pH
Good nutrition is essential to growing plants successfully. One of the first
questions to consider to improve production is, "Have you tested your soil?"
Soil pH is a measure of how acidic or "basic" (the opposite of acidic) your soil
is. Soil pH is important since it affects the growth of plants and the severity
of some diseases. pH affects the ability of plant roots to absorb nutrients.
Calcium, phosphorus, potassium and magnesium are
likely to be unavailable to plants in acidic soils. Plants have difficulty
absorbing copper, zinc, boron, manganese and iron in basic soils. By managing
soil pH, you can create an ideal environment for plants and often discourage
plant pests at the same time.
Measuring pH
pH is measured on a scale of 0-14. A soil or water pH reading below 7 is
considered acidic, while a pH reading above 7 is basic. A pH reading of 7 is
neutral, and is ideal for many plants and spray materials. The pH scale is
logarithmic, which means that a pH reading of 6 is 10 times more acidic than a
reading of 7. You can measure the pH of your soil, your spray tank water, or
your irrigation/fertigation water.
Soil: Crops, ornamentals and turf need careful pH management to maintain their
best quality and appearance. The wrong pH can lock nutrients in the soil, making
them unavailable to plant roots. A pH that's too high or low can make disease,
insect and weed problems worse.
Spray tank water: If your spray tank water is too acidic (low pH) or too basic
(high pH), the pesticides you mix in can be deactivated and may even burn your
plants.
Irrigation/fertigation water: The pH of
water you apply to your plants should match your desired soil pH. Otherwise it
will gradually change the soil pH
pH levels
Acceptable pH varies by plant type. If you're not sure what's best for your
plants, you can check a reference book or ask your seed or Ag Chemical dealer,
Cooperative Extension agent, or private consultant. Remember, when you adjust
soil pH levels you can affect plant growth, nutrition and susceptibility to
pests. When setting a pH goal for your soil, you will want to take all of these
considerations into account. Acidic fertilizers can be used to lower pH.
Limestone is often used to raise pH. The type of limestone applied and
your soil type can make a difference in how quickly and how much the pH will
change
Testing Your Soil pH
1.) Sample — When taking samples, use a soil probe or trowel, a clean plastic
bucket for collecting and mixing samples, and plastic bags or wax paper sacks to
hold sub samples for testing. Make sure that you use clean tools. If the soil in
your field is uniform, take 15 to 20 samples from random locations throughout
the field and mix them together in the plastic bucket. If the soil is highly
variable from one part of the field to the other, divide the field into several
more uniform sections and take samples from each one. Write down where the
samples were taken in a notebook. Do not take samples from only one side of the
field, only from the corners of the field, or from the same spot on each side of
the field. Also, avoid taking soil samples near lime or manure piles, animal
droppings, fresh
fertilized rows, low spots, fences and roads. When taking samples in turf and
other shallow rooted crops, sample the top three inches of the soil. In
ornamentals and other deep-rooted cultivated crops, sample the top six inches of
soil — though you may test a
shallower sample if it is taken shortly after tillage. In non-cultivated crops,
soil samples should be six to eight inches deep. With deep-rooted non-legume
crops such as corn, wheat and cotton, take a soil sample of seven inches to 24
inches in addition to the tillage sample.
2.) Mix — Place these samples in a clean plastic container.
3.) Measure — Remove a small amount (coffee measure) of 2 parts soil from your
mix and add 1 part bottle drinking water. Do not pack soil in cup and always use
a flat bottom measure cup to assure proper proportions.
4.) Shake and wait — Stir or shake the soil and water mixture vigorously. Then
let sit for 1 to 2 minutes.
5.) Test — Turn on your pH meter, be sure you have calibrated your meter before
running the test ( see owners manual ) remove the cap to expose the sensor, and
dip the sensor completely in the solution. Record the reading displayed on the
meter
Understand Your Soil Test:
The relationships among pH, soil type, and lime requirements are explained.
Accurate soil tests can be an excellent management tool. Misuse of soil tests
leads to increased production costs, yield losses, or both. The elements
required by plants for proper growth have been determined by experimentation.
