J Sci Food Agric 1997, 73, 200È206

Mineral Composition of Soils and Vegetationfrom Six Mountain Grassland Communities inNorthern SpainIsabel and Concepcio� n Garci�a-OlallaAlonso*

Estacio� n Agri� cola Experimental (CSIC), Apdo 788, Leo� n, Spain

(Received 3 November 1995 ; revised version received 3 June 1996 ; accepted 5 July 1996)

Abstract : The soil concentrations of Ca, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn,and the seasonal variation of these elements in the herbage from six plant com-munities in the Cantabrian Mountains of Spain, were determined. In eachpasture, 10 vegetation samples were collected monthly during the grazing season,together with 20 samples of soil in June to assess the soilÈplant relationships.Total elemental concentrations were determined in acid digests by atomicabsorption spectrophotometry. The results are discussed, comparing the valuesin soil and pasture samples and pointing out the implications for herbivores. Theconcentrations of Cu, K, Mg, N, Ni and Pb in soils were within the range con-sidered typical or slightly higher (except in Nardus stricta grasslands, with a highNi value) ; the values of Ca, Fe and Na were low and the concentrations of Mnand Zn surprisingly high. The mineral composition of the vegetation was notrelated to that of the soils. Seasonal di†erences with statistical signiÐcance werefound in the composition of herbage samples, except for the grasslands under theclosed cover of Genista Ñorida. Nardus stricta and Bromus erectus grasslandsshowed the best range of mineral concentrations for animal feeding during thesummer.

Key words : elemental composition, seasonal variations, mountain pastures, soils,animal requirements, livestock management.

INTRODUCTION

A large proportion of the mountainous areas in North-ern Spain are managed as common lands, divided intopastoral units called “puertosÏ. They are hired to theshepherds for summer grazing. These grasslands aresubjected to diverse mineral inputs and outputs mainlyas a result of the herbivore grazing behaviour. The con-centration of mineral elements in the soil determines theabundance and distribution of plant species (Ben-Shahar and Coe 1992) which, consequently, inÑuencethe feeding behaviour of herbivores.

Besides nutritional characteristics such as Ðbre andprotein content, it is also important to evaluate themineral composition of the grasslands, since the deÐ-ciency of an element can a†ect the cattle performance

* To whom correspondence should be addressed at : Instituteof Terrestrial Ecology, Banchory Research Station, Banchory,Kincardineshire, AB31 4BY, UK.

and an excess can be toxic (De Vos et al 1989). Theavailability of the minerals in the soil, the plant speciesand its genetic requirement for speciÐc quantities ofnutrients for its growth and reproduction a†ect the con-centration in the plants (Beeson and Matrone 1976).The concentration of an element depends also on theage of the plants (Pegtel 1987 ; Georgiadis andMcNaughton 1990), on the environmental conditions inwhich the plants grow (Montalvo et al 1975) and on thepart of the plant analysed (Barnes et al 1990). Neverthe-less, very little data are available to date on the mineralstatus of soil and plants and the relationships betweenthem in mountain grasslands.

Therefore, the objectives of this work were : (a) tostudy the mineral composition of the soils and theassociated vegetation in order to evaluate the nutrientstatus for both plants and animals ; and (b) to quantifythe seasonal changes in vegetation from di†erent pas-toral communities, pointing out the implications for theherbivores.

200J Sci Food Agric 0022-5142/97/$09.00 1997 SCI. Printed in Great Britain(

Mineral composition of mountain grasslands and soils 201

METHODS

Study area

The study was carried out in the “puertoÏ La Liviada, anarea of about 100 ha, at a mean altitude of 1500 m, inthe Cantabrian Mountains (north-east of the provinceof Leo� n, Spain). The climate is typical of a mountainousarea with Atlantic inÑuence. The mean annual precipi-tation is 1319É5 mm and the mean temperature is 5É5¡C.Winters are long and cold, with frequent snow.Summers are characterised by low rainfall.

Sampling and analytical methods

A total of 240 herbage samples (10 samples] 6communities] 4 months) were randomly collectedevery month during the grazing season of 1990 (June toSeptember) from the six most representative com-munities of pastures present in the mountainous areasof Spain and Europe. They were named after the domi-nant species : (a) Bromus erectus, (b) Genista occidentalis,(c) Nardus stricta, (d) Erica australis, (e) Genista Ñoridaand (f ) Calluna vulgaris. Samples were hand cut at soillevel, dried in a drying oven at 65¡C for 72 h and thenmilled using a hammer mill through a mesh of 1 mmdiameter.

From each type of pasture, 20 soil samples were ran-domly collected from the top 20 cm of soil, using adigging tool. The 120 soil samples were air-dried, sieved(2 mm diameter) and milled prior to analysis.

