Which is the best fertilizer? With the countless number of fertilizer
products on the market, little research has been conducted to show whether
there is significant differences among the various brands. If you have found a
particular product that produces outstanding results, and you are willing to
pay the price, then by all means, continue to use it.
Otherwise,
let me give you some fertilizer basics. In the broadest sense, nitrogen is
nitrogen (N), phosphorus is phosphorus (P), and potassium is potassium
(K). Plants only absorb nutrients that
have been broken down into inorganic, water-soluble forms. For example, whether nitrogen comes from brand
A or B, whether it was derived from anhydrous ammonia (gas) or urea, or from
manure or the compost pile, it makes no difference to the plant. Stick with a
basic N-P-K fertilizer, buy on sale, and don’t fall for promotions.
The question
now is what type of formulation to purchase?
Nitrogen only, potassium only, phosphorus only, or combinations? Nitrogen is always needed in areas of heavy
rainfall, because it is easily leeched out of the soil. Fertilizers like ammonium sulfate, ammonium
nitrate, urea and calcium nitrate are all good fertilizers for supplying
nitrogen. Calcium nitrate will also give calcium but is more expensive.
Like
nitrogen, potassium can also move in the soil with water; phosphorus moves very
slowly. The question of whether to apply potassium and phosphorus can be
answered accurately by a soil analysis.
Without an analysis, statements about soil fertility are only guess
work. Check with local university cooperative extension offices for information about soil analysis.
If an analysis is not taken, then buying a fertilizer
with all three ingredients (N-P-K) is a good idea. The only problem with that
is if the soil has adequate phosphorus, and over the years more is added, a
soil imbalance may occur, and the excess phosphorus will cause a deficiency in
iron and zinc - seen as interveinal chlorosis, a yellowing between the
veins. Also, it is cheaper to supply
nitrogen than all three nutrients. On the other hand, you can apply nitrogen
alone and supply the potassium and/or phosphorus only when deficiency symptoms
occur.
Sometimes micronutrients are added to an N-P-K
formulation. But they are added at such low amounts that they are seldom beneficial
to the plant, especially trees. If a micronutrient (zinc, manganese, magnesium)
deficiency truly occurs, buy that specific nutrient and apply to the soil or as
a foliar treatment, whichever is appropriate. Special formulations of ‘citrus
food’ or ‘avocado food’ or ‘palm food’ are good fertilizers. But note that they
are higher priced, and a basic all-purpose (N-P-K) fertilizer should work as
well.
Organic vs. Inorganic
Inorganic
fertilizers often contain rather high percentages of the major nutrients and
are applied on a per pound per acre basis.
Organic fertilizers, on the other hand, have relatively low amounts of
nutrients and are applied on a per ton
per acre basis. Although organic
fertilizers have many benefits - including improving soil structure and the
water holding capacity of the soil, feeding beneficial microorganisms and of course, acting as a reservoir of nutrients
that can be released to the soil - they are rather expensive in some places
like Hawaii. Gardeners, however, are
encouraged to take advantage of any free or inexpensive supply of organic
fertilizers, i.e., manures, in their area.
