Flashcards in Agronomy Deck (195):
What defines a 'good' pasture species?
Dense growing (out competes weeds)
Hearty (recovers well)
Tolerant to climatic extremes
Resistant to pests
What are the two classes of forage? Within those two, how are they divided?
Grasses and legumes
Within these they are divided into annuals and perennials and then into cool season and warm season.
True or false, grasses are monocots? Describe some of their characteristics.
One leaf germinates from cotyledon (seed).
Parallel leaf veins
Fibrous root system
Elongated seed stalk
True or false, legumes are dicots? Describe some of their characteristics.
Two leaves germinate from seed.
Netted leaf veins
Produce seed in a pod
Nitrogen fixation - rhizobium
Compete differently to grasses-combat weeds.
What is an annual plant?
Plant that germinates, grows, reproduces, and dies in one growing season.
What is a perennial?
Plant that has the ability to live for more than one year.
What is a biennial?
Weak perennial that usually dies after the second growing season.
Describe warm season plants.
Begin growth and/or are planted in spring or early summer. Do most of growth during warmest part of the year.
Lucerne, sorghum, kikuyu, natives.
Describe cool season plants.
Begin growth and/or are planted in Autumn or early winter. Do most of growth during the coolest months.
European plants, ryegrass.
Describe the parts of the stem.
Node - solid joint of a grass stem where leaf sheaths attach.
Internode - region between nodes.
What is a blade?
Portion of leaf connected to the sheath.
What is the leaf sheath?
Surrounds the stem above the node where it is attached.
Can be split, overlapping or closed.
What is the collar?
Region at the junction of the sheath and blade.
What is the ligule?
Appendage that clasps the stem where the sheath and blade join.
What is the auricle?
Outgrowth from the base of the blade.
What are the two different ways a leaf can grow?
What does inflorescence refer to when talking about plant characteristics?
Plant head, seed or flower/fruit.
Can be in the form of a panicle (many branches), spike (unbranched), or raceme (spikelet on one branch).
What are awns?
Appendages on ends of seeds.
Can vary in length and number.
What is the difference between a rhizome and a stolon?
Rhizome travels between plants underground, stolon is above ground
Describe the characteristics of legumes.
Dicots - two leaves from seed.
Host rhizobium bacteria
Often have taproots
What is a petiole?
Stalk by which a leaf is attached to the stem in legumes.
What is a stipule?
Pair of leaf-like outgrowths/appendages that occur at the base of the petiole.
What are stolons?
Shoots that bend to the ground or that grown horizontally above ground.
Describe the characteristics of Barley Grass.
Cool season annual, medium height (20-30cm), rolled leaf blades, hairy and pale green.
Auricle so encircle stem, ligule is short and ragged, sheath is hairless.
Seed head has a spikelet 10-25mm long and 3 per seed (foxtail shape).
Describe the characteristics of Cocksfoot.
Cool season perennial, tall growing grass that bunches, no rhizomes or stolons.
Folded leaf blades with a flattened and rolled sheath, no auricles, small ligule (2-10mm).
Seed head is clustered with slightly curved seeds.
Describe the characteristics of phalaris.
Cool season perennial, no auricles, lighter colour collar, large toothed ligule that can sometimes be hairy.
Wide, smooth leaf blade that can feel waxy. Can't feel ribs.
Seed head is dense and then spreads to narrow panicle. (Long stalk).
Describe the characteristics of Poa.
Cool season annual, short and sod forming, has rhizomes, folded leaves that are dark green in colour, no auricles, collar is sometimes hairy, pointed ligule.
Seed head is open pyramidal panicle.
Not so good for cattle.
Describe the characteristics of Italian ryegrass.
Cool season annual, bunches, high palatability and digestibility, rolled leaves with prominent ridges on upper surface. Glossy and hairless on under surface.
Well developed auricle with claws, ligule present, can have reddish tinge or purple on nodes and at base.
Seed head is solitary spike with alternately arranged spikelets. Seed have awns.
Describe perennial ryegrass.
Cool season perennial, quick to establish and good for erosion prevention.
Folded leaves, undersurface is shiny and dark green. Auricle present and short and flat ligule. Inflorescence stems are nearly naked.
Seed head is spikes with spikelets growing edgewise, no awns.
Describe the characteristics of silver grass.
