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Encouraging fine grass domination of the bowling green sward

Nature works in a very efficient way and the process of colonisation of new, bare ground by plants is no exception to this. The progression of plant species has evolved so that any bare ground is first dominated by annual seeding grasses like annual meadow grass and tap rooted weeds like dandelions. In a completely natural environment, the next stage will see perennial grasses such as fescues and bents take over from the annuals, before eventually giving way to shrubs and eventually forests. In climates where there are plentiful grazers like sheep, deer and cattle, grasslands will develop and the progression will largely stop with perennial grasses becoming the dominant plants for the long term. On bowling greens, the grazers are replaced artificially by the green’s mower and greenkeeper, except that in many cases we have regressed back to a sward dominated by the annual weed grass annual meadow grass (Poa annua). Why should this be? It’s because, through a mixture of inappropriate and even unnecessary maintenance, we have in many cases unwittingly caused the soil beneath our greens to become barren and inert, making the surface week and susceptible to ingress of annuals like Poa annua.
Turning the Tide
Fortunately, it is possible to turn this situation around predictably and without too much drama. And although you’ve probably heard lots of scary stories about how you will need to first put the Poa annua under enormous stress before over seeding with fescue/bent seed, this isn’t necessary either. It might sound too good to be true, but you can quite easily turn your green back into a fine, firm surface dominated by the fine perennial grasses, without doing anything out of the ordinary. It is possible to convert greens from predominantly Poa annua to predominantly fine grasses (bent/ fescue) without stressing the grass and the solution lies in the life in the soil itself.
Grass domination
What causes perennial grass domination as opposed to annual grass domination of the rootzone?
The supply of the main fertiliser elements (commonly called plant nutrition) is driven by soil biology. The micro-life (fungi, bacteria and a range of other micro-organisms) in the soil makes nutrients, the building blocks of plant tissue, available in plant useable form. As the nutrient requirements for plant species above ground changes so does the microbial life underground. Plants are constantly producing glucose for energy during through the process of Photosynthesis but not all of that energy is used directly by the plant to grow and live. Our fine perennial grasses use a lot of this energy above ground to grow stem and leaf tissue this feeds the above ground food chain like grazers (green mowers!). Below ground they release the energy by leaking proteins and carbohydrates as root exudates, whilst building root mass and shedding dead plant tissue as they grow bigger. This energy feeds the soil food chain of bacteria, fungi, protozoa, nematodes, arthropods and worms, or the soil food web as we’ve come to know it.
The Free Fertiliser Factory
Beneath our feet, there is the most remarkable factory where fertiliser for our turf is essentially produced for free, but only if the soil is working properly. In simple terms bacteria eat the proteins, sugars and carbohydrates that leak from the roots of the plants. Specialist fungi mop up any juice exuded by the roots that they can, but most live on the more woody cellulose and lignin found in the dead roots and shoots that would otherwise be destined to produce thatch. It is a jungle down there and in true jungle style, these bacteria and fungi become food themselves for predatory microbes including nematodes and protozoa. These predators excrete ammonium, which is then converted to nitrate by bacteria in the presence of oxygen. Nitrate can be used directly by the plants and so this amazing cycle of growth and decay continues, producing everything needed by the plants in terms of soil nutrients.
Mycorrhizae
In my March column, I focussed on a very important group of fungi that live in and around the roots of our fine grasses. These fungi are called mycorrhizae, from the Latin via Greek for fungus (myco) and root (rhiza). Mycorrhizal fungi associate with the root systems of our perennial grasses and together they form a symbiotic relationship where the fungi extend their hyphae into the soil, produce enzymes that make phosphate and other nutrients available to the plant and then transfer these nutrients, trace elements and water back to the plant in a form it can readily use to supply the raw ingredients for growth. We can think of these fungi as something akin to a root extension as they extend the effective root area of the plant many times over, allowing it to access resources from a far greater volume of soil than it otherwise would be able to. This association of fungus and root is essential to the success of the fine perennial grasses. This relationship makes perennial grasses twice as efficient as annuals, which rely on fertiliser inputs to grow. It’s not uncommon for construction specifications for new greens and sports pitches to specify that the new rootzone must be inoculated with mycorrhizal fungi from the outset. Of course, this seemingly miraculous symbiotic activity goes on in natural grassland systems and closer to home, in areas such as meadows without fertiliser inputs and without thatch building up!
Seed Production
Conversely, and as we can readily observe on our greens, Poa annua puts its energy into producing seed and we can see this almost all year round on greens that are infested with Poa. These annual plants have one major aim and as a result expend around 75% of the energy created in photosynthesis on seed production as that is their primary means of reproduction. This of course means that there is only about 25% of this energy left to go into feeding its underground support system. Poa annua does not associate positively with mycorrhizae, so the soil food web that grows underneath seed producing annual plants is very different from the soil food web that lives under perennial grasses.
Soil food web
For greenkeepers who want to produce high performance, fescue/bent dominated greens, the task is clear. We need to manage the soil food web to encourage the fine perennial grasses. Yes, believe it or not you can easily influence the type of grass you grow, and convert turf dominated by annual grasses into turf that consists of predominantly perennial fine grasses. There is no need to kill off or unduly stress the existing grass during the transition period, no need for the transition period to be painful in any way for players, club officials or most importantly, the greenkeeper! Soil on its own is a fairly sterile medium, so when the ground is bare there is no dead plant tissue to feed fungi (so they aren’t there) and bacterial levels are usually low, which means the pioneer annual plants that first colonise bare soil have growth characteristics that help them to get by with only the help of the limited soil bacteria. In these conditions, there is no active soil food web, it’s fairly inert. Ring any bells? Yes, the thatchy, anaerobic, excessively sandy and therefore inert rootzones we unwittingly create over years of mis-guided maintenance are dominated by Poa annua for a reason, there is no soil food web to speak of. We’ve already seen that Poa annua puts most of its energy into producing seed and relatively little goes underground to feed the supportive food chain, which explains why Annual Meadow Grass needs more fertiliser and water than the finer grasses. In natural conditions, as an annual, Poa aims to produce seed and then die and when this happens thatch is formed. This means there is now food for fungi and a more complex soil food web can form that supports perennial grasses. However, due to our bowling green situation being somewhat artificial, the way that we manage turf often means that this cycle gets stuck at the Poa annua stage. This is the Circle of Decline in action.
Here to help
Making a start on the transition to perennial fine grasses means using less harsh materials such as low salt fertilisers, natural bio stimulants and incorporating maintenance practices that encourage better oxygenation of the soil and a decent amount of humus to build up in the soil. This can mean taking stock and rethinking traditional practices like routinely adding more sand every year, or regular use of harmful pesticides which can contribute to inert soil conditions and hold back progress.

If I can be of help, please feel free to drop me a line to: john@bowls-central.co.uk

Caption: In many cases, bowling greens have been damaged by over use of sand

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