SOIL
TESTING
For Plant fertility
·
pH
·
Soluble Salts
Plant available
·
- (N) Ni
·
- (P) Phosphate
·
- (K) Potassium
· - (S) Sulphate
· - (Ca) Calcium
·
- (Mg
Suitable for:
·
pasture, (kg/ha)
·
potting mix, horticulture, (g/m3)
·
home garden and bio-dynamics. (g/m2)
This test will allow you to visualise the major nutrient balance of your
growing media in its plant available form.
Sampling.
The laboratory requires approx 1 cup of soil for the test.
The sample should be a composite of the area desired and up to 10 cups will
be prepared for sampling allowing a good representative sample.
A composite sample should be prepared from each different growth area. eg
Hills, Flats, Swamp. Avoid abnormal growth ares such as dung or urine patches,
water trough areas and ridges. The test results are independent of soil type and
only different growth regions need sampling.
The root zone of the plants are the best indicators of the required sampling
depth, typically 75mm for pasture and 150mm for horticultural.
If the soil cannot be delivered to the lab promptly, drying the soil in a
hot water cupboard or sun drying will stabilise nutrient activity.
When
to sample.
·
The soil test information
provides a basis for determining pre planting fertiliser requirements.
·
If plants are growing well a
test for future reference is recommended. This applies to specialist crops such
as flowers or crops that may thrive in unbalanced situations eg acid loving
plants.
·
If you have uneven growth.
·
If you need to monitor nutrient
status.
Don't sample after fertilisers have been applied and insufficient rain has
fallen to thoroughly wash the fertiliser into the
soil.
Background.
In the days before soil testing, growing characteristic's were linked to
soil types. This often reflected the physical properties more than the nutrient
content. The soil determined what crop would grow best. Traditional soil
testing has been a useful indicator of the type of fertiliser required.
The Plant Available Nutrient test looks at the soil
from the plants point of view and therefore correlates better with plant
nutrient uptake. Frequently plant growth can be increased by increasing the
nutrient concentration but it is essential that the balance between nutrients
is maintained at all times.
Hydroponic research has provided an understanding of the optimal ratios of
one nutrient to another in the plant available state. Characteristic such as
fruit or blossom yield, stem length, and disease resistance can be controlled
by controlling the nutrient balances at different stages of growth. To do this
an accurate technique to determine plant available nutrient status is required.
The Plant Available Nutrient test uses Anion --- and
Cation +++ exchanged membranes to provide the same passive extraction force as
plant roots, extracting all nutrients simultaneously. Highly purified
laboratory grade water is used as the extractant and the release of nutrients
is establish as if activated by rain.
The results of the plant available nutrient test cannot be compared with
traditional methods such as the Olsen P test but compare more favourable with
the more recently introduced Resin P test.
Results.
Plant available nutrients are
mg/kg dry weight
pH .......(acidity) 1:3 mix with
pure water.
pH is a tests that determines how acid (sour) or alkaline (sweet) a soil is.
Generally 5.5 - 6.5 is the recommended pH for most plant varieties.
pH levels below 6.0 respond to pH increasers such as lime or dolomite.
It is well recognised that adding lime to increase soil pH allows other
minerals besides those in the lime to become available. Peat soils are often
acidic. Other soils can become acidic through the use of nitrate and sulphate
fertilisers.
Boron deficiency is more common in acid soils.
Soluble salts.. or CF or Electrical Conductivity is the
measure of the total amount of minerals that leach from a
1: 3 mix of pure lab water and the soil or media sample. the result is in
micro semins/cm.
Units for soluble salts are reported in a number of different unitage but
most can be compared simply by moving the decimal point. Differences are due to
measuring sensitivity.
uS/cm or microSemins /centimetre is the most sensitive.
mS/m or milliSemins/meter is the same sensitivity
mS/cm or milliSemins/centimetre or millimhos/cm (sensitivity 1000 time less)
90 - 200 for biodynamic pasture
100 - 400 for fertilised, improved, pasture
200 - 800 for cultivated, irrigated soil
800 - 1300 for potting mixes, poly house
1000 - 3000 for hydroponic solutions, bag feeding.
These guideline values are general and the optimal available nutrient
concentrations should be based on plant type. This result is an indication of
the total amount of minerals that will leach into the moisture held within the
soil. These soluble salts contain the plant available nutrients. The balance of
nutrients is revealed is in the next stage of testing. The higher the soluble
salts the greater the plants requirement for water will be.