Limited nutritional value, cool season annual, short lived and loosely tufted. Blades are long, narrow and unrolled.
No auricles, short ligule, seed head is contracted panicle with 3-10 florets per spikelet.
Describe tall fescue.
Cool season perennial, bunches and has short rhizomes, graze early as gets fibrous early.
Coarse and tough roots, ribbed leaves with serrated edges, auricles are blunt with hair, short ligule, prominent and lighter colour collar.
Seed head is branched panicle with elliptical spikes. Short awn.
Describe red clover.
Warm season perennial, erect (grows 2-3ft tall), hairy leaves and stems, large leaves, elliptical, with prominent v shaped water mark.
Pinkish-violet flowers in dense clusters.
Describe the characteristics of subterranean clover.
Cool season annual, prostrate (globular burrs in soil), hairy leaves and stem.
Variable leaflet size (4-22mm), heart shaped to round, notch in tip.
Flower is pinkish-violet in dense clusters.
Describe the characteristics of white clover.
Giant form of white clover, warm season perennial, spreads via stolons, 8-12 inches tall.
Tri-foliage leaves, shiny underneath, obvious veins. Leaf tip is rounded to indented with fine teeth. Often has v shape pattern.
White, ball shaped flower.
Describe the characteristics of Lucerne.
Warm season perennial, 15-25 inches tall, pinnately trifoliate leaves arranged alternatively on stem, leaves toothed towards tips.
Slender stipules fused to petiole.
Flowers are generally pink-purple or White or yellow.
Increased leaves = increased nutrients/quality
What are two factors that govern herbage intake?
Quality and abundance.
True or false. How we graze pasture can affect the botanical composition of the pasture.
What did early sheep production focus on?
What are the two impacts of early sheep and cattle production?
Increased productivity - increased input into pastures.
Degradation - loss of perennial species, erosion and acidification (N left in soils).
Australia is currently carried on the back of what industry....
Used to be sheep.
True or false, there has been an enormous increase in grazing pressure in Australia over the last two centuries.
What are three reasons that the numbers of livestock have fluctuated?
Introduced pasture species
What effects did pasture legumes have on early crops?
Increased nitrogen, allowed botanical changes (native plants aren't adapted to increased soil fertility), impacts on crops and land degredation.
What are some of the major pasture related break throughs of the mid 20th century?
New sub clover varieties adapted to lower rainfall (sets seed underground-persists well in Aus also better persistence as it is an annual)
New variety of barrel medic (burrs as seeds-allowing better persistence as it is an annual)
Phosphate, sulphur, trace elements
Myxomatosis decreased rabbit numbers
What is the amelioration phase?
Large increase in sown pasture area.
5 million ha in 1950 to 25 million in 1970.
What were the main pasture species relied upon during the amelioration phase?
Annuals - Sub clover, annual medics.
Perennials - Lucerne, phalaris, Cocksfoot, ryegrass.
What happened between 1970 and 1990?
Cost price squeeze occurred - lost faith in fertiliser due to drought and decreased effectiveness.
Legume numbers declined due to phosphorus requirements.
Widespread land degredation (acidity, erosion, salinity).
Reduced flock numbers.
What are naturalised species?
Pasture species that were introduced to Australia that then became part of the vegetation without specific intervention.
Eg. Barley grass, witch grass, Patersons curse.
Describe the species changes during the exploration and exploitation phases?
Exploration phase was largely native species with the introduction of European species just beginning to occur.
Exploitation phase was introduced species had become naturalised and pastures were being used for all their worth.
Describe southern Australia's original vegetation.
Mostly woodlands (close to sparse populations of trees with understory of grasses and herbs), some shrub land, forests.
Very little natural grassland. Grasses that were present were tall warm season perennials. Eg. Poa
Describe the chain of events that lead to the change in pasture type within Australia.
1850; Original climax community with tall warm season perennials was subjected to grazing.
Became disclimax community of short cool season perennial grasses subjected to more intense grazing.
Dwarf, cool and warm season perennials had even further grazing.
1950; Dwarf cool season perennials and cool season Mediterranean annuals that then had phosphorus addition and grazing.
1990; Current pastures with sown species, introduced cool and warm season annuals
Describe the changes that occurred during the exploration and exploitation phases.
Loss of grazing intolerant species.
