Production and bromatological composition of cultivars of Brachiaria brizantha and Campo Grande stylo monocropped and intercropped under different planting methods

This study was conducted to assess the production and bromatological composition of cultivars of Brachiaria brizantha (cvs. Marandu and Xaraés) and Campo Grande stylo (Stylosanthes ssp) monocropped and intercropped under different planting methods for a period of two years. The experimental design used consisted of randomized complete blocks, with four replicates. The treatments consisted of the following forage systems: monocropped Campo Grande stylo; monocropped Xaraes palisadegrass; monocropped Marandu palisadegrass; Xaraes palisadegrass row-intercropped with Campo Grande stylo; Xaraes palisadegrass mixed-intercropped with Campo Grande stylo; Marandu palisadegrass row-intercropped with Campo Grande stylo and Marandu palisadegrass mixed-intercropped with Campo Grande stylo. The evaluations were performed for two years, with evaluations for each season of the year (autumn, winter, spring and summer) in the same plots and repeated measures over time. The Xaraes palisadegrass and Marandu palisadegrass showed similar results between the intercropping systems, indicating that both may be intercropped with Campo Grande stylo. Intercropping stylo with B. brizantha cultivars improves both pasture production and quality. However, the most efficient planting method was row intercropping because it maintains greater legume persistence in the forage system throughout the years assessed while also providing greater production and nutritional value.


INTRODUCTION
Nitrogen (N) is a key nutrient for enhancing the productivity of forage grasses.However, its use has been limited by its relatively high cost due to the extension of the areas involved and the need for frequent applications (Costa et al., 2010).Thus, the use of legumes intercropped with tropical grasses may be a more appropriate alternative for supplying N to a system (Barbero et al., 2010).The introduction of legumes adapted to the edaphic and climatic conditions of the region may increase the quantity and quality of the available forage, given the ability of these plants to biologically fix atmospheric N. The contribution is performed indirectly through fixed N transfer to the grass, which enhances the pasture's carrying capacity and prolongs its productive capacity (Barcelos et al., 2008).
There are some difficulties in implementing this system despite all the advantages of grass and legume intercropping.Several factors are implicated in having limited its expansion: the lack of legume persistence in pastures given the choice of species for its formation, deficient establishment and even poor management of the grasslands formed, with a decisive effect on legume persistence in pastures (Rosa et al., 2004).
However, with the emergence of cultivars/varieties of legumes with effective mechanisms of persistence, the system has shown a resurgence in its use in farms that is motivated by the encouraging research results of grasses intercropped with stylo, which show better dry matter production and nutritional values (Moreira et al., 2005;Lopes et al., 2011;Moreira et al., 2013).Accordingly, strategies must be designed to maintain legume persistence in forage systems.Therefore, it should be noted that one of the key issues in managing intercropped pastures is the choice of an appropriate planting system that enables an intercrop botanical composition with a good ratio of legumes.For that purpose, managing practices must be established that increase legume persistence over time.Thus, this study aimed to evaluate the production and bromatological composition of cultivars of Brachiaria brizantha (cvs.Marandu and Xaraés) and Campo Grande stylo (Stylosanthes ssp) monocropped and intercropped under different planting systems for a period of two years.

