Over the past 25 years soil carbon sequestration has been assessed in many experiments. In most, sequestration has been negative even when conservation farming practices such as crop rotation, stubble retention and minimum tillage were implemented. Recently Kirkby et al. (2013) suggested that a fixed ratio of nutrients (“stoichiometric ratio”) must be present for atmospheric carbon to be sequestered. Intensive agriculture may alter the pools of carbon (C), nitrogen (N), Phosphorus (P) and Sulphur (S) by addition of fertilizers, soil erosion, nutrient export and management of plant residues. This project will determine the long term C:N:P:S ratios of soil in some cotton farming systems.

Archived soil samples from the rotation/tillage experiments conducted by the Cotton CRC in the Namoi and Macquarie Valleys, Darling Downs and Emerald between 1993 and 2014 will be used to determine C:N:P:S ratios at selected time points with LECO analyses. The influence of these ratios on soil carbon sequestration rates will be assessed. Further, the relationship between theses stoichiometric ratios and cotton productivity will be assessed from yield data during the selected years of investigation.

The project will be carried out at ACRI and ANU. This project will build capacity and develop linkages among NSW DPI, CRDC and the ANU