Blood Supply to the Central Nervous System

Hi :) In this post we'll identify and describe the main anatomical features of the blood supply to the central nervous system.

Cerebral Blood Supply

Arteries

Although the brain of a dog is quite small, it uses up to 8% of the total cardiac output. Within the brain exists a structure known as the arterial circle of the brain. This is an elongated arterial ring located on the ventral surface of the brain and is formed by the right and left internal carotids and the basilar artery. Three vessels which supply the cerebrum arise from either side of the arterial circle. These are the rostral, middle and caudal cerebral arteries. The arterial circle also gives rise to the rostral cerebellar arteries and the caudal cerebellar arteries arise from the basilar artery, these supply the cerebellum. All of these vessels form anastomoses with adjacent vessels on the surface of the brain. The arterial circle ensures that a constant blood pressure in the terminal arteries is maintained and that alternate routes for blood flow to the brain are present. 

Veins

Within the cranial dura mater, between the periosteal and meningeal layers, are venous passages into which the veins of the brain and its encasing bone drain. These passages are also known as sinuses of the dura mater but are not found only in the dura. Blood flows from these sinuses to veins around the head of the animal and to the vertebral venous plexuses. The sinuses lack a tunica media and adventitia in their walls and contain no valves. They are divided into dorsal and ventral sets of sinuses and freely intercommunicate.

The Dorsal Set

This includes the dorsal sagittal sinus which runs from the midline region of the cribiform plate dorsocaudally in the midline within the falx cerebri. At the most caudal end of the brain there is a confluence of sinuses which run ventrally to exit the cranium and enter the internal maxillary, internal jugular and vertebral veins. The confluence also includes the paired transverse sinus and occasionally includes the straight sinus (this depends on its conformation which may vary between individuals). These sinuses exit the cranium and enter the internal maxillary, internal jugular and vertebral veins.

The Ventral Set

These sinuses drain the ventral aspect of the brain and have connections to the face, nasal cavity, orbit and upper teeth. The ventral cavernous sinuses, which are paired, are the largest ventral sinuses and arise from the orbital fissures. Additionally, petrosal sinuses are located ventrolaterally. The ventral set makes connections with the internal vertebral venous plexuses caudally.

Spinal Blood Supply

Arteries

Three arteries travel along the length of the spinal cord. Along the ventral midline of the spinal cord, in the spinal fissure, lies the ventral spinal artery. In addition, there are paired dorsolateral spinal arteries which run close to the furrows from which the dorsal roots of the spinal nerves originate. At every intervertebral foramen, dorsal and ventral root arteries join this system by linking through anastomoses to form an arterial ring.

Branches of the ventral spinal artery supply the grey matter of the spinal cord as well as the adjacent layers of the white matter by entering through the ventral fissure. The bulk of the white matter is supplied by radial twigs of the dorsolateral arteries as well as the surface arterial plexus.

Veins

Ventrolaterally within the epidural space lie a pair of vertebral venous plexuses which are thin walled and valveless and travel along the length of the vertebral column. They drain blood from the vertebrae, the adjacent musculature and the structures within the vertebral canal. Within the vertebral canal they are connected by intervertebral veins while outside they are connected by extravertebral veins. In the occipital region they connect with the ventral occipital and cavernous sinuses.

Venous Drainage of the Spinal Cord

The Blood-Brain Barrier

The brain's blood vessels have the ability to restrict certain substances from accessing brain tissue. This is known as the blood-brain barrier and contributes to a stable environment for the neurons and glial cells of the central nervous system. In most capillaries, water soluble compounds leave through gaps between the endothelial cells of the capillary and this is relatively unrestricted. In the capillaries of the brain this is restricted because the gaps between the endothelial cells are blocked by tight junctions and the exchange of solutes in the blood is highly selective. The capillaries of the brain are also surrounded by a layer of glial astrocytic 'end feet' which are thought to contribute to the formation of the capillary endothelial tight junctions during development. 

Some parts of the brain such as the pineal body, hypothalamus, pituitary gland and choroid plexuses (known as the circumventricular organs) are highly vascular and their capillaries do not form tight junctions and the blood-brain barrier is ineffective.