Opportunity for invasion of other native and exotic species.
Changes in water balance summer growing species replaced with cool season species.
Change in nutrient distribution - consume feed in one location, defecate in another.
What were some other influences that shaped the exploration and exploitation phases?
Fertiliser - P leads to increased legumes and increased N.
Attitude - foreign is good, our vegetation was useless.
Overall impact - tall warm season species replaced by short cool season species.
Large increase in N in system due to increased legumes that drove higher animal production.
Describe a basic classification of native pasture.
Species indigenous to Australia, confined to rangelands and high rainfall areas.
Generally not useful for agriculture, low percentage of legumes.
Adapted to infrequent grazing and low grazing pressure.
Adapted to low soil fertility and periodic burning.
Exist as under storey in woodland and forest.
Dominated by summer growing and tall, warm season species.
What is grazing pressure?
Number of animals per unit of feed or pasture growth.
Describe the classification of naturalised pastures.
Unsown but managed, can be fertilised. C3
Based on native species but contain exotic species that have invaded (not sown-via birds, water, livestock, machinery).
Can include legumes and annual grass species.
Eg. Soft brome, sub clover, Patersons curse, onion weed.
True or false, there is no clear distinction between native and naturalised pastures.
Native would be extremely rare if defined by no exotic species.
Describe the classification of improved pasture.
Contains sown exotic species, occur in much of the cropped and high rainfall zones.
May have been sown or spread.
Greater livestock production than native or naturalised, can withstand greater stocking rate.
Greater growth and higher quality when managed well.
Eg. Sub clover, phalaris, tall fescue, Cocksfoot, ryegrass.
What are ley pastures?
Short term (1-6years)
Usually reestablish after cropping phases and have high legume content.
Used to manage nitrogen, disease, and weeds (decreased herbicide use).
Eg. Lucerne, sub clover, annual medics, ryegrass, barley grass.
What are the three agricultural zones within Australia?
Ley farming (wheat-sheep)
Describe the characteristics of the high rainfall zone.
Average annual rainfall above 550mm/annum
Eastern Australia and SW of WA
Improved and naturalised/native pastures
Mainly permanent pastures, should be perennial species for stability.
Describe the characteristics of the ley farming zone.
Anywhere where cropping can be carried out, 350mm in east and 250mm in west.
Length of phases depends on location.
Trend away from pastures.
Annual legumes are predominant and Lucerne. This is important for N fixation.
High N leads to botanical instability, weeds can become a problem.
Crops can become grazing crops if winter feed is low.
Describe the characteristics of the pastoral zone.
Inland from Ley farming areas.
Manage via stocking policy, watering points and fire.
Species vary-mainly grass and shrubs. Eg. Saltbush and blue bush.
What are the drivers of species distribution?
Temperature and pH.
Rainfall pattern and amount - rainfall decreases with increasing distance from cost. North Aus is summer rainfall, south is winter.
What are the main drivers of plant growth?
Rainfall and temperature
Soil fertility, depth, pH
What is the growth index?
Method of using major climatic variables to understand distribution and annual growth cycle of pastures.
Takes into account moisture, temp, light.
Computer models are more reliable these days.
What are the two main factors influencing rainfall?
Amount and variability.
Variability = (90th centile - 10th centile)/50th centile
Also consider evaporation.
Discuss moisture in terms of climate.
Rainfall influences soil moisture as does evaporation.
Demand for water is set by environment.
What is evapotranspiration?
All water lost to the atmosphere.
What is potential evapotranspiration?
All the water that could be lost if the crop/pasture were well watered. ET*
What is the Ratio of actual : potential evapotranspiration?
Relative measure of supply and demand.
What is the temperature index?
Limitation on growth due to temperature
True or false, light is rarely the major limitation on growth?
What is the greatest limitation to growth in winter?
What is the formula to calculate the growth index?
GI = moisture index x temperature index x light index
Used to classify environments and for generating seasonal patterns of production
In order from greatest to least, which factors have the greatest effect on growth index?
Discuss pasture growth curves.
Vary across Australia.
Need to accurately model, growth index isn't accurate enough but pattern is close.
Describe the graph that compares green herbage available to in Vivo digestibility.
As green herbage mass increases so does digestibility, and intake to a plateau at about 1200kg/ha.
However as green herbage available increases, green pasture decreases.
