Subject: Fertilizer FAQ

From: [email-masked]
Date: 3 Apr 95 16:28:06 -0500

FERTILIZER FAQ

       Initial writing by Kay Klier, using materials from
       a wide variety of sources.  Primarily written from
       the point of view of NPK.  Needs work on using
       green manures and cover crops as nutrient sources,
       since I mainly use them to add organic matter.

                            CONTENTS:

         I.  Fertilizer overview
        II.  Plant nutrients
       III.  What is a complete formula for plants?
        IV.  The numbers on the fertilizer sack
         V.  Calculating amounts of fertilizer to apply
        VI.  When to fertilize
       VII.  Methods of application
           A.  Commercial formulations
             1.  Dry
             2.  Soluble
           B.  Natural forms
      VIII.  Fertilizers vs. soil amendments
        IX.   Approximate analyses of commonly available natural
                   fertilizers and soil amendments
           A.  Seed meals
           B.  Manures
           C.  Animal byproducts
           D.  Stem and leaf products
           E.  Miscellaneous organics
           F.  Miscellaneous inorganics
         X.  Experiences with various formulations
           A.  Osmocote
           B.  Peter's soluble general purpose
           C.  Granular commercial fertilizers
           D.  "Weed and feed" lawn fertilizers
           E.  "Lawn fertilizers"
           F.  Houseplant formulations

I. FERTILIZER OVERVIEW

Fertilizers are materials that contain appreciable amounts of
plant nutrients. Probably the most familiar categories of
fertilizer are "chemical" vs. "organic": these could better be
termed synthetic vs. natural.

The synthetic fertilizers consist almost entirely of nitrogen,
potassium and phosphorus (the three nutrients most likely to be
in short enough supply to limit growth), in forms that are
readily utilized by plants.  In contrast, the natural fertilizers
are more likely to have significant amounts of micronutrients
(trace minerals) and the macronutrients are likely to be in forms
that are not as readily absorbed-- they are in forms that must
first be metabolized by soil microorganisms before they are
available to plants.  There may also be significant bulk: useful
for tilth improvement.

Thus the synthetic fertilizers are "fast", while the natural
fertilizers tend to be more "time release".  Some people feel
that synthetic fertilizers "poison" the soil, and will not use
them in any instance; others feel that synthetics are perfectly
acceptable if used properly.

Synthetic fertilizers can be one of the major sources of
groundwater pollution (as can runoff from manure piles): the
nitrogen is in such a soluble form that it tends to leach from
the point of application.  Overfertilization of natural bodies of
water tends to lead to algal blooms and subsequent death of fish
from oxygen depletion.  High nitrate levels in drinking water can
cause reduction in oxygen carrying capacity in red blood cells.
Reduced oxygen levels can cause retardation in young children and
fetuses.  If you apply a highly soluble fertilizer, please use it
thoughtfully.

II.  PLANT NUTRIENTS
Besides carbon, hydrogen and oxygen, the essential minerals for
most plants are:
                       Chemical
        Element        Symbol     Available form:
MACRO  Nitrogen        N          NH4+, NO3-
       Phosphorus      P          HPO4-, H2PO4-
       Potassium       K          K+

SECONDARY
       Sulfur          S          SO4--
       Calcium         Ca         Ca++
       Magnesium       Mg         Mg++

MICRONUTRIENTS
       Iron            Fe         Fe++, Fe+++
       Manganese       Mn         Mn++
       Boron           B          H2BO3
       Copper          Cu         Cu++
       Zinc            Zn         Zn++
       Molybdenum      Mo         MoO4--
       Chlorine        Cl         Cl-

It is relatively rare for soils to be deficient in copper, zinc,
molybdenum or chlorine.  If needed, the micronutrients plus
magnesium are often applied as a chelated mixture.  Sequestrene
is a common US brand.

III.  WHAT IS A COMPLETE FORMULA FOR PLANTS?

Different plants require different proportions of nutrients, but
you can get some idea of the general requirements by looking at
one of the commonly used research formulations: Knop's solution
with Nitsch's micronutrients.  This will support hydroponic
growth: (soil-less culture)

IV.  NUMBERS ON THE FERTILIZER SACK

The three numbers on a commercial fertilizer bag are in the order
NPK: nitrogen, phosphorus, potassium (=kalium).  The actual
numbers are percentages: 20-20-20 fertilizer is 20% (by weight)
nitrogen, 20% phosphorus, 20% potassium.

