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CHAPTER 3
FORMS OF SOIL N,P,K
AND OTHER
ELEMENTS
NUTRIENT UPTAKE OF CROPS AND
FACTORS INFLUENCING IT
Prof. K. SÁRDI
NUTRIENT MANAGEMENT
FORMS OF SOIL NUTRIENTS
Nutrients exist in numerous different forms
(called as „nutrient pools” in the soil.
These pools range from soluble to insoluble forms:
soluble (= readily available ions in the soil solution),
weakly bound (= adsorbed, easily exchangeable ions,
also referred as available)
strongly bound (= insoluble, precipitated compunds)
IMPORTANT
Readiliy available and weakly bound forms are in
rapid equilibrium, insoluble/precipitated forms
become available only over long time periods
Conceptual diagram of major nutrient pools and pathways in soil
Available nutrients = can be taken up directly
by roots
ions of readily water-soluble, inorganic compunds in the
soil solution
easily exchangeable by roots, as cations (K+ and NH4+ ) and
anions (H2PO4-, NO3-)
adsorbed (weakly bound) forms:
• anions (e.g. phoshates, sulphates, nitrate) by organic
colloid surfaces
• cations (e.g. K+ and NH4+ ) adsorbed by clay minerals
such as illites, montmorillonites, smectites etc.
Sources of available soil nutrients:
A.) natural sources
Weathering of soil minerals
Decomposition of plant residues, animal remains
and soil microbes
N fixation by symbiotic and other soil
microorganisms (e.g. Rhisobium spp.)
Deposition of nutrient-rich sediment from erosion
and flooding
Atmospheric origin:
•
•
•
Lightning discharges
Acid rain at industrial regions
Atmospheric deposition/dry
B.) Sources under agricultural conditions
Application of mineral fertilizers
Application of manures, composts, sewage sludge
and other organic amendments /wastes/
Application of industrial byproducts
Application of ground rock powders, rock phosphate,
basalt etc.
Non-available nutrients = insoluble, strongly
bound, fixed or precipitated forms
Often called as the nutrient budget of the soil
Strongly fixed cations (K+, NH4+, Mg2+, Ca2+) in
interlayer sites of clay minerals
Structural ions of soil minerals
Nutrients taken up by soil microorganisms
FACTORS INFLUENCING NUTRIENT AVAILABILITY AND UPTAKE FROM
SOILS
MECHANISMS OF ION TRANSPORT TO PLANT ROOTS
3 Mechanisms are known in which nutrients reach the root surface:
- Root interception – physical contact resulted by root growth
- Mass flow – transport to the root as a result of transpiration
- Diffusion movement – resulted by differences in concentration
-
Rates of Root interception, Mass Flow and Diffusion in Ion Transport to Corn
Roots (Havlin et al. 2005)
Nutrient
Root
interception
Mass Flow
Diffusion
movement
Pecentages in Supply
Nitrogen N
1
99
0
Phosphorus P
2
4
94
Potassium K
2
20
78
Calcium Ca
12
88
0
Magnesium Mg
27
73
0
Sulphur S
4
94
2
Nutrient uptake by plants (crops)
-
Nutrient uptake by roots – dominant in nutrition
Nutrient uptake by leaves – additional in nutrition
Nutrient absorption by roots is a process of ion exchange at the surface
-
Ion uptake of plant is characterized by the following:
1.
Selectivity
certain ions (elements) are taken up preferentially
2.
Accumulation
concentration of elements in the plant cell sap can be
much higher than in the external solution
3.
Genotype
there are considerable differences among plant species in
ion
uptake characteristics
passive part 1
Ion uptake
active part 2
1.
Movement of low-molecular-weight solutes (e.g. mostly ions,
organic (amino) acids, sugars) from the external
solution into the cell walls of roots
this process is driven by diffusion or mass flow
2.
Ion uptake is the movement of ions from the soil
solution into the plant root against a concentration
gradient. This is followed by the solute transport across membranes.
The carrier and ion pump systems
Carriers are the specific molecules to carry on ions across the cell
membrane.
Identification of carriers has not been completely determined yet.
This process can be characterized by the following:
-
The ion is attached to a carrier
The combined unit is transported from the root surface into the root
The ion deposited inside the root with the carrier moving back across
the cell membrane to repeat the process with another ion.
Another concept
An ion pumps that assist in the transport of ions across the cell
membrane.
Important
Energy is required for both systems to work, wich is derived from root
respiration.
respiration.