MATERIALS AND METHODS
The experiment was conducted at the School of Agronomy Campus, University of Rio Verde (Campus da Faculdade de Agronomia da Universidade de Rio Verde), located at Fontes do Saber farm at a 748 m altitude, 17° 48' latitude south and 50° 55 ' longitude west.The soil was classified as Haplorthox, and its physical and chemical characteristics at the 0 to 20 cm depth layer are outlined in Table 1.The method used in the soil analysis was reported by Silva (1999).
The experimental design consisted of randomized complete blocks, with four replicates.The treatments consisted of the following forage systems: monocropped Campo Grande stylo; monocropped Xaraes palisadegrass; monocropped Marandu palisadegrass; X. palisadegrass row-intercropped with Campo Grande sytlo; X. palisadegrass mixed-intercropped with Campo Grande stylo; M. palisadegrass row-intercropped with Campo Grande stylo; and M. palisadegrass mixed-intercropped with Campo Grande stylo.The evaluations were performed over two years, with evaluations in each season of the year (autumn, winter, spring and summer) in the same plots and repeated measures over time.Each plot was 4 by 4 m, totaling 16 m 2 of plot and 6 m 2 of floor area.The row-intercropping planting system consisted of eight rows of 4 m each (four rows of grass and four rows of legume) spaced 50 cm from each other.Five and 9 kg of pure viable seeds per hectare of Campo Grande stylo and palisadegrass (Xaraés and Marandu), respectively, were used for the forage planting.The area used was in fallow and the preparation was conducted by eliminating the invasive plants by applying glyphosate at a dose of 1,500 g ha -1 .Twenty days after desiccation, 900 kg ha -1 dolomitic limestone was applied with 100% LTRN (lime's total relative neutralization); subsequently, disking and leveling were performed.During planting, 100 kg ha -1 P 2 O 5 , 60 kg ha -1 K 2 O and 20 kg ha -1 FTE BR-12 (9.20% Zn; 2.17% B; 0.80% Cu; 3.82% Fe; 3.4% Mn and 0.132% Mo) were applied using the following sources: simple superphosphate, potassium chloride and Fritted Trace Elements (FTE).Maintenance fertilization was performed in the second year using 80 kg ha -1 P 2 O 5 and 60 kg ha -1 K 2 O, derived from the simple superphosphate and potassium chloride sources, respectively.Per year, 90 kg ha -1 nitrogen was applied to the grasses, divided into three applications of the ammonium sulfate source.
Thinning was conducted following germination, thereby maintaining the same number of grass and legume plants.The ratio of forage system plants was assessed while conducting the experiment in the plot floor area by counting the grass and legume plants in all seasons of the year for a period of two years (Table 1).The evaluation times of dry mass production and nutritional value of forages were conducted in the rainy and dry periods (within each season, autumn, winter, spring and summer).The rainfall and monthly average temperature data were monitored daily during that period (Figure 1).
Two 1 m 2 samples were collected per plot for the evaluations, directing the square for each row of forages in the floor area to sample grass and legume plants.The square was randomly thrown within each plot in the mixed intercropping.Sixteen forage evaluation cuts were performed in two years, corresponding to the following periods: autumn (March 2008/2009and May 2008/2009); winter (July 2008/2009and September 2008); spring (October 2008/2009and December 2008/2009); and summer (January 2009/2010).The cuts in the autumn, spring and summer seasons were performed every 30 days of growth and every 60 days in the winter season, at a height of 20 cm from the soil.A uniformization cut of the entire experimental area was performed after each evaluation at the same cut height of the evaluated plants, clearing the waste from that area.The material collected in the field was stored in plastic bags and sent to the laboratory, where an approximately 500 g sample representative of each plot was collected and placed in a forced-air convection oven for pre-drying, with a temperature of approximately 55°C for 72 h.The samples were subsequently ground in a Willey-type mill with a 1 mm sieve and stored in plastic bags for analysis.Bromatological analyses were performed to assess the dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) according to the method reported by Silva and Queiroz (2002).The total digestible nutrients (TDN) were derived using the equations proposed by Chandler (1990).The data were submitted to an analysis of variance, and the means were compared using the Tukey's test, with a significance level of 5% probability.The analyses were performed using the split-plot model, subdivided in time, upon fitting to Gauss Markov linear models.The software used to perform the analysis of variance and the comparison of means test was the SISVAR (Ferreira, 2000).

