Factors Affecting Plant Growth
will review these factors because of the limiting effects they have on use
of plant nutrients.
of growth - The
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.
G = f (X1, X2, X3
G = measure of growth
Xi = growth factors
factors that affect plant growth can be classified as genetic or
A. Genetic Factor
Field crops - Yield potential 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. Genetic 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.
2. 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.
producer has control over the genetic factor by his choice of variety.
Field crops - highest yielding,
disease resistant, etc.
Nursery - Best appearance -
dwarf vs larger shrubs
definition - All external
conditions and influences affecting the life and development of an
are regarded as the most important environmental factors
Composition of the atmosphere
Soil aeration and soil structure
Supply 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
a. Temperature - A measure of the intensity of
heat. Plant growth occurs in a fairly narrow range - 60 - 100 degrees F
Temperature directly affects
- loss of water
of water and nutrients
rate of these processes increases with an increase in temperature. Responses
are different with different crops
cotton vs collards or potatoes
fescue vs bermuda
holds 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
Soil temperature affects water and nutrient uptake.
b. Moisture supply - Plant growth restricted by low
and high levels of soil moisture
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
1. Quality can't be
controlled on a field scale - Feasible on specialty crops
2. Intensity of light
(brightness) is an important factor.
with upright leaves being bred to intercept more light
- Photoperiodism - Plant behavior in relation to
day plants - flower only if days are longer than same critical period - 12
hours for 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, cotton, buckwheat
crops fail to flower in certain geographical areas
can be made to bloom by controlling photoperiod.
d. Composition of
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
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 release CO2
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
e. Soil aeration
soils of high bulk density and poor structure are aerated poorly.
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 vs tobacco
f. Soil reaction
- 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
g. Biotic factors
- heavier fertilization may increase vegetative growth and susceptibility
knot nematodes reduce absorption so more fertilizer is necessary.
- compete for moisture nutrients light
allelopathy - harmful
substances released by roots.
Plant Nutrients - Those elements
that are needed for higher plants to complete all life functions, and that
corrected only by the application of the specific element causing the
Non-mineral nutrients (from water
manganese, zinc, boron, molybdenum, chlorine, iron, nickel
Mineral Elements beneficial to some plants
vanadium, sodium, silicon, selenium
i. Absence of growth - restricting substances
of plant nutrients
aluminum, nickel, lead
- associated with sewage disposal, wastes from industry, mines, etc.
compounds - phenols, oil