GROWTH OF LETTUCE AND BARLEY AS INFLUENCED BY DEGREE OF CALCIUM-SATURATION OF SOIL

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Abstract
Serpentine soils from 2 localities were tested for nutrient deficiencies by a modified Mitscherlich technique using lettuce and barley. Severe deficiencies of N and P were found, and a slight deficiency of K. The complete N, P, and K combination produced low yields and disease symptoms described as a rosette in lettuce and as tip failure in barley. The leaf symptoms were reduced and the yields increased by addition of gypsum or by leaching with CaSO4, in conjunction with N, P, and K. No improvement was obtained by leaching with MgSO4 or K2SO4. As a means of achieving various cation proportions on the base exchange complex, synthetic cation adsorbents such as Amberlite and Decalso were added to soils. Ca-Amberlite added to serpentine soils with N,.P, and K produced healthy plants and excellent yields. Mg- and K-Amberlites depressed the yield and aggravated the symptoms. Sr- Amberlite gave a slight increase in yield and no appreciable change in appearance. The lettuce rosette was produced on a highly productive soil by addition of Mg- and K-Amberlites. Ca- and Sr-Amberlites added to this soil produced healthy plants. Where the symptoms appeared, the amount of Ca in the soil had not been changed, but the degree of Ca saturation was lower. Where Mg was the complementary ion, there was a sharp reduction in lettuce and barley growth as the degree of Ca saturation fell below 20%. Lettuce rosette did not appear when the Ca saturation was above 25%. Where K was the predominant complementary ion, the reduction in yield and the appearance of rosette in lettuce set in at 30% Ca saturation. Plant tissue analyses revealed the reduction in yield and the leaf symptoms to be a reflection of the low Ca status of plants grown in soils at the lower degrees of Ca saturation. The rosette symptoms were produced on lettuce plants grown in water-culture solutions low in Ca, and more severely in solns. low in Ca and high in Mg or K. Plant tissue analysis revealed this to be a function of the low Ca status of the plants under the competitive influence of Mg or K.