Three hydro‐seeding revegetation techniques for soil erosion control on anthropic steep slopes

LAND DEGRADATION + DEVELOPMENT

Land De`rad[ Develop[ 00] 204Ð214 "1999#

Copyright Þ 1999 John Wiley + Sons\ Ltd[

THREE HYDRO!SEEDING REVEGETATION TECHNIQUESFOR SOIL EROSION CONTROL ON ANTHROPIC STEEP

SLOPES

J[ ALBALADEJO MONTORO\0\1� J[ ALVAREZ ROGEL\0\1 J[ QUEREJETA\0 E[ DIłAZ0 ANDV[ CASTILLO0

0 Departamento de Conservacio�n de Suelos y Aùas\ CEBAS!CSIC\ Murcia\ Spain1 A� rea de Edafolo`(�a y Qu(�mica A`r(�cola\ ETS de Inènier(�a A`rono�mica\ Universidad Polite�cnica de Cartaèna\ Murcia\ Spain

Received 4 September 0888^ Accepted 7 November 0888

ABSTRACT

Erosion control at lowÐmedium radioactive waste disposal sites is an important concern[ A study was carried out in ElCabril "Co�rdoba\ Spain# on two 39 per cent anthropic steep slopes in order to test the e}ectiveness of hydro!seedingtechniques for controlling soil erosion[ Two groups of 09 m×2 m plots were established[ The treatments tested were]hydro!seeding with the application of vegetal mulch "VM#^ hydro!seeding with added humic acids "HA#^ hydro!seedingwith vegetal mulch and humic acids added "VM¦HA#^ and a control without hydro!seeding or soil amendment "C#[Fifteen run!o} producing rainfall events were recorded during the study period\ with intensities ranging between 1 mmh−0 and 22=5 mm h−0[ All treatments signi_cantly reduced runo} and soil loss "p ³ 9=94#[ The VM¦HA treatment wasthe most e}ective\ reducing 87=4 per cent of total soil loss[ The HA treatment "86=0 per cent reduction# was also moree}ective than the VM treatment "83=7 per cent reduction#[

A great reduction in runo} and sediment yield was observed in the treated plots during the _rst stages after hydro!seeding[ This result may be attributed to the combined e}ect of] "a# the protection against raindrop impact due to theapplication of straw and mulch to the soil surface\ and "b# a general improvement in the soil|s structure brought by theorganic amendments[ Seven months after hydro!seeding\ an increase in the density of the plant cover could be added tothe bene_cial e}ects mentioned above[ Copyright Þ 1999 John Wiley + Sons\ Ltd[

KEY WORDS] humic acids^ vegetal mulch^ dry environments^ soil conservation^ Spain

INTRODUCTION

Low!level radioactive wastes in Spain are stored in a disposal site at El Cabril "Co�rdoba#[ The earthmovingand technical activities necessary to build and to protect the integrity of the waste disposal site alter locallandforms and disturb the vegetation cover of the surrounding landscape\ leading to the formation ofunstable anthropic "made by humans# steep slopes and to an increase in runo} and erosion rates "Gray\0875^ Go} et al[\ 0882#[ To adequately predict and mitigate these erosion problems ENRESA "EmpresaNacional de Residuos Radiactivos# in collaboration with CSIC "Consejo Superior de Investigaciones Cient!i_cas# is to carry out an erosion study of the El Cabril area[

Revegetation programmes are considered the most e}ective way to control erosion processes in dry areas"Rolda�n and Albaladejo\ 0883# since the resulting vegetal cover promises to be more permanent and willneed less maintenance than any engineering structure[ Furthermore\ the aesthetic value of the landscape willbe improved "FAO\ 0874#[

A speci_c method for establishing plant cover on denuded steep slopes resulting from human activity ishydro!seeding "ITGE\ 0878#[ This technique involves the application of a homogeneous suspension of waterand seeds on the land surface[ In low productivity sites\ addition of mulches\ fertilizers and chemical

� Correspondence to] J[ Albaladejo Montoro\ Departamento de Conservacio�n de Suelos y Aguas\ CEBAS!CSIC\ PO Box 3084\ 29979Murcia\ Spain[ E!mail] jalbaÝnatura[cebas[csic[es

