Soil physicochemical and biological properties in soybean areas under no-till Systems in the Brazilian Cerrado.

No-till (NT) as a conservation practice aims to minimize soil disturbance and enhance soil sustainability. However, how NT practice affects soil physicochemical and biological properties in soybean areas remains unclear. This study selected 65 high-yielding soybean farms under a long-term NT system in the Brazilian Cerrado and collected soil samples at 0.0-0.10 m (L1), 0.10-0.20 m (L2) and 0.20-0.40 m (L3) depths. The effect of NT on soil properties and interactions with soybean productivities were assessed. Results showed that the average soybean yield of the study areas in the last three years was 4.13 Mg ha-1, with 26 areas presenting yields over 4.20 Mg ha-1. Most studied soil properties showed a depth stratification and were strongly concentrated in L1, except for S, Al3+ and aluminum saturation, which displayed lower surface and higher subsurface concentrations. Moreover, a high proportion of SOM is composed of light SOM fraction in areas of high soybean yield, with the average SOM values of 39.9, 27.8 and 19.6 g kg-1 in L1, L2 and L3, respectively. Soils under long-term NT present moderate values of enzyme activity compared with the relatively low values under conventional tillage system, especially 94 % of the plots have moderate values of activity of arylsulfatase enzymes. The data presented support the conclusion that NT system can enhance soil fertility and biological quality in soybean cultivation. Our results suggest that it is necessary to adopt NT practice because it allows increasing soybean productivity in Brazil without the need to increase the sown area, in addition to increasing productivity associated with an improvement in the agroecosystem quality, thus moving toward a more sustainable agriculture.

Shifts in taxonomic and functional microbial diversity with agriculture: How fragile is the Brazilian Cerrado?

BACKGROUND: The Cerrado--an edaphic type of savannah--comprises the second largest biome of the Brazilian territory and is the main area for grain production in the country, but information about the impact of land conversion to agriculture on microbial diversity is still scarce. We used a shotgun metagenomic approach to compare undisturbed (native) soil and soils cropped for 23 years with soybean/maize under conservation tillage--"no-till" (NT)--and conventional tillage (CT) systems in the Cerrado biome. RESULTS: Soil management and fertilizer inputs with the introduction of agriculture improved chemical properties, but decreased soil macroporosity and microbial biomass of carbon and nitrogen. Principal coordinates analyses confirmed different taxonomic and functional profiles for each treatment. There was predominance of the Bacteria domain, especially the phylum Proteobacteria, with higher numbers of sequences in the NT and CT treatments; Archaea and Viruses also had lower numbers of sequences in the undisturbed soil. Within the Alphaproteobacteria, there was dominance of Rhizobiales and of the genus Bradyrhizobium in the NT and CT systems, attributed to massive inoculation of soybean, and also of Burkholderiales. In contrast, Rhizobium, Azospirillum, Xanthomonas, Pseudomonas and Acidobacterium predominated in the native Cerrado. More Eukaryota, especially of the phylum Ascomycota were detected in the NT. The functional analysis revealed lower numbers of sequences in the five dominant categories for the CT system, whereas the undisturbed Cerrado presented higher abundance. CONCLUSION: High impact of agriculture in taxonomic and functional microbial diversity in the biome Cerrado was confirmed. Functional diversity was not necessarily associated with taxonomic diversity, as the less conservationist treatment (CT) presented increased taxonomic sequences and reduced functional profiles, indicating a strategy to try to maintain soil functioning by favoring taxa that are probably not the most efficient for some functions. Our results highlight that underneath the rustic appearance of the Cerrado vegetation there is a fragile soil microbial community.