Soil organic matter and structural stability: mechanisms and implications for management

Abstract

Summary The stability of pores and particles is essential for optimum growth of plants. Two categories of aggregates macro-(> 250 }.Lm) and micro-« 250 }.Lm) depend on organic matter for stability against disruptive forces caused by rapid wetting. Dispersion of clay particles from microaggregates is promoted by adsorption of complexing organic acids which increase the negative charge on clays. The acids are produced by plants, bacteria and fungi. However, the dispersibility of clay in microaggregates is offset by the binding action of polysaccharides, mainly mucilages produced by bacteria, but also by plant roots and fungal hyphae. The stability of microaggregates is also enhanced by multivalent cations which act as bridges between organic colloids and clays. Macroaggregates are enmeshed by plant roots, both living and decomposing, and are thus sensitive to management, and increase in number when grasses are grown and the soil is not disturbed. Lack of root growth, i.e. fallow, has the opposite effect. Various implications for management of soil structure are discussed.

Soil aggregate fraction-based 14C analysis and its application in the study of soil organic carbon turnover under forests of different ages

“…The difference in the degree of soil organic matter decomposition among different particle-size aggregates provides us an opportunity for understanding the formation mechanism of soil aggregates. Currently, various models have been employed to explain the formation of aggregates [61][62][63]. Our results seem to suggest that the formation of larger particle-size aggregates in soil is prior to that of smaller particle-size aggregates.…”

Changes in a Rhodic Hapludox under no-tillage and urban waste compost in the northwest of Rio Grande do Sul, Brazil

“…However, the use of 100 m 3 ha -1 in the 2010/11 growing season induced no differences in GMD and MWD compared to mineral fertilizer, which can be associated, partly, to the predominance of the dispersing effect of the chemical elements (Medeiros (Oades, 1984) on the aggregating effects observed in the second year. Thus, the continuous use of mineral fertilizers over time can reduce soil aggregate stability (Matos et al, 2008).…”

Storage and Turnover of Organic Matter in Soil

“…Although there are some trends with particle size, it is also evident that C pools The goal of aggregate-based soil fractionation is to isolate C pools according to their location in different soil physical structures, based on a conceptual model of stabilization of C inputs in microaggregates that cycle with macroaggregates (e.g., Oades 1984;Golchin et al 1994b;Jastrow et al 1998;Six et al 2000a;Six et al 2000b). Based in part on work by Golchin et al (1994b) and Cambardella and Elliot (1994), Six et al (2000a) developed a fractionation scheme designed to separately isolate SOM found inside and between aggregates of different sizes and stabilities.…”