Monthly chemical composition variations in grazable material of semi-arid rangelands in north-western Greece

I Mountousis, K Papanikolaou, F Chatzitheodoridis^*, C Roukos and A Papazafeiriou

Department of Animal Production, Faculty of Agriculture, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece
*Technological Educational Institute( T.E.I) of Western Macedonia., Terma Kontopoulou str., 53100 Florina, Greece
fxtheo@econ.auth.gr
Corresponding Author: Ioannis Mountousis: Municipality of Kato Klines - Kato Klines - 531 00 Florina - Greece
dkklinon@otenet.gr (Ioannis Mountousis)
klineota@yahoo.gr (Ioannis Mountousis)

Abstract

The present study was conducted to evaluate the effects of growing season and altitude on the chemical composition of grazable material in a semi-arid region of Municipality of Siatista, North-western Greece.The effect of harvest month and altitudinal zone on aboveground biomass production and chemical composition (crude protein (CP), ash, ether extracts (EE), NDF, ADF, cellulose, and lignin) as well as calcium (Ca) and phosphorus (P) concentrations were studied in herbage samples harvested from 10 experimental cages placed in 2 different altitudinal zones (lower zone: 500 to 1000m - upper zone: 1000 to 1600m) throughout the experimental period (May-October 2004). Sample collection was accomplished by cutting aboveground biomass at a height similar to that grazed by small ruminants.

The statistical analysis showed an important effect (P<0.05) of the harvest month and altitudinal zone on the aboveground biomass production, while it didn't seem to be affected by "month x altitude" interaction. Ash, EE, fibre fractions and CP contents as well as P and Ca:P concentrations affected significantly (P≤0.01) by the harvest month but not the Ca concentration. It was found that altitudinal zone had a significant (P<0.001) effect on EE, fibre fractions (except NDF) and CP contents as well as (P<0.01) Ca concentration, whereas altitudinal zone had no significant (P>0.05) effect on ash content and P and Ca:P concentrations. None (except CP content) of measured parameters affected by "month x altitude" interaction. Protein requirements of sheep covered only at the beginning of the growing season, while P may be seasonal sufficient for ruminants, especially cattle.

The data suggest that additional protein sources and P mineral supplement should be supplied in order to meet the needs of the grazing animals.

Keywords: Altitudinal variations, biomass production, chemical composition, Greece, subalpine rangelands

Introduction

Traditional stockfarmings of ruminants (sheep, goat and cattle) utilize in a high degree the Greek native grazing lands. Both, herbaceous and woody plants should occur in grazing lands as they are considered important contributors to grazing animals nutrition (Papachristou and Nastis 1993a, b; Espejo-Diaz 1996). However, because of the thoughtless use of pasturelands, often supplementary feed is required to compensate animals for pasture deficiencies (McDowell 1985). Grassland nutritional quality is affected by abiotic and biotic environmental factors including soil type, climatic regime, botanical composition and range improvement practices (Pérez-Corona et al 1998; Ramirez 1999, George et al 2001). On open rangelands, the quality and quantity of forage varies appreciably with climate and often leads to nutritional inadequacy (Ramirez 1996). At landscape scale, topographic factors such as slope, aspect and altitude, together with soil characteristics such as nutrients, structure and texture which largely depend on underlying geology, influence the biomass production and quality of grazable material of pasturelands (Mutanga et al 2004).

Protein content and digestibility of dry matter have been emphasized as the main determinants of forage quality (Pérez-Corona et al 1998). However, much less attention has been paid to minerals (especially calcium and phosphorus) even though they also influence forage quality and can depress feed intake when levels are low (Provenza 1995).

Stockmen managers need to understand nutritional dynamics of forages on rangelands to sustain adequate growth and reproduction of their animals. In a similar vein, those marketing pasture should also be aware of nutritional characteristics of their forages to assure reception of equitable payment. Despite a long history of livestock grazing in north- western Greece, there have been few concerted efforts to quantify annual nutritional dynamics of many of the region's pasturelands.

The quality of grazable material is of great significance to animal production as nutrition is an important factor of the feeding cost of farm ruminants (Kitsopanidis et al 1986; Zioganas et al 2001). Quality is the parameter that includes the concentration of the partial nourishing constituents (chemical composition), the biomass quantity that was consumed (food intake), the digestibility and the segregation of metabolism products of the animals (Βιιxton 1996).

Although chemical methods can not directly assess the food value of grazable material, they are based on the statistic correlation in order to assess the digestibility and food intake. However, in combination of the use of patterns, they are increasingly used to foresee animal's productivity or to define the factors that may restrain animal's production (Minson 1981). The protein and cellular content, as well as the rate of inorganic elements of grazable material and digestibility, are highlighted as the major factors of pastures' quality (Ballard et al 1990; Pérez-Corona et al 1998).

