Productive and nutritional characteristics of Piatã-grass in integrated systems

Características produtivas e nutricionais do capim-Piatã em sistemas integrado

SUMMARY

This study aimed to evaluate the pasture productive and nutritional characteristics of Brachiaria brizantha cv. BRS Piatã in integrated systems with different densities of trees. Considering as plot the systems: integrated crop-livestock-forest with rows of trees (eucalyptus) spaced at 14 m and 357 trees ha^-1 (ICLF-14m), ICLF with rows of trees spaced at 22 m and 227 trees ha^-1 (ICLF-22m) and the integrated crop-livestock (ICL) with five remaining native trees ha^-1; period of the year as subplots, and sampling points as subsubplots (A, B C, D, and E) arranged perpendicular to trees alleys. It was evaluated the production of forage and leaf blade dry mass, leaf:stem ratio, soil coverage, radiation photosynthetically active interception, canopy height, crude protein (CP), neutral detergent fiber (NDF), in vitro digestibility of organic matter (IVDOM) of the leaf blade, and stem associated with the leaf sheath. There was a significant difference (P<0.05) for all variables due to the month within the integrated systems. Mainly in January and March, showing the forage and leaf blade dry mass reduction due to a higher trees density. System with higher trees density showed the lowest soil coverage and canopy height sampling points A and E in ICLF-22m showed lower forage and leaf blade dry mass production and soil coverage. The system with higher trees density showed lower value of NDF of the leaf blade, and higher CP contents. The IVDOM of the leaf blade was higher in ICLF systems. For the evaluated parameters the best results were for the ICLF-22m.

Key words:
agroforestry; Brachiaria brizantha; crude protein; shading; tropical pasture

RESUMO

Objetivou-se com este estudo avaliar as características produtivas e nutricionais da pastagem de Brachiaria brizantha cv. BRS Piatã em sistemas integrados com diferentes densidades de árvores. Considerando como trama os sistemas: planta integrada-pecuária com fileiras de árvores (eucalipto) espaçadas a 14 m e 357 árvores ha-1 (ICLF-14m), ICLF com fileiras de árvores espaçadas a 22 m e 227 árvores ha^-1 (ICLF-22m) e o cultivo-pecuária integrado (ICL) com cinco árvores nativas restantes ha^-1; período do ano como subparcelas e pontos de amostragem como sub-sub-parcelas (A, B C, D e E) dispostas perpendicularmente às vielas das árvores. Foi avaliada a produção de massa seca de lâmina e folha, relação folha: caule, cobertura do solo, intercepção fotossintética de radiação, altura do dossel, proteína bruta (PB), fibra de detergente neutro (FDN), digestibilidade in vitro de matéria orgânica (DIVMO) da lâmina da folha e haste associado com a bainha da folha. Houve uma diferença significativa (P <0,05) para todas as variáveis devido ao mês dentro dos sistemas integrados. Principalmente em janeiro e março, mostrando a redução da massa seca da forragem e das folhas devido a uma maior densidade de árvores. O sistema com maior densidade de árvores mostrou a menor cobertura de solo e a altura do dossel. Os pontos de amostragem A e E em ICLF-22m apresentaram menor produção de massa seca e lâmina foliar e cobertura do solo. O sistema com maior densidade de árvores apresentou menor valor de FDN da lâmina da folha e maior índice de PB. A DIVMO da lâmina da folha foi maior nos sistemas ICLF. Dos parâmetros avaliados os melhores resultados foram para o sistema ICLF-22m.

Palavras-chave:
agroflorestal; Brachiaria brizantha; proteína bruta; sombreamento; pastagem tropical

INTRODUCTION

The integrated crop-livestock-forest system, known as agroforestry system, is a planned agroforestry practice, aiming to take advantage of each interactions, and have benefits without damage to both parties (PACIULLO et al., 2011).

Herbaceous forage growth on shaded environments, present variations influencing productivity dynamics and numerous forage characteristics (GARCIA et al., 2010), provided by changes in quantity and quality of light available in the understory (SOARES et al., 2009), thus influencing the nutritional value and productivity dynamics.

