Stability of soil aggregates in relation to organic constituents and soil water content

Abstract

The effects of soil organic matter content, soil water content and duration of wet-sieving on aggregate stability of soils with contrasting cropping histories were investigated. Longterm pasture samples had a greater aggregate stability than long-term arable samples. However, air-drying aggregates before wet-sieving increased the aggregate stability of long-term pasture samples, but decreased that of long-term arable samples. With increasing duration of wet-sieving, the proportion of water-stable aggregates declined until a near-constant value was reached for each sample. Thus, within a sample there are aggregates possessing a wide range of stabilities; with increasing time under arable cropping there is an increase in the proportion of unstable aggregates present, and the measured aggregate stability, therefore, declines. Unstable aggregates (defined as those dispersed after wet-sieving for 1 min) generally had lower organic matter content than stable ones (those still intact after sieving for 15 min).The aggregate stability of a regrassed site (13 years of arable plus 2 years of pasture) was markedly higher than that of a corresponding site from 15 years of arable cropping. Nonetheless, levels of organic matter (organic C, total N and hydrolysable carbohydrate) were almost identical at the two sites. However, aggregates from the regrassed site did have a higher biomass C and water-extractable carbohydrate content than those from the 15year arable site. For a group of soils with varying cropping histories, aggregate stability was significantly more closely correlated with hot water-extractable carbohydrate content than with organic C or hydrolysable carbohydrate content. It is suggested that the hot water-extractable carbohydrate fraction may represent a pool of carbohydrate involved in the formation of stable aggregates.

Estabilidade de agregados e distribuição de carbono e nutrientes em Argissolo sob adubação orgânica e mineral

“…O manejo, o uso e o tempo de utilização promovem diversas alterações nas propriedades do solo, como por exemplo, na estrutura, que está relacionada à agregação. A matéria orgânica é um dos principais agentes de formação e estabilização de agregados, e a diminuição de seu conteúdo no solo pelo cultivo é uma das maiores causas de deterioração da estrutura do solo (Haynes & Swift, 1990;Wendling …”

Early changes in water-stable aggregation induced by rotation and tillage in a soil under barley production

“…Haynes and Swift (1990) (Tisdall and Oades 1979;Jastrow 1987). The involvement of the aliphatic fraction in the stabilization of soil macroaggregates was also suggested (Capriel et al 1990 performed with an apparatus similar to that described by Bourget and Kemp (1957) An analysis of variance for split-plot was used to determine the significance of the rotation and tillage effects, and the date effect was analyzed using the univariate repeated-measure approach (Freund et al 1986).…”

Carbohydrates in hot water extracts of soil aggregates as influenced by long-term management

“…The hot-water extractable pool is probably dominated by mucigel of microbial origin (6,25). The monosaccharide composition of microbial carbohydrates clearly differs from that of plant material; microorganisms produce predominantly galactose (G) and mannose (M), while plant tissue and root mucigels are the major sources of arabinose (A) and xylose (X) (26,27).…”

“…In both soils the carbohydrate C content was lowest in the 4.0-8.0 mm fraction. Several longterm studies have shown that rotation with legumes can increase the amount of carbohydrates in soil (6,10,18). Soil carbohydrates were strongly influenced by soil management systems, including amendments with bark compost or leaf litter (19).…”

“…Non-specific extraction methods, such as strong acids or bases do not differentiate between total carbohydrate content and DEBOSZ, VOGNSEN, AND LABOURIAU 624 ORDER REPRINTS the more specific carbohydrate sub-pool that is involved in aggregate stability (1). Haynes and Swift (6) suggested that hot-water extractable carbohydrates might represent such a pool. Hot water is considered not to solubilize or hydrolyze plant structural carbohydrates (1,7) and should, therefore, be relatively enriched in non-structural plant carbohydrates and extracellular microbial carbohydrate (8).…”