That's it for this post. If you have any questions please feel free to ask :)

Soil Biology

Hello :) In this post we'll take a look at the factors which contribute to a healthy soil biota and how this biota keeps soil healthy. We'll also discuss the relationships between the major species in the food web in soils and the function of each species in maintaining soil health.

Soil is alive as it contains billions of microbes, as well as microscopic animals and larger animals such as termites and earthworms. Without this life, normal soil processes will fail and plant growth cannot be sustained. There are three main drivers which ensure that this life continues. This includes:

1. Organic Matter From Plant Residues: this is the fuel for the biota (the animal life present in the soil). The more fuel there is, the more biological activity occurs.
2. Cultivation: In the short term this results in much microbial activity. However, this results in a reduction in organic matter and this ultimately lowers biological activity. 
3. Soil pH: Microbial activity slows down as soils become more acidic. Animals such as earthworms also prefer less acidic environments. The optimal pH is above 5.5.

The Food Web

There are four categories of life which are present in soils, these are microflora, microfauna, mesofauna and macrofauna. 

Microflora (μm): 

This includes bacteria, fungi and mycorrhizae (fungi which form a symbiotic relationship with the roots of a plant).

Fungi: 

These are plant-like cells which grow in thread-like structures (called hyphae) which makes up a mass called a mycellium. There are three groups of fungi:

1. Decomposers (Saprophytic fungi): they convert dead organic matter into fungal biomass, carbon dioxide and organic acids and are capable of degrading cellulose, proteins and lignin. They convert these substances into a material that is more accessible to other organisms.
2. Mutualists: these have a symbiotic relationship with plants as they colonise plant roots and help the plant to obtain important nutrients. The mass that they form also hides the plant's roots from pests and pathogens. The best known fungal mutualist is Mycorrhizal fungi.
3. Pathogens: These fungi penetrate plants and decompose their living tissue and this weakens or kills the plant.

Bacteria:

These small organisms exhibit a rapid response to changing environmental conditions and require moisture, warmth and a carbon substrate. Different species of bacteria have different roles, such as:

• Decomposers: these break down organic matter, especially in the early stages of decomposition when moisture levels are high.
• Sulphur Oxidisers: these convert sulfides (which can't be used by plants) into sulfates (which are used by plants).
• Aerobes (need oxygen) and Anerobes (don't need oxygen). These bacteria may produce harmful toxins when the soil is saturated with water.
• Actinobacteria: these slowly break down humates (organic residues of decaying organic matter) in soils.
•  Nitrogen fixers: eg. rhizobium. These are able to extract nitrogen from the air and convert it to plant-usable nitrogen.
• Disease Suppressors: a variety of bacteria have been used commercially to suppress diseases.

Microfauna (μm): 

This includes bacterial and fungal feeding protozoa as well as bacterial and fungal feeding nematodes. Nematodes are small non-segmented worms which are between 50μm and 1mm long. They play have three important functions in soils:

1. Nutrient cycling: for example ammonia stored in the bodies of bacteria and fungi. 
2. Dispersal of microbes: the bacteria and fungi move around the soil by 'hitching a ride' on the nematodes. 
3. Disease and pest control: beneficial nematodes are able to kill several pests such as borers, grubs, thrips and beetles.

A Thrip
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Furthermore, there are three functional groups of soil nematodes, this includes:

• Saprophytic: these are decomposers as they break down organic matter. They are the most abundant type of nematode in soils and their presence improves the structure of the soil.
• Predacious: these feed on other nematodes as well as bacteria, fungi and protozoa.
• Parasitic: These are problematic as they feed on plant roots and slow down their plant growth.

Protozoa are single celled organisms which are very common in soils and their main food source is bacteria and fungi. They play an important role in regulating the populations of soil microbes and their activity may release nutrients which are available for use by plants. They may also prey on some pathogenic bacteria and fungi which is beneficial for agriculture.  

Mesofauna (mm): 

This includes microarthropods (Collembola and mites). Collembola are small organisms which are generally only a few millimetres long. They are also known as springtales. These organisms consume organic materials that are partially decomposed and thus feed on bacteria and fungi as well as speed up the decomposition process. 