J[ ALBALADEJO MONTORO ET AL[

Copyright Þ 1999 John Wiley + Sons\ Ltd[ LAND DEGRADATION + DEVELOPMENT\ 00] 204Ð214 "1999#

205

stabilizers improves the soil conditions necessary for plant germination and growth[ Hydro!seeding has beenused in several major landscaping schemes\ especially in areas where conventional equipment cannot gainaccess or which are too steep "Simpson\ 0877^ Thomson and Ingold\ 0877#[ The success of this methoddepends on many factors "Tilton\ 0885# including] "a# the properties and concentration of every componentof the suspension^ "b# the land|s characteristics^ "c# the correct choice of plant species^ "d# preventing transportof the seeds to other areas by runo} or wind^ "e# improvement of soil conditions to help growth[

To ensure the growth of introduced plants in dry areas of low productivity\ the physical properties andfertility of the soil should be improved _rst "Albaladejo et al[\ 0885#[ The most e}ective way of doing this isthrough amendment with organic compounds\ which are easily assimilated by soil microorganisms[ Thisprocess reactivates the microbiology of a soil and improves its structure "D(�az et al[\ 0883#[

We hypothesized that hydro!seeding steep\ low productivity soils of dry areas would be more e}ective ifcarried out jointly with organic amendments\ and that readily incorporated and metabolized organiccompounds would be most e}ective in improving soil physical properties[ To check this hypothesis\ threeorganic compounds were tested] "0# humic acids\ "1# vegetal mulch and "2# humic acids¦vegetal mulch[ Theobjective of this paper was to evaluate the e}ectiveness of the three hydro!seeding methods on runo} anderosion control on the arti_cial slopes generated by the technical activities involved in the control and safestorage of medium and low!level radioactive wastes[

STUDY SITE

The experimental area was located at El Cabril\ in the Sierra de Albarrana\ in the northwest of Co�rdobaProvince\ Spain "N 27 >93?31ý\ W 4 >13?39ý#[ The land morphology is mountainous with an altitude between499Ð799 m above sea level[ The climate of the area is Mediterranean\ with an average annual temperatureof about 07 >C and mean annual rainfall of 549 mm[ Most of the rainfall occurs between October and April[The mean potential evapotranspiration is about 749 mm year−0 with low values in winter and very highvalues in the summer[ The soils are siliceous\ developed from schist or quartzite with a pH ranging between4=9 and 5=4[ Soils are sandy "64 per cent sand\ 4 per cent silt\ 19 per cent clay# and have a low organic mattercontent "ENRESA\ unpublished data#[ Most of the soils of the surrounding area are classi_ed as Typic orLithic Xerorthents "USDA\ 0887#[

The potential vegetation of most of the study area consists of Mediterranean oakwood "Quercus rotund!

ifolia L[#[ Through degradation\ oakwood has been widely displaced by di}erent types of shrubs including]Quercus coccifera L[\ Pistacia lentiscus L[\ Erica arborea L[\ Rosmarinus of_cinalis\ and Genista cinerea "Vill[#D[C[ A}orestations with pine "Pinus pinea L[\ Pinus pinaster Aiton\ and Pinus halepensis Miller# are alsowidespread in the area[ On the arti_cial steep slopes the vegetation cover is sparse and irregular\ with Cistus

ladanifer\ Cistus populifolius L[\ Cistus salvifolius\ Cistus monspeliensis\ Pinus pinea\ and Rosmarinus of_cinalis

being the most abundant species[

Characterization of the Anthropic Slopes

Each anthropic slope is 599 m long×39 m wide\ with a 39 per cent average slope[ The total surface of thedisposal site is about 8=5 ha[ The soils in the anthropic slopes were classi_ed as Haplic Xerarents "USDA\0887#[ Soil samples for analytical characterization of the slopes were obtained in October 0882[ A rectangulargrid sampling scheme was used[ Eight transects with four sampling points each were selected on each slope[Soil physical properties were determined on undisturbed soil samples collected using steel cores 4 cm in bothheight and diameter[ The water!holding capacity was measured in these samples using a combination of thesand!box method "Stakman et al[\ 0858# modi_ed by Martinez!Ferna�ndez "0889# for −49 kPa suction\ anda pressure membrane for −0499 kPa suction[ Saturated hydraulic conductivity was measured in the lab!oratory using a constant head permeameter "Kessler and Oosterbaan\ 0879#[ The percentage of stableaggregates was assessed using the simulated rain method "Benito et al[\ 0875# modi_ed by D(�az et al[ "0883#[Available P was determined by Watanabe and Olsen|s method "0854#\ with extraction according to Olsen et

