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FORAGE & GRAZING LANDS

Early Developmental Responses of White Clover Roothair Lengths to Calcium, Protons, and Aluminum in Solution and Soil Cultures

^a USDA-ARS, Dale Bumpers Small Farms Research Center, 6883 South Highway 23, Booneville, AR 72927
^b USDA-ARS, Appalachian Farming Systems Research Center, 1224 Airport Road, Beaver, WV 25813

^* Corresponding author (dbrauer{at}spa.ars.usda.gov)

Acidic soils tend to limit the nodulation of forage legumes and roothairs are important for Rhizobia binding and the initiation of nodule formation. This study examined the effects of Ca, pH, and Al on the length of roothairs in nutrient solutions and soils with white clover (Trifolium repens L., cultivar Huia) seedlings. The lengths of roothairs of 1- to 2-d-old seedlings was not affected by increases in solution Al up to 24 µM in nutrient solution experiments, but showed a pronounced optimum at a predicted root surface pH of 3.8. Roothair lengths of white clover seedlings 2 to 10 d after planting were also assessed in a Gilpin series silt loam collected from New, WV, and amended with various levels of lime. Soils ranged in pH from 4.6 to 5.3 and soil base saturation of Al from 46 to 8%. No significant differences in roothair lengths as a function of soil pH and/or soil available Al were observed. Previous results conducted under similar experimental conditions demonstrated that soil pH–soil-available Al adversely affected on root elongation and nodulation. When results from this and the previous reports are considered together, the combined results suggest that root elongation and nodulation were more sensitive than roothair length to acidic soil conditions.

Abbreviations: DE, days of exposure • MRHL, mean roothair length