10

SOIL, NUTRITION AND FERTILIZERS

Rotation

Fertility factors to consider when including corn in the crop rotation:

Yield potential of corn following various crops

N credits following crops

P needs after different crops

The ability of corn to retrieve N located below the rooting depths of other crops

Corn yields vary depending on the previous crop according to

Manitoba Agricultural Services Corporation (MASC).

Note: Irrigated potatoes are likely grown on coarse sands

dependent on supplemental irrigation. When such

irrigation is not supplied, corn yields would expect to be

limited also.

Factors other than pests can account for corn yield differences

following various crops.

Low residue crops tend to have warmer spring soil tem-peratures.

High water use crops may limit the water for corn and conversely low water use crops may leave stored soil moisture for corn use.

Pulse crops or heavily fertilized crops may leave residual N for used by corn. Corn may root 4-5’ deep under Manitoba conditions and retrieve nitrogen leached below the root zone of other crops.

Residues from herbicides used in previous crops may impair corn growth.

Soil compaction or soil erosion associated with previous cropping activity

Phosphorus uptake is impaired following canola or summerfallow due to low levels of the beneficial fungi, my-corrhizae.

TABLE 2. Relative response of corn yield following various crops in Manitoba (1997-2001)

Previous crop % of MB corn

acreage following

this crop

Yield index

compared to

corn after corn

Corn 16% 100

Dry beans 11% 133

Cereals 28% 104

Potatoes –

irrigated

10% 73*

Potatoes –

dryland

1% 133

Sunflowers 5 % 106

11

Soil Factors Important in Corn Production

The major physical soil characteristics influencing corn production are drainage and water-holding capacity (WHC). The

relative affect of soil texture on both these soil properties is reported in Table 3.

Well-drained soils with a sandy loam or silty clay loam texture are

best suited to corn production. These soils have good internal

drainage, which allows the soil to dry out and warm up early in the

spring yet store moderate amounts of moisture for crop use.

Excessively wet soils impact corn growth and production in several

ways:

Wet soils remain cooler in the spring, which delays emer-gence and growth

Corn is more susceptive to injury or death. Seedlings can only tolerate flooding for 3-4 days, whereas corn at 24” will suffer after only 24 hours of flooding

Reduced oxygen levels in wet soils restricts root growth and nutrient uptake

Nitrogen loss due to leaching and denitrification can be sub-stantial

May prevent timely field operations, such as seeding, inter-row cultivation and herbicide spraying, side-dressing N ferti-lizer and harvest

A combination of tile and surface drainage may be needed on poorly drained soils.

Soils coarser in texture than sandy loams have low water-holding capacity, but will produce satisfactory corn yields if

adequate moisture can be provided by frequent rainfall or irrigation. These soils are more prone to periods of drought.

During pollination, corn transpires up to 1/3” of water per day, and moisture stress has greatest impact on yield at this

time. Coarse soils are also vulnerable to leaching losses of nitrate-nitrogen in periods when the crop is not aggressively

using soil water.

Soils heavier in texture than clay loams can be satisfactory for corn production if they are naturally well-drained or sur-

face and sub-surface drainage is provided.

Salinity causes germination problems and poor corn growth. One of the main effects of salinity is to limit water uptake

and any slight moisture stress will aggravate the problem. Therefore, soils having electrical conductivity (EC) greater

than 4 ms/cm must be avoided and those with EC of 2-4 ms/cm must be managed properly.

Salinity is measured using two methods. The commercial method of 1:1 (soil:water) produces values approximately two

times greater than the official, but more time-consuming and expensive, saturated paste method. Ensure you are

aware of the method of soil test reports of charts to ensure proper interpretation.

Relative corn yield as a percentage of maximum yield potential drops rapidly with increasing salinity—for example at

ECs of 2, 4, 6, 8 and 10 dS/m using the saturated paste method, yields is 96, 72, 48, 24 and 0 percent of the maximum

yield potential (source—Franzen 2012. Managing Saline Soilds in North Dakota. See Table 6.)

