PPT - Practical Farmers of Iowa

Plant Nutrients
Assessment of Nutrient Needs
Visual inspection of crops for deficiency symptoms
• Damage could have occurred already
• Symptoms may not be reliable
Soil tests to measure nutrient levels
• Growers depend on this method to determine lime
and fertilizer needs
Tissue testing for nutrients in plants
• May uncover problems that soil test misses
Soil Testing
Soil sampling
Soil Interpretation
Soil testing
Take a Good Soil Sample
to Help Make Good Decisions
Taking a Soil Sample
Sampling Area
Should not exceed 10 acres
For row crops
Sampling Depth
Rotation field 2
Rotation field 1
Conventional tillage: 6-9 inches
No till: Use special pH sample in
top 2”
Sod or pasture: 2-3 inches
Tree Crops: 18-24 inches
Soil Test Results
pH: Acid, Neutral, Alkaline
Soil Test Rating: VL, L, M, H, VH, EH
(How much of a nutrient is available)
Soil Test Index:
(How high or how low a nutrient is in the soil)
Soil Test
Very Low (H)
Low (L)
Medium (M)
High (H)
Soil Test
Severe deficiency
Moderate deficiency
Near optimum: some fertilizer
Adequate for most crops
Very High (VH)
Two to four times the amount considered
adequate; none should be applied
Extremely High (EH)
Excessive; none should be applied
Phosphorus, Potassium, Magnesium, calcium
Additional Resources
(1) Nitrogen Fertilizer Recommendation for Corn in Iowa
(2) Iowa State University Soil Testing Lab
(3) Extension Publications.
Plant Food Elements
Used in Large Amounts
Used in Small
Primary Nutrients Secondary
Nitrogen (N)
Calcium (Ca)
Iron (Fe)
Phosphorus (P)
Magnesium (Mg)
Manganese (Mn)
Potassium (K)
Sulfur (S)
Zinc (Zn)
Copper (Cu)
Boron (Bo)
Chlorine (Cl)
Cobalt (Co)
•Nitrogen is a primary component of proteins and is part of
every living cell.
Functions of Nitrogen
• Speeds growth
• Vigorous growth, large leaves, and long stem internodes.
• Required for the formation of dark green pigment: chlorophyll.
• Promotes better production of chlorophyll hence it is required
for better source of forage, feed and human nutrition.
• Plants use water best when they have ample nitrogen.
Excess Nitrogen
Soft, weak easily injured growth
Stems are weaker and more easily to lodge
• Soft growth is more prone to diseases and insects
• Overly rapid growth slows maturity and ripening of many
• N promotes vegetative rather than reproductive growth
of flowers and leaves.
• Over-fertilized tomato plants promote lush growth
but few fruits
Nitrogen deficiency
Slow growth and stunting
Plants lack dark green color of well fed plants: Chlorosis
• Phosphorus is part of chromosomes and genes and so it is
involved in plant reproduction and cell division.
• P spurs early and rapid growth and helps a young plant
develop its roots
• P helps plants resist cold and diseases
•P speeds up crop maturity
•P aids blooming and fruiting
•P improves the quality of grains and fruits
Phosphorus Deficiency
There is stunted growth but plants could remain green.
Plants have a purple tint to leaves and stems, starting on lower
Older leaves
Potassium (Potash)
• Activates enzymes needed in the formation of protein, starch
cellulose and lignin.
•It is important in the formation of thick cell walls and strong,
rigid plant stems.
• Regulates the opening and closing of pores in the leaf through
which water, oxygen and carbon dioxide pass.
• Important in the development and ripening of fruits like apples
or tomatoes
• Needed for proper growth of root and tuber crops
Potassium Deficiencies
Seen less often than the other primary nutrients.
Shortages occur primarily in sandy heavily leached soils.
“Marginal scorch” or burnt edges of lower, older leaves
Secondary Nutrients
Functions of Calcium
• Required by plants mainly to build cell wall
• Crispness of apples come from calcium pectate in the fruit cells
• Ca largely controls soil pH and helps in the formation of soil
• Calcium plays a role in protein formation and carbohydrate
movement in plants
Calcium Deficiencies
• Commonly appear in fruits and vegetables.
