Treatment of an acid soil with bentonite used for wine fining: effects on soil properties and the growth of Lolium multiflorum.

When used to fine wines, bentonite acquires a protein load that makes it a potentially useful fertilizer. Other properties of bentonite are also potentially useful for soil amendment. In the work described in this paper, waste bentonite from a winery was applied to an acid soil, and its effects on soil properties and on the growth of Lolium multiflorum were evaluated. Soil N, K, and P contents all increased, as did pH and cation exchange capacity. Biomass production increased as the dose of bentonite increased up to 5 g kg(-1), decreasing at larger doses (possibly as a result of falling potassium/magnesium ratio and increasing electrical conductivity). Environmental drawbacks of waste bentonite include its high soluble copper content, although its conversion in the soil to less soluble forms reduces its potential phytotoxicity. The copper, manganese, and zinc contents of the ryegrass crop were low.