Biosolid effects on soil and native plant production in adegraded semiarid ecosystem in central Spain

Anaerobically digested biosolid was surface-applied at three

rates, 40, 80 and 120 Mg ha±1, to a degraded semiarid

ecosystem of the central region of Spain to determine the

effects of biosolids on soil chemical properties, total plant

cover and total above ground biomass 1 year after its

application. Biosolid amendment had little impact on soil

chemistry and nutrient levels. However, available P and

N-NO3 increased signi®cantly after application of biosolids.

The concentration of total soil heavy metals, Zn, Pb, Cd, Ni,

Cr and Cu increased with the application of biosolids as

compared against the control plot, but these increases were

not statistically signi®cant. The levels of DTPA-extractable

soil heavy metals did not change in the treated plots. Total

plant cover and total biomass production increased

signi®cantly in the biosolid treated plots. The most

favourable soil and vegetation results were found in 40 and

80 Mg ha±1 biosolid application rates.

I. WalterG. CuevasS. GarcõÂaF. MartõÂnezDepartment of Sustainable Use of Natural Resources, Instituto

Nacional de InvestigacioÂn y TecnologõÂa Agraria y

Alimentaria, Madrid, Spain

Keywords ± Biomass; biosolids; degraded soil; plant cover;

soil heavy metals; soil nutrients; Spain

Corresponding author: I. Walter, Department of Sustainable

Use of Natural Resources, Instituto Nacional de InvestigacioÂn

y TecnologiÂa Agraria y Alimentaria, Po Box 8111, 28080-

Madrid, Spain (E-mail: walter@inia.es)

Received 7 September 1999, accepted in revised form

10 October 1999

Introduction

Throughout history semiarid ecosystems in the central

region of Spain have gone through a large number of

different uses. Regardless of the causes, during the last

century these regions have experienced an overall reduction

of plant cover and an increase in bare soil. These areas are

frequently low in soil organic matter and plant-available N

and are low in fertility, produce little plant cover, have poor

structure and erode very easily (Whitford et al. 1989;

Fresquez et al. 1990).

Degraded semiarid soils may bene®t from the nutrients

provided by municipal biosolids when incorporated or

surface-applied as an organic fertilizer (USEPA 1980).

The addition of organic materials to soil adds nutrients, but

can also improve soil biological and physical-chemical

properties, and consequently speed plant establishment. The

establishment of improved plant cover has a feedback effect

with the addition of more organic biomass and the

development of a rooting system through the soil. Biosolids

have a high organic matter content and can be a source of

slow-release N and P and microorganisms (bacteria, fungi,

and actinomycetes) capable of reactivating the soil's own

micro¯ora and favouring the reactivation of its own vegetal

cover. (Sommers 1977). The application of biosolids to

de®cient semiarid calcareous soils stimulates plant growth on

account of increased availability of essential micronutrients

(O'Connor et al. 1983). The bene®ts and hazards of applying

biosolids to land have been extensively studied in the ®eld of

mining reclamation (Sopper & Seaker 1983; Sabey et al.

1990) and in agricultural systems (Walter et al. 1994; Sloan

et al. 1997; Snyman et al. 1998). However, little work has

been done in the semiarid central region of Spain (or

elsewhere in the semiarid Mediterranean ecosystems) to

evaluate the effects of biosolids on soil chemical properties,

plant cover and plant yields on native species.

Waste Manage Res 2000: 18: 259±263

Printed in UK ± all rights reserved

Copyright # ISWA 2000

Waste Management & ResearchISSN 0734±242X

259

The objectives of this study were to determine the effects

of anaerobically digested biosolids at three application rates

on (i) soil chemicals and heavy metal concentrations, and

(ii) plant foliar cover and above-ground biomass production

of native species on a degraded semiarid ecosystem.

Materials and methods

In April 1997, anaerobically digested biosolid (see Table 1)

obtained from the wastewater treatment plant of Madrid (La

China) was surface applied to a degraded semiarid soil site

35 km south-east of Madrid city. The source of this biosolid is

mainly fed by municipal waste water. The study design was a

completely randomized block in which all four blocks were

perpendicular to the slight slope (8%) of the terrain. Each

block contained four 3 3 10 m plots (with a 1-m buffer zone

between plots and 3 m between blocks) randomly assigned to

one of the following treatments: 0, 40, 80 and 120 Mg ha±1.

The climate of this area is Mediterranean, with a mean

annual precipitation of 350 mm and 16.88C of annual

temperature average. The soil is described as Lithic

xerorthents, according to Soil Taxonomy (1975). The plant

canopy cover is scarce (, 40% density) and it is mainly

composed of an herbaceous mixture of plants and slowly

growing low bushes (graminaceae, Plantago albicans, Helian-

temum aspererun, Teucriun pseudochamaepitys, Thymus

zygis, Centaurea melitensis, etc.)

