Introduction

The perennial ryegrass (Lolium perenne L.) along with alfalfa (Medicago sativa L.) forage species are grown in more temperate regions of Mexico, for use in grazing sheep or cattle, for its high yield per hectare, nutritional quality and ease to grow in different types of soil (^{Bolanos et al., 1995}); however, efficient pasture management is essential to maintain high productivity and quality of forage without promoting the deterioration of the same, which is achieved with different strategies defoliation either by reducing or increasing the intervals and intensity of harvest , to promote regrowth rate in plants and reduce losses by death and decay of forage (^{Hernandez-Garay et al., 1997}; ^{Chapman and Lemaire et al., 1993}).

Associations of grasses and legumes is an excellent choice in fodder production as there is currently a need to increase not only productivity but also sustainable resource efficiency (^{Lüscher et al., 2014}). The use of associations of grasses and legumes allows higher nutritional value and dry matter yield, activity that helps lower production costs compared to the use of balanced diets and thus ensure high production; and from the point Ecologically, legumes improve soil fertility by fixing atmospheric nitrogen, thereby reducing the use of chemical fertilizers, as well as better light interception and seasonal distribution of biomass production (^{Camacho and Garcia, 2003}; ^{Gonzales et al., 2004}).

In this regard, ^{Cook et al. (1990)} and ^{Rojas et al. (2005)}, consigned in the temperate region of Mexico, the white clover can contain on average from 168 to 270 g crude protein kg^-1 MS and set from 57 to 232 kg N ha^-1 (^{Zanetti et al., 1999}), and is preferred association with grasses such as perennial ryegrass and orchard. ^{Villareal et al. (2014)} in orchardgrass found the highest rate of growth in summer with 107 kg DM ha^-1 d^-1 with a frequency of 4 weeks and grazing intensity of 3-5 cm, while in autumn was 77 kg MS ha^-1 d^-1 frequency of 6 weeks and an intensity of 3-5 cm. The white clover association, orchardgrass and perennial ryegrass has come to produce up to 52% more fodder when the percentage of white clover on the prairie is 40% and can reach up to 65% more when it grazes in spring-summer range 28 days (^{Castro et al., 2012}). Seasonal patterns of distribution of forage are influenced by variations in climate, so it is important to know the speed seasonal growth of forage species of interest. Therefore, in associations of grasses with legumes it is important to determine the best partnership from the point of view of seasonal distribution, growth rate and persistence of the meadow. This research aimed to evaluate orchard grass monoculture seven associations, clew, perennial ryegrass and white clover in different proportions for different attributes: growth rate, plant density and intercepted radiation (%).

Materials and methods

The experiment was conducted from september 2012 to september 2014, at the Experimental Field of the Graduate College, Campus Montecillo, Texcoco, State of Mexico, located at 19° 29' north latitude and 98° 53' west longitude at an altitude of 2 240 meters. The climate is temperate humid, with annual rainfall of 636.5 mm rainfall in spring-summer and annual average temperature of 15.2 °C (^{García, 2004}). The floor area is sandy loam, slightly alkaline pH 7 to 8 (^{Ortiz, 1997}). The meadows were established in February 2010. The planting of grasses was conducted in rows 30 cm (grasses), while the legume was planted perpendicular with a row spacing of about 30 cm; based on the densities of 20, 30 and 5 kg ha-1 for orchardgrass, perennial ryegrass and white clover respectively.

The meadows were not fertilized and in the dry season, irrigation at field capacity every two weeks were provided. Before starting the investigation, a grazing uniformity was performed with sheep which were used as defoliants garnering approximately 5 cm above the ground and delimiting plots with electric fence. The grazings were performed every 4 weeks in spring and summer and every 5 to 6 weeks during autumn and winter, respectively.

The restriction to the legume was 10 and 50% minimum and maximum, respectively. Treatments consisted of the following associations: 20-40-40, 00-50-50, 40-20-40, 50- 00-50, 20-70-10, 70-20-10,100-00-00, 40-40-20 % of skein (Ov), ryegrass (Ba) and white clover (Tr), respectively. The treatments were randomized in 24 experimental plots of 9 by8m.

Growth rate. The seasonal average growth rate of associations and grass alone, was calculated performance data obtained in each grazing and repetitions each, with the following formula:

TC=R/T

Where: TC= seasonal average growth rate (kg MS ha^-1 d^-1); R= seasonal yield (kg MS ha^-1) and T= days after each season.

Plant density. At the beginning of the experiment, a fixed box 1 m² randomly in each experimental unit was placed. One day after each grazing the number of plants present in grasses (clew, perennial ryegrass) was recorded, while in the legume (white clover) was through coverage (%) and thus obtained the average plant by species seasonally.

Intercepted radiation. A day before each grazing, were randomly five readings of radiation intercepted by repetition with the method of wooden meter in each experimental unit. Readings were taken at approximately 13:00 h. The procedure consisted of placing the rule on the soil surface (under the canopy), with north-south orientation and immediately after, the shaded centimeters were counted, which represented the percentage of radiation intercepted by the crop canopy.

