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Abstract
Single applications of ammonium lignosulfonate (ALS, ca. 6 t solids/ha) were made at four commercial potato fields in Ontario (sites K, V, W, and G in 1998, 1999, 2000, and 2000, respectively). Potato tubers were planted 2-4 weeks after ALS incorporation. The effects on potato scab, verticillium wilt, tuber yield, soil chemistry, and soil microbiology were determined in the year of application, and for a second crop at sites K (1999), V (2000), and G (2001). Potato scab severity was significantly reduced (50-80%) by ALS treatment in the year of application at all sites. Significantly less scab was present for the second crop at sites K and G. The incidence of Verticillium dahliae infected plants was also significantly decreased (40-50%) by ALS treatment at all sites in the year of application and for the second crop at site K. Ammonium lignosulfonate significantly increased total tuber yield by 2.5 times at site G in 2000. There was no effect on tuber yield at the other sites. However, marketable yield (tubers with <5% surface scab) was significantly increased three- to seven-fold over the control plots at all sites in the year of application. Although marketable yield was consistently higher in subsequent crops at all sites, it was only statistically significant at site G. Soil pH was immediately reduced following application of ALS by 0.4-0.6 units at all sites except site W, where it had no effect. Soil pH returned to control levels by the second season at all sites except site G, which remained one log unit lower than the control treatment. Numbers of soil microorganisms increased two- to eight-fold at all sites within weeks of ALS application. Fungal numbers increased the most and remained elevated for two seasons at site K compared with control plots. The results of this study clearly demonstrate that use of ALS as a soil amendment can significantly reduce the severity of potato scab and verticillium wilt in potato crops.