THREE HYDRO!SEEDING REVEGETATION TECHNIQUES IN SPAIN


206

Table I[ Chemical characteristics of the humic substancesemployed

Total humic extract 19 per centHumic acids 03=7 per centFulvic acids 9=08 per centPhosphorus "P1O4# 9=995 per centPotassium "K1O# 3=03 per centSodium 9=08 per centCalcium 9=18 per centMagnesium 9=96 per centIron 643 mg kg−0

Copper ³9[4 mg kg−0

Manganese 29=3 mg kg−0

Zinc 1=9 mg kg−0

al[ "0843# and determination according to Murphy and Riley "0851#[ Available K was determined bySchollemberger and Simon|s method "0843#[ Total organic carbon "OC# and nitrogen "N# were assessed bypretreatment with HCl to eliminate carbonates\ followed by combustion at 0919 >C and determination in anautomatic carbon and nitrogen analyser[ Particle size distribution was assessed using Robinson|s pipettemethod after eliminating the carbonates with sodium hexametaphosphate[

MATERIALS AND METHODS

Plot Desi`n and Treatments

Two sets of four 2×09 m runo} plots were installed\ one on the east!facing slope and the other on the west!facing slope[ The average slope was about 39 per cent in both aspects[

Each plot was bordered by sheet!metal strips driven about 199 mm into the ground[ Surface runo} andtotal sediments were intercepted at the lower end of the plot and routed to a storage tank "capacity of 1999l#[ Each tank was equipped with a pressure sensor connected to a datalogger[

Four di}erent plot treatments were established in November 0882 on both slope aspects[

"0# Hydro!seeding with application of vegetal mulch "plot VM# and straw["1# Hydro!seeding with application of humic acids "plot HA# and straw["2# Hydro!seeding with application of vegetal mulch\ humic acids "plot VM¦HA# and straw["3# Control plot "plot C#] without hydro!seeding or soil amendment[

Hydro!seeding was carried out by applying a homogeneous mixture of water\ seeds\ fertilizer "NÐPÐK 04Ð04Ð04# and chemical stabilizer "made of alginates# at high pressure to the land surface[ The same level offertilizer "24 g m−1# and chemical stabilizer "09 g m−1# was applied to all the treated plots[ A commercialmixture of seeds was applied at 24 g m−1#[ The composition of this mixture was] 4 per cent Dactylis `lomerata

L^ 09 per cent Lolium riìdum Gaudin^ 09 per cent A`ropyron trachycaulum^ 04 per cent Festuca festorina

L[^ 04 per cent Lolium perenne L[^ 04 per cent Medicaò sativa^ 2 per cent Vicia villosa Roth^ 6 per centTrifolium repens^ 09 per cent Spartium junceum L[^ 4 per cent Sanùisorba minor^ 4 per cent A`ropyron

intermedium "Host# Beauv[The humic acids used were a mixture of humic and fulvic acids "19 per cent total humic extract# water

soluble in all proportions\ with a pH of 4=2 and bulk density of 0=12 Mg m−2 "Table I#[ The humic acidswere applied in combination with the hydro!seeding mixture at a dose of 9=0 l m−1[ The vegetal mulch "a



207

Table II[ Physical and chemical characteristics of the vegetal mulchemployed "sterilized Dermont IIþ#

Moisture 53 per centBulk density 9=03 g m−2

Porosity 75Ð84 per centElectrical conductivity 131 mS cm−0

pH "H1O# 3=4Ð4=4Total organic carbon 83 per centEasily oxidizable organic carbon 79Ð89 per centNitrogen 1=34 mg kg−0

