Corn: Fertility Management
| Corn
| Soybeans | Forages
| Cereals | Dry
Edible Beans | Pub
811: Agronomy Guide > Corn
> Fertility Management
Table of Contents
NitrogenCorn responds well to nitrogen, so adequate availability
of nitrogen is critical to profitable corn production. However,
excess nitrogen adds unnecessary expense and increases the risk
of nitrate movement to groundwater. Nitrogen deficiency first appears on the lower leaves, manifested as yellowing, beginning at the tip of the leaf and proceeding down the midrib. Eventually, the yellow areas will turn brown and die. Plate 1.
Nitrogen deficiency shows up on lower leaves first. Yellowing begins
at the leaf tip and proceeds down the midrib. In young plants, yield loss will occur long before
nitrogen deficiency symptoms appear, so yellowing is not a reliable
indicator of the need for nitrogen fertilizers. Two methods can be used to determine optimum nitrogen rates:
It is common to see symptoms of nitrogen deficiency in the lower leaves as the plants near maturity, even when there is adequate nitrogen for optimum yield. Nitrate-Nitrogen Soil TestSoils can vary greatly in their ability to supply nitrogen. The
amount of nitrate-nitrogen present in the soil at planting time,
or just before side-dress, can be a useful indicator of a soil's
capacity to supply nitrogen. Use of the soil test for nitrate-nitrogen
should result in a more efficient and profitable use of nitrogen
as well as a reduction in the risk of nitrate movement into groundwater. Many of the factors included in the general recommendations will influence the soil nitrate levels, so the recommendations for the nitrate-nitrogen soil test should be viewed as separate from the general nitrogen recommendations. Research is ongoing to find methods to incorporate the soil test into the general recommendations as an adjustment. Time of Sampling
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A. Base N Requirement (choose from Table A) |
_________ | |
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B. Yield Adjustment (Yield (T/ha) _____ * 13.6) = |
+_______ | |
| C. Heat Unit Adjustment | ||
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Your CHU-Mls |
= __________ |
+ _______ |
|
D. Previous Crop Adjustment (Choose from Table D) |
- ________ | |
| E. Price Ratio (PR) Adjustment for
Nitrogen Relative to Corn Price (Choose from Table E) |
- _______ | |
| F. Total N recommendation (A+B+C-D-E) | = _______ | |
| G. Deduct Starter N | - ________ | |
| H. Deduct Manure N Credits1 | - ________ | |
| I. Preplant Additional N (F-G-H) | =_______ | |
|
or |
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| J. Sidedress Additional N (If Additional N is applied side-dress, multiply value I by the appropriate value in Table J) | _________ | |
1 Manure N Credits can be found in Chapter 9, Soil Fertility and Nutrient Use.
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Ammonium Acetate Potassium Soil Test (ppm)
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Rating1
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Potash (K2O)2 Required
kg/ha
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|---|---|---|
|
0-15
|
HR
|
170
|
|
16-30
|
HR
|
160
|
|
31-45
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HR
|
140
|
|
46-60
|
HR
|
110
|
|
61-80
|
MR
|
80
|
|
81-100
|
MR
|
50
|
|
101-120
|
MR
|
30
|
|
121-150
|
LR
|
0
|
|
151-250
|
RR
|
0
|
|
251+
|
NR3
|
0
|
100 kg/ha = 90 lb/acre
1 HR, MR, LR, RR, and NR denote, respectively, high,
medium, low, rare and no probabilities of profitable crop response
to applied nutrient. Profitable response to applied nutrients occurs
when the increase in crop value, from increased yield or quality,
is greater than the cost of the applied nutrient.
2 Where manure is applied, reduce fertilizer applications
according to the amount and quality of manure see Table
9-8, Typical Amounts of Available Nitrogen, Phosphate and Potash
From Different Types of Organic Nutrient Sources.
3 When the response rating for a nutrient is "NR,"
application of this nutrient in fertilizer or manure may reduce
crop yield or quality. For example, phosphate applications may induce
zinc deficiency on soils low in zinc and may increase the risk of
water pollution. Potash application on soils low in magnesium may
induce magnesium deficiency.
Nitrogen Application
The major portion of the nitrogen should be applied in the spring,
preplant, pre-emergence or side-dressed before the corn is 30 cm
(12 in.) high. Fall application is not recommended because of the
potential for high losses.
A portion of the nitrogen may be applied in a band at planting.
Ensure that safe rates of fertilizer near the seed are not exceeded.
