Microbial processes under cotton – Katherine Polain

Katherine Polain working on soil research in the fieldTitle: Sub-soil microbial processes under rotational cotton crops in Australia.

Project Description

Soil microbial communities contribute significantly to soil organic matter formation, stabilisation and destabilisation, through nutrient cycling and biodegradation. The majority of soil microbial research examines the processes occurring in the top 0 cm to 30 cm of the soil, where organic nutrients are easily accessible. In soils such as Vertosols, the high clay content causes swelling and cracking. When soil cracking is coupled with rain or an irrigation event, a flush of organic nutrients can move down the soil profile, becoming available for subsoil microbial community use and potentially making a significant contribution to nutrient cycling and biodegradation in soils.

At present, the mechanisms and rates of soil nutrient turnover (such as carbon, nitrogen and phosphorus) at depth under cotton rotations are mostly speculative and the process-response relationships remain unclear, although they are undoubtedly underpinned by microbial activity.

This project aims to determine the contribution and role of soil microbiota to the accumulation, cycling and mineralisation of carbon, nitrogen and phosphorus through the whole root profile under continuous cotton (Gossypium hirsutum) and cotton-maize rotations in regional New South Wales, Australia.

Approach

Throughout the cotton growing season (pre-crop, in-crop and post-crop), a series of analyses will be completed to determine microbial diversity, activity and contribution to nutrient cycling down the soil profile and between crop systems, using:

  • High-throughput sequencing to measure microbial diversity
  • Respiration incubations (basal and substrate induced) to measure microbial activity
  • MicroResp experiments to determine microbial substrate preferences (C and N)
  • Soil nitrogen measurements (mineral N) to determine where mineralisation is occurring
  • qPCR to quantify the microorganisms involved in different aspects with the soil nitrogen cycle
  • δ18O stable isotope measurements to determine microbial turnover of inorganic phosphorus

Outcome

The data collected from this project will contribute to our understanding of the microbial processes occurring in cropped vertosol soils, ultimately leading to improved practices.

Users

Researchers, Policy makers, crop growers.