Mites are also very abundant in soils and there are two categories of these creatures:

• Mesostigmata: these are predators and can be successfully used as biological control agents.
• Oribatida: which feed on decomposing material, bacteria and fungi. When these feed, they shred the organic material into smaller pieces and this increases the surface area available to bacteria and fungi during decomposition.

Macrofauna (cm): 

This includes enchytraeids, macroarthropods and earthworms. Earthworms improve the soil by improving:

• nutrient availability: they feed on plant debris and make this material more available to plants
• drainage: burrowing by earthworms loosens and aerates the soil. This also dramatically improves water infiltration.
• soil structure: earthworm casts cement the soil particles together and this forms water-stable aggregates. 

An Earthworm

 

That's it for this post, see you next time :)

Introduction to the Physical Properties of Soils

Hello : ) In today's post we'll begin looking at the physical properties of soils. We'll discuss the components of soil texture, what a soil profile is, the importance of soil structure, as well as what factors lead to water repelling soils. 

Before we begin, you may be wondering why veterinary students have to learn about soils. Well, it turns out that many of the health problems in animals arise because of soil health issues. For example, a mineral deficiency in a soil may lead to mineral deficiencies in animals which eat the pasture grown from that soil.

It's also helpful to have a bit of background knowledge about the soils that can be found in Australia. Because Australia is quite an old continent our soils tend to be old, salty, clayey, nutritionally and organically impoverished as well as structurally challenging. In addition, not much new soil is produced so it is important that soil erosion is kept to a minimum. 

Soil Texture

Texture refers to a description of the proportions of sand, silt and clay in the soil. Sand includes particles which are between 0.02 - 2mm in diameter. Silt, also known as loam includes particles from 0.002-0.02mm in diameter. Clay includes particles which are less than 0.002mm in diameter. The texture of a soil influences several things including:

• the supply of air in the soil
• the availability and movement of water and nutrients
• the ease of root growth
• erosion potential
• organic matter level. 

Clay soils retain more moisture and nutrients than sands but a greater amount of water is unavailable to plants. These soils are also prone to water logging and compaction from livestock and machinery.

 Sandy soils have a poor ability to retain moisture and nutrients but they allow plants to extract these with little effort. However, these soils are prone to nutrient leaching but the retention of nutrients can be improved by increasing the amount of organic matter present and incorporating clay. They are also prone to the development of water repellency but the addition of clay can prevent this.

Soil Profile

Soil is made up of various horizontal layers known as horizons. There are three horizons:

1. A Horizon or Topsoil: most of the available plant nutrients and soil organisms are here. The upper part of this horizon is often darker because of a higher organic matter content. 
2. B Horizon or Sub-soil: this contains materials leached from the A horizon. The depth and water holding capacity of this layer greatly affects the value of the soil.
3. C Horizon or Parent Material: this is either rock or partly decomposed sand or clay deposited thousands of years ago. The ability of roots and water to travel through this layer has a large impact on plant growth.

 Soil Structure

 This refers to how soil components are arranged into aggregates. This is important for the permeability of the soil to water and air as well as root penetration and seedling emergence and the resistance to erosion. Aggregates are formed from a combination of sand, loam, clay organic mater and components of fungi. The more clay that is present, the greater the bond between the particles and the structure improves. Soil structure is important because good structure leads to an abundance of soil pores which allow the movement of water, air and microbes and provide a minimal resistance to root growth.

Water Holding Capacity

Soil can hold water in three ways:

• Chemical water: this is water which is tightly held by electrostatic forces to clay surfaces and is unavailable to plants. 
• Gravitational Water: this is held in large soil pores and rapidly drains out of the soil under gravity. It can only be used by plants while it is present. 
• Capillary water: this is water held in pores that are small enough to hold water against gravity. The smaller the pore, the harder it is to remove the water.

After the soil has been saturated and all the gravitational water has drained, the soil is at field capacity. When the plants have used up all the accessible water from the soil it is at wilting point. The structure and texture of soils affect the amount of water that is held in the soil and that can be used by plants. Smaller soil particles have a higher surface area that larger particles and the amount of water absorbed by the soil increases as the surface area does too. The leaves less water available to the plants. 

