Saskatchewan, Canada
April 19, 2004
Measuring stored soil water
combined with soil testing this spring will help growers apply
the optimum amounts of fertilizer and maximize their
profitability, says David Blais, the
Canola Council of Canada
Agronomist for North Western Saskatchewan.
Spring moisture conditions vary
greatly across the prairies. One of the key processes
controlling a plants nutrient uptake is the amount of soil
moisture available. Growers need to determine the amount of soil
moisture, determine existing soil fertility levels and then
establish target yields. With that information growers can
calculate exactly how much fertilizer to apply. If growers do
not perform this analysis there is a good chance either too
little or too much fertilizer will be applied. "Too little and
the crop will not reach its optimum potential and too much can
be like throwing your fertilizer down the drain," he declares.
He adds that there are simple
tools available to help growers choose target yields and proper
fertilizer rates to achieve these yields.
Here are the steps to
determining target yield:
Step 1: Use a soil
moisture probe to help determine the amount of stored soil
moisture. To make a soil moisture probe, use a 3 1/2-long,
1/2"-wide metal rod, mark 6" segments down its length and weld a
handle at one end and a ball bearing at the other. Push the
probe into the ground in a single motion until it hits dry soil.
A rock or frozen ground will also stop the probe so withdraw and
repeat. The depth penetrated in feet indicates the depth of
stored water. Sample a minimum of 15 to 20 sites per field and
record the average soil moisture depth.
Step 2: Use Table 1 to
determine the amount of stored moisture in a foot of moist soil
in your soil zone, then multiply the average soil moisture
depth.
| Table 1.
Plant available water stored per foot of moist soil for
various soil textures |
| Soil Texture
|
Inches of Soil
Moisture/foot Moist Soil |
| Sand |
0.75 |
| Loamy Sand |
1.0 |
| Sandy Loam |
1.25 |
| Loam |
1.5 |
| Clay Loam |
1.75 |
| Clay |
2.0 |
| Source: SAFRR |
Estimate growing season
precipitation and add it to the stored moisture value. Then use
the appropriate formula for your soil zone and crop in Table 2
to determine the yield potential of the crop to be planted.
| Table 2.
Yield equations for wheat, barley and canola by soil zone. |
|
Soil Zone |
Wheat (CWRS) |
Barley |
Canola |
| Dry Brown |
Y=(WU
2.5) X 3.5 |
Y=(WU
2.5) X 5.3 |
Y=(WU
2.5) X 2.0 |
| Brown |
Y=(WU
2.25) X 3.75 |
Y=(WU
2.25) X 5.7 |
Y=(WU
2.25) X 2.5 |
| Dark Brown |
Y=(WU
2.0) X 4.0 |
Y=(WU
2.0) X 6.0 |
Y=(WU
2.0) X 3.0 |
| Thin Black |
Y=(WU
1.75) X 4.25 |
Y=(WU
1.75) X 6.4 |
Y=(WU
1.75) X 3.3 |
| Black |
Y=(WU
1.5) X 4.5 |
Y=(WU
1.5) X 6.7 |
Y=(WU
1.5) X 3.6 |
| Gray |
Y=(WU
1.25) X 4.75 |
Y=(WU
1.25) X 7.2 |
Y=(WU
1.25) X 4.0 |
Source: SAFRR
Y = Yield (bu/ac) (The equations are based on pre-1990
varieties)
WU = Water use (inches stored soil moisture + estimated
in-season precipitation) |
Example;
For a loam textured soil in the thin black soil zone with 2 _'
of moist soil, 8" of growing season precipitation and 3 _"
stored water gives:
WU= 8"+3.75"=11.75"
Y= (11.75"-1.75") X 3.3=33.3 bu/ac
Include yield potential and
amount of stored water values for each field when submitting
soil samples to aid the lab in making more accurate
recommendations.
Yield potential can be
influenced by.
- New varieties, especially
hybrids, tend to yield higher than older varieties under
similar moisture and fertility situations.
- Direct seeding increases
soil organic matter and conserves soil moisture.
- Maintaining crop residue
conserves soil moisture and increases mineralization of
organic matter to usable nutrients.
"If your analysis shows soil
moisture is limited, apply the necessary fertilizer for your
moisture situation and top dress more if moisture conditions
improve in late May and early June," advises Blais. |
