soil testing: what it does and where is it going?...soil testing: what it does & where is it...
TRANSCRIPT
Soil testing: what it does and where is it going?
Karen Daly
Teagasc
Soil Fertility Conference, 19th October 2016.
Lyrath Co. Kilkenny
Soil testing: what it does & where is it going?
• What are we testing?
• Why we test:
• Major nutrients in soils we have to keep an eye on: Phosphorus
• Soil type effects
• Bringing more soil information into to testing
• New methods in development at Teagasc
Soil: a complex medium
sand
silt
….
.
clay
water
air
Microbial communities
water
Soil-water interface
(Soil solution)
45
5
25
25
Composition of mineral soil (%)
Minerals
OM
water
air
What are we testing?
Athea Castleisland Doonbeg Kishkeam Rossmore
Sites/surfaces for nutrient &
trace element retention – Al,
Fe, Ca,
Nutrient or Trace
element X
Nutrients and trace elements in soils ‘removal’
X
Fixed X
Available
reserves
X
available
Nutrients and trace element depletion or ‘removal’
X
Fixed X
Available
reserves
X
available
Crop offtake
Nutrients and trace elements in soils
fixed Available
reserves Available
Crop offtake fertiliser
input
Phosphorus pools in soils
Fixed P
500-1500
mg/kg
Available
reserves
100 mg/kg
Available
P 10mg/kg
Crop offtake Fertiliser
P input
Interpreting soil test P
results: excessive Index 4
Fixed P Available
reserves
P
Available
P
Crop offtake Fertiliser
P input
Tap in on full – oversupply.
Interpreting soil test P
results - optimum
Fixed P Available
reserves
P
available
P
Crop offtake Fertiliser
P input
Index 3 = Good supply only when needed by crop
Interpreting soil test P results: low/deficient
Fixed P
Available
reserves Available
P
Crop offtake fertiliser
input
not enough nutrient in
reserve to supply to solution
build up rates need
to build up reserves
Phosphorus: think in
terms of supply
Fixed P
500-1500
mg/kg
Available
reserves
100 mg/kg
Available
P 10mg/kg
Crop offtake Fertiliser
P input
Build back up labile P reserves to keep supply going.
Phosphorus: think in
terms of supply
Fixed P
500-1500
mg/kg
Available
reserves
100 mg/kg
Available
P 10mg/kg
Crop offtake Fertiliser
P input
Build back up available P reserves to keep supply going.
Index 3 = good supply
Build up influenced by soil type
Fixed P High Al to P
ratio Available
P
Crop offtake fertiliser
input
Index 1, 2
High Al influence P supply
Al:P ratio is too high – P
unavailable (strongly bound).
At lower Al:P, P is
easily released,
Al
P ? P
P ? P
?
?
?
p High P fixing soils
7.3 mg/l
Phosphorus availability is influenced by soil properties
Current trends in soil P fertility
14% 14% 15% 22% 24%
30% 27% 27% 31%
26% 25% 26%
28% 30%
29% 28% 27%
30%
30% 29% 28%
25% 25%
23% 24% 24%
22%
30% 32% 30% 25%
21% 18% 21% 22% 17%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
Trend in Soil P Index
P Index 4
P Index 3
P Index 2
P Index 1
high
Optimum
deficient
low
Where?
Current methods:
Soil sampling typically every 2- 4 ha,
once in 5 years.
Limited to small number of elements:
P, K, Mg, LR.
Almost never for texture, organic
matter & other soil attributes
Phosphorus soil test and what they measure?
• There are many different tests out there.
• Amount of P extracted by any one test depends on the soil
pools that are responsive to that test
(e.g. Mehlich3>Olsen>Morgan-P)
• A soil P test must access the same pools that the plant can,
No soil test is universal
Soil properties of soils
mapped at landscape
scale Manage soil fertility at
field or paddock scale
Soil testing:
Good idea to know the soil as well as test it.
Is it acidic in nature?
Al?
Clay?
Important soil properties to consider: pH, Al, Ca, %OM
Emerging techniques:
New methods for soil testing capture more soil properties
No chemical extraction,
lower cost & rapid results.
One scan gives info about
soil pH, OM, Al, Fe, Ca,
texture etc.
NIR / MIR
• Sample interacts with
light source
• Get spectral
information on the
chemical makeup of
the sample.
Spectra produced when infrared is absorbed by a soil sample
gives the overall chemical profile of the soil
A H Jean Robertson, H Rachael Hill, Angela M Main. 2013. Soil spectroscopy workshop. FAO.
Rome.
IR applications - collect multi-parameter data from a single scan
Athea Castleisland Doonbeg Kishkeam Rossmore
• % OM at surface horizon
• % sand, silt, clay along profile
• extractable Al, Fe, Ca in each horizon
• pH, CEC, TN, TOC,
Multi-parameter: Soil attributes affecting soil fertility – not
captured by current methods
What does this mean for soil testing?
Spatial scales
Temporal scales
Multi-parameter data
Model/forecast
soil fertility
indicators
Thank you for your attention
Johnstown Castle
Wexford