KINETICS OF SOIL NITROGEN MINERALIZATION FROM UNDISTURBED AND DISTURBED SOIL

Download KINETICS OF SOIL NITROGEN MINERALIZATION FROM UNDISTURBED AND DISTURBED SOIL

Post on 18-Feb-2017

214 views

Category:

Documents

2 download

Embed Size (px)

TRANSCRIPT

  • KINETICS OF SOIL NITROGENMINERALIZATION FROM UNDISTURBED

    AND DISTURBED SOIL

    Ariel Ringuelet* and Omar AntonioBachmeier

    Catedra de Edafologa, Facultad de Ciencias Agropecuarias,

    Av. Valparaso s/n. C.C. 509, Cordoba 5000, Argentina

    ABSTRACT

    Knowledge of soil nitrogen (N) mineralization processes is

    essential for modeling soil processes in agriculture. Many authors

    have found discrepancies in N mineralization between disturbed

    and undisturbed samples. Nevertheless, most simulation models

    use a first-order kinetic model (exponential model) for all the

    layers under study, devised from studies using disturbed and

    superficial samples. The goal of the present study was to establish

    the best kinetic model to explain and predict N mineralization as

    affected by sample disturbance and soil depth in two soils of the

    semiarid region of Argentina. Disturbed (D: sieved ,2 mm andquartz mixed) and undisturbed (UD) samples from two

    Haplustolls were subject to successive incubations and extractions

    to assess N mineralization rates. The amount of N mineralized in

    3703

    DOI: 10.1081/CSS-120015916 0010-3624 (Print); 1532-2416 (Online)

    Copyright q 2002 by Marcel Dekker, Inc. www.dekker.com

    *Corresponding author. E-mail: aringuel@agro.uncor.edu

    COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS

    Vol. 33, Nos. 19 & 20, pp. 37033721, 2002

    2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

    MARCEL DEKKER, INC. 270 MADISON AVENUE NEW YORK, NY 10016

  • disturbed samples was up to 200% greater than undisturbed.

    Replicate D samples from the Torriorthentic had significantly

    higher variability p , 0:05 than samples from the Torrifluventic.In the latter, UD samples had a kinetic heterogeneity that was not

    apparent in the D samples. These results suggest that the

    incubation-technique for D samples is ineffective for these soils.

    Key Words: Nitrogen; Mineralization; Undisturbed samples;

    Kinetic models

    INTRODUCTION

    Knowledge of the quantity of N supplied to a growing crop from

    mineralization of soil organic matter is important to improve the efficiency of

    N fertilizer and reduce the risks of polluting water resources and atmosphere.

    There exists a wide variety of chemical and biological methods to assess N

    mineralization in the laboratory and in situ.[1] The question arises, whether

    the mineralization on disturbed samples can adequately predict mineralization

    for in situ structure soil conditions (undisturbed samples).

    Stanford and Smith[2] developed an incubation method using disturbed,

    dried and rewetted soil samples at 358C. They suggested that nitrogenmineralization follows first-order (exponential) kinetics for a wide variety of

    soils, where the first-order constant k was found not to differ significantly

    between soils, whereas the initial pool of potentially nitrogen (N0) varied widely.

    Since then, many authors have used this method, and the concept involved in it, to

    study mineralization processes.

    Alternatives to the exponential model have been proposed: a double

    exponential model[3] with two components of potentially mineralizable nitrogen,

    each representing organic pools that differ in their resistance to decomposition

    (i.e., different rate constants). Bonde and Rosswall[4] modified this model by

    replacing the resistant pool with a linear term that accounted for an apparently

    unlimited organic pool (zero order kinetics). While exponential models can best

    explain N mineralization from plant residues,[5] linear models seem to be

    adequate to represent nitrogen mineralization from soil humus,[6] a more resistant

    organic fraction. Simard and Ndayegamiye[7] found that the cumulative N

    mineralization curves were best described by the Gompertz equation, derived

    from the assumptions that the mineralization rate increases in the early stages and

    the efficiency of the release process will decrease with time because of the slower

    activity of the mineralizing flora or the exhaustion of mineralizable N.

    RINGUELET AND BACHMEIER3704

    2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

    MARCEL DEKKER, INC. 270 MADISON AVENUE NEW YORK, NY 10016

  • Although many N mineralization kinetic models have been proposed, most

    crop yield simulation models use first-order (exponential) kinetics for different

    organic matter pools, namely litter, manure, humus, stable, fresh organic N,

    active organic N, biomass, and soil organic pools.[8] This over-simplification

    masks dynamic changes in N mineralization, originating from root activity,[9]

    from type, placement and timing of residue input,[5] by differences in

    management histories[10] and by seasonal fluctuations.[11]

    Most N mineralization studies have been conducted on disturbed samples.

