Phosphorus Nutrition
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Transcript of Phosphorus Nutrition
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A regional newsletter published by Potash & Phosphate Institute (PPI) and
Potash & Phosphate Institute of Canada (PPI
Multi-Reg
January 20
Co-authors:
The cotton planthas five main growth stages:1) germina-
tion and emergence, 2) seedling establishment, 3) leaf area
and canopy development, 4) flowering and boll develop-
ment, and 5) maturation. An effective way of assessing the
development, or progression of physiological events, of a
cotton plant is with heat units or growing degree days. A
heat unit is expressed in degrees Fahrenheit and is defined
by the following equation:Heat Unit = [(daily maximum temperature + daily
minimum temperature) 2] 60.
Figure 1shows an example of a timeline that generally
describes the relationships among time, heat unit accumula-
tion, and cotton development. Proper nutrition helps assure
that a cotton crop remains healthy throughout the season,
and that it progresses through each stage of development
with minimal stress.
Phosphorus (P) is an important nutrient in cotton
production for several reasons. It is essential for vigorous
root and shoot growth, promotes early boll development,
hastens maturity, helps overcome the effects of compaction,increases water use efficiency, and is necessary for energy
storage and transfer in plants. Approximately 30 lb P2O
5/A
is taken up for every bale of cotton produced.Of the total
uptake, slightly less than 50% (14 lb P2O
5) is removed per
harvested bale. Phosphorus uptake by cotton closely
follows the pattern of dry matter accumulation (Figure 2).
By first flower, the crop has accumulated about 20% of the
total seasonal uptake. After this time, the rate of uptake
increases dramatically. By peak bloom, about half of the
crops P has been taken-up, and by first open boll the crop
has taken up over 70% of its needs.
Peak daily uptake of P occurs 60 to
100 days after planting and can
exceed 1.4 lb P2O
5/A/day. Failure to
maintain the uptake demand during
the peak period will result in plant
stress, yield loss, and a decline in
lint quality. Phosphorus uptake iscompleted by the time the crop
reaches the 50% open boll stage.
Phosphorus Nutrition of Cotton
Dr. C.S. (Cliff) Snyder,
Southeast Director
Potash & Phosphate Institute (PPI)
P.O. Drawer 2440, Conway, AR 72033-2440
Phone: (501) 336-8110; Fax (501) 336-8110
E-mail: [email protected]
Dr. W.M. (Mike) Stewart,
Great Plains Director
Potash & Phosphate Institute (PPI)
P.O. Box 6827, Lubbock, TX 79493
Phone: (806) 795-3252 Fax: (806) 795-59
Email: [email protected]
Approximate days
after planting
Approximate heat
units after planting
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Emergence Squaring Peak bloom Harvest1st bloom 1st open boll
May June July August September NovOctober
0 80 525 1060 1470 1640 2280
95% mature
Figure 1. A production timeline for irrigated cotton in the Texas High Plains(Source: R. Boman).
Figure 2. Accumulation of N, P, and dry matter by cotton.Phosphorus accumulation is directlyproportional to dry matter accumulation, whileN is slightly higher through most of the season(Source: D. Krieg).
Time (Days)
0 30 60 90 120 150
Maximumaccumulation,
%
0
20
40
60
80
100 Dry weight and phosphorusNitrogen
First Square
First Flower
Peak Bloom
First open boll
20% open boll
*
*
*
*
*
*50%open boll
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RN 03034
To ensure proper seed and lint development, adequate
soil P levels must be built and maintained.There are other
important reasons to build soil test P levels into the high or
medium to high range: to increase root growth for efficient
uptake of other nutrients, capitalize on good weather
years and minimize risk associated with bad weather
years, raise soil productivity, increase yield potential of all
crops in the rotation, and improve grower profit potential. A
rule of thumb for raising soil test P is that it takes 6 to 14 lbP
2O
5/A above crop removal to build soil test P by 1 lb/A on
sandy loam to silt loam soils.
Figure 3illustrates the results of research in North
Carolina on a sandy loam Coastal Plain soil. The economic
Mehlich 3 P critical level was 33 parts per million (ppm), or
80 lb/A using an 8 in. sampling depth. The authors reported
that once the optimum soil test P was achieved, about 33 lb
P2O
5/A/year would be needed just to maintain the soil test P
in a cotton, corn, and peanut rotation.
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70 80 90 100
0 to 8 in. Mehl ich 3 P, ppm
Relativeyield,
%
Soil test for 95%of maximum yield
Estimated economic critical level
Figure 3. Relative yield response by conventional-tillagecotton to soil test P in North Carolina.
The critical fertilizer P rate to achieve 95% of the maximum
cotton yield on this low P soil was determined to be 96 lb
P2O
5/A for the disk-till system and 80 lb P
2O
5/A for no-till.
Placement of P fertilizer can be an important consideration
in some circumstances. Banded application of P may be
beneficial, especially where soil test levels are low or in
reduced tillage systems. Rates of fertilizer in-furrow with theseed are limited due to possible seedling damage and
toxicity. For example, research has shown that rates of 11-
37-0 fluid fertilizer greater than 2.5 to 2.8 gal/A can reduce
cotton stands and yield, and rates greater than 1.5 gal/A are
generally not recommended.
Insufficient P results in dwarfed plants, delayed fruiting
and maturity, and reduced yield.While placement of P
fertilizer is not as important as in the production of many
other crops, banding P can increase yields in some situa-
tions (e.g., reduced or no-till, compacted soil conditions).
Use soil tests to help determine the optimum P application
rate.Soil test levels should be maintained in the medium to
high range to assure consistent production, and that P does
not limit cotton yield and quality.
Figure 4. Six-year average cotton response to P rateand tillage in Tennessee.
An example of response to fertilizer P is shown in Figure
4. The study was conducted from 1994 through 1999 on
Loring silt loam (loess) at Milan, Tennessee. Yields were
increased with P fertilization in both tillage systems, but the
response to P fertilization was greater in the no-till system.
700
800
900
1,000
1,100
1,200
0 40 80 120
Disk till No-till
P2O5, lb/A/year
Lintyield,
lb/A
Initial Mehlich 3
soil P (< 5 ppm)
For more about Phosphorus Nutrition of Cotton,a PowerPoint slide presentation is available free at
www.ppi-ppic.org/presentations/cotton
Multi-Region
January 2003
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