Climate data. In Figure 1 the average of the maximum and minimum seasonal temperature recorded during the experimental period is observed. The maximum temperature was between 21 and 26 °C, while the minimum temperature was between 3 and 10 °C. The highest temperature was presented in the spring of both years, with an average of 26 °C. The lowest temperature was presented in the fall and winter seasons with 5.7 and 3.6 °C, respectively. Acumulative precipitation was obtained in the first year of 424.81 mm, spring-summer 2013 the highest rainfall was obtained with 378.28 mm (89%). The accumulated rainfall in the second year was 332.8 mm, obtaining the highest rainfall in the spring and summer of 2014 with 289.78 mm (87%). In seasons with low rainfall: autumn and winter of two years, irrigation at field capacity every two weeks was provided.

Figure 1 Average temperature maximum, minimum, accumulated rainfall and irrigation to field capacity during the study period (09-2012 to 09- 2014) (http://www.cm.colpos.mx/meteoro/). 

Statistical analysis. To compare the effect of the associations studied, an analysis of variance with mixed models procedure (^{SAS, 2009}), with a randomized block design with three replications was performed. The comparison of means was performed using the adjusted Tukey test (α= 0.05).

Results and discussion

Growth rate. Table 1 shows the seasonal average growth rate occurs during the experimental period. In the first year, the TC average of all associations was 51 kg MS ha^-1 d^-1 and 3 kg MS ha^-1 d^-1 in the second year (48 kg MS ha^-1 d^-1). In both years, associations 20-70-10, 40-20-40 and 20-40-40 of Ov- Ba-Tr obtained the highest TC and were statistically different from the others (p< 0.05), while orchard grass only he got the lowest TC (34 and 30 kg MS ha^-1 d^-1) for both years (p< 0.05).

Table 1 Seasonal changes in the growth rate (TC; kg MS ha^-1 d^-1) of orchard grass (Dactylis glomerata L.) alone and associated with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) for two years of study. 

On the other hand, regardless of associations, during spring and in both years was recorded as TC with an average of 68.5 kg MS ha^-1 d^-1, followed by summer with an average of 57.5 k kg MS ha^-1 d^-1 after winter with an average of 42 kg MS ha^-1 d^-1, and finally the winter season with an average of 31 kg MS ha^-1 d^-1 (p< 0.05). These results agree with those reported by ^{Velasco et al. (2001)} and ^{Brown et al. (2015)}, where they found the highest rate of growth in spring and summer. Meanwhile ^{Villareal et al. (2014)} in orchard grass reported the highest growth rate in spring and summer with an average of 98.5 kg MS ha^-1 d^-1 regardless of the intensity and frequency of grazing.

These growth rates are higher than those reported in this investigation, however; when this work had already been started three years from planting so their persistence and therefore probably decreased the dry matter yield and growth rate. Such behavior is generally attributed to the ability of orchard grass, perennial ryegrass and white clover to compete for light, water and nutrients whose effects are evident in the rate of appearance and elongation of leaf area (^{Durand et al., 1999}). In autumn, the lowest growth rate can be attributed to the low temperatures recorded in the period as ^{Hernandez-Garay et al. (1997a)} indicate that low temperatures cause reduced growth and herbage accumulation rate, direct influence of a lower rate of occurrence and leaf expansion.

Meanwhile, ^{Brock and Tilbrook (2000)} mention that changes in the growth rate in the different seasons, are directly related to temperature, and to have the best expression in the growth temperatures of 18 required and 21 °C for perennial ryegrass and clew, respectively, while for white clover 24 °C. Meanwhile, ^{Sanderson (2010)} in a two-year investigation into associations clew and white clover, found on average the highest growth rate in the spring with 62 kg MS ha^-1 d^-1, followed by summer with 47 kg MS ha^-1 d^-1. These growth rates are consistent with those of the research in spring and summer of both years.

Plant density. In Table 2 are observed seasonal changes in plant density, where the average first year of orchard grass was 24 plants m^-2 and decreased to 23 plants m^-2 for the second year. In both years, the orchard grass alone (100-00-00) was the one that had the highest density, with an average of 31.5 plants m^-2, while the association 20- 40-40 Ov-Ba-Tr showed the least average density of 15 plants m^-2 (p< 0.05). The ryegrass was the species with the lowest density of plants throughout the investigation with an average of 3 and 2.5 plants m^-2 for the first and second year, respectively, without differences. The association 00-50-50 Ov-Ba-Tr was the one that registered the highest density of plants m^-2 of perennial ryegrass with an average of two years of 4.8 plants m^-2, and associations 40-40-20, 20-70-10, 20-40-40 and 70-20-10 of Ov-Ba-Tr were those which had the lowest density with an average of 2 plants m^-2 for both years (p< 0.05).

Table 2 Changes in plant density (m^-2) of orchard grass (Dactylis glomerata L.) alone and associated with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) for two years of study. 