Water Repellence

Some soils can become water repellent and water is unable to infiltrate the soil. This is due to a hydrophobic material, derived from the decomposition of plants, which may coat the soil particles. Soils with lower clay amounts are more susceptible to water repellence. Water repellence leads to patchy pasture germination - some of the areas of the land have pasture growing on them while others don't. This leads to a loss in production for the farm.

That's all for this post, if you have any questions please feel free to ask in the comments section below : )

Photosynthesis and Principles of Pasture Growth

Hello :) In this post we'll take a look at the process of photosynthesis and the differences between the C3 and C4 photosynthetic pathways. We'll also discuss the impacts of water, light intensity, temperature and leaf area on photosynthesis. We'll finish off by going over the principles of pasture growth and managing leaf area. Enjoy!

Photosynthesis

Through a process called photosynthesis, plants trap light energy in a form useful to the plant by combining carbon dioxide with water to form simple carbohydrates. This is summarised in the equation below:

6CO2 + 12 H2O →→→ C6H12O6 + 6O2 + 6H2O

The carbon dioxide comes from the air while the water comes from the moisture of the soil. The simple carbohydrates are used for plant growth and maintenance or are stored.

Photosynthesis occurs in chloroplasts which are located in the mesophyll cells in the leaves of C3 plants. In C4 plants it takes place in these cells as well as the bundle sheath cells.  The process takes place on the surface of thylakoids and in the stroma of the chloroplasts. Chlorophyll pigments are found in the chloroplasts and they are light absorbing pigments which capture solar energy.

Two different reactions occur during photosynthesis. These are:

1. Light dependent reaction: chlorophyll absorbs energy from sunlight and uses it to oxidise water and produce oxygen and energy (in the form of ATP and NADPH).
2. Light Independent Reaction (aka Dark Reaction): this involved carbon fixation using energy from the light reactions to produce carbohydrates (this is the Calvin Cycle).

C3 and C4 Photosynthetic Pathways

In C3 plants carbon dioxide is fixed to a 5 carbon sugar known as RuBP in a reaction catalysed by the enzyme Rubisco. The 3 carbon compounds are rearranged into sugar phosphates which are used for the synthesis of carbohydrates and new RuBP. The Rubisco enzyme is also able to oxygenate RuBP to carbon dioxide by photorespiration (especially when there is a high temperature and light intensity for the plant). This is a distinguishing feature of C3 plants as this doesn't occur in C4 plants.

With C4 plants, carbon fixing and carbohydrate synthesis occur in different cells. Mespophyll chloroplasts release energy from light dependent reactions but do not have the enzyme Rubisco. Carbon dioxide is fixed as a 4 carbon compound and transferred to bundle sheath cells where carbon dioxide is concentrated. In these plants, the Calvin cycle occurs in the absence of oxygen and no photorespiration occurs. This makes C4 plants more efficient at fixing carbon than C3 plants.

In addition, C3 plants grow in low temperatures (optimum is 20-25° C) while C4 plants prefer high temperatures (optimum: 25-30°C). C4 plants are also more efficient at using water and achieve higher photosynthetic rates than C3 plants.

The efficiency of photosynthetic processes increases at high light intensity and at the optimum temperature for the plant. Efficiency also increases with an increase in atmospheric carbon dioxide and when optimum levels of water are available to the plant. The amount of light intercepted by the plant's leaves also has an impact on photosynthesis.

Pasture Growth

 

There are two important principles when it comes to understanding pasture growth and management.

1. The Optimum Growth Phase: there are three phases:
1. Slow growth after grazing (low yield)
2. Rapid growth because of an increase in leaf surface area (increasing yield)
3. Slow growth due to the shading by other plants which are now tall. (yield reaches a maximum but then starts to decline).
   The optimum yield is reached between phase 2 and 3. 
2. The Need to Rest Grasses after Grazing: some species need to be rested. This is because there is a certain number of leaves present per tiller and the time it takes for each leaf to appear may change depending on the season. In winter, a new leaf is likely to appear every 10-15 days while in summer this period is reduced to 5-7 days. 

