Macronutrients

Report
Tim Shaver & Richard Ferguson
University of Nebraska-Lincoln

C, H, O = 95% of plant weight
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N, P, K = Primary (macro) nutrients

Ca, Mg, S = Secondary nutrients

Micro-nutrients = B, Cu, Fe, Mn, Mo, Zn, Cl
Mass Flow

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Dissolved nutrients in water flowing toward the
root.
Soluble and abundant elements (N, Ca, Mg, S)
Diffusion
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Movement of nutrients from an area of high
concentration to an area of low concentration
Low concentration area created by active
uptake of nutrients at the root (K and P)
Interception
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Root growth explores new soil regions
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N is the most frequently deficient nutrient in
crop production.
The ultimate source of N is N2 gas, which is
78% of the earth’s atmosphere.
Higher plants cannot metabolize N2,
therefore, N2 must be converted to plant
available N.

N2 can be converted to plant available forms
through several processes:
◦
◦
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Symbiotic microorganisms (legumes)
Non-symbiotic microorganisms
Lightning (electrical discharges) forming N oxides
Synthetic manufacture (N fertilizers)
Plant available forms:
Nitrate (NO3-)
Ammonium (NH4+)
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1) Atmospheric, plant, & animal residue N is added to
the soil.
2) Organic N in residue is mineralized to NH4+ by soil
organisms (mineralization).
3) Most NH4+ is converted to NO3- by nitrifying bacteria
(nitrification).

4) NH4+ and NO3- are taken up by plants.

5) Various loss mechanisms
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Used in the formation of proteins which
provide the framework for plant structures in
which biochemical reactions occur.
N is an integral part of chlorophyll
(photosynthesis).
N is associated with high photosynthetic
activity, vigorous growth, and dark green
color.

Generally stunted, and yellow in appearance.

Anhydrous Ammonia:
◦ NH3 + 2O2

H+ + NO3- + H2O
Urea:
◦ (NH2)2CO + 4O2

2H+ + 2NO3- + CO2 +H2O
Ammonium Nitrate:
◦ NH4NO3 + 2O2
2H+ + 2NO3- + H2O

Monoammonium Phosphate:
◦ NH4H2PO4 + O2

2H+ + NO3- + H2PO4- +H2O
Diammonium Phosphate:
◦ (NH4)2HPO4 + O2
3H+ + 2NO3- + H2PO4- + H2O
Phosphorus:

Phosphorus is an
essential plant nutrient
◦ Energy Transfer (ATP)
◦ Good Supply of P
 Increased root growth
 Early maturity
 Greater straw strength in
cereals
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Band application on winter wheat
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Second most
important nutrient
for crop growth
◦ Lower need than N
P is a relatively
immobile nutrient
Fewer loss
mechanisms in the
environment than N
Can become
unavailable in the
soil.

Monoammonium Phosphate:
◦ NH4H2PO4 + O2

2H+ + NO3- + H2PO4- +H2O
Diammonium Phosphate:
◦ (NH4)2HPO4 + O2
3H+ + 2NO3- + H2PO4- + H2O
Stunted in Growth
 Abnormal dark-green color
 Reddish -purple color
(Severe deficiency symptom)

◦ Often seen in early spring on low phosphorus
sites.
◦ Often as soils warm, phosphorus deficiency
symptoms disappear.
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Essential plant nutrient
Next to nitrogen, crops absorb more K than
any other nutrient
Soil K is related to soil minerals (feldspar,
mica) and not organic matter like N and P
Western Nebraska has high quantities of K
due to the mineral makeup of the soil and
climate (low weathering).
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Depending on soil type, 90 to 98% of K is in
relatively unavailable forms.
Over time, soil minerals weather, slowly
releasing K to more plant available forms.
Absorbed by roots as K+ ion.
Responsible for enzyme activation and water
uptake (osmotic “pull”).

Potassium chloride (KCL)
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Potassium sulfate (K2SO4)
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Potassium magnesium sulfate (K2SO4•MgSO4)
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Potassium nitrate (KNO3)

Nebraska soils with 125ppm or greater
considered sufficient.
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Urea Example:
◦ (NH2)2CO
◦ Molecular Weight
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(from periodic table):
N = 14(2)=28
H = 1(4)=4
C = 12(1)=12
O = 16(1)=16
60
N = 28/60 = 46%

Efficient N fertilizer use requires that credit is
given for sources of N already available in the
soil.
Nitrogen cycle (source: http://www.epa.gov)
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Residual Nitrate (NO3)
Organic Matter Mineralization
Organic Materials (Manure)
Previous Crop (Legumes)
Irrigation (NO3 Content)
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Nitrogen fertilizer rates can be substantially
reduced by accounting for N Credits.
N credits can vary widely.
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Deep soil sampling
Material analysis
Previous crop credit
Irrigation water sampling
Soil scientist uses
hydraulic probe to extract
soil samples (Photo
courtesy of USDA NRCS).