The objective of this study was to evaluate the effects of growing season and altitude on production and chemical composition of the herbage of typical semi-arid mountain grassland in West Macedonia, Greece.

Materials and methods

Study area

This study was conducted in the pasturelands of Municipality of Siatista, West Macedonia - Greece (40^o 12΄ to 40^o 18΄ N, 21 ^o 30΄το 21^o 40΄E, 500-1600m above sea level). The basic geological substrate of the whole research area is consisted of metamorphic rock textures (i.e. phyllites, gneisses and limestone) of the west Pelagonic geotectonic zone. The fertility of the soil varies depending on slope, exposure, degradation and vegetation. The mountain and topographic lie is quite tense and, in combination to the climate conditions that change from zone to zone, create an impressive variation of flora from the lowest to the upper most zones. The climate approaches the Greek climatic conditions having as major characteristics long lasting and very hot summertime, soft winter and humidity in all seasons of year. The monthly average air temperature as well as rain precipitation in the decade 1992 - 2001 was 13.0ºC and 337mm respectively (HNMS 2005).

The studied pasturelands, which cover 4.021 hectar, were grazed by 19.787 small ruminants and 491 dairy cattle. They were divided in two seasonal areas according to grazing time (Papanikolaou et al 2002). That is, from 600 to 1300m, they are grazed during spring and autumn, while over 1300m they are grazed in summer. Their productivity and maturity time were mainly affected by climatic and soil conditions as well as grazing management in last decades.

Sample collections and preparation

The research work was conducted during the year of 2004, from May to October. Ten experimental cages, sized 6m x 5m, fenced with metallic net 1.5m high in order to obstruct free - range grazing, were placed. Five experimental cages were placed in each of the two altitudinal zone (lower zone: 500-1000m, upper zone: 1001 - 1600m).

Each experimental cage was divided into 36 equal parts. In the beginning of each month, from May to October aboveground biomass was collected from 6 different of the 36 equal parts. Sample collection was accomplished by cutting aboveground biomass imitating the way of small ruminant grazing (Odum 1971). The collected biomass was stored in paper bags and was weighted immediately afterwards. In laboratory all samples were oven-dried at 68⁰C until a steady weight.

The proportion of moisture was estimated by the difference of the immediate weight in the fields and the weight after drying.

Afterwards it followed the grinding of the plant samples and the storage to glass containers, which were prepared and ready for chemical analysis. The chemical composition of the samples was defined based on the AOAC methods (1999), as far as dry matter, ash and crude protein were concerned (Kjeldahl's distillation method), while EE were defined with diethyl ether extraction in a Soxhlet apparatus and the definition of fibre fractions (NDF, ADF, cellulose and lignin) was achieved by Goering and Van Soest (1970) method. Samples were also analyzed for calcium (Ca), and phosphorus (P. An acid digest was prepared by oxidizing each sub-sample with a nitric/perchloric acid (2:1) mixture. Aliquots were used to estimate Ca by flame photometry and P by spectrophotometeric methods (Khalil and Manan 1990). Each sample was analysed in triplicate.

Statistical analysis

The data were analyzed statistically using univariate ANOVA testing for the effects of sampling month, altitudinal zone separately and month x altitude interaction, using the SPSS 12.0 (SPSS 2003). It was also carried out an analysis of the correlation and a stepwise regression of the variables with the help of the former statistic method. The significance level was assessed to P<0.05, except the existence of a different indication.

Results and discussion

Aboveground biomass production

The statistical analysis showed an important effect (P<0.05) of both, harvest month and altitudinal zone, on the aboveground biomass production, while "month x altitude" interaction didn't seem to affect significantly the biomass production (Table 1).

The typical shape of grassland growth is a sigmoid curve, increasing to a maximum and then decreasing (Pérez-Corona et al 1998). Biomass production in two zones resembled this pattern.

Aboveground biomass production showed a differentiation among subsequent or different months in both altitudinal zones. However, it presented similar fluctuation in production, which was increasing from May to October, showing its peak in July in the lower (94.29 ± 17.66 g DM /m²), as well as in the upper zone (204.58 ± 122.35g DM /m²) (Fig 1).

According to George et al (2001), precipitation determines the beginning and the end of growing period of plants, while the air temperature usually determines the amount of aboveground biomass production during the vegetative period.

