The Right Form of Phosphorus Fertilizer will Improve Your Yields
Dr. D. Mathur, product Chemist and Plant Physiologist
Apart
from nitrogen, potassium and phosphorous are the two most mobile major
nutrients essential for crop production. These nutrients influence virtually
all the biochemical processes and developmental phases of plants. Potassium
helps in regulation of water balance while phosphorous keeps the metabolic
machinery functional in plants.
Recently
farmers in south eastern Alabama, southern Georgia and northern Florida
have experienced problems that seem to be related to the use of ammonium
phosphite as starter fertilizer instead of Ammonium polyphosphate (Alabama
Cooperative Extension System, May, 2004). The difference in phosphorous
ionic form lead to the problems encountered by these farmers. As mentioned
below phosphite is the fungicidal form of phosphorous that is not recognised
by roots for uptake and metabolism compared to the most acceptable form
called phosphate. Although, phosphite can get oxidised by soil microbes
to phosphates , but most recent research has shown that phosphite reduced
the root and shoot growth @ 24 kg/ha (Barrett, 2002). McDonald et al.,
2001 found that phosphite is not utilized, but may trick phosphorus deficient
plants into not mimicking typical P deficiencies. Wells et al., (2000)
found that toxicity symptoms in alfalfa disappeared after 21 days. Harris
(2003) applied both phosphate and phosphite starter and foliar fertilizers
on cotton to compare its growth response to different
P sources, and found that phosphite treated plants were shorter compared
to phosphate treated plants
(Fig. 1). Phosphite injury to corn in Southeast Alabama 2004
The
typical symptoms of phosphite injury to plants closely mimic glyphosate
damage (Fig. 2), an amino acid inhibitor herbicide. Glyphosate contains
a terminal phosphite group that imparts herbicidal property to the glyphosate
molecule.
Armed
with this latest knowledge ,Spraygro Liquid Fertilizers' product chemist
Dr Deepak Mathur has developed the worlds highest liquid PK formulation
‘PICK 20-40' . This formulation has an NPK ratio of 0:20:40 w/v
and contains the most recognisable forms of potassium and phosphorous
ions for efficient uptake, distribution, growth and productivity.
PICK 20-40 is a non-phosphite phosphorous fertilizer with a near neutral formulation to harvest the best crop.
PICK
20-40 can be conveniently applied through the drippers at early stages
of crops and through the leaves ( foliar ) during the fruiting
and later stages of growth to produce the best quality crop with higher
yields. .Phosphites should not be used as a substitute for
plant – available , orthophosphate forms of phosphorous . Phosphite is
not immediately plant available and could lead to plant toxicities in
sensitive crops if high rates are applied . Phosphite damage appears amazingly
similar to glyphosate injury to crops .
fig 2 - phosphite stunted corn (L) compared to normal corn
Metabolic functions of Phosphorous
Phosphorous
provides the energy to cells to multiply and grow. The phosphate ion present
in the fertilizers get attached with adenosine moity to synthesize adenosine
triphosphate (ATP), the energy currency of cells. Another biomolecule
synthesised by the photosynthetic tissue contains phosphate ion, called
reduced nicotinamide adenine dinucleotide phosphate (NADPH) that drives
the fixation of carbon dioxide to form starch. Phosphorous impoverished
plants exhibit characteristic deficiency symptoms including
• ·
purple (anthocyanin pigment)
colouration of leaves and petioles
• ·
purple and weak stems
• ·
enhanced root growth at
the cost of shoot development
• ·
increased root to shoot
ratio
· low yields
· low yields
The
ability of plants to acquire phosphate-P during deficiency conditions
also increases due to the synthesis of phosphate transporters. These biomolecules
also transport phosphite ions. Phosphite is rapidly absorbed and translocated
within the plant. However, the uptake is pH dependent and subject to competition
by phosphate ions. Phosphite in presence of a small quantity of phosphate
will not be recognised by phosphate transporters. Despite having similar
mobility, the phosphite is a non-metabolized form of phosphorous and plants
cannot use this as the sole source of phosphorous. Phosphate can be assimilated
into organic P compounds within minutes of uptake.
Potassium
Potassium
is a highly mobile nutrient and must be incorporated in any nutritional
program. Traditionally, potassium is often ignored in the crop production
system, as a result the growers are now experiencing potassium deficiency
in their farm. Potassium must be applied early in the season for root
uptake or through the foliage only at later stages of growth, as roots
do not absorb potassium generally after flowering. Crops such as cotton
and potatoes have high potassium requirements due to the substantial leaf
area
development.
Potassium regulates the opening and closing of stomata, the site of gas
exchange for photosynthesis and water loss through transpiration. Potassium
is also a component of some enzymes actively participate in photosynthetic
reactions. Foliar application of potassium especially during fruit development
period promotes fruit size, aroma and carbohydrate synthesis. The deficiency
symptoms of potassium include
·
Marginal and leaf tip
necrosis due to the enhanced synthesis of polyamines
·
Poor quality fruit and
fruit size
·
Late season blotchy
chlorosis
Poorly developed root system
· Plants wilt easily with imposition of marginal water stress
For
further information contact SPRAYGRO LIQUID FERTILIZERS ph
08-84477266, www.spraygro.com.au
Literature
Cited:
Barrett,
SR, BL Shearer and GE Hardy (2002). Australian J. Bot.
Lucas,
RE, DD Warncke and VA Thorpe (1979). Agron. J. 71, 1063-1065.
McDonald,
AE, BR Grant and WC Plaxton (2001). J. Plant Nutr. 24, 1505- 1519.
Mitchell,
C and J Adam (2004). Alabama Coop. Ext. Sys., S-04-04. May 2004.
Wells,
KL, JE Dollaride and RE Mundell (2000). Comm. Soil Sci Plant Anal.
31, 2707-2715.