Collected composite soil samples (12 cores per plots)

from a depth of 0 to 15 cm were taken from each of the

plots in March 1997 (pretreatment) and in April 1998

(1 year after the biosolid applications). The samples were

air-dried, and subsequently crushed to pass a 2-mm sieve.

All 16 composite soil samples from each of the two

sampling periods were analysed for determining their

chemical-physical properties by following of®cial Spanish

methods (Ministry of Agriculture, Fisheries & Food 1994).

The concentrations of soil total heavy metals were

determined in the HNO3-HCl extract (McGrath &

Cunliffe 1985) and in a DTPA (diethylenetriaminepentaa-

cetic acid) extract (Lindsay & Norvell 1978) by using a

sequential, multi-element inductively coupled plasma

(ICP) emission spectrometer (Perkin Elmer 400). The

methods of biosolid chemical analyses have been previously

described by Walter et al. (1989). Some chemical and

physical properties of the pretreatment soil and biosolids

are reported in Table 1.

The vegetation was measured in March, May and

September 1998 (12, 14 and 18 months after the biosolid

application, respectively) to obtain the percentage of total

plant canopy cover and above ground plant biomass. Total

plant canopy cover was estimated by measuring 16 individual

microplots of the treatment plots (0.22 m 3 0.22 m) along a

randomly permanent transect. Above ground plant biomass

was also randomly measured in each sampling period by

harvesting total vegetation on six 0.22 m 3 0.22 m quadrats.

All biomass was sampled at ground level by hand clipping.

Plant tissues samples were oven dried at 658C for 48 h, and

then weighed.

Variations in soil chemical properties, total plant cover

and plant yields amongst the unamended and biosolid

treatments were analysed using a one-way analysis of

variance at the 5% probability level. Duncan's multiple

range test was also used at the 5% probability level.

Results and discussion

One year after the surface application of biosolid the soil

chemical properties (Table 2) showed some de®nite changes.

All soil chemical properties were not signi®cantly higher in

biosolid treatments with respect to control, except for P,

Table 1. Chemical and physical properties from the pretreatment soil (mean from 16 plots) and biosolid

pH E.C.d Sm±1

CaCO3

g kg±1

OrganicMatterg kg±1

Totalg kg±1

PhosphorusAvailablemg kg±1

Totalg kg±1

NitrogenNH4-Nmg kg±1

NO3-Nmg kg±1

PotassiumAvailablemg kg±1

Texture

Soil 8.3 0.15 478 33.5 ± 7.9 2.18 3.95 7.23 205 Sandy loam

Biosolid 8.6 1.62 ± 434 10.6 613 25 2762 134 ± ±

Total and DTPA-extractable heavy metals (mg kg ±1)

Zn Pb Cd Ni Cr Cu

Total DTPA Total DTPA Total DTPA Total DTPA Total DTPA Total DTPA

Soil 23.2 0.93 36.6 1.40 0.54 nd 7.1 0.14 10.2 nd 6.44 0.32

Biosolid 445 106 252 94 1.0 0.28 15.3 5.6 48.5 0.32 174 17.20

nd, not detectable (below the detection limit). E.C., electrical conductivity.

I. Walter, G. Cuevas, S. GarcõÂa, F. MartõÂnez

260 Waste Management & Research

NH4-N and NO3-N. Organic matter levels did not

signi®cantly change with biosolids amendment even at the

highest rate. Fresquez et al. (1990), found similar results for

organic matter in a degraded semiarid grassland site south-

western USA. Electrical conductivity (EC) was higher in the

intermediate and high biosolid treatments than in the

unamended control but these increases were not statistically

signi®cant. White et al. (1997), reported a greater increase in

EC (more than 2 dS m±1) when 90 Mg ha±1 of biosolid was

applied on a silty clay loam soil. No similar pattern was found

at our study site with biosolid application rates above

90 Mg ha±1. The lowest increase of EC found in the present

study could be a result of the soil texture (Table 1) and the

exceptional high seasonal precipitation, which probably

lowered the salt content through leaching. Soil pH

decreased from 8.1 to 7.9 with biosolids application. The

small decrease in soil pH was probably on account of acid-

producing microbial reactions in the soil (Miller 1973).

