Highly Weathered Soils and
Tropical Environments:
Opportunities and Constraints
Russell Yost
Tropical Plant and Soil Sciences
University of Hawai`i at Manoa
Honolulu, Hawai`i
Goals – Opportunities and Constraints with
Highly Weathered Soils
• Food security
– High diversity of crop types (both annual and
perennial) relative to temperate crops 
Stability of production systems
• Environmental Health
– Opportunity for perennial cover of soil 
improved conservation
Highly weathered soils - Constraints
• Tropical environments: vs Temperate
– Affecting Productivity, Stability, Resilience
• Climate and Weather
– Day length is shorter and fewer days with optimal degree-day energy leading to
lower genetic potential of crop productivity.
– Tropical, sub-Tropical environments often are characterized by high intensity
rainfall, which can challenge water and nutrient management and conservation
• Greater soil weathering leading to:
– Nutrient insufficiencies, both less nutrients and less nutrient retention capacity –
lower ECEC
– Element toxicities of Al and Mn
– Affecting Environmental Health
• Nutrient leaching an increased concern
– Higher rainfall intensity, soils with lower water holding capacity
• Conservation agriculture more difficult in annual cropping systems
– High intensity rainfall can challenge water and nutrient management and
conservation
Food Security
• Desirable characteristics of
food production systems:
– “Productivity” – large quantities
– “Stability” – sustained production each year
– “Resilience” (previous “Sustainability”)
• ability to restore production
– “Equitability” – all members of society have access.
– “Autonomy” – low dependence on outside input
Conway’s Characteristics of agroecosystems. 1987; Cuc, Gillogly,Rambo. 1990.
Agroecosystems of the Midlands of North Vietnam. East-West Center, Honolulu, HI
A structure for information in problemsolving soil constraints:
• Four components
– “Diagnosis” – “Does a problem exist?” Is special
attention / management needed?
– “Prediction” – “How to fix the problem?” What
does science say is needed?
– “Economic Analysis” – “Is the proposed solution
(Prediction) feasible and profitable?”
– “Recommendation” – “How to best inform /
transfer the above information to the grower, user,
producer?” Assist in learning the process.
Yost et al., 2012. Efficient Decision-making in Agriculture. Intech Press.
Highly weathered soils --Characteristics
affecting productivity
– Acidity – Al, Mn toxicity and the “soil acidity
syndrome”
• Toxicities of Al, Mn, and H+
• Low nutrient content and retention (ECEC)
– Phosphorus – usually high reactivity,
• Acid soil reactions – presence of alpha hydroxls,
largely a consequence of mineralogy
• Calcareous soil reactions – still often an issue in
Tropics – coastal, reef systems
Effects of Al on root growth and water utilization
Table. Cotton grown on a Paleudult soil.
Root wt.
Subsoil pH
% of total
% of available water extracted
> 5.0
50
80 – 100
< 5.0
14
40 -- 70
Doss & Lund Agr. J. 67:193.
Photo: Credit Dr. N.V. Hue and
J. Hanson, University of Hawai`i
Crotolaria juncea, L. on a high Al soil. Photo:
7
Credit R. Yost, University of Hawai`i
Effects of Al on root growth
Translocation of Ca from roots to tops was decreased by
Al: Blockage of the apoplastic pathway?
Drawing: Wikipedia: Apoplast, Oct. 2012
8
Constraints to Productivity
Acidity – High soil Mn
• Manganese toxicity
Mn toxicity
symptoms on
cowpea Vigna
unguiculata. L.
on Wahiawa
soil, Hawai`i
(highly
manganiferous
soil). Normal
leaf on left, Mn
toxic leaf on the
right.
9
Constraints due to Acidity – Mn
toxicity
• Mn toxicity -- a balance between rate of
Mn absorption vs. rate of plant growth
– How to assess / compare the two rates?
• Relative Absorption Rate (RARMn) - Mn absorption
per unit of Mn already contained in the plant.
• Relative Growth Rate (RGR) - Growth as a fraction
of the existing growth (biomass). (See Radford,
Crop Sci. 3:171-175. )
Relative Absorption Rate: Rufty, Agr. J. 71:638; Jocelyn Bajita, 2003,
The Dynamics of Manganese Toxicity. Ph.D. Dissertation. University of
Hawai`i.
10
Constraints due to Acidity - Review
• Aluminum toxicity
– Reduced root growth caused by impaired cell
division resulting in impaired growth and
function. Probably resulting from DNA
disruption
– Reduced Ca translocation to plant tops –
apoplastic absorption pathway may be closed
by Al.
– Reduced P sorption due to precipitation with
Al in roots, free space, and cell walls
11
Constraints due to Acidity - Review
• Manganese toxicity
– No major effect on roots, top growth reduced
– Concentrates in plant leaves, often margins
leading to crinkling
– Appears to be nearly passive transport due to
transpiration (mass flow).
