No abstract

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, and 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 Al 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 Al 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 Al and Mn levels combined with enhanced Ca and P availability are thought to be major reasons for these benefits.

Cicer milkvetch (Astragalus cicer L.) is one of several legume species which has been used for the stabilization of Massachusetts roadsides. In this study the following treatments were combined in soil and water culture experiments: pH levels 4.2, 5.4, and 6.3, and aluminum levels of 0, 2.5, and 5.0 ppm added to soil, 0, 5, and 15 ppm Al in water. The objective was to examine the interactions among soil treatments, factors of acid soil infertility, and the chemical composition and growth of cicer milkvetch (‘Lutana’). Dry weights and root penetration doubled in response to soil pH 5.4. At soil pH 6.3 manganese in the soil and in the plant tissue rose to high levels while dry weights and root penetration declined. On the other hand, dry weight of tops and root elongation were significantly greater at pH 5.4 and 6.3 than at pH 4.2 in water culture. Soil Al treatments were positively related to water soluble soil P and soil Mn availability. Nutrient solution Al additions significantly enhanced Al in tops. Also, the 5 ppm Al level significantly stimulated root elongation, while 15 ppm Al was related to reduced elongation. Dry weights were not significantly affected by Al treatments in soil or water culture. The apparent acid tolerance of cicer milkvetch, plus the buffering capacity of this soil, and the sufficient supply of P at all treatments in water culture apparently diminished the A1 treatment effects. Cicer milkvetch growth is enhanced by CaCO3 application of at least 1,750 ppm to this soil for these reasons: percent Ca and P of tops rose above critical levels, while excess soil Mn and Al levels declined, allowing enhanced root penetration of the soil.

Phosphorus uptake by barley @er cent of dry tissue) grown on four acid soils each treated with four amounts of lime and P, correlated equally well with EPC (equilibrium P concentration = concentration of P supported in solution at field capacity) and with diffusion supply of P to root cylinder surfaces calculated from the soil indices including EPC, a soil capacity factor maintaining that concentration, and a diffusion coefficient.Calculated rates of P supplied by diffusion to primary root cylinder surfaces were too low to account for P found in plants. If the remainder of the observed P uptake was assigned to root hairs, the ratios of calculated root hair surface area to estimated root cylinder surface areas necessary to account for the difference were in reasonable agreement with ratios for barley reported by other workers. IntroductionPLANT P uptake has been empirically correlated with soil P in solution, with labile P content of soil, and with the P buffering capacity (the ratio between labile P and solution P) of soil (CUMV and Sutton, 1967, Ozanne and Shaw, 1968;Dalal and Hallsworth, 1976;Holford and Mattingly, 1976). In a theoretical analysis of the factors controlling P uptake, Olsen et al. (1962; 1963; 1965; 1968) derived an equation for the diffusion rate of P through soil to the root surfaces. Applying this equation to calcareous soils, they predicted the minimum solution P concentration that would allow plants to take up P at a rate reportedly optimal for good growth. Their equation included the soil diffusion coefficient, the soil buffering capacity to replenish solution P, and the P-concentration difference between soil solution and root surface. Using the same variables, Brewster et al. (1977) simulated Pdelivery to plant roots by diffusion processes.We tested the applicability of this equation to four acid soils from southeastern U. S. These soils are rich in kaolinite, differ widely in their concentrations of A1 and Fe oxides and have a more complex P chemistry than calcareous soils. We measured P uptake by barley and tested the correlations of per cent P in barley values with Equilibrium P concentrations (EPC = Concentration of P supported in solution at field capacity) and the amount of diffusible P calculated from measured soil indices. These were compared with estimates from the plant -uptake data.