* Available water holding capacity in 4 foot rooting zone = the amount of water a soil can hold at field capacity that is available for crop uptake and growth.

TABLE 3. Soil suitability for corn according to

Texture AWHC*

(in/4 ft

depth)

Water

infiltration

(in/hr)

Limitation

Coarse

sand

4 in >10 in/hr Droughtiness

Sand loam 9 in 2 in/hr Droughtiness

Poor drainage

on “wet sands”

over clay

Loam 11 in 1 in/hr

Clay loam 12 in 0.5 in/hr Poor natural

Clay 14 in 0.04 in/hr Poor natural

drainage

12

NUTRIENT REQUIREMENTS

Adequate fertility is an essential step for profitable corn production. Sixteen essential plant nutrients are required for

growth, and an insufficient supply of any of these essential nutrients can have a detrimental effect on plant growth and

ultimately, crop yields. All but three of the essential nutrients (C, H, O) are derived from the soil. Nitrogen, phospho-

rus, and to a lesser degree, potassium and sulphur, are likely to be of concern for Manitoba crop production. Calcium

and magnesium are used in modest amounts by corn. Since Manitoba soils are largely derived from dolomitic lime-

stone, these nutrients are well-supplied. Typical nutrient uptake and removal of a corn crop is illustrated in Figure 6.

Other elements, including chlorine (Cl), boron (B), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and molybdenum (Mb) are called micronutrients and are required in smaller amounts (Figure 7). Most soils in Manitoba are adequately supplied with micronutrients. Copper and zinc are the two micronutrients most likely to be deficient in Manitoba soils. Copper availability may be low in peat soils and high in pH, low organic matter, sandy soils. Corn is sensitive to Zn defi-ciency, which may be found on highly calcareous (high lime content) soils and when subsoil has been exposed by ero-sion or land levelling. Soil testing, tissue sampling and visual deficiency symptoms are used to diagnose micronutrient deficiencies.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fertilizer Application

Soil and tissue testing are two ways to determine the available nutrient status of a field. Reliable test results and rec-

ommendations depend upon:

Proper soil and tissue sampling

Proper analysis techniques

Sound fertilizer recommendation guidelines

Details on these principles are covered in Manitoba’s “Soil Fertility Guide”.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fertilizer Placement, Timing and Rates

Corn performance and efficiency of applied fertilizer N, P and K is influenced greatly by fertilizer placement and timing.

0

20

40

60

80

100

120

140

160

Nitrogen

(N)

Phosphate

(P205)

Potassium

(K20)

Sulphur (S) Calcium

(Ca)

Magnesium

(Mg)

Grain Stover

FIGURE 6. Macro and secondary nutrient uptake and

removal by a 100 bu/ac grain corn crop (Soil Fertility

Guide)

0

0.5

1

1.5

2

2.5

Chlorine (Cl) Boron (B) Copper (Cu) Iron (Fe) Manganese

(Mn)

Zinc (Zn)

Nutrient

lb n

utr

ient/acre

Stover

Grain

FIGURE 7. Micronutrient uptake and removal by a 100

bu/ac corn crop (Soil Fertility Guide)

13

Nitrogen (N)

Nitrogen is required for proper growth and development. It is taken up continuously by the plants through to maturity.

A large part of the N accumulated in the leaves and stem is translocated to the grain as it matures and about 2/3 of the

N in the plant will be found in the grain at maturity. See Figure 8—Nitrogen uptake and partitioning by a 146 bu/ac

grain corn crop.

Placement:

Nitrogen fertilizer efficiency is increased via in-soil

banding by minimizing potential losses due to immobili-

zation, denitrification, leaching, volatilization and weed

uptake. Band placement of N is generally 20% more

efficient than broadcast application.

There are several options for band placement of N in

corn:

Sub-surface banded into soil prior to seeding (in spring or previous fall)

Side banded at seeding

Mid-row banded at seeding

Sub-surface banded or side-dressed between the rows after emergence

Surface banded after seeding

Using directed UAN solution

The type of seeder will influence placement options. Those seeding with row-crop equipment and wider rows have the

option of side-dressing N after seeding, sometimes at the same time as inter-row cultivation. Those seeding with air

seeders in narrow rows may choose to mid-row band N at seeding.

