BFH-HAFL investigated three non-hardy green-manure mixtures and their effect on organic maize: A legume-rich green manure showed very high nitrogen enrichment and a positive effect on the early juvenile development of maize.
Nitrogen (N) is a scarce element in organic farming, especially on no-livestock or low-livestock arable farms. The use of legumes and green-manure mixtures to enrich, conserve and convert nitrogen is therefore advantageous. While no-till cropping systems are beneficial in terms of soil protection, they are very challenging without herbicide application.
Comparison of green-manure mixtures and primary tillage
At BFH-HAFL, three non-hardy green-manure mixtures were developed for low-livestock or no-livestock organic farms, which could be suitable as an intercrop before maize for organic no-till cultivation. The three mixtures ‘ML1’, ‘MS1’ and ‘ML2’ contain different species and proportions of legumes and non-legumes (Table 1).
Over a period of three years, initially in a block trial and then in seven strip trials, both the agronomic properties of the mixtures and their effects on the successive maize crop were compared in relation to tillage (with or without plough).
Rapid soil cover and high N enrichment
The trials showed that all three green-manure mixtures emerged rapidly after seeding in August and quickly produced a lot of biomass. Forty days after seeding, the soil cover of the green manures averaged between 74 and 91% depending on the year, with no significant difference between the mixtures. However, after the green manures froze over the winter, the two legume-rich mixtures ML1 and especially ML2 (Figure 1) covered the soil up to 20% more and thus suppressed weeds more effectively than MS1. The latter contains a relevant proportion of sunflower, which covers the soil less well after freezing. Furthermore, MS1 was measured to have the highest C/N ratio, which may result in a slower decomposition of biomass and a temporary immobilisation of N in the soil.
In the strip trials, all three mixtures achieved similarly high biomass yields: between 44 and 48 dt DM/ha within two months. However, the ML2 mixture with 58% legumes achieved a significantly higher nitrogen yield of 174 kg N/ha than the MS1 mixture with only 32% legumes and 132 kg N/ha.
Positive effect on maize in the juvenile stage
Also in the strip trials, ML2 showed a better effect on maize plant height compared to MS1. This was especially true in the earlier phase of juvenile development five weeks after seeding. At this stage, the maize plants on the reduced-tillage plots were no smaller than those on the tilled plots. However, ploughing had the best effect on maize yield (between 26 and 32 dt DM/ha additional yield).
The block trial showed that later reduced tillage, carried out shortly before seeding, resulted in significantly smaller maize and lower chlorophyll content compared to earlier tillage. This is related to the delayed heating and N mineralisation in the soil with reduced tillage.
- The ML2 legume-rich green-manure mixture is very well suited for no-till organic maize cultivation on low- or no-livestock farms with limited nitrogen supply.
- It can produce very high nitrogen enrichment while also achieving dense soil cover over the winter and thus effective weed suppression.
- An appreciable advantage is that the juvenile development of the successive maize crop is not delayed, as the fixed nitrogen is mineralised in good time.
- However, reduced tillage should ideally be carried out at least two to three weeks before maize seeding rather than shortly before.