RESULTS AND DISCUSSION
Table 2 shows no significant effect (P<0.05) of the legume ratio on the different forage systems, which remained constant in the autumn and summer seasons of the first year, when assessing the ratio of Campo Grande stylo intercropped with Xaraes and M. palisadegrasses.In winter and spring, the greatest ratio of Campo Grande stylo was found in row intercropping with Xaraes palisadegrass.Conversely, no statistically significant difference (P<0.05) in the legume ratio was found in the other systems.However, there was a decrease in the legume ratio, especially in grass-mixed intercropping, given the low resistance of that legume in the dry period.The limitation of Campo Grande stylo in tolerating water stress, unlike several other tropical legumes, which have a greater ratio in the animals feeding during winter, considered the dry season in the Midwest region, must be noted.Natural reseeding of that legume occurs in winter because its plants are predominantly annual or biannual (Embrapa, 2000).The comparison of seasons within each forage system in the first year shows that the legume ratio for Campo Grande stylo row intercropping with X. palisadegrass was similar in autumn, winter and spring, differing only in the summer, which showed the lowest ratio.Conversely, in the other systems, a statistically significant effect (P<0.05) occurred only in the autumn, recording the highest legume ratio Table 2 shows that the highest ratio of Campo Grande stylo in the autumn, winter and spring occurred with row intercropping X. palisadegrass when assessing the forage systems for each season of the second year.Conversely, there was a decline in the legume ratio in the other planting systems, especially for mixed intercropping of the legume with the grasses.Similar results were found by Aroeira et al. (2005), who noted that the dry mass availability of Mineirão stylo forage linearly decreased throughout the experimental period, when assessing Brachiaria decumbens intercropped with Mineirão stylo and that of B. decumbens varied with the climatic conditions.No statistically significant effect (P>0.05) of the legume ratio was found for the row intercropping systems among the seasons of the year when assessing the seasons of the year within each forage system.However, a decrease in the legume percentage occurred with mixed intercropping, especially in the summer, with a ratio of only 10% legumes.This decrease in the legume percentage in the intercrop system may be explained by competition for water, light and nutrients, as B. brizantha plants have a lower photosynthetic efficacy (C4 cycle) in tropical conditions, outperforming the legume, which is a C3 cycle plant (Aroeira et al., 2005).Figure 2 shows that the highest ratios of Campo Grande stylo in the different systems were found in the first year of the evaluation, when comparing the forage system within the years evaluated.There was a significant reduction in legume ratio from the second year, especially when performing the mixed intercropping, reaching only 10% in the second year, compared to 35% in the first year.This shows that the best intercropping method in the experimental conditions for favoring legume persistence is row intercropping because it maintains the most balanced ratio of grasses and legume in the stem.
Table 3 shows that only row-intercropped X. palisadegrass differed from the other systems in autumn and winter, with greater production of dry mass, when evaluating the production of dry mass of the forage systems within each season.This finding results from the better rate of resprouting and, consequently, a greater accumulation of this grass forage in periods of low rainfall, enabling the satisfactory production of forage even in the dry period of the year.Flores et al. (2008) report that X. palisadegrass has advantages over other cultivars of Brachiaria, including a higher rate of resprouting and greater forage production, which ensures a greater yield per area.
In spring, the greatest production occurred in the row and mixed intercropping systems, which differed from the other forage systems (Table 3).This greater production in the intercropped systems is associated with the presence of legume, which significantly contributed to increasing the production given the soil nitrogen supply (Lopes et al., 2011).The ratio of Campo Grande stylo is also important to maintain the balanced supply of forage because it offsets the natural decline in the production of monocropped grasses.A better production of dry matter was also found in intercropped systems by Schunke and Silva (2003), who noted that the largest production was found in B. decumbens intercropped with Campo Grande stylo, showing that introducing the legume into pasture systems significantly contributes to an increase the dry matter availability of pastures.Barcellos et al. (2008) explain that nitrogen transfers will occur below and above the soil surface, directly or indirectly to the nearest plant, whether by N excretion from the legume rhizosphere, decomposition of roots and nodules, connection through root mycorrhizae of the grass with those of the legume or even by the action of the soil fauna on the roots and nodules of the legume.In the summer, the greatest production was found in the row intercropping systems, which showed an increase in production of 16.0 and 6.54% when compared to mixed intercropping with Xaraes and M. palisadegrasses, respectively.This increase in production in row intercropping results from the greater presence of Campo Grande stylo following the natural resprouting, which occurred in the dry period (winter), and the greater availability of water, light and temperature in the summer, enabling the development of new plants, increasing the production and maintaining the greater persistence of the legume.Furthermore, the legume presence in the system increased the soil nitrogen contribution and favored the greater grass growth, which explains the greater production of dry mass in these systems.Pinheiro (2011) found lower dry mass production values than those found in the present study, with a production of 4.678, 6.276 and 4.004 kg ha -1 in the seasons of spring, summer and autumn, respectively, when studying Campo Table 3. Mean production of dry matter (kg ha -1 ) for the forage systems evaluated at different seasons of the year.Grande stylo intercropped with Tanzania grass.An interesting factor observed in the study is the similar production between monocropped Campo Grande stylo and grasses.The high production of that legume resulted from the natural bank of seeds it produces in the dry season.A better development of that legume occurs with favorable conditions of soil fertility, temperature and rainfall, with a high production of dry matter.Those results indicate that Campo Grande stylo is recommended for intercropping with grasses and that this legume shows great potential for use as protein bank during the growth season.The comparison of the seasons of the year within each forage system shows that the production in winter was different from all other seasons, in all systems (Table 3).This fact was expected because the temperature and rainfall conditions (Figure 1) were limiting factors for development, hampering the growth and formation of new tillers; the reduction in the number of hours of light per day disfavors the process of photosynthesis.Figure 2 shows that the greatest productions of dry mass of Campo Grande stylo monocropped and row-intercropped with palisadegrasses were found in the second year.This shows that legume persistence increases in the system when forage plants are row-intercropped because the legume is not fully competing with palisadegrasses, given the spacing between forages; thus, the production of dry matter is favored throughout the year because the legume has the ability to fix atmospheric nitrogen to the soil-plant system (Barcellos et al., 2008).However, there was a decline in the production of the mixed-intercropping system, as demonstrated by the lower legume ratio in this system.Table 4 shows that the monocropped Campo Grande stylo reached the highest CP levels in the autumn, followed by row and mixed intercropping with grasses, when evaluating the CP levels in the forage systems within each season of the year.In the winter, only monocropped grasses differed from the other systems, with lower CP levels.Conversely, all of the forage systems were affected in the spring, with the highest CP levels found in monocropped Campo Grande stylo, followed by row-intercropped Xaraes palisadegrass.That finding results from the greater ratio of stylo in the row intercropping system, following natural reseeding.However, in the summer, the intercropped systems showed similar CP levels for methods ways of planting.

