The Mulgowie Farming Company, a family-owned producer of sweet corn and green beans, is known for its commitment to sustainable farming practices. Based in Mulgowie, Lockyer Valley, Queensland, the company teamed up with Soil Wealth ICP to explore whether legume cover crops could effectively supply nitrogen to sweet corn. This trial, conducted on a 16-hectare paddock of black clay cracking soils, assessed how legume cover crops could be used to optimise nitrogen availability to a sweet corn crop.
Trial setup
The aim of the trial was to determine whether a legume cover crop, specifically faba beans, could meet the nitrogen needs of a sweet corn crop.
Faba bean seeds inoculated with rhizobia bacteria were broadcast sown in June 2023 at 200 kg/ha.
Different cover crop termination strategies were tested to compare their effectiveness in releasing nitrogen to the subsequent corn crop.
The trial area was divided into four treatments:
- Green: Faba beans were terminated green at flowering via incorporation.
- Spray: Faba beans were sprayed with herbicide and rolled, leaving the residue on the soil surface.
- Harvest: Faba beans were grown to maturity and harvested for grain, with stubble left on the surface.
- Fallow: No faba bean crop (control).
When sweet corn was direct-drilled in December 2023, half of each treatment area received base fertiliser, while the other half did not, allowing the researchers to assess whether the cover crop alone could provide sufficient nitrogen. All areas were side-dressed with nitrogen in January 2024, and the sweet corn was harvested in February 2024.
Data collection was extensive, including monthly soil nutrient testing, soil temperature and moisture monitoring, and plant tissue and biomass sampling. These measurements provided insights into nitrogen cycling and the effectiveness of each treatment in supplying nitrogen.
Key findings
While the results were impacted by weed pressure, the trial demonstrated that legume cover crops, particularly faba beans, may effectively supply nitrogen to sweet corn.
The method of termination seems to play a crucial role in the speed of nitrogen release, with green incorporation providing the fastest nutrient availability. Harvesting the faba beans for grain removes significant nitrogen, impacting soil health and nitrogen cycling for future crops.