Depending on the forage species and shading level, there is usually a positive influence on the nutritive value of grasses such as higher crude protein levels, cell wall content reduction, and digestibility increase (PACIULLO et al., 2007). However, there is a trend to produce less forage, mainly due to the lower light radiation in the understory (ALMEIDA et al., 2012).

The forage growth in the integrated system depends on its shading tolerance and shade percentage imposed to the understory. Shading caused by tree species may impair or favor forage growth, depending on the degree of shading and the amount of solar radiation that is intercepted by the tree canopy, as it restricts the interception potential of the forage that responds for this situation with adaptation and acclimatization phenotypical (OLIVEIRA et al., 2014; PACIULLO et al., 2011; GOBBI et al., 2009). In this context, it is worth highlighting the Brachiaria brizantha (Syn. Urochloa brizantha) cv. BRS Piatã by presenting adaptation to shading, high foliar growth rate, good nutritional value (VALLE et al., 2007), an average productivity of 11.5t ha^-1 of dry matter in conventional grazing system (DIM et al., 2015).

In this regard, this study aimed to evaluate the productive and nutritional characteristics of Piatã-grass in agroforestry system.

MATERIAL AND METHODS

The experiment was performed at Campo Grande – MS, Brazil (Latitude 20° 27’ South; Longitude 54° 37’ West; Altitude of 530 m). The experimental area consists of red Latosol (SANTOS et al., 2006), characterized by clayey, acid pH, low base saturation, high aluminum concentration, and low phosphorus content.

The climate, according to Köeppen (1948) classification, belongs to the transition range between Cfa and Aw tropical rain; and the average annual rainfall is 1,560 mm. During the experiment, climate data were collected at the weather station of Embrapa Beef Cattle, located at 3 km of the experimental area, from September 2014, corresponding to the end of dry season, to February 2015, corresponding to the beginning of the wet season (Table 1).

Table 1
Mean values of maximum temperature (Tmax), minimum temperature (Tmin), relative humidity (RH), and rainfall from 2014 to 2015

Month	Tmax (°C)	Tmin (°C)	RHmin (%)	Precipitation (mm)	Global radiation (μmol m-2 s-1)
September	32.3	20.3	22	66.0	163.5
November	30.8	19.9	32	217.8	163.7
January	32.2	21.2	44	263.6	187.8
March	31.1	21.1	49	164.4	181.8

This study evaluated the pasture of April 2014, with Brachiaria brizantha cv. BRS Piatã [Syn. Urochloa brizantha], in integrated systems established in 2008/2009, which is the agroforestry system (ICLF) with hybrid eucalyptus seedlings “urograndis” (Eucalyptus urophylla × Eucalyptus grandis, clone H 13) in two arrangements of trees: one in simple lines, spaced 14 m between the lines, 2 m between plants, and density of 357 trees ha^-1 (ICLF-14m); another with eucalyptus seedlings in simple lines, spaced 22 m between the lines, 2 m between plants, and density of 227 trees ha^-1 (ICLF-22m), and agropastoral system (ICL, control) with five remaining native trees ha^-1. Each system consists of four paddocks of 1.5 ha^-1 area, in a total of 12 experimental paddocks.

The experimental design for plant component was performed in split-split-plot randomized blocks design with four replications. Plots treatments consisted of integrated systems ICLF-14m, ICLF-22m, and ICL. Subplots treatments correspond to the time of the year (spring and summer), and the split-plots treatments corresponded to the sampling places: A, B, C, D and E

Forage evaluations were performed in two perpendicular transects to trees rows per plot. In each transect, five equidistant points were delimited (A, B, C, D and E), where A and E were located at 2 m from trees trunks, and C correspond to the intermediate position, totalizing ten samples per plot.

At each point of 1.0 × 1.0 m, the canopy height measure was performed from the distances average of the plant base to the leaves curvature, measured with rulers graduated in centimeters in each point, within each plot; the soil coverage was visually evaluated and determined in percentage, then the forage was cut at surface level with a brush cutters. Two transects randomly arranged in the pasture were considered for system with native remaining trees. Cut material in 49-day intervals was taken to the laboratory, and weighed and divided into sub-samples.

