Title: Starter Fertilizer Specifics
Tom Jensen, PhD. Agronomy, CCA, P.Ag.
Northern Great Plains Director
International Plant Nutrition Institute (IPNI)
102 - 411 Downey Rd., Saskatoon, SK S7N 4L8
Email: [email protected]
Introduction
I am pleased to represent the International Plant Nutrition Institute (IPNI) at the Manitoba
Agronomist Conference. IPNI is a year-old organization that came from the reorganization of
the former Potash and Phosphate Institute. IPNI has the following mandate:
• A not-for-profit, scientific organization dedicated to responsible management of plant
nutrients for the benefit of the human family
• Unified, scientific voice for the world’s fertilizer industry
• Define the basis for appropriate use and management of plant nutrients, focusing on the
environmental and economic aspects
What is Starter Fertilizer?
It is a small amount of a multi-nutrient fertilizer applied in close proximity to or in a seed-row. It
is used to supply needed nutrients to improve early season growth and establishment, and often
improves yield or quality of the harvested portion of a crop.
What are the Forms of Starter Fertilizers?
Usually it dominantly contains phosphorous (P) and nitrogen (N), and may contain a number of
other macro, secondary and micro-nutrients. Some of the common granular and liquid
formulations are as follows:
•
Granular
– MAP 11-52-0
– 16-20-0-15S
– 13-33-0-15
– Europe Composite multi-nutrient granules (i.e. 20-10-10-3S)
– Blends N, P, K, S, etc.
•
Liquid Formulations
– 10-34-0
– 6-24-6
– Designer formulations to desired analysis
One of the common questions about starter fertilizers and specifically the P portion of the starter
is whether or not orthophosphates in the fertilizer are more efficacious then polyphosphates.
The simple answer is that there is very little difference under most field conditions. It is first
important to understand how P fertilizers are manufactured, and the chemical and physical
characteristics of these two general types of P fertilizers.
The P used to make P-containing fertilizer originates from rock phosphates that are natural
deposits of fluoroapitite (Ca10F2(PO4)6). These materials are mined in different areas of the
world, and are igneous or sedimentary in origin, with the latter sedimentary deposits constituting
the majority of world reserves. There are a few different methods used to treat the rock
phosphate to increase the solubility and availability of the P for crop use. The most common
method is called “Wet-Process Phosphoric Acid” and is simply the acidulation of finely ground
rock phosphate with sulfuric acid in the presence of water. The chemical reaction is
summarized as the following:
(Ca10F2(PO4)6) + 10H2SO4 + 20 H20 Æ 10 CaSO4●2H2O + 2HF + 6H3PO4
phosphate rock
sulfuric acid water
gypsum
hydrogen orthophosphoric
fluoride
acid
(Western Fertilizer Handbook, 2002).
Dilute orthophosphoric acid (28% P2O5) is separated from the other reaction end-products and
normally concentrated by evaporation of water to a 42% P2O5 content. This material can be
used to formulate P fertilizers as a reaction ingredient by reaction with ammonia (NH3) to form
mono-ammonium phosphate (NH4H2PO4, fertilizer analysis of 11-52-0), or with a potassium (K)
containing solution to form mono-potassium phosphate (KH2PO4, fertilizer analysis of 0-51-34).
Further heating of 42% P2O5 phosphoric acid causes more loss of water to the point that the
concentration of P2O5 can be increased to around 50% and is commonly called “merchant
grade” phosphoric acid. The phosphoric molecules exist in the orthophosphoric form.
Polyphosphoric acid is made when the merchant grade acid is heat treated to the point where
orthophosphoric acid molecules begin linking together with a corresponding loss of water as
steam (dehydration). The water in the steam originates from a combination of a hydroxyl ion
(OH-) and a hydrogen ion (H+) off the ends of adjoining orthophosphoric acid molecules. There
is a loss of one molecule of water for every two orthophosphoric acid molecules that link
together as show below:
Figure1. Condensation removal of water from orthophosphoric acid to produce pyrophosphoric
acid. (Western Fertilizer Handbook, 2002).
The greater the amount of heat applied the greater the number of linked orthophosporic acid
molecules and the P2O5 concentration can be increased. For example if the acid is heated and
enough water driven off a phosphoric acid with a P2O5 concentration of 75% P2O5 can be
produced. This product has 53% orthophosphoric acid, 40% pyrophosphoric (two phosphoric
molecules linked together), and 7% tripolyphosphoric (three phosphoric molecules linked
together) (Western Fertilizer Handbook, 2002).
