EFFECTS OF CROPPING ON CARBOHYDRATE CONTENT AND WATER-STABLE AGGREGATION OF A CLAY SOIL

In a previous study, the mean weight diameter of water-stable aggregates of a clay soil was increased by up to 50% after two growing seasons under barley and alfalfa compared to fallow or corn. The objective of the present study was to determine whether rapid changes in water-stable aggregation under different crops were related to changes in soil carbohydrate content. Compared to fallow or corn, cropping to barley and alfalfa for 2 yr did not affect the soil C and N contents but significantly increased carbohydrate content by up to 25%. The correlation (r = 0.63, P = 0.001) between aggregate mean weight diameter and carbohydrate content suggested that at least part of the change in water-stable aggregation was related to carbohydrates. Treatment of the soil with sodium periodate prior to wet-sieving confirmed the partial involvement of carbohydrates in the stabilization of aggregates by crops. The remainder of the crop effect on aggregation was removed by sodium tetraborate which suggests that more-humified, though ill-defined, organic substances were also involved. Key words: Carbohydrates, aggregate stability, barley, alfalfa, corn, periodate