Photosynthesis
Plants use light energy and chlorophyll to make sugars for plant growth from water and carbon dioxide.
6 CO2 + 12 H2O C6H12O6 + 6O2 + 6H2O
Light and Chlorophyll
Carbon dioxide Water Glucose Oxygen Water
Functions of Nutrients in Plants
• Carbon, Hydrogen and Oxygen make up 95% of the dry matter weight of plants.
– Carbon dioxide from air is converted in the plant to sugars, starches, proteins, enzymes, and a multitude of other organic compounds.
– Oxygen is a component of most organic compounds, must be present for plant roots to function.
– Hydrogen and oxygen form water which makes up most of the weight of living plants. Hydrogen is a constituent of most organic compounds and is involved in many of the chemical reactions in the plant.
17 Essential Plant NutrientsSource of Plant Nutrients
From AirCarbon (C)
Oxygen (O)
From WaterHydrogen (H)
Oxygen (O)From Soil
Nitrogen (N) Calcium (Ca) Boron (B)
Phosphorus (P) Magnesium (Mg) Chlorine (Cl)
Potassium (K) Sulfur (S) Copper (Cu)
Iron (Fe)
Manganese (Mn)
Molybdenum (Mo)
Zinc (Zn)
Nickel (Ni)
Partially decomposed residue of plants, animals, etc. Humus is the more stable residue 1-3%
decomposes annually
Soil Organic Matter -
• Improves soil structure, water holding capacity, etc.• Provides for good soil tilth• Provides CEC• Source of essential plant nutrients
90-98% of N abd S30-50% of P;Micronutrients
SOIL ORGANIC MATTER
Soil Microbes Mineralize and Immobilize Plant Nutrients.
Plant UnavailableForm
Plant AvailableForm
Organic nutrients Inorganic nutrientsMineralization
Immobilization
Estimated Residue Production by Various Crops ??
lb per bu yieldWheat 100Corn 60Sorghum 60Soybean 45Sunflower 36
NRCS – calculation factor
Crop Residue Decomposition Assumptions
Weight of Plow Layer (6-7”) of Soil Equals 2,000,000 lb/acreCrop Residues are about 43% Carbon (C) About 67% of residue carbon is lost as microbial CO2 If Adequate N Available. May be 75 - 80% loss if N is limiting.Assume SOM is 59% carbonAbout 1-3 % of SOM is decomposed each year
Increasing SOM Content
Assume 45 bu/a wheat provides 4,500 lbs residue4,500 lb residue x 43% C = 1,935 lbs Total C/A1,935 lbs C x 67% = 1,300 Lbs C Respired By Microbes1,935 - 1, 295 = 640 lbs Carbon Remaining
640 / 59% = 1,085 lbs SOM Formed
Assume A Soil With 2% SOM and 2% Is Mineralized Per Year = 800 lbs SOM Mineralized Per Year
Net SOM addition = 1,085 – 800 = 284 lbs SOM per year
Effect Of 20 Years Residue Management(KSU, Ottawa)
20 Year YieldResidue
TreatmentGrainBu/a
Residue Ton/a Soil pH
Organic Matter
Removed 1178 27.4 6.0 3.0Normal 1190 27.8 6.1 3.3Doubled 1175 27.7 6.2 3.7
Effect Of 20 Years Wheat Residue Management(KSU, Holcomb)
Residue Treatment Soil pH
Bray P (ppm)
Exch. K (ppm)
Org. Matter
Burned 8.0 28 515 1.8Removed 8.0 24 500 1.7Normal 7.9 26 540 1.8Double 7.9 20 570 2.0
LSD (0.05) 0.1 NS 20 0.1
Effect of N Rate and Tillage Method on Soil Organic Matter Content
_________________________________________________________Depth,N Soil Organic Matter
in. Rate No-Till Conventional _________________________________________
Lb/Acre % %
0-2” 0 3.70 2.1675 5.08 2.41
150 4.82 2.40
2-6” 0 1.88 2.3875 2.21 2.40
150 2.34 2.31 _________________________________________
Ions are Electrically Charged MoleculesCation: Positively Charged Ion +Anion: Negatively Charged Ion -
NutrientCations in Soil Anions in Soil Potassium NitrateAmmonium SulfateMagnesium PhosphateCalcium ChlorideManganese BorateZinc MolybdateHydrogen
NonnutrientsSodium HydroxylAluminum Bicarbonate
Carbonate
Microscopic View of Clay• Layered much like mica
or a deck of cards• Expand and contract with
moisture• Ions like K+ can be
trapped between the layers.
