‘Sward swaps’ offer carbon credits and cash-back
Introducing slow-growing, low-maintenance ‘carbon grasses’ to open public spaces would significantly improve the nation’s quest for carbon credits and dramatically reduce grass-cutting costs, it is argued.
Our ‘green and pleasant land’ is massively under performing in terms of its environmental benefit and contribution. It is estimated that the green infrastructure – urban green spaces, parks, recreation grounds and other public access-managed grassland areas – embraces more than 300,000 hectares (or 1,160 miles2). It is here, with ‘greenfield regeneration’, where we could make ‘green’ so much greener.
With a local government spend of over £500 million per annum on grass cutting and maintenance, significant long-term savings of at least 30 per cent can be achieved by using slow-growing, low maintenance cultivars. Such cultivars would still achieve that managed grassland, ‘green lawn’ effect, but some also offer significantly sustainable attributes, including:
• Hugely efficient bio sequestration (carbon storage) capabilities – performing 300 per cent more efficiently than traditional amenity grassland varieties; and
• Exceptionally deep-rooting cultivars assist soil structure formation and aggregation, enhancing the soil’s capability to receive, store and infiltrate excessive rainfall. As such, they align strongly with the currently desirable sustainable urban drainage systems (SUDS) initiatives and in turn, through their deep roots, contribute to the mechanical stability and longevity of urban green space areas.
Putting carbon back where it belongs
We are all aware that we are emitting far more carbon than the Earth can currently absorb. Assuming we all have relatively basic understanding of the global carbon cycle – whereby we identify carbon sources and subsequent bio sequestration – currently this cycle is unbalanced on a global scale and huge governmental efforts and environmental mitigation measures (Climate Change Act 2008 and the Kyoto protocol) are being realised to redress the imbalance.
Extensive bio sequestration in areas of permanent perennial grassland has attracted a lot of global focus as a particularly efficient method of sequestering atmospheric carbon dioxide as solidified carbon compounds within global soil regimes.
It is fascinating to note that one hectare of permanent perennial grassland has the annual capacity to sequester 13 tonnes of carbon within the soil, compared with one hectare of deciduous woodland that comparatively will only sequester two tonnes. This remarkable fact challenges the misconception that ‘to plant a tree is to save the Earth’!
The answer is literally under our feet, we need to put carbon back where it belongs – in the soil. All we need is sunlight and green grass.
Carbon grass introduction
Tufts University in Boston has extensive analysis of grassland bio sequestration and demonstrates that carbon is effectively and incrementally stored within a soil medium for 50 plus years showing annual increases before the carbon levels begin to plateau. This soil organic matter (carbon) can be accurately measured, with the acid loss technique being the preferred test methodology.
Imagine the benefit of being able to measure and record stored atmospheric carbon dioxide as a carbon compound within the soils of a permanent grassland area: carbon offsets, carbon credits, carbon audits and carbon trading – all contributing to the desirable ‘low carbon economy’.
Consider a grass plant rather like an iceberg. The grass plant biomass comprises about one part above ground, grass leaves (the sward) and four parts beneath ground, in the extensive root system. As long as that status quo is maintained and those permanent managed urban green infrastructure areas are left undisturbed, the soil organic matter within those public green spaces increases incrementally for decades.
Having identified the benefits of incorporating ‘carbon grasses’ within the national green infrastructure, how can this be implemented practically? The answer is ‘sward swap’, a non-destructive and discreet method of exchanging grass cultivars over a given area to introduce carbon grasses.
No ploughing or cultivation is required, nor is surface disturbance. Spray off the existing sward (systemic non-residual herbicide) and immediately follow with intensive overseeding of carbon grass cultivars. As the existing sward dies, the new cultivars germinate and grow within the dying sward providing an indecipherable transition from old sward to new.
The dying sward takes seven/eight days after herbicide application to demonstrate discolouration as it dies off, which conveniently correlates with the germination period for the new grasses coming through. The old sward provides a physical biological protective germination barrier to the new sward.
Once the new sward has reached a height of approximately 30mm, ongoing mowing maintenance may resume in order to help develop the sward and create dense grass covering.
It’s so simple it’s just got to work, and my field trials of the process have provided encouraging feedback.
What of the cost? It’s easy to argue that the reduced maintenance costs, mowing fertiliser and irrigation easily cover the sward swap process.
Being a realist, carbon grasses and sward swap are not the ‘silver bullet’ solution to climate change. There’s certainly more to life than grass. But it’s a good place to start.
Robert’s ‘Unlock the secrets of the soil’ presentation was one of a number of presentations made at The Sustainable Green Infrastructure Conference organised by Green Social Engineering. The conference presentations make interesting reading for groundsmen, and seminar slides/videos are accessible at: www.greensocialengineering.org