Vegetative vs reproductive pathways

	Seed survival in soil - <2 years for grasses, >50 years for many weeds and legumes ('hard' seed)
	Some people manage pastures for seed production and natural reseeding
	In NZ Chapman found trivial contribution from natural reseeding in white clover
	Hume and Barker found as many as 10% of grass plants were from natural reseeding (especially for ryegrass and brome, not for orchardgarss or reedcanary grass)
	In grassland 99.9% of tillers and growing points have resulted from vegetative reproduction - an understanding of vegetative mechanisms is critical to understanding grassland dynamics (population ecology)
	Chapman concluded that reproductive pathways are irrelevant in predicting pasture growth - but might have a role in extreme cases where total vegetation loss has occured (e.g. soil loss by erosion, or stand loss from drought)
	Ecologically, the agroecosystem function for reproduction has largely been assumed by humans. Where we have serious stand loss, we intervene with seed introduction.
	Reproductive mechanisms do remian critical for annual species such as hop clover, Poa annua and many weeds

Principles of tillering

	Yield = tiller density * tiller size These components are negatively correlated
	data from Hopkins 2000	-3/2 rule
	Fertilizer will drive the relationship to fewer/larger tillers – and greater yield
	Tillers form in the axil of leaves Leaf appearance and tiller production are intrinsically related Seed head formation marks the end of leaf appearance (for that tiller) – meristems at the tiller base remain viable and can form numerous daughter tillers in its place Not all the potential tiller sites actually become tillers
	Factors controlling site filling: O Apical dominance O Nutrient competition ü Red:far-red ratio Leaves intercept red light – light at the base of a tall canopy will have more far-red light which supresses tillering. Defoliation (or artificial red light) allows red light to the tiller bases, stimulates a higher proportion of site filling – and promotes tillering. Short pastures (especially turf) will have a higher tiller density than tall pastures
	Seasonal patterns of tillering During summer and fall – vegetative tiller production continues as already described Spring growth is dramatically affected by reproductive tillers. Generally taller pastures and the number of dying tillers can result in a loss of stand density – which can slow subsequent forage yield.

  Tiller density and drought

	Inadequate control of spring pasture can result in fewer tillers at the onset of summer
	Low tiller density and dry conditions preventing large tillers can result in reduced yield.
	Close spring grazing to increase tiller density did not result in any difference in summer yield, but did result in more tillers surviving drought and faster recovery of autumn yield

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  Principles of legume growth

	Alfalfa (p12) Has no mechanism for clonal (vegetative) spread Regrowth occurs in the axil between leaves and stems, however, for most cases the leaves will have died and the new growth comes from the plant crown – usually below ground Damage to the plant crowns by treading damage during wet conditions or disease can irreversibly reduce the life of a stand The trigger for activation of these otherwise dormant meristems is altered red:far-red ratio from cutting for hay. The grazing alfalfa ‘Alfagraze’ has been selected for higher numbers of growing stems – resulting from a greater proportion of meristematic sites developing. Alfagraze also has a tendancy for crowns to be buried rather than partly emerged – thus protecting the growing zone.
	Red clover Similar growth pattern as alfalfa One variety of red clover which has stems which can form roots at nodes is Astrid (Tasmania). Astrid has poor production in USA. There is potential for selection of more persistent red clovers – which have the ability for vegetative spread. The rooting phase is more seasonal than for white clover (occurring in fall) and is especially sensitive to grazing damage during that period.
	White clover
	§	White clover produces stolons which root at the nodes (leaf junction with the stolon).
	§	Each node has a meristematic zone which can produce a flower or a new branch stolon. As for grasses not all meristematic zones become active – reasons for variation are not well understood.
	§	Clover population density is measured by the density of nodes (growing points)
	§	In NZ there is a wide range in the extent of branching.
	§	Densely branching white clovers (similar to Dutch) are used in less productive environments. These varieties have high node densities,tend to have better drought survival, and are more tolerant of close grazing
	§	Sparsely branching varieties (similar to Ladino) are used in more productive environments. There is a negative correlation between branches and leaf size Branching is triggered by the red:far-red ratio. As for grasses – close grazing will result in a greater node density. Inter-node distance is also controlled by red:far-red ratio. The distance between nodes will lengthen in long pasture – the plant appears to be growing in search of a more desirable light regime

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  Species mixtures

Changes in botanical composition is due to changes in the relative number and size of growth units e.g. a change to close grazing will favor species with the capacity to produce smaller and more tiller (kentucky bluegrass vs tall fescue) infrequent defoliation managements (such as for hay) are usually detrimental to white clover populations. Conversely, more frequent cutting or grazing will favor white clover.

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  Root vs shoot competition

Below-ground root competition is as significant and intense as above-ground competition

Species with a more extensive root system (larger and finer = greater surface area) will be more competitive at low fertility (kentucky bluegrass vs white clover)

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