Structuring potential of some cover crops and crambe in Haplortox under no-tillage system

Structuring potential of some cover crops and crambe in Haplortox under no-tillage system Luciene Kazue Tokura*, Deonir Secco, Luiz Antônio Zanão Júnior, Jair Antonio Cruz Siqueira, Reginaldo Ferreira Santos, Marcos Felipe Leal Martins, Alessandra Mayumi Tokura Alovisi, Luiz Carlos de Oliveira, Ronaldo Hissayuki Hojo, Natália Pereira, Maurício Antônio Pilatti, Macarius Cesar Di Lauro Moreira, Bruna de Villa and Marta Juliana Schmatz

An experiment was conducted at the Agronomic Institute of Paraná -IAPAR, at the Experimental Station of the municipality of Santa Tereza do Oeste -PR, in Hapludox of clayey soil.Studies with the use of plants cover crops with vigorous root system in different systems of soil management systems are needed, in order to have a diversity of species capable of producing different amounts of crop residues which by decomposing, can alter the physical attributes and consequently, the productivity of the successor culture.The objective of this study was to evaluate the effect of crambe crop and plant cover crops in succession on the physical characteristics of a Haplortox under no-tillage system.The experimental area has been cultivated under no-tillage system for 18 years.The experimental area consisted of 15 plots, each plot with 20x25 m.In 12 plots, plant cover crops were planted, six species of summer and six of winter and the last three consisted of plots with no-tillage system with gypsum application, no-tillage system with scarification and traditional no-tillage (control) in a completely randomized design.The physical attributes of this soil were soil density (DS), total porosity (PT), microporosity (Micro), macroporosity (Macro) and saturated hydraulic conductivity (Ksat) of the soil in the periods of 2014 (initial characterization of the soil) and 2015 (after crambe culture).The microporosity (0.0-0.1 m layer) and Ksat (all soil layers) presented significant differences between treatments in the period of 2015.Microporosity was lower in the pigeon pea coverage (PP) (36.08%), while the largest occurred in the coverage of crambe C5 (45.38%).The Ksat was higher in the dwarf pigeon pea (DPP) (298.20 mm h

