Exploring approaches to undersowing tenderstem broccoli to benefit soil health

Summary

A farmer in the Wye and Usk Catchment is working with a broccoli grower to trial different cover crops to protect the soil beneath broccoli and kale crops. They will trial two different seed mixes, and measure which cover crop works best to protect the soil, thereby reducing environmental impacts from soil loss and nutrient run off. They also want to improve the conditions for the picking gangs and produce a grazeable cover crop at the end of the broccoli harvest.

The trial is coordinated by The Wye and Usk Foundation.

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How it works

• Tenderstem broccoli is often grown on rented land in rotations that also include potatoes and maize which can deplete soil health increasing risk of erosion.
• Because of the size and spacing of the plants, much of the field is bare soil, making it vulnerable to soil erosion and soil and nutrient loss, both of which are drivers of failing water quality in rivers such as the River Wye.
• With increasing demand and production of tenderstem broccoli in the UK, and particularly the Wye catchment, the industry is coming under pressure to reduce soil erosion associated with the crop.
• Under-sowing crops with suitable, low growing species (cover crops) is known to be effective for reducing soil erosion and soil nutrient loss.
• This is not the standard practice when growing tenderstem broccoli.
• The group want to find out whether the soil benefits of cover crops are applicable to broccoli production, without compromising yield and the practicalities of farming the crop.

Trial design

The broccoli is planted in July, and the cover crop will be undersown as soon afterwards as is practical; roughly 4-6 weeks later (this will depend on weed pressure and the need for inter-row hoeing).

The group will measure:

• Yield impact on tenderstem 
• Trafficability of soil
• Ease of picking (staff questionnaire)
• Infiltration 
• Soil structure and rooting depth
• Soil aggregation
• Sediment loss
• Yield of undersown crop for grazing (plate meter)
• Soil and nutrient loss
• Carbon footprint