Below 500kg/ha you have ingestion of dead material (500kg/ha is the point at which amount of intake and amount of green pasture match).
About 500 you have increased selection opportunity.
What factors influence the rate of intake?
Available herbage per cow
Total availability of herbage
Plant type (tropical/temperate)
Duration of grazing
What is intake?
Amount of feed consumed over time per animal or per animals liveweight or per animal metabolic weight.
Size of bite, number of bites, amount of time
What is DMD?
Dry matter digestibility
Percentage of dry matter that is retained by the animal and not lost in faeces.
What is OMD?
Organic matter digestibility.
Percentage of organic matter retained by the animal, minus the mineral components (ash).
What is crude protein?
The protein content of the feed, usually calculated as N x 6.25
Assumes protein is 16% N.
What is metabolisable energy?
Utilisable energy of the feed.
Expressed in MJ ME/kg DM
Closely related to OMD and DMD.
What is the basis of variation between OMD and ME?
Describe plant cell walls.
Rigid - presence of lignin which is not digestible.
Cellulose in cell walls that is partially digestible.
Hemicellulose that is bound in walls and protected by lignin.
As the cell wall ages the lignin content increases.
Protein present that degrades more in young herbage.
Describe the differences between C3 and C4 plants.
C4 have bundle sheath and extra lignification.
C3 has higher protein content.
Ration of mesophyll to bundle sheath is 3.7:1 in C4 and 8:1 in C3.
C4 have higher hemicellulose and more cell wall contents.
Describe differences between legumes and grasses in terms of cell walls.
Legumes have lower cell wall material - less cellulose, hemicellulose, and silica.
Legume fibre is retained in the rumen for shorter periods; reticulate venation, lower volume of vasculature and more easily fractured.
Tropical species have higher fibre content that temperate.
Describe what occurs in plants as their cells age.
Soluble content decreases and cellulose, hemicellulose and lignin increase. Stems lignify faster than leaves. Ageing decreases the ratio of leaf to stem (reduces digestibility as the stem ages the soluble CHO content decreases).
Legume leaves don't lignify.
Describe what effect increased fibre has on intake.
Increased fibre means increased time in rumen, decreasing intake.
What effect does temperature have on lignification?
Higher temperatures increase growth and therefore lignification.
What are the effects of water and light on digestibility?
Low light means lower soluble CHO and therefore lower digestibility.
Water deficits retard ageing and development, stalling decline in digestibility to a point
What is the equation to determine forage intake?
Animal energy requirements/digestible energy concentration (ME)
Only works if pasture quality is not the limitation.
What two factors limit forage intake? How can these be used to determine forage intake?
Rumen fill/Time in rumen
Work if pasture quality is the limitation.
Which plant factors affect intake?
Grass species and variety - intake closely related to amount of leaf.
Leaf versus stem - intake of leaf is 59% greater than stem. Leaf breaks down in rumen faster.
Particle size - ground and pelleted forage passes faster through rumen. However pellet ting usually depresses digestibility.
Legumes versus grasses - legumes have less fibre so intake is greater and have higher level of OM so pack in rumen more densely.
Water content - no difference between fresh and partly dries however intake can be depressed in very wet forage.
Protein and minerals - intake reduced if protein falls below 6-8% (microbes need this). Likewise for various minerals.
What are the basic principles of sward structure?
Rate of intake generally related to digestibility of feed - low quality has longer retention.
Rate of intake faster on high, leafy, dense pasture.
Animals select food that they can eat faster.
Tall, erect, leafy herbage has higher consumption rate.
Leafiness increases intake ratio.
Sheep and cattle rarely bite more than 36,000 times per day.
Sward structure and 'green' are overriding factors in selection.
What does grazing pressure relate?
Stocking pressure and amount of pasture available
Describe the differences between the grazing habits of cattle and sheep?
Cattle have longer rumen retention time, greater cellulose breakdown capability and better digestion of low quality feed.
Sheep graze closer to the ground than cattle.
Discuss clover disease in ewes.
Caused by oestrogens (phyto-oestrogens) in sub and red clover.
Causes low lamb marking %, dystocia, post natal mortality, ewe infertility, uterine prolapse, lactating in virgin ewes, teat development in wethers.
Cows aren't affected because they have much higher oestrogen levels.