Phosphorous 08=1 mg kg−0

Potassium 82=7 mg kg−0

Calcium 39=9 mg kg−0

Magnesium 08=3 mg kg−0

commercial product whose characteristics are shown in Table II# was spread manually over the soil surfaceafter hydro!seeding\ at an application dose of 0=4 kg m−1[ The estimated cost of hydro!seeding with addedhumic acids was about ,US9=64 m−1\ the vegetal mulch about ,US9=8 m−1 and the combination of bothtreatments about ,US0 m−1[

After hydro!seeding\ the surface of all the treated plots was covered with straw at an application dose of0 kg ha−0\ in order to protect the seeds from wind and rain and keep them in place[

Plant Cover

The percentage of plant cover in the experimental plots was measured in May 0883 and March 0886[ Threeequidistant\ transversal transects were selected in every plot[ A line running the length of the transects waslaid out and plant cover density was determined using a framework of pins oriented at right angles to thetransects at 09 cm intervals "Kershaw and Looney\ 0874#[

Runoff and Soil Loss Measurements

Measurements in the experimental plots were carried out from January 0883 to January 0885[ Runo} volumewas measured as depth in the tanks using a pressure transducer connected to a datalogger[ Soil loss wasmeasured taking _ve aliquots of one litre from di}erent depths of the tank\ after thorough stirring\ and afurther _ve when draining the tank[ Sediment concentration was taken to be the average of these measure!ments[ Total rainfall for every event was measured with a tipping bucket rainfall gauge "sensitivity 9=1 mm\range 9Ð199 mm of rain per hour# connected to the datalogger\ and the data corresponding to the 04 eventsthat produced quanti_able runo} and sediment yield were selected[

The e}ect of the di}erent treatments on the percentage of plant cover\ sediment yield and runo} weretested by a non!parametrical analysis of variance "KruskalÐWallis test#[ Comparative analysis betweentreatments was tested for signi_cance at the a:2 and a:3 level of con_dence\ a being 9=94 or 9=0[

RESULTS AND DISCUSSION

Characteristics of the Slopes

The overall physical properties and nutrient status of the soil in the arti_cial slopes revealed its poorcondition for plant establishment and growth "Table III#[

The water retention capacity of the soil was very low with mean values of 9=003 and 9=932 g g−0 at −49and −0499 kPa respectively[ Since the ground slope was very steep and the rainfall events were very irregularin time\ plants were subjected to periods of severe water de_cit[ Saturated hydraulic conductivity had a high



208

Table III[ Soil characteristics of the anthropic slopes in the disposal site of El Cabril

n Mean SD Min[ Max[

Total N "g kg−0# 32 9=44 9=16 9=10 0=17Available P "g kg−0# 058 8=13 6=8 9=9 22=7OC "g kg−0# 32 3=8 2=1 9=20 1=5Assimilable K "g kg−0# 51 1=96 9=44 0=0 2=7Fine sand "per cent# 39 25=3 4=4 10=7 35=2Coarse sand "per cent# 39 22=6 3=4 15=9 37=0Silt "per cent# 39 08=4 3=2 4=4 16=6Clay "per cent# 39 8=03 3=2 4=5 03=4Water content at −49 kPa "g g−0# 097 9=003 9=927 9=997 9=132Water content at −0499 kPa "g g−0# 095 9=032 9=903 9=910 9=178Stable aggregates "per cent# 280 18=1 05=9 3=4 76=8K sat[ "cm h−0# 203 2=4 8=4 9=9 169=9

degree of spatial variability\ ranging from 9=9 to 169=9 cm h−0[ In spite of the coarse soil texture\ the meanvalue was very low\ 2=4 cm h−0 "025 values of the 203 measurements made were 9=9 cm h−0#[ This lowhydraulic conductivity was due to the poor structure of the soil in the arti_cial slopes[ The mean percentageof stable aggregates was 18=1 per cent[ These unfavourable soil physical characteristics and the steepness ofthe slopes clearly increase the erosion risk[

The nutrient content re~ected the low soil fertility level[ The organic carbon ranged between 9=2 and 01=5g kg−0 with an average value of 3=8 g kg−0[ Because of the high correlation between soil structure andorganic matter "Parr et al[\ 0878#\ the low content of the latter was probably the main reason for theunsuitable physical characteristics recorded[ Available P and K were low for plant nutrition purposes "TableIII#[

