Serpentine-derived Henneke soil from 23 sites was tested in greenhouse studies to determine nutrient deficiencies for subclover (Trifolium subterraneum L.), and to evaluate for soil Ca status.
The soils (pH 6.3–6.9) were generally very deficient in P and S. When P and S were supplied, Ca increased subclover yields on 17 of the 23 soils, K on 10 soils, and Mo on 14 soils.
Applications of P and S increased these two elements in clover tops from below critical levels to adequate.
Yields were correlated with Ca and Mg in the plant and soil by the equation: Y = a[1−b exp (−cX)], where Y = relative yield, X = the variable under study, and a, b, and c are coefficients which determine the characteristics of the curve. The R2 values which are a measure of goodness of fit, occurred in descending order as follows: Percentage of Ca in clover tops > exchangeable Ca expressed as a percentage of the cation exchange capacity > exchangeable soil Ca > ratio of Ca/Mg in clover tops = ratio of exchangeable Ca/Mg in the soil > exchangeable Ca expressed as a percentage of the sum of the exchangeable cations. The R2 values were significant at the 1% level.