2. Early scientists had interesting ideas about plant growth.
Aristotle thought the “stuff” for plant growth came from
the soil, and Jean Baptiste van Helmont tested the
hypothesis that plants absorbed soil for growth, but only
a small amount of soil disappeared (started with 200 lbs
and after five years, had 169 lbs. 3 oz. of soil and an
almost 200 lb tree), so he concluded that the water he
provided caused the growth.
3. Later, Stephen Hales suggested that plants are
nourished by air. So just what materials are used by
plants to support growth? Van Helmont was partially
correct, water is used (in fact, @ 80-90% of an
herbaceous plant is water) and some minerals are
also absorbed from soil making up about 4% of the
dry mass of the plant (this would account for some of
the “lost” soil), and Hales was also partially correct in
that CO2 is incorporated into glucose making up
about 96% of the dry mass of the plant (making
structures like cell walls or stored for future energy
use like starch).
4. Minerals
All organisms require minerals for growth.
•1. Mineral nutrients are essential chemical elements that plants absorb
from the soil as inorganic ions.
•2. Although more than 50 elements have been found in plant tissues, many
of these are most likely not essential to plant growth.
•3. Essential nutrients are those that are required for a plant to grow,
complete its life cycle, and reproduce. Three criteria for essential nutrients
are: (1) the nutrient is required for growth or reproduction, (2) no other
element can substitute for it, and (3) it is required for a specific structure or
metabolic function not because it aids in the uptake of a different essential
nutrient. This can be determined by using hydroponics (growing plants in
water and adding nutrients in a controlled manner)
5. Nutrients need by plants can be categorized as
either macronutrients that are needed in relatively
large amounts (nine of the essential elements are
macronutrients), and micronutrients that are
needed in relatively small amounts (eight of the
essential elements are micronutrients).
Studies have indicated that most plants need 17
essential nutrients.
6. Plant Essential Nutrients by Source -
Essential nutrients are required by all
plants to complete their life cycle
Macronutrients - air and water Carbon (C), Hydrogen (H), Oxygen (O)
Macronutrients - soil Nitrogen (N), Phosphorus (P), Potassium
(K), Calcium (Ca),
Magnesium (Mg), Sulfur (S)
Micronutrients - soil Iron (Fe), Manganese (Mn), Zinc (Zn),
Copper (Cu), Nickel (Ni),Boron (B),
Molybdenum (Mo), Chlorine (Cl)
Plant beneficial nutrients
Beneficial nutrients enhance the growth
of some plants.
Cobalt (Co), Silicon (Si), Vanadium (V),
Sodium (Na)
Mnemonic Devices
7. Mineral deficiencies most commonly result in
stunted growth and discolored leaves. But the
symptoms do vary depending on the element,
its role in plant growth, and its mobility within
the plant.
8. Plant Nutrient Type Visual symptoms
Nitrogen
Deficiency
Light green to yellow
appearance of leaves,
especially older leaves;
stunted growth; poor fruit
development.
Excess
Dark green foliage which may
be susceptible to lodging,
drought, disease and insect
invasion. Fruit and seed crops
may fail to yield.
Phosphorus
Deficiency
Leaves may develop purple
coloration; stunted plant
growth and delay in plant
development.
Excess
Excess phosphorus may cause
micronutrient deficiencies,
especially iron or zinc.
Potassium
Deficiency
Older leaves turn yellow
initially around margins and
die; irregular fruit
development.
Excess
Excess potassium may cause
deficiencies in magnesium
and possibly calcium.
9. Calcium
Deficiency
Reduced growth or death of
growing tips; blossom-end rot
of tomato; poor fruit
development and appearance.
Excess
Excess calcium may cause
deficiency in either magnesium
or potassium
Magnesium
Deficiency
Initial yellowing of older leaves
between leaf veins spreading
to younger leaves; poor fruit
development and production.
Excess
High concentration tolerated in
plant; however, imbalance with
calcium and potassium may
reduce growth.
Sulfur
Deficiency
Initial yellowing of young
leaves spreading to whole
plant; similar symptoms to
nitrogen deficiency but occurs
on new growth.
Excess
Excess of sulfur may cause
premature dropping of leaves.
10. Iron
Deficiency
Initial distinct yellow or
white areas between veins of
young leaves leading to spots
of dead leaf tissue.
Excess
Possible bronzing of leaves
with tiny brown spots.
Manganese
Deficiency
Interveinal yellowing or
mottling of young leaves.
Excess
Older leaves have brown
spots surrounded by a
chlorotic circle or zone.
11. Zinc
Deficiency
Interveinal yellowing on
young leaves; reduced leaf
size.
Excess
Excess zinc may cause iron
deficiency in some plants.
Boron
Deficiency
Death of growing points and
deformation of leaves with
areas of discoloration.
