Download Constraints to cropping soils in the northern grains region

Constraints to cropping soils
in the northern grains region
Rockhampton
Emerald
A decision tree
Qld
Bundaberg
Taroom
Kingaroy
Roma
Is your paddock or parts of your paddock showing poor
crop growth and yield, despite good starting moisture and
adequate in-crop rainfall?
If so, look for the following: diseases, insect pests, nematodes,
herbicide damage, weeds, or frost damage.
If these are not the cause, your soil may be limiting plant
growth. Use the decision tree below to help identify soil
constraints.
BRISBANE
Toowoomba
St George
Goondiwindi
Brewarrina
Narrabri
NSW
Tamworth
Dubbo
Newcastle
Do the roots show honey brown
discoloration, dark lesions, or knotting?
Biological constraints
Do the leaves or stems show characteristic
symptoms of nutrient imbalance?
Nutrient constraints
Is the soil surface crusting, hard setting,
sealing or waterlogged (water ponds for
several days after rain)?
Surface sodicity
Coffs
Harbour
Is the rooting depth restricted by rock, a dense clay
layer, hard pan, or a traffic or plough pan (roots
deformed or growing at a right angle)?
Physical constraints
Are fresh roots absent from the rooting zone
(less than 1 metre soil depth)? Is the subsoil
wet after a dry finish?
Chemical constraints
Is subsoil structure coarse or dense? Is subsoil
drainage lacking?
Subsoil sodicity
Biological constraints
Nutrient deficiencies
Good and bad soil organisms affect
plant growth. Problems occur when
there is a reduction in the activities of
good organisms such as earthworms and
vesicular-arbuscular mycorrhizae (VAM),
or an increase in pathogens or plantparasitic nematodes.
Better crop varieties, improved agronomy and higher
yields, along with continuous cropping without adequate
fertiliser, have resulted in widespread soil nutrient
depletion—especially of nitrogen, phosphorus and zinc.
Pathogenic fungi and nematodes often
Crown rot
build up in monoculture cereal cropping
systems in the northern grains region. These include crown
rot and common root rot, as well as root-lesion nematodes
that can be as deep as 60 centimetres at peak times.
Subsoils are generally lower in nutrients than the surface
layer. This can reduce yield in dryland regions, where
continued root growth and function are essential to enable
crops to extract water from the subsoil.
Signs of nutrient deficieny include: pale yellow old leaves
(lack of N), dark green foliage and purple old leaves (P),
and water-soaked strips on young leaves (Zn).
What can I do?
What can I do?
Identify the problem then focus on farm hygiene, crop
rotation and growing resistant crops and cultivars.
Identify the nutrient disorders. To restore soil nutrients,
use a balance of organic and inorganic fertilisers, and
incorporate legumes and ley pastures in crop rotations.
Encourage the build up of beneficial organisms through
moist soil and a good supply of organic substrate (full
stubble retention and no-till).
Use direct drilling because mechanical tillage is detrimental
to VAM and earthworms, and it promotes attack by
nematodes and soil-borne diseases.
Physical constraints
Physical constraints decrease oxygen and
water movement in the soil. Compacted
soil and soil with a high physical strength
impede root growth.
Compacted soil layers or layers of high
bulk density (>1.5 g/cm3) are widespread
in the region. Subsoil compaction is
natural and also caused by heavy traffic
and tillage on wet soils.
Phosphorus (P) deficiency
Root problem
Man-made compaction occurs in the top
20 centimetres in most cropping soils, but can be deeper
especially below wheel tracks. Compacted layers may be
visible, measured as high penetration resistance (>2 MPa),
or indicated by distorted root growth.
What can I do?
Deep ripping may benefit soils with hardpans or
compacted layers; but it can be costly, has varying levels
of success, and could bring up highly sodic subsoil. Deep
ripping is rarely worthwhile financially without some type
of Controlled Traffic Farming (CTF), as compacted layers
quickly re-form under wheel tracks.
Opportunity cropping and growing deep, tap-rooted
pasture plants such as lucerne help form pathways through
a compacted layer. Fibrous-rooted plants can remove more
moisture from the soil and help shrink and crack Vertosols,
which assists self-repair.
Zinc (Zn) deficiency
Nitrogen (N) deficiency
Chemical constraints
solubilities. Only highly soluble salts such as sodium chloride
inhibit water extraction or are directly toxic to roots.
Chemical constraints can be toxic to plants and also limit
the plant’s ability to take up water by decreasing the
osmotic potential of the soil water.
Soil salinity is commonly measured as electrical
conductivity (EC) in a 1:5 soil:water extract and expressed
as dS/m. EC measurements do not discriminate between
salt types.
