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DIFFERENCES IN CORN HYBRIDS TO STARTER PLACEMENT AND RATE
F. M. Rhoads, I.D. Teare*
All authors, Univ. of Florida, NFREC, Rt. 3 Box 4370, Quincy, FL
32351. Florida Agric. Exp. Stn. Rep. No. NF 94-2. *Corresponding
Corn (Zea mays L.) hybrids differ in response to starter
fertilizer, but the cause is not known Two glasshouse
experiments were conducted to characterize a responsive and a non-
responsive corn hybrid in relation to root growth, P and N uptake,
and nutrient uptake efficiency. Applied phosphorus levels of 0,
10, 20, or 30 mg kg- were mixed with the total soil volume (1.5 L)
in pots in experiment I. Nitrogen was applied at a constant rate
(100 mg pot-') and also mixed with the total volume of soil.
Phosphorous rates were 0, 30, or 60 mg kgI' in experiment II.
Varying P levels and one level of N (200mg pot-') were mixed with
total soil volume (BC) or banded (BD) 5 cm vertically below the
soil surface and 5 cm horizontally from the seed planted 2.5 cm
deep. The soil was obtained from the A horizon of Norfolk loamy
fine sand (fine loamy, siliceous, thermic, Typic Kandiudult) with
low available P and high P fixing capacity. Root weight was 31%
and 48% greater for the non-responsive hybrid (NK 508) than the
responsive hybrid (G4733) for experiment I and II, respectively.
This indicates that the non-responsive hybrid was able to tap a
larger N and P supply than the responsive hybrid in low P soil with
high fixation capacity. The responsive hybrid produced a
significant (P = 0.05) increase in root weight due to banding N
only, but the non-responsive hybrid did not respond to N placement.
The conclusion was that hybrid response to starter fertilizer was
a function of differences in root growth.
Environmental factors that influence response to starter
fertilizer are soil temperature, phosphorus (P) immobilization, and
low fertility soils. Low soil temperatures reduce root growth
(Mackay and Barber, 1984) which in turn reduces nutrient uptake of
plants with limited root systems. Early planting dates, to
maximize corn yield potential (Wright et al., 1988) often result in
exposure of young seedlings to low soil temperatures. Starter
fertilizer increased corn yield in every case when either air or
soil temperature was below normal in a Canadian study (Ketcheson,
1968). Poor seedling growth resulting from low nutrient
availability of N and P in cold soils can occur irrespective of
residual soil fertility levels (Touchton and Hargrove, 1983). Both
N and P are considered essential ingredients in starter fertilizers
* (Ketcheson, 1957) to offset low N and P availability in cold soils
(Cassman and Munns, 1980; and Wallingford, 1978).
Some soils have a high capacity to fix or immobilize
fertilizer P, thereby reducing its availability to plants with
limited root systems. Research has shown that there is an optimum
fraction of soil with which to mix a given amount of fertilizer P
in order to obtain maximum P uptake in a given soil (Anghinoni and
Barber, 1980). Where one rate of P was applied to three soils, the
greater the adsorption of P by the soil, the lower the fraction of
P-treated soil necessary to maximize P-uptake. Response to starter
fertilizer in soils with high P adsorption (as in the Southeast)
will be due to added P. Low fertility soils provide a more
favorable environment for plant response to starter fertilizer than
high fertility soils. Placing starter fertilizer in a band near
the seed in a low fertility soil .gives a dramatic increase of
nutrient concentration in the limited root zone of young seedlings
and promotes more rapid growth.
