Can large seed size compensate for deep seeding in organic barley (Hordeum vulgare) and oat (Avena sativa) production? An assessment of farm-saved seed

Abstract

Greater seeding depths are often used in organic production to compensate for drier soil conditions caused by pre-seeding tillage. We hypothesized that reduced crop performance from deeper seeding could be compensated through larger seed. Field experiments were conducted in Carman, Manitoba, Canada, in 2015 and 2016. Barley (Hordeum vulgare) and oat (Avena sativa) seed lots were sieved using standard industry sieves (from 0.08 cm to > 0.32 cm × 1.91 cm in barley seed lots and from 0.08 cm to > 0.28 cm × 1.91 cm for the seed lots of oats) and classified into small, medium, and large seed sizes for each seed lot. The proportion of small, medium, and large seeds varied depending on farmer seed lot. Seed lots were sown at shallow (2.5 cm) and deep (6.4 cm) depths in organic fields. Deeper seeding and use of small seed size resulted in decreased grain yield and increased weed biomass. This trend occurred in both years but was only significant in 2015. No seed size by seeding depth interactions were observed for crop emergence, weed biomass, grain yield, or dockage for oat or barley over the 2-year study. In two instances, crop biomass was greater with larger compared with smaller seed at shallow seeding depths. This research indicated that large seed did not compensate for lower crop productivity and higher weed biomass owing to deep seeding, but that large seed and shallow seeding independently led to more positive outcomes for organic barley and oat production.