Transcript Crop Mechanism

Sharing the results of “in-class
exercise” of Sept. 14
Remember the scale . . .
Completely agree . . . . . Completey disagree
1 . . . . . . . . . . . . 5 . . . . . . . . . . . . 10
1) Science education is important – 24
students marked “1” w. ave. of 1.6
2) I have a good foundation in science – 9
students marked “1” w. ave. of 2.6
3) My science education is typical – midscale “5” received more marks. Ave. of 47
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Sept 14 “in-class” cont.
4) More science could and should be
taught K-12.
 15 chose “1”, with ave. of 2.4
 Which areas merit more attention?

– 11, Chemistry – 9, Physics – 7,
Agriscience – 6, Environment – 4, Ecology –
3, with Anatomy, Botany, Earth Science,
Meteorology, “All” receiving “2” votes
 Biology
Obs. on “in-class” Sept. 14
Quite apparent that students tried to
respond using good English.
 Several students pointed out that science
teaches students “critical thinking skills.”
 One statement merits some discussion “not everyone meant to be a scientist”

Crop Physiology – Ch. 3 -71

How can we harvest the sun more
efficiently, while using/conserving the
natural resources of soil and fresh water in
the most prudent manner possible?
Yield -71

Product per unit area (per unit time),
usually as dry matter, or specified
moisture content (e.g., corn grain yield is
calculated at 15.5% moisture.)
Types of Yield -71
Biological = total dry matter produced per
plant or per unit area, everything, including
roots. However, often, just the aboveground parts are used. Need to check.
 Economic = weight or volume produced
per unit area of the marketable portion, at
standardized market moisture content.

Harvest Index ! -72
Ratio of economic yield to biological yield.
 **** This is the characteristic that plant
breeders have modified to increase
economic yield.
 Meanwhile, biological yield has changed
very little, if any.

Components of grain yield -72

YIELD =
 Plants/area
 Heads/plant
 Seeds/head
 Weight/seed
*
increasing one,usually results in decrease in
one or more of the others
Plant Growth Curve -72
Plant Growth Regulators – 72+
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Auxins – cell elongation – “master regulator,”
e.g., IAA
Gibberellins – elongation, but chemically
different than auxins, e.g., gibberellic acid
Cytokinins – cell division, differentiation, e.g.,
zeatin
Growth Inhibitors – inhibit growth and
development, e.g., abscisic acid, or phosphon
Ethylene – hastens fruit ripening
Demo results, to be reported later

The exercises described on pp 73-76+ are
expected to be reported in time for Quiz 3,
via lecture.
Photosynthesis and Respiration -77
Photosynthesis -77

6CO2 + 6H2O + light (in presence of
chlorophyll) produces . . .
C6H12O6 (sugar) + O2
Respiration - 78
Oxidative breakdown of organic
compounds
 Energy (stored in high energy bonds–ATP)
and growth are products of respiration

Ps. and Resp. compared -78
PS .
in green cells
occurs w/light
uses H2O and CO2
releases O2
weight increases
accumulates food
Resp.
in every cell
all the time
burns sugars
releases energy
weight decreases
breaks down food
Terminology - 78
Net Photosynthesis (Pn), also NAR =
Photosynthesis minus respiration
 Leaf Area Index (LAI) = ratio of total leaf
area of crop plants divided by land area
occupied
 Canopy = aerial portion of plants

PS – Respiration = NAR
Sunlight, factors
1) Quality (think of rainbow)
 2) Intensity (interception)

 Efficiency

of interception is a sub-factor
3) Duration (daylength, photoperiod)
 Compare
June 21 daylength for Miami and
New York City – which city has longer days?
The visible light spectrum -79
Plant tissue and light quality
Wavelengths absorbed – blue and red
 Wavelengths reflected – green and yellow
 Wavelengths which penetrate leaves and
inhibit germination of species which
require light for germination – far-red

Light quality -80
Importance of good plant
distribution within canopy
1) light needed for Ps
 2) inhibit germination of weed species
needing light
 3) reduce moisture loss through
evaporation
 4) for species depending on N-fixation,
shading the soil benefits N-fixing bacteria

Example of light interception
benefits - 80
Table 6 – Light interception/soybean yields
 Row width - % light intercept. - % yield in.

