Why measure yield?

	Pasture yield is the most important determinant of system performance, yet is the most difficult to define and measure
	Visual estimates can be subject to significant error
	Pasture mass is the principle determinant of stocking rate
	Pasture mass is used to measure carbon flows and predict sequestration

Instantaneous (biomass) vs dynamic (growth)

	Instantaneous measurement: the amount of grass/forage/herbage present at any point in time. described as: pasture yield, production, mass, cover measured as: kgDM/ha, lb/acre, height, AUM (animal unit months)
	Dynamic measurement: change in mass over time described as: growth, growth rate, yield, herbage accumulation, net primary productivity (NPP) measured as: kgDM/ha/d, kgDM/ha/yr

  Measurement

	Q - What should be measured??? Answer - it depends on the purpose!!
	Quadrat cutting – typically with hand or electric shears, or mechanical harvester
	Advantages Few errors Inexpensive Intuitive Generates a sample for other measurements	Disadvantages Samples a small area Laborious Requires a dry weight Operator error Destructive
	Other measures of mass Correlation with height - Rising plate meter, sward stick Eye estimation Spectral reflectance/remote sensing Capacitance meter
	Methods to measure growth rate Herbage accumulation following defoliation Change in mass over a regrowth period Dilemma of continuous grazing - where grazing continues herbage accumulation is often in a grazing exclosure cage. This can lead to over-estimation of yield Photosynthesis chamber (CO2 depletion) Predicted with modeling Predicted from animal intake/production or climate/environment

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  Difficulties in measuring forage production

	Continuous grazing
	Weeds-should these be included in yield?
	Pasture death
	è	Poor quality, avoided by stock
	è	Poor animal performance if forced to graze dead matter
	è	Lost opportunity for green yield
	è	Critical for determining NPP Yield = NPP – death
	è	Critical for predicting changes on soil organic matter (carbon sequestration)
	è	Almost impossible to measure – high errors during periods of high decomposition

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