Cultivars are main forms of control - modern cultivars have lower levels.
Rapid fermentation - producing bacteria bloom and large amount of gases produced (CO2 and CH4).
Steers on Lucerne can produce up to 2L of gas per minute.
Bloat occurs when bubbles form - prevents belching and results in increased rumen pressure. End of suffocating due to pressure against lungs.
Pasture factors include; high soluble protein content, low fibre, rapid digestion, high concentration of small feed particles. Often associated with lush growth of legumes (Lucerne, clover varieties) in young to early reproductive stages of growth. Can be caused by winter wheat.
Manage by balancing legumes and grasses, spray with bloat oils/tannins, graze in pm, graze later in development (protein decreases with age), feed hay before grazing to increase fibre so they can't eat as much as fast (increased cud chewing, decreased bubbles).
Strip grazing can reduce bloat as reduces selection to whole plant.
Plasma Ca to low to support normal nerve and muscle function. Blood alkalinity is ultimate cause, caused by large cation, anion difference.
Low K forages reduce cation anion difference, Lucerne OK as long as it hasn't been fertilised with K.
Prevent through manage by managing dry cows, feed low K or increase anions in feed.
Grazing of fresh grass material in late autumn/early winter.
More common in older females and in early lactation.
Mg required daily because it is excreted in urine and milk.
Low blood Mg levels are indicators, ultimate cause is low Mg in cerebro-spinal fluid.
More common in Bos Taurus.
Level of Mg in herbage dependent on K in soil, energy, Ca and P availability, and levels of organic acid, fatty acid and N in herbage.
Low salt causes high K in rumen, decreasing Mg uptake.
High K in rumen also decreases Mg uptake when P is deficient and/or N/protein levels are high.
Treatment involves feeding 4kg/hd per day, causemag, pastures with higher legume content.
Discuss nitrate poisoning.
NO3 accumulates in plant tissue if high N in soil, growth rapidly decelerates (low light, temp, drought).
NO3 reduced to NO2 in rumen, toxic in high levels, convert haemoglobin to methaemoglobin, unable to carry O2 = death.
Many C4 species implicated, eg. Sorghum, corn.
Mucous membranes go brown as blood goes brown.
Manage through pasture management; control weeds, don't let cattle gorge on immature cereal crops or root crop tops, prevent access to recently sprayed weeds and highly fertilised crops particularly 7days post rainfall, low temp and cloudy weather.
Don't overstock, this can result in more stalk material being consumed, also avoid strip grazing for this reason.
Never feed mouldy hay and feed high nitrate forages as silage (nitrate reduced by fermentation).
What is an endophyte?
Fungus that infects grass.
Confers persistence via insect resistance to grass.
Discuss disorders associated with endophytes.
Produce toxic compounds for livestock.
Plants with endophytes persist as insects avoid them.
Discuss ryegrass staggers/perennial ryegrass toxicosis (PRGT).
Infection by wild fungus that benefits grass, increases persistence, seedling vigour, tillering, and insect pest resistance.
Causes low growth rate, neurological disorders (staggering).
Manage pasture by sowing safe perennial ryegrass or other species, favour legumes, or top pasture (crown and tops have higher % of fungi).
Discuss fescue toxicosis.
Similar to ryegrass staggers but fungus and toxic compound differ (ergavoline).
Three different disorders - fescue foot, summer fescue toxicosis, fat necrosis.
Only occurs in NSW where the grass has grown for long period.
Discuss phalaris staggers.
Low Co or high Mg are associated with staggers.
Insufficient Co in rumen means indole alkaloids aren't broken down and absorbed in rumen, affects brain and spinal cord.
Older cultivars have higher incidence.
Mainly affects sheep, cattle can be affected but just show ill thrift.
Prevent with Co bullets or lick blocks.
High soil Mn leads to low Co availability (June-September).
Causes sudden death, worse in fresh shoots during water stress.
Cell grazing and rotational grazing pose higher risk.
What characterises low quality feed?
Low digestibility (<60%)
Low metabolisable energy (<8.5MJ/kg DM)
High fibre levels have low digestibility due to high concentrations of pectin, cellulose, hemicellulose and lignin.
What is the big trade of in terms of hay?
Cutting time versus quality decline.
Often decided by favourable weather conditions - must reduce chance of spoilage.