 20*”
 40*”
84
75
* = Same population densities
115
100
Species differ in light utilization
Comparisons of C3 and C4 -83
C3 plants
Primarily cool season
Max of ~60% intensity
Low C02 uptake
Lower yielding
Less efficient water use

C4 plants
Prim. warm season
Uses 100% intens.
Higher CO2 uptake
Higher yielding
Higher ef. H2O use
Notes on carbon fixation (Ps)
Calvin cycle (all plants) produce 3-carbon
chain products – known as C3 species
 Hatch & Slack (discovered another
pathway in 1960s) in tropical grasses+,
producing 4-carbon products – known as
C4 species
 Increasing levels of CO2 help C3 close Ps
gap with C4 species.
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Leaf angle and light interception
- 82
Chalkboard explanation
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Gain from upright leaves – diminishing
returns from higher sunlight
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Light demo (with leaves)
Remember: one leaf shape
does not fit all farmers
Upright leaf varieties have allowed farmers
to increase yields provided that they had
the nutrients and water
 Limited input farmers (e.g., developing
world) get higher yields from traditional,
more-horizontal leaf varieties
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Mid-Chapter review

There are many practical applications of the info
on auxin effects (produced in rapidly growing
tissue):
 1)
promotes elongation
 2) inhibits lateral bud development – (lateral buds
have three options –
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
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Develop into stem replacement
Develop reproductive organs (seed)
Remain dormant)
 ****Destroyed
by sunlight (see next)
Review, continued
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Applications:
 1)
population densities result in shading
differences – and consequences –
- barrenness, if too high a density (e.g., corn)
 - excessive branching (e.g., soybeans) if density
too low
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 2)
make your landscape plants and trees
“bushier”
Transport and Uptake - 83
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Defined as “movement of organic and
inorganic solutes from one part of plant to
another”
 Amino
acids (formed in leaves and roots from
sugars and nitrogen) move in phloem
 Water and minerals move in xylem
Transpiration/Evapotranspiration 84
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Keeps the plants cool – necessity (graph)
Requires considerable water to evaporate
Evapotranspiration adds the evaporation
component. Good plant spacings minimize
evaporative losses, keep soil from overheating –
esp. imp’t in legumes which rely on N-fixing
bacteria
Water requirement (ETR) - 85
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
Also known as “evapotranspiration ratio”
Defined as “units of water to produce unit of dry
matter”
 Varies


 ***
from about 325 to 1500+
Sorghum and millets being in 325 range (C4 species)
Rice at upper end of ETR (C3 species)
When ETR is divided by harvest index (HI) in grain
crops, we get the units of water to produce unit of
grain (e.g., 325 / 0.50 = 650 for most efficient crops)
Reviewing imp’t concepts
Plant breeders, working on grain yield
improvement, have changed the harvest
index (esp. wheat and rice, but others too).
Most species had HI of 0.20-0.25 when pl.
breeders started making crosses and
selections for higher grain yield.
 Now, those improved crops are in range of
0.50 His. Theoretical maximum =~ 0.60

So, what constitutes drought
tolerance then?

Several aspects:
species use water more efficiently – lower ETRs
 Perennial crops have dormancy mechanism
 Indeterminate more tolerant than determinate species
(Indeterminate have longer flowering period – the
most susceptible stage to moisture stress)
 Plant crops during cool season to avoid heat
 Deep roots
 C4
Let’s look at some examples
Crop
Cotton
Millets
Sorghum
Alfalfa
Small grains
Mechanism
dormancy
C4, some short cycle
C4 and dormancy
Deep root system
Grow in early spring
(low stress period)
Indeterminate soybeas - flower over longer period
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Why wasn’t corn on that list?
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Corn is monoecious – imperfect flowers, same
plant
Corn plant is efficient but problem with grain
production
arises as result of apical dominance – the
top of the plant takes precedence over lower parts
(tassel gets limited resource while silk is retarded – if
and when moisture returns and silk emerges, there
may not be any pollen available)
 Problem
Mineral uptake methods -86

Root growth, interception (here is where
unusually wet spring weather can result in
lower yields – roots not well distributed)
 Fungi
(mycorrhizae) help contact more
nutrients
Nutrient flow with moisture flow in soil
 Diffusion, from high to low concentration

