Rates of Change in Soil Structural Stability under Forages and Corn

Abstract Data on rates of change in soil structural stability under different cropping systems are scarce. Field measurements of changes in dispersible clay (DC) and wet aggregate stability (WAS) were made during 3 yr in six forage treatments and conventional and zero‐till corn ( Zea mays L.). The study was conducted on a silt loam soil (fine‐silty, mixed, mesic Typic Haplaquept intergrading to fine‐silty, mixed, mesic Typic Eutrochrept) near Elora, ON, Canada. The DC and WAS changed exponentially with soil water content at time of sampling and were adjusted for this parameter before calculating changes with time. No increases in structural stability occurred during the 3‐yr time period within the corn treatments. In contrast, all of the forage treatments resulted in highly significant rates of structural improvement. A half‐life parameter was used to quantify these changes. Calculated half lives for the different forages were similar in magnitude, being approximately 2.7 and 5.4 yr for DC and WAS, respectively. Across the treatments, highly significant correlations were found between rates of structural stabilization and mean root length ( r = −0.57 for WAS, significant at P = 0.01), mean root weight ( r = −0.56 for DC and −0.65 for WAS, significant at P = 0.01) and the coefficient of variation for soil water content ( r = −0.64 for DC and −0.56 for WAS, significant at P = 0.01). Forages may promote structural improvement through their influence on the amplitude of wetting and drying cycles. In addition, large increases in stability were observed over the intervening winter months, suggesting a freeze‐thaw effect.