A modeling approach to quantifying soil macroaggregate dynamics

Abstract

. 2002. A modeling approach to quantifying soil macroaggregate dynamics. Can. J. Soil Sci. 82: [181][182][183][184][185][186][187][188][189][190]. While several researchers have suggested that soil aggregate turnover is a significant control on organic matter dynamics, the quantification of soil aggregate dynamics has yet to be achieved. Quantification of soil aggregate turnover is essential to testing any hypothesis concerning the relationship between aggregate turnover and organic matter dynamics. The goal of the current work was to propose a modeling approach to the quantification of soil macroaggregate dynamics. The approach taken was to define model compartments representing water-stable soil aggregate size fractions and describing the flows between compartments using first-order kinetics. Soil aggregate data from a 2-yr field study on two contrasting soils were used to calibrate the model and yielded soil aggregate mean residence times ranging from 4 to 95 d, where aggregate dynamics were generally two to three times more rapid in a Gray Luvisol compared to a Black Chernozem. The model was subsequently used to predict the distribution of applied tracer spheres in water-stable aggregate size fractions from an initially free state. The models closely predicted the Dy "mean weight diameters" (Dy-MWD) after two growing seasons. While the models have several limitations, they offer the first attempt to quantitatively describe soil macroaggregate dynamics, which is essential to predicting the response in organic matter dynamics to changes in aggregate dynamics. [181][182][183][184][185][186][187][188][189][190]. Plusieurs chercheurs soutiennent que la rotation des agrégats dans le sol commande sensiblement la dynamique de la matière organique. Pourtant, nul n'a encore quantifié la dynamique des agrégats du sol. Avant de tester la moindre hypothèse sur les liens entre la rotation des agrégats et la dynamique de la matière organique, il importe de quantifier cette rotation. L'étude dont il est question ici avait pour but la création d'un modèle qui permettrait de quantifier la dynamique des macro-agrégats dans le sol. L'approche retenue consistait à paramétrer les compartiments du modèle correspondant aux fractions hydrostables d'agrégats d'une granulométrie donnée et à décrire les échanges entre ces compartiments par la cinétique au premier degré. Les auteurs se sont servis des données sur les agrégats recueillies lors d'une étude sur le terrain de deux ans, sur deux sols contrastants, pour étalonner leur modèle. Ils ont obtenu un temps de rétention moyen de 4 à 95 jours pour les agrégats, la dynamique des agrégats étant généralement 2 à 3 fois plus rapide dans le luvisol gris que dans le tchernoziom noir. Par la suite, ils ont utilisé le modèle pour prévoir la répartition de traceurs sphériques, de l'état libre aux fractions hydrostables de granulométrie donnée. Les modèles prédisent étroitement le rapport entre le Dy et le diamètre moyen pondéré après deux périodes végétatives. En dépit de leurs limites, ces m...

Effect of conventional and minimum tillage on physical and biochemical stabilization of soil organic matter

“…However, little is known about the temporal dynamics of the aggregate distribution in soils (Plante et al 2002;De Gryze et al 2006;Álvaro-Fuentes et al 2007;Olchin et al 2008).…”

“…However, two sampling dates are not adequate to provide the basis for accurate quantitative estimates of aggregate turnover. For instance, Plante et al (2002) reported that soil macroaggregate mean residence times in different soils ranged from 4 to 95 days, where aggregate dynamics were generally two to three times more rapid in a Gray Luvisol compared to a Black Chernozem. De Gryze et al (2006) estimated turnover times for macroaggregates and microaggregates to be 30 and 88 days, respectively.…”

Calcium-mediated stabilisation of soil organic carbon

“…Formation of soil aggregates is the most widespread microscale process that leads to the physical separation of SOC, typically labelled as occluded SOC. The relation between aggregation and the stability or accumulation of SOC has been repeatedly demonstrated Moni et al 2010;Monreal et al 1997;Plante et al 2002;Skjemstad et al 1993;Virto et al 2008Virto et al , 2010. Formation of aggregates has conventionally been thought to involve the electrostatic flocculation of soil separates into stable domains 2-20 lm in size (Ghezzehei 2011), which are then bound by organic or inorganic cementing agents (Jastrow 1996;Six et al 2004).…”

Effect of plant communities on aggregate composition and organic matter stabilisation in young soils

“…Both occluded fractions are mainly allocated in microaggregates, although heavy occluded POM is also found in macroaggregates and thus provide additional information on the C stabilised in that aggregate size class (Golchin et al 1998). Due to the natural turnover of aggregates -5-30 days for macroaggregates (De Gryze et al 2006;Plante et al 2002), 88 days for microaggregates (De Gryze et al 2006) -the POM fractions are periodically redistributed between inside and outside parts of aggregates. Accordingly, the C contents in free and occluded POM can be similar.…”