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GWAA

The Garden Writers Association


Last Update 06/03/08

Manures and Soil Amendments


 Plants Need a Well-balanced Diet Too!

Dirt, plants love it, but it is one thing that Florida truly lacks.  Sure, we have sand all over this state, but sand tends to be  humus-less, sterile and quick draining.  Not the preferred growing medium for plants.

Manure, on the other hand, is anything that has been added to the soil to increase its fertility for plant growth.  Manures can be divided into two classes: Organic or inorganic.   Organic manures are derived from decaying material of plant or animal origin.   Inorganic manures, also know as fertilizer, are derived from chemical processes -- most often they are man-made.

 

Organic manures often provide more than one of the many substances Soilneeded by plants for their growth.  Inorganic manures usually provide only one of the many substances needed by plants for their growth.  Inorganic manures fill a specific nutritional need of the plant, much like a vitamin pill.  If the plant is lacking a specific substance, inorganic manures can quickly fill that plant's need.  Thus, indiscriminate use of fertilizers may well result in an unbalanced diet for the plant.  The most common effect of this in the case of flowering plants is the use of too much nitrogen.  This causes abundant green growth (i.e. leaves) at the expense of flowers.

Fertilizers quickly break down to provide specific nutritional needs to plants.  Organics need time to be broken down into the simple chemical substances required by plants.  Thus organic manures tend to be safer to use when feeding plants as they rarely tend to "burn" then.  But if you have ever applied too much inorganic fertilizer to a plant (such as accidentally spilling a pile of weed and feed on your grass) you know the damage that it can do in a short amount of time because of the over-concentration of nutrients in one spot at one time.  Always use inorganic fertilizers with care.

Organic Manures -- Almost any kind of organic matter may be used as manure, but some kinds are better than others.  Organic manures vary widely in the amount of plant nutrients that they contain.  Some are more concentrated than others.   Compost is one of the less concentrated organic manures, but it is extremely valuable in adding extra body to soils especially the sandy ones we are plagued with in most of Florida.  Compost can also help to lighten heavy clay soils like those in some areas in the northern part of the state.

 

Simple Chemical substances are taken up by plant roots in dilute solution.   Organic substances are complex and insoluble and must be broken down or decomposed before they may be taken up by a plant's roots.  Therefore, organic manures which break down or decay quickly are available to the plant faster than those which decay slowly.  The rate of decay is a function of temperature.  The higher the temperature, the more quickly the nutrients in the manure will become available to the plant.  At the same time, the quicker that the nutrients become available to the plant the more rapidly those nutrients will be depleted.  In practice, too much organic manure applied at once will decompose before the plant may make use of it.   So smaller applications of manure applied frequently are more beneficial to the plant than larger applications applied less frequently.

Types of Manures:

Cow, Horse or Sheep Manure -- Are the most common organic manures available.  Elephant manure (when the circus is in town) may be used in the same way as Cow, Horse and Sheep Manure.  These manures may be used by mixing with soil or by adding them to compost.  When fresh, they may be mixed with water and the resulting manure tea applied  to the soil around the plants.  These manures, when dried, may be also mixed with potting soil.  Because these manures do not contain a high proportion of plant food frequent applications are required.

Urine -- Yes, pee.  Whether from man or animals it is an extremely valuable manure as it contains a higher proportion of nitrogen than Cow, Horse, Sheep or Elephant Manure.  As the valuable chemical substances are already in solution they are immediately available for plant use.  Urine should not be used fresh but kept for a few days then diluted at a ratio of 1 to 4  with water.  It may then be applied directly to the ground around plants.  Urine is also useful as a source of added nitrogen to compost.  Be aware that urine should be kept in a closed container out of the house prior to use as it will definitely become stinky.

Poultry Manure -- This is available from Chickens, Duck, Geese, Turkeys, Pigeons, Parrots, and so on.  Poultry manure may be used fresh when mixed with soil or as a poultry manure tea after first being rotted for a short time in water.  Poultry manure is more concentrated than the cattle manures mentioned above as it is high in nitrogen.  Poultry manure should be stored in a closed container as it is foul-smelling.

Bat Guano -- This comes from caves inhabited by bats.   It is somewhat of a boutique fertilizer and tends to be rather expensive for small amounts.  Bat Guano is usually higher in phosphorus than nitrogen and may be used in the same way as cattle manure.

Bone Meal -- This organic fertilizer is made from the bones of animals which have been used as food.  It contains nitrogen but is valued more for its phosphorous and calcium content.

