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Playing catch-up with arable’s focus on soil health and productivity

British Dairying Magazine Feature February 2020 –

Looking over the hedge at arable crop growing, improving soil health and thereby productivity has become mainstream. Is it the same here in grassland, where soil is cultivated less often than for arable crops, or indeed not at all in permanent grassland?

It would be easy to assume there’s not much that needs to, or indeed can, be done with soil health, unless you grow maize of course.

But here’s food for thought. Just one teaspoon of soil contains up to 50,000 species of micro-organism: bacteria, fungi, protozoa, nematodes, and very many kinds of creepy-crawly. On a larger scale, University of Chicago Professor Rick Stevens calculates that 1kg of soil contains more microbes than there are stars in the entire known universe [ref 1].

The numbers are colossal: 1030 (that’s 10 followed by 30 zeros) microbes in 1kg soil, which is a million times more than 1024 stars. Slightly more down to earth here in the UK, soil scientist Dr Martin Wood of Earthcare Technical Ltd says the typical total weight of microbes in one hectare’s topsoil is the same as 12 adult sheep [ref 2].

This is just as important for grass as arable crops because the larger any locality’s biological community – its biome*- the healthier the soil. Healthy soil is more productive than unhealthy soil. [*biome = biological community]

Rather than N, P and K content, Dr Wood suggests that soil health is determined by organic matter content (>3.5% organic carbon); no capping or compaction; plentiful earthworms (about 25 per spadeful); porous and aerated structure; and moist but not waterlogged condition. All of these together create conditions for a healthy and vigorous soil biome of microscopic life forms.

Clearly, spreading slurry makes a worthwhile contribution of organic matter, which in turn helps soil structure. But many samples of slurry in particular are far from benign, explains Liz Russell from EnviroSystems UK.

“As all farmers know, fibre floats to the surface during storage and creates a crust, through which light and oxygen cannot penetrate,” she explains. “Below this, small particles sink and form a sludge at the bottom, with a liquid portion above it. Without oxygen, anaerobic microbial activity creates acidic, septic and foul smelling conditions in both the liquid and sludge layers.

“While spreading this contributes plant nutrients and organic matter, it also inoculates soil with a high loading of anaerobic microbes washed into the ground in an acidic soup.”

To assess the impact of this, EnviroSystems has been involved in a PhD research project with Lancaster University. One aspect was a respirometry test to measure carbon dioxide (CO2) production from soil samples as an indicator of its biome’s metabolic activity.

Two different cattle slurries were added to soil samples and assessed. One was inoculated with a slurry bug treatment (SB on the graphic) that stimulates aerobic respiration producing CO, and the other untreated (label S).

The project report confirms a consistent increase was found in cumulative carbon dioxide concentration from soils across the experiment, consistent with respiration of carbon during the soil incubation, and that the highest respiratory activity was observed from treated slurry [ref 3].

The research also conducted phospholipid fatty acid analysis (PLFA) as an indicator of microbe proliferation in the soil samples, also finding a higher level in soil with treated slurry.

EnviroSystems’ involvement in this research was prompted by anecdotal reports from farmers about plentiful fresh pasture grass being ignored by hungry high yielding cows. Liz Russell explains: “It’s deeply frustrating to watch cows turned out onto fresh grass and not see them put their heads down to graze – and it’s not as unusual as you might think.

“What’s even more disconcerting is that it’s happening more on farms that take great pride in their grassland management and are used to growing bumper crops of grass.

“Yet successful farming is totally dependent upon the soil. It’s every farm’s most important asset but for at least 40 years soil health has been compromised by management practices promoted to farmers.”

On a growing number of farms, Mrs Russell has witnessed biological slurry conditioning and reduced nitrogen fertiliser transforming pastures from “plenty but unpalatable” into “lush and irresistible”, though it’s not an overnight process.

Moreover, biological treatment also minimises crust formation on stored slurry and helps create uniform consistency from surface to the bottom. “This means minimal stirring is required before spreading, reducing markedly the workload and fuel consumption involved,” she explains.

“Clearly, this reduces costs and helps improve the farm’s carbon footprint. However, over the long term, I’m convinced that the value of improving the soil microbiome will overshadow these more immediate gains.”

References:

[1]. http://www.tedxnaperville.com/talks/rick-stevens/, viewed 28 July 2016.

[2]. Dr Martin Wood, 27 July 2016. Great Soils: Soil health and bottom line. Webinar: AHDB Horticulture Great Soils programme.

[3].Dr M Fernanda Aller, Vito Abbruzzese, July 2016. The chemical and microbiological effects of bacterial + enzyme conditioning on livestock slurry and agricultural soil (unpublished, copy on file at Envirosystems UK Ltd). Lancaster University (research is part funded by the European Regional Development Fund).