Response of nutrient cycle functional nutrient genes to prolonged no-till practices and crop rotations in a farming system experiment in North Carolina

Background/Question/Methods

Two major modifications (no-till practices and improved crop rotations) have reshaped agriculture especially in sustainability context. Both have been shown to improve soil structure and quality in supporting crop growth. Soil microbes are the sole mediators for biogeochemical cycles for major nutrients such as C and N. However our knowledge of microbial responses to no-till and crop rotation is limited to the activity and structure of microbial communities at a rather coarse resolution. Microarray technology targeting ~47,000 functional genes, GeoChip 3.0, was used to investigate the microbial response in detail, especially for functional constituents in nutrient cycles. A long-term experiment was designed to contrast the impact of conventional tillage (CT), no-tillage (NT) and non-managed systems called successional (SC) fields.

Results/Conclusions

Soil physical and chemical properties showed highly significant responses (P < 0.001) to both no-till (R=0.684) and crop rotations (R=0.523). The response of microbial community structure was significant to no-till (R=0.063) and crop rotations (R=0.102) as well. The percentage of functional genes detected was lowest in SC, but it was comparable to NT and CT fields. The responses in functional gene diversity (H’), richness and normalized abundance were not significant to treatments, but the responses of nitrification functional genes in diversity and richness were significant (P<0.05). Extractable N, net mineralized N and respiration were significantly correlated with most subgroups of nutrient cycles in NT field. Multivariate correlation analysis identified similar sets of soil properties were most significantly associated with NT field functional genes. These may indicate better adaptation of microbial communities in NT soil to soil nutrients without major disturbance, such as tilling. Together the responses in nutrient cycle functional genes to no-tillage and crop rotations were apparent in the structure of microbial communities, but not in diversity and abundance.