A common liquid fertilizer containing nitrogen (N) and P is ammonium poly-phosphate (analysis
of 10-34-0). This product is made by reacting a 68% P2O5 phosphoric acid with anhydrous
ammonia under controlled conditions. The process is known as the TVA tee reactor process.
When the ammonia, a strong base, mixes with the acid the resulting exothermic reaction
produces a large amount of heat. This heat accompanied by dehydration produces a high
amount of linking of phosphoric acid molecules into polyphosphoric acid. For example 70% of
the phosphate in 10-34-0 is in polyphosphate form and 30% of in orthophosphate form (Agrium,
2008).
Plants can absorb P into their roots in both the orthophosphate and polyphosphate forms. In
the soil, polyphosphate converts to orthophosphate by hydrolysis (adding on water). The time
required for polyphosphate hydrolysis to occur varies with soil conditions and temperature, and
is accomplished by both chemical and biological reaction of polyphosphates with water. The
biological reactions have been shown to be the most rapid and effective with enzymatic activity
of phosphotase associated with plant roots and microorganisms being the most important
(Havlin et al 2005). Chang and Racz (1977 cited in Havlin et al 2005) reported that temperature
has a great effect on increasing the rate of pyrophosphate hydrolysis with the amount of
hydrolysis being 42%, 63% and 84% after 72 hours respectively at 5 °, 20 ° and 35 ° C (41 °, 68
° and 95 ° F). Under cool, dry conditions, hydrolysis may take longer. The efficiency of
polyphosphates with more than 80 % water solubility is considered to be equal to, but not better
than orthophosphates (MSUE 2005).
Polyphosphates is as effective as orthophosphates and it is only under cool and dry conditions
that there may be a slight advantage to the orthophosphate forms. In a review of published
literature comparing ammonium orthophosphates and polyphosphates Murphy (1979)
concluded that it was difficult to predict precisely when one source might be more effective than
the other.
How Much Starter Fertilizer Should be Used?
It is important to add sufficient so that the early crop requirements for additional nutrients are
supplied but not so much that ammonia or salt toxicity adversely affects the germinating and
emerging crop. There are useful guidelines available that suggest safe rates of N, P, K in seedrow starter fertilizers. There are differences between crops and soil-types. Manitoba
Agriculture, Food and Rural Initiatives has an information item on its website that gives
guidelines for seed-row fertilizer rates.
(i.e. http://www.gov.mb.ca/agriculture/soilwater/soilfert/fbd02s18.html)
There are Many Different Ways Fertilizers are Used in Different Crops and
Cropping Systems..
In corn production starter fertilizer has been an N-P-K blend of a low amount of fertilizer (e.g. 20
N-30P2O5-10 K2O) that is placed 100 mm to the side and 100 mm (2” x 2”) below the corn
seed. However there has been use of liquid starter fertilizer applied at lower rates directly in the
seed-row of corn quite successfully. It is usually applied at lower rates to that noted above (e.g.
10N-15P2O5-5K2O), so as not to reduce corn seed germination and emergence.
Seed-row Applications in Small Grain and Oils Seed Crops is a Common Practice
in Western Canada
It is common to apply granular or liquid starter fertilizers in the seed-row of small grains or
canola crops. Rates commonly used are about 7 lb N-30 lb P2O5 per acre. It is also common
to add in potassium (K) and sulfur (S) into the seed-row blend. Care must be taken not to add
too much as there can be ammonia and salt toxicity if safe-rates are exceeded.
Conclusion
Seed-row starter fertilizer can help improve crop yields and, or grain quality. It is commonly
used in the small grain and canola production and is becoming more common in corn
production.
References
Agrium, 2008. Ammomium Polyphosphate Fertilizer.
http://www.agrium.com/products_services/ingredients_for_growth/phosphate/1289.jsp
Havlin, J.L., Beaton, J.D., Tisdale, S.L., and Nelson, W.L. 2005. Soil Fertility and Fertilizers, an
Introduction to Nutrient Management. Pearson Education, Inc.
Michigan State University Extension (MSUE) Bulletin, 2005, N-P-K
Fertilizershttp://www.canr.msu.edu/vanburen/e-896.htm
Murphy, L.S. 1979. MAP, DAP, Poly and Rock. North Central Extension-Industry Soil Fertility
Workshop, Hilton Inn, St. Louis, MO, Oct. 31-Nov. 1.
Western Fertilizer Handbook, 2002, California Plant Health Association, Sacramento , CA