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Introduction
| Targeting
achievable yield goals | Conclusion
Introduction
Crop
yield is influenced by many factors, some of which we can control and
others over which we have no control. Setting achievable yield goals must
take into account the effect these factors have on yield. This discussion
will highlight sources of information to help determine what is a
reasonable achievable yield as well as tools to help determine the
likelihood of achieving that yield.
Targeting Achievable Yield Goals
What is an
achievable yield goal? Is it a SWAG or is it based on data or information
that gives you some assurance that the yield is in fact achievable? Not
only must the information show that a yield is achievable but it must give
an indication of the likelihood of achieving that goal. To set a yield
goal you need information.
A farmer’s past yield
achievements is a good place to start in targeting yield goals. Records
going back several years will help fine tune the setting of target yields
as yields vary from year to year. Each field or soil type will have
different yield potentials so records specific to fields are useful. One
of the handiest sources of yield information on a field by field basis
(and even a soil type basis) is yield maps. Several years of yield maps
for a particular piece of ground will give you a good idea of the
achievable yield potential. If yield maps are not available a good look at
records of grain harvested will suffice.
Another valuable source of
information to help assess realistic achievable yield goals is the Alberta
Management Insights program (AMI). This is a compilation of Alberta crop
insurance data that serves as a benchmark to assess an individual’s crop
yield in relation to area yields. AMI is available on the web at http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex2647?opendocument .
Along with the records of grain yields one
should also assess the farming practices and weather conditions that led
to those yields. The drought of 2002 caused major yield reductions - it
would not be reasonable to use those drought yields as targets unless you
are sure another drought is going to occur. Similarly if past yields were
influenced by less than adequate plant nutrients one would not use these
past yields as targets unless the plan was to continue to supply less than
adequate nutrients.
After deciding what is a reasonable and
achievable yield for the area or soil type there are a few other things
that can be done to fine tune your estimate of achievable
yields.
Area and field soil moisture reserves
The amount
of stored soil moisture is going to have a large effect on crop yields. In
season precipitation also has a large effect on crop yields however
expected precipitation is difficult to forecast. Soil moisture reserve is
something that can be measured and used to adjust target yields. If soil
moisture levels in the spring are high the chances of a high yielding crop
improve. There are a number of information sources to help assess soil
moisture reserves. These include the Alberta Soil Moisture maps found on
the web at http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/cl6678?opendocument
and
the Saskatchewan Soil Moisture maps at http://www.agr.gov.sk.ca/docs/crops/integrated_pest_management/soil_fertility_fertilizers/stubble.asp .
These sites have both fall and spring soil moisture maps as well as
other pertinent moisture information. The soil moisture maps are a good
place to start when assessing yield potentials for the coming year, but
keep in mind the information presented in these maps is of a regional
nature and may not reflect individual field conditions.
Individual field soil moisture conditions are best measured in the
field. This can be done when soil sampling in the fall or spring simply by
noting the depth of moist soil during the sampling process. If you are
having trouble getting the soil probe down to even 6 inches as happened in
the fall of 2002 and again last fall you know it’s dry. Try to assess soil
moisture to a depth of a meter or so as plants will access moisture from
that deep and deeper.
A handy tool for soil moisture assessment
that is easier to use than a soil probe is the Brown probe. This probe
consists of a steel ball welded on to the end of a steel rod with a
handle. The probe is easily pushed into the soil as long as soil moisture
is high. As soil moisture levels decrease the probe gets harder to push
into the soil and is near impossible to push into dry soil. Soil moisture
levels can be determined by how deep the probe can be inserted. If the
Brown probe can be easily inserted to a meter or more you know the soil
has lots of moisture and the chances of a high yielding crop are greatly
improved. As well in crop soil moisture assessment can be carried out with
soil probes or the Brown probe in order to assess the potential for split
application of nitrogen fertilizer. Instructions on how to build and use a
Brown probe are on the web at: http://www.agr.gov.sk.ca/docs/crops/integrated_pest_management/soil_fertility_fertilizers/stubble.asp
In
field inspection and soil sampling
To get a good picture of
productive capability of a field an in field inspection is critical. This
can be carried out while soil sampling, noting areas of Solonetzic soils,
depth of A horizon for different landscape positions and other features of
the field. These all influence the productive capability of a field and
the expected reasonable yield target.
Soil sampling is critical in
order to achieve target yields. Soil tests not only give you valuable
information regarding the nutrient status of the field but also point out
some of the other yield limiting factors such as acid soils or high sodium
soils.
An important point to note regarding soil sampling for
nitrogen fertility recommendations is the depth of the soil sample
- especially important in drought years. The drought of 2002 resulted in
large amounts of soil nitrogen being left in the surface six inches of the
soil. Fertility recommendations from soil labs use an estimate of soil
nitrogen down to two feet. In the fall of 2002 a standard six inch soil
sample would result in an overestimation of the available nitrogen down to
two feet. This over estimation of available nitrogen would in turn lead to
an under recommendation for fertilizer nitrogen. Target yields would be
hard to achieve if the crop was under supplied with nitrogen.
To
avoid this situation one should sample to a greater depth in increments of
six inches or to a depth of at least one foot as one increment. The single
deeper sampling will address the nitrogen stranding issue but is not as
useful as a deep sample in increments for monitoring such things as soil
pH, organic matter levels and E.C.
Conclusion
Targeting achievable yields takes many
factors into account. By assessing crop production records, soil moisture
conditions, soil fertility levels and carrying out some in-field
inspections reasonable target yields can be set. These steps alone are not
going to insure that the target yields are met as other factors (such as
seeding date, weed, insect and disease control etc.) affect final yield,
however these tools and techniques will go a long way to targeting those
achievable yields.
Roger Andreiuk
Reduced Tillage LINKAGES
4301-50 street,
Leduc, Ab. T9E 7H3 |
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