In the experimental area, after July, because of the high temperature and low moisture in the soil, plants matured rapidly. In the last two decades a gradual degradation of the mountain and hill grasslands of the region has taken place as a result of either overgrazing of some areas or undergrazing of others (Boyazoglu and Flamant 1991; Skapetas et al 2004). As a consequence, productivity is low and this situation is made worse through unfavourable climatic and soil conditions, poor management techniques specifically in the lower zone.

The aboveground biomass production had a negative relation (P>0.05) to the harvest month (r= -0.256), ash (-0.126) and lignin (r= -0.235) content as well as Ca (r= -0.136) and P (r= -0.203) concentrations. On the contrary, it had positive relation (P>0.05) to the NDF (r= +0.282), ADF (r= +0.056) content and Ca:P (r= +0.011) concentration. It was found also, that biomass production positively correlated (P<0.001) with altitudinal zone (r= +0.447) and (P<0.05) EE (r= +0.335) content (Table 2).

To measure the quantity of interdependence of herbage production of pasturelands and altitudinal zone, that are statistically significant (P<0.05), it was carried out a stepwise multiple regression (Table 3).

Crude protein, ash, ether extracts and fibre fractions content

The CP content decreased as the growing season progressed in both altitudinal zones, showing its minimum (4.76 and 7.03 % of DM in the lower and upper zone respectively) in August. Statistical analysis showed that both, the harvest month and the altitude (P<0.001), as well as (P<0.05) "month x altitude" interaction, influenced significantly the crude protein content (Figure 1).

The statistical analysis indicated a positive correlation among CP to biomass production (r= +0.197), Ca (r= +0.089) and Ca:P (r= +0.012) concentration, as well as a positive relation (P<0.01) to altitudinal zone (r= +0.625) and ash (r= +0.405) and EE (r= +0.614) content. On the contrary there was a negative correlation (P<0.05) to the harvest month (r= 0.334), NDF (r= - 0.591), ADF (r= - 0.829), cellulose (r= - 0.801) and lignin (r= - 0.795) content and P (r= -0.100) concentration (Table 2).

As plants advance in maturity, their leaf/stem ratio usually decreases.The CP also declines with stage of maturation (Pérez-Corona et al 1998; Vázquez-de-Aldana et al 2000). Consequently, the rapid reduction of CP content is due to the different phenological stage of vegetation. It has been proved (Peterson et al 1992; Sheaffer et al 1992; Buxton 1996) that the ripening of plants concludes in the reduction of crude protein content on leaves and stems, but also leads to a greater analogy of stems, which have lower crude protein content than this of leaves, to the produced biomass.

To ewes that weigh approximately 50 kg the daily protein needs of preservation come up to 95g kg ^-1 (9.5%) of dry matter (NRC 1985). In both altitudinal zones, it was proved that these needs were adequately covered only in the beginning of the experimental period whereas for the rest of the period additional protein sources should be supplied in order to cover the needs of preservation of the grazing animals.

Mean ash content was found to be 7.91 % and 8.48 % of DM in the lower and upper altitudinal zone respectively (Figure 2).

Ash content influenced significantly (P<0.01) by the harvest month, while there was not influenced by altitudinal zone and "month x altitude" interaction (Table 1). Ash positively correlated with altitude (r= +0.106), EE (r= +0.086) and (P<0.01) CP (r= +0.405) content whereas it had been negatively correlated to Ca (r= -0.023), P (r= -0.098) and Ca:P (r= -0.053) concentrations, NDF (r= -0.409) content, harvest month (r= -0.185) and herbage production (r= -0.126). It was found also negative relation (P<0.05) between ash and ADF (r= -0.449), cellulose (r= -0.470) and lignin (r= -0.305) content (Table 2)

Month-to-month of ether extracts content was quite variable among different altitudinal zones. In the lower zone, the peak of EE content (1.72 ± 0.90 %of DM) showed in early June, while the minimum value (0.97 ± 0.24% of DM) indicated in late August. The peak of EE content (2.21± 0.57% of DM) in the upper zone, indicated at the beginning of growing season while the minimum value (1.08± 0.23% of DM) indicated in September (Figure 2). Statistical analysis showed that EE content influenced significantly (P<0.001) by both, harvest month and altitudinal zone, while there was no influence by "month x altitude" interaction (Table 2). Ether extracts content positively correlated (P≤0.05) with altitudinal zone, biomass production and CP content, while it was indicated negative relation to harvest month, fibre fractions and mineral concentrations (Table 2).

Fibre fractions contents were increasing till early August and then declined till late October in the upper zone while, in the lower zone, they were increasing continuously (except NDF) as the growing season progressed (Figures 3 and 4).

