Blog ILVO BLOGS from the Experimental Platform for Agroecology in Hansbeke: How to sow through mulch

First mulching, then sowing, it doesn't get neater than that. On June 2, 2021, at the Experimental Platform for Agroecology in Hansbeke, we tested two overseeding machines: the SimTech T-Sem 300A and the Sky EasyDrill. The specific question was to what extent the seed drills were able to successfully sow a maize-bean seed mixture through a mulch layer (pre-composted mixture of wood chips and grass clippings) into the soil. In the same trial, we also worked with a second scenario: What happens if you sow first - with a test field sowing machine - before applying the mulch? The tests showed that you can indeed sow through the spread mulch when the mulch layer is thick enough (i.e. +- 10 cm). We also got good results where we first sowed, and then mulched. In this blog, you can read about the technical specifications of the overseeder and about seeding through the mulch.

To sow through the mulch layer, the disc for the seeding element is important. It has to cut through the mulch in order to finally plant the seed at the right depth in the soil. Therefore it is important to use the right machines.

Mechanical overseeder

The SimTech owned by farmer Marc Verhofstede is a mechanical seeder. The seed falls down and is collected by a sponge-feeding system which allows seeds with different seed sizes to be used. That's how it can sow small seeds like grass and clover but also larger seeds like corn and bean. The system brings the seed into the seeding tube after which it ends up behind the coulter, in the trench. It also has a wide range of seeding densities, from 2 to 400 kg per hectare. The standard seeding width is 15 cm. By blocking every other seeding tube, the seeding width becomes 30 cm. The pressure roller drives the sponge feeding system so it doesn't need a PTO to the tractor. The pressure roller, together with the three-point attachment to the tractor, determines the sowing depth.

Demonstratie SimTech doorzaaimachine

Pneumatic overseeder

The Sky EasyDrill that belongs to contractor Gert Annendyck is a pneumatic seeder. The seed is distributed by air pressure over the different seeding tubes. A disc makes a trench where the seed falls into, then the pressure roller covers the seed back. The three seed tanks make it possible to sow three different seeds or seed mixtures. This makes it possible to simultaneously apply soil improvers. With the machine it is possible to sow at two different sowing depths. The sowing elements follow the ground relief independently. This guarantees a constant sowing depth even if the soil is uneven. With the adjustable pressure on the seeding elements from 0 to 250 kg, even in the driest conditions with hard soil, seeding is possible. The Sky EasyDrill also has a wide range of seeding densities from 1 to 450 kg per hectare. The distance between the seeding elements is 16.6 cm.

Demonstration of Sky EasyDrill overseeder

Sowing information

We sowed a maize-bean mixture at 30 kg per hectare at 2 cm depth in the soil. We took into account the mulch layer of +-4 cm through which the seed has to grow.

With the SimTech, we sowed in rows with 15 cm spacing. The Sky EasyDrill did a stereo sowing, row pairs at a distance of 49.8 cm and 16.6 cm from each other. With the trial field seeder, seeding was done according to the classic seeding pattern with 75 cm between rows.

With the Sky EasyDrill, the mulch layer of 6cm seemed to prevent a sufficiently deep seed placement in the soil. With the mulch layer of +-4 cm, the two overseeders were able to successfully seed into the soil but the mulch layer was slightly mixed with the soil. Only at the location where the layer was 6 cm did the mulch stay nicely in place.

Concluson: either apply a thick mulch layer or mulch after sowing

Overseeding through a +/- 4 cm thick layer of a pre-composted mixture of chips and grass clippings resulted in mixing of the mulch layer with the soil. With a thicker mulch layer +/- 10 cm of fresh material, this mixing might possibly be avoided. Alternatively, seeds can be sown in the normal way before applying the mulch.

Also read our blog entry about using mulch.

The Experimental Platform for Agroecology in Hansbeke is a collaboration between ILVO, PHAE en RHEA. The 50 ha of organic fields offers a unique experimentation space for agroecological principles. We regularly blog about these experiments via the ILVO website and social media.