Green Manure Seed Mix

A legume-based green manure crop puts nitrogen and organic matter back into tired soil. Green Manure Mix combines oats, faba beans and vetch: the legumes fix nitrogen, the oats' fibrous roots help break up the soil, and the crop is mulched or dug in after about 6–8 weeks of growth. Green manure also improves soil structure and water retention. The mix suits areas with 350 mm or more of rainfall and soils from sands through to heavy clays, sown at 50–75 kg/ha.

It usually helps, mainly through extra nitrogen and better soil. Vetch is valued for its benefits to following cereal and oilseed crops, which are usually greater than from other pulses. Faba beans make more soil nitrogen available to the next crop, and up to 40% of the nitrogen in a faba bean crop is below ground. As a guide, legumes fix around 15–25 kg of nitrogen per tonne of shoot dry matter, so a bulky, well-nodulated stand returns the most.

Green Manure Mix is fast growing and is usually ready to mulch or dig in about 6–8 weeks after sowing, while the plants are still green and soft. The legumes flower around July to August. Leaving it longer builds more biomass and more fixed nitrogen, so balance that against your next sowing date. Working the crop into the soil makes it break down faster, while mulching and leaving the residue on the surface protects the soil and reduces evaporation.

Allow about a month between digging in a green manure and sowing or planting out, because freshly decaying green material can hamper the growth of the next crop. Plan backwards from your sowing date: Green Manure Mix needs about 6–8 weeks of growth before mulching, plus roughly a month to break down. Material worked into the soil breaks down faster than residue left on the surface, so incorporate it if your planting window is tight.

Sow Green Manure Mix at 50–75 kg/ha. It's a large-seeded mix, so it goes in deeper than pasture seed: faba beans are normally sown 5–8 cm deep and vetch 4–6 cm. Faba bean seed is big, and some seeders need adjusting to handle it. The higher end of the rate gives a denser stand that competes harder with weeds and produces more biomass to return to the soil.

Sow Green Manure Mix in autumn, from the break into early winter. Its components suit that window: faba beans are planted in mid to late autumn, and vetch is best sown from mid-April to the end of June, with earlier sowings yielding better in trials. The mix flowers around July to August. If it's preparing ground for a spring or summer crop, an autumn sowing gives it time to grow, be mulched and break down before you plant.

Yes, unless the seed has been pre-inoculated. The nitrogen a green manure adds depends on its legumes forming nodules with the right rhizobia. Faba beans need Group F inoculant and vetch needs Group E, so the two legumes in Green Manure Mix use different groups. Ask us about inoculating the blend before you sow, and sow inoculated seed promptly so the rhizobia stay alive.

Yes, Green Manure Mix can be grazed for extra feed, but every bite removes biomass that would otherwise go back into the soil. Graze lightly and leave plenty of growth to mulch or dig in. Watch the vetch closely. If rust appears in a vetch crop, don't graze it, as rust-infected vetch can cause abortion in pregnant ruminants. Common vetch is very palatable at all growth stages and has a high feed value.

It isn't the right choice for paddocks that sit wet. Green Manure Mix is not rated for waterlogging, and common vetch in particular does not tolerate it. Choose well-drained paddocks, on sands through to heavy soils, with at least 350 mm of rainfall. On country that waterlogs, look at a pasture or cover crop built on waterlogging-tolerant species instead, or sow the green manure only on the better-drained parts of the paddock.

It can be a useful step. In Green Manure Mix the oats help crowd out weeds that germinate with the crop, and because the crop is mulched or worked in while still green, weeds growing in it are destroyed at the same time. Time the finish to the weeds, not just the crop: whether you cultivate, mulch or spray out, do it before the target weeds set seed. For spray-out, that means at or before their milky dough stage.