Photosynthetically active radiation (PAR) readings were performed in each sampling point, by a ceptometer model PAR-80, Decagon Devices. A reading in both canopy top and ground level was performed at each point. Samples were separated in leaves (only foliar blade), stems (leaf sheath and stem) and aged material (leaves or stems with more than 50% of the dry area), then taken to drying in forced air chamber at 55°C, until reaching constant mass in 72 hours. After pre-drying, subsamples were ground separately in “Thomas Wiley” mill grinder, model 4, using 1 mm mesh sieve, identified and packaged in glass pot for chemicalbromatological analysis.

Forage productivity and different components as leaf and stem of living material were estimated based on dry matter. By dry matter data of leaf:stem fraction, it was calculated the leaf:stem ratio (L/S ratio), according to the methodology described by Mannetje (1978).

Bromatological composition, crude protein (CP), neutral detergent fiber (NDF), and in vitro organic matter digestibility (IVDOM), was evaluated from a representative sample, by means of near infrared reflectance spectroscopy (NIRS), according to Marten et al. (1985). Statistical analyzes were submitted to variance analysis, and the averages were submitted to Scott-Knott test with 5% probability, by using the SAS - Statistical Analysis System, version 8.0 (2002).

RESULTS AND DISCUSSION

There was a significant difference between the periods of the year and the integrated systems for all variables (Table 2).

Table 2
Total forage dry matter (TFDM), leaf blade dry matter (LDM), leaf:stem ratio (L/S ratio), soil coverage (SC), photosynthetically active radiation (PAR), and pasture height according to the period of the year, in three integrated systems

System	Period of the year
	September (2014)	November (2014)	January (2015)	March| (2015)	SEM1
TFDM (kg ha-1)
ICL	2.234aB	1.726aC	2.007aB	2.867aA	67.76
ILCF14m	498cB	464bB	637cB	1.024cA	52.01
ICLF 22m	1.156bB	839bC	1.230bB	2.172bA	78.11
LDM (kg ha-1)
ICL	451aC	520aC	960aB	1.091aA	36.64
ILCF14m	64bC	135bC	237cB	511cA	27.22
ICLF 22m	167bC	266bC	678bB	834bA	38.46
L/S ratio
ICL	1,95aB	2,60aA	2,30aA	1,10aC	0.093
ILCF14m	0,35cB	1,45bA	1,20bA	1,55aA	0.071
ICLF 22m	1,25bC	2,50aA	1,60bB	1,00aC	0.119
CS (%)
ICL	77aB	73aB	83aA	73aB	0.79
ILCF14m	37bB	27cC	41bB	46bA	1.77
ICLF 22m	50bB	50bB	75aA	51bB	1.63
PAR (μmol m-2 s-1)
ICL	858aB	1.691aA	553aC	1.527aA	66.02
ILCF14m	875aA	657bB	158bC	970bA	69.22
ICLF 22m	913aB	741bB	105bC	1.247abA	76.62
Pasture height (cm)
ICL	32aB	30abB	42bA	43aA	0.86
ILCF14m	26aB	24bB	25cB	49aA	1.56
ICLF 22m	31aC	34aC	56aA	47aB	1.41

• Averages followed by the same letters, uppercase letters in the lines, and lowercase letters in the columns, belong to the same grouping by Scott-Knott test at 5% probability.
• ICL = integrated crop-livestock; ICLF22m = integrated crop-livestock-forest, spaced 22 m between lines; ICLF 14m = integrated crop-livestock-forest spaced 14 m between lines.
• SEM¹ = Standard error of the mean.

March presented higher production of TFDM and LDM (kg ha^-1) in all studied systems; however, ICL showed the highest total forage production of 2,867 kg ha^-1 and leaf blade of 1,091 kg ha^-1. However, November presented lower forage production of 839 kg ha^-1 for THDM variable of ICLF-22m. September and November presented lower production of LDM in ICLF-22 and 14m, assuming an average production around 216 and 99 kg ha^-1, respectively.

The increment in the total forage dry matter and in the leaf blade can be associated with less trees competition for light, nutrients, and water, according to Martuscello et al. (2009), environments with shading level increased linearly reduces the dry matter production of Brachiaria decumbens and B. brizantha.