Corn hybrids have been shown to respond differently in grain
yield to starter fertilizer (a small amount of N and P fertilizer
band applied near the seed at planting) in a 3 yr field experiment
at Quincy, Florida (Teare and Wright, 1990). Some were consistent
positive responders, some were not responders and some were
inconsistent. Hybrid characteristics that influence grain yield
response to starter fertilizer include rate of root growth, P-
uptake efficiency, N-uptake efficiency, rate of top growth, and
growth response to temperature. Hybrids that are highly sensitive
to temperature are expected to be inconsistent in response to
starter fertilizers because when temperature is higher than normal
a positive response is not likely to occur while below normal
temperatures would probably result in a positive response. A
hybrid having a high rate of root growth that produces a large root
system, and a high efficiency of N and P uptake is considered to
have root adequacy under suboptimal conditions (i.e., cold or high
P fixing soils) and is not expected to have a positive response to
starter fertilizer. A hybrid having a slow rate of root growth,
resulting in a small root system, and/or low nutrient uptake
efficiency does not have a root adequacy under suboptimal
conditions and a positive response to starter fertilizer is
Two experiments were conducted to compare the root growth and
* N and P uptake efficiency of pre-selected responsive and non-
responsive corn hybrids to starter fertilizer application. Our
hypothesis was that a corn hybrid not positively responsive to
starter fertilizer has a more rapid rate of root growth and/or a
higher N and P uptake efficiency than a corn hybrid that
consistently responded positively. The objective of experiment I
was to measure the differences between hybrids in root growth with
varying phosphorous rates at a constant N and K rate on responsive
and non-responsive corn hybrids. The objectives of experiment II
were to measure the differences between hybrids in root growth,
total nutrient uptake and efficiency of P and N uptake from
broadcast (BC) and banded (BD) fertilizer (band placement was used
S to simulate starter fertilizer) applications to define root
METHODS AND MATERIALS
'Deltapine G4733' and 'Northrup King 508'(hereafter referred to
as G4733 and NK 508, respectively) were selected because G4733
consistently gave a positive grain yield response to starter
fertilizer and NK 508 consistently gave no response to starter
fertilizer in a 3 year field study at Quincy, Florida (Teare and
Wright, 1990) leading to the premise that G4733 was root adequate
and NK 508 was not root adequate. The corn hybrids were seeded in
pots (15 cm wide by 12 cm deep) containing 2 kg of soil. The
potting soil was taken from the A horizon of Norfolk loamy fine
sand (fine loamy, siliceous, thermic, Typic Kandiudult) low in
available P because of a high fixation capacity. Seed for
experiment I and II were planted on 15 August 1991 and 17 March
1992 in two glasshouse studies at Quincy, Florida. Average minimum
and maximum temperatures were 21' and 32' C, respectively, in
experiment I and 11' and 24 C in experiment II. Six seeds were
planted 2.5 cm deep at the center of each pot. Plants were thinned
to two per pot at the two-leaf stage. Both experiments were limed
by mixing 2000 mg CaO pot-' uniformly with 2 kg of soil. Soil pH
was determined with a pH meter in a 1:1 v/v soil:water slurry for
each experiment. Soil for the first experiment averaged pH 6.1
with a range of + 0.7 and a standard deviation of 0.2. For the
second experiment, soil average was pH 6.7 with a range of + 1.2
and a standard deviation of 0.3.
The P rates for experiment I were 0, 10, 20, and 30 mg kg"'
(Table 1) (1mg kg-1 is approximately equal to 2 kg ha'-) (triple super
phosphate). Placement of P was mixed with total soil volume in the
pot to simulate broadcast application (BC). The N (100 mg N pot-'
[mg pot-' is approximately equal to kg ha-1]) and K (281 mg K pot-')
were kept constant and applied as potassium nitrate (KNO3).
Since some P deficiency was observed in experiment I, the
highest P rate was doubled in experiment II and P rates changed to
0, 30, and 60 mg kg'. Nitrogen and K rates were increased
correspondingly to 200 mg pot-' as NH4NO3and 415 mg K pot-' as K2SO4.
Phosphorus and N were applied broadcast (mixed with total soil
volume) or banded across the center of the pot in a V cut to 5 cm
below the surface and 2.5 cm wide at the top. Seed was planted at
2.5 cm depth and 2.5 cm from the edge of both sides of the top of
the V or 5 cm horizontally from the center of the V. The single
* rate of N was broadcast, banded with the P, or banded alone with
broadcast P at the 60 mg kg-' rate (Table 2).
Plants were harvested 33 days after seeding for experiment I
and 41 days after seeding for experiment II. Roots were separated
from the soil by washing the soil through a screen with tap water.
Root dry-matter yield was determined after drying to constant
weight at 70C. Top dry-matter data was collected but not reported.
Tissue P was determined separately for roots and tops on a
colorimeter by the molybdenum-blue method after ashing plant
samples at 5000C. These values were multiplied by the grams of root
and top dry-matter to determine total P uptake of roots and tops.
Tissue N was determined by micro-kjeldahl procedures and total N
uptake was calculated in the same manner as was P. Soil-test P
(sampled at harvest) was determined in a Mehlich-1 extract (Hanlon
and Devore, 1989), using the molybdenum-blue method. In general,
Mehlich-1 extractable soil P at harvest was increased about 7 or 8
mg kg-' by each 30 mg kg-' fertilizer P in experiment II.
