Concentration and distribution of extractable elements in soil as affected by tillage systems and fertil

Concentration and distribution of extractable elements in soil as affected by tillage systems and fertil

Concentration and distribution of extractable elements

in a soil as affected by tillage systems and fertilization

R.S LavadoU, C.A Porcelli, R Alvarez

Departamento de Suelos, Facultad de Agronomıa, Uni´ ¨ersidad de Buenos Aires, A¨ San Martın 4453, 1417 Buenos Aires,´

Argentina

Received 20 September 1998; accepted 21 March 1999

Abstract

Because of crop production intensification, we hypothesize that concentrations of trace elements will increase and stratify in the soils of the Pampean region We studied the effects of conventional and zero-tillage and phosphorus fertilization on concentration and stratification of trace elements in a typical soil of the area The experiment was

conducted at the Pergamino Agricultural Experimental Station 33 8569 S; 608349 W There were three treatments: i

pasture; ii conventional tillage CT ; and iii zero tillage ZT The crop sequence was wheat, soybean and corn An annual average of 90 kg N rha and 18 kg Prha was applied Two composite samples of each plot were obtained in

5-cm increments until 20 cm depth The soil was characterized and aluminum Al , arsenic As , cadmium Cd ,

chromium Cr , cobalt Co , iron Fe , lead Pb , mercury Hg , manganese Mn , molybdenum Mo , nickel Ni ,

selenium Se and zinc Zn , were extracted with DTPA and boron B was extracted with hot water All the element

concentrations were determined with ICP-AES Concentrations of B av 0.48 mg rkg , Cd av 0.20 mgrkg Cr

Ž -0.01 mgrkg , Hg -0.005 mgrkg , Mo -0.01 mgrkg , and Se av 3.33 mgrkg showed no significant differences Ž Ž Ž

between tillage treatments Copper max value 1.46 mgrkg , Fe max value 76.27 mgrkg , Mn max value 10.48

mg rkg and Ni max value 0.65 mgrkg concentrations were higher under CT but Zn max value 2.03 mgrkg , Co

Ž max value 0.34 mgrkg and Pb max value 0.94 mgrkg showed higher concentration under ZT on topsoil As Ž

compared with the tillage treatments, the pasture soil showed lower concentrations of Co max value 0.16 mg rkg ,

Cu max value 1.10 mg rkg , Ni max value 0.36 mgrkg and Pb max value 0.66 mgrkg but higher As max value

0.09 mg rkg , Fe max value 83.55 mgrkg , Mn max value 13.78 mgrkg and Zn concentrations For some trace

elements Co, Pb and Zn the extractable concentration and stratification was linked to OM and pH For other elements the behavior observed in our experiment could not be explained Surface concentrations of Co, Cu, Ni and

Pb was higher in cropped soils and this would be accreditable to fertilizer applications Q 1999 Elsevier Science B.V All rights reserved.

Keywords: Trace metals; Fertilization; Tillage systems

U

Corresponding author Fax: q54-11-4524-8076.

E-mail address: lavado@ifeva.edu.ar R.S Lavado

0048-9697 r99r$ - see front matter Q 1999 Elsevier Science B.V All rights reserved.

PII: S 0 0 4 8 - 9 6 9 7 9 9 0 0 0 9 5 - 9

1 1 Introduction

It has been widely known for more than 30

years that soil organic matter and nutrients

usu-ally stratify when soils are not plowed for a long

stratification process might increase nutrients

Ž availability and crop absorption Singh et al 1966;

