Effects of pH, P, and Al on the Growth and Chemical Composition of Crownvetch

Massachusetts roadsides often consist of acid, infertile soil which is subject to erosion when without adequate cover. Crownvetch (Coronilla varia L.) is a legume which has been introduced for the purpose of rapid, attractive, arid inexpensive stabilization of such sites. The response of crownvetch to soil acidity and correction of this condition have not been closely examined. This investigation consisted of combining three pH, two phosphorus and three aluminum rates in soil and water culture studies. The objective was to study the effects of the soil treatments on factors of soil acidity, as well as the chemical composition and growth of crownvetch. By studying the relationships among these factors it was hoped to better characterize the acid tolerance and cultural requirements of this species. In both media, mean dry weights increased as pH was increased from 4.2 to 5.4. Yields did not increase further at pH 6.3. Reduced P availability and excess exchangeable soil Mn, which resulted from the high lime level, appear to be involved in restricted plant growth at a soil pH of 6.3. Root A1 content was negatively correlated with top weights; however, neither pH nor Al treatments were related to root length in soil and water culture. A mean exchangeable A1 level of 4.5 ppm (at the highest Al rate) in soil and 5.0 ppm A (and above) in water culture appreciably diminished the growth rate of crownvetch. The high Al additions in these studies became more of a problem to plant growth at low pH and P conditions. It was found that the soil P application resulted in a lower incidence of symptoms of leaf black spot and enhanced root penetration. Liming this soil to pH 5.4, and applying 75 ppm P (168 kg/ha) significantly benefited the growth crownvetch. Optimum soil A1 and Mn levels combined with enhanced Ca and P availability are thought to be major reasons for these benefits.