Acidity
In acid soils (pH <5.5), aluminium and manganese
become more soluble; they may become toxic as their
concentration in the soil water rises. Aluminium inhibits
root growth in most plants and induces calcium,
phosphorus and molybdenum deficiencies. In the northern
grains region, subsoil acidity is common in soils dominated
by N2-fixing brigalows and belah.
Gypsum: EC values will be
high if significant quantities
of gypsum are present. If
the high EC reading is due
only to gypsum there are no
concerns for crop growth.
The dissolution of soluble
gypsum will not restrict
the roots from extracting
water unless other salts are
present.
What can I do?
Lime is the most economical ameliorant for surface soil
acidity, but it leaches very slowly making it unsuitable
for rapid amelioration of acid subsoils. Deep placement is
effective, but costly and difficult. It is cheaper to prevent
subsoil from acidifying in the first place, by adding lime.
White gypsum banding
Chloride and sodium:
Measuring sodium and
particularly chloride
concentrations in soil
provides a better indicator
of ion toxicity and why a
crop has problems extracting
water (see table 1). Chloride
salts are highly soluble and
can accumulate to toxic
Chloride affected wheat
concentrations in plant tissue.
Chloride accumulation in some species causes toxicity and
a drop in grain yield.
Research shows that acidity in lower layers is slowly
reduced when lime is applied to maintain the surface soil
at a pH of 5.5 or more.
Alkalinity
In alkaline soils, an abundance of anions such as
carbonates and bicarbonates contribute to the high pH.
At soil pH >8.0, toxicity of carbonate and bicarbonate
can reduce crop growth and yield, and/or induce nutrient
deficiencies.
What can I do?
Add elemental sulphur to acidify these soils. Large
amounts of elemental sulphur would be needed to reduce
the soil pH of clay-dominated soils, which may be costly.
Table 1. Concentration of chloride and sodium in soil
Low
Medium
High
Surface soil
Salinity
Salinity is the presence of dissolved salts in soil or water. A
high concentration of salts can cause ion toxicity and affect
a plant’s ability to absorb water.
<300 mg Cl/kg
300-600 mg Cl/kg
>600 mg Cl/kg
<200 mg Na/kg
200-500 mg Na/kg
>500 mg Na/kg
Subsoil
Several salts are found in northern region soils, including
sodium chloride (common salt), calcium sulphate (gypsum)
and calcium carbonate (lime). Different salts have different
<600 mg Cl/kg
600-1200 mg Cl/kg
>1200 mg Cl/kg
<500 mg Na/kg
500-1000 mg Na/kg
>1000 mg Na/kg
Figure 1. Soil classification based on pH (1:5 soil:water)
Acidic
0
1
2
3
4
Toxicities of Al, Mn, Fe
Deficiencies of Ca, Mo, P
5
6
7
Ideal pH for
plant growth
8
9
10
11
12
Alkaline
13
14
Sodicity
Toxicity of Na, HCO3
Deficiencies of Ca, K, Zn, Mn
What can I do?
If the surface and/or subsoil have a high EC reading and a
high concentration of sodium and/or chloride, grow crops
and their cultivars that are tolerant to chloride. Threshold
values of chloride that cause 10 per cent and 50 per cent
reduction in grain yield suggest that bread wheat, barley
and canola are more tolerant than chickpea and durum
wheat (see table 2).
Table 2. Thresholds for chloride concentrations in soil (mg/kg)
10% yield reduction 50% yield reduction
Bread wheat
700
1500
Barley
800
1500
Durum wheat
600
1200
Canola
1200
1800
Chickpea
600
1000
Field trials suggest that for bread wheat, cvs. Baxter and
Sunco may perform better than some other cultivars
commonly grown in the northern grains region. For
chickpea, Moti has performed slightly better than Jimbour.
Work on this is continuing.
In paddocks with medium to high levels of chloride,
consider growing pasture or forage crops. In paddocks
with very high constraints, consider permanent pasture
such as grass-lucerne pasture or agro-forestry such as
native wisteria (Pongamia pinnata), which may be tolerant
to salts.
Sodicity
Sodicity is an excess of sodium ions relative to other
cations (calcium, magnesium and potassium). A high
proportion of sodium can lead to soil dispersion.
Salinity can mask the dispersive behaviour of sodic soil.
Sodicity and salinity both occur in many subsoils of the
northern grains region. The effect of these two is nonadditive; plant growth is primarily limited by salinity.
However, sodic impermeable subsoil does not allow the
drainage that would otherwise help to move salts out of
the surface layers.
High surface soil sodicity
leads to surface crusting,
cloddy seedbed, poor
water infiltration (more
run-off) and increased
water-logging.
In subsoils, high sodicity
often leads to a coarse
or dense structure that
restricts soil water and air
movement. The subsoil may
become oxygen deficient
and take on a mottled
“rusty” appearance.
