Transcript Soil Colloids and Soil Chemistry

Potassium, Sulfur,
Calcium, Magnesium
Section K
SWES 316
Potassium in Plants
• First or second in amount taken up by most
plants (N is usually first)
• Main functions
– Osmotic control
– Enzyme activation
• Deficiencies
– Mobile nutrient--firing, spotting, necrosis of leaf
tips or edges, causes weak stems
K Deficiency
Corn
K Deficiency
Alfalfa
Soybean
Nutrient Removal (kg/ha/yr)
N
P
K
N/K Ratio
Broccoli (100 lb yield)
0.44
0.07
0.35
1.25
Celery (100 lb yield)
0.19
0.05
0.42
0.45
Corn (bushel of grain
– 56 lb)
0.75
0.19
0.24
3.0
Alfalfa (ton)
56
6.6
50
1.12
Oranges (ton)
8.8
0.8
9.1
0.97
Source: Plant Nutrient Use in North American Agri., PPI, 2002
Soils Depleted in K
Potassium Fertility
• K is most likely to be deficient under
conditions of:
– Acid, weathered soils
– Sandy soils
– With high K-use crops (e.g. alfalfa)
western part of the U.S., K
• In most of the ______
deficiencies are uncommon
• However, very high crop demand for K can
sometimes create deficiencies in any soil
% of soils testing medium or lower for K
Data from PPI, 2001
Cotton Response to K in AZ
†
Treatment
Soil
Foliar
Lbs of K2O/acre
0
0
0
18.4
200
0
200
18.4
400
0
400
18.4
Lint Yield
‡
DPL 90
Pima S-7
lbs/acre
OSL§
LSD0.05
CV(%)
1089
1008
986
1018
1111
1095
0.30
NS
10
458
511
563
521
538
510
0.40
NS
15
† Potassium source was soil incorporated after planting by banding.
‡Sum
of four 4.6 lb K2O/acre foliar applications using KNO3 as the K source.
§observed
significance level for the treatment differences, or the probability that
there are no differences among treatments
Source: Silvertooth et al., 1996
Grapefruit Response to K in Florida
Initial soil test K = very low
Source: Obreza, Better Crops with Plant Food, 2003
Alfalfa Response to K in Indiana
Initial soil test K = 90
ppm (very low)
Source: Joern et al., Better
Crops with Plant Food, 2003.
Turf Response to K in Georgia
Source: Trenholm et al., Better Crops with Plant Food, 2001
Potassium in Soils
• Almost all soil K is in inorganic forms:
• Minerals
– K-feldspars
– Clays (often called “fixed” K):
• Primary micas (biotite, muscovite)
• Secondary clays (illite)
• Exchangeable
– K+ on cation exchange sites
• Available: K+ in soil solution
from PPI
Interlayer (“fixed”) K in Illite
K in soil clays
Planar position
Inner position
Hydrated and
exchangeable
cation
Inner position
Edge
position
Hydroxy Al (or Fe) islands
Potassium in Clays
• The availability of K+ on clays to plants
depends on position on the clay (micas, illite):
– inner sites - low availability, “fixed” K in illite
– edge sites - moderate availability
– planar sites - high availability “readily
exchangeable”
Potassium Equilibrium in Soils
Soln. K+
Exch. K+
Fixed K+
Mineral K+
Solution
planar sites
edge sites
inner sites
feldspars
K in solution is usually <1% of exchangeable K
Exchangeable K is usually <1% of fixed K
K availability to plants depends on adequate K reserves and fast
reactions to replenish solution K
K-fixing Soils
• The reverse process of K release from clays is called
K “fixation”, and “fixed” K is essentially that in
inner positions of 2:1 clays.
• Some clays, especially illite (hydrous mica), and
vermiculite, can trap or “fix” added K in inner
positions, rendering it unavailable to plants.
Montmorillonite doesn’t fix K.
• Soils high in these clays are known as “K-fixing” soils,
and pose special management problems, e.g.
San Joaquin Valley, CA.
Soil and Plant Tests for K
• The most common soil test for K is an
ammonium acetate extract, which is then
analyzed for K. This test is widely applicable
across many soils.
– “Critical” value often used is 150 ppm.
– This means ____________________.
• Plant tests - total K in plants, or soluble K
tests in plant sap. Guidelines exist for many
crops.
Add a solution of ammonium acetate
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+ +
NH4
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
K+
Ca2+
K+
NH4+
NH4+
Note: Ammonium acetate
extraction will remove only the K+
on planar and edge exchange
sites, and K+ in solution.
