Reducing sudden death syndrome in soybean by amending the soil with chloride

Sudden death syndrome (SDS) caused by Fusarium solani (Mart.) Sacc. f. sp. glycines form, nov. is a soil-borne disease that affects soybean [Glycine max (L.) Merr.] grown in soils with a high yield potential. Research indicates that take-all [Gaeumannomyces graminis (Sacc.) Arx & Oliv. var, tritici Walker], a soil-borne disease in wheat (Triticum aestivum L.), can be partially controlled by chloride (Cl-) containing fertilizers. Field research was established in 1992 to evaluate Cl- rates and application timing on SDS. The research was expanded in 1993 to evaluate fertilization of two soybean cultivars in a soybean-corn rotation. The research was conducted on a Falaya silt loam (coarse-silty, mixed, acid, thermic, Aeric Fluvaquents) having a history of SDS. The experimental design of the first test was a split-plot. Main plots were 42, 83, 125, and 166 lb potassium (K) acre(-1) applied as KCl. Subplots were timing of the fertilizer application, at planting or one month later. To evaluate the Cl- effects K2SO4 was applied at 125 lb K acre(-1). The second experimental design was a split-split plot. A soybean-corn rotation was the main plot. Subplots were fertilization rates of 0, 42, 83, and 166 lb K acre(-1) applied as KCl plus 166 lb K acre(-1) applied as K2SO4. Two additional subplot treatments were 42-42 and 83-83 lb K acre(-1) as split applications of KCl. The sub-subplots were soybean cultivars. Plots were visually rated for SDS incidence and severity before leaf drop. Root ratings were made from ten randomly selected plants per plot with infected roots. Rotation of soybean with corn improved yields, but also increased SDS incidence, severity, and the number of plants with infected roots. Yields from both experiments were unaffected by fertilization. Disease incidence, severity, and root infection were reduced by applying relatively high Cl- rates. The SDS symptoms were greater when treatment applications were delayed rather than applied at planting. The Cl- effect was less on soybean following corn. The fertilization effect also differed with cultivars. These data support the concept that SDS infects plants soon after planting.