The leaf:stem ratio (L/S ratio) for ICL was higher in November and January with average of 2.45. ICLF-14m showed a higher leaf:stem ratio in November, January and March. ICLF-22m showed the highest ratio in November with 2.50. It is probably the highest leaf:stem ratio presented in the months aforementioned, because of the rainy season, and favorable environmental resources for plant development.

Green leaves show high crude protein content, as well as digestibility and consumption, which is an advantage for grazing since the leaves have better nutritional value. According to Araújo et al. (2013) the leaf:stem ratio is a variable influenced by the incident radiation level, and may result in stem etiolation reducing the leaf:stem ratio, or in a contrary way, may result in leaf size increase, increasing the leaf:stem ratio.

According to Gobbi et al. (2009), shaded grasses provide structural, adaptive, and competitive changes in the leaves to capture more light and invest in higher assimilate proportion. These authors also report that the increase of shoot: root ratio, elongation of stems and leaf blade, reduction of branching and tillering, the increase of specific leaf area and changes in leaf: stem ratio are morphological alterations of grasses under shading conditions.

Therefore, in this study, we observed that the denser arrangement of trees reduced the leaf: stem ratio especially in September, November and January.

The highest soil coverage percentage (SC) was observed in January for ICL and ICLF-22m, 83% and 75%, respectively. However, ICLF-14m presented the highest soil coverage percentage in March, even though, was lower than the other systems, 46%. The soil coverage variable response in this study is an indication that the wider spacing of eucalyptus favored for higher soil coverage, since areas with higher trees density present less incident radiation intercepted by the canopy.

The soil coverage, provided by Piatãgrass is associated with the pasture productive capacity, which present less space of uncovered areas. On the other hand, the soil coverage is an important opportunity to prevent the soil surface from water runoff, and hence erosion (GALHARTE & CRESTANA, 2010). Thus, the weed reduction is guaranteed, improving soil quality, and increasing the forage species productivity.

The highest incidence of photosynthetically active radiation (PAR) occurred in ICL, in November and March, with an average of 1,609 μmol m^{- 2} s^-1. ICLF-22m showed the highest value in March, 1,247 μmol m^-2 s^-1. However, this has not differ statistically from values presented by ICLF-14m, for all analyzed months. It was expected that ICLF-14m presented lower solar radiation on canopy in September and November, due to their lower leaf:stem ratio in the same period, where PAR intercepted and absorbed by the leaves, by means of chloroplast pigments would be different between systems.

Biomass productivity of a culture is related, among other factors, to the radiation photosynthetically active fraction absorbed by canopy. According to Martins et al. (2010), chloroplastid pigments contents, chlorophyll, and carotenoids are related to the photosynthetic efficiency of plants, therefore, the radiation quantity ratio incident on the cultivation environment provides an adjustment in the plants photosynthetic system, which is essential for the absorption efficiency and energy transfer for photosynthetic processes.

The radiation quantity reduction incident on canopy of cultivated forage in understory can interfere with the shoot development and root growth, decreasing them. The absorbed PAR represent the efficiency in which the plant absorbs the incident photosynthetically active radiation (PAR_i) in the canopy, which is variable over the cycle, and in the growth and development conditions of plants (FONTANA et al., 2012).

In the case of pasture height variable, the highest values were observed in ICLF-22m and ICLF-14m, in March, as well as the highest average height observed for ICL was 42.5 cm in January and March. Piatã-grass growth was favored by wet conditions provided by treetop, by the highest PAR values recorded in March, and the weather condition presented by the month (Table 1).

Plant growth depends on the availability of favorable environmental factors, and assimilates partitioning between shoot and root. In case of cultivated pastures when shaded, it present strategies in response to less light, in order to reach a higher extract and go out of the shadow, starting the stem elongation process (SILVA et al., 2009), and reducing the tillers population density (SBRISSIA & SILVA, 2008).

The higher stems length and petioles can represent a plant effort to increase its access to the light available to the canopy (PERI et al., 2007). However, pastures under shading show lower forage dry matter, compensating it showing higher crude protein content and in vitro digestibility of organic matter (ALMEIDA et al., 2012).