Levels of available P soil were signi®cantly higher in the

biosolid treatments than in the unamended control. With

the application of biosolids, P increased linearly from 11 in

the unamended soil to 42 and 80 mg kg±1 in the 40 and

80 Mg ha±1 biosolids treatments, respectively. There were no

signi®cant differences between the intermediate and the

high application rates in NaCO3H-extractable P. White et al.

(1997), also reported increases in available P soil 1 year after

the application of biosolids. The two forms of inorganic N,

which comprises the available N pool, increased with the

biosolids application, but NO3-N showed the greatest

increase in the concentrations. NO3-N concentrations in

the soil surface layer are relatively high, and therefore,

application rates above 80 Mg ha±1 pose a potential hazard

for contamination of surface waters in case of signi®cant

runoff. At the highest biosolid application rate NO3-N-value

was about 15 fold more than its original value. This is

probably a result of the breakdown of organic-N derived from

the microbiological activity. In contrast, NH4-N concentra-

tions only showed a moderate increase at the highest biosolid

application rate.

The concentrations of all total soil heavy metals studied

were high as a result of the biosolids amendment (Table 3),

but these increases were not signi®cantly different. Levels of

DTPA extractable heavy metals in soil did not signi®cantly

change with biosolid treatments (Table 3). These results are

probably a result of the high pH and the high carbonate

content in this soil (Table 1). The amount of DPTA Cd and

Cr were below analytical detection limit (, 1 mg Cd kg±1

and , 0.8 mg Cr kg±1). The results obtained deserve special

consideration since heavy metals frequently limit biosolid

applications. These results differ from the results reported by

Aguilar et al. (1994), who observed a linearly increase in

DTPA Cu and Cd concentrations with biosolids application.

At our study site a remarkable change of native plants

has been observed 1 year after the surface application of

biosolids, with a reduction of perennial species and an

increase of annual plants (GarcõÂa 1999). These facts are

similar to those obtained by Biondini & Redente (1986),

who reported that plant diversity decreases in presence of

high nutrient levels. No similar pattern was found by Pierce

(1994) who reported that perennial grasses and shrubs

remain the dominant species in a semiarid shrubland after

biosolid treatment. Total plant canopy cover (Table 4)

increased signi®cantly in the three sampling periods. These

increases showed a peak at low and intermediate biosolid

rates. Biosolids applied at 120 Mg ha±1 did not signi®cantly

increase plant cover as compared with the results obtained at

the lowest biosolid rate in the three sampling periods,

March, May and September. The fast growth of plant cover

observed at both low and intermediate application of

biosolids with respect to the unamended control may be a

result of an increase of soil fertility mainly P and N-NO3

(Table2). Pierce et al. (1998), reported that biosolid

application rates up to 40 Mg ha±1 did not signi®cantly

increase plant canopy cover of a semiarid shrubland 2 years

following treatment. However, Harris-Pierce (1994),

reported signi®cant increases in perennial plants cover

1 year following land application of biosolids to a native

shortgrass prairie in northern Colorado.

Table 2. Chemical properties from unamended and biosolid amended soils

TreatmentMg ha±1 pH

ECdS m±1

OrganicMatterg kg±1

Pmg kg±1

AvailableKg kg±1

Totalmg kg±1

NitrogenNH4-Ncmol kg±1 NO3-N CEC

0 8.1 a 0.15 ab 41.9 a 11.1 c 271 a 2.42 a 1.41 b 10.00 c 19.78 a

40 7.9 a 0.15 ab 36.4 a 42.6 b 244 a 2.08 a 2.57 b 8.27 c 18.30 a

80 8.0 a 0.17 ab 41.4 a 80.7 a 252 a 2.80 a 2.63 b 51.59 b 19.72 a

120 7.9 a 0.19 a 36.6 a 80.3 a 271 a 2.25 a 9.11 a 142.4 a 18.72 a

Mean within the same column followed by the same letter are not signi®cantly different at Pi0.05. EC, electrical conductivity; CEC, cation exchange capacity.

Biosolid effects on soil and native plant production

Waste Management & Research 261

Total above ground production collected in March

(12 months after biosolid application) was signi®cantly

greater for low biosolid amended plots than for the

unamended control plots or the highest biosolids rate

(Fig. 1). Despite the fact that total yield production in the

intermediate sludge treatment is larger it is not statistically

signi®cant as compared with low and unamended plots.

Total plant production collected in May was signi®cantly

greater for 40, 80 and 120 Mg ha-1 biosolid amendments,

with yield values almost ®ve times those of the unamended

control plots. These increases can be directly attributed to a

improvement in soil fertility derived from biosolid applica-

tion. Although 120 Mg ha±1 biosolid treatment had a total

yield of about 700 and 550 g m±2 larger than the control

(110 g m2) in both May and September samples, respec-

tively, those values were not higher than the lower or the

intermediate biosolid rates. This fact could be a result of a

combination of different factors (biological, chemical and

physical) associated with this application rate which

partially limits plant growth as compared against other

biosolid treatments. There were no signi®cant differences

between May and September sampling at the 80 Mg ha±1

application rate.