What level does forage need to be dried to in order to reduce heating and deterioration?
Bailed at 75-80% DM content, 20-25% moisture.
Discuss hay making.
Pasture is dried very rapidly after cutting but then slows.
Leaf lamina dries more quickly than stems, legumes more slowly than grasses (originally through cuticle, then lamina).
Water loss depends on the frequency of turning of the swathe, the sooner the better.
STEM IS THICKER THAN CUTICLE SO TAKES LONGER TO DRY
What is the rate of hay drying affected by?
Length of stubble - increases as stubble increase
Type of mower - faster drying with drum mowers (breaks cuticle).
Turning or tedding (fluffing up) the swathe (can cause reduction in DM).
Conditioning - cuticle damaged through crushing, crinkling or abraded.
What effect can rakes have on hay?
Can cause loss of leaf (high quality component) due to faster drying than stem.
Discuss conditioning in terms of hay making.
Increases speed of stem drying so leaves don't over dry.
Increases rate of water loss from grasses.
Leads to less turning, raking, etc.
Over drying is the biggest problem - moisture must be monitored.
Rain events decrease the quality of conditioned hay more than unconditioned, this is because it leaches nutrients (soluble carbs) from the shatter stems.
What are the forms of losses in hay Making?
DM decline - can be up to 14% for pasture hay and 20% for Lucerne.
Losses greater in poor weather.
Machinery losses - every raking operation incurs a penalty (higher if drier).
Shattering is major source of loss, esp in conditioned hay.
Respiration - prolonged period in field under moist conditions can incur losses up to 19%.
20% losses if left in field.
All losses tend to be a cost to quality-loss of cell contents and decline in digestibility.
Feeding out hay - losses up to 40% if fed on ground - due to handling ex store, environmental factors (wind, rain), animal factors (trampling, fouling), microbial degredation.
Conditioning can reduce time in field
Leaching losses - depends on timing - greater if cell membranes are dead.
Storage - can be as high as 10% even when protected from rain.
Pasture/forage cut and chopped, heaped together and then respiration of CHOs leads to production of CO2, energy and water.
Respiration can decline within 30mins if O2 efficiently excluded.
Higher energy than hay.
Get better silage from younger crops as they have lower DM and O2.
If using older pastures they need to be finely chopped.
How does ensiling preserve herbage?
Encourages the fermentation of carbohydrates into lactic acid by lactobacillus bacteria - this reduces pH.
Very low pH in the absence of O2 inhibits the growth of clostridial and preserves the silage better.
Desired pH is 4.2
What occurs if clostridia can grow in silage?
Produce lactic acid and also butyric acid which reduce the nutritive value.
They also cause increased pH and produce putrefying compounds such as acetic acid and putrescine.
If soluble CHO levels are low then this lowers lactic acid production. Therefore pH is not low enough to inhibit clostridia.
What effect does reducing respiration in silage have?
Limits the temperature increase and therefore limits clostridia growth.
What % of DM should you aim for in silage? Why?
To high for clostridia which grow at 20-15% DM
What forms of losses does silage incur?
Typically around 7%
Up to 50% clostridial, respiratory and lactobacillus losses are low.
Liquid losses on unwilted silage - up to 14% DM (proteins and carbs)
Covering silage is a key loss if it is not properly wrapped.
Additives can be used to reduce losses.
Is DM intake for silage lower than intake for fresh material or hay?
Discuss the effect of cutting on pastures?
The timing of the cut is crucial to its effect on botanical composition.
Usually cut pastures have higher legume content, cutting decreases the amount of grass.
Early cuts are used for silage, late cuts are for hay.
Give some examples of summer forage crops.
Sorghums - high yielding but low protein and digestibility.
Cattle get better utilisation but prussic acid (cyanide) formation is a problem under low growth conditions or in early growth.
Millets - better quality than sorghum, no cyanide.
Soybeans, Cowpeas, lablab beans - poor recovery from grazing.
Name and discuss some winter forage crops.
Winter cereals - oats, barley, wheat.
Legumes - field peas, lupins.
Sown early to make use of early rainfall and supplement pasture production in autumn.
New winter wheat offers more flexibility, higher yields, and decent grazing values.
Can be sown into existing pasture.
What is stubble?
a form of standing feed that can be utilised over summer/autumn.
