Influence of Lime and Phosphate on Nodulation of Soil-Grown Trifolium subterraneum L. by Indigenous Rhizobium trifolii

Abstract

Previous research had identified four serogroups of Rhizobium trifolii indigenous to the acidic Abiqua soil (fine, mixed, mesic Cumulic Ultic Haploxeroll). Nodulation of subterranean clover ( Trifolium subterraneum L.) by two of the serogroups, 6 and 36, was differentially influenced by an application of CaCO 3 which raised the pH of the soil from 5.0 to 6.5. These studies were designed to characterize this phenomenon more comprehensively. Liming the soil with either CaCO 3 , Ca(OH) 2 , MgO, or K 2 CO 3 significantly ( P = 0.05) increased the percent nodule occupancy by serogroup 36, whereas the percent nodule occupancy by serogroup 6 was decreased, but the decrease was significant ( P = 0.05) only after application of either CaCO 3 or Ca(OH) 2 . Application of KH 2 PO 4 (25 mg of P kg of soil −1 ), which did not change soil pH, also significantly ( P = 0.05) increased the percent nodule occupancy by serogroup 36. Application of KH 2 PO 4 in combination with Ca(OH) 2 produced the same increase in nodule occupancy by serogroup 36 as did individual application of the two materials. Soil populations of serogroup 36 consistently, and in the majority of cases significantly ( P = 0.05), outnumbered those of serogroup 6 before planting and after harvest regardless of soil treatment or the outcome of nodulation. Soil chemical and plant analyses provided no evidence that liming was simulating phosphate addition by increasing the availability and subsequent uptake of soil P i by the subclover plants. Liming did, however, result in a significant transformation (30 to 50 mg of P kg of soil −1 ) of P i from the residual soil P i fraction into an NaOH-extractable organic P fraction during the preplant equilibration period.

Genetic Structure of Rhizobium leguminosarum biovar trifolii and viciae Populations Found in Two Oregon Soils under Different Plant Communities

“…Site A is an improved subclover (T. subterraneum L.)-orchard grass (Dactylis glomerata L.) pasture located on a northwest-facing toe slope of Soap Creek Valley, approximately five miles north of Corvallis, Ore. Vicia species do not occur on the site because of heavy grazing by cattle. The soil is a silty-clay loam of the Abiqua series (fine, mixed, mesic, Cumulic Ultic Haploxeroll), and the site and soil characteristics have been described in detail elsewhere (1,3). Site C is an unimproved, ungrazed, open woodland area located mid-slope on the southeast-facing side of Soap Creek Valley.…”

Determination of viability within serotypes of a soil population of Rhizobium leguminosarum bv. trifolii

“…Soil samples were collected from a depth of 0 to 5 cm from a silty clay loam of the Abiqua series (Cumulic Ultic Haploxeroll) under permanent pasture. The physical and chemical characteristics of the soil have been described elsewhere (1,7). By using a soil tube auger, 20 soil cores were removed from within each of six grids (1 by 1 m) spaced 20 m apart along a transect running diagonally across the pasture.…”

“…Although immunofluorescence has allowed researchers to determine the densities of individual serotypes within indigenous soil populations of Bradyrhizobium japonicum (31,(36)(37)(38) and Rhizobium leguminosarum bv. trifolii (1,7,45), concern has been expressed about the proportion of cells which are viable within populations of soil rhizobia observed by immunofluorescence (3, 14,16,22,35). Even though there is evidence that nonviable rhizobia cannot persist for significant lengths of time in soil (5, 10), it is a longestablished fact that only a small fraction of the total bacterial population in soil enumerated by microscopy can be cultured (13,28,29,34,40,42).…”

Rhizobium -Legume Symbiosis and Nitrogen Fixation under Severe Conditions and in an Arid Climate

“…Application of KH 2 PO 4 (25 mg of P per kg of soil) to acidic soils significantly increased the percent nodule occupancy of Trifolium subterranean by R. leguminosarum bv. trifolii (17). The nodulation and N 2 fixation (nitrogenase activity) of T. vesiculosum increased significantly after the addition of P (100 mg per kg of soil) and K (300 mg per kg of soil); nitrogenase activity was doubled when the P concentration increased to 400 mg per kg of soil (194).…”

“…Amelioration of subsoil acidity was also done by applying coal-derived calcium fulvate (324), and this treatment increased the pH more than did amelioration by gypsum, Ca-EDTA, Ca (OH) 2 , or CaCO 3 . Previous reports also indicate the importance of liming for improvement of growth and nodulation of legumes in acidic soils, since they indicated that liming raised the pH from 5 to 6.5 and increased the percentage of nodule occupancy of T. subterraneum (17). However, amelioration by lime and other substances, e.g., carbonate, must be optimized to avoid increasing the pH to a level which would be inhibitory to growth and symbiotic performance of legumes.…”