Conclusions

One year after the application of municipal biosolids to a

degraded semiarid ecosystem the level of essential nutrients

for plants increased, without increasing soil heavy metal

such as Pb, Cr and Cd. This increase in soil nutrients, mainly

inorganic N and P, is the result of the addition of biosolid

nutrients. No signi®cant differences were observed in the soil

chemical properties at 40 Mg ha±1 treatment rate. Higher

treatment rates (above 80 Mg ha±1) in semiarid ecosystems

subject to signi®cant runoff might pose a hazard for surface

water contamination by NO3-N.

Surface application of biosolids increased total plant cover

and total biomass yields. Plant growth was enhanced mainly

through biosolid nutrients supply but also through the

improvement of biological and physical soil properties. The

Table 3. Heavy metals (total and available) from unamended and biosolid-amended soils

Treatment TotalZn

DTPA TotalPb

DTPA TotalCd

DTPA TotalNi

DTPA TotalCr

DPTA TotalCu

DTPA

Mg ha±1 mg kg±1

0 23.7 a 0.92 a 34.9 a 2.03 a 0.52 a nd 6.4 a 0.16 a 10.5 a nd 5.25 a 0.37 a

40 19.7 a 1.04 a 29.1 a 1.86 a 0.53 a nd 6.5 a 0.14 a 12.7 a nd 5.99 a 0.42 a

80 27.8 a 1.32 a 40.7 a 2.26 a 0.56 a nd 8.3 a 0.17 a 12.2 a nd 6.25 a 0.63 a

120 27.6 a 1.40 a 46.3 a 2.00 a 0.58 a nd 7.9 a 0.18 a 14.5 a nd 8.77 a 0.71 a

Mean within the same column by the same letter are not signi®cantly different at Pi0.05. nd: not detectable (below the detection limit).

Fig. 1. Plant biomass from unamended and biosolid amended soils for the three sampling periods.Bars, within the same sample period, by the same letter are notsigni®cantly different (Pi0.05).

I. Walter, G. Cuevas, S. GarcõÂa, F. MartõÂnez

262 Waste Management & Research

degraded soils used in this study require biosolid rates between

40 and 80 Mg ha±1 to increase soil chemical properties as well

as to provide signi®cant improvements in herbaceous

productivity. Sludge applied at 120 Mg ha±1 also produced

signi®cant increases in many bene®cial soil chemical proper-

ties but did not signi®cantly increase plant yields above those

yields obtained when biosolids were applied at 40 and

80 Mg ha±1 rates.

Further studies are needed to evaluate possible changes in

soil chemical properties and on vegetation growth responses

that could be produced in the medium and long-term.

Acknowledgements

The authors gratefully acknowledge the collaboration of Ma

del Rosario Ortega PeÂrez for revision of the English

manuscript. We also extend our thanks to the Environ-

mental Department of Madrid for providing the study site

and the Municipality of Madrid for provided the biosolids for

this project.

ReferencesAguilar, R., Loftin, S. R. & Fresquez, P. R. (1994) Rangeland restoration

with treated municipal sewage sludge. In: Clapp C.E. et al. (eds)

Sewage Sludge: Land Utilization and the Environment. Madison, WI,

USA: SSSA Miscellaneous Publishers, pp. 211±220.

Biondini, M. E. & Redente, E. F. (1986) Interactive effect of stimulus and

stress on plant community diversity in reclaimed lands. Reclamation,

Revegetation Research 4, 211±222.

Fresquez, P. R., Francis, R. E. & Dennis, G. L. (1990) Sewage sludge effects

on soil and plant quality in a degraded, semiarid grassland. Journal of

Environmental Quality 19, 324±329.

GarcõÂa, S. (1999) EvaluacioÂn de los efectos sobre la vegetacioÂn de la

aplicacioÂn de residuos orgaÂnicos en un suelo semiaÂrido degradado de la

Comunidad de Madrid. (Effects of organic wastes application on native

vegetation in a degradated soil of the Madrid Community).

Postgraduate Research project from Universidad Complutense de

Madrid, Spain (Biological Sciences School).

Harris-Pierce, R. L. (1994) The effect of biosolid application on native

rangeland soils and vegetation. MS Thesis. Colorado, USA: Colorado

State University of Fort Collins.

