Suzanne Boschma, Peter Perfrement, Mark Brennan and Sarah Baker | NSW Department of Primary Industries and Regional Development | Tamworth Agricultural Institute, 4 Marsden Park Road, Calala, NSW 2340
Annual fodder crops are an important component of livestock enterprises as they provide high quality feed for growing animals. Traditionally, these crops comprise a single species such as forage oats, a forage brassica or a dual-purpose crop. However, mixed species fodder crops are becoming more widely sown. There are many factors that determine the composition of these mixes, including regional suitability and producer preference. Complexity varies from simple two-species mixes such as oats and ryegrass, to multi-species mixes that contain ten or more species. Seed sizes in these mixes can therefore be highly variable, ranging from small seeded species like brassicas to large seeded species such as vetch. During discussions with producers and advisors, we have been regularly asked what the optimum sowing depth is for these more complex mixes. This is an important consideration when seed of the species are sold mixed or a seeder only has one seed box. We conducted a demonstration to provide some insight into this question.
Plots of a locally acquired and commercially available multi-species mix were sown in March 2023. The mix was comprised of 10 species (Table 1). Seed was sown at 37.5 kg/ha (1.5 times the recommended sowing rate) into 13 x 3 m plots using a disc seeder with 0.25 m row spacings. There were four sowing depths: 10, 20, 40 and 80 mm. The seed shoe was clear of the soil surface for each sowing depth, ensuring precise seed placement in the soil, except for the 80 mm depth. At this depth, the shoe disturbed the soil surface meaning that the depth was greater than 40 mm, but not necessary 80 mm.
Plant establishment was assessed four weeks after sowing. Plant counts were recorded for the four component groups in the mix: cereal, annual ryegrass, brassica and legume along 16 lengths of 0.5 m row (i.e. total of 8 m row). Individual counts were converted to plants/m2 and standard errors were calculated.
At sowing, there was good soil moisture below 30 mm, which meant that seed sown at the 10 and 20 mm depths were placed into dry soil whereas seed sown at the 40 and 80 mm depths were placed into adequate soil moisture to germinate the seed. Good rainfall immediately following sowing removed this difference in soil moisture.
The cereals and annual ryegrass emerged well at the 10–40 mm sowing depths, establishing with 42 and 62 plants/m2 on average, respectively (Table 2). At 80 mm, emergence was almost half that of the shallower depths. Seedling emergence of the brassicas was highest at 40 mm, followed by 10–20 mm and lowest at 80 mm. Legume emergence was highest when this component was sown at 20 mm and lowest at 80 mm.
Total plant densities were highest when the multi-species mix was sown to 20–40 mm depth (Table 2). Plant densities were less than half of the maximum when seed was sown at a depth of 80 mm. For the 10 species included in this multi-species mix, placing seed at a depth of 20–40 mm resulted in the optimum seedling emergence. The recommended sowing depths for the individual species in the mix varies. For example, a depth of 0–10 mm is recommended for tillage radish, 5–20 mm for annual ryegrass and clovers, through to 20–50 mm for cereals and 30–50 mm for grain pea. This demonstration suggests that, when choosing a sowing depth for mixed seed, selecting a depth that is maximum for the species requiring the shallowest depth (generally the smallest seeded species) is a good rule of thumb. Placing seed deeper into soil moisture at sowing is often an advantage, but could compromise the emergence of some species resulting in poor or failed establishment of these species if the depth is too great.
This project was funded by Meat and Livestock Australia and NSW Department of Primary Industries as part of the ‘Mixed species annual fodder crops to increase grazing animal production (P.PSH.1358)’. Seed was provided by AMPS, Tamworth.