The experimental design for each experiment was a randomized
complete block containing four replicates. Statistical analysis
consisted of analysis of variance, regression analysis, and single
degree-of-freedom contrasts (Steel and Torrie, 1960).
RESULTS AND DISCUSSION
Root growth, total P uptake (root and top), and P uptake
efficiency (P uptake/g roots) were measured in experiment I for two
hybrids that reacted differently to starter fertilizer application
in a previous field experiment (Teare et al., 1990). Deltapine
G4733 grain yield had consistently responded positively to starter
fertilizer (RH) and Northrup King NK 508 had consistently given no
response to starter fertilizer (NRH). Mean root dry matter (a
measure of root growth) was 28% greater in NK 508 (NRH) than in
G4733 (RH) in experiment I (Table 1). Total P uptake of roots and
tops of the two hybrids increased linearly in relation to the
amount of P applied and the total P uptake of the NRH was 29%
greater than the RH. Phosphorous uptake efficiency (mg P/g roots)
* was not significantly different between hybrids. Since there was no
significant difference between hybrids in P uptake efficiency the
increased P uptake by the NRH was due to increased root growth,
which indicated that root growth of the NRH was sufficient to
obtain P for maximum yield without starter fertilizer.
Band placement (to simulate starter fertilizer) of P (varying
amounts) and N (a constant amount) was added to experiment II for
comparison with broadcast fertilizer application to define root
adequacy. The hypothesis was that band placement would increase
root growth by minimizing P and soil contact to a much greater
extent than broadcast application (mixing the N and P in the total
soil volume). All hybrids should respond to banding in low P soils
with high fixation capacity, but the hypothesis was that a small
root system would respond to banding more in proportion to size
than a large root system which would exploit a larger soil volume
and obtain more available P.
Dry-matter yield of roots of both hybrids was increased by
band placement at each P fertilizer rate in experiment II (Table
2). Band placement of N and P at 30 mg P kg-' compared to broadcast
increased root growth of the RH by 103 % (3.19 vs. 157 g pot-1) and
of the NRH by 80% (4.68 vs. 2.60 g pot-). The difference between
hybrids was even greater at 60 mg P kg1 with band placement
producing 1345 (4.75 vs. 2.03 g pot-1) more root weight than
broadcast for the RH but only 72% (6.56 vs. 3.81 g pot-1 more for
the NRH. This supports the hypothesis that a slower growing
(smaller) root system responds to starter fertilizer more in
proportion to size than a larger (faster) growing root system .
Root growth was 48% greater for the NRH than RH, averaged
overfertilizer treatments. Total P uptake was 25% greater and
total N uptake was 16% greater for NRH than RH. However, P uptake
efficiency was 17% greater and N uptake efficiency was 30% greater
for RH than NRH. Increased uptake efficiencies were not great
enough to offset the difference in root growth.
Band placement of N was compared to broadcast N root growth
dry-matter yield of the RH was increased 76% (3.58 vs. 2.03 g pot-1)
but the increase of the banded over-the broadcast N (4.45 vs. 3.81
g pot-) fpr NRH was only 17% and was not significant (P > 0.05).
The total N uptake of the NRH was influenced more by P rate (137
vs. 175 mg) than by N placement (175 vs. 177 mg). The opposite was
true for the RH which showed a 20 mg (104 vs. 124 mg) increase due
to P rate and a 57 mg (181 vs. 124 mg)increase due to N placement.
Nitrogen uptake was increased 46% (181 vs. 124 mg) in the RH by
band applied N, but only 1% in the NRH (177 vs. 175).
Both experiments are in agreement that the NRH had the largest
root system in terms of dry-matter yield and also took up the most
P in a starter fertilizer system. The RH was most efficient in
taking up N and P per g of roots but this was more than offset by
the enhanced root system of the NRH. We conclude that the
difference in response between the two hybrids to starter
fertilizer was due to a difference in growth of root systems.
As previously stated, only one of these hybrids responded to
band placement (starter fertilizer) of N and P in the field
* experiment where Mehlich-1 P was high (>31 mg kg'1). However, both
hybrids responded to band placement of P and N in the low P soil of
the pot experiments. Since only the hybrid that responded to N and
P in the field responded to N placement in the potexperiments, this
suggests that the positive response of some hybrids to starter
fertilizer in the field may be due to N placement. The difference
between these hybrids in response to N placement may explain why
conflicting results have been obtained with starter fertilizers
containing N and P (Teare and Wright, 1990).
