EFFECTS OF CROPPING ON MACRO-AGGREGATION OF A MARINE CLAY SOIL

Abstract

Field and growth chamber experiments were conducted to evaluate the short-term effects of selected crops on macro-aggregation of a Kamouraska clay soil. Under field conditions, the growth of barley (Hordeum vulgare L.) and alfalfa (Medicago sativa L.) for up to 2 yr resulted in increased macro-aggregate size and stability compared to a fallow control and to initial conditions. Under these two crops, the proportion of water-stable aggregates of the 2- to 6-mm fraction increased from 25% in May 1986 to 40% in September 1987 at the expense of the 0.25- to 1.0-mm fraction which decreased from 37% to 19% over the same period. Macro-aggregation after 2 yr was not different in corn (Zea mays L.) and fallow control. Seasonal variations in aggregate stability were significant but small and less important than the effects of cropping treatments. Results of the growth chamber experiment agreed with those obtained under field conditions suggesting that controlled environment experiments can be used to model cropping effects on the aggregation of this soil. Key words: Aggregation, soil structure, clay soil, corn, barley, alfalfa