With the global situation for fertiliser being what it is, many farmers are understandably looking for even more opportunities than usual to reduce usage and spending in this area.

We wanted to highlight some of our data around N fertiliser and pasture growth from last season, that may have been missed by some amongst our more extensive season summary, and discuss our learnings that have come with it. We want to emphasize that going cold turkey is not a strategy we would recommend, and what occurred in Sri Lanka is a perfect example as to why that is.

We monitored per paddock pasture growth on a weekly basis throughout last season, and the results can be viewed by  clicking here

Even with the synthetic fertilisers that the ryegrass/white clover (RG/WC) regenerative paddocks received, they still were some of the worst performing paddocks on the farm, with all 4 paddocks falling within the bottom 6 for growth.

To understand why this occurred, and why the diverse pastures did so well without N (especially over summer) we need to understand soil biology, plant microbiomes and how the soil food web functions.

In recent decades, scientists have come to realise that all living things are holobionts, which is an assemblage of a host (plant or animal) with many other species living in or around it (microbiome).

In nature, plants pass aspects of their microbiome through their seeds, just as our mothers did for us. Additionally, the plant roots will form symbiotic relationships with soil biology as it is germinating, and this relationship will provide benefits to one another that will be discussed in more detail below.

However, our poor performing RG/WC pastures were established with 190 kgN/ha/year and developed with this easily accessible water-soluble inorganic N source. Since this N is so readily available to the plant’s roots, it does not need to expend energy developing the symbiotic relationship with soil microbiome that would typically be seen in nature. This will also weaken the microbiome that the progeny of this plant receives, making the issue compound over generations. When N fertiliser is removed too quickly there is no time for the plant or the soil biology to adapt, and this will leave the plant hungry for nitrogen and struggling with growth, as demonstrated by our 4 paddocks last season.

The second reason these RG/WC paddocks under performed was because of the lack of diversity.

Since 2002, there has been an on-going biodiversity trial in Germany called the Jena Experiment, that has had many interesting findings. They set up 20×20 m plots, some were monocultures, other had 2, 4, 8 or 16 species in it (4 functional groups when it was 4 species or more, not just 4 different grasses). They are looking at a range of factors such as biomass production, beneficial insects, soil microbial activity and water balance and they are finding time and time again that biomass increases as the number of plant species (from different families) in the mix increases. It is worth noting they also found that high diversity plots (8 or 16 species) accumulated 21.8% more carbon than low diversity plots.

They also trialled with different rates of Nitrogen (0, 100, or 200 kgN/ha) and again found that high diversity produced greater plant yield than high N. The Smart Grass Project in Ireland and the Diverse Forages Project at Reading University have found similar findings.

Many will assume that these results are solely due to legume content of the mixes, as they can fix Nitrogen from the atmosphere that the pasture can utilise, and while this is a significant contributing factor, it is not the only potential source of N for these plants.

First, there are a large number of bacteria that have genes that can code for nitrogenase, which are enzymes that catalyse the reduction of (N2) to ammonia (NH3). Since that atmosphere is 78% N2, we have a readily available source for these bacteria to synthesize. However, like humans, epigenetics play a role in genes becoming activated or de-activated, and nitrogenase won’t be activated until there is a quorum of bacteria that carry this gene.

The second source of N, and many other nutrients, is from the soil food web. In a plant that has been established in healthy, bio-complete soil, there will be trillions of microbes living in the rhizosheath alongside the plant roots. Some microbes, especially fungi, can reside within the root as well.

These microbes provided nutrients in two main ways, first through a symbiotic relationship with the plant, where the plant releases exudates (mainly sugars) which go down into the roots and are exchanged with the fungi and bacteria for other nutrients that they mined from the soil. There are massive amounts of exchangeable nutrients tied up in the sand, silt and clay and while plants don’t have the enzymes to breakdown these soil mineral particles, bacteria and fungi do, and this is part of how old growth forests sustain themselves for millennia.  The more species of plants, the larger the variety of exudates and the larger the species variation of the microbes that consume these various exudates. Diversity is the key.

The second way nitrogen is provided to the plant via the soil food web is from the waste of microbes aka the poop loop. All living organisms have different ratios of carbon to nitrogen.

Bacteria – 5:1

Fungi – 20:1

Green leaves — 30:1

Protozoa – 30:1

Nematodes – 100:1

Brown Plant Material – 150-200:1

Deciduous wood – 300:1

Conifer wood – 500:1

With a diverse and healthy soil food web, when a protozoa feeds on bacteria, it will need to eat 6 individuals to acquire it’s necessary 30 molecules of carbon, but as it only needs 1 molecule of nitrogen, 5 molecules of N will be released as protozoa waste for the plant to utilise. When you take into consideration the number of times this is happening each day, it becomes clear that there is more than adequate N being cycled through this biological process.

Considering that Arabidopsis (the most rapidly growing plant on the planet) only requires 0.2 ng per cm2 of root/day, a healthy soil food web can easily provide the Nitrogen needs of any plant and any remaining waste/N will be taken up by the bacteria and fungi.

Because of all these benefits, we have been focusing on improving soil biology on all Align Farms for the past 5 seasons, alongside our soil consultant, Canaan Ahu (Soil Matters). On our conventional pastures, we are applying lower rates of liquid synthetic fertiliser and chemicals to minimise damage to the soil microbiome as well as adding humates, fulvic acid and fish hydrolysate to feed and encourage microbial growth. We did not expect the RG/WC paddocks to go well without N, but we did it for the purposes of the trial and to validate our expectations.

Hopefully this sheds some light on our results and provides perspective on why we would encourage farmers to experiment with lowering N in different ways, but not to go cold turkey overnight. Focus should be placed on increasing diversity and soil biology. We are using the Soil Food Web to monitor our soil biology annually, with the next sampling scheduled for November.