There was a significant difference between the periods of the year and integrated systems on the parameters related to forage quality shown in Table 3.

Table 3
Crude protein (CP), neutral detergent fiber (NDF), and in vitro digestibility of organic matter (IVDOM) of leafe blade and stem+sheat, according to the period of year, in three integrated systems

System	Period of the year
	September	November	January	March	SEM1
Leaf Blade
CP (%)
ICL	8,55cB	10,10cA	7,90bB	10,30cA	0.16
ICLF22m	11,45bA	12,40bA	9,80bB	13,25bA	0.32
ICLF14m	13,30aC	14,45aB	11,50aD	16,65aA	0.27
NDF (%)
ICL	70,95aB	70,15aB	76,75aA	71,20aB	0.37
ICLF22m	69,95aB	68,65abB	75,50aA	69,10abB	0.45
ICLF14m	65,25bC	67,40bB	72,25bA	67,95bB	0.47
IVDOM (%)
ICL	58,45bB	62,70bA	52,30bC	58,85cB	0.53
ICLF22m	66,40aA	67,20abA	55,20bB	64,70bA	0.83
ICLF14m	68,30aB	69,95aB	60,15aC	72,30aA	0.86
Stem + sheath
CP (%)
ICL	5,90aA	6,65cA	5,40bA	5,90bA	0.10
ICLF22m	6,05aB	8,60bA	5,80bB	6,60bB	0.27
ICLF14m	6,25aC	10,35aA	7,75aB	9,75aA	0.25
NDF (%)
ICL	75,50aB	75,00aB	79,70aA	78,60aA	0.35
ICLF22m	77,50aA	73,45abB	78,90aA	78,90aA	0.40
ICLF14m	76,35aA	71,40bB	76,15bA	74,55bA	0.39
IVDOM (%)
ICL	51,65aA	54,65bA	52,70aA	51,40bA	0.44
ICLF22m	51,60aB	58,80aA	53,00aB	50,80bB	0.85
ICLF14m	48,05aC	61,30aA	55,60aB	59,40aA	0.69

• Averages followed by the same letters, uppercase letters in the lines, and lowercase letters in the columns, belong to the same grouping by Scott-Knott test at 5% probability.
• ICL = integrated crop-livestock; ICLF-22m = integrated crop-livestock-forest, spaced 22 m between lines; ICLF-14m = integrated crop-livestock-forest spaced 14 m between lines.
• SEM¹ = Standard error of the mean.

The higher crude protein content of the leaf blade was observed in March, 16.65% in ICLF-14m. However, the same system had the lowest percentage in January, 11.5% for the same variable. Probably, the best response can be related to the favorable microclimate that trees provided in the understory, promoting moisture retention and nutrient recycling; however, the particularity presented in January, can be explained by the influence of the higher radiation photosynthetically active interception in the canopy (Table 2).

According to some authors (GOBBI et al., 2010; SOUSA et al., 2010; PACIULLO et al., 2011) in areas under trees influence, grasses have higher crude protein content than in full sun, being attributed to the higher nitrogen (N) recycling and soil moisture.

Fiber content in neutral detergent fiber (NDF) of leaf blade of Piatã-grass showed no significant difference throughout the year in ICL, except for the highest value obtained in January, 76.75%. This value is consistent with the results shown by ICLF-22m, in the same observation period. The lower NDF content was observed in ICLF- 14m, in September. Dim et al. (2015) working with Piatã-grass, observed that the higher the pasture height, the higher the NDF content, corroborating with the results analyzed in ICLF-22m.

For in vitro digestibility of organic matter of leaf blade, the lowest percentages were observed in January, in ICL and ICLF-22m, which have not differed from each other, and ICLF-14m with 52.30, 55.20, and 60.15%, respectively. Reputedly, the most satisfactory values found for ICLF-14 in March, and for ICLF-22m in September and November are associated to crude protein content higher than the minimum required, i.e., 7% for ruminants (NRC, 1996), can reflect in a good steers performance in grazing (MERTENS, 1994).

