Unit 4: Nutrients

Chapter 7

Unit 4: Nutrients

Unit 4 Objectives: Understanding of essential plant

nutrients and their roles Nutrient action in the soil Knowledge of soil testing and

interpreting nutrient needs Soil pH and how it affects nutrient

availability Deficiency symptoms

Unit 4: Nutrients Essential Nutrients and their Roles

Chemical elements needed by plants for normal growth and development called nutrients

16 essential elements divided into groups Nonmineral elements

C, H, O H & O supplied from carbon dioxide and water

through photosynthesis Primary Minerals

N, P, K

Unit 4: Nutrients Secondary Minerals

Ca, Mg, S Micronutrients

B, Cl, Cu, Fe, Mn, Mo, Zn

Mineral nutrients supplied by the soil through nutrient uptake

Sugars produced by photosynthesis are responsible for most plant growth

Unit 4: Nutrients

Fertilizers Added to soil to help supply needed

macro- and/or micronutrients N

One of the most abundant and mobile nutrients

Part of every plant cell Soils may contain ~5000 lbs./ac. 78% of Earth’s atmosphere

Unit 4: Nutrients Part of chlorophyll What do we observe when N is lacking?

Starts at the tips of lower leaves Slower growth Spindly stalks and stems

Manufactured most commonly into what form? How is it made? What else can be manufactured?

Unit 4: Nutrients N and the Environment

Very mobile Very susceptible to many physical, chemical,

and biological processes Significant losses are possible

Where does it go? Leaching, erosion, denitrification,

volatilization >50% of all N supplied to the soil may never

be used by the crop Nitrification

Regardless of how N is applied to the soil, it ends up in Nitrate form

Unit 4: Nutrients Process converts ammonium from organic

matter or fertilizers to nitrate Only ammonium not converted is trapped

by soil clays Performed by soil bacteria

Once converted to nitrate, becomes part of soil solution

Leaching Nitrates held only slightly by soil colloids

and humus (why?) Move w/ soil water Ammonium is held tightly in the soil (why?)

Unit 4: Nutrients Nitrate losses during the growing season in

medium and fine-textured soils estimated at <5% (greater in coarse-textured soils)

Erosion Nitrates primarily lost in runoff water Ammonium and organic forms of N lost in

sediment Denitrification

Occurs only under anaerobic conditions Bacteria convert nitrate back to N gas Estimated losses of 15-30% of total applied

N from an area flooded for just 3-5d

Unit 4: Nutrients Losses from well-drained soils usually small

Volatilization Occurs when urea converted to ammonium

carbonate when applied to warm moist soils Breaks down into ammonia gas Lost into atmosphere if this occurs on the

soil surface Usually <10%, but can be great if urea is

topdressed, then followed by 3+d of warm dry conditions

Incorporation or injection will eliminate this loss

Unit 4: Nutrients Nitrogen Cycle

Must be pulled from the atmosphere to be used by plants Fertilizer plants N fixation by green plants

N can take many forms from atmosphere to soil to plant and back

Nitrogen Fixation Elemental N removed from the atmosphere by

soil bacteria called rhizobia Live on nodes of legume plant roots Can provide more N to the soil than they

use

Unit 4: Nutrients Organic Matter (Humus)

Decomposition/decay of plants into soil organic matter

Rate of decomposition & amount of N released depends on C:N ratio <25:1 – plant/animal residues are quickly

converted to large amounts of N that can be used by growing plants

Conversion process called mineralization >25:1 – N is immobilized in the soil,

decomposition is slow, bacteria rob N from the soil, N deficiencies can occur

Unit 4: Nutrients Material that has completely decomposed

called humus C:N ratio of ~12:1 Controls the release of N in soil Humus contains ~5% N Soil w/ 1% organic matter will have ~1000

lbs. N/ac. (only ~2% is available annually)

P Very immobile

Only moves if soil particles move Lost via plant removal and erosion

Unit 4: Nutrients Must be near plant roots to be used Soil Reactions

Soil P amounts closely related to pH Maximum availability at slightly acid pH P will form insoluble compounds w/ other

elements under higher or lower pH’s P Sources

DAP & Triplesuperphosphate are main fertilizer sources DAP generally used in dry bulk fertilizers TSP available in bags/bulk