Forage systems
The CP levels varied with the seasons of the year (Table 4).Campo Grande stylo differed in the winter from the other seasons, with lower CP levels.This finding results from the low resistance of that legume in the dry period of the year, when natural reseeding occurs.The highest CP levels of X. palisadegrasses and M. palisadegrasses monocropped and mixed-intercropped with Campo Grande stylo were found in the autumn, followed by spring and summer, and similar levels were found among the seasons.Conversely, the CP levels of row-intercropped X. palisadegrasses and M. palisadegrasses were similar in the autumn and spring, differing only from the summer and winter.The mean CP levels (129.7 g kg -1 ) in the systems of palisadegrasses intercropped with Campo Grande stylo in the summer were higher than those found by Aroeira et al. (2005), who reported a mean level of 105.0 g kg -1 when B. decumbens was intercropped with Stylosanthes guianensis in the summer (December).The highest levels of CP in all of the forage systems were found in the autumn, and the lowest were found in the winter because the climatic conditions, including temperature and rainfall (Figure 1), were limiting for the development of forage.Another factor influencing this difference could be related to pasture maturation, as the cut was performed at a longer growth cycle (60 days) than in the other seasons (30 days) in response to the seasonality of forage production, thereby decreasing its nutritional value.Almeida et al. (2002) noted lower CP levels than those found in the present study while studying the effect of the season of the year on the nutritional values of M. palisadegrass, with levels of 97.0 g kg -1 in the rainy season and 89.0 g kg -1 in the dry season.The levels of CP found in Campo Grande stylo monocropped and intercropped with palisadegrasses, regardless of the evaluation period, are well above the level needed to not restrict bovine pasture consumption.This fact results from the advantages that intercropping the palisadegrasses and the legume brings to the improvement in forage nutritional quality (Moreira et al., 2013).The levels of CP were not affected (P>0.05) when comparing the monocropped and row-intercropped systems in the first and second years of the evaluation (Figure 4).However, there was a decrease in the levels of CP in the mixed intercropping systems with X. palisadegrasses and M. palisadegrasses of 31.7 and 30.4% in the second year, respectively.This result is important for managing the implementation of intercropping with Campo Grande stylo and B. brizantha cultivars.This is because mixed intercropping shows lower legume persistence in surviving next to polisadegrasses, with a ratio percentage of only 10% (Table 2) in the second year of system implementation.Conversely, legume persistence and its likelihood of remaining in the system increase when intercropping is conducted in rows because the spacing between plants is 50 cm, favoring legume development as it does not compete with the palisadegrass, which is more aggressive in its uptake of water and nutrients.This occurs because B. brizantha is one of the most aggressive palisadegrasses, complicating the stability and persistence in pastures intercropped with hearbaceous or low-size legumes (Barcellos et al., 2008).
Table 4 shows that the highest levels of TDN in the autumn were found in monocropped Campo Grande stylo, followed by intercropped palisadegrasses, when analyzing the levels of TDN in forage systems within each season of the year.In winter, only stylo differed from the other forage systems with higher levels of TDN.In spring, the lowest levels were found in monocropped palisadegrasses, which differed from the other systems.In summer, Campo Grande stylo monocropped and row-intercropped with palisadegrasses showed the highest levels of TDN, followed by the mixed-intercropping systems and monocropped palisadegrasses.It is noteworthy that the levels of TDN were estimated based on the levels of NDF; therefore, the lower levels of TDN are necessarily recorded in the monocropped palisadegrass systems, wherein they showed the highest values of NDF.The levels of TDN of the forage systems varied with the seasons of the year for the period evaluated (Table 4).The levels in Campo Grande stylo were similar between the seasons studied.The monocropped palisadegrass levels of TDN in the autumn and summer were similar, differing from the winter and spring.Conversely, row-intercropped Xaraes palisadegrass only differed from the other seasons in the summer.The lowest level of TDN of row and mixed-intercropped M. palisadegrass was found in the winter.The mixed-intercropped X. palisadegrass levels of TDN in the winter and spring were similar, differing from the autumn and summer.Van Soest (1994) explains that numerous factors, including plant species, temperature, light intensity, water availability, latitude, maturity, type of crop and forage intercropping, affect the chemical composition of the plants and, consequently, the availability of energy from food.Therefore, higher levels of TDN are noticeably reached when the legume is intercropped with the palisadegrasses.Comparing the levels of TDN between the years of evaluation (Figure 5), only monocropped Campo Grande stylo differed from the other systems, and the highest level was found in the second year.However, the levels of TDN in the other forage systems were similar between the years evaluated.