– Not usually common at soil pH > 6.5, except in
Hawai`i on manganiferous soils
• Proton (H3O+) toxicity
– Occurs but not usually serious unless soil pH is <
4.0 on mineral soils.
12
Limited nutrient content and
retention capacity
• Leaching losses may be greater: Higher
rainfall intensity, lower soil silt content, less
water retention by soil
– Nutrient loss by leaching – higher in general
– Ca, Mg
• Low retention capacity due to acidity
– Variable charge soils (Al & Fe oxides) have
less charge in acid soil (pH dependent
charge)
Constraints to Productivity – Low Nutrient
Content and Capacity (low ECEC)
• Type of charge on soil minerals and
dominant soils.
– CEC= Sc*Cc example: Vertisols
– CEC= Sc*Cv example: Oxisols & Ultisols
– CEC= Sv*Cv example: Andisols
• S= specific surface (m2 g-1), c= constant, v= variable,
C= surface charge density (esu m-2), (c=constant,
v=variable)
Uehara and Gillman. 1981. The Mineralogy,
Chemistry, & Physics of Tropical Soils with Variable
Charge Clays. Westview Press.
14
Constraints to Productivity – Ameliorating
Soil Acidity or improving plant tolerance
• Two options
– Change the soil to meet the plant
requirements (traditional) – lime the soil
• May alleviate toxicity locally, but maybe lime is
expensive or not available
– Change the plant to match extensive soil
conditions – find adapted species / varieties
• May alleviate toxicity, but does it alleviate problems
with low nutrient content?
15
Constraints to Productivity – Ameliorating
Soil Acidity or improving plant tolerance
• Change the soil to meet the plant
requirements (traditional)
– Neutralization of soil acidity:
3Al3+ + CaCO3 + 6H2O = 3Al(OH)3 + Ca2+ + HCO3 - + 2H+
| H2O + CO2↑
– The neutralization of acidity by lime (CaCO3 ) is usually based
on two properties:
• Fineness of the material (% passing sieves: )
• Neutralization value relative to CaCO3 -
16
Alleviating toxicities: Liming
Liming material – Chemical quality
CCE (Calcium Carbonate
Equivalent)
CaCO3 (Calcite)
100
CaO (burnt lime)
179
CaMg(CO3)2 (Dolomite)
109
Ca(OH)2
136
MgCO3
119
CaSiO3
86
Limestone Quality – Physical properties
Limestone particle size (passing mesh)
Effectiveness
Retained on 8 mesh
0
Passing 8 mesh retained on 60 mesh
50%
Passing 60 mesh
100%
Tisdale and Nelson: Soil Fertility and Fertilizers. Macmillan
17
Constraints to Productivity –
Neutralization of soil acidity
– Neutralization of soil acidity:
3Al3+ + CaCO3 + 6H2O = 3Al(OH)3 + Ca2+ + HCO3 - + 2H+
| H2O + CO2↑
– What matters most is the anion:
• Al3+ + CaCO3 (lime)  Al(OH)3 – adds Ca and
increases pH – Very effective
• Al3+ + CaSO4 (gypsum) – adds Ca but doesn’t increase
pH and does complex with Al to reduce toxicity as
complex Al – SO4 species. Not so effective
• Al3+ + CaSiO4 (silicate slag) – adds Ca and does
increase pH. Effective
• Al3+ + Ca(NO3)2 (calcium nitrate) – adds Ca and but
doesn’t increase pH. Not so Effective
18
Constraints to Productivity –
Neutralization of Soil Acidity
• Exchangeable (KCl-extractable Al) as a criterion for lime
application (Kamprath, SSSAP 34:363.)
Maize: (Zea mays, L.)
% Al saturation
Soil pH
% Relative Growth
68
4.4
18
44
5.1
98
27
5.6
100
Upland rice (Oryza sativa, L.)
% Al saturation
Soil pH
% Relative Growth
63
-
40 – 80
40
-
100
19
Constraints to Productivity –
Neutralization of Soil Acidity
• Calculating the amount of limestone
necessary to neutralize toxic Al:
– Cochrane et al. – used Al as a liming criterion,
but adjusted for variation in plant tolerance of Al:
• Lime needed (cmolc kg-1)=1.5[Al – RAS(Al+Ca+Mg)
/100 ]
– Where Al, Ca, Mg are KCl-extractable cations measured in
the original soil.
– RAS – required %Al saturation of the particular crop. Varies:
e.g. RAS of mungbean=0, Cowpea=40, Maize=20, Upland
rice=60, Sugarcane=75%.