Unit 4: Nutrients Other sources include:

Animal manure, sludge, plant residues, etc. Mineral Apatite – main source for P fertilizer

manufacturing Mined in: FL, NC, WY, MT, TN

K Second most-used nutrient Also relatively immobile Most common deficiency symptom is

scorching or browning along leaf margins or lower/bottom leaves

Unit 4: Nutrients Soil Reactions

Found in greatest quantity in the soil, available amounts are relatively small Most tied up w/ other soil minerals Considerable amounts trapped between clay

particles K Sources

Most K is mined from deposits found from ancient seas Largest deposit in Saskatchewan, CAN

Muriate of Potash most common source of K fertilizer

Unit 4: Nutrients

Secondary & Micronutrients Just as important for plant growth, but

needed in much smaller amounts S

Most present in organic form Becomes available upon decomposition of

organic matter Mineralized to sulfate form

Subject to leaching and immobilization by microbes

Unit 4: Nutrients May be supplied from atmosphere by rain May be present in some lower-grade

fertilizers as an impurity Gypsum can be used to increase soil S

levels Plants absorb in sulfate form Constituent of amino acids, proteins,

vitamins, enzymes Also contribute to distinct odors

Mustard, onion, garlic Required for N fixation

Unit 4: Nutrients Ca

Supplied by soil minerals, organic matter, fertilizer, lime

Primary ion on CE sites Essential part of plant cell wall structure Helps w/ transport/retention of other

nutrients Provides strength Critical balance w/ Mg and K

Abundance of one can cause deficiencies of the other two

Unit 4: Nutrients Mg

Sources Soil minerals, organic matter, fertilizers,

dolomitic limestone Held on CE sites like Ca, K Part of chlorophyll and essential for

photosynthesis Activates many plant enzymes Relatively mobile in the plant

Can be translocated from older to younger plant parts to prevent deficiencies

Unit 4: Nutrients Micronutrients

Most apt to limit crop growth under several conditions Highly leached acid sandy soils Muck soils Soils high in pH or lime Soils heavily cropped and fertilized w/

macronutrients Fe

Essential for chlorophyll synthesis Part of many plant organic compounds Antagonist w/ Mn

Unit 4: Nutrients Cu

Essential for growth Activates many enzymes Deficiencies interrupt protein synthesis Excess Cu can cause Fe deficiency

Mn Absorbed in ionic form Believed to activate many enzymes Antagonist w/ Fe Availability closely related to soil pH

Deficiencies can occur in slightly acid/alkaline soils

Unit 4: Nutrients Zn

Controls synthesis of indoleacetic acid which dramatically regulates plant growth

Also active in enzyme activity Mo

Important for enzymatic activity, N fixation Inadequate Mo can cause N deficiencies Required in minute amounts

B Regulates the metabolism of CHO in plants Needs vary w/ crop, and high levels may

damage B sensitive crops

Unit 4: Nutrients Nutrient Availability & Plant Uptake

Nutrients must be available in the soil in forms the plant can absorb to be effective

Absorption occurs when plant roots come into contact w/ soil solutions that contain these nutrients

Nutrients held by soil particles Although large amounts of nutrients may be

found in the soil, small quantities are actually available

Unit 4: Nutrients Unavailable nutrients may be found in the

following forms: Insoluble chemical compounds – P and micros Unweathered or Undecomposed soil minerals –

most all nutrients can be in this form Organic Matter or Plant Residues – mostly N or

S Trapped by Soil Particles – lots of K, some

ammonium Greatly affected by soil pH

Unit 4: Nutrients Nutrient Interactions

How one nutrient may help/hinder the uptake of another Conditions may affect Nutrients may also vary

Examples: Ammonium-potassium: ammonium can

interfere w/ K uptake, can create K deficiencies in some crops

K-Mg: K can reduce uptake of Mg at high rates, can result in Mg deficiencies

Unit 4: Nutrients P-N: P uptake increased in presence of N P-Zn: high P can reduce uptake of Zn

