Stressing plants to create a healthier crop isn’t a new process. According to a guidebook written in the 1600s (and recounted by Iida Hidetoshi in 2014), “Japanese farmers enthusiastically treaded seedlings in winter because they empirically knew that treading prevented spindly growth, strengthened the roots to grow and spread, shortened plant height, increased tillers and ear length and eventually gave a good yield.”
The process is called ‘mugifumi’; ‘mugi’ refers to wheat and barley, and ‘fumi’ means treading. The practice continues with farmers and children walking on grain seedlings on small farms and rollers pulled by tractors doing the work on larger farms. The process starts when seedlings have three leaves and is practiced several times every 1.5 weeks. Mugifumi is most effective in dry soil.
Scientists found that treading wheat seedlings by foot led to healthier seedlings and an increase in grain production by 54 per cent. The effect may be due to release of hormones in response to the stress. Another theory is that the wounds created by trampling lead to greater evaporation of water, and this makes the plants more cold-tolerant. Either way, trampling works as long as it’s not too frequent, too excessive or at the wrong time (e.g., when the plant is too large).
Source: Hidetoshi, Iida. Mugifumi, a beneficial farm work of adding mechanical stress by treading to wheat and barley seedlings. Frontiers in Plant Science. 2014. Volume 5. Page 453.
— Janet Wallace