Preplant application of anhydrous ammonia should be on an angle to the direction of planting to minimize any fertilizer

injury of seeds placed above injection zones. Safety is also determined by the depth of ammonia injection, which

should be at least 4” below the depth of seeding.

Side-banding is optimal placement for phosphorus fertilizer, but efficiency may be reduced if excessive rates of N and/

or K are applied in a typical 2” to the side and 2” below the seed in this band. High rates may burn seedling roots, or

inhibit root growth into the concentrated band to access critical early season P. For this reason, no more than 300 lb/

acre of total fertilizer product should be applied in a side band.

Side-dressing should be completed by the time corn reaches the 6” height. Further delaying application risks root prun-

ing and wet weather that may thwart field operations. Cornbelt studies indicate that “skip-row” application of side-

dressed N (placed between every second row) is as efficient as placing N between every row. With these skip-row ap-

plications, the same rate is maintained, but output per shank is doubled with half the amount of shanks applying ferti-

lizer.

Figure 8. Nitrogen uptake and partitioning in

grain corn (Manitoba, 2003, 146 bu/acre).

14

There are several options for broadcast applications of nitrogen for corn:

Broadcast and incorporated with tillage

Broadcast without incorporation

Broadcast into the standing crop

Fertigation in irrigation water

Broadcast and incorporated applications can be utilized pre-plant or post-planting. Surface applied N into corn is de-

pendent on rainfall, or some kind of incorporation, to move it into the root zone, to reduce losses. When rainfall is de-

layed, surface applications of urea-based fertilizer (including UAN solutions) are vulnerable to loss due to volatilization,

particularly under conditions of high temperatures, drying winds and low organic matter, high pH, light-textured soils.

Surface banded N after seeding is usually done by dribble banding UAN solutions, and although volatilization losses are

not eliminated, they are minimized compared to broadcast application.

Broadcast applicationss of urea into growing corn may injure the growing point if granules fall into the whorl. Likewise,

dribbled UAN solution should be directed between the corn rows if possible to reduce flow into the whorl.

TIMING NITROGEN APPLICATION:

N losses are expected to be higher for fall-applied than spring-applied, therefore spring-applied is considered to be 20%

more efficient. These losses may be greater if the nitrogen is applied too early in the fall (prior to mid-September) or

when soil temperatures at the 4” depth are greater than 5oC.

In a practical sense, time and method of application should be based not only on the needs of the crop and potential

losses from the soil, but also on the co-ordination of the soil fertility program with an efficient overall farm manage-

ment system. Select a time and method of N application that permits preparation of a good seedbed, conserves soil

moisture, aids in prevention of soil erosion, allows for timeliness of operations and is consistent with maximization of

net returns.

Wet conditions in May and June leaves N vulnerable to losses. Side-dressing in June is best applied as anhydrous am-

monia or UAN, and should be completed by the time corn reaches 6” in height, if the fertilizer is placed in moist soil

and if serious injury to the root system, through root pruning, is avoided.

Splitting of nitrogen applications between preplant and post seeding may be desirable on soils that are particularly sus-

ceptible to leaching (eg. Irrigation of coarse sands).

NITROGEN SOURCES:

All sources of nitrogen fertilizer will perform well when applied at the right time and placement. Since corn has delayed

N uptake compared to our cool season cereal and canola crops, the nitrogen is more vulnerable to loss in the spring. An

option is to use a slow or controlled release nitrogen products, such as polymer coated urea ( eg. ESN 44-0-0). Manito-

ba research has shown benefits to this controlled release nitrogen source in very wet springs, but no difference under

typical or dry conditions.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DEFICIENCIES: Nitrogen deficiencies cause stunted, spindly, yellow plants, reduced yield and delayed maturity.

Older leaves will show a V-shaped yellowing of the inner leaves with margins remaining green. Old

leaves show deficiencies first.

Excessive N can reduce yield, increase harvest moisture and N03 accumulation in the stalk.

