Water-Stable Aggregation in Relation to Various Cropping Rotations and Soil Constituents

Abstract

The effects of four cropping systems on water-stable aggregation were compared. Two methods of wetting the soil, (1) by capillarity and (2) under vacuum prior to wet-sieving, were also compared. Various soil constituents were determined to assess their roles in the promotion of granulation and stability. Water-stable aggregation in grassland was significantly higher than in the other three long-term rotations, corn once in 9 years, continuous wheat, and 4 years alfalfa in 10 years. No significant differences in water-stable aggregation were found among the other three rotations.Wetting the soil by capillarity was judged to give a better index of soil aggregate stability than wetting under vacuum. Organic carbon and stable aggregation were positively correlated in the grassland soil and in the soil of the cultural treatments combined over all depths, suggesting an important role of organic matter in stabilization of soil aggregates. It is pointed out, however, that in cultivated soils the cultivation or the type of root system of the crops may override the influence of the organic carbon. Total soluble salts were positively correlated with aggregation in a few treatments.

Organic matter and water‐stable aggregates in soils

“…There have been numerous correlations between the content of organic carbon in soils and water-stable aggregation and some of these are shown in Table 1. The correlations have not always been good for any one or all of the following reasons: (a) only part of the organic matter is responsible for water-stable aggregation, (b) there is a content of organic carbon above which there is no further increase in water-stable aggregation, (c) organic materials are not the major binding agents, (d) it is the disposition rather than the type or amount of organic matter which is important, and (e) some of the water stability in virgin soils is related to physical factors such that the particle reorganization associated with the first disturbance of virgin soil reduces water stability (Heinonen, 1955;Malik et al, 1965, Greenland, 1971bLow, 1972;Tisdall and Oades, 1980b). The stability is sometimes related better to free is a measure of roots and hyphae.…”

Landmark papers

“…There have been numerous correlations between the content of organic carbon in soils and water-stable aggregation and some of these are shown in Table 1. The correlations have not always been good for any one or all of the following reasons: (a) only part of the organic matter is responsible for water-stable aggregation, (b) there is a content of organic carbon above which there is no further increase in water-stable aggregation, (c) organic materials are not the major binding agents, (d) it is the disposition rather than the type or amount of organic matter which is important, and (e) some of the water stability in virgin soils is related to physical factors such that the particle reorganization associated with the first disturbance of virgin soil reduces water stability (Heinonen, 1955;Malik et al, 1965, Greenland, 1971bLow, 1972;Tisdall and Oades, 1980b). The stability is sometimes related better to free organic materials than to total organic carbon because this fraction acts as a substrate for microbial production of organic glues (Oades, 1967), and/or because this fraction is a measure of roots and hyphae.…”