    Some investigators have found discrepancies in N mineralization between

    disturbed and undisturbed samples. Nordmeyer and Richter[12] observed that in

    undisturbed samples N mineralization increases nearly linearly with time,

    whereas disturbed samples show clearly a mineralization flush during the first 20

    incubation days, showing that any disturbance introduced by soil preparation has

    a strong influence on subsequent N mineralization. Cabrera and Kissel[13]

    obtained considerable N mineralization overprediction using disturbed samples,

    possibly explained by the pretreatment of soil samples prior to the incubation.

    Drying and rewetting the soil is known to induce a flush of nitrogen

    mineralization.[14] Mineralization rates decrease with succesive incubation

    periods in undisturbed samples,[15] suggesting a mineralizationimmobilization

    process in soil microsites.

    The purposes of the present study were to find N mineralization models that

    would properly describe the data obtained with disturbed and undisturbed

    samples and to determine whether the models obtained for disturbed samples

    could in any way be used to predict the pool of N mineralized under undisturbed

    conditions.

    MATERIALS AND METHODS

    Soils

    The work was undertaken in soils of the Semiarid Chaco Region in

    Argentina, a vast phytogeographical region where soil N is limiting and there is

    scant knowledge of its dynamics.

    Two soils of fluvial origin, representative of the area surrounding the Cruz

    del Eje River valley, in the Province of Cordoba, Argentina, were used. One was

    a coarse loam mixed thermic Torrifluventic Haplustoll, of average fertility, and

    the other was a sandy-loam mixed thermic Torriorthentic Haplustoll, of low

    fertility (Table 1).

    The selected plots in these two soils were in bare fallow at the time of

    sampling (May of 1994). A furrow-irrigated squash crop (Cucurbita pepo ) was

    harvested two months earlier, without incorporating residues. Before that, there

    KINETICS OF SOIL N MINERALIZATION 3705

    2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

    MARCEL DEKKER, INC. 270 MADISON AVENUE NEW YORK, NY 10016

  • had been alfalfa for three years, and, previously, five years of alternate

    horticultural crops (tomato and squash).

    Soil Sampling

    Three sites for each soil were randomly chosen (Fig. 1): two cropped (CrA

    and CrB), and a noncropped site (NCr). The latter was included in order to

    understand the changes in N dynamics that result from soil alteration, since this

    site had not been under cultivation disturbance for the last 30 years. The three

    sampled sites were in a straight line perpendicular to the direction of the furrows.

    The distances between the samples sites were approximately 100 m randomly

    selected.

    In each site, a 0:70 m 0:70 m area was defined, where samples were takenat two depths: in and below the tillage layer (1518 cm and 3033 cm, respecti-

    vely). The tillage layer depth was chosen in order that the first depth was selected

    just below the tillage disturbance layer, in order to get undisturbed soil cores. The

    3033 cm sampling depth corresponds to the central layer of the AC horizon.

    The effect of soil physical disturbance was assessed by taking intact cores

    which were used in the incubation studies (UD) with similar soils which were

    sieved to create a disturbance effect (D). There were three repetitions for each

    type of sample (Fig. 1).

    Subsamples in the laboratory were composite samples taken from each

    depth within each sampling area. Replicates for UD were three cores taken 40

    (^5) cm apart, within the sampling area.

    UD samples were taken with a steel cylinder (7.5 cm diameter), and

    transferred to a PVC cylinder of the same inner dimension with the help of a

    Table 1. Selected Characteristics of the Soils Used in the Study

    Soil Torrifluventic Haplustoll Torriorthentic Haplustoll

    Depth (cm) 1020 2535 1020 2535

    Organic carbon (g kg21) 17.2 8.4 9.5 5.3

    Total N (g kg21) 1.8 1.2 1.2 0.9

    Phosphorus (mg kg21) 19.5 20.9 7.2 1.3

    pH 7.5 8.0 7.3 8.2

    Clay (g kg21) 181 161 106 101

    Silt (g kg21) 384 299 190 190

    Sand (g kg21) 435 539 704 709

    Texture class Loam Sandy loam Sandy loam Sandy loam

Recommended

View more >