Abstract
The effects of lime and gypsum applications were determined on lettuce yields, soil pH and extractable aluminum for 10 organic soils. No increase in yield attributable to liming was found beyond pH 4, and a significant yield depression occurred with gypsum treatments. Further, the more acid soils outyielded the less acid but denser cultivated soils. Although the limestone applications increased soil pH significantly, significant treatment–soil interaction effects were found, and were ascribed to lower soil-limestone reactivities of the denser, less acid organic soils. Consequently, soil pH change upon liming was significantly correlated with bulk density and percent ash. Maximum yields were obtained at extractable aluminum levels lower than 0.1 meq/100 g soil. Further, potentially toxic levels of extractable aluminum disappeared at the same pH as maximum attainable lettuce yields; consequently, its possible toxicity was associated with pH effects in these soils. Field experiments with radishes grown on two organic soils gave initial increases in yields. This effect was surmised to be due to increased N-mineralization, because subsequently the controls outyielded the liming treatments.
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