Where it is desirable to apply high rates of nitrogen at planting,
it should be placed in a separate band greater than 10 cm (4 in.)
from the seed row.
Solid forms of nitrogen or urea-ammonium nitrate solutions (UAN)
may be applied to the soil surface without incorporation. However,
incorporate urea or UAN applied on crop residues into the soil immediately
to prevent ammonia volatilization losses. Under dry conditions,
the effectiveness of all forms of nitrogen may be improved by incorporation.
If UAN solutions contact leaves, burning and yield reductions may
occur.
Anhydrous ammonia, applied with conventional equipment, should
be placed a minimum of 15 cm (6 in.) deep in the soil. For preplant
applications, applicator outlets should be no more than 50 cm (20
in.) apart. For wider spacings, a 4-day waiting period before planting
is recommended to avoid damage to seedlings.
When appropriate equipment is used, ammonia may be applied with
a cultivator or disc, a minimum of 10 cm (4 in.) deep with the ammonia
outlets spaced no more than 50 cm (20 in.) apart.
Phosphate and Potash
Adequate phosphorus and potassium are necessary for optimum corn growth and yield, although the response to these nutrients is not as evident as with nitrogen. Phosphorus deficiency does not show any obvious symptoms, although phosphorus-deficient plants will be stunted and may have a darker green or purplish colour. Purple leaves may also be an indication of cool weather stress or root injury.
Plate 2. Purple corn. Purple
leaves on corn is most often caused by cool weather stress or root
injury. Occasionally, it is an indication of phosphorus deficiency.
Potassium deficiency symptoms appear on the lower leaves of the plant first, showing as yellowing and browning beginning at the tip and proceeding back along the outside margin of the leaf. Both of these nutrients will exhibit "hidden hunger," where yields are reduced by a deficiency of one or both of these nutrients even though no deficiency symptoms are visible.
Plate 3. Potassium deficiency
shows up on lower leaves first, as yellow and browning at the leaf
tip, and proceeds back along the margin of the leaf.
Phosphate and potash recommendations for corn are presented in
Table 1-25, Phosphate and Potash Recommendations
for Corn Based on OMAFRA-Accredited Soil Tests.
For information on the use of this table or if an OMAFRA-accredited
soil test is not available, see Fertilizer
Recommendations.
Where soil tests indicate that large amounts of phosphorus and potassium are required, the major portion may be broadcast and incorporated in the fall or spring. Where soil tests show a moderate or small requirement for these nutrients, apply a fertilizer containing nitrogen (preferably in the ammonium form) and phosphorus, or nitrogen, phosphorus and potassium as a starter at planting. All of the phosphorus and some of the potassium may be applied in a band 5 cm (2 in.) to the side and 5 cm (2 in.) below the seed Table 9-21, Maximum Safe Rates of Nutrients.
Seed-Placed Fertilizer
Field trials over several years have shown that an application
of 10-15 kg/ha (9-13 lb/acre) P2O5 directly
with the seed will give greater yield increases than 20 kg/ha (18
lb/acre) P2O5 in a side band. At phosphorus
soil tests of 13-45, this "with-seed" application is more
likely to give a profitable response than a side-band application.
At soil tests below 13, application of 10-15 kg P2O5/ha
(9-13 lb P2O5/acre) with the seed may also
be profitable but cannot replace the requirement for additional
phosphorus in the side band or broadcast.
Fertilizers applied with the seed that contain nitrogen in the
ammonium form must be low in salt and must not contain either urea
or diammonium phosphate Table
9-21. They must also be distributed uniformly to avoid toxicity
to the germinating seed. Application of more than 15 kg/ha (13 lb/acre)
P2O5 with the seed in 75-cm (30-in.) wide rows is not recommended.
Maximum Safe Rates of Fertilizer
Applying too much fertilizer to corn may result in crop injury, either from excessive salts or ammonia Plate 8.
Plate 8. Fertilizer injury burns the primary root, delaying growth until secondary roots develop. Plant emergence will be uneven.
The more concentrated the fertilizer and the closer it is to the
seed, the greater the risk of crop injury and the lower the safe
rate. Maximum safe rates are given in Table
9-21. Note that slight reductions in crop growth and yield are
possible with these application rates under adverse weather conditions.
Secondary and Micronutrients
Magnesium
Magnesium is plentiful in most Ontario soils, but deficiencies can occur on acidic, sandy soils. The symptoms appear first as yellow striping of the lower leaves. As the deficiency worsens, the upper leaves may become striped while the lower leaves turn reddish-purple.