Better is there is less rainfall - quality decline is slower, moisture hastens the breakdown of pasture residue.
What does the use of stubble allow?
allows paddocks to be spelled after autumn break.
Reduces stubble load.
How is stubble utilisation improved?
Stock immediately after harvest.
Stocking with sheep allows selection of more digestible fraction - allows them to maintain weight for 6 weeks. Cattle is 12 weeks.
When do cool season grasses initiate flowers?
When they are exposed to low temperatures and long nights.
When are carbohydrates stored in grasses?
late in the growing season
Where is new growth in grass initiated from and when?
In spring, new growth is initiated from the crown using carbohydrate reserves stored in the roots, rhizomes, stolons and/or stem bases.
True or false, not all tillers produced by the plant are reproductive tiller.
Do reproductive or vegetative tillers grow taller?
What effect do seed heads have on vegetative tillers?
As seed heads develop they produce plant hormones that retard the development of other vegetative tillers.
Do vegetative tillers ever become reproductive tillers?
Yes - the become reproductive tillers in the following season for perennial pasture species.
How can you promote the development of vegetative tillers?
by removing the seed head via grazing or clipping.
What factors affect plant growth?
How does defoliation stress forage plants?
Reduces or eliminates photosynthesis.
Stops nutrient uptake from the soil.
In legumes, N fixation stops within hours of harvest.
How do plants regrow after harvest?
From carbs produced by remaining leaf area (LAI).
From carbohydrate reserves - root and remaining stem.
What does LAI mean?
Leaf area index.
When does root mass decrease?
When carb reserves are being utilised. All energy goes into new leaf growth as pasture regrows.
What effect does repeated grazing have on root mass?
Repeated grazing causes repeated loss of root mass, this leads to decreased root nutrient uptake, ultimately resulting in plant death due to inadequate nutrients.
Where does the first leaf get its energy for growth?
From root reserves
Where does the second leaf get is energy for growth?
Root reserves and photosynthesis.
Where does the third leaf get its energy for growth?
Mainly from photosynthesis
As leaf area index increases, discuss what happens to growth rate, DM production, gross photosynthesis.
As LAI increases DM production increases as does gross photosynthesis to a point (photosynthesis values are double that of DM). Growth rate increases as a curve at plateaus as the LAI reaches a 'thick canopy' stage.
When is pasture growth rate maximised?
Fairly high LAI; 90% max at >5 LAI.
Low LAI limits growth (Autumn).
What does actual DM in the paddock depend upon?
How much is lost in respiration and partitioned in the roots.
True or false, the LAI needed to support maximum intake is LESS than that required for maximum growth.
What happens to pasture utilisation as DM increases?
Animals eat green parts of the plant and leave the dead sections which have a high percentage of DM.
What happens to pasture if utilisation isn't high enough?
Large proportion of pasture mass is lost to death as the plant growth rate exceeds intake rate leading to an increase in DM.
Discuss the grazing principle of repeated grazing at low LAI.
Plant energy reserves are depleated, smaller root systems are present, poorer soil moisture access and reduced nutrient uptake and growth/survival.
What do bare patches of soil lead to?
What is the rule of thumb in terms of grazing principles?
Take half and leave half.
Removing the top layer of pasture increases vegetative tillering.
Recommended that most pastures are grazed at, or just prior to leaf maturity. (between 3-5 leaves).
What is the relationship between animal intake and pasture residual?
Research indicates that 80% of variation in grazing intake is correlated with post-grazing residual.
When forage mass drops below critical level, intake is restricted.
This is about knowing when to get your livestock off a pasture.
What are the 3 phases of plant growth?
Phase 1 - poor root systems, low amount of feed on offer, 7-15days.
Phase 2 - decreased root damage from grazing, increased pasture utilisation, 7/15-18/35days. Rapidly increasing feed on offer
Phase 3 - high DM, maximum feed on offer, days 18/35.
In which phase does maximum pasture growth occur?
What is growth limited by in pastures <1000kg/ha?
What is growth limited by in pastures >2500kg/ha?
What forms of management can be used to optimise plant growth?
Avoid production of seed heads, keep the plant vegetative (top pasture with slasher or periodically graze).
Maintain leaf canopy.
Recharge plant root reserves.
Vary rest periods by season and rainfall.
