Dr Sam McNally1, Dr Mike Beare1, Dr Roberto Calvelo Pereira2, Dr Mike Hedley2
1New Zealand Institute For Plant And Food Research, Lincoln, New Zealand, 2Environmental Sciences Group, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand
Increasing soil organic carbon (SOC) has been proposed as one method to reduce atmospheric CO₂ concentrations and in turn help offset agricultural greenhouse gas emissions. In New Zealand grasslands, SOC is typically concentrated at the surface and declines rapidly with depth (i.e. stratified). The use of full inversion tillage (FIT) during a pasture renewal (FIT-renewal) event provides an opportunity to redistribute and increase the SOC stock. Multiple field trials were established in New Zealand (North and South Islands) to assess the effects of FIT performed during pasture renewal on the SOC stock, dry matter production, nitrogen losses and agronomic costs. The field sites covered a range of soil types and simulated pasture renewal in either spring or autumn conditions. For all the sites, FIT resulted in a redistribution of the SOC in the top 30 cm by depositing C rich topsoil below 10 cm and bringing low C subsoil to the surface providing an opportunity to increase SOC stocks at the surface. Dry matter production was increased following FIT-renewal across all sites with greater yields (~30% higher) observed in the trials with a grass-crop-grass rotation following FIT. An accumulation of mineral N following FIT-renewal appeared to increase the risk of NO₃- leaching during an autumn renewal. The increase of mineral N and consequent leaching risk was reduced over the winter/spring period through the use of a catch crop (forage oats ad Italian ryegrass). In a North Island site leaching losses were reduced under FIT compared to other renewal treatments (e.g. direct drill and shallow till) when a brassica crop was included in the spring renewal rotation. Our results demonstrate that the additional agronomic costs (e.g. tillage, fertiliser) associated with FIT is more than offset by the increase in dry matter production of the renewed pasture/crop.
Biography: Sam is a Scientist at the NZ institute for Plant and Food research based in Lincoln, NZ. His research is focussed on SOM dynamics particularly on-farm solutions to increasing SOM. Other research interests are nutrient management in agriculture, reducing GHG emissions and sustainability of agricultural/horticultural systems.