Growth of perennial forage legumes in acidic soils of the Appalachian hill-lands after liming

A major constraint to the renovation of forage legume-based pastures on acidic soils of the Appalachian hill-lands is thought to be the absence of effective rhizobia. A growth chamber experiment was done with aluminum (Al) toxic, low pH (greater than or equal to 4.2) soils from four series (Berks, Lily, Tate, and Westmoreland) that were planted with alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), or birdsfoot trefoil Lotus corniculatus L.). These soils, without lime addition, were previously shown not to contain effective, naturalized populations of rhizobia for these plant species. However, a non-toxic, pH 6.8, Watauga soil was shown to have such rhizobia but only for alfalfa. In the present study, these five soils were reexamined after liming to pH greater than or equal to 5.5 for effective, naturalized populations of rhizobia and the efficacy of soil inoculation with commercially available rhizobia. In addition to effective, naturalized R. meliloti for alfalfa in the Watauga soil, similar populations of R. trifolii for red clover, and R. lotus for birdsfoot trefoil, were now found. Such rhizobia were also found for alfalfa in the Lily soil and for red clover in the Lily and Tate soil. Thus, liming allowed the expression of effectiveness of natural rhizobia that otherwise would not have been detected in soil pot experiments without lime. Inoculation of the toxic soils after lime addition with commercial rhizobia was effective in about half of the soil-plant combinations that did not contain populations of effective, naturalized rhizobia. Asymbiotic shoot growth of all the plant species was significantly (P less than or equal to 0.05) correlated with soil pH over a range of 5.5-6.6. These results indicate that, in the absence of effective, naturalized populations of rhizobia, improvement of rhizobial inocula could increase forage production by approximately 34% for some species on some of the toxic soils, even after the pH of the soils is increased to greater than or equal to 5.5.