The levels of NDF (Table 5), of the forage systems within each season of the year were affected (P<0.05).In autumn, Campo Grande stylo showed the lowest levels, followed by row-and mixed-intercropped systems, which showed similar levels.In winter, the levels of NDF of palisadegrasses monocropped and mixed-intercropped with Campo Grande stylo did not differ from each other, showing similar levels.The high levels of NDF found in winter result from the longer growth cycle (60 days), promoting pasture maturation.Therefore, there was a reduction in growth rate and consequently an increase of stems compared to leaves, leading to lower levels of CP and higher levels of fiber.Similar results were found by Moura et al. (2011), who noted that the NDF levels of Campo Grande stylo decreased with the resprouting age (50 days), albeit without great losses in forage quality.Conversely, the NDF levels in the spring and summer were affected by the planting method, showing that the levels in mixed intercropping were similar to the monocropped grasses, with the highest levels of NDF.However, lower levels of NDF were found in the row intercropping system, given the greater legume presence in this system, which shows lower fiber levels than palisadegrasses (Van Soest, 1994).
Table 5 shows that the Campo Grande stylo levels of NDF were similar when comparing the seasons of the year.However, the lowest values of NDF for the monocropped palisadegrasses were found in the autumn and summer, given the better climatic conditions (Figure 1) for the development of forage.Moreover, the intercropped systems only differed from the other seasons in the winter, with higher levels of NDF.This increase results from the increase in cell wall components, which occurs as the plant ages, most likely resulting from the reduced percentage of blades and increased ratio of rods, raising the fibrous components (Costa et al., 2007).Van Soest (1994) reports that the NDF level is the most limiting factor of roughage intake, and the levels of cell wall components are higher than 550 g kg -1 and correlate negatively with forage intake.Comparing the levels of NDF between the years evaluated (Figure 6), a statistically significant effect (P<0.05) was only found in the mixed intercropping systems, with the highest NDF levels in the second year.This finding results from the lower ratio of Campo Grande stylo plants when performing mixed intercropping, providing higher fiber levels, given the lower percentage of legume in the second year, which show lower levels of NDF than palisadegrasses because they have a C3 cycle.However, the levels of NDF were similar between the years evaluated in the monocropped and row-intercropped systems.
Table 5 shows that Campo Grande stylo had the lowest ADF levels, followed by the row-and mixed-intercropping systems and finally the monocropped palisadegrasses, which had the highest levels of ADF.This pattern was true in all seasons of the year given the higher ratio of lignin found when analyzing the ADF levels for the different forage systems in different seasons.These results show the importance of the legume presence in the intercropping with palisadegrasses because it benefits the quality of pastures, thereby improving the forage digestibility.In that same study, Moreira et al. (2013) found digestibility levels of 767.8 g kg -1 for monocropped Campo Grande stylo and 704.4 and 689.3 g kg -1 upon row-and mixed-intercropping stylo with X. palisadegrasses and M. palisadegrasses, respectively.Low fiber levels are desirable because the decrease of fiber in the forage enables an improvement in intake, digestibility and animal performance, according to Van Soest (1994).The ADF levels of Campo Grande stylo were similar for all seasons of the year (Table 5).However, the highest ADF levels for monocropped and row-and mixed-intercropped palisadegrasses were found in the winter.This finding results from the higher ratios of stems, which were accumulated with plant aging and the unfavorable climatic conditions of this season also (Figure 1), which hampered the development of new tillers.The mean levels of ADF in the winter were 375.82 g kg -1 for intercropped palisadegrasses and 426.60 g kg -1 for monocropped palisadegrasses.According to Noller et al. (1996), forages with ADF levels of approximately 300 g kg -1 or less will be consumed at high levels, whereas those with levels above 400 g kg -1 will be consumed at low levels.Figure 7 shows that the highest ADF values of Campo Grande stylo monocropped and mixed intercropped with palisadegrasses were found in the second year, when comparing the levels of ADF between the years evaluated.However, the ADF levels of monocropped and row-intercropped palisadegrasses were similar between the years evaluated, showing the advantage of this form of planting because it maintains the levels of fiber unstable throughout the year, given the legume presence.