Quintino et al. (2013), evaluating Piatãgrass production and nutritional value in different cutting ages in integrated systems, observed that the in vitro digestibility of organic matter was lower in rainy season (January), when the weather conditions favored pasture growth. The authors argue that this behavior may be related to competition between plants in the system, leading to increased leaf senescence and stalk length, contributing to the reduction of forage digestibility, just as occurred in this experiment.

Euclides et al. (2009) evaluating the nutritive value of Brachiaria brizantha, Marandu, Piatã, and Xaraés cultivars, in full sun, found average values of CP, IVDOM, and NDF in leaf blade and stem for Piatã-grass: 8.2%; 50.1%, and 73.0%, respectively. Different from the agroforestry systems evaluated in this study, it was observed that, due to the arboreal component, the grass composing the understory has a higher nutritional quality.

Evaluating ICL system, it was observed the average content of 5.96% of crude protein in stem and sheath, and only ICLF-14m stood out in November and March, with the highest average of the systems, approximately 10.1%.

The lower NDF content of stem and sheath were observed in ICLF-22m and 14m, in November. However, it was observed that ICLF-22m have not presented significant difference when compared to ICL, in September and November.

ICL and ICLF-22m showed the lowest average content of 51.1%, of IVDOM, of stem and sheath in March; ICLF-14m showed an average of approximately 60.4% in November and March.

In general, the crude protein content and in vitro digestibility of organic matter found in foliar blades were higher than those found in stem and sheath, except in neutral detergent fiber. Probably due to the higher lignified tissues rate of such fraction.

Santos et al. (2012) and Simoni et al. (2014) consider that the nutritive value of tropical grasses reduces insofar as occur the increase of senescent material quantity present in the pasture when the plant get closer to flowering stage, with higher involvement of stems in relation to leaves on biomass total composition, resulting in the decrease of crude protein content and digestibility, and increase of neutral and acid detergent fiber content.

Analyzing the delimited points in transects (A, B, C, D, and E), Table 4, it was observed that the lowest dry matter value of total forage in ICL was found in C, and there was no significant difference among other sampling points. Within ICLF-14m, C showed the highest dry matter production of the total forage, 730 kg ha^-1, whereas sampling points near the trees, represented by A and E, showed the lower biomass production, an average of 510 kg ha^-1. Although ICLF-22m showed similar behavior, it presented higher values for C point (1,640 kg ha^{- 1}), and lower values for points A and E (average 1,141 kg ha^-1). The PAR probably influenced to obtain the lowest values in these sampling points.

Table 4
Total forage dry matter (TFDM), leaf blade dry matter (LDM), soil coverage (SC), photosynthetically active radiation (PAR), according to sampling location in three integrated systems

System	Sampling location
	A	B	C	D	E	SEM1
THDM (kg ha-1)
ILC	2.293aA	2.221aA	2.004aB	2.199aA	2.324aA	67.76
ICLF 14m	471cB	794cA	730Ab	734cA	550cB	52.01
ICLF 22m	1.189bC	1.433bB	1.642aA	1.390bB	1.093bC	78.11
LDM (kg ha-1)
ILC	836aA	763aA	673aB	770aB	740aB	36.64
I ICLF 14m	192cA	269cA	260bA	274cA	190cA	27.22
ICLF 22m	416bB	534bA	569aA	524bA	388bB	38.45
SC (%)
ILC	79aA	76aA	74aA	75aA	79aA	0.79
ICLF 14m	35bB	39bA	42bA	41cA	33Bc	1.77
ICLF 22m	48bC	60cB	64aA	60bB	49bC	1.62
PAR (μmol m-2 s-1)
ILC	1.181aA	1.226aA	1.119aA	1.081aA	1.178aA	66.02
ICLF 14m	729bA	828bA	751bA	693bA	325bB	69.22
ICLF 22m	563bB	991abA	1.094abA	985abA	126bC	76.61

• Averages followed by the same letters, uppercase letters in the lines, and lowercase letters in the columns, belong to the same grouping by Scott-Knott test at 5% probability.
• ICL = integrated crop-livestock; ICLF-22m = integrated crop-livestock-forest, spaced 22 m between lines; ICLF-14m = integrated crop-livestock-forest spaced 14 m between lines.
• SEM¹ = Standard error of the mean.

