the least limiting water range and - ufpr · adv. soil sci., 1985. the introduction of nlwr =>...
TRANSCRIPT
The Least Limiting Water Range and other “indicators”: the threat they represent for soil physics in Brazil
Quirijn de Jong van [email protected]
My interpretation of some messages transmitted at this meeting
Dennis Timlin: Soil physics is needed in crop growth modeling – and much more information is needed
Nelson da Costa: Advanced mathematics is an important tool
Marcel Schaap: We should not forget about the uncertainty in our parameters, and learn how to deal with that
Luiz Pires: Advanced techniques are available and being developed, also in Brazil
Nunzio Romano: Field capacity: do we need it in soil physics?
Round Table 1: The importance of data acquisition and spatial and temporal data management - aspects of scale and resolution.
Jan Vanderborght: Root water uptake and plant transpiration can be modeled in 3D using soil physical and plant physiological parameters
SOIL PHYSICS
Modeling and measurement of soil physical properties
Predicting behavior of “natural” or “managed” ecosystems
SOIL QUALITY (Warkentin and Fletcher, 1977)
“fitness for use” (Larson and Pierce, 1991)
“the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation” (Karlen et al., 1997, Soil SSSA Ad Hoc Committee on Soil Quality)
“a measure of the condition of soil relative to the requirements of one or more biotic species and or to any human need or purpose”
Soil physical knowledge should be linked to modeling
• Prediction of system behavior
• Concept• Development• Calibration• Validation• Sensitivity analysis
XXVII
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RM S (kg kg-1 d-1)
MS (kg ha-1)
Input parameter
Ou
tpu
t p
aram
eter
The sensitivity of a model output to an input parameter indicates the (im)possibility of excluding that parameter for predictionpurposes!
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RM S (kg kg-1 d-1)
MS (kg ha-1)
Some common “indicators” of soil physical quality
• Bulk density• Aggregate stability• OM content• Available water• …
The quality of an indicator depends on its capability of representing those soil attributesto which the (state-of-the-art) model shows sensitivity
the search for a single “indicator” for “soil physical quality” is, probably, an irrational effort – mission impossible”
LeteyAdv. Soil Sci., 1985
The non-limiting water range (NLWR)LeteyAdv. Soil Sci., 1985
The introduction of NLWR => LLWR in the Brazilian soil physics world by Álvaro da Silva (ESALQ/USP) in the 1990s
The Brazilian follow-up: 11700 hits on Google Scholar, 3960 since 2011 for “Intervalo Hídrico Ótimo” –IHO = LLWR.
NONE of these
publications evaluated the adequacy of the LLWR to describe the soil quality
prpwpairfcLLWR ,max,min,0max
The definition os the LLWR as usedsince the 1990s in Brazil:
fcair pwp pr
hfc = -10 kPa air = s -0.10 hpwp = -1500 kPa pr ~ 2 MPa
Wat
er c
on
ten
t
Bulk density
s = 1 – r / rs
air = s - 0.1fc
pr
pwp
… and a very popular type of graph
“critical” density
Is this the challenge? Is this SOIL PHYSICS?
Is this Modeling and measuring soil physical properties ?Is this Predicting system behavior ?
Wat
er c
on
ten
t
Bulk density
s = 1 – r / rs
air = s - 0.1fc
pr
pw
p
“critical” density
prpwpairfcLLWR ,max,min,0max
fcair pwp pr
hfc = -10 kPa air = s -0.10 hpwp = -1500 kPa pr ~ 2 MPa
pr saturation
0 pwp fc air
LLWR?
Drought stress
Mechanical stress
Anoxic stress
21
crit
Thinking about the limiting water contents …
Challenge #1
FIELD CAPACITY
hfc = -10 kPa ??
RBCS 12:211-216, 1988
Challenge #1
FIELD CAPACITY
hfc = -10 kPa ??
Simulation of a drainage
experiment:Pressure head versus depth
at the instant corresponding
to qbot = 1 mm d-1 for five
soil depths
Challenge #1
FIELD CAPACITY
hfc = -10 kPa ??
Challenge #1
FIELD CAPACITY
In non-layered soils:
Challenge #1
FIELD CAPACITY
qfc = 0.1 mm d-1
a = 1.5 m-1
hfc ≠ constant!
330
Challenge #2
PERMANENT WILTING POINT (or critical water content?)
hpwp = -1500 kPa ??
Challenge #2
PERMANENT WILTING POINT (or critical water content?)
loamy clay
loamy sand
loamy clay
loamy sand
h, -cm h, -cm
h, -cm
K, m
m d
-1
M, c
m2
d-1
MLC
/ M
LS
h
hl
dhhKM
Matric Flux Potential M
Challenge #3
LIMITING AIR-FILLED POROSITY
air = s - 0.10
Wouldn’t that depend on…and…and……
Challenge #3
LIMITING AIR-FILLED POROSITY
Challenge #3
LIMITING AIR-FILLED POROSITY
103
min22
22
max
min42
p
p
DOO
ZSa
atm
a
Challenge #4
LIMITING PENETRATION RESISTANCE
• Real value depends on crop type, health, DVS, …• Measuring instruments do not mimic root
growth strategies• Corresponds to dry conditions – relevance?
pr ~ 2 MPa
Challenge #4
LIMITING PENETRATION RESISTANCE
Wat
er c
on
ten
t
Soil density
s = 1 – r / rs
air = s - 0.1fc
pr
pwp
“crítical” density
Challenge #X
How to handle the LLWR in layered soil profiles?
hfc = -1
0 kP
a
a
ir = s -0
.10
hp
wp
= -15
00
kPa
p
r ~ 2 M
Pa
soil PHYSICS?
SOIL PHYSICS =Modeling and measuring soil physical properties Objective: predicting the behavior of “natural” or “managed” ecosystems… and you can never do that by measuring alone.
So what can we conclude about the LLWR?
It is a classical concept that comprises some of the most limiting soil attributes to crop growth;
Its value cannot be assessed in a simple manner and depends on soil, crop and atmospheric conditions that vary over time;
It is incapable of dealing with vertical heterogeneity in terms of soil and plant (rooting) properties;
The LLWR (or any other ‘indicator’) is not the way towards increased soil physical understanding and should notguide our research (although it will implicitly be in our minds while performing specific investigations).
BUTWHY do I consider the LLWR (together with other “indicators”) a threat to soil physics in Brazil?
SOIL PHYSICSIndicators, quality, S, LLWR
Thank you for your attention!
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0.010.1
1
10100
1000
dep
th, m
hydraulic conductivity, mm d -1
1 d
q bot=
13.4
mm
/d
0.60 m
3 d
q bot=
4.3
mm
/d
9 d
q bot=
1.3
mm
/d
27 d
q bot=
0.38
mm
/d
81 d
q bot=
0.11
mm
/d
0 d
0.01
0.1
1
10
1
10
100
Bott
om fl
ow, m
m d
-1
Time of redistrib
ution, d
0.60 m
t interval for
qbot= 1 mm d
-1
qbotinterval fo
r
t = 11 d