INTRODUCTION
In no-tillage, the maintenance of vegetation cover and residues on the soil surface provide a continuous supply of organic residues and can occur for improvement of some soil physical properties, such as aggregation, infiltration, permeability, among others (Bertol et al., 2004).Knowledge of decomposition of plant residues and release of nutrients is essential for no-tillage system (Canova et al., 2015).Among the soil physical properties, the soil structure can be regarded as the most important under the agricultural point of view, because fundamental conditioning attributes are assigned to the soil-plant relationships (Torres et al., 2013).
Thus, when the areas in no-tillage system are handled improperly (no crop rotation, but a succession of soybeans/corn with the movement of the soil surface or even insufficient soil cover), they provide negative changes in soil physical properties due to compression.One of the measures taken to break these layers is the practice of scarification (Gabriel Filho et al., 2000;Spoor, 2006;Jin et al., 2007), although this process breaks the compacted layers, it makes the soil susceptible to the new compressions (Tormena et al., 2002;Botta et al., 2006), since the benefits of this practice has shown short duration in the physical characteristics of the soil, with a tendency to return to its original condition in a short time (Busscher et al., 2002).
The introduction of plant cover crops with root traits that can grow in soils with high strength has been an alternative that can promote the decompressing of the soil and potential to improve the structural quality, even helping in the cycling of nutrients leached in depth.In addition, the use of cover crops aims to protect the soil against erosion, maintain greater amount of organic matter in the soil and relieve the effects of compression by leaving stable biopores where the roots of succeeding crops can use these to grow deeper (Botta et al., 2004;Hamza;Anderson, 2005;Oliveira et al., 2011;Crusciol et al., 2012;Ferrari Neto et al., 2012;Nascente and Crusciol, 2012).
Another cover that has attracted attention is the crambe culture (Crambe abyssinica Hochst), which also has a root system that can reach depths greater than 15 cm (Carlsson et al., 2007) and can be used as a winter crop and it is an alternative to the crop rotation.Oplinger et al. (1991) reported that under stress conditions, plants develop long roots, which later become conical.Crambe is an oleaginous belonging to the family of cruciferous vegetables, the same of rapeseed and canola.Originating in the hot, dry region of Ethiopia, the crambe was domesticated in the cold, dry zone of the Mediterranean.Due to its origins, it tolerates drought and cold, and is suitable for autumn/winter plantations in Brazil.
In Brazil, researches on the crambe were first carried out by the MS Foundation, to evaluate the culture of behavior as ground cover in no-tillage system.Culture has short annual cycle, from 85 to 90 days, drought tolerance, good grain production from 1000 to 1500 kg ha -1 and up to 38% oil content (PITOL, 2008).According to Feroldi et al. (2012), culture can be an alternative to be cultivated after soybean harvest, in the period of March and April.
Studies with the use of plants cover crops with vigorous root system in different systems of soil management systems are needed, in order to have a diversity of species capable of producing different amounts of crop residues that by decomposing alter the physical attributes and consequently increasing the crop yield.Thus, the aim of this study was to assess the impact of ground cover species, management system and crambe cultivation on soil structure.
Before the experiment, soil samples were collected for the initial physical characterization, in the layers of 0.0-0.1,0.1-0.2 and 0.2-0.3m (Tables 2, 3 and 4) in year 2014.The chemical samples were collected in triplicates in layers of 0.00 to 0.20 m (Table 1).The experimental area is being cultivated in no-tillage system for 18 *Corresponding author.E-mail: lucienetokura@gmail.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License   --------------- The conduction of the experiment began in March 2014 with the implementation of six species of summer vegetation and six of winter, followed by soybean (2014/2015 harvest).The last application of liming in the area was held in 2011 with 3 ton ha -1 of limestone (PRNT 85%) (Souza et al., 2005).
The experimental area consisted of 15 plots, in a completely Table 2. Average values of soil density (DS), total porosity (PT), microporosity (Micro), macroporosity (Macro) and hydraulic conductivity of saturated soil (Ksat) with the incorporation of summer plant cover crops and crambe culture and in three management systems, in the soil layer of 0-0.1m (average of four replications) in the initial characterization (2014) of soil and after handling of crambe (2015).Averages followed by the same capital letters on the line and lower case in the column do not differ by Tukey test at 5% significance.PM = pearl millet; DPP = dwarf pigeon pea; SH = sunn hemp; PP = pigeon pea; R = rattlebox; VB = velvet bean; C1 = black oat; C2 = common Oat; C3 = Cereal Rye; C4 = black oat + cultivated radish; C5 = black oat + white lupine; C6 = black oat + garden pea; C7 = SNTS: Scarified no-tillage system; C8 = GNTS: Gypsum no-tillage system; C9 = NTTS: No-tillage traditional system (control).