Statistical analysis showed that all fibre fractions strongly affected (P<0.001) by the harvest month as well as the altitudinal zone (except NDF), while it was indicated no affection of "month x altitude" interaction (Table 1). The NDF content correlated positively with harvest month, altitudinal zone, biomass production and Ca and P concentrations, while it was found negative relation of NDF to ash, EE and CP content and Ca:P concentration (Table 2). The ADF, cellulose and lignin contents indicated similar relations to harvest month, altitudinal zone, biomass production, ash, EE and CP content and to mineral concentrations (Table 2).

Mineral concentrations

Mean Ca concentration was found to be 0.860 % and 1.030 % of DM in the lower and upper altitudinal zone respectively (Figure 5).

According to NRC (1985), these values were higher than those of sheep requirements (0.20 to 0.82% of DM), as well as than those of cattle requirements (0.32 % of DM, NRC 1996). In Tanzania (Rubanza et al 2005) as well as in Spain grazing land's (Pérez - Corona et al 1998) Ca content was found to be, also, higher than that suggested by the NRC (1985 and 1996) sheep and cattle requirements, respectively. Christoforidou (2004), reported from Chalkidiki peninsula, northern Greece that in an over-grazed shrubland, Ca content varied from 1.44% to 0.74% for the period from April to October. Ca concentration influenced significantly (P<0.01) by the altitudinal zone, while there was no influence by harvest month and "month x altitude" interaction (Table 1). The relation of Ca concentration with the other measured parameters is shown in Table 2.

Month-to-month of P concentration was quite variable among different altitudinal zones. An average P value was found to be 0.233 % and 0.236 % of DM in the lower and upper altitudinal zone respectively (Figure 5). These values were greater of the lower sheep requirements (0.16% of DM) suggested by NRC (1985), but lower of the higher sheep requirements. However, P concentration had lower mean levels, than those (0.27 % of DM) of grazing cattle requirements (NRC 1996), in both altitudinal zones. P concentration affected significant (P<0.001) by the harvest month, while there was no affection by the altitudinal zone and the "month x altitude" interaction (Table 1). It was found (Table 2) a positive relation between P content and altitude, harvest month, fibre fractions and Ca concentration. On the contrary P content correlated negatively with aboveground biomass production, ash, EE and CP contents and Ca:P concentration. Contents of minerals in forages, including P, decrease with plant maturity (McDowell 1996). Phosphorus deficiency is most likely to occur when ruminants graze native forages (Greene 2000). For grazing ruminants, while calcium is adequate in forages, phosphorus, however, can be deficient in these forages (Ward and Lardy 2005).

Ca:P ratio showed its minimum during August (2.21 in the lower and 3.06 in the upper zone) and its peak at late September (5.74 in the lower and 6.79 in the upper zone) in both altitudinal zone (Figure 5). Statistical analysis showed that Ca:P ratio was affected significantly (P<0.001) by the harvest month while there was no affection by altitudinal zone and "month x altitude" interaction (Table 1). According to many researchers, the ideal ratio Ca:P in ruminant feeds, is 2:1 (Liamadis 2003). In our study, during the whole experimental period, the Ca:P ratio was higher than the ideal 2:1. Relative researches has shown that this ratio could be vary from 1:1 to 7:1, without unfavourable effects, if it would provided satisfactory quantities of vitamin D. Ruminants are characterized by remarkable ability of tolerance in wider quantitative relations Ca:P, because they browse high amounts of dry grazable material rich in vitamin D (Liamadis 2003). These results obtained in the current experiment were in agreement with those findings.

Conclusions

• Semiarid pasturelands usually supply livestock with high food quality during spring but forage quality declines rapidly as grazable material matures. Moreover, a gradual degradation of the mountain and hill pasturelands of the region has taken place as a result of poor management techniques and made worse through unfavourable climatic and soil conditions.

• Crude protein content was enough to cover only the maintenance needs of ewes at the beginning of the growing season and then declined. Fibre fractions were increasing continuously as the growing season processed. Ash and EE contents showed a similar variation and decline till late August and increased afterwards to the end of experimental period. Month-to-month mineral concentrations were quite variable among different altitudinal zones. Ca concentration was above ruminant requirements while P content was slightly higher of lowest sheep requirements but much lower of cattle requirements. Ca:P ratio found to be higher than the ideal 2:1 ratio during the whole period.

• It was recommended that additional protein sources and P supplement should be supplied in order to cover the needs of preservation of the grazing animals during the grazing period in our experimental area. Furthermore rational range management techniques are required to elevate the quality and quantity of grazable material and maintain the traditional pastoralism of these landscapes.

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Received 26 July 2006; Accepted 20 September 2006; Published 1 November 2006

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