We can illustrate the second principle by using ryegrass (which has 3 leaves per tiller) as an example. If the grass plant has just been grazed and there are no leaves left on the plant, the plant must use sugars from its energy stores in order to create a new leaf. This new leaf will allow photosynthesis to occur and the plant will be able to replenish its sugar stores. Once two to three leaves are present the sugar stores in the plant are quite high and this will allow the plant to regrow if it is grazed at this point in time. Thus, animals should only be allowed to graze the grass after the three-leaf stage. If the grass is grazed at an earlier stage more than once, the plant will not have enough sugar reserves to generate a new leaf and the plant will die. This is because the plant hasn't been given enough time to push up a new leaf in order to photosynthesise. Grasses should be rested for a period of time to allow a sufficient amount of leaves to grow. It has also been shown that the duration of grazing has an effect on pasture production. It seems that the optimum grazing duration is one day as this will result in the most pasture growth. 

However, some pastures don't need to be rested. Examples include sub-clover and broad leafed weeds as these species can maintain some leaf area for photosynthesis and replenishment of carbohydrates even when grazed low to the ground. Thus these species can tolerate continuous grazing.

That's it for this post, see you next time :)

Morphology and Growth of Grasses and Legumes

Hi there :) In today's post we'll be having a look at some of the characteristics of grasses and legumes as well as the process of germination, growth and seed production.

Grasses

Grasses have a wider adaptation than any of the other flowering plants and can be classified as cool or warm season species. Cool season species use the C3 photosynthetic pathway while the warm season species use the C4 pathway.  Grasses are characterised by there cylindrical jointed stems, their long narrow leaves with parallel veins, their fibrous root system and the fact that they are monocotyledon. A monocotyledon is a plant that has only one embryonic leaf in their seed.

Monocotyledon (Left) vs Dicotyledon (Right)
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Different species of grasses may grow for different lengths of time and they may be known as annuals, biennials, or perennials. Annuals die each year after they have produced seed while in Biennials, this cycle is extended to two years. Perennials produce both vegetative and flowering shoots each year for a few to many years.

Grasses may also grow in different ways. Three growth habits exist:

• Bunch Type (Caespitose) - this produces clumps of grass tillers. 
• Stoloniferous - this produces stolons which trail on the soil surface. It has root at the nodes and normal green leaves. 
• Rhizomatous - Rhizomes grow beneath the soil surface and the grass has white, small, scale-like leaves. 

A rhizome is a stem of a plant that is usually found underground. Most grasses are diploid which means that they have two sets of chromosomes per cell. Some grasses (such as some ryegrasses) have four sets of chromosomes per cell and are known as tetraploid. Tetraploid grasses have a larger cell size, broader leaves and fewer tillers. They also have more soluble carbohydrates and less fibre and experience a greater intake by ruminants.

Important Temperate GrassesSome important species of grasses which we have been asked to become familiar with are listed below:

• Annuals:
• Lolium rigdum (annual ryegrass)
• Lolium multiflorum (Italian ryegrass)
• Hordium lepornium (barley grass)
• Vulpia bromoides (silver grass) 
• Bromus millis (soft brome grass)
• Perennials:
•   Lolium perenne (Perennial Ryegrass)
• Festuca arundinaciea (Tall fescue)
• Phalaris aquatica (Phalaris)

 Basic Structure

Basic Structure of a Grass Plant
Source

The basic structure of a grass plant is shown above. These plants are composed of multiple connected growth units called tillers. Each tiller produces roots and leaves.

A grass seed is called a caryopsis and consists of the endosperm, which is a large store of starch, and an embryo. The embryo is composed of the primary shoot (or plumule), the root (or radicle) and a scutellum (the first leaf). Germination involves the uptake of water by the seed and this stimulates respiration, cell division and the secretion of enzymes. These enzymes work to break down the starch in the endosperm into sugars. The sugars pass to the embryo to support the growth of the radicle and plumule.

At the tip of the shoot (the apex), a region called the apical meristem is the source of all the above-ground parts of the plant. The shoot also has nodes, which are the points of attachment of each leaf, that are separated by internodes. Internodes are stem tissue which separate one node from another.

When the apical meristem produces a leaf it also produces an axillary meristem (which are also known as 'buds') which can develop into a new tiller. These buds may also grow into rhizomes or stolons which are important storage organs useful for plant expansion. Each grass leaf develops as a blade connected to a sheath which surrounds the stem above the node. The plant grows from the bottom and pushes 'old' leaves upwards. The number of leaves per tiller remains constant throughout the life of the plant, this means that it will produce a constant turnover.