Ca2+
Ca2+
Ca2+
K+
NH4+
K+
Ca2+
NH4+
NH4+
NH4+ NH4+
K+
NH4+
NH4+
Ca2+
K+
K+
Ca2+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
K+
Soil with exchangeable cations
Ca2+ K+
Measure amount
of K+ released
Properties of Selected Soils
Soil Series
Total K
(g kg-1)
Exchangeable
K
(mg kg-1)
Clay Mineralogy
Antho
22.0
366
S>MI>K
Gilman
21.1
280
S>MI>K
Glenbar
20.1
257
S>MI=K>Q
Grabe
24.8
549
S>MI>K=CA
Indio
17.3
315
S>MI=K>Q
Pima
26.0
430
S>MI K Q
Casa Grande
29.9
560
S<MI>K<PG
Mohall
27.7
309
S=MI<K
Superstition
31.0
100
S>MI=K=PG>Q
Gadsden
18.1
460
S>MI=K>Q
S-SMECTITE; MI-MICA; K-KAOLINITE; Q-QUARTZ; CA-CALCITE;PG-LYGORSKITE
Calculated Sufficiency and K
Desorption
Soil Series
Sufficienc
y
Level K
(mg kg-1)
Difference between K Desorbed
Exchangeable and Per 30 min.
Sufficiency (mg kg- (mg kg-1)
1)
Antho
143
223
18
Gilman
136
144
17
Glenbar
138
119
15
Grabe
171
378
16
Indio
158
157
12
Pima
169
261
13
Casa Grande
137
423
33
Mohall
141
168
16
Superstition
120
-20
11
Gadsden
173
287
13
Summary of Clay
Mineralogy in Arizona
• Clay mineralogy was a mixed composition of
smectitie, mica, kalonite, palygorskite, calcite,
and quartz.
• All soils contained K bearing mica, typically
associated with high K release rates.
• These soils contained negligiable amounts of
vermiculite, known for a high capacity to fix K.
1600
Pima
Casa Grande
Mohall
Gilman
Indio
K Release, mg kg-1
1400
1200
1000
800
600
400
200
1600
Gadsden
Glenbar
Antho
Grabe
Superstition
K Release, mg kg-1
1400
1200
1000
800
600
400
200
0
0
200
400
600
800
Cumulative Time, hours
Cumulative K released to calcium resin by clays
of ten representative soils on a whole soil basis.
K Release, mg kg-1
10000
Pima
Casa Grande
Mohall
Gilman
Indio
8000
6000
4000
2000
K Release, mg kg-1
0
6000
Gadsden
Glenbar
Antho
Grabe
Superstition
5000
4000
3000
2000
1000
0
0
200
400
600
800
Cumulative Time, hours
Cumulative K released to calcium resin by ten representative soils.
K Fertilizers
• Inorganic:
– Solids: KCl (0-0-60), K2SO4 (0-0-52), KNO3,
(13-0-45) mixed in combination with N, P
– Liquids: Solutions of K solids
• Organic:
– Fresh manures average 1 to 2.5% K, all is highly
soluble and available. Composted organics
contain much less (<0.3% K).
• Remember that K fertilizers are expressed
as %K2O
Potassium Applied in
Irrigation Water
Crop
Broccoli
Melon
Carrots
Lettuce
Onions
Sweet Corn
Irrigation AE=70%
Irrigation
Water (cm)
71
74
60
30
84
71
Irrigation K
(kg ha-1)
50
52
42
21
59
50
Comparison of K Applied in Irrigation
Water and Amount Accumulated by
Crop
Crop
Irrigation K
(kg ha-1)
Broccoli
50
Crop
Accumulation
(kg ha-1)
238
Melon
52
176
Carrots
42
409
Lettuce
21
192
Onions
59
196
Sweet Corn
50
119
600
Soil Test Na (mg/dm3)
500
400
300
200
100
100
200
300
400
500
Soil Test K (mg/dm3)
600
Other Vegetable Crops Showing
Responses to Na when K Limiting
• Celery (Harmer and Benne, 1945;
Harmer et al. 1953).
• Cabbage (Costigan and McBurney,
1983; Costigan and Mead, 1987).
• Lettuce (Pereira and Westerman, 1978;
Burns, 1986; Burns and Hutsby, 1986;
1987; Costigan and Mead, 1987).
• Tomatoes (Figdore et al., 1987;1989).
Sodium Applied in Irrigation
Water
Crop
Irrigation
Water (cm)
Broccoli
55
Melon
60
Carrots
62
Lettuce
27
Onions
79
Sweet
Corn
60
Irrigation
=ET/(1-LR)
Irrigation Na
(kg ha-1)
719
785
806
355
1030
780
Tips for Managing K
• Soil test first!!! Many soils don’t need K.
• K loss is not usually a problem in most soils,
except very sandy soils.
• K does not cause environmental problems.
• Beware of K-fixing soils!
• K can be applied significantly in advance of
plant needs, because of the low risk of loss.
Important Things About Sulfur!
• Plants use about 10% as much S as N.
• S is a lot like N:
– 50-90% in soils is organic (humus, microbes)
– Subject to many microbial transformations
• Atmospheric deposition is important (acid rain)
• Highly weathered soils are most likely to be Sdeficient (except with SO2 deposition)
Air Pollution and Sulfur
Sulfur in Plants
• Plants about as much S as P (10% as much as N)
• Used for:
– amino acids cysteine, cystine, methionine
– proteins, enzymes
– ferrodoxins (necessary for photosynthesis)
• Deficiencies: semi-mobile nutrient, usually
produces chlorosis
S Deficiency - chlorosis of older
leaves or whole plant
Wheat
Corn
Sulfur in Soils
• In humid regions, as much as 90% of S may be found
in organic forms (humus)
– subject to mineralization--immobilization reactions like N
• In arid regions, at least 50% of S is in inorganic forms
Gypsum - CaSO4.2H2O
(minerals, especially ___________________)
SO4 2• The available form of S is ___________.