Frequent shifts of short duration (dont let pasture get below 1000kg/DM).
Provide adequate soil nutrients.
What is the reason behind providing rest periods and residual pasture management?
Increases productivity and puts the grazier in the position to extend the grazing season through; quicker green up in the srping, quicker recovery from drought.
What are the most important plant nutrients?
P, N, K, S, Ca
What are Australian soils deficient in?
Due to weathering and erosion.
Binding by soil (eg. basalt clay).
Measured in Colwell/Olson (mg/kg) - target 50-75mg/kg, annual soil test.
What is the maintenance application rate for P?
Which nutrient has the most effect on pasture response?
Fixed by legumes.
Pastures need to be actively growing.
What are indicators of responsive pastures to N?
Patchy, pale, green-yellow colour (think growth over urine patches).
Predominantly grass pasture.
Late autumn/early spring.
What is the application rate for N?
Urea is 46% N
10mm rain required.
What is stocking rate?
number of animals per area.
Generally 40-80% of carrying capacity.
Discuss stocking rate.
Major determinant of production from grazing systems.
What is PGR? What is it affected by?
Pasture growth rate.
Affected by stocking rate. Over stocking leads to decreased growth.
What happens to legumes under low stocking rates?
They don't compete well, less N fixation and less long term production.
What does overgrazing during drought often result in?
Kills perennial species and leads to an increase in annual weeds.
What effect does stocking rate have on soil properties?
Grazing increases the bulk density (weight of soil per volume) - less porosity.
Reduces infiltration with grazing.
Increases soil strength with grazing.
INCREASED SR INCREASES BULK DENSITY AND REDUCES WATER INFILTRATION
Discuss the link between SR and animal nutrition.
Increased SR limits intake, more accute during periods of greatest demand.
Effects of SR on digestibility and botanical composition will also have a direct effect on intake.
As SR increases the performance of animals more closely follows that of......
in terms of availability of feed.
Discuss the effects of SR on repro.
Negatively effects ovulation.
Decreases lambing/calving % at high rates.
Increased SR decreases milk production, but milk production per ha is increased.
Discuss SR and lamb and calf growth.
Lambs affected most in first 6 weeks due to effects on milk production.
Big interaction with availability to get animals to market specs - increased SR increases time to market and makes market specs hard to meet.
Discuss SR and fibre production.
Decline in fleece weight per head with increased SR.
Increased SR leads to lower fibre diameter but also increased risk of wool tenderness.
What effects does short pasture have on animal health?
Greater teeth wear, greater risk of pregnancy toxaemia (lack of feed at critical times), increased internal parasites.
How many bites do cows take in 24hrs?
What is the major grazing management decision? What is it closely related to?
Is maximising production per head more economically efficient than maximising production per ha?
No, maximising production per ha is the most efficient.
What are the two principles of grazing management?
Establish grazing residual and rest period targets.
compromise between livestock and pasture production.
What are two forms of grazing management systems? What are the classes within them?
Continuous - set stocking, put and take.
Intermittent - rotational, time control, strip, strategic, mob stocking, deferred grazing, creep grazing.
Discuss set stocking grazing.
animals graze an area continuously at a
predetermined level for a defined
Discuss put and take grazing.
pasture is continuously grazed with a variable
number of livestock adjusted according to feed availability
or back fat score
Discuss strip grazing.
intensive rotational grazing using electric
fences to allow livestock access to small % (ie strip) of pasture -ensures long rest and high
Discuss time control grazing.
Form or rotational
subdivisions –or cell grazing –quality implications
Discuss rotational grazing.
Involves a series of paddocks grazed in
sequence based on time schedule (lucerne 3 wks on, 6 wks off), pasture availability, animal productivity. May be on whim usually 1-3 wks grazing
What is strategic grazing?
Uses logical strategy.
Ie. to manipulate pasture composition.
Tactical, not routine.
May involve rotational stocking for a period then set stocking or use of various stock types.
What is mob stocking?
grazing with a large mob of stock at a
particular time to reduce weed population
What is deferred grazing?
area of pasture kept free from livestock
for a period -to reserve feed for an anticipated shortage or to allow regeneration of annuals in perennial and annual pastures
What is creep grazing?
When young stock are allowed to move
into an area before adult stock or using different stock types
eg, cattle, then sheep