Nitrogen rates can be determined using UNL
Extension publications specifically written for
individual crops.
These publications are located at:
http://www.ianrpubs.unl.edu

UNL recommendations can be determined
from tables or from equations (corn example,
In: EC117):
Soil Nitrate
ppm
1
3
6
9
12
18
24
Yield Goal (bu/ac)
60
90
120
150
180
210
240
270
Organic Matter 1%
Recommended N rate based on soil N, yield goal and soil organic matter (lb N/acre)
90
120
155
185
220
250
280
315
75
105
140
170
200
235
265
295
50
80
115
145
180
210
240
275
25
60
90
120
155
185
215
250
5
35
65
100
130
160
195
225
0
0
20
50
80
115
145
175
0
0
0
0
35
65
95
130

UNL Corn N Recommendation Algorithm:
◦ N need (lb/ac):
Photo courtesy of USDA NRCS
35
+(1.2 x EY)
-(8 x N ppm)
-(0.14 x EY x OM)
-credits
[35+(1.2xEY)-(8xNO3-Nppm)-(0.14xEYxOM)-credits]

Algorithm Example:
◦ Expected Yield (EY) = 200 bu/ac; OM = 2%
◦ Soil Nitrate (Surface 8 inches) = 5 ppm
[35+(1.2xEY)-(8xNO3-Nppm)-(0.14xEYxOM)-credits]
35
+(1.2 x EY(200)) = 240
-(8 x N ppm(5))= 40
-(0.14 x EY(200) x OM%(2)) = 56
Photo courtesy of USDA NRCS
35 + 240 – 40 – 56 = 179 lbs N/ac

N Credits:
◦ Previous Soybean: 45 lbs/ac
◦ Previous Alfalfa: 150 lbs/ac (70-100% stand)
120 lbs/ac (30-69% stand)
90 lbs/ac (0-29% stand)
◦ Water: 1 ppm N = 2.7 lbs/ac
*Photos courtesy of USDA NRCS

N Credit Example:
◦ Previous Crop: Soybean (45 lbs/ac)
◦ Water: 3 ppm (3 x 2.7 = 8 lbs/ac)
◦ N recommendation: 179 lbs/ac
◦ N Credits: 45 + 8 = 53 lbs/ac
Photo courtesy of USDA NRCS
◦ N recommendation (credits): 126 lbs/ac
◦ Table recommendation: 155 – 180 lbs/ac
Tim Shaver
Nutrient Management Specialist
UNL WCREC

N, P, K = Primary (macro) nutrients

Ca, Mg, S = Secondary nutrients

Micro-nutrients = B, Cu, Fe, Mn, Mo, Zn, Cl

Zn, Fe, and Sulfur most common deficiencies
in NE.
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Soil minerals
Soil organic matter
Crop residue
Manures/organic amendments
Fertilizers, Pesticides
Irrigation water
The atmosphere
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Corn and dry beans sensitive
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Other crops more tolerant
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Deficiency expression
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Stunted crop, short internodes
Reduced chlorophyll production
Striping on corn leaves
Often seen early in season then visual symptoms
may disappear

Water solubility controls fertilizer Zn availability (40
to 50% required)
◦ ZnSO4, Lignosulfonate, ZnEDTA are best

ZnEDTA is 2 to 5 X more effective than other high
water soluble sources.

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Wide spread problem from western US to
Iowa
Lack of chlorophyll caused by plant’s inability
to take up Fe from soil
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Severity depends on crop & soil
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Major problem of lawns and gardens
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FeSO4·7H2O
Foliar – 1% FeSO4·7H2O solution
FeEDDHA
Oxysulfates, FeGels, FeSO4·H2O
Look for cheaper sources of by-product
ferrous sulfate
Foliar a last resort
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S is a secondary nutrient
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Required for protein formation
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Deficiencies primarily on sandy soils
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Early season deficiency more common with
cool, wet soils (no or reduced till, high water
table, river valleys)
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Sulfates
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21-0-0 (24% S)
K or K-Mg sulfates (18% S)
CaSO4 (16-18% S)
ZnSO4 (14% S)
Phosphates (16-20-0{15%}: newer have low S)
Thiosulfates
◦ 12-0-0-26S (ATS)
◦ 0-0-25-17S (KTS)
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Elemental S
◦ 90% - 99% S depending on granulation
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Fertilizer placement options generally involve
surface or subsurface applications.
This depends on:
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Crop and crop rotation
Soil test level
Mobility in the soil
Equipment availability
Using Global Position System equipment for precision application of
fertilizer. (Photo courtesy of USDA NRCS).
Pre-plant:
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Band:
◦ Surface (Dribble)
◦ Subsurface (Knife)
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Broadcast:
◦ Surface
◦ Incorporated
Nutrient Applicator (Source: http://www.deere.com)

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At Planting:
Band
◦ Surface
◦ Subsurface
 Below and to side of seed
◦ Starter (pop up)
Application of anhydrous ammonia fertilizer at planting time
(Photo courtesy of USDA NRCS).
After Planting

Sidedressing
◦ Anhydrous
◦ Fluid Sources (UAN)
 Surface and Subsurface

Topdress
◦ Solid and Liquid Sources
Nitrogen being applied to growing corn (Photo courtesy of USDA NRCS).

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