Affecting Plant Growth
will review these factors because of the limiting effects they
have on use of plant nutrients.
progressive development of an organism.
expressed as dry weight (total of the part we're interested in
such as grain), height, length, diameter
of an annual plant related to time is an S shaped curve for an
or one growing season for a perennial plant.
related to the factors affecting it.
= f (X1, X2, X3 .....Xn)
= measure of growth
= growth factors
factors that affect plant growth can be classified as genetic
Field crops - Yield
is determined by genes
of the plant. A large part of the increase in yield over the
years has been due to hybrids and improved varieties. Other
characteristics such as quality, disease resistance, drought
hardiness are determined by the genetic makeup. Corn hybrids
are an example of a dramatic yiel incease resulting from genetics.
engineering is now becoming an important tool in changing
a plants potential.
Nursery crops and turf - not interested in total growth as much
as appearance. Ex. is Bermudagrass
Coastal bermudagass- As a forage the grower is interested
in yield and feed quality.
Tifdwarf - Golf greens - interested in appearance, cover,
wear resistance not how much total growth occurs.
Variety and Plant Nutrient needs-Hybrid corn producing 200 bu/ac
requires more plant nutrients than a hybrid producing 100 bu/ac.
As potential crop yields are increased, the plant nutrients
required are increased. Current research in the Soil Science
and Genetics department is concerned with developing corn hybrids
that use nitrogen more efficiently - Produce more grain per
pound of N - fertilizer.
A producer has control over the genetic factor by his choice
crops - highest yielding, disease resistant, etc.
- Best appearance - dwarf vs larger shrubs
- All external conditions and influences affecting the life and
development of an organism.
following are regarded as the most important environmental factors
of the atmosphere
Soil aeration and soil structure
of mineral nutrients
Absence of growth-restricting substances
can be a limiting factor in plant growth. These environmental
factors do not act independently example - inverse relationship
between soil moisture and air
Temperature - A measure of the intensity of
heat. Plant growth occurs in a fairly narrow range - 60 - 100
Temperature directly affects
- loss of water
of water and nutrients
The rate of these processes increases with an increase in
temperature responses are different with different crops
vs collards or potatoes
vs bermuda grass
generalizations hold within a crops range of adaptation
Temperature also affects soil organisms nitrifying bacteria
inhibited by low temperature. pH may decrease in summer due
to activities of microorganisms
Soil temperature affects water and nutrient uptake
- Plant growth restricted by low and high levels of soil moisture
can be regulated with drainage and irrigation
good soil moisture improves nutrient uptake
moisture is a limiting factor fertilizer is not used efficiently.
intensity and duration of light are important
Quality can't be controlled on a field scale - Feasible
on specialty crops
Intensity of light (brightness) is an important factor.
with upright leaves being bred to intercept more light
- Photoperiodism - Plant behavior in relation to day length
long day plants - flower only if days are longer than same
critical period - 12 hours Grains and clovers
short day plants - flower only if days are shorter than a
critical period soybeans.
indeterminate - flower over a wide range of day lengths. Tomato,
crops fail to flower in certain geographical areas
can be made to bloom by controlling photoperiod.
of the atmosphere
makes up 0.03 per cent of air by volume. Photosynthesis converts
CO2 to organic material in the plant. CO2
is returned to atmosphere by respiration and decomposition
a corn field or closed greenhouse CO2 level may
drop and become a limiting factor in growth.
CO2 can increase crop yields respiration of plants
and animals - decomposition of manure or plant residue may
growth and quality can be enhanced by supplemental CO2.
Growth responses have been shown with tomatoes, lettuce, cucumbers,
flower crops, greens, peas, beans, potatoes
pollutants in sufficient quantities are toxic to plants sulfur
dioxide - provides sulfur at low levels
soils of high bulk density and poor structure are aerated
space is occupied by air and water so the amount of air and
water are inversely proportional to the amount of oxygen in
the soil. On well drained soils, oxygen content is not likely
to be limiting to plant growth.
vary widely in their sensitivity to soil oxygen. Paddy rice
pH influences availability of certain nutrients ex phosphate
availability low on acid soils. Al is toxic to plants
affected by pH
scab controlled by keeping pH below 5.5
- heavier fertilization may increase vegetative growth and
susceptibility to disease
knot nematodes reduce absorption so more fertilizer is necessary.
- compete for moisture nutrients light
- harmful substances released by roots.
essential nutrients - any element that functions in plant metabolism
(from water and air)
manganese, zinc, boron, molybdenum, chlorine, iron
to some plants
vanadium, sodium, silicon,
of growth - restricting substances
concentrations of plant nutrients
nickel, lead - associated with sewage disposal, wastes from
industry, mines, etc.
compounds - phenols, oil