• Natural (i.e. unfertilized soils) S availability is mostly
related to:
–
–
–
–
Soil organic matter content (more = more S)
Weathering (more = less S)
Soil minerals
Proximity to pollution sources
Atmospheric inputs
• SO2 is an important component of air
pollution. It may react with H2O to form
H2SO4
__________.
• Inputs to soil from the atmosphere may be as
high as 110 kg S/ha/yr.
• Amount of inputs depend on:
– Pollution controls
– Proximity to pollution source
The Sulfur Cycle
• Similar to the N cycle:
– Mineralization--immobilization of S
– Autotrophic S oxidation (pyrites) similar to
nitrification
– S reduction--reduction of SO42- under
anaerobic conditions. Like
denitrification
______________.
– SO42- can leach, but to a lesser extent than
nitrate. Not an environmental hazard.
Sulfide Oxidation
Mine tailings (spoils) may become acidic because of the
oxidation of pyrite (FeS2):
FeS2 + H2O + 7/2O2 → FeSO4 + H2SO4
Sulfur Availability
• Related to:
– Soil pH and weathering - S is usually depleted in
weathered soils
– Irrigation - water often contains lots of sulfate
– Redox - flooded conditions result in S losses
– Texture - sandy soils tend to have less S than
clayey soils
– Pollution - high air pollution with S leads to high
soil availability
Sulfur Fertilizers
• Western soils rarely need fertilization with S:
– Soils not highly weathered
– Irrigation water contains SO42– Amendments added for alkalinity control contain S
• Eastern soils may need S:
– Gypsum (CaSO4.2H2O)
– Potassium sulfate K2SO4
Fertilizing with S
• S is (mobile, immobile) in soils.
• What does this mean about fertilization?
• What about environmental considerations?
Nutrient Mobility in Soil
Soil volume exploited
for mobile nutrients:
N, S
Soil volume exploited
for immobile nutrients:
Most others
Important Things about Ca
• Ca is abundant in many soils.
• Soil pH is largely related to exchangeable Ca2+
(base saturation)
• Most soil Ca is exchangeable Ca2+ or in other
minerals - feldspars, carbonates
• Most western soils have enough Ca for crop
needs.
Ca in Soils
• Total Ca in soils ranges from 0.1 to 25%. It is
arid, semiarid regions.
most abundant in ____________
• Important mineral forms include feldspars and
CaCO3
other primary silicates, and _____________
in semi-arid and arid regions.
• Ca2+ is the available form and the dominant
non-acid
exchangeable cation in _____________
soils.
Mg in Soils
• Total Mg in soils ranges from 0.1 to 4%. It is
arid, semiarid
highest in soils of _______________
regions.
• Important mineral forms include primary
silicates, Mg carbonates, and Mg sulfates.
• Mg2+ is the plant-available form and, next to
non-acid
Ca2+, is a dominant cation in ____________
soils.
Ca and Mg in Plants
• Calcium:
– Strengthens cell walls
– Needed in large amounts by developing fruits
– Immobile in plants, older parts of roots cannot absorb it,
so a supply is needed at growing tip
• Magnesium:
– Central atom of chlorophyll
– Osmotic regulation
– Mobile in plants
Ca Deficiency
Tomato
“blossom-end rot”
Lettuce
“tip-burn”
Mg Deficiency
Potato
Cabbage
Ca Deficiency
• Ca is most likely to be deficient under conditions of:
– weathered, acid soils
– sandy soils
• However, Ca deficiency can occur in surprising
places:
– Fruit crops (High Ca demand)
– Plant structures out of the transpirational stream
– Vegetable crops with small root systems
• Ca deficiency can be difficult to correct:
– Highly immobile in plants
– Highly immobile in soils
– Only taken up by the youngest part of root system
Ca and Mg Fertilization
• The need for Ca and Mg is usually (not
always) related to soil pH:
– Lime adds Ca2+
– Dolomitic lime adds Ca2+ and Mg2+
• Ca and Mg immobile in most soils (except
very sandy soils).
• What does this mean about fertilization?
Ca and Mg Fertilizers
• Ca fertilizers:
– Solids - gypsum, calcium nitrate
– Liquid - calcium ammonium nitrate (CAN-17)
• Mg fertilizers:
– Solids - magnesium sulfate (epsom salts)
– Liquid - magnesium nitrate
• Organics - fresh manures are good sources of
Ca, composted are not.
Special Notes on Ca
• As mentioned before, Ca deficiencies can
occur, even on soils testing “high” in Ca.
• This is most likely to occur with lettuce,
tomatoes, and other fruiting crops.
• Supplying adequate Ca can be a problem foliar applications of soluble materials, soil
side-dressing of Ca fertilizers may be needed.