Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 2007
Publication Date: April 10, 2007
Citation: Larkin, R.P. 2007. Relative Effects of Biological Amendments and Crop Rotations on Soil Microbial Communities and Soilborne Diseases of Potato. Soil Biology and Biochemistry. 10:1016. 40:1341-1351. Interpretive Summary: Soilborne diseases are persistent problems in potato production and sustainable management options are needed. The use of crop rotations and biological amendments to actively alter or manipulate soil microbial communities in an attempt to develop natural disease-suppressive soils is a promising management approach. Biological amendments may include commercial biocontrol agents with known activity against soilborne pathogens, and diversified microbial inoculants, such as mixtures of beneficial microorganisms, mycorrhizae, and compost teas. In this research, a variety of different biological amendments were assessed alone and in conjunction with different crop rotations for their effects on soil microbial communities and soilborne potato diseases. All amendments affected soil microbial community characteristics, but crop rotation effects were greater. Mycorrhizae reduced soilborne diseases of potato in field trials, but a biostimulant and mix of fermenting microorganisms (EM) did not. When used in three different crop rotations, compost tea and a mix of beneficial microorganisms (Mix) reduced multiple soilborne diseases in some rotations, but not others, and no amendment was effective in continuous potato. This research indicates that biological amendments can be useful for enhancing disease control, but crop rotations are most important in shaping soil microbial communities, and that the right combination of rotations and biological amendments is needed for effective disease suppression. These results have important implications for future development of sustainable disease management practices.
Technical Abstract: Various biological amendments, including commercial biocontrol agents, microbial inoculants, mycorrhizae, and an aerobic compost tea (ACT), were evaluated, alone and in conjunction with different crop rotations, for their efficacy in introducing beneficial microorganisms, affecting soil microbial community characteristics (SMCC), and reducing soilborne diseases of potato in greenhouse and field trials in Maine. Most amendments successfully delivered microorganisms into the soil, altering microbial populations, activity, and SMCC (as determined by FAME analysis) to various degrees from 2 to 24 weeks. In field trials, effects on microbial characteristics, soilborne diseases and tuber yield were variable, with some microbial inoculants and a biostimulant producing no significant effects, whereas arbuscular mycorrhizae reduced stem canker and black scurf by 17-28%. When used in three different 2-yr crop rotations (barley/ryegrass, barley/clover, and potato), amendments reduced soilborne disease and improved yield in some rotations, but not others. ACT and the combination of ACT with a mixture of beneficial microorganisms (Mix) reduced stem canker, black scurf, and common scab on tubers by 18-33% and increased yield 20-23% in the barley/rye rotation, but not in the other rotations. Mix also reduced disease (20-32%) in the barley/clover rotation only. Both crop rotation and amendment treatments significantly affected SMCC, but rotation effects were more extensive. These results indicate that certain rotations were better able to support the added beneficial organisms from amendments and enable more effective biological control, and that favorable crop rotations may be more influential than amendments in managing SMCC.