Excess
Leaf tips become yellow
followed by necrosis. Leaves
get a scorched appearance
and later fall off.
12. Soil differs in quality depending of
the relative proportions of sand
(large particles), silt (fine particles),
and clay (finest particles). Plants do
best in loam soils that have about
the same proportions of sand, silt,
and clay. Knowledge of these basic
physical properties of soil (texture
and composition) helps people
understand why it is important to
conserve soil, and understand the
limitations of different soil types and
help promote sustainable
agriculture. Agronomy is the study
of food crops and other plants used
for humans and includes the study of
soil.
13. Soil Conservation
Soil Formation is a very slow process that involves:
Physical events like fragmentation (by weathering
e.g, by temperature changes and abrasion) of the
parent material consisting of rocks or other
geological deposits and Biological events:
Organisms (e.g., lichens) also play a role in
weathering, Humus is the resulting decaying
organic matter that is formed and constitutes an
important ingredient of the soil. Humus is
important in that it consists of essential nutrients as
well as changes the pH of the soil, and other
organisms also play a role in soil formation.
14. Erosion
the wearing away and
transportation of soil by
water or by wind. Erosion
can be natural or
accelerated by human
activities. This occurs on a
large scale. It is estimated
that between 1992 and
1997, erosion resulted in
the loss of 1.9 million tons
of topsoil from U.S.
farmland.
15. Desertification
the conversion of cropland,
pasture, and rangeland into
desert or land too arid to be
farmed. Causes include:
drought, global warming,
overgrazing, overcropping
semi-arid lands and
deforestation. This is
occurring in many regions: the
U.S. (an example would be the
Dust Bowl), Africa, Australia,
Brazil, Iran, Afghanistan, China
and India. This is a very
serious problem
16. Farmland Conversion
The loss of fertile
farmland to development
(farmland conversion) is a
major problem in many
regions. In the U.S. for
example, 1.3 million acres
of farmland are developed
each year (homes,
businesses etc.)
17. Irrigation
The amount of irrigated
cropland is substantial and
produces @ 33% of our
food. However, since the
1980s land irrigation has
decreased. There are
many problems with
irrigation including
salinization and overuse of
water resources.
18. Waterlogging
Approximately 10% of the
world’s irrigated cropland
suffers from waterlogging
that suffocates plants and
makes soil difficult to
cultivate.
19. Salinization
(a result of mineral
buildup in irrigated soil
after evaporation) also
reduces food production.
About ¼ of the world’s
lands are affected.
21. Soil erosion and desertification
can be reduced or stopped by
various methods: minimum
tillage (decreasing land
disturbance), contour farming
(planting crops perpendicular to
the slope), strip cropping
(planting multiple crop species in
alternating strips), terracing
(using small earthen
embankments that run across the
slope of the land), gully
reclamation (using rapidly
growing plants), and shelterbelts
(rows of trees planted around
fields).
23. Water should be used
more efficiently to
prevent salinization and
loss of this valuable
resource. Special
drainage systems could
also help reduce
salinization.
24. Appropriate use of fertilizers is
needed to replace nutrients in soil.
Nitrogen, Phosphorus, and
Potassium are common components
of synthetic fertilizers that have
greatly increased crop yields.
However, these elements cause
other environmental problems (e.g.,
eutrophication of lakes and ponds).
The use of organic fertilizers from
animal and plant waste is advocated
for sustainable development. In
addition, crop rotation especially
involving the periodic planting of
legumes that replenish Nitrogen, can
reduce the use of synthetic
fertilizers.
25.
26. Instead of converting non-farm land,
the productivity of existing
agricultural land could be increased.
This could be accomplished by the
cultivation of hybrids, selective
breeding for high production and
pest resistance, and genetic
engineering (although controversial).
The Green Revolution has increased
the productivity of a great deal of
land, BUT it is becoming apparent
that these increased yields may be
temporary and that the methods
used in the recent past actually
cause the deterioration of land by
soil degradation, and erosion
27. Protecting wild stocks that
give rise to cultivated
species requires habitat
protection
The utilization of native
species (e.g., the winged
bean of the tropics) could
help meet the increasing
food demands.
28. Aquaculture is a relatively
new way to produce a
high protein food source,
fish and preserve native
fish stocks.
29. Various pests destroy at
least 30% of crops. Pest
management is thus
necessary, but
alternatives to the
application of broad
spectrum, potentially
harmful should be utilized
for sustainability.
30. Also eating lower on the
food chain would increase
total crop yields due to
the low productivity
associated with meat
production.
The implementation of
new government policies
is necessary for
sustainability to be
realized.
31. Phytoremediation can be
used to reclaim some areas
that have become unfit for
agriculture or wildlife due to
the activities of humans that
result in contamination with
heavy metals or organic
pollutants. This is a new
nondestructive method for
reclaimation. It involves
using certain plants that
extract these pollutants
from the soil.