Soil and plant samples were acid digested(hydrochloric and nitric acids) before determination ofCa, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn, concentra-tions by atomic absorption spectrophotometry (DeRuig 1986). The soil content and the seasonal variationof these elements in the pastures were studied. The ele-ments were not extracted prior to analysis. The nitrogencontent was determined after Kjeldahl digestion. P wasnot determined because A� lvarez et al (1990) had pre-

viously shown it to be deÐcient for herbage productionin the mountains of Leo� n, whereas there were few datafor other elements in this area.

The data were analysed by means of a factorialanalysis of variance, a Tukey test being used to test fordi†erences between means for all data. For the plantsamples, both species and months, were considered in a6 ] 4 factorial design (six pasture communities and foursampling times).

RESULTS AND DISCUSSION

The pastures studied were located on two di†erent soiltypes, which deÐned the soil composition (Table 1).Grasslands dominated by N stricta and those under GÑorida, E australis or C vulgaris shrubs were growing onacid soils (proto-ranker and brown ranker) with a meanpH of 4É6, 4É0, 4É4 and 4É6, respectively, while grasslandswith B erectus and G occidentalis were located on cal-careous bed-rock (lithosols), with a mean pH of 6É2 and7É1, respectively (Alonso, 1994). This fact is reÑected inthe di†erences of concentration of elements such as Caand Ni which were highest in the high pH soils andsigniÐcantly di†erent from those in the more acid soils(P\ 0É001) (Table 1). Ca showed also higher concentra-tions in the plant material of the grasslands with Berectus and G occidentalis (Table 2).

Mineral concentration in soils

The communities with species from the family Ericaceae(E australis and C vulgaris) showed relatively low valuesof Ca, Cu, K, Mn and Na in the soil. For the rest of theelements, statistically signiÐcant di†erences where foundamong the communities (P\ 0É001 ; except for Niwhere P\ 0É01). The soil substrata had as much inÑu-ence as the organic matter or other soil parameters andthe concentrations in the soil were poorly correlatedwith those of the plants (Alonso 1994).

TABLE 1Mean values of concentration (kg g~1) in the soil samples of each of the elements analysed in the six communities (n \ 60)

Ca Cu Fe K Mg Mn N Na Ni Pb Zn

Bromus erectus 5481 43É0 21506 3361 2394 Èa 1É10 2429 34É8 171É6 ÈaGenista occidentalis 8226 33É0 18442 1664 6099 704 0É59 801 37É4 52É5 136Nardus stricta 749 37É4 21795 2150 1823 4820 0É70 1500 19É8 72É9 314Erica australis 517 24É0 25435 1295 3646 242 0É62 527 18É8 49É3 147Genista Ñorida 602 28É4 23185 1237 1259 424 0É75 1564 21É5 42É1 140Calluna vulgaris 420 23É1 12758 1136 912 235 0É54 517 23É1 38É8 81

SE 850É85 2É06 2339É23 110É23 247É95 486É60 0É04 303É80 2É73 6É80 21É71SigniÐcance *** *** *** *** *** *** *** *** ** *** ***

a È, not tested.b ***, P\ 0É001 ; **, P\ 0É01.

202 I Alonso, C Garc•�a-Olalla

TABLE 2Mean values of concentration (kg g~1) in the plant material for each of the elements analysed in the 4 months (n \ 240)

Ca Cu Fe K Mg Mn N Na Ni Pb Zn

Bromus erectus 9356 7É0 206 10847 2147 388 1É96 648 5É5 11É1 91É9Genista occidentalis 7694 6É9 120 11078 1628 78 1É79 513 5É4 6É2 36É2Nardus stricta 3000 5É9 234 12720 1882 1124 2É00 1069 5É3 11É1 102É7Erica australis 2894 4É7 97 9806 1370 368 1É54 814 4É7 4É7 46É5Genista Ñorida 1824 5É8 185 10889 2051 877 1É90 493 4É7 10É1 78É4Calluna vulgaris 4327 4É3 72 9429 1643 162 1É66 657 5É2 4É3 38É3SE 337É90 0É29 17É54 505É08 90É43 28É61 0É04 82É81 0É38 0É47 2É56

June 3630 7É7 156 15479 1651 523 2É14 765 4É9 5É6 59É5July 5823 6É2 183 10900 1950 512 1É88 509 4É5 7É5 70É6August 5665 3É9 115 7024 1639 428 1É32 70 4É9 8É5 58É7September 4279 5É3 156 9776 1907 536 1É89 821 6É2 10É0 73É9SE 275É89 0É23 14É32 412É40 73É83 23É36 0É03 67É61 0É31 0É38 2É09

SigniÐcanceaCommunities *** *** *** *** *** *** *** *** NS *** ***Month *** *** ** *** ** ** *** ** *** *** ***

a ***, P\ 0É001 ; **, P\ 0É01 ; NS, not signiÐcant.

