LONG-TERM MANAGEMENT AND CLAY DISPERSIBILITY IN 2 HAPLOBOROLLS IN SASKATCHEWAN

The water dispersibility of clay influences soil physical properties such as water infiltration, surface crusting, and water erosion. The development of the Water Erosion Prediction Project (WEPP) model, which uses water-dispersible clay in the algorithm for estimating interrill erosion, has created a need to understand the factors controlling clay dispersibility. This study evaluated the effects of long-term (greater-than-or-equal-to 24 yr) crop rotations and management on water-dispersible clay in two contrasting soil types in southern Saskatchewan. Cultivated soils were 0.4 to 21 times more dispersive than nearby grassland soils. Among the rotation treatments, a 6-yr rotation, which included 1 yr of summer fallow, 2 yr of spring wheat (Triticum aestivum L.), and 3 yr of bromegrass (Bromus inermis Leyss.)-alfalfa (Medicago sativa L.) hay, had the greatest impact, giving dispersible clay values (151-244 g kg-1) that were substantially lower than those for continuous wheat (361-441 g kg-1) and wheat-fallow rotations (354-483 g kg-1). Fallow frequency and fertilizer treatment had little effect. Water-dispersible clay was negatively correlated (r = -0.79*** and -0.86***) with wet aggregate stability. The results suggested that both of these characteristics are influenced by organic binding agents produced during crop growth. Although soil management had a major effect on clay dispersibility, total clay content may be the dominant factor when a wide range of cultivated soil types are considered. However, management history and aggregate stability data should be taken into account when attempting to predict dispersible clay from total clay content.