Lindsay, W. L. & Norvell, W. A. (1978) Development of a DTPA soil test

for zinc, iron, manganese and copper. Soil Science Society of America

Journal 42, 421±428.

McGrath, S. P. & Cunliffe, C. H. (1985) A simpli®ed method for the

extraction of metals Fe, Zn, Cu, Ni, Ob, Cr, Co and Mn from soils and

sewage slidges. Journal of Science Food Agricultural 36, 794±798.

Ministry of Agriculture, Fisheries & Food. (1994) Metodos O®ciales de

AnaÂlisis, tomo III (Of®cial Spanish Methods of Analysis, III). Madrid,

Spain: DireccioÂn General de Politica Alimentaria.

Miller, R. H. (1973) Soil microbiological effects of recycling sewage sludge

and waste ef¯uents on land. In: Proceedings of the Joint Conference on

Recycling Municipal Sludge and Ef¯uents on Land. National Technical

Information Service US PB-227106. Champaign, IL: US Department of

Commerce, pp.79±88.

O'Connor, G. A., Essington, M. E., Elrashidi, M. & Browman, R. S. (1983)

Nickel and Zinc sorption in sludge-amended soils. Soil Science 135,

228±235.

Pierce, B. L. (1994) The effect of biosolids application in a semiarid

rangeland site in Colorado. MS Thesis. Colorado, USA: Colorado

State University of Fort Collins.

Pierce, B. L., Redente, E. F., Barbarick, K. A., Brobst, R. B. & Hegeman, P.

(1998) Plant biomass and elemental changes in shrubland forages

following biosolids application. Journal of Environmental Quality 27,

789±794.

Sabey,B.R.,Pendleton,R.L.&Webb,B.L. (1990)EffectofMunicipalSewage

SludgeApplication ongrowthof tworeclamationshrubspecies incopper

mine spoils. Journal of Environmental Quality 19, 580±586.

Sloan, J. J., Dowdy, R. H., Dolan, M. S. & Linden, D. R. (1997) Long-term

effects of biosolids application on heavy metal bioavailability in

agricultural soils. Journal of Environmental Quality 26, 966±974.

Snyman, H. G., de Jong, J. M. & Aveling, T. A. S. (1998) The stabilization

of sewage sludge applied to agricultural land and the effects on maize

seedlings. Water Science and Technology 38(2), 87±95.

Soil Taxonomy (1975). Agricultural Handbook N:456, Soil Conservation

Service: USDA.

Sommers, L. W. (1977) Chemical composition of sewage sludge and analysis

of their potential use as fertilizers. Journal of Environmental Quality 6,

225±232.

Sopper,W.E.&&.Seaker,E.M.(1983)Aguide for revegetationofminedland

ineasternUnitedStatesusingmunicipalsludge.Pennsylvania,USA:The

Pennsylvania State University of Press, University Park, PA, USA.

USEPA (US Environmental Protection Agency) (1980) Utilization of

municipal wastewater and sludge for land reclamation and biomass and

production. EPA-430/9±81±02. Washington, DC, USA: Of®ce of

Water Program Operations.

Walter, I., Miralles, R., Funes, E. & Bigeriego, B. (1989) CaracterizacioÂn de

los lodos residuales de las estaciones depuradoras del Plan de

Saneamiento integral de Madrid. (Characterization of sewage sludges

from treatment plants in Madrid). InvestigacioÂn Agraria: ProduccioÂn

Vegetal 4 (3), 377±392.

Walter, I., Bigeriego, M. & Calvo, R. (1994) Efecto fertilizante y

contaminante de lodos residuales en la produccion de trigo en secano.

(Fertilazer and contamination effect of sewage sludges on wheat

production). InvestigacioÂn Agraria: ProduccioÂn, ProteccioÂn Vegetal 9 (3),

501±507.

White, C. S., Loftin, S. R. & Aguilar, R. (1997) Application of Biosolids to

degraded semiarid rangeland: nine-year responses. Journal of

Environmental Quality 26, 1663±1671.

Whitford, W., Aldon, E. F., Freckman, D. W., Steinberger, Y. & Parker,

L. W. (1989) The effects of organic amendment on soil biota on a

degraded rangeland. Journal of Range Management 42, 56±60.

Table 4. Plant canopy cover percentage from unamended and biosolid-amended soils

TreatmentMg ha±1 March May September

0 42 c 65 b 30 c

40 77 a 100 a 47 ab

80 58 b 98 a 53 a

120 44 a 53 b 40 b

Mean within the same column followed by the same letter are not signi®cantlydifferent at Pi0.05.

Biosolid effects on soil and native plant production

Waste Management & Research 263