3. In the layer of 10 - 20 cm the averages of winter crops were of 0.50 m3m-3 when used the mechanical handling and 0.49 m3m-3 when used chemical management (Table 4).
For the evaluation performed after the soybean harvest, the total porosity values established on the average of 0.51 m3m-3 in the 0-10 cm both in mechanical handling and for chemical management. In the layer of 10 - 20 cm values were of 0.50 m3m-3 and 0.49 m3m-3 for the managements mechanical and chemical respectively (Table 5). These results are similar to those obtained by Sanchez (2012), that by checking the physical properties of the soil and yield of soybean in succession to winter crops have been obtained in the layer of 0 - 10 cm of soil, results show that the treatments showed no significant differences in porosity with medium that varied between 0.61 and 0.69 m3m-3, having a cycle of winter cover crops, until the moment of its flowering, not producing any change in this property.
Soil density
The values of density obtained for both layer of 0 - 10 cm as to layer of 10 - 20 cm showed no significant difference between the treatments. For the evaluation performed after the crop management mean values ​​were 1.19 Mg m-3 and 1.20 Mg m-3 for the mechanical and chemical handlings respectively in the 0 - 10 cm. And in the layer of 10 - 20 cm the averages were of 1.27 Mg m-3 for the mechanical handling and 1.28 Mg m-3 for the chemical management (Table 4). The same occurred in the evaluation carried out after soybean harvest, there was no difference for soil density (Table 5), in both managements and in different cultures, with an average of 1.27 Mg m-3 for the depth of 0 - 10 cm and 1.32 Mg m-3 for the layer of 10 - 20 cm.
The density values ​​for all treatments are well below critical levels. For Reinert and Reichert (2001), the values considered ideal for the development of the cultures are approximately 1.45 Mg m-3 for clay soils. Reinert et al. (2008) in studies with different species of coverage of winter in Clayey found that the root growth was normal until the limit of density of 1.75 Mg m-3. Soils with high density cause restrictions on root growth of crops being that the root system focuses near the surface (Seidel et al., 2009). However, Argenton et al. (2005) found that in Rhodic Oxisol, the deficiency of aeration begins with soil density close to 1.30 Mg m-3, while Klein (2006), for the same soil class based on limiting water range, noted that the limiting density was 1.33 Mg m-3. In compacted soil, the number of macropores is reduced, the micropores are larger amount and density is also higher (Jimenez et al., 2008).
Resistance to penetration
There was a significant effect (p<0.05) of culture on the resistance to penetration in the layer of 0 - 5 cm depth, after the harvest of winter crops (Table 6). In this layer, the values obtained for the soil penetration resistance, demonstrate that the oat and crambe showed significant differences, offering modifications to the ground in this property, with values of 0.91 and 1.43 Mpa respectively after the harvesting of the crops of winter. This positive effect of oat, in decreasing soil resistance, was also ratified by Neiro et al. (2003), that evaluated the soil resistance to penetration in a Oxisol, with rotation and succession of crop under no-tillage verified that the treatment with crop rotation (wheat/oat/corn/soybean) presented lower values of resistance to penetration in the layer of 15 to 20 cm. This result obtained for oats, probably due to the positive effect of the root system of culture of oats, which acts by conducting biological soil scarification, reducing soil compaction in this treatment.
It is important to stand out that crambe has taproot system being eficiente in the unpacking to deeper layers of the soil, however these roots that have large diameter provide greater constrain to development and penetration in compacted soil. Already the oats is a plant with dense and branched roots type that shows efficient penetration and decompression of the upper layers of the soil, thus justifying the results obtained in this research.
According to the USDA (1993), the value considered as limiting factor and causing strong restriction to root growth for many annual crops is 2.0 Mpa, but can vary according to the texture and organic matter content of the soil. De Maria et al. (1999), studied soil preparation systems (heavy harrow and direct seeding) and concluded that there was soil compaction between 10 and 35 cm (2.09 and 1.86 MPa) and 10 and 20 cm (2.52 MPa) respectively, evaluated through the resistance of soil (Figure 3).
Genro Junior et al. (2004) found the resistance to penetration in a clayey Oxisol under no tillage with crop rotation, a great temporal variation and was associated with the variation of soil moisture for each condition of soil density or state of compaction. In this same evaluation the authors obtained the largest state of soil compaction at layer around 10 cm depth and the lowest in the superficial layer, up to 7 cm. Beutler and Centurion (Table 7), it was found that there was no significant difference between the results, that is, the different cultures of winter and the different managements not influenced in the weight of a thousand grains of soybean, that is, as there was no change to the physical soil, also did not change the absorption of water and nutrients and did not affect soybean.
In the studied conditions was found the interaction between the factors (crops × managements) modifies the macroporosity in camanda of 0 - 10 cm after the harvest of the soybean. The use of cover crops plants in winter with chemical or mechanical handlings and soybean cultivation in succession does not alter the macroporosity, microporosity, total porosity and density, but the oats decreases the resistance to penetration. The soybean yield is not affected by the cultivation of cover plants and managements of winter.
The authors have not declared any conflict of interests.
The work receives financial support from the Higher Education Personnel Improvement Coordination - CAPES Brazil.
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