Impact of Crop Rotations on Soil Microbes and Potato Diseases

1. The Potato Systems Planner:Cropping System Impacts on Soilborne Diseases and Soil MicroorganismsRobert Larkin,Tim Griffin,John Halloran,andWayne Honeycutt, USDA-ARS New England Plant, Soil, & Water Laboratory Orono, Maine CONCLUSIONS: Crop rotations have substantial and varying impacts on soil microbial communities and soilborne potato diseases depending on the specific crop. Each crop resulted in unique soil microbial characteristics. Canola and rapeseedcrops prior to potato were most effective in reducing soilborne diseases, whereas soybean, green bean, and red clover resulted in high disease levels (comparable to continuous potato). In 3-yr rotations, cropping sequence (order) is also important. The crop immediately preceding potato has the greatest impact on potato diseases. Less desirable rotation crops can be used if not preceding potato. Results of this research may be useful for making cropping system management decisions and are available in the Potato Systems Planner CD. SUMMARY: Different 2-yr and 3-yr crop rotations, consisting of barley/clover, canola, green bean, millet, soybean, and sweet corn in various combinations followed by potato, were evaluated for their effects on the development of soilborne potato diseases and soil microbial communities over several cropping seasons in Maine. All rotations significantly affected soil microorganism populations and activity, resulting in unique microbial profiles. Rotations with canola or rapeseed preceding potato were most effective at reducing the soilborne diseases stem canker and black scurf, caused by Rhizoctonia solani, and common scab, caused by Streptomyces scabies (25-75% reduction relative to continuous potato). Barley, millet, and sweet corn rotations were somewhat effective in reducing disease (15-40% reduction). However, potato following soybean, green bean, or red clover, resulted in high disease levels of stem canker and black scurf. These results, along with data on yield, nitrogen recycling, and economic viability, were used to develop The Potato Systems Planner, an interactive CD-Rom decision-support tool to aid in establishing improved cropping and disease management systems for potato production. Also included in the Planner CD is a Potato Disease Database, containing descriptions, symptoms, and management information for 19 of the most common potato diseases. Potato disease information was compiled and edited from The Compendium of Potato Diseases (2nd Ed. 2001, APS Press). The Planner CD is available upon request (email: Wayne.Honeycutt@ars.usda.gov). Soil Microbiological Parameters Measured: Populations of total culturablebacteria and fungi from dilution plate counts; Soil microbial activity, substrate utilization profiles from GN2 Biolog plates; Soil microbial community characteristics from fatty acid methyl ester (FAME) profiles. Potato Cropping Systems Research: 2-yr rotations (2 entry pts) – est.1997, 1998; Newport, ME RCB, 4 reps. Plots 24.4 x 3.7 m, ‘Russet Burbank’ potato Barley w/red clover (underseeded) - Potato Canola - Potato Green Bean - Potato Millet (1997-2000), Rapeseed (2001+) Sweet Corn - Potato Soybean - Potato Potato - Potato Related Publications: Larkin, R.P. 2003. Characterization of soil microbial communities under different potato cropping systems by microbial population dynamics, substrate utilization, and fatty acid profiles. Soil Biol. Biochem. 35:1451-1466. Larkin, R.P., and Griffin, T.S. 2006. Control of soilborne diseases of potato using Brassica green manures. Crop Protection (In Press). Larkin, R.P., Griffin, T.S., and Honeycutt, C.W. 2006. Crop rotation and cover crop effects on soilborne diseases of potato. Phytopathology 96:S64 (Abstract). Larkin, R.P., and Honeycutt, C.W. 2006. Effects of different 3-yr cropping systems on soil microbial communities and Rhizoctonia diseases of potato. Phytopathology 96:68-79. 3-yr rotations (2 entry pts) - est.1998; Presque Isle, ME RCB, 4 reps. Plots 30.5 x 3.7 m, ‘Russet Burbank’ potato Soybean - Canola Soybean - Barley Green bean - Sweet corn Potato - Potato Barley - Clover Sweet corn - Canola Canola - Sweet corn Sweet corn - Soybean B Microbial activity a A Bacteria populations a B Common scab A Black scurf ab a a ab b b bc b a a c b c ab ab ab ab ab ab c a b ab bc ab Optical density d bc b b c b b c c c bc Propagules/g soil (x106 ) d Disease incidence (% of tubers) e d c Disease severity (% coverage) d c c b cd c d b Fig. 1. Effect of different 2-yr crop rotations on the severity of soilborne tuber diseases, A) black scurf and B) common scab averaged over 6 field seasons (2000-2005). Fig. 2. Effect of different 2-yr crop rotations on A) soil bacterial populations and B) soil microbial activity (as represented by average substrate utilization in Biolog plates) measured following the rotation crop and potato crop (3-yr avg). Fig. 3. Effect of different 3-yr crop rotations on the incidence of black scurf averaged over 3 field seasons (2001-2004).