Most existing studies on the mineral composition ofboth plants and soils have been carried out in lowlandareas ; little similar work has been carried out in moun-tainous areas. This altitudinal di†erence may explainwhy our soil analysis data in this study di†ered fromthose of other authors ; in particular :

K, Mg, Mn, N, Ni, Pb and Zn concentrationsI Cu,were in the range or slightly higher than what isconsidered typical in mountain grasslands(A� lvarez et al 1990 ; Garci� a et al 1992) and inother ecosystems (Knezez and Ellis 1980 ; Morenoet al 1992). It was not possible to determine reli-able soil Mn and Zn for B erectus community.

Fe and Na values were lower than in otherI Ca,soils (Fried and Broeshart 1967 ; Knezez and Ellis1980 ; Jones and Thomas 1987 ; Garci� a et al 1992),in some cases below the optimum for plantgrowth reported by Rains (1976).

The concentrations of some heavy metals (Pb andZn) in some communities were surprisingly high for amountainous area far from urban or industrial inÑu-ences (except for the presence of a ski resort within2 km).

Zn values obtained would correspond to contami-nated soils (Gupta 1989 ; Van Dorst et al 1989). TorresMarti� n and Gallardo Lara (1991) found that the con-centration of Zn in the soil increased slowly when thevegetation was cut and since these communities aremostly overgrazed, this may be an explanation of ourresults. The concentration in the soils of G Ñorida, theless utilised community, was not very high, even thoughit is the closest to the road.

Bromus erectus grasslands showed the highest Pbconcentration, which was signiÐcantly di†erent from the

rest. This community, which lacks shrub species, is oneof the most widely utilised by cattle, being in some areasovergrazed. Pb is potentially toxic to all organisms,including human beings (Mengel and Kirkby 1982),who can accumulate it up to toxicity levels. Neverthe-less, a high concentration in the soil can be due to thebed rock composition (Jones and Clement 1971 ;Kabata-Pendias and Pendias 1984). This might be thecause in this case, because there are no emission sourcesclose by. The data were higher than those considered asthe mean concentration, but they were within the rangeof variation of this element and well below the300 kg g~1 that the European Union considers asupper limit in uncontaminated soils (Van Dorst et al1989).

Mineral concentration in plants

Di†erences in the chemical composition and thereforein the nutritional quality of the plants have been recog-nised since the Middle Ages (Beeson and Matrone1976). Soil Ca and pH can have a great e†ect on thevegetation and hence, calcareous rocks usually have acharacteristic Ñora, as seen in “La LiviadaÏ.

The concentration of the mineral elements in asoluble form in the plants is a useful indicator of what isavailable to animals, although only a small fraction isused (Burridge 1987). On the other hand, the geochem-ical study of the soil or the detailed analysis of thechemical composition of the plant material can be avaluable tool for predicting or detecting mineral deÐ-ciencies in livestock, because, although young leaveshave more protein (N) and less Ðbre, these also have alower concentration of other elements (Egan 1975).

Mineral composition of mountain grasslands and soils 203

Most of the elements in the plant samples of LaLiviada showed concentrations in the range of whatother authors considered normal for upland com-munities (Ferrer et al 1976 ; Marrs et al 1989 ; A� lvarez etal 1990 ; Garci� a et al 1990), except for Mn, Ni and Pbwhich were higher (Garci� a et al 1990).

There is no conclusive trend in the variations for anyelement throughout the grazing period, and, as found inprevious studies, di†erent patterns were observed foreach community. There were three types of pattern :

(1) Elements whose concentration decreases fromspring to summer, and increases again at the endof the period : N, K, Mg (except for B erectuscommunity) and Cu (Montalvo et al 1975 ;Garci� a Gonza� lez and Alvera 1986 ; Garci� a et al1990) (Fig 1).

(2) Elements with relatively high concentrations insummer : Ca and Zn (Fig 2), and Mg (in Berectus (Fig 1). Hopkins et al (1994) also found

higher concentrations of Ca, Zn and Mg inAugust than in May in permanent and sownswards.

(3) Elements with irregular pattern of variation : Na,Fe, Mn, Ni and Pb (Montalvo et al 1975 ; Joneset al 1989) (Fig 3).

