Earlier swathing opens a new pathway for subterranean clover seed harvest

Earlier swathing offers a promising new method for harvesting subterranean clover seed, according to recent research. Traditionally, seed is collected from fully dry crops after multiple passes of suction harvesters, which disturbs the soil and can lead to burr loss. Two experimental studies explored a novel approach: cutting and lifting green plants using modified peanut-harvesting equipment, then drying the plants in windrows for later seed collection and threshing.

The results showed viable seed could be recovered before the crop became fully dry, creating a potential pathway for reduced machinery passes and soil disturbance.

A commercial-scale trial in Western Australia compared swathing a subterranean clover seed crop on November 25 and December 1, 2022, with conventional suction harvesting in February 2023. The modified peanut digger successfully lifted and windrowed the crop, although soil attached to plants and weeds became tangled in the machinery.

Despite this, seed recovery on Nov. 25 moved nearly 100% of available seed into the windrow, compared to 61.3% using a single suction harvester pass after three preparatory tillage operations. Seed swathed on December 1 had comparable germination (98.0%) to that harvested by suction in February (97.5%).

However, seedlings from earlier-harvested plants showed slightly lower vigor. Burr attachment strength declined over time for all cultivars, while harvest loss increased in four of six cultivars, suggesting earlier harvesting is beneficial. Factors like soil moisture, crop biomass, burr burial, and soil conditions can influence the timing and effectiveness of swathing.

The commercial trial demonstrated that conditions can change rapidly, causing seed extraction efficiency to decline by nearly 16 percentage points during the six days between swathing treatments. This indicates the practical harvest window may be narrow and dependent on factors like cultivar, paddock, and season.

The findings demonstrate that complete desiccation is not necessary for viable seed recovery, and earlier swathing could reduce burr loss, machinery passes, soil disturbance, and reliance on aging equipment. While substantial equipment refinement and changes to paddock and harvest management would be needed, the results suggest that green subterranean clover can be harvested successfully, providing another option for industry consideration as machinery availability, production costs, and environmental expectations evolve.