Experience has shown that soils differ greatly in their capacity to supply these
elements. The amount of each element supplied by a soil depends on several
factors. Two important ones are: (1) the type of
material from which the soil was formed, and (2) the treatment the soil has
received since being placed under cultivation. Not all of a particular element
in a soil is available to a plant. Thus, the soil test must be able to predict
whether a soil contains sufficient amounts of available nutrient elements for a
specific crop. The acid and base levels of a soil solution are important because
microorganisms and plants are responsive to
their chemical environment. Three possible chemical reaction conditions for the
soil solution are acidity, neutrality, and alkalinity. The reaction of the soil
solution can be defined by an index using the concentration of hydrogen ions in
the soil solution. This index is called the pH. A pH of 7 is neutral, pHs less
than 7 are acid, and pHs greater than 7 denote a basic (alkaline) condition.
Soil pH can be an indicator of the kind of nutrient
problems to expect in a soil. Obviously the pH is not a "cure-all" analysis, but
may indicate a possible problem, which may then be investigated with additional
analysis. In mineral soils, pH is a general indicator of soil nutrient
availability, presence of free lime (calcium carbonate), presence of excess
sodium, and excess hydrogen. Almost all soils are mineral soils; thus, soil pH
is a good indicator for possible nutrient problems. For example,
sulfur is available from pH 5.5 to 8.5; boron, copper, and zinc are most readily
available from pH 5 to 7; and iron and manganese are abundant below pH 5, but
moderately available from pH 5 to 7. Iron chlorosis frequently occurs at pH
above 7.7.
Factors influencing pH
Initially, factors such as parent material, rainfall, and type of vegetation
were dominant in determining the pH of soils. Under cultivation, however,
organic acids from plant roots, repeated use of acid-forming fertilizers, plant
removal, and replacement of calcium and magnesium by hydrogen eventually lowers
the pH of topsoil. Most of the nitrogen and phosphorus fertilizers used today
are acid forming. For example, about 1.5 pounds of lime is required to
neutralize the effect of applying 1 pound of anhydrous ammonia to the soil. Some
irrigation water contains substantial quantities of calcium and magnesium
bicarbonates (lime) which help neutralize the acidifying effects. Thus, soils
(without free lime) under production become increasingly acid unless lime is
artificially applied or is present in the irrigation water. This means farmers
need to frequently check soil pH to
determine whether they are maintaining a proper soil acidity level.
Electrical Conductivity ( EC )
EC stands for electrical conductivity, or the ability of a solution to conduct
electricity. Electricity moves efficiently through water with high levels of
salt present (high EC), and with more resistance through pure water (low EC). EC
indicates how much dissolved salt is in a given sample. That's why EC is also
referred to as TDS (total dissolved salts) or salinity (the amount of salts in a
solution). All nutrients are salts, so EC is a measure of
your total nutrients. Knowing your EC levels will help in plant production and
monitoring of inputs. Moisture in soil that has a high salt level will not move
into the plant's roots, causing drought symptoms, even when there is plenty of
water present.
EC is measured in mS/cm (milliSiemens per centimeter), but in older literature
it was referred to as mmhos/cm (millimhos per centimeter). One mS/cm is
equivalent to one mmhos/cm. Various EC meters measure in different ranges. Some
meters even read low enough levels to measure in μ S/cm (micromhos per
centimeter). It takes 1,000 μ S/cm to equal one mS/cm or one mmhos/cm
Testing methods
Measuring the EC of aqueous solutions is fairly simple. You calibrate the meter
(see your operator manual) then submerse the sensor into the liquid. The best
method for your Milwaukee EC meter is a 2:1 method of mixing two part soil with
one part bottled
drinking water, then testing the soil slurry. For convenience, you can also test
the same solution you prepared for pH readings in a 2:1 ratio (See Testing for
pH for procedures). Your local Extension agent or land grant university are good
sources of additional information on how to take soil EC measurements.
EC Meter Reading Interpretation
0.00 - 0.25 Very low - indicates probable deficiency.
0.25 - 0.75 Suitable for seedlings and salt-sensitive plants.
0.75 - 1.50 Desirable level for most Ag plants.
1.75 - 2.25 Reduced growth, leaf marginal burn.
EC in fertigation systems
Fertigation is a system that applies soluble fertilizer to plants through
irrigation water. It's common in greenhouse, hydroponics and irrigated
high-value crop and ornamental production. Adding fertilizer to irrigation water
increases the EC. To use EC to check fertilizer levels, take an EC reading of a
precise mixture of your fertilizer and irrigation water in the desired
concentration. You can check your fertigation water at any point along the
system. Its EC should match your sample. If it doesn't, check the injectors,
valves and nozzles in the system for blockage or other problems. Always check
the EC of your water first, and subtract that number from the EC reading of your
solution to determine your fertilizer concentration.