The reproductive growth of grass plants is stimulated by the length of each day as well as the temperature. During reproductive growth, the internodes of the stem elongate. This causes rapid expansion of the stem which lifts the tip of the shoot above the soil surface. The inflorescence (which is the reproductive structure) develops from the tip of the shoot (the shoot apex). 

Legumes

Legumes are dicotyledons and can be annual, biennial or perennial. They are valued for their ability to fix nitrogen.  Some important legume species which we need to know about are listed below:

•  Annuals:
• Trifolium species (annual clovers)
• Medicago species (annual medics)
• Biserrula pelencinus (Biserrula)
• Ornithopus species (Serradellas)
• Perennials:
• Medicago sativa (lucerne)
• Lotus species (birdfoot trefoil)

After the seeds of the legume are fertilised, it enlarges and the ovary wall develops into a pod. The embryo within the seed contains two cotyledons which enclose the embryo and serve as the energy source during germination. This is because legume seeds contain little or no endosperm.  Legumes have hard seeds and hardseededness is a mechanism of seed dormancy that allows the formation of a persistent seed bank. An impermeable layer in the seed coat prevents the uptake of water and germination. The rate of breakdown varies between species and cultivars and is mainly dependent on temperature.

During germination, the seed absorbs water and the root emerges to develop as a simple tap root. This website has a nice diagram that explains some of the features of a young legume plant. The hypocotyl elongates and straightens after penetrating the soil surface. The cotyledons are pulled above the soil surface and open for photosynthesis. The roots continue to grow and start to develop secondary roots. Following this, the first unifoliolate leaf and the first trifoliolate leaf emerge, the main stem then elongates and a leaf is produced at each node. The axillary buds at the cotyledonary nodes form new shoots or branches.

The legume shoots grow the most from the tip of the stems, and the end of branches and stolons, at a place called the terminal bud (or the shoot apex). If the terminal bud is removed, the plant is stimulated to branch out from leaf axils, nodes or the crown.

Leaves develop from primordia (an organ or tissue in its earliest recognisable stage of development) at nodes in the plant. In legumes, cell division and expansion takes place uniformly across the leaflets. Three leaflets are attached to a node. 

The flowering of legumes is influenced mainly by temperature and the length of day. The inflorescence arises from a bud either at the tip of the shoot or the tip of the leaf. Most legumes are cross pollinated by insects.

That's it for this post, if you have any questions please feel free to ask in the comments section below :)

 

 

Common Pasture Types in Different Regions

Hello :) In this post we'll be looking at some of the common pasture types that can be found in the different regions of Australia. 

The first post for this unit looked introduced us to what pasture is as well as where pastures are used in Australia. I'll be referring to the same diagram as shown below:

Where Pastures are Used in Australia
Source

The northern half of Australia is known as a tropical region while the southern half is referred to as the temperate region. 

Northern Australia

The cattle industry in northern Australia relies heavily on native pastures. This region is dominated by tall perennial grasses such as bluegrass and giant spear grass. Sown tropical pastures in this region include rhodes grass, panic grass and kikuyu which are prominent in more inland areas. 

Southern Australia 

Native species of pasture in the southern half of the country include wallaby grass, weeping grass and redgrass along with silver grass, barley grass and capeweed. 

Temperate Perennial Zone 

The two most common grasses in these areas include perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). These species, which are well adapted to grazing, experience high production rates and form the backbone of the dairy industry world wide. However, they are only found in areas which receive large amounts of rainfall and require nitrogenous fertilisers. 

White Clover

Perennial Ryegrass

Temperate Perennial Grass - Annual Legume Zone

Phalaris (Phalaris aquatica) is most common here and is the most drought tolerant temperate grass sown in the country. Phalaris is usually sown with subterranean clover (Trifolium subterraneum)

Phalaris

Subterranean Clover

 Annual Temperate Pasture Zone

Subterranean clover and annual medics (Medicago spp) are used together and have been the basis for the legume ley pasture system used in the Australian Wheat belt. Subterranean clover shows an increased resistance to acidic soils while the annual medics produce more hard seed, thus these two types of pasture complement each other.