Blood Meal --  This is a concentrated organic manure.  It is high in nitrogen and must be kept in an airtight container as it is hygroscopic (attracts water).  When this happens,

some of its nitrogen value is lost.

Fish Meal or Fish Emulsion --  This is a good fertilizer, but tends to be extremely fishy smelling.  However, it is a good source of nitrogen and some phosphorous.

Seaweed --  With beach access available in most of Florida, this is a fairly easy manure to obtain at no cost.  Seaweed is an excellent source of calcium and potash.  Prior to using seaweed though, be sure to wash it thoroughly to remove the salt.  Dig it directly into the soil or compost it.

Sludge (or Milorganite®) --  While it has a slight odor, dried sludge is safe to use and mostly odorless.  It may be added to the soil or compost pile.

Green Manure --  Grass and weeds that have been cut from your lawn or pulled from your garden make a good humus.  Be sure to allow them to rot well in the compost pile before using as pieces of the roots and seeds may re-grow where you least want them to.  Green manure helps to add body to sandy soil.

Inorganic or Artificial Manures:

These manures, or fertilizers, are either of mineral origin (Florida is famous for its phosphorous mines) or man-made through chemical processes.    Because these fertilizers are relatively simple in structure, they break down and are available to plants rather quickly.  Fertilizers are available as 'Complete Fertilizers' with varying degrees of chemical compositions or as individual chemicals such as Nitrogen, Phosphorous or Potash.  In either case the fertilizers are also available as timed release or quick acting.

Artificial manures are often more expensive than organic fertilizers, but tend to be easier to use, less odorous  and may be stored longer without deteriorating.  They can not, however, add texture to sandy soils as can organic manures.  Also, these fertilizers must often be stored in containers with tight fitting lids as they tend to be hygroscopic and also break down when exposed to air.

Fertilizers should be kept away from children and animals and old fertilizers disposed of carefully.  Under no circumstances should they be dumped into storm sewers or canals as they will make their way to Florida's water supplies and adversely effect both the water quality and the biota of our lakes and canals.

The mixture or composition of inorganic fertilizer is expressed by the amount of Nitrogen, Phosphorous and Potash they contain.  This is shown on the fertilizer container as percentages of N, P and K.  There are varying combinations of these elements and often other substances such as Calcium (Ca), Magnesium (Mg), Boron (B) and Manganese (Mn) are added to the fertilizers as supplemental ingredients.   Nitrogen is used by plants for the normal healthy growth of green plant tissues such as leaves and stems.  Too much nitrogen will cause rapid growth of leaves and soft stems which tend to be an open invitation for attack by pests and diseases.   Phosphorous is responsible for good root development, disease resistance and flower and fruit production.  Potash also helps to promote disease resistance in plants as well as encouraging higher fruit production.

Common Fertilizers:

Ammonium Sulfate -- A soluble salt which is an excellent source of Nitrogen.  Use with care as it may promote an excess of green growth and make your plants weak, spindly and susceptible to disease.

Ammonium Nitrate -- Useful to increase soil acidity.

Nitro-chalk -- A mixture of Ammonium Nitrate and Limestone.  Useful in neutralizing acid soils.

Calcium Cyanamide -- A source of Nitrogen and helps to de-acidify the soil.  It must be used carefully as it may kill young plants.

Urea -- Another good source of Nitrogen, but once again, must be used carefully as it will promote an excess of green growth and make your plants weak, spindly and susceptible to disease.

Rock Phosphate -- A naturally occurring product that is not soluble in water.  Useful for soils with a high degree of organic matter, but will not break down and be useful to plants in sandy or neutral soils -- needs acidic soils to be catalyzed.  A little goes a long way.

Magnesium Phosphate -- Useful in promoting chlorophyll production in plant leaves necessary for healthy plant growth.

Superphosphate -- Partly soluble in water and quickly available for plant use.

Potassium -- An essential element deficient in our sandy soils.

Calcium -- Another essential element for most plants.   Also known as lime, it helps to neutralize the acidity of acidic soils and allows the release of plant nutrients that would otherwise be bound in the soil and unavailable to plants.  Lime should be applied carefully as it may cause a deficiency of other elements in plants if used in large quantities.  Lime is available in several forms:   Quicklime (Calcium Oxide), which should be handled careful because when exposed to moisture it heats up and will cause burns;  Hydrated Lime which is Quicklime diluted with water;  Ground Chalk (ground Limestone or Calcium Carbonate);  and   Magnesium Lime (or ground Magnesium Limestone).

 

 

 

 

 

 

 

 

 
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