White clover was the species that showed the highest density with 41 plants and 38 plants m^-2, for the first and second year, respectively (p< 0.05). The association 00-50-50 Ov-Ba-Tr, in both years, had the highest density with an average of 66.5 plants m^-2, while the association 40-40-20 Ov-Ba-Tr was that he recorded the lowest density in two years, with an average of 30 plants m^-2 (p< 0.05). The highest density of white clover plants coincides with the largest contribution of white clover in the botanical composition and forage Table 2. Changes in plant density (m^-2) of orchard grass (Dactylis glomerata L.) alone and associated with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) for two years of study. yield in winter for both years. Regardless of species, plant density was maintained and can be attributed to the meadow was three years after planting and therefore plants tend to stay longer in the first year is when the largest number of plants is lost. Meanwhile ^{Sevilla et al. (2001)} mention that the death of plants is higher in spring and other seasons, plant density tends to remain; moreover, that the minimum density required to not affect its growth is 30, below which, the prairie markedly decreased forage production.

These plant density changes are reflected in the growth rate of the crop and are attributed to environmental conditions, especially temperature (Figure 1) for its direct influence on photosynthesis (^{McKenzie et al., 1999}). In this regard, ^{Hernandez Garay et al. (1999)} mention that stem density can be manipulated by defoliation, changing the frequency and intensity of harvest can be increased stem density in perennial ryegrass. ^{Moreno et al. (2015)} reported associations of grasses and legumes white clover contribution was higher in autumn and winter and lower in spring and summer. In this regard, ^{Chapman and Lemaire (1993)} entered the grasslands respond differently to management practices that will affect their persistence and intensity effect performance and harvest interval way. In this particular research species benefit from the management and temperature were provided orchard grass and white clover.

Intercepted radiation. Regardless of the association during the spring season of both years, most intercepted radiation with an average of 92% (Table 3), and lower in autumn the second with an average of 78% of intercepted radiation was presented (p< 0.05). Only associations 20-40-40, 40-20- 10 and 20-70-10 of Ov-Ba-Tr reached 95% of intercepted radiation during spring of the first year, it is worth noting that these same associations have the highest rate growth (Table 1) and therefore forage yield. On average the first year and second year the associations were intercepted more solar radiation 20-70-10, 40-20-40, 40-40-20, 70- 20-10 and 50-00-50 of Ov-Ba- Tr averaging 89.2 and 87% for the first and second year, respectively; while only orchard grass (100-00-00) was the lowest radiation intercepted average of 74 and 71% for the first and second year, respectively (p< 0.05).

Table 3 Seasonal changes in intercepted radiation (%) of orchardgrass (Dactylis glomerata L.) alone and associated with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) for two years of study. 

The above data show that the ability of associations to interpret solar radiation depends on the percentage of each species associated and environmental conditions to which they were exposed during their previous growth each harvest (^{Federick et al., 1999}; ^{Horrocks and Vallentine, 1999}; Da Table 3. Seasonal changes in intercepted radiation (%) of orchardgrass (Dactylis glomerata L.) alone and associated with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) for two years of study.

Silva and Hernandez-Garay, 2010). Here, ^{Sevilla et al. (2001)} mention that the minimum density required to not affect its growth is 30 plants m^-2, below which, the prairie markedly decreased forage production, growth rate and intercepted radiation. Similar results were found ^{Flores et al. (2015)} in nine associations orchard grass, perennial ryegrass and white clover, where regardless of the association, the intercepted radiation presented the following descending order: summer > spring > autumn > winter with 93, 92, 88 and 86%, respectively.

Relationship between growth rate (TC) and intercepted radiation (RI). In the Table 4 shows the regression coefficient (R²) between the growth rate and intercepted radiation is observed. Except for the association 40-20- 40 Ov-Ba-Tr where there was no significant difference (p> 0.05) between TC and RI, all other treatments had close relationship between these variables, the greater the higher growth rate It is intercepted radiation. The growth rate varied seasons (Table 1) and the main factors were temperature and light hours as during spring and summer temperatures were recorded and CT and RI older were presented, otherwise to winter, where observed the minors TC and RI.

Table 4 Regression coefficient (R²), growth rate (TC) between intercepted radiation (RI) two years in clew (Dactylis glomerata L.), alone and in association with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.). 

In this regard, ^{Hernandez-Garay et al. (1997}b) indicate that the population dynamics of stems is a function of the rate of occurrence and death of stems, different rates with the handling and the station and these in turn with the leaf area index and growth rate (^{Lemaire and Chapman, 1996}). In research with alfalfa, to evaluate the frequency and intensity of grazing found that the maximum intercepted to 95%, radiation matched the highest leaf area index (3.6) and growth rate (^{Teixeira et al., 2007}).

Conclusions

Associations 20-70-10, 20-40-40 and 40-20-40 of Ov-Ba- Tr showed the highest growth rates, and lower, the recorded orchard grass alone. Regardless of the association, the highest and lowest growth rate occurred in spring and autumn, respectively. The density of plants in grasses did not vary between year, however, the legume had higher and lower density of plants in the first and second year. Associations intersected 95% of solar radiation were 20-40-40, 40-20-40, 20-70-10 Ov-Ba-Tr spring only in the first year. There is a close relationship between the growth rate and intercepted radiation.