CHEMICAL COMPOSITION OF SPECIES-RICH PASTURES - M. Pinto^[36], G. Besga^[37] and M. Rodríguez^[38]

SUMMARY

Several authors have been working on the nutritive aspects of herbs and wild species reporting that their concentrations of Ca, Mg, Na, Co and Se are higher than those found in sown species (Fisher, 1996). In this sense, the introduction of wild species can supply high amounts of some elements as Ca or Mg that improve the mineral supply to the animals. In spite of this, there is still a lack of information to accurately evaluate the nutritive values, expected yields and management conditions of species-rich pastures. The objective of this work is to compare the chemical composition of species-rich pastures with L. perenne-T. repens pastures widespread species of Basque Country pastures.

Three hundred and fifty pasture samples were collected in 1988 and 1989, and the botanical composition and pasture chemical composition determined. Five botanical groups were defined “ryegrass”, “white clover”, “other grasses”, “other legumes” and “other species”.

Results show that plant Ca and Mg has significant correlation coefficients for all the groups. There is positive correlation between Ca and Mg plant concentrations and the 'other species' percentage, this means that an increase in the proportion of dicotiledoneus species as Taraxacum officinale or Plantago lanceolata in the pasture, which are the predominant “other species” found in this study, can increase the Ca and Mg supply to animal nutrition which agrees with the results described by Hopkins (1995). Besides, a positive relationship between 'other species' group and P and S herbage concentrations has been found.

INTRODUCTION

Agricultural policies in the European Union are enhancing the increase of biodiversity in all the ecosystems included in pastures. The effect that a species-rich pasture can have on animal nutrition is related to its chemical composition. In this sense, several authors have been working on the nutritive aspects of herbs and wild species reporting that soil macro and microconcentrations are higher than those found in sown species (Fisher, 1996). In spite of this, there is still a lack of information to accurately evaluate the nutritive values, expected yields and management conditions of species-rich pastures. Although, traditionally, high productive species have been sown as the ideal animal food, it seems that these species, such as Lolium perenne, can be deficient in N, P, Mg, Na and, even Ca in terms of animal nutrition. In this sense, the introduction of wild species as dandelion or others can supply high amounts of some elements as Ca, K or Mg to the animals. It is important to establish the nutritive value of the most common herbs, which can be found in species-rich pastures. The objective of this work is to compare the chemical composition of species-rich pastures with L. perenne and T. repens, habitual constituents of Basque Country pastures.

MATERIALS AND METHODS

Three hundred and fifty pastures and their soils were sampled between 1988 and 1990 in the north of the Basque Country. Soil conditions, pH as well as nutrient contents, were distributed on a wide interval. The average soil parameters are shown in Table 1.

For herbage and soil sampling a 0.5x1 m frame was thrown randomly. Grass inside the frame was cut and soil was sampled from 0 to 5 cm depth. Herbage samples were taken back to the laboratory where botanical composition was determined by hand separation. Herbage samples were separated into five groups, 1) only L. perenne; 2) only T. repens; 3) other grasses; 4) other legumes; and 5) other species.

Soil parameters were determined following MAPA analytical methods (MAPA, 1981).

Herbage chemical composition was determined as follows: Nitrogen by the Kjeldhal method, K, Ca, Mg, Fe, Cu, Zn, and Mn after a nitric-perchloric acid digestion by atomic absorption spectrophotometry (Zasosky and Burau, 1977), P by colorimeter using the phosphomolybdovanadate method and, S by turbidometry (MAFF, 1981).

RESULTS

In the Basque Country, permanent pastures are mainly composed of T. repens and L. perenne due to intensification by the farm management but there is a number of wild species present, the most frequent in the 'other grasses' group were: Holcus lanatus (26.7 percent), Dactylis glomerata (21.5 percent), Poa trivialis (18.6 percent) and Agrostis tenuis (13.8 percent); in the 'other legumes' group: Trifolium pratense (63.5 percent), Lotus cornicolatus (19.8 percent), Medicago sativa (12 percent) and Vicia sativa (11.4 percent) and in the 'other species' group: Taraxacum officinale (52.9 percent), Plantago lanceolata (25.5 percent) followed by Ranunculus acris (7.3 percent).

Table 1. Mean of soil fertility parameters for the 350 studied pastures.

*Numbers within parenthesis are standard deviations.

Table 2. Pasture yield and chemical composition related to “other grasses” percentage.

Table 3. Pasture chemical composition and dry matter related to “other species” percentage.

Table 4. Correlation coefficients between pasture chemical composition and percentage contribution of botanical groups.

*** highly significant;
** very significant;
* significant;
- ; not significant.

The absence or presence of these species has a remarkable effect on dry matter production and nutritive value of pasture. Thus, when the relationship between the “other grasses” group percentage, dry matter and chemical composition (Table 2) is considered, it is observed that Ca and P concentration in plant tissue is negatively affected by an increasing percentage of “other grasses”.

When the “other species” group is studied it can be observed that dry matter decreases dramatically when “other species” percentage increases (Table 3).

However, some nutrient concentrations in herbage, as Ca, Mg or S, increase when “other species” group increases to 75 percent, decreasing once this percentage is reached, in this way the lower production could be balanced out by a higher amount of nutrients in herbage.

Table 4 correlation values between chemical composition and percentage of contribution of the different botanical groups is shown. Low correlation coefficients but highly significant are found, especially for Ca and Mg, which decrease as grasses contribution to the pasture grasses increases and increase when legumes and “other species” percentage increases.

CONCLUSIONS

It can be said that species-rich pastures can be a good supply of mineral elements for animal nutrition if botanical composition is balanced in such a way that dry matter production is not severely affected. The presence of moderate percentages of herbs can provide an extra input of some nutritive elements as Ca and Mg.

REFERENCES

Fisher, G.E.J. & Baker L.J. 1996. The chemical composition of forb species in grassland. 16^th Meeting of European Grassland Federation pp 429-432. Grado, Italian.

Hopkins, A., Adamson, A.H. & Bowling, P.J. 1994. Response of permanent and reseeded grassland to fertilizer nitrogen. 2. Effects on concentrations of Ca, Mg, K, Na, S, P, Zn, Mn, Cu, Co and Mo in herbage at a range of sites. Grass and Forage, 49, 9-20.

MAFF. 1981. The analysis of agricultural materials (RB427) p. 156-157. Ministry of Agriculture and Fisheries and Food, London, U.K.

MAPA. 1981. Métodos oficiales de análisis de suelos y plantas. Ministerio de Agricultura, Pesca y Alimentación, Madrid

Zasoski, R.J. & Burau, R.G. 1977. A rapid nitric-perchloric acid digestion method for multi-element tissue analysis. Comm. Soil Sci. Plant Anal., 8(5), 425-436.