The ICLF-14m presented lower production of LDM at all analyzed point. ICLF-22m showed an average of 542 kg ha^-1 in B, C and D points.

According to Leonel et al. (2009) the low incidence of light in canopy in C4 grasses, decrease the forage dry matter production, since it requires higher quantity of light energy for assimilates production in order to perform photosynthesis.

ICL showed not significant difference for soil coverage variable, and with regard to sampling points, it showed a higher percentage of soil covered, an average of 76.6%. Within ICLF-22m, C point showed the highest soil coverage. This is probably due to sampling point position be more central between trees rows, favoring the sunlight capture.

According to Gobbi et al. (2011) plants create acclimatization mechanisms in response to shading, trying to attenuate light allowing their survival.

PAR was influenced by sampling location in ICLF-22m, the highest PAR were observed in B, C and D points, showing an average of approximately 1,023 μmol m^-2 s^-1. However, this system does not differ significantly from values presented in ICL and ICLF- 14m, on B, C and D points. Possibly, the intermediate region between trees rows may have contributed to the results because of the higher solar incidence.

According to Oliveira et al. (2007b), solar radiation incidence depends on the distribution of trees, where higher light transmission levels is found in arrangements with higher spacing between lines and rows of the trees, which was observed in this study.

Table 5
Crude protein level (CP) of the foliar blade, stem and sheath of Piatã-grass, according to the sampling location, in three integrated systems

System	Sampling location
	A	B	C	D	E	SEM1
Leaf Blade
CP (%)
ICL	9,13bA	9,00cA	9,25bA	9,13cA	9,56cA	0.16
ILCF14m	13,88aB	14,38aA	13,63aB	13,00aB	15,00aA	0.32
ILCF22m	12,75aA	10,81bB	10,38bB	11,06bB	12,38bA	0.27
Stem + sheath
CP (%)
ICL	6,13bA	5,94bA	6,13 bA	5,69bA	5,94bA	0.10
ILCF14m	8,50aA	8,31aA	8,44aA	9,19aA	8,19aA	0.27
I ILCF22m	8,13aA	6,75bB	6,06bB	6,00bB	6,88abA	0.25

• Averages followed by the same letters, uppercase letters in the lines, and lowercase letters in the columns, belong to the same grouping by Scott-Knott test at 5% probability,
• ICL = integrated crop-livestock; ICLF 22m = integrated crop-livestock-forest, spaced 22 m between lines; ICLF 14m = integrated crop-livestock-forest spaced 14 m between lines.
• SEM¹ = Standard error of the mean.

Sampling location did not influence the crude protein content of leaf blades within ICL. They were higher in ICLF-14m, in E, with 15% of CP, and in ICLF-22m, in A and E with an average of 12.57%. ICLF-22m showed the lower crude protein contents in B, C and D, with 10.8% of CP. Possibly, the lowest CP contents are associated with the higher intensity of light on Piatãgrass, increasing the structural compound and increasing the cellular contents.

According to Soares et al. (2009) the photosynthetic radiation increment on forage is influenced by increasing the spacing between trees, which reduces the percentage of crude protein.

With regard to crude protein present in stem and sheath, the highest content was found in ICLF-22m, in A and E, 7.51%. In ICLF-14m, B and E points showed an average of 14.69% of CP.

Researcher as Paciullo et al. (2011, 2007) and Soares et al. (2009) reported that the highest contents of crude protein in pasture, in natural shading conditions, can be associated to trees presence favoring the increase of organic matter, and consequently, increasing the nitrogen cycling.

Integrated crop-livestock-forest system spaced 22 m, stands out with higher crude protein values and in vitro digestibility of organic matter.

The lower tree density provides marginal improvements in nutritional parameters of the Piatã grass in relation to the systems with greater density of trees, but it stands out in relation to the production of biomass.

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Publication Dates

• Publication in this collection
  Apr-Jun 2018

History

• Received
  31 Oct 2017
• Accepted
  21 May 2018