IMPROVEMENT OF STRUCTURAL STABILITY OF A CLAY LOAM WITH DRYING

A stable soil structure is important to maintain agricultural productivity and reduce environmental pollution. This study was conducted to identify mechanisms by which structure is rendered more stable after short-term changes in cropping history. Changes in cropping systems were found to increase the response of soil structural stability on drying of a Brookston clay loam (mesic Typic Haplaquoll). Three years of bromegrass (Bromus inermis Leyss.) production following 20 y of continuous corn (Zea mays L.) improved the stability of aggregates > 0.25 mm as water content decreased. This increased response on drying was a primary factor in the short-term beneficial effect of bromegrass on stability and was attributed to organic material displaced using a tetraborate buffer at pH 9.4. The decrease in the dispersible-clay fraction with decreasing water content was unaffected by changes in cropping history, but the response of the dispersible-clay fraction to a change in water content also involved tetraborate-sensitive material.