How Does 40 Years of No-till Affect Soil Microbial Nitrogen Dynamics

View the project final report

Commodities

• Agronomic: corn, soybeans

Practices

• Crop Production: conservation tillage, continuous cropping, cover crops, cropping systems, crop rotation, fertilizers, no-till, nutrient cycling
• Soil Management: soil analysis, soil microbiology

Loss of nitrogen (N) from agricultural systems presents a major issue for the environment but also results in a monetary loss for farmers. Farming practices such as reduced/no-till practices provide benefits to the farmers by decreasing erosion and compaction. It is unclear, however, how long-term reduced or no-till impact microbial N dynamics and N2O loss. Microbial N cycling processes that increase the utilization or retention of N include nitrate reduction to ammonium (NA) and nitrous oxide (N2O) reduction to di-nitrogen (N2O consumption) gas. The overall goal of this project is to identify how tillage affects these processes and identify practices that result in reduced loss of reactive nitrogen (NO3- and N2O). To investigate the effects of tillage, soils in a 40-year- old long-term tillage experiment comparing no-till, chisel/disking, and moldboard ploughing will be analyzed. Quantification of N loss as N2O will be made throughout the growing seasons in 2018 and 2019 in the tillage treatments. Microbial N dynamics (NA and N2O consumption) will be measured using molecular methods in rhizosphere and bulk soils of cover crops (wheat and rye) and main crops (corn and soybean). Results from this research will provide much needed information regarding the effects of long-term no-till on soil N cycling. Results will be communicated in extension publications and presented at field days and workshops to disseminate the results to farmers and extension agents.

Objective 1: Investigate the effects of different long-term (40 years) tillage practices on crop N capture.
Expected outcome: Crops grown in the continuous no-till plots will have increased N uptake compared to crops in the conventional or reduced tillage plots.

Objective 2: Determine how different long-term tillage practices affect N2O emissions. Expected outcome: No-till is expected to release similar N2O emissions as compared to chisel/disk and moldboard ploughing is expected to release the highest cumulative N2O emissions.

Objective 3: Evaluate how the microbial communities associated with NA and N2O consumption change in relation to a) tillage practices, b) bulk soil versus rhizosphere soil, and c) rhizospheres of different crops.
Expected outcome: a) Bacteria and archaea containing nosZI and nosZII genes will be lower in the no-till plots due to the higher bulk density, higher water filled pore space, and more anaerobic conditions anticipated in the no-till plots. b) Rhizosphere soils will have higher concentrations of C, leading to higher concentrations of genes responsible for carrying out N2O consumption and NA compared to the bulk soil samples. c) Rhizosphere soils of soybean will have higher concentrations of N, will lead to higher abundances of nosZ-carrying bacteria.

Objective 4: Investigate the effects of tillage on NA and N2O consuming rhizosphere communities of different crops.
Expected outcome: Bacterial NA and N2O consuming rhizosphere communities will be most similar within tillage treatments and least similar across tillage treatments.

Objective 5: Evaluate how the denitrification and N2O consumption potential of the soil communities from the long-term tillage experiment is affected by different a) tillage practices, b) bulk soil versus rhizosphere soil, and c) rhizospheres of different crops.
Expected outcome: a) The denitrification potential is expected to be highest in the moldboard ploughed plots, where N2O emissions are also expected to be higher (see objective 1), while N2O consumption should be highest in the no-till soils. b) Rhizosphere soils will have higher denitrification and N2O consumption potential, due to the increased microbial biomass and increased availability of C expected. c) Rhizosphere soil from soybeans are expected to have the highest denitrification potential, while wheat is expected to have the highest N2O consumption potential.

The overall objective of this project is to determine how long-term no till agriculture impacts microbial N dynamics of soils and ultimately crop N uptake in a corn-soybean-small grain rotation.