An improvement of the physical properties and fertility of the soil in combination with hydro!seeding wasconsidered appropriate[ The addition of organic materials improves the physical properties and fertility ofa soil "Mbagwu and Bazzo.\ 0877^ Pagliai and Vittori Antisari\ 0882^ Albaladejo et al[\ 0883^ Giusquianiet al[\ 0884# and decreases soil erodibility "Stocking and Albaladejo\ 0883#[

The most abundant species in the plots prior to hydro!seeding "Table IV\ marked with¦# were Cistus

ladanifer\ Cistus salvifolius\ Cistus monspeliensis\ Coronilla dura and Rosmarinus of_cinalis\ the cover hardlyincreasing from the beginning of the experiment to May 0883[

Plant Cover after Hydro!seedin`

Although seven months after hydro!seeding the plant cover percentage had increased in all the treated plots\only signi_cant di}erences were obtained between plot HA and plot C "Table V#[ The high variability in theplant cover between slopes must have been responsible for this result\ since the overall density of the plantcover was higher on the east slope than on the west slope[ This was to be expected since the east slope is lesssunny\ which leads to a higher moisture content than on the west slope\ facilitating plant establishment[

An analysis of biological types showed the predominance of plant with annual life forms in the treatedplots "Figure 0#[ An initial explosion of annual plants in plots treated by soil amendment has been observedby several authors "e[g[ D(�az et al[\ 0886#[ This has been attributed to the pioneer behaviour of this type ofplant whose rapid growth is favoured by the added nutrients[ Among the species introduced with the hydro!seeding\ a grass "A`ropyron trachycaulum# showed a rapid development in the _rst stages of colonization\but two legumes "Trifolium repens and Medica`o sativa# showed the highest cover three years later "TableIV#[ Ga}ney and Dickerson "0876# found that legumes were much more e}ective than grasses for revegetatingcoarse textured soils[

Native species\ including Cistus ladanifer\ Cistus salvifolius and Cistus monspeliensis were the most abun!



219

Table IV[ Species composition and cover in experimental plots at El Cabril

) Mean Cover

May 0883 March 0886

Plot Plot Plot Plot Plot Plot Plot PlotC VM HA VM¦HA C VM HA VM¦HA

Anaàllis arvensis L[ "A# Ð Ð Ð Ð Ð ³0 ³0 3Anthyllis comicina L[ "P# Ð ³0 Ð Ð Ð ³0 Ð ³0Avena barbata Pott ex Link "P# 1 ³0 0 ³0 2 Ð Ð ÐBrassica barrelieri L[ "A# 0 Ð 0 Ð 1 Ð Ð Ð¦Cistus ladanifer L[ "P# 5 3 09 7 6 09 01 7¦Cistus monspeliensis L[ "P# 29 09 06 00 24 04 19 01¦Cistus salvifolius L[ "P# 01 03 8 09 04 19 04 01¦Coronilla dura Boiss "P# 1 0 0 0 2 ³0 4 1Echium plantaìneum L[ "P# Ð Ð 0 Ð Ð Ð 1 0�A`ropiron trachycaulum L[ "P# Ð 03 8 3 0 5 3 Ð¦Erodium cicutarium L[ "A# 0 3 2 3 0 ³0 0 6¦Geranium rotundifolium L[ "A# ³0 1 0 0 1 ³0 0 ÐHelanthemum sp["P# Ð Ð Ð Ð Ð ³0 Ð ÐHordeum leporinum "Link# Arcang[ Ð 1 2 1 ³0 ³0 3 Ð"A#¦Hyparrhenia sp[ "P# 2 0 Ð 0 4 Ð Ð ÐLamarckia aurea "L[# Moench "A# 2 6 01 8 1 09 04 5¦Launaea nudicaulis "L[# Hook "P# 1 1 Ð 1 3 2 0 2Leontodon lonìrrostris "Finch + P[A[ Ð 2 09 1 Ð 04 01 2Shell# Talavera "A#�Medicaò sativa L[ "A# 0 3 01 4 3 04 01 2Ornithopus compressus L[ "A# Ð 8 1 Ð Ð 04 Ð ÐPha`nalon sp[ "P# Ð Ð Ð 0 0 Ð Ð 2Polycarpon tetraphyllum L[ "A# Ð 3 0 0 Ð ³0 Ð Ð¦Rosmarinus of_cinalis L[ "P# Ð 19 Ð 12 Ð 17 Ð 16�Sanùisorba minor Scop[ "A# Ð 4 4 1 Ð 3 Ð ÐSenecio vulàris L[ "A# Ð 4 0 Ð Ð 3 2 ÐSonchus tenerrimus L[ "A# 0 0 ³0 0 ³0 Ð 0 ÐSperùlaria rubra "L[# J[ Presl + K[ ³0 0 Ð 0 Ð Ð 0 ÐPresl subsp[ lonìpes L[ "P#Trifolium anùstifolium L[ "A# Ð 0 Ð Ð Ð ³0 Ð ÐTrifolium fraìferum L[ "P# ³0 ³0 Ð Ð ³0 Ð Ð Ð�Trifolium repens L[ "P# Ð 4 1 0 2 3 0 0Tuberaria ùttata L[ "A# ³0 ³0 ³0 Ð ³0 Ð Ð Ð

