STRUCTURAL STABILITY STATUS AS AFFECTED BY LONG-TERM CONTINUOUS MAIZE AND BLUEGRASS SOD TREATMENTS

The effect of long-term continuous fertilized and unfertilized corn and bluegrass crops on the structural stability status of a clay loam soil was studied. Water-stable aggregates were measured with and without an ethanol pretreatment and before and after the extraction of unbound lipids and after hydrophobic lipids were extracted with chloroform. Compared to corn, sod and wooded plots had three to four times more stable aggregates associated with the dispersive and dissolution action of water and two to three times more stable aggregates associated with slaking forces. The data also indicate that the stability of aggregates associated with bound organic materials was affected by cropping history rather than fertilization. Although the unbound lipids varied significantly between treatments, the unbound lipids were responsible for a similar amount of stable aggregates when compared against dispersive and dissolution action of water and slaking forces. The results indicate that the mono- and diesters compounds had disappeared in the Apl layer of fertilized corn, whereas these compounds were still present under unfertilized corn, sod and wooded areas. From a practical viewpoint, the results suggest that under natural conditions, soil aggregates (dry or wet) may be more affected by the dispersive and dissolution action of water than by slaking forces caused by air entrapment following sudden rewetting.