- Cochrane et al. An equation for liming acid mineral soils to
compensate crop aluminum tolerance. Trop. Ag.57:133.
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Constraints to Productivity – Ameliorating
Soil Acidity or improving plant tolerance
• Option 2 – Change the plant for soil
conditions – select a tolerant species
– Select or change the plant to match extensive
soil conditions – find adapted species
• Many plants tolerate high levels of toxic Al:
– Tea, azalea, pineapple, rye, cranberry, bermudagrass, star
grass, buckwheat, peanut, Proteaceae family, pangola
grass, brachiaria grass, rubber, blueberry, Norway spuce
(Kamprath and Foy, 1985)
21
Constraints to Productivity – Ameliorating
Soil Acidity or improving plant tolerance
• Option 2 – Change the plant for soil conditions
– select a tolerant variety within a desired
species
– Select or change the plant to match extensive soil
conditions – find adapted varieties
• Many plants have varieties with high acidity tolerance:
– Rice,alfalfa, tomato, soybean, ryegrass, snap bean, cotton,
maize, sunflower, pea, sweetpotato, green algae, and among
pathogens.
– Taro (Calisay, personal communication 1995)
– Modern rice varieties can tolerate as much as 75% Al
saturation (CIAT, Colombia).
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Constraints to Productivity – Ameliorating
Soil Acidity or improving plant tolerance
• Option 2 – Change the plant for soil conditions
– Select or change the plant to match extensive soil
conditions – find adapted species / varieties
• Very successful approach: wheat, rice, soybean, sorghum
• Problem: Does tolerance to Al provide tolerance to Mn?
– Not always: Ex. Desmodium ovalifolium – Al tolerant, but is highly
susceptible to Mn toxicity.
May be related to avoidance mechanism.
Organic acids in the
rhizosphere.
• Note: overliming
above pH 6.0 can be
serious.
23
Variation in soil reactivity to added
phosphorus
Prediction – case of P
bc  b0
Preq 
* a1 * d * BD * placement factor
a2
•
•
•
•
•
•
•
•
Where: Preq=Predicted amount of P fertilizer
bc = Critical level of P for specified crop
b0 = Measured extractable P in the field
a2 = P buffer coefficient (PBC, increase in extractable
P per unit added P)
a1 = slow reaction coefficient
d = depth of incorporation(value of 10 to 20cm typical)
BD = bulk density
placement = function of the fraction of row width
fertilized
25
Crop property
Prediction – case of P
bc  b0
Preq 
* a1 * d * BD * placement factor
a2
•
•
•
•
•
•
•
•
Where: Preq=Predicted amount of P fertilizer
bc = Critical level of P for specified crop
b0 = Measured extractable P in the field
a2 = P buffer coefficient (PBC, increase in
extractable P per unit added P)
a1 = slow reaction coefficient
d = depth of incorporation
BD = bulk density
placement = function of the fraction of row width
fertilized
26
Prediction – case of P
bc  b0
Preq 
* a1 * d * BD * placement factor
a2
Soil factors
•
•
•
•
•
•
•
•
Where: Preq=Predicted amount of P fertilizer
bc = Critical level of P for specified crop
b0 = Measured extractable P in the field
a2 = P buffer coefficient (PBC, increase in
extractable P per unit added P)
a1 = slow reaction coefficient
d = depth of incorporation
BD = bulk density
placement = function of the fraction of row width
fertilized
27
Prediction – case of P
Soil management factors
bc  b0
Preq 
* a1 * d * BD * placement factor
a2
•
•
•
•
•
•
•
•
Where: Preq=Predicted amount of P fertilizer
bc = Critical level of P for specified crop
b0 = Measured extractable P in the field
a2 = P buffer coefficient (PBC, increase in
extractable P per unit added P)
a1 = slow reaction coefficient
d = depth of incorporation
BD = bulk density
placement = function of the fraction of row width
fertilized
28
Summary:Constraints
• Acidity – Adjust the soil or Change the
plant
• Low nutrient content and capacity –
variable charge soils
• High P sorption capacity
• Apply principles of Precision Agriculture:
The right kind, the right amount, at the
right time in the right place.
Summary:Constraints
• Use a structure of information:
– Diagnosis of problem – grower skill
– Prediction of solution – scientific input
– Economic evaluation -- scientific input
– Recommendation to be given to the grower,
producer – Develop information tools:
software, social media, depends on the
grower producers.
Deep appreciation to:
• China Agricultural University,
– Professor Fuzuo Zhang, China Agricultural
University, (Funding and Support)
– Professor Xinping Chen, China Agricultural
University,
– Professor Yuanmei Zuo, China Agricultural
University, Organization, Communication
• Chinese Academy of Agricultural Science
hosts (CATAS)
Thank you
• Questions please!