At Oakdale in NSW, grower Phil Bartolo is exploring strategies to reduce input costs, improve soil health, and enhance nutrient cycling within his farming system. By incorporating cover crops and reduced tillage into his practices, the grower aims to achieve sustainable management of nitrogen for a brassica crop, while also simplifying weed control. It is also important that any new practices align with existing operations, such as lime and compost applications.
The trial set-up
The demonstration site has two primary objectives:
- To effectively use legumes to supply nitrogen for a brassica crop
- To manipulate the timing of nitrogen release to align with the crop’s nitrogen demands.
Cover crop treatments include straight oats, a mix of oats and faba beans, and a bare fallow control. Termination methods involve an application of herbicide at flowering-stage combined with rolling and crimping down the biomass. For brassica bed preparation, three approaches are being tested: speed discing, strip rotary hoeing, and full rotary hoeing as the control.
Progress
In August 2024, cover crops were direct drilled into brassica stubble at high rates to obtain good amounts of biomass. Pre-planting soil nutrition and biology tests were conducted in June, and biomass and residue analyses were completed at flowering in November.
To evaluate the impact of cover crops on soil health and nutrient cycling, full soil nutrition and biology tests was completed before planting the cover crops in June 2024; biomass production, along with carbon (C%) and nitrogen (N%) content of the cover crop residues, was assessed at flowering in November 2024.
Five weeks after termination, in December 2024, soil nitrogen levels were measured, and additional analyses of carbon and nitrogen content in the cover crop residues were conducted to track nutrient cycling and residue breakdown.
Results so far
Initial results revealed that both cover crop treatments – straight oats and the oats-faba mix – produced similar biomass at approximately 7 t/ha dry weight. However, the straight oats treatment provided better weed suppression, likely due to its higher proportion of oat biomass compared to the mix.
Soil nitrogen levels varied across treatments, with the bare fallow control exhibiting the highest available nitrogen at 22.2 kg/ha, followed by oats-faba at 17.5 kg/ha and straight oats at 15.7 kg/ha. These results suggest that nitrogen availability is influenced by both cover crop residues and organic matter mineralisation.
Cover crops will remain on the soil surface until 4-8 weeks before cabbage planting in mid-2025. During this period, nitrogen cycling will be closely monitored, both in the lead-up to ground preparation and planting and throughout the brassica crop’s growth.
This trial highlights the potential of cover crops and reduced tillage as tools to enhance soil health, improve nitrogen management, and reduce production costs. As the project progresses, further insights will be gathered to refine these practices and ensure their compatibility with broader farm operations.