Crop roots cannot grow
in a saturated soil (due to
the lack of oxygen). Even
though the subsoil is wet,
this water is not really
available to the crop.
Crusting
Cloddy seedbed
What can I do?
Gypsum application improves surface sodicity by
flocculating soil, leading to better infiltration and the
exchange of calcium for sodium.
In soils with moderate surface sodicity (ESP = 12), the
application of gypsum at 2.5–5.0 t/ha significantly
improves wheat grain yield. For correcting subsoil sodicity,
high application rates of gypsum, sufficient rainfall and
time are required. Improved subsoil drainage may also help
salts to leach from the upper layers.
Dispersion is the disintegration of clay aggregates into
individual particles when wet, resulting in milky or cloudy
water. In the paddock, the soil will be poorly drained and
the subsoil may remain saturated for long periods.
Sodicity ranging from none to complete (left to right)
No Gypsum
Gypsum (2.5 t/ha)
Chemical constraints decision tree
Electrical Conductivity (EC; dS/m)
Check soil for electrical conductivity
Top 10 cm soil
Subsoil
Plant growth is not
affected by salinity if:
Plant growth is affected
by salinity if:
Low EC <0.3 dS/m
Low EC <0.7 dS/m
High EC >0.3 dS/m
High EC >0.7 dS/m
Check soil for exchangeable
sodium per cent (ESP)
and/or dispersion
No dispersion
(ESP <6)
Check soil for sodium and
chloride concentration
Dispersion
(ESP >6)
Cl >300 mg/kg
Cl >600 mg/kg
Check the soil pH
(1:5 soil:water)
Cl <300 mg/kg
Cl <600 mg/kg
and/or
Na >200 mg/kg
Na >500 mg/kg
pH <5.5
Check for gypsum crystals
and sulfur concentration
pH >8.0
S >100 mg/kg
Acidity
constraint
Alkalinity
constraint
S <100 mg/kg
Sodicity
constraint
Osmotic effect
due to high salt,
and Na/Cl toxicity
High EC due to
gypsum: No constraint
to crop growth
No gypsum – other
salts are causing
the problem
Table 3. Agronomic practices for varying levels of constraint
Low constraints
Medium constraints
High constraints
(<600 mg Cl/kg, <500 mg Na/kg in
top 1 m soil depth)
(600-1200 mg Cl/kg, 500-1000 mg
Na/kg in top 1 m soil depth)
(>1200 mg Cl/kg, >1000 mg Na/kg in
top 1 m soil depth)
• Cereals-legume rotation
• Grow tolerant cereals (wheat, barley,
canola)
• Consider alternative land use (saline
forage/pasture production, agroforestry/forestry system)
• Consider canola if soil profile
is full
• Match inputs to realistic yield
• Manage crown rot and nematodes
• Consider tolerant cultivars
• Try opportunity cropping to use
available water
• Manage crown rot and nematodes
• Avoid crops or grow tolerant cereals
• Match inputs to realistic yield
• Avoid legumes and durum wheat
• Try opportunity cropping to use
available water
Maximising production
Good agronomic management helps minimise the water
and other physiological stresses imposed by subsoil
constraints. In paddocks with subsoil constraints,
successful cropping can be achieved by:
•
•
•
•
•
•
maximising fallow efficiency with short fallows;
effective weed control;
suitable rotations for disease minimisation;
matching nutrients to realistic yield expectations;
appropriate species and cultivar selection; and
timely crop sowing.
Farmers discuss good agronomic management
Further reading
1. Subsoil constraints to crop production in northeastern Australia: A reference manual. 2004. Brisbane:
Department of Primary Industries & Fisheries
2. Subsoil constraints to crop production: Impact, diagnosis
and management options. 2004. Brisbane: Department of
Primary Industries & Fisheries (Crop Note)
3. Cereal diseases: The ute guide. 1999. Canberra: Grains
Research & Development Corporation & TOPCROP
Australia (GRDC006)
4. Living soils – better soil. 1999. Canberra: Grains Research
& Development Corporation. (GRDC070) (for information
about beneficial soil organisms)
5. Winter cereal nutrition: The ute guide. 2001. Canberra:
Grains Research & Development Corporation & TOPCROP
Australia (GRDC004) (for information about nutrient
deficiency symptoms)
Queensland
New South Wales
Department of Natural Resources & Water Call Centre
Ph. 13 13 04 Email [email protected]
Department of Primary Industries – Tamworth
Ph. 02 6763 1100
Department of Primary Industries & Fisheries Call Centre
Ph. 13 25 23 Email [email protected]
© The State of Queensland (Department of Natural
Resources and Water) 2007
Acknowledgements: Farmers and advisors from northern grains region
Disclaimer: This leaflet is for general information only and does not cover
all circumstances. Seek advice and read widely before making decisions or
taking action.
#scu18876 - 6/2/07
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