Hargrove 1985 The two main causes of

stratifi-cation are crop residues accumulation on topsoil

and fertilizers application Blevins et al 1983

that fertilization is the most important factor for

phosphorus stratification For some

ents Cu, Fe, Mn, Zn the stratification was also

established Hargrove, 1985; Edwards et al., 1992

but the behavior of other elements is far less

known Oliver et al 1993 recorded higher Cd

concentrations in wheat under zero tillage, as

compared with minimum or conventional tillage

but Cd concentration in soils EDTA extraction

did not show apparent differences under

zero-minimum or conventional tillage

Trace elements are normally found in

phos-Ž phate fertilizers Charter et al 1995; Todorova

and Dombalov 1995 and fertilization for long

Ž periods increases their concentration in soils He

and Singh, 1993b; Taylor, 1997 These elements

are absorbed by plants and some are

contami-nants, which might become a risk for the

environ-ment and health Among these eleenviron-ments Cd, Cr,

Ni, Pb and the micronutrients Cu and Zn can be

Ž

mentioned Charter et al., 1995; Jeng and Slingh,

1995 The bioavailability of these elements

de-pends upon their chemical forms in soils, which is

related to clay content and mineralogy, the

or-ganic matter type and content, pH and Eh

Ž changes, among other factors Fergusson, 1991;

Lee et al., 1997 Several authors have found a

direct relationship between organic matter or Al

concentration and extractable trace element

centration i.e Lee et al 1997 Extraction with

DTPA or EDTA are used as a measure of

bioavailability Fergusson, 1991

The agricultural production on the very fertile

carried out with conventional tillage and without

fertilizer from its start, 100r120 years ago From

the last years, both the use of reduced tillage systems, including ZT, and phosphate fertilization are increasing dramatically The widespread use

of this technology along the time will affect the soil properties of the region Among them, we hypothesize that concentrations of trace elements will increase and stratify in those soils However,

as a consequence of the recent introduction of zero tillage and the lack of fertilization history, there are no old field experiments in the region combining tillage and fertilization With this limi-tation, our objective was to study the effects of

Ž

zero-tillage and phosphorus fertilization on con-centration and stratification of extractable ele-ments in a representative soil of the Rolling Pampa, the most productive area of the Pampas

2 Materials and methods

We worked in an experiment performed at the Agricultural Experimental Station located in

Per-gamino Series, fine illitic thermic Typic Argiudoll

ŽTable 1 In 1979 three soil treatments started:

Ž i a pasture of Festuca arundinacea, which never

was fertilized; ii conventional tillage CT which consisted of moldboard-plowing the soil up to 15

a vibrocultivator; iii zero tillage ZT , where the soil was cropped under direct drilling The experi-ment had a randomized block design, with two

50 m The crop sequence was wheat and soybean

in one agricultural cycle and corn in the following cycle The plots were fertilized annually,

as urea and triple superphosphate, respectively

In autumn 1997, two composite samples from each plot were obtained by mixing 10 subsamples collected at random These samples were ob-tained from the following layers: 0]5, 5]10, 10]15

All soil samples were air dried and grounded The following soil properties were analyzed:

ganic matter OM by dry combustion; pH in a 1:1 soilrwater ratio; exchangeable cations by

ex-Table 1

a

Concentration and distribution in depth of organic matter, macronutrients, and other soil components

Ž Treatment Depth cm

b

a ZT, zero tillage, fertilized; CT, conventional tillage, fertilized; past, pasture, not fertilized Different small letters mean

significant differences P -0.05 among treatments Different capital letters mean significant differences P-0.05 among depths.

b Exchangeable cations: meq r100 g.

traction with ammonium acetate followed by

atomic absorption determination; available

elements: As, Cd, Co, Cr, Fe, Pb, Hg, Mn, Mo,

Ni, Se, Zn, and Al were extracted with DTPA and

determined with ICP-AES; B was extracted with

hot water and determined with ICP-AES The

analytical procedures were standardized using

reference material In all cases, standard

dures described by Sparks et al 1996 were used

The experiment was a factorial with three

treatments four depths and two replications All

data were subjected to ANOVA, and when

Duncan’s test was performed to separate means

3 Results and discussion

Table 1 shows the stratification and changes in

concentration of organic matter, macronutrients

and other soil components under the influence of the treatments This behavior resembled that one

Ž previously found in the area i.e Alvarez et al

1995 and elsewhere Among trace elements, B

concentra-tions among treatments or depths Cadmium, with

showed no differences among treatments but dif-ferences in depths The highest Cd concentration was found on top soil The remainder trace ele-ments were affected by the treatele-ments either in their concentration or in their depth distribution