¦ Species at the beginning of the experiment[ � Species introduced by hydro!seeding[ "A#\ annual life forms^ "P#\ perennial life forms[

Table V[ Percentage of vegetal cover in May 0883\ seven months after hydro!seeding "values are means2mean standarderror along three transects in each treatment#\ in the four experimental plots

Treatment East slope West slope Mean cover

VM 7427 5528 64=528=5 abHA 8224 59204 76=724=9 bVM¦HA 7725 7127 66=525=7 abC 60203 29209 49=5201=9 a

Mean values followed by the same letter do not di}er at the a:3 level of con_dence\ a being 9=0[ "Non!parametrical analysis of variance\KruskalÐWallis test[# VM\ hydro!seeding¦vegetal mulch^ HA\ hydro!seeding¦humic acids^ VM¦HA\ hydro!seeding¦humicacids¦vegetal mulch^ C\ control\ without hydro!seeding or soil amendments[



210

Figure 0[ Biological types of plants in experimental plots at El Cabril in May 0883\ seven months after hydro!seeding[

dant species on all the plots in March 0886[ This was not surprising since these are the most commonshrub species in the surrounding area[ Among the species introduced with hydro!seeding\ Medica`o sativa\San`uisorba minor\ Trifolium repens and A`ropyron trachycaulum\ in this order of abundance\ were observedto be growing in the treated plots[

Greipsson and El!Mayas "0888#\ when studying the reclamation of barren lands in Iceland by aerialseeding\ found that Festuca rubra cv[ Leik had a high cover after two years of seeding but failed to create acover for long enough to facilitate a rapid succession[ Regular fertilizer applications for _ve years were notenough to ensure its survival[ This result was partially attributable to the high nutrients requirements of thisspecies and the poor fungi population of the soil[ Native plants were favoured by fertilization but declineddue to the lack of nutrients in the soil when it ceased[

Further study is necessary to con_rm the tendencies observed in plant colonization of these anthropicsteep slopes three years after hydro!seeding[ The development of native species must be specially followedto ensure an adequate plant cover when species from hydro!seeding decline[

Precipitation\ Runoff and Sediment Yield

Fifteen runo} and sediment producing events were registered in the study area during the two years of theexperiment "Figures 1 and 2#[ These _fteen rainfall events included 70 per cent of the total precipitationrecorded within this period[ Due to the drought of the years 0883 and 0884\ total rainfall during the studyperiod was only 632 mm\ with a high degree of variability between events[ The precipitation of the eventsranged between 2 mm and 066 mm[ The most abundant and intense storms occurred in November andDecember 0884[ The I29 "maximum 29!min rainfall intensity# of the rainfall events recorded during the studyperiod ranged between 1 mm h−0 and 22=5 mm h−0[

The very low hydraulic conductivity and low percentage of stable aggregates of the soil\ together with thesteep slope\ might lead one to expect severe erosion rates on these arti_cial slopes[ However\ the soil lossesin the control plots during the two years of experiment ranged from 9=4 to 019=2 g m−1 per event in block 0\and from 9=34 to 21=9 g m−1 in block 1 "Figure 2#[ Runo} in the control plot ranged from 9=8 to 16=3 mm inblock 0 and from 0=3 to 21 mm in block 1[ Total runo} during the experiment was higher in block 0 "85=8mm# than in block 1 "79=7 mm#[

