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turf grass

Turf grass leaf growth factors

Moving on from yesterday’s post which detailed the structure of grass plants, today I want to go into more detail about the processes and factors related to the growth of turf grass.

Leaf Growth
When we think of turf it’s easy to imagine that each individual blade of grass is a plant. However, each of the blades we see in the turf is a single leaf of a plant that might have many other leaves. All growth occurs from the base of the leaf so that the bit we cut off is always the oldest part of the living plant tissue and it is this feature that allows the grass to be mown frequently without undue injury. Although the main function of the leaf is to manufacture food for the plant through photosynthesis and increase the biomass of the plant the leaf can also take in water and nutrients to some degree.

Factors which affect leaf growth

Environment
As we observed in the post introducing warm and cold season grasses there are certain environmental factors that affect the growth of the turf grass leaf.

Temperature
Temperature is one of the most critical factors in leaf growth.

  • Cool season (C3) grasses have an optimum temperature range of 160 to 240C
  • Warm season grasses (C4) have an optimum range of 270 to 350 C

Sunlight
Sunlight is the main energy source in photosynthesis which the plant must do to produce food in the form of carbohydrates. In shade the density of turf will decline significantly which is a sign that there is much less biomass (plant tissue) being created by the plants.

Soil
For successful growth the plants need a favourible soil environment that allows for unhindered root growth. When rooting is curtailed so is leaf growth.

Cultural factors

Mowing height
When the grass is allowed to grow higher this results in more leaf tissue and therefore a greater leaf area for photosynthesis which in turn results in a greater production of carbohydrates for plant food.

Nutrition

  • Nitrogen (N) – an increase in available Nitrogen will typically result in increased leaf growth.
  • Iron (Fe) – the availability of Iron helps to ensure that the plant has the correct level of chlorophyll synthesis which is needed for the photosynthetic process to work efficiently.
  • Water – a very high percentage of plant tissue is water and this makes it critical to plant survival and healthy growth.
  • Diseases – the control or discouragement of disease pathogens is essential to strong and vigorous plant growth.

Next time we’ll look at some of the different growth habits you will encounter in turf grass management.

Meantime, why not share your views in the comments? or drop me a line.

Photo thanks to Kevin Dooley

 

Structure of a grass plant

How Grass Works

Since I did a little bit of an introduction to turf grass botany yesterday by talking about cool and warm season grasses, there has been further interest from readers in exploring turf grass botany.

There’s no better place to start than at the beginning, so today we will look at the basic shoot structure of the grass plant. Of course there is a lot of variation between species in how these structures appear but the following is a broad overview of turf grass plant shoot structures.

Shoot
This is the basic functional unit of the plant and consists of a short stem with leaves appearing alternately from nodes along the stem.

Stem
The stem is the main trunk of the plant that can take the form of a crown, which is a kind of bunched up stem where all of the leaf producing nodes are stacked one on top of the other or of an elongated stem (stolon or rhizome) that grows laterally either on or below the soil surface with widely spaced internodes from which new shoots and roots can appear. Lastly it can appear as a long upright stalk with widely spaced internodes (leaf producing points) ending in an infloresence/flower which is called a culm; more commonly called a seed head. The main functions of the stem are:

  • sites of buds where new shoots or roots can be initiated.
  • the movement of water, nutrients and food (carbohydrates) between the roots and the leaves.
  • storage of food for emergencies such as drought or injury.

Nodes
These are the bulbous points on the stem where leaves, roots or branches of the stem are initiated. These nodes are key to the recovery of turf grass from wear and tear and other natural stresses such as heat and drought, insect and disease injury. They are key structures in determining the recuperative potential of the turf grass plant.

Internode
The internodes are the sections of the stem between nodes and these sections rather than just being the bits between the all important nodes, are key areas of activity in the plant. This is where the translocation (transport) of water, nutrients and already photosynthesised food (carbohydrate) occurs.

A key point to note here is that if you cut through the stem, new growth will be stimulated from the immediately adjacent nodes on each side of the plant to form new shoots or roots depending on their position on the plant. This is why frequent mowing is so important in producing a dense turf.