Iron and Mn concentrations were higher under

CT but decreased significantly in depth Zn strati-fied significantly in both treatments but on topsoil

and from 5 to 25-cm depth their concentration

Table 2

a

Concentration and distribution in depth of arsenic, copper, iron, lead and manganese mg rkg

Ž

a

ZT, zero tillage, fertilized; CT, conventional tillage, fertilized; Past, pasture, not fertilized Different small letters means

significant differences P -0.05 among treatments Different capital letters means significant differences P-0.05 among depths.

was significantly higher under CT Cu

concentra-tion was significantly higher under CT and showed

no trends to stratify Hargrove 1985 found that

in an Ultisol, Mn and Zn accumulated on topsoil under ZT Meanwhile, Cu concentrations were not affected by different tillage systems and Fe

Fig 1 Concentration and distribution in depth of zinc in zero-tillage ZT , conventional tillage CT and pasture Past Different

small letters mean significant differences P-0.05 among treatments Different capital letters mean significant differences

ŽP-0.05 among depths .

Ž Ž Ž Fig 2 Concentration and distribution in depth of cobalt in zero-tillage ZT , conventional tillage CT and pasture Past Different

small letters mean significant differences P-0.05 among treatments Different capital letters mean significant differences

ŽP-0.05 among depths .

concentration decreased under ZT Edwards et

tillage or rotations From the remainder trace

elements, Co and Pb showed significant higher

concentrations on top soil under ZT, but arsenic

and nickel did not show differences related to

tillage systems Arsenic did not show stratification

but the other trace elements showed a significant

decrease downwards

Shuman and Hargrove 1985 found that the

organic matter accumulation and changes in soil

pH affected the micronutrients distribution and

that Zn was very sensitive to pH changes

wards et al 1992 found high lineal relationships

between OM and Mn and Zn concentrations, but

those relations improved when pH was included

in the equations Carter and Gupta 1997 found

that the tillage systems affected the Cu, Mn, Mo

and Zn crop absorption, because of the changes

in soil pH He and Singh 1993a , on the other

hand, did not find any correlation between OM

and DTPA extracted Cd, under field conditions,

but they found a significant relation between OM

and DTPA extracted Cd, under controlled

tions As a general view, Fergusson 1991 pointed out that levels of extractable trace elements not always can be explained as a function of changes

in soil properties This was the case in this study for B, Cd, Cr, Hg, Mo and Se Cobalt, Fe and Mn showed higher concentrations on top soil under

CT, with slightly higher pH values and lower OM and Al Only the higher contents of Co, Pb and

Zn in top soil under ZT were related to higher

OM and Al contents and lower pH in those soils The comparison between both cropped treat-ments and the pasture showed that in the latter there were lower values of Co, Cu and Pb concen-trations on top soil and Ni concenconcen-trations lower

in all depths This can be attributed to the enrich-ment in trace eleenrich-ments in cropped soils from phosphate fertilizers The values of Fe, Mn and

Zn were higher in the pasture soil and another process must be taken into account: the nutrient uptake by the non-fertilized crop and the exporta-tion by the harvest Arsenic showed a unique behavior: higher concentrations in all depths

un-Ž Ž Ž Fig 3 Concentration and distribution in depth of nickel in zero-tillage ZT , conventional tillage CT and pasture Past Different

small letters mean significant differences P-0.05 among treatments Different capital letters mean significant differences

ŽP-0.05 among depths .

der pasture as compared with cropped soils

Per-haps a remainder of old arsenate, as insecticide,

applied to the pasture

4 Conclusion

The DTPA extractable trace element

concen-trations are low in general and for some elements

they are around the detection limit For some

trace elements Co, Pb and Zn the extractable

concentration and stratification was linked to OM

and pH For other elements the behavior observed

in our experiment could not be explained Surface

concentrations of Co, Cu, Ni and Pb was higher

in cropped soils and this would be accreditable to

fertilizer applications

Acknowledgements

The research was granted by the National

search Council of Argentina CONICET

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