The Soil Wealth Integrated Crop Protection (ICP) team is excited to be partnering once again with Mulgowie Farming Company. Building on insights from their previous collaboration, this new trial aims to refine the management of organic nitrogen from legume cover crops to better match the nutrient demands of high-value vegetable crops like sweet corn, while also addressing broader soil health considerations.

“The previous 2023-2024 trial demonstrated how the way we handle cover crops can have a profound impact on nutrient availability and overall soil health,” Steph Tabone reflects.

“This time, we would like to push further, aiming to strike a balance between rapid nutrient cycling and minimal soil disturbance.”

The last trial included several cover crop management strategies, each revealing critical insights. The green-incorporated faba bean cover crop, for example, demonstrated rapid nitrogen release, aligning well with the nutrient uptake demands of the corn crop, but required aggressive tillage. In contrast, the sprayed and surface-retained treatment released nitrogen much more slowly, potentially missing peak crop demand.

The trial also revealed that harvesting the legume for grain removed about two-thirds of the nitrogen from the system, reducing the amount available for subsequent crops. In contrast, the harvest of sweet corn cobs resulted in only a small amount of N removal, with a large proportion of N remaining in the paddock in the unused corn biomass. Therefore consideration needs to be given to nutrient cycling into following rotations.

Managing organic nitrogen to better match vegetable crop demand

With these lessons in mind, the new demonstration trial aims to answer critical questions for growers, such as whether a mixed legume and grass cover crop can effectively supply nitrogen to a corn crop, potentially reducing the need for synthetic nitrogen fertilisers. It also seeks to identify termination methods that best align the timing of nitrogen release from cover crop residues with the nitrogen needs of sweet corn, and to understand the impact of removing biomass for forage on nutrient availability and overall crop performance.

Incorporating the learnings from last year’s trial, this season’s demonstration includes a forage barley and field pea cover crop. This combination is designed to scavenge excess nitrogen with the barley, encouraging the legumes to fix atmospheric nitrogen and provide a more sustainable nutrient supply. Additionally, the trial will explore alternative termination techniques, including a rolling stalk chopper, which offers a middle ground between rapid nutrient release and minimal soil disturbance, potentially providing more balanced nutrient availability.

The four main treatments being tested are:

  1. Fallow (control)
  2. Harvest for livestock forage at first flower (conventional practice)
  3. Cover crop terminated at full flower using a buffalo rolling stalk chopper (this treatment will chop up the residue roughly and lightly incorporate to reduce aggressiveness of tillage, yet hopefully still deliver nitrogen effectively to the corn crop).
  4. Cover crop terminated at full flower by mulching and leaving on the soil surface (this treatment will help to eliminate tillage but encourage quicker breakdown of residues and release of N through mulching).

These approaches aim to assess how termination methods influence nitrogen availability, residue breakdown, and overall crop performance under varying seasonal conditions. For example, mulching might provide better erosion control during heavy rainfall, while light incorporation could improve nitrogen release during drier conditions.

Progress so far includes the successful sowing of the cover crop at 30 kg/ha each of forage barley and field pea, with the legumes inoculated to support nitrogen fixation. The trial is now moving into the active monitoring phase, which will include monthly soil nitrogen assessments and biomass quality measurements as the cover crops reach termination.

The Soil Wealth ICP team is keen to provide growers with practical insights that can help optimise nutrient management, reduce fertiliser costs, and improve soil health across diverse cropping systems.

“As this iteration of the demonstration progresses, the team hopes to shed light on new strategies that can helping growers achieve more resilient, productive soils,” Steph said.

Stay tuned for more updates on the Soil Wealth ICP here