Effect of an anionic soil conditioner on water stable aggregation of three Hawaiian soils

The primary purpose of soil conditioner application is to enhance a soil's resistance to erosion processes by increasing the water stability of aggregates. In this study, a wrist-action shaker was used to assess the aggregate stability of three Hawaiian soils treated with an anionic surfactant soil conditioner (AGRI-SC). Aggregates of 2.00 to 4.00 mm in size were treated with Agri-SC at rates of 1 to 100,000 times the manufacturer-recommended rate of 0.30 L ha(-1). The manufacturer-recommended application rate of Agri-SC was effective for only the most stable soil tested (Kaneloa Oxisol), ineffective for the Lualualei Vertisol, and adversely effective for the Molokai Oxisol. For higher application rates ranging from 10 to 10,000 times recommended, stability of large aggregate fractions increased for the Kaneloa Oxisol. In sharp contrast, the same application rates decreased aggregate stability of the Molokai Oxisol. For the third, least stable soil (Lualualei Vertisol), Agri-SC was relatively ineffective, except at very high application rates (1,000 and 10,000 times recommend). Finally, at the extremely high application rate of 100,000 times recommended, aggregates for all soils were peptized. These results suggest that careful attention should be given to the application of soil conditioners with anionic surfactants as active ingredients, for aggregate response to various application rates appears to be soil dependent.