Seasonal di†erences in Pb concentrations have beenreported by some authors (Jones et al 1989) and similarpatterns were found in hay meadows for Mg, K and Fe(Garci� a et al 1992). This can be related to the biochemi-cal changes in plants during maturation, the older partsbeing more concentrated in heavy metals. Chocarro etal (1989) pointed out that some variations in elementalcomposition in the herbage with time depend more onthe phenological status than on the species composition.Pb uptake by grasses seems to be minimal and their Pbcontent is more likely to be due to atmospheric deposi-tion (Jones et al 1989) in mountain soils. The lower Pbconcentration in G Ñorida soils and pasture may be due

Fig 1. Seasonal trend in the K, N, Mg and Cu concentrations of in the six grassland communities. (E a, E australis ; B e, B erectus ;G f, G Ñorida ; N s, N stricta ; G o, G occidentalis ; C v, C vulgaris ; Jn, June ; Jl, July ; Ag, August ; Sp, September.)

Fig 2. Seasonal trend in the Ca and Zn concentrations of the six grassland communities. (E a, E australis ; B e, B erectus ; G f, GÑorida ; N s, N stricta ; G o, G occidentalis ; C v, C vulgaris ; Jn, June ; Jl, July ; Ag, August ; Sp September.)

204 I Alonso, C Garc•�a-Olalla

Fig 3. Seasonal trend in the Na, Fe, Mn, Ni and Pb concentrations of the six grassland communities. (E a, E australis ; B e, Berectus ; G f, G Ñorida ; N s, N stricta ; G o, G occidentalis ; C v, C vulgaris ; Jn, June ; Jl, July ; Ag, August ; Sp, September.)

to the deposition of the mineral on the leaves of theshrub, which have a mean cover of 90È100% over theground surface, which would protect the herbaceousstrata.

There were few signiÐcant correlations between themineral content of soil and plant material. Soil Mg isrelatively well correlated with other minerals in theplants (up to 0É46), except with plant Mg (Alonso 1994).The second highest index appeared between soil andplant K (0É12). This element was described by PintoTobalina et al (1991) as the only one, together with P,which showed a correlation between soil and plants.Thus, the total metal concentrations in soils is not agood analytical criteria to asses metal contents in plants(Gupta 1989).

Following the data of Grace (1983) (Table 3), Fe, K,Mg, Ni and Zn presented adequate values for the nutri-tional requirements of animals, while Ca, Cu and Na,were deÐcient at least during some periods in somecommunities during the stay of the animals on the

mountain. Nevertheless, the high species diversity (132species were found in the area), with both shrubs andherbaceous plants, allows the animals to select a highquality diet, to compensate for the imbalance betweenmineral elements and Ðbre content and to rectify minornutrient deÐciencies within a short distance. The lives-tock feed on every community depending on the avail-ability of feeding resources and other factors, such asthe availability of shade or the weather conditions.

CONCLUSIONS

A large spatial heterogeneity was found in the chemicalcomposition of soils and herbage, considering the rela-tively small area studied.

The data here presented suggest that the mineralcomposition of the soil is not likely to be a limitingfactor for the plant growth in the grasslands studied,although further experiments are necessary to verify

TABLE 3Mineral requirements of sheep and cattle (following Grace 1983) in terms of their concentration on

grasslandsa

Ca Cu Fe K Mg Mn Na Ni Pb Zn

Bromus erectus CS CS CS CS CS CS cs CS CS CSGenista occidentalis CS CS CS CS cS CS cs CS CS CSNardus stricta cS cS CS CS CS CS cS CS CS CSErica australis cs cs CS CS cS CS cs CS CS CSGenista Ñorida cs cS CS CS CS CS cs CS CS CSCalluna vulgaris CS cs CS CS cS CS cs CS CS CS

a Abbreviations : Bold, upper-case letter : adequate for animal feeding. Regular, lower-case letter :deÐcient for animal feeding. C, cattle. S, sheep.

Mineral composition of mountain grasslands and soils 205

this. Soils in B erectus and G occidentalis grasslandsshowed the highest concentrations for the elementsanalysed. The vegetation data are in the range con-sidered as typical with concentrations unlikely to limitanimal productivity, except for short periods insummer. However, since the herbivores move throughthe whole area and feed on the di†erent plant com-munities, they can avoid deÐciencies with a varied diet.

It can be concluded that the mineral composition ofthese mountain grasslands is adequate for animal con-sumption, since in a relatively small area these grass-lands showed di†erent and complementarycharacteristics. Furthermore, the presence of livestock isdesirable in order to maintain these communities in aproductive state with a high biodiversity.

ACKNOWLEDGEMENTS

The authors wish to thank Dr C Campbell and Dr S EHartley for his suggestions and the help in checking theEnglish language and the referees for their comments onthe manuscript. Financial support was provided byDGICYT by means of the PB87-0349 and PB89-0039projects.

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