K+
WITH A MAGNET IN THE SOIL
Unlikes Attract Likes Repel Unlikes Attract Likes Repel
CLAY
CLAY
NO3 - NITRATE
PO 4-
PHOSPHATE
CLAY
CLAY
NH4+
AMMONIUM
Ca++ CALCIUM
Surface Charges of Soil Colloids
The Tremendous surface area of soil colloids has a net negative electrical charge.
Clay
NH4+
Ammonium
Unlikes attract Clay -
NONitrate
3-
Likes Repel
Cations Are Not ‘Stuck’ To CEC Sites –They ‘Exchange’ With Cations In Soil Solution
SO=4
Soil Colloid
Cl-
K+ Mg++Ca++ Ca++
NH+4
NO-3
H2PO-4
Na+ Na+
Soil Solution
CEC Sites
Effect of Soil-herbicide Bonding on Herbicide Performance
ClaySoil Solution or Vapor Phase
Herbicide
Organic Matter
Herbicide
Equilibrium reaction, not a permanent bonding to soil
• Cation exchange capacity is the result of permanent negatively charged sites on soil colloids - clays and soil organic matter
• Cations can attach to these sites and detach again in exchange for other cations
• CEC is expressed in mmol per 100 gm soil of soil
How Soil Retains Nutrients
Soil’s CEC indicates several properties
• CEC 15-40 (High)– High clay and humus– More lime needed to
correct pH– Greater capacity to
hold nutrients– High water-holding
capacity
• CEC 1-10 (Low)– High sand content– Less lime needed to
correct pH– Nitrogen and
potassium leaching more likely
– Low water-holding capacity
Cation Exchange Capacity
Soil Texture Type CEC meq./100g.Sands 2-5
Sandy Loam 5-12
Loams 10-18
Silt and Silty Clay Loams 15-30
Clay and Clay Loams 25-40
Soil Colloid Exchange Capacity(meq/100 grams soil)
Kaolinite 3 -15Illite 20 – 40
Montmorillonite 20 – 100Organic Matter 100 - 300
Cation Exchange Capacity
Cation Exchange Capacity (CEC)What Does Soil CEC Do? How Do We Use?
Indicates the soils ability to supply cations
Affects the amount of limestone needed to correct soil acidity
Provides an estimate of soil texture (% clay)
Mobile and Immobile Nutrients
Roots absorb nutrients from the water film
Immobile nutrients, such as P and K, do not move far
Water Film
Soil Colloid
(clay or humus)
Root Hair
Ca++
NH4+
K+
Mg++
NO3-
SO4=
H+
H+
K+
Zn++H+H+
K+
HPO4=
Ca-H2PO4
H+Ca++
H+NO3-
Cation Bonding StrengthCations with greater bonding strengths are held on exchange sites more tightly and are released into the soil water solution less easily than others.
Cation Bonding Strength1. Hydrogen Strongest
2. Aluminum
3. Calcium
4. Magnesium
5. Potassium
6. Ammonium
7. Sodium Weakest
The Concept of the Most Limiting Factor
“Just as the capacity of the wooden bucket to hold water is determined by the height of the shortest stave, crop yields are restricted by the nutrient in shortest supply!”