Factors influencing crop nutrition
Internal factors
Genetic factors
Nutrition characteristics
of species and varieties
Morphological characteristics
-
shoot: root ratios
- root development
External faxtors
Environmental factors
- climatic and weather conditions
- water supply
- air (components)
- light conditions (radicance)
soil properties
-
Nutrient requirement, dynamics
-
Temperature requirement
requirement
-
pH tolerance, salt tolerance
- nutrient supply
- soil atmosphere, moisture
water: air ratio
- soil pH, texture
- soil organic matter
- microorganisms
pH TOLERANCE OF SEVERAL CROPS
Acidic
Optimum pH range
is narrow
Tolerant
pH range is relatively
wide
SENSITIVE
Rye
Wheat
Barley, Alfalfa
Potato (sweet and
white)
Corn,
Barley (several
varieties)
Sugarbeet,
Sweetclover
Tobacco,
Cotton
Peas
Soybeans
Beans
Rice,
Sunflower
Cabbage
Canola
Lettuce
Cucumber
Strawberries
Tomatoes
Onions
Buckwheat
Lentil, Radish
Carrots
Source: Brady, 1990)
Optimum pH ranges of different crops
(Havlin et al. 2005)
pH RANGES
CROPS
4.5
Alfalfa
Apples
Barley
Cabbage
Corn
Onions
Peas
Potatoes,
Sweet
Potatoes,
White
Sorghum
Soybeans
Wheat
5.0
5.5
6.0
6.5
7.0
7.5
RELATIVE YIELD OF CROPS AS AFFECTED BY SOIL pH
(in percentages of maximum yield)
pH
CROP
4.7
5.0
5.7
6.8
7.5
Sweet
clover
0
2
49
89
100
Barley
0
23
80
95
100
Alfalfa
2
9
42
100
100
Red clover
12
21
53
98
100
Corn
34
73
83
100
85
Soybean
65
79
80
100
93
Wheat
68
76
89
100
99
Oats
77
93
99
98
100
Source: Field Experiment Station, Ohio, USA 1983
RELATIVE SALT TOLERANCE OF CROPS
Tolerant
Moderately
tolerant
Moderately
sensitive
Sensitive
Barley
Barley, forage
Alfalfa
Apple
Cotton
Broccoli
Broad bean
Apricot
Wheat grass,
tall
Sorghum
Cabbage
Bean
Sudan grass
Corn
Carrot
Bermuda grass
Wheat
Cowpea
Celery
Cucumber
Grapefruit
Lettuce
Lemon
Pea
Onion
Peanut
Orange
Rice, paddy
Peach
Soybean
Sugarcane
Potato
Sugar beet
Strawberry
Tomato
Brady N. (1990)
Principal soil conditions resulting Mineral Stresses
on Plants (Epstein & Bloom, 2005)
Mineral Stress
Characteristics
Salinity
High salt concentrations, mostly
sodium (Na)
Sodicity
Excess (more than 10 %)
percentage of Na in the cation
exchange sites
Heavy metal and Al toxicities
Common in acid soils, due to the
increased solubility of these metals
Micronutrient deficiencies
Common in calcareous soils, due
to the low solubility level of these
elements (insoluble, precipitated
forms)
Low Ca/Mg ratios
Serpentine soils with Ca/Mg ratio
1:1 or lower (optimum is 2:1 to 3:1)
Low soil fertility
Low levels of available nutrients,
mostly N and P
Soil Conditions Resulting Shortages of Available Nutrients and
Inducing Nutrient Deficiencies for Crop Plants
Nutrient
Soil Conditions resulting Shortages in availability - inducing deficiency
N
Excess leaching with heavy rainfall low organic matter content of soils,
burning the crop residue
P
Acidic, organic, leached, and calcareous soils, high rate of liming
K
Sandy, organic, leached, and eroded soils, high liming application,
intensive cropping system
Ca
Acidic, alkali, or sodic soils
Mg
Similar to calcium
S
Low organic matter content of soils, use of N and P fertilizers containing
no sulfur, burning the crop residue
Fe
Calcareous soils, soils high in P, Mn, Cu or Zn, high rate of liming
Zn
Highly leached acidic soils, calcareous soils, high levels of Ca, mg, and
P in the soils
Mn
Calcareous silt and clay, high organic matter, calcareous soils
B
Sandy soils, naturally acidic leached soils, alkaline soils with free lime
Mo
Highly podzolized soils, well-drained calcareous soils
Source: Fageria et al., 1991.
AVAILABILITY RANGES OF NUTRIENT ELEMENTS DEPENDING ON
SOIL pH
Maximum availability for the majority of
nutrients: at pH = 6.5 i.e. under slightly
acidic conditions
Availability of metal cations (mostly
microelements) increases with acidity,
with the exception of Molybdenum.