See page 20 for images showing nitrogen deficiencies in corn plants.

15

Phosphorus (P)

Phosphorus is required for plant growth and seed development. Considered immobile in the soil, P is taken up by the

root by diffusion over short distances through the soil solution. Phosphorous is taken up continuously during the grow-

ing season. Large amounts of P are required after tasseling and during the ripening period. Most of the P accumulated

in the leaves, stalks and husks is translocated to the grain at maturity when about 70% of the P in the plant is in the

grain.

Placement is dually important; to create a high probability that plant roots will come into contact with these applied

nutrients, and that minimizing soil contact will result in more availability. Banding a small amount of P2O5 near the seed

can result in more vigorous growth of the seedling, referred to as a ‘pop-up’ or ‘starter’ effect.

Band applications of P are superior to broadcast applications under conditions frequently observed in Manitoba; low

soil test P levels, cold and wet soil conditions at seeding and calcareous soils that fix substantial quantities of P. Broad-

cast applications may need to be 2-4 times greater in order to equal growth and yield achieved by band placement.

Phosphorus uptake is impaired following canola (brassica crops) or summerfallow due to low levels of vesicular arbus-

cular mycorrhizae, which aids in phosphorus uptake. Mycorrhizae are a naturally occurring beneficial fungus that as-

sists many plants (excluding canola) to increase uptake of phosphorus. The hyphal threads or strands of the fungi act as

an extension of the root system and increase interception and uptake of nutrients. Mycorrhizae may increase the

effective rooting volume of young plants by up to tenfold.

Research studies indicate that application of phosphate fertilizer to corn only partially overcomes this early season P

uptake impairment. Phosphorus uptake may be greater under zero tillage systems, which do not disturb established

hyphal strands.

DEFICIENCIES: Deficient seedlings appear stunted and weakened. Leaves and stems will often show purpling or

reddening. Ears may have irregular rows and twisted ends with underdeveloped kernels and grain

will have higher moisture content at harvest.

See page 20 for images showing phosphorus deficiencies in corn plants.

Figure 9. Phosphorus uptake and parti-

tioning in grain corn (Manitoba, 2003,

146 bu/acre).

16

Potassium (K)

Most Manitoba soils contain sufficient potassium for crop uptake, however, soils that are likely to be low in K are fre-

quently those same lighter-textured soils that are suited to corn production, so soil testing is recommended. Rapid up-

take of K starts at about the same time as the start of rapid plant growth and is maintained only until the grain starts to

be formed, at which time the uptake of K is complete. Most of the potassium taken up by the plant remains in the

leaves and stalk. Large quantities of potassium can “leak” from

the plant during the grain drydown stage.

Considered immobile in the soil, K is taken up by the root by

diffusion over short distances through the soil solution.

Efficiency of band applications of potassium is greater than broadcast application, especially when requirements are

low. Band options include preplant banding or side-banded at seeding. The N and K content of fertilizer restrict the

quantity of fertilizer that can be safely seed-placed.

DEFICIENCIES: Yellowing and drying of leaf margins, especially on older leaves; stunted plants with short inter-

nodes; delayed maturity and plants may frequently lodge or blow down late in the season.

See page 21 for images showing potassium deficiencies in corn plants.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sulphur (S)

Sulphur is a key component of several important amino acids that are required for the development of proteins and

enzymes, and taken up by the roots in the form of sulphate. Elemental sulphur fertilizer must be oxidized by soil micro-

organisms to the sulphate form. Sulphate-S may leach in coarse soils, and levels within the field often vary, depending

upon soil type and slope position. It is not uncommon for low lying, heavy soils to contain many times more sulphate-

sulphur as light-textured hilltops.

DEFICIENCIES: General stunting, delayed maturity, and

yellowing of new foliage. Deficiencies are most likely to oc-

cur in well-drained soils, and soils with low organic matter.

See page 21 for images showing sulphur deficiencies in corn

plants.

Figure 10. Potassium uptake and partitioning in

grain corn (Manitoba, 2003, 146 bu/acre).

