Monday, August 5, 2013

Fertilizers - Nourishing the Garden


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.