Transcript Soil Sampling and Fertilizer and Lime Recommendations

Soil Sampling for Fertilizer and
Lime Recommendations
Why soil sampling and testing?
• Soil sampling and testing is an investment which
leads to profitable use of lime and fertilizers.
• A nutrient management program starts with a
representative composite soil sample and
continues with the lab analysis, interpretation of
the results and ends with an appropriate
recommendation.
• Evaluation of changes in soil pH and available
nutrient levels over time requires collection of
soil samples.
Soil Sampling
• Goals:
1. To collect a soil sample that is representative
of a field or portion of a field
2. To obtain info. about a field and use that info.
to make management decisions
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Nutrient management
Herbicides
Crops
Others
3 Basic Approaches
• Random
• Grid
• Management Zones
Before Soil sampling…
• Get the knowledge (County Soil Survey Report)
about the differences in soil characteristics
within the fields and these differences include:
- Productivity
- Field topography
- Texture
- Drainage
- Color of topsoil
- Past management
Continue…
• A composite sample: consists of a number of subsamples thoroughly mixed.
• If the sampling area and past management features
are reasonably uniform, each composite sample in a
random system can represent 10 or 15 acres. Grid
sampling will represent considerably less area.
Management Zone sampling will generally represent
larger areas.
• However, most likely these soil features are quite
variable within a single field. Thus, areas with
reasonably uniform soil characteristics (management
zones) should be identified before sampling.
Sampling a Field
1. Random
• Sample should represent no more than 1015 a
• 20 cores composited to produce one sample
• Collected in a zig-zag pattern across the field
• Advantage
• Relatively inexpensive
• Disadvantage
• Get an average not a measure of variability
Sampling a Field
1. Random
Sampling a Field
2. Grid
• Field is divided into equal areas
• Generally 300’ x 300’ (2 a)
• 10 cores (min.) composited within each grid
cell in a 10” radius around a georeferenced
point
• Advantage
• Provides a good assessment of variability
• Disadvantage
• Expensive
Intensive soil sampling
• Variable rate technology (VRT) allows
different amounts of fertilizers to be applied
across the field on the basis of available
nutrient levels.
• Intensive soil sampling is required to produce
a nutrient map with various levels.
• Grid sampling is the main approach.
• From the economics standpoint, grid size 300
* 300 feet is enough, but for some research
purposes, a finer grid size is desirable.
• A continuous nutrient level map can be
developed based on intensive grid sampling.
A grid sampling and nutrient map
of P
Sampling a Field
2. Grid
Sampling a Field
3. Management Zone
• Divides field into areas that are similar for a
defining characteristic
• Utilization of a dense data set (next slide)
to define mgt zone boundaries
• 20 cores composited to produce 1
sample/zone
• Collected in a zig-zag pattern across the
zone
• Zone borders & sampling points can be
georeferenced
• Advantage/Disadvantage
• Provides an assessment of variability better
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Precision Ag technologies for
defining boundaries of soil
sampling mgt zones
Grid sampling results
Soil conductivity
Aerial imagery
Soil pH
Near-infrared
Yield maps
Slope
Determine the uniform soil
areas
• Consult your
County Soil
Survey Report to
determine the
soil types.
Soil Maps
Elevation
Slope
Ec
Soil conductivity (Veris & Em38)
On-the-go pH
On-the-go NIR
Average standardized yield
Variability in yield
Some other factors…
• Management history
-Cropping rotation
-manure spreading
-Limestone application and stockpiling.
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Unusual spots should be avoided or
sampled separately when needed
- Atypical or exhibits plant growth problems
-Trees in the fields
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Field edges
Soil sampling equipment
• Soil sampling
probe/screw
augers/shovel
• Plastic pail
• Clean containers for
samples: sample boxes
or paper bags
• A sketch map indicating
each soil
unit/management zone
to be sampled will be
helpful.
• Here are some
examples:
Sample collection
• Once the sampling area has been defined, a
composite sample may be made from each unit.
- Use a zig-zag sampling pattern
• Each sample should consist of vertical cores or slices
of soil approximately 0.5-0.75 inch thick.
• Keep the core/slice depth consistent. Especially for
reduced-tillage and no-till systems because of
nutrient stratification.
• Subsoil Samples can provide additional information
on lime or fertilizer recommendation,when
- Coarse textured soils with finer textured zone in the
subsoil
- The soil is organic
Timing of sampling and testing
• Soil pH and extractable nutrient levels do vary some
with the time of the year. Therefore, it is best to take
samples at the same time of the year to track
changes in nutrient status.
• Do not wait when additional soil sampling is needed,
for example when crop management systems are
changed.
• Early soil test results may allow a timely
development of a fertility management plan. For
example, liming should be done 6 month before
planting to let the lime fully incorporate into the soil.
Frequency of sampling
• In most cases, it is adequate to sample and test the
soil once every 3 years.
• Some soils (e.g. sandy soil) with low (<6 me/100g)
cation exchange capacities (CECs) may need more
frequent sampling.
• Intensive cropping systems undergoing large fertilizer
input and possible high crop removal. Annual soil
sampling and testing is suggested (e.g. vegetable
crops grown on sandy soils).
• In large farm operations, the fertility program based
on entire farm sampling at one time may not be
practical, although good practice, sampling and
testing 1/3 of the acreage each year is an alternative.
Soil sampling summary
• Develop a map of uniform areas within the field. Make use
of soil survey maps, topography and management history.
• Designate the sampling areas of economic importance.
• For each composite sample, collect 20 cores to the
appropriate depth using a zigzag pattern.
• Thoroughly mix the soil cores in a plastic bucket. Partially
dry very wet samples before mixing.
• Fill a soil sample bag or box with the composite sample.
• Fill out the information form with all the pertinent cropping
management information.
• Send the composite soil sample and information sheet to a
reliable soil testing lab for analysis.