Figure 11. Sulphur uptake and partitioning in

grain corn (Manitoba, 2003, 146 bu/acre).

17

Micronutrient Deficiencies

Calcium (Ca)

Deficiency results in a ladder-like effect with leaf tips stuck to the next lower leaf. (Not seen in Manitoba soils.)

Magnesium (Mg)

Deficiency results in yellowing of upper leaves and intervenal chlorosis of older leaves. (Not seen in Manitoba soils.)

Zinc (Zn)

Deficiency results in intervenal chlorosis on new corn leaves. Pale white bands between the leaf margin and mid-vein

in the basal part of leaf, and under severe deficiencies, new leaves may be completely white.

Deficiency occurs most frequently on high pH, low OM soils in years with cold wet springs.

Iron (Fe)

Deficiency causes pale, yellowish-green plants with distinct stripping the full length of leaf. Symptoms are similar to

zinc, occurring on the same types of soils.

Copper (Cu)

Deficiency causes youngest emerging leaves to be yellow and the tips may die.

Boron (B) and Molybdenum (Mo)

Unlikely to be deficient in MB soils.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manure

Corn has a high demand for nutrients and is a very suitable crop for manure application. Table 4, from the Soil Fertility

Guide, illustrates the opportunity for manure to supply nutrient needs of the corn crop.

As with fertilizer nutrients, manure N is optimized through sub-surface banding. In order to maintain timely planting

and to minimize soil compaction, manure should be applied to dry soils in the fall prior to seeding. Unlike cereals, corn

will tolerate areas of inadvertent excessive manure application without lodging.

TABLE 4. Average nutrient analysis of manure and the amount available for crop use the year applied

Type of

manure

Number

of

samples

Total N

(avail)*

Ammon-

ium N

Organic N Phosphate

P2O5

(avail)*

Potassium

K2O

Sulphur

S

Dry matter

content

%

LIQUID Lb./1000

gallons

Hog 36 23 (18) 16 7 15 (7.5) 13 1.4 2

Dairy 7 26 (18) 14 12 13 (6.5) 29 2.4 6

SOLID Lb./ton

Hog 3 14 (6) 2 12 15 (7.5) 16 2.5 35

Poultry 2 34 (12) 2.3 32 30 (15) 28 6.5 57

Beef 33 9 (3) 0.3 9 4 (2) 11 1.4 30

Manitoba Agriculture, Food and Rural Initiatives, Soil Fertility Guide, amount available for following crop use; for nitrogen =

18

Fertilizer Recommendations

TABLE 5. Nitrogen recommendations for corn (based on a spring banded application)

Nitrogen Recommendation (lb/ac) Target Yield

Grain Yield bu/ac 130 115 100 85

Silage Yield t/ac @ 70% moisture 19.4 17.1 14.9 12.6

Fall Soil NO3-N

lb/ac in 0-24 in Rating

20

30

40

50

60

70

80

90

100

VL

L

M

M

H

H

VH

VH

VH+

260

225

200

170

140

110

80

55

25

205

170

145

115

85

55

25

0

0

150

115

90

60

30

0

0

0

0

95

60

35

5

0

0

0

0

0

P2O5

lb/ac

Soil potassium (ammonium

acetate K test)

K2O lb/ac Soil Sulphate-Sulphur

in 0-24 in.

S lb/ac Soil phosphorus

(sodium bicarbonate P test)

ppm lb/ac Rating SB * ppm lb/ac Rating SB* PPI** lb/ac Rating

0

5

10

15

20

20+

0

5

10

15

20

25

30

35

40

40+

VL

VL

VL

L

M

M

H

H

VH

VH+

40

40

40

35

30

20

15

10

10

10

0

25

50

75

100

125

150

175

200

200+

0

50

100

150

200

250

300

350

400

400+

VL

VL

VL

L

M

M

H

H

VH

VH+

100

90

80

75

65

55

50

40

30

0

200

180

160

150

130

110

100

80

60

0

0

5

10

15

20

25

30

35

40

40+

VL

VL

VL

L

L

M

H

H

VH

VH+

20

20

20

20

20

20

0

0

0

0

TABLE 6. Phosphorus, potassium and sulphur recommendations for corn

*SB = based on side band applications for row crops

** PPI = based on broadcast and preplant incorporated

Fertilizer recommendations have been developed and verified for corn in Manitoba (see Tables 5 & 6). Recommenda-

tions are based on soil testing and on target or expected corn yield for nitrogen. Proper soil sampling strategies and

procedures are outlined in Manitoba’s Soil Fertility Guide.