When choosing a fertilizer formulation, choose a balanced
fertilizer for most purposes, one in which the three numbers are
approximately equal.  If you wish to favor growth of leaves over
flowers (for instance for a leafy vegetable crop, or a lawn,
choose a fertilizer with a higher first number; for flowers or
fruits, choose a higher middle number, for better root growth,
choose a higher last number.  NPK: leaves: flowers: roots

V.  CALCULATING AMOUNTS TO APPLY

Typically, a soil test will tell you that X pounds per thousand
square feet will be required for a certain level of productivity
(those who are fortunate enough to think metric can use
appropriate units).  As an example, consider someone who has just
gotten a recommendation to apply 3 lbs of N per thousand square
feet, in a divided (spring and fall) application.  Our hapless
homeowners wish to get their money's worth from the new mower he
purchased for their 20,000 sq ft bluegrass lawn.

To determine how many square feet a bag of fertilizer will cover
at 1 lb per 1000 sq ft, multiply the weight of the bag by the
percentage nitrogen on the label, then multiply by 1000.
Assume this 30-1-1 fertilizer is sold in 40 lb sacks.  One bag
will cover 40 * .30 * 1000 = 12,000 sq ft at that rate..  But
since we want 3 lbs N per 1000 sq ft, one sack will cover 4,000
sq ft, and our homeowners will buy 5 sacks of fertilizer
(20,000sq ft/(4,000 sq ft/sack)) and use 3 sacks in the spring
and 2 in the fall...

VI.  WHEN TO FERTILIZE

Quickly absorbed fertilizers should be applied only when a plant
is about to begin a growth spurt, or during heavy growth.  You
should not fertilize heavily just before a plant will be going
into dormancy (this may keep the plant from "hardening off"
properly, and can result in winter damage.  If you choose to use
"high management" on a plant (heavy fertilization), you should
also count on increasing water to the plant.  If you anticipate
major insect damage (perhaps a hatch of grasshoppers), decrease
fertilization:  tender plant tissues are more subject to damage
than tissues that grew more slowly.  In general, a _slightly_
"hungry" plant is more resistant to pests and diseases than an
overfed one.

Overfeeding can also result in salts building up in the soil.
The salt build-up decreases the water potential of the soil, and
can actually reach the point that a plant cannot extract enough
water from a moist but salinized soil.  These soils must be
"cured" by leaching with tremendous amounts of water.

Although a "proper" fertilization regime would include soil and
plant analyses, most of us guesstimate fertilizer requirements.
A cautious approach to guesstimation is to observe the plants for
nutrient deficiency symptoms  (you'll need to compare to photos
often found in basic agronomy, horticulture or botany texts).  If
any are suspected, apply a weak fertilizer and observe for
increased growth.  If this is observed, you can repeat the
application.  Stop as soon as any signs of overfertilization
(weak, floppy growth, all leaves and no flowers, salt burned
leaves) are observed.

Slow release fertilizers can be applied at almost any time, and
there is relatively little danger of "burning" the plants.
Notable exceptions are urine or fresh manures, which can be very
high N.  Composted manures are less "lively".

VII.  METHODS OF APPLICATION
   A.  COMMERCIAL FORMULATIONS
       1.  DRY
Basic forms of commercial fertilizer include dry granular, slow
release (e.g. Osmocote (tm)), and soluble.  Granular fertilizers
are usually broadcast or used as a side dressing (dug into a
trench near the plants), slow release fertilizers are often used
for high-value crops like greenhouse plants and as "starters"
when planting trees or shrubs.

Two additional forms of dry fertilizer are available: fertilizer
"spikes" meant to be hammered into the soil near trees or shrubs,
or inserted into soil of potted plants, and solid pellets meant
for use in such devices as the Ross Root Feeder (tm).

       2.  SOLUBLE
Soluble fertilizers (Peters is a popular US brand) were once
nearly confined to greenhouse use, but are now becoming popular
for foliar fertilization of lawns and bedding plants.  These are
usually applied diluted in large quantities of water, using a
hose-end sprayer or proportioning device (e.g. Hoze-on
proportioner (tm)).  They may also be injected directly into
irrigation systems.  Because these soluble fertilizers are
readily available to plants, most growers have found that using
weaker solutions more often than label recommendations give
superior results.  A typical schedule might be 20-25% of the
recommended strength applied at weekly intervals rather than the
suggested monthly intervals.

