Bacterial and biochemical indicators of agricultural management for soil under no-till crop production

FIGUEROLA ELM; GUERRERO LD; FERRARI A; ROSA S; ERIJMAN L; WALL LG

Simposio; 14th International Symposium on Microbial Ecology (ISME14); 2012

The increasingly use of no-till agriculture, adopted in many areas of the world as an alternative to conventional farming, may contribute to reduce the erosion of soils and the increase in the soil carbon pool. However, the advantages of no-till agriculture are jeopardized when its use is linked to the expansion of crop monoculture. The aim of this study in a frame of a multidisciplinary project was to survey bacterial communities and Fatty Acids Methyl Ester profiles to find indicators of soil quality related to contrasting agriculture management in soils under no-till farming. Four sites in production agriculture, with different soil properties, situated across a west-east transect in the most productive region in the Argentinean pampas, were taken as the basis for replication. Working definitions of Good Agricultural Management and Poor Agricultural Management were adopted for two distinct scenarios in terms of crop rotation, fertilization, agrochemicals use and pest control. Non-cultivated soils nearby the agricultural sites were taken as additional control treatments. Tag-encoded pyrosequencing was used to deeply sample the rDNA from bacteria residing in soils corresponding to the three treatments at the four locations. Although bacterial communities as a whole appeared to be structured chiefly by a marked biogeographic provincialism, the distribution of a few taxa was shaped as well by environmental conditions related to agricultural management practices. A statistically supported approach was used to define candidates for management-indicator organisms, subsequently validated using quantitative PCR. Using a different approach, principal component analysis of Whole Cell Fatty Acids showed a clear separation of natural sites from the agricultural sites, and also a strong separation by geographical location of the natural sites. The Neutral Lipids Fatty Acids profile was the most revealing for differences in the structure of fatty acid composition concerning agricultural managements. The most relevant fatty acid groups for land use discrimination were mono-unsaturated, poly-unsaturated, straight chain and methylated ones. The neutral lipid fatty acid 20:0 show higher values in Good Managements than in Poor ones, while the fatty acid 18:1w7c was increased in Poor Managements compare to Good ones. Based on these results we propose two potential management indicators to discriminate between sustainable vs. non-sustainable agricultural practices in the Pampa region: 1) the ratio between the normalized abundance of a selected group of bacteria within the GP1 group of the phylum Acidobacteria and the genus Rubellimicrobium of the Alphaproteobacteria and 2) the ratio between the normalized abundance of 20:0 and 18:1w7c. Interestingly, there is consistency between both indices, in that fatty acid 18:1w7c is the most abundant membrane fatty acids in bacteria of the genus Rubellimicrobium, the potential marker for Poor Agricultural Managements.