Recognition of gypsum-responsive soils

Abstract

Gypsum response for 53 soils has been measured in terms of air-dry crust strength (resistance to penetrometer, Y1) and subterranean clover seedling emergence (Y2) in three glasshouse experiments. It was also measured in terms of hydraulic conductivity (Y3) of samples taken from the treated and untreated soils at the end of the experiments, and this proved to be the most sensitive response measure. Relationships between these response measures and a variety of soil properties have been examined by regression and canonical correlation analyses. A regression of Y3 on three properties, i.e. dispersion index, and percentage exchangeable sodium and magnesium, gives the greatest predictability (R2 86%). Regressions involving a pair of easily determined properties, dispersion index and pH, give reasonable predictability (R2 = 70, 73 and 77% respectively for Y1, Y2, and Y3). Limits to the values of Y1, Y2, and Y3 have been set to provide three categories of gypsum response, viz. strong, moderate and little or no response. It is argued from a general understanding of the ameliorative process that the predictive equations should be of value beyond the areas sampled in the present study.