The statistical analysis did not detect signi_cant di}erences between blocks as regards runo} and sedimentyield\ in spite of the higher maximum values recorded in block 0[ The reason is that both runo} and erosionwere very similar in the two aspects for 02 out of the 04 rainfall events considered "Figures 1 and 2#[ Onlythe data corresponding to the three most abundant and intense storms recorded showed important di}erences



211

Figure 1[ Runo} production in the four experimental plots of El Cabril[ Numbers above rain graph indicate I29 values[

between blocks\ almost exclusively attributable to the very high values of sediment yield observed in thecontrol plot of the east slope[ The percentage of aggregate stability was locally higher and soil texture wascoarser on the sector of the west slope where the experimental plots were installed\ which could explain thesedi}erences between the control plots[

All the treatments showed signi_cant reductions "p³ 9=94# in runo} and soil loss "Table VI# as comparedwith the control[ The VM¦HA treatment was the most e}ective in reducing runo} "75=9 per cent# andsediment yield "87=4 per cent# and the HA treatment gave very good results too "70=3 per cent and 86=0 percent\ respectively#[ The VM treatment was slightly less e}ective than the other two with a reduction of 61=2per cent in runo} and 83=7 per cent in sediment yield[

The great reduction in runo} and sediment yield in the treated plots during the _rst stages after hydroseed!ing may be attributed to the combined e}ect of the following factors on the soil surface] "a# protectionagainst raindrop impact "Mostaghimi et al[\ 0878# due to the application of straw and vegetal mulch to thesoil surface^ and "b# the reduction in soil erodibility arising from an increase in in_ltration and water retentioncapacity\ and a general improvement in the soil|s structure brought about by the organic amendments "Guptaet al[\ 0866^ Khaleel et al[\ 0870^ Stocking and Albaladejo\ 0883#[ Seven months after hydro!seeding\ theincrease in the density of the plant cover could be added to the bene_cial e}ects mentioned above "Elwell



212

Figure 2[ Sediment yield in the four experimental plots of El Cabril[ Numbers above rain graph indicate I29 values[

Table VI[ Total runo} and total sediment yield in the di}erenttreatments over the study period

Treatment

C VM HA VM¦HA

Runo} "l m−1# 066=1 38=0 22=9 13=7Sediment yield "g m−1# 239=8 06=5 09=0 4=0

and Stocking\ 0865^ Albaladejo and D(�az\ 0889^ Francis and Thornes\ 0889#[ The e}ectiveness of thetreatments was not seriously a}ected by the intense drought of the years 0883 and 0884[

In spite of the good results provided by the three treatments\ signi_cant di}erences were found amongthem as regards sediment yield[ The VM¦HA and the HA treatments reduced soil loss more e}ectivelythan the VM treatment "p³ 9=94 and p³ 9=0 respectively#[ Liquid humic acids are more readily incorporatedinto the soil\ quickly promoting microbial populations growth\ improving soil structure and decreasing soilerodibility "Rolda�n et al[\ 0883\ 0885#[



213

Muzzi et al[ "0886# indicated a high degree of e}ectiveness in increasing plant cover and reducing soilerosion when hydro!seeding was applied jointly with jute mats and tillage[ The e}ect of jute mats could besimilar to the e}ect of the vegetal mulch added by us\ although the joint addition of humic acids gave greaterimprovement in the e}ectiveness of hydro!seeding[

CONCLUSION

The joint application of hydro!seeding and organic amendments proved to be very e}ective in reducingruno} and erosion on arti_cial steep slopes under dry conditions[ When hydro!seeding is followed by surfaceapplication of straw\ it is more e}ective to use humic acids\ which are easily incorporated into the soil andquickly improve its structure\ than to add additional mulch[

ACKNOWLEDGEMENTS

This research was supported by funds provided by ENRESA[ The authors gratefully acknowledge thissupport[

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Three hydro‐seeding revegetation techniques for soil erosion control on anthropic steep slopes

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Transcript of Three hydro‐seeding revegetation techniques for soil erosion control on anthropic steep slopes