Recementation of Crushed Ortstein by Blueberry Leaf Extract

Cementing of sand grains by organo-Al and organo-Fe complexes is thought to be a gradual process and takes at least a few thousand years. The resulting ortstein inhibits root penetration. Blueberries (Vaccinium corymbosum L.) in isolated regions of blueberry fields in Michigan experience reduced growth that has been attributed to the presence of ortstein. Growers have used deep tillage to break up ortstein in these regions with only temporary benefits. This study was conducted to determine (i) if crushed ortstein would recement upon exposure to aqueous blueberry leaf extract, (ii) rate of recementation, (iii) the degree of recementation, (iv) the strength of recemented materials, and (v) the nature of the cementing agents. Crushed ortstein from Saugatuck sand (sandy, mixed, mesic, shallow, ortstein Typic Durorthod) was passed through a 2-mm sieve and used in column experiments to assess recementation. Aqueous blueberry leaf extracts were added daily to crushed ortstein columns for 1.5-, 3-, 6-, and 12-wk periods. Green and brown blueberry leaves were used to prepare extracts and compare the effect of leaf age on recementation. The degree and strength of aggregation were assessed by determining the amount of treated ortstein remaining on a 2-mm sieve, and by tensile strength analysis of aggregated material. Extensive recementation (96% aggregation) of crushed ortstein occurred after 1.5 wks. Cementation was highest in the upper layers and decreased with depth in the column. Degree and strength of cementation tended to increase with duration of the experiment. Green leaf extract caused more recementation of crushed ortstein than brown leaf extract. Recementation is thought to result from relocation of Al by organic compounds, originating from leaf extracts, to contact points between sand grains.