Soil
randomized experimental design.In 12 plots were implanted plants cover crops (six of winter and six of summer) and in three plots with different management systems (gypsum no-tillage, scarified notillage and traditional no-tillage, the latter used as control).The plots cultivated with summer cover crops were pearl millet (PM), dwarf pigeon pea IAPAR 43-Aratã (DPP), sunn hemp (SH), pigeon pea (PP), rattlebox (R) and velvet bean (VB), and the other six species of winter vegetation cover were: white oat UPFA Gaudéria, black oat Cabocla IPR.cereal rye IPR 89, black oat + cultivated radish IPR 116 association, black oat + white lupine association and black oat + garden pea IAPAR 83 association (the choice was based on soil cover species with good root development, use by some producers and more adapted to the region).The gypsum no-tillage system consisted of an application of 3 t ha -1 of gypsum in the surface (the gypsum was applied to evaluate its effect on the root system of plants); the scarified no-tillage suffered a scarification up to 0.3 m deep.Each plot had an area of 500 m 2 (20 x 25 m), as shown in Figure 2. Before the implementation of species of vegetation cover, the area was dried out with application of glyphosate herbicide in the dosage of 3.5 L ha -1 .The summer cover crops and crambe crop were deployed in March 31, 2015.The crambe was grown in 9 plots (consisting of 6 winter covers portions of the previous year and 3 with management systems).Summer covers were sown with pearl millet (15 kg ha -1 ), sunn hemp (25 kg ha -1 ), rattlebox (15 kg ha -1 ), both with spacing of 0.17 m, dwarf pigeon pea (30 kg ha -1 ), pigeon pea (50 kg ha -1 ), with spacing of 0.34 m and velvet bean (70 kg ha -1 ), with spacing of 0.45 m, using a New Holland tractor model TT3840 equipped with seeder with nine lines of Metasa Kuhn PDM PG 900 brand without fertilization.The plots with crambe were seeded with 12 kg ha -1 (FMS hybrid bright) using seeder-fertilizer with six lines of Metasa Kuhn brand with spacing of 0.34 m and seeding density of 40 seeds per meter without fertilization.The species desiccation of the summer cover crop occurred in flowering time with original roundup application (4 L ha -1 ).Subsequently, Triton was used for plant residues to be evenly distributed in the area.
The mechanical handling system was conducted in the plot to 0.30 m deep at October 20, 2014 through scarification, using a New Holland tractor TL85 EXITUS model equipped with Kohler scarifier of five adjustable rods with 0.50 m spacing, cutting blade, depth limiter and harrowing roller.Cultural practices for the control of weeds, pests and diseases were carried out in the experimental area according to technical recommendations for crambe culture using a tractor/hydraulic sprayer set with a capacity of 600 L and 14 m-spray bar in order not to have interference of the weed community on the crambe development and productivity.Historical data of rainfall and average temperature for the region of Santa Tereza do Oeste -PR, in addition to the monthly average rainfall, minimum, maximum and average temperature for the study period are presented in Figure 3.
Undisturbed soil samples were collected after the crambe management on October 08, 2015, to determine the physical attributes of the soil at depths of 0.0-0.1 0.1-0.2 and 0.2-0.3m with the aid of steel rings with known volume and four replications in Table 3.Average values of soil density (DS), total porosity (PT), microporosity (Micro), macroporosity (Macro) and hydraulic conductivity of saturated soil (Ksat) with the incorporation of summer plant cover crops and crambe culture and in three management systems, in the soil layer of 0.1-0.2m(average of four replications) in the initial characterization (2014) of soil and after handling of crambe (2015).Averages followed by the same capital letters on the line and lower case in the column do not differ by Tukey test at 5% significance.PM = pearl millet; DPP = dwarf pigeon pea; SH = sunn hemp; PP = pigeon pea; R = rattlebox; VB = velvet bean; C1 = black oat; C2 = common Oat; C3 = Cereal Rye; C4 = black oat + cultivated radish; C5 = black oat + white lupine; C6 = black oat + garden pea; C7 = SNTS: Scarified no-tillage system; C8 = GNTS: Gypsum no-tillage system; C9 = NTTS: No-tillage traditional system (control).

Soil
each layer.It was determined, the density of the soil (DS) by the volumetric ring method; total porosity (PT) by the percentage of soil water saturation; microporosity (Micro) (EMBRAPA, 1997), macroporosity (Macro) by sand column (Reinert and Reichert, 2006) and hydraulic conductivity of saturated soil (Ksat) (EMBRAPA, 1997).
Statistical analysis was performed for data collection using System for Analysis of Variance -SISVAR ® (Ferreira, 2010) software.Average variables were compared by Tukey test at 5% probability.