Conclusion
The X. palisadegrasses and M. palisadegrasses showed similar results between the intercropping systems, indicating that both may be intercropped with Campo Grande stylo.The intercropping of stylo with the cultivars of B. brizantha improves pasture production and quality.However, the most efficient planting method was row intercropping because it maintained greater legume persistence in the forage system throughout the years evaluated and provided greater production and nutritional value.Campo Grande stylo is indicated for intercropping with grasses and has a great potential for use as a protein bank given the high production of dry mass during the growth season.

Figure 1 .
Figure 1.Rainfall (mm) and average temperatures (°C) as monitored during the period from January 2008 to February 2010 in Rio Verde-Goiás (GO), Brazil.

Figure 2 .
Figure 2. Ratio of Campo Grande stylo depending upon intercropping with X. palisadegrasses and M. palisadegrasses in the different forage systems evaluated in the first and second years.Means followed by different letters differed from each other according to Tukey's test (P< 0.05).

Figure 4 .
Figure 4. Crude protein levels of forage systems evaluated in the first and second years.Means followed by different letters differ from each other according to Tukey's test (P <0.05).

Figure 5 .
Figure 5.Total digestible nutrients levels of forage systems evaluated in the first and second years.Means followed by different letters differ from each other according to Tukey's test (P <0.05).

Figure 6 .
Figure 6.Neutral detergent fiber levels of forage systems evaluated in the first and second years.Means followed by different letters differ from each other according to Tukey's test (P <0.05).

Table 1 .
Physical and chemical characteristics of the soil in the forage systems evaluated in the years 2008 and 2009.

Table 2 .
Ratio of Campo Grande stylo (%) as a function of intercropping with Xaraes and Marandu palisadegrasses in the different forage systems and seasons of the year for a period of two years.