Introduction

Quality (pg 103-104)

Intensity (pg 104)

Duration (daylength) (pg 105-108)

Temperature (pg 108-113)

Farm Management

Introduction

	Light and temperature are the fundamental determinants of forage response – the drivers of seasonality
	Variation in seasonal growth between forages occurs because species vary in their response to light and temperature
	Light & temperature are closely related – e.g. high light intensity, long days, and high temperature all occur during summer
	Light and temperature interact – spring forage growth rates are higher than would be predicted than just using temperature alone – the combined effect of warm temperature and increasing daylength (to promote flowering) are required to obtain spring growth rates
	These are climatic effects and often there is not much that can be done in practice, but knowledge does help us understand forage crop and avoid management mistakes

Light Quality

Not all light has equal value

Wave-length classes have specific effects

>800nm

• no benefit, this heats the plant and increases water loss.
• Many plant responses to high solar radiation (heating) are to reduce leaf area (and minimize radiation load) – wilting, leaf closure, leaf curling, and in extreme cases leaf loss have the benefit to the plant of reducing radiation, but result in production loss
  

700 nm-800 nm

• Far-red effects (pg 109)
• High proportion in transmitted light, shading effects
• Etiolation
• Reduced tiller appearance, increased internode extension of stolons
  

610-700 nm

• red effects
• photosynthetic range
• Red:far-red ratio
• tiller initiation
• short internode length
  

510-610 nm

• no absorbance
• green wavelengths are reflected/transmitted and give plants their color
  

<400 nm

• UV range
• stunts plants
• UV increasing
  

• Units are those for density - mmol photons/m²/s, W/m²
• Shade effects (agroforestry)
• 95% light interception & LAI
  

6 latitude determines daylength, Ohio 40^o north

6 Winter light 7:30 am – 4:30 pm 9-hr days

6 Summer light 5:30 am – 8:30 pm 15-hr days

6 a) Long-day plants - only flower with long days e.g. most forage species e.g. lespedeza

b) short day plants - only flower with short days (long nights)

c) day-neutral plants - flowering is insensitive to daylength

6 Day length

á Maximum temperature for growth

á Optimum temperature for growth

C4 30^oC, C3 16^oC, legumes 20^oC

á High temperature effects - usually associated with drought, high water use will cool leaves by up to 10^oC, however eventually water loss will exceed supply and result in stomatal closure and high leaf temperature.

á Freezing effects
á Acclimation – solute accumulation will lower the freezing point by up to 10^oC

á Fall sown vs spring-sown forages

á Heaving (pg 112)		click to enlarge (71kb)
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1) Light management – timely harvest/grazing to minimize excessive leaf cover (LAI greater than 3) or periods of low leaf cover (LAI less than 1)

2) Species and variety selection (Fig 5.7)

• High cold tolerance e.g. Big bluestem, bluegrass, wheatgrass


• Medium e.g. Tall fescue, orchardgrass, fall-dormant alfalfa


• Low cold tolerance e.g. Ryegrass, non-dormant alfalfa

3) Fall management and fertilizer (use K not N, Fig 5.10)

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