RESULTS AND DISCUSSION
Tables 2, 3 and 4 shows the values of soil density (Mg m -3 ), total porosity (%), microporosity (%), macroporosity (%) and hydraulic conductivity of saturated soil (mm h -1 ) in the treatments of summer plant cover crop and the crambe culture and in the management systems: SNTS: Notillage system with soil scarification; GNTS: Notillage system with application of 3 t ha -1 gypsum; NTTS: No-tillage traditional system (control) in the initial characterization (2014) of soil and after handling of crambe (2015) in soil layer of 0.0-0.1;Table 4. Average values of soil density (DS), total porosity (PT), microporosity (Micro), macroporosity (Macro) and hydraulic conductivity of saturated soil (Ksat) with the incorporation of summer plant cover crops and crambe culture and in three management systems, in the soil layer of 0.2-0.3m (average of four replications) in the initial characterization (2014) of soil and after handling of crambe (2015).
0.01-0.02and 0.02-0.03m, respectively.There was a significant interaction between the periods (results obtained in the initial soil characterization and after management of crambe) and management systems at the surface layer of 0.0-0.1 m (Table 2), for all physical parameters evaluated, and in the culture crambe the differences were more significant.Between periods, the lowest ; 61.2%), respectively in the period of 2014.For this same soil layer, there was significant difference between the coverage in the 2014 period, for the DS and PT.
In 2015, the average values of DS (1.07 and 1.14 Mg m -3 for crambe C3 and C9-NTTS) were higher than the previous year.In the same period, there was no difference for the DS, PT and Macro between the vegetation cover.The other parameters (Micro and Ksat) were significant.Any significant differences were merely random.Regardless of soil density, the presence of biopores, soil structure faults, and capillary discontinuity provided by the sample are sufficient parameters to alter the values.
In the period of 2015, significant differences between treatments occurred for microporosity (0.0-0.1 m soil layer) and Ksat (all soil layers).Regarding micro volumes, difference occurred among the periods observed for crambe C3 (40.78%), with lower values in 2015.Among the coverings, higher percentages were observed for crambe C5 (45.38%) and smaller for pigeon pea coverage (PP -36.08%) did not differ from the others, in 2015.
Significant differences occurred between the periods for Macro and Ksat.For Ksat, differences occurred between vegetable toppings.Between periods, larger macro percentages were checked for the covers of sunn hemp (SH -17.66%), pigeon pea (PP -21.46%) and crambe C2 (18.99%), and as minors to the crambe C9-NTTS (14.29%) in 2015.Although, in the present study, the macro values (18.08%) for the dwarf pigeon macro and Ksat in 2014.The highest values were for crambe C8-GNTS (49.68%) and lower for coverage CS (39.48%), crambe C3 (39.60%) and C4 (39.74%).The micro presented the highest values for the CS coverage (19.325%) and the lowest values for the crambe C2 (13.35%).The highest Ksat was observed for crambe C7-SNTS (59.78 mm h -1 ) and the lowest for C1 (11.63 mm h -1 ).The results in Table 1 indicate that from 0.1 m depth, there was no difference among the DS values, PT, Micro, and Macro and between management systems, that is, the effects of the treatments were restricted to the first 0 1 m deep, with the exception of crambe C9-NTTS (96.81 mm h -1 ) in the layer of 0.1-0.2m and C8-GNTS (86.08 mm h -1 ) and SH (79.32 mm h -1 ) in the soil layer of 0.2-0.3m, in 2015.
A possible explanation for these results may be due to atypical climatic factors that occurred during the crambe cycle, showing that it could express all its genetic potential as structural soil culture.The accumulated rainfall rates were 546 mm (Figure 2), which are distributed to the full flowering with 223 mm, followed by a low rainfall (12 mm) until the beginning of maturation and excessive rainfall (311 mm) at the end of maturation, exceeding the historical average.According to Pitol (2008), the water requirement of the crambe crop is 150 to 200 mm until full bloom.The authors did not report that higher rates could damage the crop, but after flowering there was little rain and rainfall above 20 mm near the harvest.According to Roscoe et al. (2010), the ideal is the absence of rains near the harvest, being tolerable rains smaller than 20 mm.According to SIMEPAR (2016), in the first half of July 2015, there was a high precipitation accumulation, exceeding the average of the region.The rains were incessant and intense, accompanied by a high incidence of lightning, wind gusts of moderate to strong and hail.While in the second half, the lowest temperatures of the year were recorded with low intensity of frost formation.While the mean temperature for the post-emergence period of crambe ranged from 8 to 26°C.According to Roscoe et al. (2010), crambe presents a good productive performance at 25°C.However, Falasca et al. (2010) and Knights (2002) reported that for the vegetative phase, the best temperature is between 15 and 25°C.

Conclusion
In the period of 2015, the significant differences between treatments occurred for microporosity (0.0-0.1 m layer) and Ksat (all soil layers).Microporosity was lower in the pigeon pea coverage (PP) (36.08%), while the largest occurred in the coverage of crambe C5 (45.38%).The Ksat was higher in the dwarf pigeon pea (DPP) (298.20 mm h -1 ) and sunn hemp (SH) (163.39 mm h -1 ) coverage in the 0.0-0.1 m layer.

Figure 1 .
Figure 1.Aerial image of the layout of the 15 plots.

Table 1 .
Result of chemical analysis for each experimental stand in the beginning of the assessment for the present study on layers from 0

Figure 2 .
Figure 2. Sketch of the plots, with soil cover crops (summer and winter) and three management systems.

Figure 3 .
Figure 3. Monthly average rainfall and average temperature for the period of 26 years (historical average), obtained from the Meteorological Station of the Agronomic Institute of Paraná -IAPAR, Experimental Station of Santa Tereza do Oeste -PR.Minimum, maximum and average temperature from March/2015 to August/2015.