• Apple growers prevent “water core” (collapse of cell walls) in
apples by spraying trees with Ca.
•This is similar to “blossom end rot” in tomatoes.
Soil dries out and slows movement of Ca to roots during rapid
root development.
• Ca deficiency cause misshapen roots on root vegetables.
Functions of Magnesium
•It is an essential ingredient in chlorophyll formation
Each chlorophyll molecule has one magnesium atom at the center
•Magnesium activates a number of important enzyme systems
•Mg is involved in protein, carbohydrates and fat synthesis
Functions of Sulfur
•Needed in the formation of proteins and chlorophyll
•Aids in the formation of nodules in legumes and seed production
•S improves stress tolerance.
•Alfalfa, members of the mustard family and members of the onion
family need much sulfur.
•The pungent flavors derive from sulfur compounds
Sulfur Deficiencies
•Stunted growth
•Older leaves are pale green – similar to N-deficient plants
•These form special organic-metal molecules called Enzymes.
Enzymes activate biological reactions in living systems.
•The difference between enough and too much can be quite
narrow, sometimes only a few pounds per acre
Please apply elements with caution
Effect of pH on nutrient availability
Functions of Iron
•Iron is part of many enzymes necessary for the formation of
•It is an abundant element in rocks and soils but it is also one
of the most commonly deficient micronutrient
Symptoms of Iron Hunger
“Chlorosis”: Yellowing of interveinal leaves.
Mainly new leaves
Functions of Manganese
•Speeds up germination and crop maturity
•Helps uptake of several other nutrients
•Functions in chlorophyll development
Symptoms of Manganese Deficiency
•Chlorosis on new leaves
Functions of Zinc
Needed in the metabolism of protein
Involved somehow in the production of chlorophyll
Symptoms of Zinc Deficiency
Fruit crops including peaches and citrus are sensitive to zinc
Field crops also include corn, soybeans, cotton, and potatoes
Symptoms include spots on leaves
Chlorosis between veins is also
Added to the soil to provide essential nutrients to plants
Fertilizer Material
Chemical compounds or mixtures
containing nutrient
Mixed fertilizer
Weed and Feed fertilizers
Liquid fertilizers
Fertilizer Spikes
Slow-release fertilizers
Fertilizer Grade:
13 - 13 - 13
% Potash K 2 O
% Phosphate
(P2 O 5 )
Some Popular Fertilizer Grades Available
in Alabama
Fertilizer Grade
% of all Grades sold
in Alabama
13 - 13 - 13
8 - 24 - 24
8 - 8 - 8
5 - 10 - 15
7 - 21 - 21
5 - 15 - 30
18 - 46 - 0 (diammonium phosphate)
0 - 20 - 20
3 - 9 - 18
10 - 10 -10
15 - 0 - 15
Examples of Fertilizer Calculations
120 Ib N, 60Ib Phosphate, 60 Ibs potash per acre
Fertilizer Grade: 13 - 13 - 13
Before Planting
60/13% percent = 461 pounds / acre of 13 - 13 - 13
Amount needed
Analysis of source
Size of Garden : 50 x 20 = 1,000 square feet
1 acre = 43, 000 square feet
1,000 square feet = 1,000 / 43,000 = 0.023 acres
Fertilizer needed = 0.023 x 461 pounds per acre = 0.6 Ib
Examples of Fertilizer Calculations
120 Ib N, 60Ib Phosphate, 60 Ibs potash per acre
Fertilizer Grade: 13 - 13 - 13
Use ammonium nitrate (34 - 0 - 0)
Amount needed per acre = 60 / 34% = 176 pounds
Size of Garden = 0.023 acres
Amount required for side dressing = 0.023 x 176 = 4 pounds
“Per 50 ft x 20 ft garden apply 6 pounds of 8 - 8 - 8
at planting and sidedress with 4 pounds of 8 - 8 - 8”
Fertilizer Grade Available: 13 - 13 - 13
At Planting
6 Ib (expected) x 8 (required) / 13 (available ) = 3.7
4 x 8 / 13 = 2.5 Ib, 13 - 13 - 13

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