Growers of some specialty plants have reported problems with
colored soluble fertilizers (a dye is added so the person who is
watering can see if fertilizer or plain water is coming from the
hose).  Some manufacturers are now producing soluble products
without the tracker dye.  Crops often reported affected by the
dye include ferns, lower plants and orchids.

Highly soluble fertilizers like these can pollute groundwater
unless carefully applied.

   B.  NATURAL FERTILIZERS
Because these generally have lower analyses than commercial
fertilizers, generally much larger quantities are applied.  This
has the advantage of improving soil tilth by adding organic
matter, and these generally require no additional micronutrient
correction.  You can also get a fair amount of exercise spreading
and digging in a natural fertilizer.

Another common way to use these fertilizers is as a "tea", an
infusion of (for instance) manure in water.  Water is added to a
container of manure, the contents stirred and allowed to settle,
then the water siphoned off for use, often on potted plants.
Additional water can be added and the process repeated.
<<<ANYBODY GOT FAVORITE RECIPES??? MINE IS HIGHLY NON-
QUANTITATIVE!>>>

VIII.  FERTILITIES VS. SOIL AMENDMENTS

Natural fertilizers are often used not just for their nutritive
value, but to improve soil tilth.  Commercial fertilizers are
generally not useful for tilth improvement.  However, other soil
amendments, like gypsum or agricultural lime, affect the
availability of soil nutrients by their effect on soil pH.

IX.  APPROXIMATE ANALYSES OF COMMONLY AVAILABLE NATURAL
       FERTILIZERS AND SOIL AMENDMENTS.

                       N     P     K    comments
A.  SEED MEALS
Alfalfa meal           2.4   0.2   2.1
Coffee grounds         2     0.3   0.2  acidic; add lime;
                                           caffeine residues may
                                           inhibit germination

Cottonseed meal        6     2     1    cotton is a high
                                           pesticide crop
Soybean meal           7     0.5   2.3

B.  MANURES
Bat guano (fresh)     10     3     1    
Bat guano (subfossil)  2     8     0    
Chicken manure (dry)   4     4     2
Cow manure (dry)       2     2.3   2.4  compost or apply in fall
Horse manure           1.7   0.7   1.8  
Pig manure (dry)       2     1.8   1.8  neighbors downwind will
                                         complain
Sheep manure (dry)     4     1.4   3.5

C.  ANIMAL BYPRODUCTS
Blood meal            10     0     0    
Bone meal              3    12   0-0.5  1 yr P availability
Bone meal (steamed)    1    11     0    
Crab meal (shrimp m., seafood m.)
                       4     3     0.5
Eggshell               1.2   0.4   0.1
Feather meal          11     0     0
Fish emulsion          4     1     1    5% sulfur
Fish meal           5-11   3-6   0-3    may attract cats and
                                           other carnivores
Horn & hoof meal   12-14     2     0    1 year N availability
Worm castings          0.5   0.5   0.3

D.  STEM AND LEAF PRODUCTS
Bluegrass hay          1.8   0.6   1.8  
Corn stover (dry)      1.2   0.4   1.6
Corn stover (green)    0.3   0.1   0.3
Cowpeas (dry)          3.1   0.6   2.3
Cowpeas (green)        0.4   0.1   0.4
Fescue hay             2.1   0.7   2.4
Grass clippings (green)0.5   0.2   0.5
Hairy vetch            2.8   0.8   2.3
Lespedeza hay          2.4   0.8   2.3
Oak leaves             0.8   9.4   0.1
Orchard grass hay      2.3   0.7   2.8
Red Clover hay         2.8   0.6   2.3
Sweet clover hay       2.2   0.6   2.2
Timothy hay            1.8   0.7   2.8
Wheat bran             2.6   2.9   1.6
Wheat straw            0.7   0.2   1.2
White clover (green)   0.5   0.2   0.3

