Components of soil testing
Interpretation and recommendations
the greatest source of error.A ten-acre field weighs 20,000,000
lbs. and may be represented by a one-lb soil sample.
obtain soil boxes and information sheets.
soil tube or auger
Plastic bucket (clean). Galvinized buckets will contaminate
sample with Zn and copper.
Taking the sample
Divide fields into sampling areas which are as uniform as
possible in regard to soil type, topography, cropping history
and past fertilization.
The sampling area may vary from 1-15 acres. Small areas that
are different for some reason and cannot be treated separately
should be avoided. If you can give the small spot special
attention, make it a separate sample.
Depths of sampling
Annual crops - plow depth, usually 6-8"
Perennial - (alfalfa, pasture, turf) 4"
Number of cores or subsamples per sample - Take 12-15 cores
at various spots in the sampling area. Place in the bucket
to make a composite sample representative of your field.
Mix the composite sample well. Fill box to proper level. label
with name, address and field identification (be sure
to keep a record of how you identified the field, use
Fill out the information
area sheets are available - sample with depth on good
and bad areas.
for precision farming systems.
a part of the total nutrients in the soil. The values are of
little use in themselves. The method must be calibrated against
nutrient rate experiments in the greenhouse and field.
The North Carolina soil testing lab extracts soil samples
3 extractant, which removes an estimate of plant available
The concentration of plant nutrients in the extract is determined
Different extractants are used at different labs.
of analytical data
levels of nutrients in the extractant has to be calibrated with
crops have different calibration curves because plants do not
have the same nutrient needs.
requirements - based on crop requirement (desired pH), present
pH, amount of acidity to be neutralized
rate of N not based on soil test. Based on crop requirements
A diagnostic tool to be used in combination with soil analysis.
Based on the concept that the amount of specific nutrient element
in the plant is directly related to thequantitv of that element
Usually done only when a problem arises
Interpreting the results of plant tissue analysis is difficult.
Collecting samples slide set
Usually done prior to or at the beginning of a reproductive
Sample the correct plant part - on instruction sheet - usually
most recently matured leaves.
Do not sample dead plants etc. - see instruction sheet
Place sample in paper mailing envelope. (Not in plastic) so
begin to air dry. Let succulent plants (cabbage, potatoes) air
dry a day before mailing.
Take samples from an area with normal plant for comparison.
There is year to year and soil to soil variation in analysis.
crop varieties also differ
Fill out the form
Take a soil sample at the same location and the same time and
send along with plant sample
The fee for plant analysis is $5.00 per sample.
sufficiency ranges in plant tissue.
Agronomic Services Soil Testing Section
tour of the NCDA Soil Testing Lab
Purdue turf fertilizer calculator
Fertilizer calculations for greenhouse crops