That's all for this post, if you have any questions please feel free to ask :)

 

An Introduction to Pastures in Australia

Hi :) This post will introduce you to pastures and their use in Australia. We'll discuss what makes pastures important and also have a look at how pastures have changed in Australia since European settlement as well as how and where pastures are used for animal production.

Before we begin, let's go over some terminology which is certainly worth knowing. Firstly, the definition of 'pasture' is "a population of herbaceous ('non-woody') plants with a relatively short growth habit and continuous ground cover." This includes grasses, legumes and herbs and may grow in tropical or temperate climates. Pastures can be annual, that is they produce seed and then die, or perennial, they are alive continuously. A 'grassland' is land on which the vegetation is dominated by herbaceous plants with little woody vegetation. These can be found in regions of Africa, China and Mongolia. A 'rangeland' is land on which the indigenous or native vegetation is predominantly shrubs, grasses and forbs and which are managed more extensively. 'Forage' refers to the edible part of plants that provide feed for animals or can be harvested for feeding to animals. 

The Importance of Pastures 

The characteristics of pastures influence what animals eat and how fast they grow. High quality pasture provides an animal with more food to eat. The more food available, the more the animal will eat and the more they eat, the more they grow. This allows the farmer to earn more money because the animal will produce more milk, wool, meat etc. Grasslands and rangelands are important because they occupy about half of the world's land area and are mostly used for the production of livestock and wild herbivores. In addition, the demand for food is expected to more than double in the near future as the world's population continues to increase. Pastures help people produce food. Meat production world wide has increased dramatically in recent years and this has been termed the "Livestock Revolution". Meat production requires good pasture. 

The Change in Pastures Since European Settlement in Australia 

After the European settlers arrived in Australian in 1788 there was a massive replacement of natural vegetation (this includes trees, shrubs and native grasses) on 25 million hectares with sown pastures in southern Australia. From about the years 1800 to 1900 the sheep and cattle industries were quite large and there were massive changes in grasslands due to grazing and the clearing of native vegetation. Various annual grasses and forbs were also introduced to Australia during this time. The years 1900 to 1950 saw the beginning of agricultural research which brought improvements such as sub-clover and superphosphate. These resulted in a significant increase in production. The 'ley-farming' system also began being used during this time and trace element deficiencies in soils were discovered. However, war, depression, rabbits and drought brought about massive land degradation and these new practises weren't used. 

Between 1950 and 1970 saw the rapid expansion of pasture in Australia. Myxomatosis eliminated the rabbits and there was a wool boom. In addition, the government provided tax concessions for pasture improvement and there was greater access to more pastures that were adapted to Australian conditions. Further declines in native grassland were experienced. The 70's saw multiple droughts as well as new diseases, insects and pests. Increased soil acidification and salinity as well as more intensive cropping also occurred. Farmers were put under economical strain too and so there was less money to buy fertiliser. 

The period of time between the 80s and now can be described as the 'restoration' phase of development. This is because of the land care and sustainability movement and the fact the people began tackling soil erosion, acidification, compaction and salinisation problems. There is now a greater focus on the use of perennial pastures and a greater range of more locally adapted legumes are used.

Where and How Pastures Are Used in Australia

Several environmental factors influence the growth and persistence of pastures, these factors include:

• The amount and distribution of rainfall
• Seasonal temperatures
• Solar radiation

Different pastures have different levels of adaptation to the factors that influence growth.

Where Pastures are Used in Australia
Source

 We've been asked to focus on remembering the zones that are in the southern half of Australia only. It is also important to note that these pasture types aren't delineated by soil type. Instead, other factors (such as location, topography, rainfall amount and distribution, and how easy it is to clear vegetation) determine how land is used.

 Australian farming systems currently use pastures is several ways:

• As Permanent Pastures: this is when land is continuously used to grow pasture. This is usually done on land that is difficult to crop.
• Ley Farming: this is when the farmer alternates between growing pasture and a crop on the land. ie on year 1 pasture will be grown, on year 2 a crop will be grown, on year 3 pasture will be grown and so on. 
• Phase Farming

That's it for this post, if you have any questions don't hesitate to ask :)