Plate 4. Magnesium
deficiency appears first as yellow striping of the lower leaves.
These may turn reddish-purple later as deficiency progresses.
Dolomitic lime is an excellent source of magnesium where limestone
is required to correct soil acidity and should be used whenever
the magnesium test is less than 100 ppm. For further information,
see Soil Acidity
and Liming.
Few soils that do not need lime will require magnesium. Magnesium
application is recommended only if the magnesium test is under 20
ppm. On these soils, magnesium can be supplied either by magnesium
sulphate or, if potassium is also required, by sulphate of potash
magnesia. Apply 30 kg/ha (27 lb/acre) of water-soluble magnesium.
Over-application of potassium can induce magnesium deficiency. For this reason, it is important to monitor soil potassium levels closely and restrict potash application rates to those recommended by the OMAFRA-accredited soil test.
Sulphur
Sulphur deficiency in corn has not been observed in Southern Ontario. Most corn-growing areas of the province receive adequate sulphur as acid precipitation. Corn grown in Northwestern Ontario may respond to the inclusion of 15 kg/ha (13 lb/acre) of sulphate sulphur with the fertilizer.
Zinc
Zinc deficiency occurs on corn in Ontario. Visible symptoms on the leaves (Plate 5 on page 279) are the best indications of deficiency, but soil tests are also useful. Zinc deficiency usually appears as a broad white band near the base of the younger leaves on a corn plant. In severe deficiencies, the entire leaf in the whorl will be white (known as "white-bud"). Response to zinc should not be expected unless deficiency symptoms are quite marked.
Plate 5. Zinc deficiency appears as a broad white band near the base of the leaf on younger plants.
When zinc is required, it may be applied to the soil mixed in the fertilizer at rates supplying 4-14 kg/ha (3.5-12.5 lb/acre). The higher rate should be sufficient for up to 3 years. Not more than 4 kg/ha (3.5 lb/acre) should be banded at planting. Zinc may be applied as a foliar spray at rates supplying 60 g/100 L (0.6 lb/100 gal). A wetting agent should be added. Spray to leaf wetness.
Manganese
Manganese deficiency in corn is rare, although there have been a few occurrences reported on muck soils with high pH in Southwestern Ontario. Corn is much more tolerant of low soil manganese levels than soybeans or cereals. Manganese deficiency in corn appears as an olive-green discolouration of the leaves, occasionally with faint striping. Foliar application of manganese is the most effective way to correct a deficiency.
2 Maximum normal concentrations are more than adequate but do not necessarily cause toxicities.
Correct the deficiency as soon as detected by spraying the foliage with 2 kg/ha (1.8 lb/acre)of actual manganese/ha from manganese sulphate (8 kg/ha (7.1 lb/acre) of manganese sulphate) in 200 L of water. A "spreader-sticker" in the spray is recommended. If the deficiency is severe, a second spray may be beneficial. Prior to applying micronutrients, take care to properly clean out the spray tank of a sprayer that has been used to apply herbicides.
Other Micronutrients
Other micronutrients are not likely to be deficient in corn in
Ontario. Some micronutrients, such as boron, can be toxic if applied
to corn, particularly if applied in a band or in the starter/pop-up
fertilizer.
Plant Analysis
The most appropriate growth stage for sampling corn for plant analysis
changes for different nutrients. For most nutrients, sampling the
mid-third of the ear leaf at silking is most appropriate. For phosphorus
and zinc, sampling the whole plant when 5-6 leaves are visible is
more appropriate. See Table 1-26, Interpretation
of Plant Analysis for Corn, for normal concentrations of nutrients.
For sampling at times other than those indicated above, take plant
samples from both deficient and healthy areas of the field for comparative
purposes. For plants with six leaves or less, sample the total above-ground
plant. From seven leaves to silking, sample the youngest fully developed
leaf. Take a soil sample from the same areas and at the same time
as the plant samples. For more information, see the section Plant
Analysis.
Foliar Fertilization
The foliar application of nutrients to corn has not proven effective
in most instances. The rates of nutrients required cannot be applied
as a foliar spray without causing damage to the leaf, unless numerous
small applications are made. The exception is correction of some
of the micronutrient deficiencies, but even in these cases it is
often more economical to apply the nutrient to the soil.
For more information:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
E-mail: ag.info.omafra@ontario.ca
| Author: | OMAFRA Staff |
|---|---|
| Creation Date: | 30 April 2009 |
| Last Reviewed: | 30 April 2009 |