Nutrient absorption thru roots -86
May be passive (mass flow) uptake
 Or may be active (energy expended to
absorb nutrients)
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Biological N-Fixation (BNF) - 87
Rapidly growing interest, with increasing
cost of chemical fertilizers
 Organic farmers depend on BNF
 Legumes fix more N than all of fertilizer
manufacturers
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Process of Rhizobium infection
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Bacteria survive in soil, and build up pop’n when
suitable host present
Bacteria infect root hair, resulting in tetraploid
cell formation and nodule formation
Nodules may be visible after about two weeks,
and N-fixation starts about 7-10 days later
Nodules need sugars from Ps (graph)
Symbiosis (symbiotic organisms)
Defined as “two or more organisms living
together for the benefit of each other”
 Legume plant and N-fixing bacteria
(Rhizobium) is example
 For contrast –

 Parasite
(mistletoe)
 Epiphyte (e.g., Spanish moss)
Imp’t concepts:

Some bacteria infect more than one crop –
cross-inoculation groups – the “cowpea”
group, for example, includes:
 Cowpeas
 Peanuts
 Pigeonpea
 Some
weeds (FL beggarweed, for example)
Other symbiotic (?) N-fixers -87

Azospirillum lives in the rhizosphere (not in
roots) of some grass species –
 live
on exudates from the grass roots and
fixes some nitrogen.
 seems to be most productive in moist
environments
Non-symbiotic N-fixers -87
Azotobacter and Clostridium – “free-livers”
inhabiting soil and fixing low level of
nitrogen, without associating with living
plants
 Cyanobacteria (formerly blue-green algae)
– important in rice cultures

What is the approximate amount of
N fixed by each category?
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Rhizobium (Bradyrhizobium in soybeans) is
most productive – 50 ~ 300 lbs N/year
Azospirillum – 40 lbs N/year probably is upper
expectation – there interesting research
Azotobacter – 20-40 lbs N/year
Cyanobacteria (the blue-green algae) – possibly
as high as 60 lbs N/year
 **for
comparison -130 bu corn requires ~175 lbs N~
from various sources
Germination requirements -88
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
1) water
2) suitable temperature (see Fig. 12)
 Note
that differences in temps for germination are
factors in use of “nurse” crops to establish forage, and
reduce weed competion – small grains germinate at
low temps
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
3) oxygen
4) light – some species
 Tobacco
 Grassy
weeds
Etiolation -88

Def: elongation of plant stems grown in
absence of light, or low light intensity
(shaded). Why? (high levels of auxin)
 Recall
that sunlight destroys auxin
Tillering, Branching, Barrenness 89

Tillering is the production of secondary
stems from crown area, promoted by –
 Sunlight
 Moisture
 Fertility
 Cool

temperatures in small grains
Warm temperatures in rice
Branching, 89

Branching is the development of axillary
buds and may or may not be desirable –
 Desirable
in certain landscape and tree spp.
 Some farmers find undesirable in soybeans
as branches may form too close to ground
and some branches will be knocked off the
plant by the “reel” on combines and lost.
Barrenness -89
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Too much shade = too much auxin =
inhibition of lateral buds and if enough,
results in barrenness.
Crop Development -89
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Reproductive development
growth – most of vegetative
growth before reproductive growth,
comparatively short flowering period –
possibly a risk
 Indeterminate growth – vegetative and
reproductive growth overlaps, over a longer
period. Longer flowering period.
 Soybeans have both Dt. and Indet. types
 Determinate
Time of Flowering, Photoperiodism
- 90
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
Daylength affecting time of flowering and
subsequently, maturity
Types:
Day Plants – flower as days are getting longer –
(most cool season crops)
 Short Day Plants – flower when daylengths are
shorter than some critical maximum – usually summer
and fall (most warm season crops)
 Day Neutral Plants – daylength not factor, but temps.
 [Day Exact – flower only when daylength is precise
(e.g., sugarcane)]
 Long
Plant photoperiod classification -90
Please see Table 13, page 90
 There is one notation that needs to be
made.

 Maize
is listed as “short day” – true for
primitive corn – modern corn varieties use
temperature – “Growing Degree Days”
 Modern maize should be listed as Day Neutral
Phytochrome - 91

Is a light-sensitive pigment in plant
 Long
days (short nights) increase
Phytochrome Far Red (PFR) – stimulates
short day plants to flower
 Short days – (long nights) stimulate
Phytochrome Red (PR)
 Graph
Explanation of Sun/Earth
interaction

Using globe and flashlight