Soil pH Acid/base balance of the soil Highly acid/alkaline soils can negatively affect

nutrient uptake and/or production Causes of Acid Soils

High losses of Ca, Mg, K from erosion, leaching, and crop removal

Conversion of ammonium to nitrate results in soil acids

Unit 4: Nutrients Adjusting Soil pH

Can be easily adjusted to any desired range Adjustments should only be made based on

soil test results What would we apply to adjust soil pH

up/down? What are the recommended pH ranges for

some common crops? (See pg. 155) Lime Sources

Most economical source is ag lime

Unit 4: Nutrients Dolomitic – contains Mg

When might we use this? Calcitic – contains only Ca Functions

“Sweetens” the soil (most plants don’t prefer acid soils)

Improves availability of plant nutrients Increases effectiveness of applied N, P, K Increases microbe activity, especially for N

fixation and decomposers Improves plant growth and yields

Unit 4: Nutrients

Soil Testing Most accurate method for determining

fertilizer needs Measures soil pH and available nutrients Most fertilization problems associated w/:

lack of/improper use of N, P, K, and lime

Unit 4: Nutrients Collecting the Sample

Must be a representative sample Take a large composite sample Mix for one representative sample Each sample shouldn’t represent >10 ac.

How do we collect a sample? What are some new technologies being

used?

Unit 4: Nutrients

Foliar Symptoms Vary w/ plant species What other things can produce foliar

symptoms? Suspicion of nutrient deficiencies should

be confirmed w/ other diagnostic methods

Unit 4: Nutrients Tissue Testing

Rapid Tissue Testing Green tissue collected for analysis Chemicals used to test for present elements Accuracy may be sacrificed for speed Dry tissue testing more accurate

Dry Tissue Testing Uses dry leaves or plants Entire leaf ground up and tested for selected

nutrients Should be very accurate

Unit 4: Nutrients More expensive and time-consuming

compared to Rapid Testing or Soil Analysis Plant part sampled and stage of

development critical to interpretation of results

Choosing the Fertilizer Source Many fertilizers available to supply

needed nutrients If fertilizer supplies only one nutrient –

called straight material (urea, muriate of potash)

Unit 4: Nutrients If contain each of 3 primary nutrients –

called complete or mixed fertilizer Can be purchased bag or bulk How do we determine N, P, K amounts in

a fertilizer? What forms are they in?

Solid or Liquid Fertilizer? Performance is equal if equal amounts are

applied Makes little difference to the plant

Unit 4: Nutrients Selection should be made based on:

Availability Economics Other factors

Fertilizer Placement Soil characteristics, crop, nature of

fertilizer material should be considered when determining method of application

Things to consider: Provide adequate nutrient quantities in the

root zone

Unit 4: Nutrients Irregular distribution can lower

effectiveness of fertilizer Early seedling stimulation usually

advantageous – fertilizer should be placed near seedling roots

Rate and distance of fertilizer movement depend on the soil, can be carried up in dry conditions, or down in wet conditions

Fertilization in dry conditions may do more harm than good to the plant

N, K more readily soluble than P and should not be placed in as high a concentration near plant roots

Unit 4: Nutrients Reduction in soil moisture increases salt

concentration and can result in crop injury P should be placed in the root zone due to

immobility Banding fertilizers can reduce rates by 50%

compared to broadcast Slows conversion of P to unavailable forms

Foliar Fertilization Feed plants through leaves, stems, etc. Should only be used in a supplementary role Can only apply in small amounts (why?)

Unit 4: Nutrients Can be expensive Most appropriate to supplement micros

Other Fertilization Sources Animal Manures

Nutrient concentration is generally low, but some quantities of all nutrients are present

Nutrient content may be variable What might affect this?

General Rules of Thumb: ~16T on manure produced/hd/yr regardless of

species

Unit 4: Nutrients Adding superphosphate to manure can reduce

ammonia volatilization Not appropriate for intensive livestock

operations (why?)

Hydroponic Requirements What is hydroponics? Can be especially effective for some

vegetables (spinach, tomatoes) Bath plant roots in nutrient solution

Must be changed weekly due to plant depletion

Unit 4: Nutrients Avoid problems w/ weeds, soil textures,

diseases Must balance all chemical and physical

conditions properly to work All essential plant nutrients must be

supplied in solutions Imbalances of elements can cause serious

problems

Unit 4: Nutrients

Unit 4 Assignment: Chapter Review Questions pgs. 165-166

#’s 6-10, 12-15 Each question 2 points Due next class!