E.  MISCELLANEOUS ORGANIC
Apple pomace           0.2   0     0.2
Compost (commercial)   1     1     1
Compost (homemade, high nutrients)
                       4     4     4    
Compost (homemade, low nutrient)
                       0.5   0.5   0.5  
Kelp meal            1-1.5 0-0.5 1-2.5
Milorganite (Milwaukee sewage sludge)
                       6     4     0
Oyster shell           0     0     0    31-36%  calcium + trace     
                                           minerals
Sawdust                0.2   0     0.2  uses lots of N as it rots
Sewage sludge, Iowa, average of 40 municipalities: very wide
ranges, depending on source
                       2.77  1.41  0

F.  MISCELLANEOUS INORGANICS
Ammonium nitrate      33     0     0    soil acidifier
Ammonium sulfate      21     0     0    strong acidifier
Aragonite              0     0     0    96% calcium carbonate
Borax                  0     0     0    10% boron
Calcitic limestone     0     0     0    65-80% calcium carbonate
Colloidal phosphate    0     2     2    
Dolomitic limestone    0     0     0    51% Calcium carbonate,
40% magnesium carbonate
Epsom salts            0     0     0    10% magnesium, 13% sulfur
Granite meal           0     4     0    67% silica, 19 trace
minerals
Greensand              0     1.5   6.1  32 trace minerals +
                                         10 year release K
Gypsum                 0     0     0    22% calcium, 17% sulfur
Muriate of potash: see potassium chloride
Potassium chloride     0     0    60    commonly used in
                                          commercial fertilizers
Potassium nitrate     13     0    44    basifier (makes soil more
                                          alkaline)
Rock phosphate         0     3     0    32% total P, 32% Ca,
                                         11 trace minerals
Soft phosphate         0    18     0    2-3 yr P availability
Superphosphate         0    20     0    12% sulfur
Sulfur elemental or flowers of sulfur
                       0     0     0    99% sulfur; soil
                                          acidifier.
Treble superphosphate  0    45     0
Urea                  45     0     0    highest available N in
                                          granular form

X.  EXPERIENCES WITH VARIOUS FORMULATIONS

   A.  Osmocote
One midwestern botanist with a tendency to forget to fertilize
greenhouse plants has had good results with osmocote; others have
reported poor results with other crops and better management.

   B.  Peter's soluble general purpose
Useful for most greenhouse crops, general bedding crops.  Too
high in nitrogen for good vegetable crops.  Blue tracking dye is
suspected in difficulties with orchids, ferns and lower plants.
Uncolored forms available.  Easy to handle.  May require
supplementation with micronutrients in greenhouse soils.

   C.  Granular commercial fertilizers.
Generally cheap and convenient; general purpose and easy to keep
on hand.  Buy by cost per pound of nutrients:  10 lbs of 15-15-15
at $1.30 is a better deal than 10 lbs of 10-10-10 at $1.00.
Broken sacks of dry granulars can often be purchased cheaply at
farm supply outlets.  5-10-5 is a typical "tomato" or "flowering
houseplant" formulation.  10-10-10 or similar near-equal number
formulation is an all-purpose balanced fertilizer.

   D.  "Weed and feed" lawn fertilizers
Combination herbicides and high nitrogen formulations.  Consensus
of the net seems to be that these are unneeded and polluting; a
more balanced lawn fertilizer and perhaps spot applications of a
selected herbicide (or a dandelion digger!) is a better choice
for lawn, people and environment.

   E.  "Lawn fertilizers"
Formulations like 43-1-1 encourage leaf growth at the expense of
root growth.  A more balanced fertilizer is better if clippings
are removed.  If clippings are allowed to rot in place, or
returned to the lawn as compost, potassium and phosphorus are
reclaimed, so a better choice would be a fertilizer in the
vicinity of 20-5-5.  High N fertilizers can be applied just a few
weeks before a special occasion requiring a deep green lawn
without harm if the lawn is basically healthy.

   F.  Houseplant formulations
Specialty houseplant formulations are common and expensive; a
soluble 10-10-10 or similar balanced fertilizer promotes good
growth of most plants; plants grown for their flowers may benefit
from 10-15-10 or similar formulations.  30-10-10 is a common
formulation for epiphytic orchids growing in pots.  In general,
do not fertilize a newly potted plant or one that is about to
enter dormancy.  Resume fertilization when new growth starts.