A review of knowledge: inter-row hoeing & its associated agronomy in organic cereal & pulse crops

Summary

The aim of this project was to establish the “state of the art” for inter-row hoeing and its associated agronomic practices in organic cereal and pulse crops. To achieve this a detailed review of literature was undertaken.
• To facilitate inter-row cultivation in cereal and pulse crops, some adjustment of row spacing may be required. For cereals, drilling crops in 25 cm rows can reduce yield compared with normal drilling practice, primarily due to greater intra-specific competition amongst the crop (i.e. competition between crop plants).
• The yield penalty resulting from widely spaced crop rows can be minimised using a number of approaches, depending on the drill:
1. Reducing the seed rate in widely spaced crop rows can help to minimise excessive intra-specific competition.
2. Band sowing the crop in wide rows can also help to minimise intra-specific competition as the seed is distributed over a greater area.
3. Using a twin-row arrangement can completely overcome the yield penalty.
• The recommended row spacing for peas (up to 20 cm) and beans (up to 35 cm) does not require any further adjustment for inter-row hoeing.
• Recent developments in automated guidance of inter-row hoeing equipment mean that weeding operations can now be conducted a much higher speeds (10 km h-1). This has highlighted the limitations of some of the cultivators currently used (e.g. ‘A’ blades), as excessive soil throw can occur at this high speed. Rolling cultivators may prove to be the most suitable at high forward speeds. For manually guided hoes working at slower speeds (5 km h-1), ‘A’ and ‘L’ blades offer an effective low cost solution.
• In terms of the timing of inter-row hoeing, it is suggested that weeding operations should be conducted at an early stage in the growing season, as the weeds that emerge with or shortly after the crop are the ones that pose the most significant threat for crop yield. Weeding on two occasions can provide better levels of weed control than weeding once, but weeding more frequently offered little additional benefit. Reductions of weed biomass of up to 99 % have been reported as a result of inter-row hoeing, although this has not always resulted in a positive crop yield response. This is probably due to crop damage resulting from inaccurate hoeing, a problem that can be overcome with automated guidance.
• There is some evidence to suggest that mechanical weeding operations can mineralise soil bound nitrogen.
• The impact of inter-row hoeing on ground nesting birds is uncertain. Early indications suggest that skylarks prefer to nest directly adjacent to or in the crop row rather than between rows.
The information contained within this review should enable farmers to make best use of inter-row hoeing in their arable crops.
There are a number of areas that require further research and development:
• The interaction of seed rate and row spacing needs to be confirmed in organic systems.
• Relatively little is known about the mechanisms of weed kill and the detailed interaction between the cultivator blade, the weed and the soil. This is particularly important with the new automated guidance equipment that allows weeding at high forward speeds.
• The timing and frequency of inter-row hoeing has received very little attention. The optimum weed control timings are based on small-plot crop:weed competition studies and need to be verified under field scale management with inter-row hoeing equipment.
• Finally, the impact of inter-row hoeing and widely spaced crop rows on ground-nesting birds has not been looked at directly, but is of importance.
Please see the main report for a more detailed summary before the full text.