Anghinoni, I., and S.A. Barber. 1980. Predicting the most
efficient phosphorus placement for corn. Soil Sci. Soc. Am.
Cassman, K.G., and D.N. Munns. 1980. Nitrogen mineralization as
affected by soil moisture, temperature, and depth. Soil Sci
Soc. Am. J. 44:1233-1237.
Hanlon, E.A., and J.M. Devore. 1989. IFAS extension soil testing
laboratory chemical procedures and training manual. Florida
Cooperative Extension Service. Circular 812.
Ketcheson, J.W. 1957. Some effects of soil temperature on
phosphorus requirements of young corn plants in the
greenhouse. J. Soil Sci. 37:41-47.
Ketcheson, J.W. 1968. Effect of controlled air and soil
temperature and starter fertilizer on growth and nutrient
composition of corn (Zea mays L.) Soil Sci. Soc. Amer. Proc.
MacKay, A.D., and S.A. Barber. 1984. Soil temperature effects on
root growth and phosphorus uptake by corn. Soil Sci. Soc. Am.
Steel, R.G.D., and J.H. Torrie. 1960. Principles and procedures
of statistics. McGraw-Hill, NY.
Teare, I.D., and D.L. Wright. 1990. Corn hybrid-starter
fertilizer interaction for yield and lodging. Crop Science.
Touchton, J.T., and W.L. Hargrove. 1983. Grain sorghum response
to starter fertilizers. Better Crops Plant Food 67:1-3.
Wallingford, W. 1978. Phosphorus in starter fertilizer. p. 62-79.
In C. P. Ellington (ed.) Phosphorus for agriculture. Potash
& Phosphate Inst., Atlanta, GA.
Wright, D.L., I.D. Teare and B.T. Kidd. 1988. Ontogeny of.maize
in relation to sequential cropping. Trop. Agric. (Trinidad)
Table 1. Dry matter yield, total P uptake and P uptake per gram of
roots of G4733 and NK 508 two corn hybrids. Single
degree-of-freedom comparisons for effect of hybrid are
shown at the bottom. Experiment I. (33 days after
Total Nutrient uptake
P treatment Root P uptake efficiency
Rate Placementt Dry-matter (Root & top) (P g1 of roots)
-----g pot-'----- mg pot-1
Responsive hybrid (G4733)
0 -- 0.95 2.18 2.32
10 BC 1.14 3.14 2.69
20 BC 1.68 3.67 2.23
30 BC 1.85 5.47 3.00
Non-responsive hybrid (NK 508)
0 -- 1.31 3.16 2.41
10 BC 1.68 3.56 2.05
20 BC 1.92 5.19 2.71
30 BC 2.28 6.74 2.99
Orthogonal comparison Roots Total-P mg P g-1 roots
G4733 vs NK508 31.02** 8.42** N.S.
tBC = P mixed with total soil volume, WB = P mixed with 25% of soil
volume. N was mixed with total soil volume in all treatments.
**denotes significance at 1% probability. N.S. = not significant.
Table 2. Dry matter yield, total P and N uptake, P uptake per gram of
roots, and N uptake per gram of roots of G4733 and NK 508.
Single degree-of-freedom comparisons for effect of hybrid are
shown at the bottom. Experiment II. (41 days after planting).
P treatment Nitrogen Roots (Root & Top)
Rate Placementt placement Dry matter P N
---g pot-'--- --mg pot-'--
- ---------------------Responsive hybrid (G4733)-----------------
0 BC 1.15 1.59 54 1.42 4
30 BC BC 1.57 2.77 104 1.82 6
60 BC BC 2.03 4.74 124 2.36 6
60 BC BD 3.58 9.05 181 2.53 5
30 BD BD 3.19 5.63 165 1.81 5
60 BD BD 4.75 11.22 179 2.44 4
Non-responsive hybrid (NK
0 BC 1.91 2.08
30 BC BC 2.60 4.46
60 BC BC 3.81 7.72
60 BC BD 4.45 9.65
30 BD BD 4.68 7.39
60 BD BD 6.56 12.43
Dry-matter Total uptake Uptake mc g-1 roots
Comparison Tops Roots P N P N
G4733 vs NK 508 35.12** 58.09** 19.70** 20.97** 10.28** 37.63**
tBC = N and P mixed with total soil volume, BD = band placement of N and
P was 5 cm below soil surface and 5 cm horizontal from seed.
Selected degrees of freedom, F values, and level of significance from
*,**,*** denotes significance at 0.05, 0.01, 0.001 probability.
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