Seed Root System
Plant depends on the energy reserves from
the seed until permanent roots are
developed
Relative N Uptake for Wheat
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32Weeks after Emergence
Perc
ent N
Upt
ake
JointingJointing
Tillering CompleteTillering Complete
FF MM AA MMJJDDNN
BootBoot
Mechanisms of Nutrient Uptake
Nutrients are absorbed by roots as ions from the soil water or solution.
• Diffusion - movement of ions from a zone of high concentration to a zone of lower concentration. – Short distances: Immobile nutrients
• Mass Flow - movement of ions in soil solution as water moves.– Longer distances: Mobile nutrients
• Root Interception - root grows to the nutrient – Unexplored soil zone
Relative Importance of Soil Supply Mechanisms*
Supply Mechanism, %Nutrient Interception Mass Flow Diffusion
Nitrogen 1 99 0
Phosphorus 3 6 94
Potassium 2 20 78
Calcium 171 429 0
Magnesium 38 250 0
Sulfur 5 95 0
* 150 bu/A corn crop Barber, 1995
Root Competition for Mobile Nutrients
• Roots compete for mobile nutrients with other plants
• Roots compete little for immobile nutrients with other plants.
• What is effect of plant population or weeds on competition for mobile and immobile nutrients?
Nutrient Mobility & Plant Competition
• Mobile nutrients:– Suited to surface
application.– Large root uptake
zone
• Immobile nutrients:– Incorporated.– Limited root uptake
zone
Root Patterns For Several Crops
Potato SugarBeet Soybean Corn Alfalfa
Depth
in
Feet
0
2
4
6
Small Grains
Crop Rooting Patterns
• Crops having deep roots can absorb water and mobile nutrients from the subsoil.
• Fertilization generally increases plant root growth.
• Nutrient mobility and crop rooting patterns affect fertilizer placement.
• Soil Sampling Recommendations:– Sample the surface 0 – 6” depth for immobile nutrients,
such as P and K.– Sample 0 – 24” deep for N, Cl and S since they are soluble,
mobile nutrients.
Review Exercise1. Three essential elements involved in photosynthesis are carbon, oxygen, and hydrogen.
a. True. b. False.
2. Indicate which groups are primary nutrients __________, secondary nutrients __________, and which are micronutrients ____________________:
a. Boron, copper, iron.
b. Nitrogen, phosphorus, potassium.
c. Aluminum, sodium, fluorine.
d. Calcium, magnesium, sulfur.
3. Soil colloids (clay and organic matter) have __________ electrical charges on their surfaces. a. Positive. b. Negative. c. Neutral. d. No.
4 P i i l h d i ll d i hil h i h i h i
5. Which one of the following generally is the largest contributor to CEC in most soils?
a. Sand. b. Silt. c. Clay. d.Humus.
6. __________ is an important plant nutrient in cation form.
a. Potassium. b. Sodium. c. Nitrate. d. Phosphate.
7. CEC, an abbreviation for Cation Exchange Capacity, is an important measure of the amount of cations a soil can hold in an exchangeable form.
a. True. b. False.
88.oils with a relatively high cation exchange capacity of 15 to 40 meq/100 g can generally be expected to have 89.: High capacity to hold nutrients b High sand content
9. __________ and __________ are considered immobile nutrients in most soils while __________ and __________ are mobile nutrients, easily transported by soil water.
a. Na + b. H2 PO4- c. K + d. NO3
- e. SO4
10. Soil sampling of the surface 6-7” soil layer only is recommended for __________ nutrients while deeper sampling is recommended for __________ nutrients.
a. Mobile. b. All. c. Immobile. d. Organic.
111.he judicious use of fertilizer generally increases plant root growth and the ability of roots to forage for water and nutrients. a. True. b. False.
12. Immobile nutrients are taken up by plant roots primarily through:a. Diffusion of nutrient ions to the root
b. Mass flow of water to the root