Nitrate ............ is the first of the major nutrients required by
plants. Deficiencies result in poor growth
with pale green leaves resulting from low levels of chlorophyll pigment in
the leaf. High levels result in succulent lanky plants, susceptible to pest
attack and have week stems.
In the pasture situation nitrogen is fixed from the air to the soil via
bacteria in clover species. This is a constant process and expected pasture
levels can therefore be lower with no loss of pasture performance. When low the
establishment of good clover is recommended in preference to dependence on nitrogen
fertilisers. The use of nitrate in excess of plant requirements results in
losses through leaching.
Levels 2 - 10 are expected for pasture. Horticulture and potting mixes
generally have 5 - 20.
Phosphate.........is the most applied fertiliser in N.Z's fertiliser
history. Plant available levels drop in acid soils. It is believed that
phosphate is not leached and that a bank of phosphate builds up in the soil.
Phosphate is of greater importance to root development and therefore root crops
such as potatoes, kumara and carrots. It also appears to be important to bulb
development. Some bulb storage problems have been associated with low
phosphorus levels.
low levels have also been associated with delayed maturity. Phosphate
counter acts excess nitrogen use.
Animal health problems can result from overuse.
Plant’s phosphate requirements are lower by a factor of 10 than any of the
other major nutrients. Deficencies syptoms show first in the older leaves as a
yellowing with dark green young shoots.
Level of 0.8 - 108 in pasture and 2 - 25 in cultivated land and potting
mixes are expected. Phosphate in potting mixes
requires regular additions to maintain levels.
Potassium........... Low levels result in slow and unthrifty growth,
low yield and small fruit size. Symptoms are often seen as spot on the leaf and
the leaf margins yellow, turn browns and folds under. Potassium has a balancing
effect on nitrogen and phosphorus. Levels should be 1 - 6 times higher than the
magnesium. Potassium is found at concentration equal to nitrogen in plant
tissue.
Potassium is second to nitrate in its leachability.
Levels between 52 and 4205 are expected.
Sulphur................Most important to good legume formation. High
levels are common in volcanic and peaty soils. very high levels can be
responsible for the acid nature in calcium low soils. Deficencies in pot grown
plants are rare. Sulphur level are often high in peaty soils.
Levels of 3 - 70 are expected.
Calcium............... is the second most applied nutrient as it is
the main ingredient of lime. Deficency is seen as a general stunting of plant
growth. Various plant and fruit disorders are associated with calcium
deficiency.. Hydroponic has shown that acceptable levels of calcium can be
associated with calcium deficiency symptoms in plants if the potassium,
magnesium or ammonium get very high.
Calcium is required in high concentration by the plant but also plays a role
in pH control of the soil maintaining the availability of other nutrients and
disease control.
Levels expected are 10 - 100
Magnesium......... competes with
potassium and calcium but is required in much lower quantities (4 - 7 times
lower.) . Increasing potassium with Muriate of Potash may reduce magnesium
availability problems if magnesium levels are close to the lower expected
values. Grass staggers in cattle have been linked to magnesium deficiencies due
to application of excess potassium. Magnesium deficiency is seen as a yellowing
between the veins of the mature leaf . The leaf will eventually die.
Expected magnesium levels are 105 - 5015 for pasture and 5 - 25 in potting
mix. The higher levels in pasture is more for animal health than plant health.
The ratio of magnesium to potassium should be 1:6 and the ratio of magnesium to
calcium should be 2 :7.
Dose rate information is not provided.
Further testing is required along with further specific information on
expected growth or health targets.
Fertiliser availability varies from supplier to supplier and each supplier
has recommended dose rates for the products they supply.
Information is provided on the type of fertiliser required.
When animal health is a concern, problems such as bloat, milk fever or grass
staggers, can be prevented with more managed fertiliser applications. Keep
stock of the pasture until the rain has washed the fertiliser from the pasture.
This method of soil testing has been designed to provide diagnostic
information that allows you to grow healthier plants and provide a basis for
the efficient use of fertiliser.
The test results do not indicate the reserve of a nutrient but rather the
size of the available pool of nutrients.
Further laboratory analysis with particular problem soil allows in more
specific fertiliser types and application rates to be given. This type of testing
is more applicable to situations where plant health appears good but fruit are
small, yield is low, colour is lacking, etc.
Nutrients are only one factor that influence healthy plant growth. Nutrients
can effect the susceptibility to pest and disease but light, temperature, water
and fresh air are also necessary .
Cost
Single test $80 inc GST