Beyond N-P-K:
Chemistry of Soil and Water and
How they Effect our Fertilizer
Practices
David Wm. Reed
Department of Horticultural Sciences
Texas A&M University
1
17 Essential Elements
Supplied Naturally (by H20, O2, CO2)
C, H, O
Macronutrients
N, P, K, Ca, Mg, S
Micronutrients or Trace Elements
Fe, Cu, Mn, Zn, B, Mo, Cl, Ni
1
Where Do All the Nutrients Come From?
N
P
K
Ca
Mg
S
Fe
B
Other Micro
Incorporated into Soil or Growing Medium - Pre-Planting
complete fertilizer
X
superphosphate
X
X
X
?
X
dolomitic lime
X
gypsum
X
X
X
X
iron sulfate
X
micronutrient mix
X
X
X
all
Supplied Post-Planting as Granular, Liquid or Slow-Release Application
complete fertilizer
X
X
X
?
Epsom salt
X
X
soluble micronutr.
X
some pesticides
X
irrigation water ppm
>3-5
>1
X
all
Cu,Mn,Zn
0.3-1.5
2
Water: EC, pH Alkalinity
Collect water sample
Meters Used
•pH:
•Soluble Salts or EC:
•Alkalinity:
pH meter
conductivity meter
alkalinity test kit or paper
Compare reading to Interpretation Table
2
Meters Used
pH
EC
alkalinity kit
Meters Used
Combination
EC & pH
Meter
2
3
Water: Soluble Salts and EC
Relative Hazard
None
Electrical
Conductivity
Little
Moderate
High
Severe
dS/m or mmhos/cm
0.2
<0.7
0.7-2
2-3
>3
1400 - 2100
>2100
ppm
Soluble Salts
140
<490
490 - 1400
4
Water: Alkalinity
Recommended Alkalinity Levels
Minimum
Maximum
ppm
meq/l
ppm
meq/l
Plugs and/or seedlings
38
0.75
66
1.3
Small pots and shallow flats
38
0.75
86
1.7
4" to 5" pots and deep flats
38
0.75
106
2.1
6” pots and long term crops
63
1.25
131
2.6
5
Soil/Media: Soluble Salts (EC) & pH
Collect soil/medium sample below surface
Extract with water (1:2 dilution)
Filter
Meters Used
•pH:
•Soluble Salts or EC:
pH meter
conductivity meter
Compare reading to Interpretation Table
7
Soil/Media: pH
SME
Extract
Optimum pH 5.5 - 6.5
1:2 or 1:5 Dilution
Slurry
Extract
Slurry
Pour-Through
5.4 6.2
5.5 - 6.5
5.4 - 6.2
5.5 - 6.5
7
Soil/Media: Soluble Salts (EC)
Electrical Conductivity (EC)
dS/m or mmho/cm
SME
1:2 Dilution
1:5 Dilution
Pour-Through
Established plants
2.0-3.0
0.8-1.2
0.3-0.6
3.0-5.0
Seedlings, plugs
1.0-2.0
0.5-0.9
?
?
8
Graphical Tracking pH and EC
4
EC (dS/cm)
3
2
1
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Weeks after Planting
8
Graphical Tracking of EC
9
Selecting a Fertilizer Based on the
Form of Nitrogen
Nitrogen exists in two forms
Ammoniacal (NH4+, urea)
Nitrate (NO3-)
Nitrogen form used affects
Type of growth
Type fertilizer, acid vs. basic
pH of the soil or growing medium
9
Selecting a Fertilizer Based on the
Form of Nitrogen
Form of Nitrogen Influences Type Growth and is Seasonal
Nitrogen Form
Type Growth
•lush
growth
High Ammoniacal
•larger leaves
(>25%)
•longer stems
•hardy plant
High Nitrate
•compact growth
(>75%)
Used For
•foliage
plants
•flowering plants early
•warmer & summer
•flowering
plants
finishing
•cooler & winter
9
Selecting a Fertilizer Based on the
Form of Nitrogen
Form of Nitrogen Influences Soil/Medium pH
Nitrogen Form
High Ammoniacal
(>25%)
High Nitrate
(>75%)
Type Fertilizer
acid
basic
Soil/Medium Reaction
pH decreases &
becomes more acid
pH increases &
becomes more basic
10
Selecting a Fertilizer Based on the Form of Nitrogen
Acid versus Basic Fertilizers
Fertilizer
% NH4*
Potential Acidity
Potential Basicity
21-7-7 acid
100
1560
20-18-18
15-15-15
20-0-20
73
52
25
710
261
40
20-0-20
15-5-15
15-0-15
69
28
13
0
15.5-0-0 Ca nitrate
6
400
13-0-44 K nitrate
0
460
0
135
319
10
Fertilizer Label Lists Potential Acidity
Label Fertilizer Analysis
11
Micronutrients in Acid Vs. Alkaline Soil
(especially heavy metals: Fe, Mn, Zn, Cu)
Selection of Heavy Metal Carriers based on Soil pH
Nitrogen Form
Acid Soil
Alkaline Soil
Sulfates
effective
not very effective
Chelates
effective, but
expensive so why use.
most effective
11
Which Chelate to Use?
11
11
Which Chelate to Use?
Highest pH Still Effective
Chelate
6
lignosulfonate, citrate,
HEDTA
6.5
7.5
any pH
EDTA
DTPA (330)
EDDHA (138)
Fertilizer Label Lists Chemicals Used
11
12
Rose Rootstocks Tolerance to Alkaline Soil
Rose species/cultivar
R. canina
R. manettii
R. odorata
R. sp. “Mexican”
R. fortuniana
R. multiflora 'Dan Whiteside'
R. multiflora ‘Brooks 56'
R. multiflora 74-3
R. 'Dr Huey'
Chlorosis Rating
(5=green to 1=yellow)
5.0
4.9
4.8
4.8
4.4
2.7
2.7
died
died
12
Rose Rootstocks Tolerance to Alkaline Soil
13
EarthKind Landscape Roses
TM
(http://aggie-horticulture.tamu.edu/earthkindrose/index.html)
13
EarthKind Landscape Roses
TM
Cultivar
Flower Color
Flower Type
Blooming Period
Ht x Wd (feet)
Category
2x6
shrub
Ground Covers
Sea Foam
creamy white
double
April-November
Dwarf Shrubs
Marie Daly
Pink
semi-double
April-November
3x3
polyantha
The Fairy
light pink
double
April-November
3x4
polyantha
Small Shrubs
Caldwell Pink
lilac pink
double
May- November
4x4
found
Easy Going
yellow
double
April-November
4x4
floribunda
Knock Out
cherry red
semi-double
April-November
4x4
shrub
Livin' Easy
apricot-orange
double
April-November
4x4
floribunda
Perli d'Or
peach
pompon
April-November
4x4
polyantha
Medium Shrubs
Belinda's Dream
Pink
double
April-November
5x5
shrub
Climbing Pinkie
pink
semi-double
April-November
5x7
polyantha
Else Poulsen
pink
semi-double
April-November
5x5
floribunda
Katy Road Pink
pink
semi-double
April-November
5x4
found
Mutabilis Butterfly Rose
yellow, pink,
crimson
single
April-November
6x6
China
13
Belinda’s Dream
(developed by Dr. Robert Basye)