Leaf
The grass leaf is the part we think of as the blade (although that has a more specific meaning in botany) and grows laterally out of the stem at a node. The leaf consists of an upper blade which is flattened and a basal sheath which encircles the stem at the node from which it arises. The leaf is the key food producing structure of the plant as it contains chlorophyll, the green pigment responsible for the capture of light energy from the sun. The leaf is a hive of food producing activity, being the main site of photosynthesis in the grass plant. It is the leaf that when combined with many thousands of others, forms the turf that we need for bowling.

Blade (leaf)
Rather than referring to the whole leaf, the blade is actually the flattened portion of the leaf furthest from the stem, although in species such as Festuca (Fescues) the flattening is barely perceptible.

Sheath (leaf)
This is the tubular portion of the leaf surrounding or wrapping around the stem at a node. Usually referred to as the basal sheath, it contains some chlorophyll which gives it a green colour.

 

So that’s the basic structure of the turf grass plant in very brief terms. Next time I will dig a little deeper and look at how grass plants actually grow.

As always, if you have anything to add, observations or questions just add a comment below or drop me a line.

Grass plant image thanks to Wackymacs   

Seashore Paspallum Green

Cool Season and Warm Season Grasses

My post from yesterday sparked a few questions by email about the term “Cool Season Grass”, a question only likely to crop up in the UK once every decade or so when we eventually get some hot summer weather! A brief summary of the differences between warm and cool season grasses below:

Cool Season Grasses
Cool Season turf grasses are best adapted to growing during the cool and moist periods of the year and do most of their growing in the UK during late spring/early summer. In a decent summer you will see growth rate tail off in mid summer and this will usually be followed by another growth spurt in late summer/early autumn. The cool season grasses are best adapted to grow well in temperatures ranging from 150 to 240 C. This group includes all of the usual turf forming suspects that are common in the UK such as Agrostis (Bent grasses), Poa (meadow grasses), Festuca (fescues) and Lolium (rye grasses).

Warm Season Grasses
The warm season turf grasses are best adapted to growth in the temperature range of 270 to 350 C, they grow best during the warmest part of the year and can go dormant and even suffer injury during cold weather. Dormancy typically kicks in at around 10 degrees when the entire turf will take on a yellow colour. Examples of the warm season grasses that some of our American, Australian and South African readers will be familiar with are Axonopus (Carpet grass), Cynodon (Bermuda grass), Paspalum (Bahia grass and Seashore paspallum) and Zoysia (Zoysia grass).

Photosynthesis
The main difference between the two groups is the way in which they photosynthesise or produce food for themselves. The first product of photosynthesis in cool season grasses is a 3 Carbon sugar molecule so these grasses are commonly referred to as C3 grasses. In warm season grasses the first product of photosynthesis is a 4 Carbon sugar molecule, so they are referred to as C4 grasses. C4 photosynthesis is thought to be an evolutionary adaptation that has allowed grasses to thrive in very warm and tropical environments.

Transition Zone
However, there is a band of territories around the world where the annual climatic conditions are not suitable for one type of turfgrass all year round, especially if you want to produce a nice green turf. It is too hot in summer for cool season grasses to stay healthy and too cold in winter for the warm season grasses. This is called the transition zone and turf managers in these areas sometimes use over seeding methods to produce an actively growing, green stand of turf all year round. This typically means that they will over sow their warm season turf with rye grass seed in the autumn and the turf will transition from warm to cool season grass in the winter. When spring comes they will put undue stress on the cool season grass in order to make room for the recovering warm season species to take over again.

I was recently teaching golf industry professionals in Southern China, which is in this transition zone and the golf club where I was staying has gone to extreme lengths to make sure its customers are kept happy all year round. They have two greens at every hole, one with creeping bentgrass for the winter period and one with seashore paspallum for the summer period.

I will write a bit more on photosynthesis soon. Meantime if you have any questions just drop me a line as usual or leave a comment on this post.