Soil Testing for Macronutrients Levels
of Nitrogen – Phosphorus – Potassium:
Once testing for EC has been accomplished and areas of low or very high EC
readings are determined it is advisable to perform a chemical soil analysis to
establish the macronutrient level. First a general overview of the three
essential nutrient elements and at the end of this section a table of
macronutrients levels for optimum plant
growth is provided.
Nitrogen:
Nitrogen ( N ) is a unique element in that it composes 80% of the earth’s
atmosphere. Plants, for the most part, cannot utilize atmospheric nitrogen.
However the legume group of plants have the capability to convert atmospheric
nitrogen into a form which can be utilized by the plant. Nitrogen fixation by
legumes is conducted through a symbiotic association between the plant root and
Rhizobium bacteria in the soil. The site where the
nitrogen capturing process occurs is in the visible nodules formed on the plant
roots. Some of the most common legumes are peanuts, soybeans, lespedeza,
alfalfa, clovers, and vetches. The most common sources of nitrogen for
non-legumes are through the decomposition of organic matter and application of
commercial nitrogen fertilizers.
Nitrogen is a component of the chlorophyll in plants, thus giving plants the
rich green color characteristic of a healthy plant. Nitrogen promotes succulence
in forage crops and leafy vegetables. When used at the recommended rates,
nitrogen improves the overall quality of leaf crops and stimulates the
utilization of phosphorus, potassium and other essential nutrient elements.
Given the benefits of nitrogen in crop production, it is important to note that
excessive nitrogen can have an adverse effect on crops. Excess nitrogen can
delay crop maturity, increase lodging due to weakened stems, produce excessive
vegetative growth at the expense of fruit set, and cause potential health
hazards for man and
animal due to nitrate accumulation in leafy vegetable or forage crops. Nitrogen
is an indispensable nutrient element but it must be utilized properly to reap
maximum benefit.
Phosphorus:
Phosphorus ( P ) is necessary for the hardy growth of the plant and activity of
the cells. It encourages root development and by hastening the maturity of the
plant, it increases the ratio of grain to straw, as well as the total yield. It
plays an important part in increasing the palatability of plants and stimulates
the formation of fats, convertible starches and healthy seed. By stimulating
rapid cell development in the plant, phosphorus naturally increases the
resistance to disease. An excess of phosphorus does not cause the harmful
effects of excessive nitrogen and has an important balancing effect upon the
plant.
Potassium:
Potassium ( K ) is a positively charged basic metal cation whose total content
in most mineral soil, except sandy natured soils, is greater than most other
major nutrient elements. It is estimated that 2.3% of the Earths surface is
potassium. However most of this potassium is not available to plants because it
is either bound in primary
minerals or is fixed in the interlayer of clay minerals. Since clay soils
develop from the decomposition of potassium rich primary minerals, it follows
that soils high in clay content usually have a relatively high potassium
content. As potassium in the soil solution is diminished by plant uptake it is
replenished by exchangeable potassium from soil colloids. Potassium fixed in the
inter layer of clay minerals also contributes to the soil potassium supply even
though it is not considered as readily available. Depending on the type of clay
mineral and its resistance to weathering actions, the potassium supply may or
may
not be adequate for maximum crop production. This evaluation of supply can be
made with the Milwaukee NPK soil test, since exchangeable colloids and potassium
in the soil solution are the forms of potassium measured by the soil test. In
this light the soil test for potassium content reflects that portion of soil
potassium which is readily available to plants, and depending on the soil test
level may or may not be an adequate supply for good crop yields. Soils which fix
potassium serve as a bank which safeguards against leaching and ultimately, in
time, returns potassium to the exchangeable form which can be withdrawn and
utilized by plants. Soils which are predominantly sand with little or no clay
have extremely low levels of native potassium and are subject to sever leaching.
In most cases annual potassium applications are required to grow satisfactory
crops.
Soils of this nature are common thought the Southeastern region of the United
States.
Potassium in plant nutrition enhances disease resistance by strengthen stalks
and stems. It activates various enzyme systems within plants. Potassium
contributes to a thicker cuticle which guards against disease and water loss. It
controls the turgor pressure within plants to prevent wilting. Potassium
enhances fruit size, flavor texture and development and it is involved in the
production of amino acids, chlorophyll formation, starch formation, and sugar
transport from leaves to roots.
Advance Greenhouses