19

Selection of an appropriate expected yield is critical to developing a nitrogen recommendation. The yield goal should be

challenging, yet realistic and achievable in a good year.

Consider the following:

Past yields on the same field.

Discounts for soil limitations — eg. salinity and drainage.

Assess your management level — from farm yields for the past 5 years, drop the low and the high yield and de-

termine the average. Add 10—15% to this average for a target yield.

Hybrid maturity and yield potential.

Previous crop effect.

Stored soil moisture and anticipated rainfall.

There is an opportunity to fine-tune nitrogen applications in corn since the final N application can be done in-crop.

Techniques can be used in-season to assess crop nutrient sufficiency and to determine the need to apply additional N

or to hold back applications. These include the use of in-season soil testing, early tissue analysis or use of the SPAD

chlorophyll meter. Consult your crop advisor for details.

Corn is most likely to respond to the micronutrients zinc and copper in Manitoba soils. There are several options for

source, timing and application method of micronutrient fertilizers. Application options are broadcast and incorporated,

soil banded or foliar. Broadcast and thoroughly incorporated application generally maximizes, nutrient uptake by in-

creasing opportunity for root interception. Broadcast and incorporated micronutrient fertilizers are recommended as

follows:

Pre-plant incorporate 10-15 lb/ac zinc as zinc sulphate or 2-3 lb/ac zinc as zinc EDTA chelate.

Pre-plant incorporate 5-10 lb/ac copper as a copper sulphate or 1-2 lb/ac copper as EDTA copper chelate.

On peat, incorporate 5-15 lb/ac copper as copper sulphate or 1-3 lb/ac copper as EDTA copper chelate.

Banded micronutrients at lower rates have been observed to be effective but residual effect will be shorter. Likewise,

foliar applications may also be effective to correct deficiencies diagnosed early in the growing crop.

Producers neglecting to soil test, must resort to using

general recommendations as follows:

TABLE 8. Fertilizer requirements for corn lacking a soil

test

Previous crop

Fallow/ or

forage

legumes

Stubble Phosphate Potassium* Sulphur

Lb P2O5 /ac Lb K2O/ac Lb S/ac Lb N/ac

0-30 65-135 30-40 30-100 20

*On sandy-textured or organic soils

Micronutrient Extractant Critical level Marginal

Copper (Cu) DTPA 0.2 ppm

5.0 ppm for

peat soil

0.2-0.4 ppm

5-12 ppm on

peat soil

Iron (Fe) DTPA 4.5 ppm

Manganese (Mn) DTPA 1.0 ppm

Zinc (Zn) DTPA 1.0 ppm

TABLE 7. Soil test criteria for micro-nutrients

Yield response to applied micronutrient is more likely

when soils test in the critical and marginal range.

20

Figure 12. Nitrogen deficient corn (L)

versus non-deficient corn (R ). Photo

by John Heard—MAFRI.

Figure 13. Phosphorus deficient corn (L) versus non-

deficient corn (R ). Photo by John Heard—MAFRI.

Figure 14. (L, below) Phosphorus deficient corn as a result of

corn on canola syndrome. Photo by Morgan Cott—MCGA.

Figure 15. (R, below): Phosphorus deficient corn as a result of

corn on canola syndrome, close-up. Photo by Morgan Cott —

MCGA.

21

Figure 16. Potassium

deficient corn. Photo by

John Heard—MAFRI.

Figure 17. Non-

deficient corn (L) ver-

sus sulphur deficient

corn (R ). Photo by

John Heard—MAFRI.

22

NOTES

23

NOTES