A Soil‐on‐Agar Method to Evaluate Acid‐Soil Resistance in White Clover

White clover ( Trifolium repens L.) is adapted to the Appalachian region but is rarely found on strongly acid soils. To select for improved acid‐soil resistance we needed an effective and efficient soil‐based procedure. Our objective was to develop a simple, rapid, nondestructive technique that could be used to evaluate acid‐soil resistance of clover accessions. Our technique uses a thin layer of acid, Al‐toxic soil on top of solidified water agar. Germinated white clover seed, selected for uniform radical length of about 1 mm, are transplanted into the soil. Root emergence from the soil into the agar is visually observed. We evaluated the technique using non‐limed (pH 4.2, Al saturation 70%) and limed (pH 5.0, Al saturation 14%) Porters soil (coarse loamy, mixed, mesic Umbric Dystrochrept) and four white clovers, two larger‐leafed (ladino) clovers developed in the USA, and two smaller‐leafed cultivars from New Zealand. Root emergence was observed daily for 10 d. Root emergence from the limed and nonlimed soil began on day one and on day four, respectively. This delay in emergence indicates that the clover seedlings were responding to toxic factors in the acid soil that were alleviated by liming. The larger‐leafed cultivars emerged more slowly than the smaller‐leafed cultivars in the non‐limed soil but were similar to them in the limed soil. The soil‐on‐agar technique allows easy collection of root growth data, is rapid, nondestructive, and can be used with large populations. The technique should be useful for characterization of acid‐soil resistance of white clover and other small‐seeded species. We suggest that seedlings whose roots emerge more quickly from acid soil are more resistant than those whose roots emerge later and that the technique has promise for selecting resistant and susceptible populations.