MEASUREMENT
LBS/ACRE
PPM
Soil Test CATEGORY
Recommendation SUMMARY
Field name: #12
Sample date: December (no
P
20
10
very low
30 lbs P2O5/acre
sample for PSNT will be taken)
K
58
29
very low
200 lbs K2O/acre
Soil type: clay (somewhat
poorly drained)
Mg
138
69
high
none
Manure added: none
Ca
8,168
4,084
high
none
Cropping history: continuous
pH
6.8
no lime needed
corn
Crop to be grown: corn
CEC
21.1 me/100g
OM
4.3%
rotate to forage legume crop
N
no N soil test
100–130 lbs N/acre
*All nutrient needs were determined using the Mehlich 3 solution (see table 21.3C).
Note: ppm = parts per million; P = phosphorus; K = potassium; Mg = magnesium; Ca = calcium; OM = organic matter; me = milliequivalent; PSNT = pre-sidedress nitrate test; N = nitrogen.
What can we tell about soil #3 based on the soil test?
3. Nitrogen fertilizer is probably needed in large amounts (100 to 130
• The high pH indicates that this soil does not need any lime.
pounds/acre) for high N-demanding crops, such as corn. If no in-season
• Phosphorus and potassium are low. [Note: 20 pounds of P per acre is
soil test (like the PSNT) is done, some preplant N should be applied
low, according to the soil test used (Mehlich 3). If another test, such as
(around 50 pounds/acre), some in the starter band at planting (about 15
Morgan’s solution, was used, a result of 20 pounds of P per acre would
pounds/acre) and some side-dressed (about 50 pounds).
be considered a high result.]
4. One way to meet the needs of the crop is as follows:
• The organic matter is relatively high. However, considering that this is a
a. broadcast 500 pounds per acre of an 11-0-44 bulk blended fertilizer;
somewhat poorly drained clay, it probably should be even higher.
b. use 300 pounds per acre of a 5-10-10 starter; and
• About half of the CEC is probably due to the organic matter and the
c. side-dress with 150 pounds per acre of ammonium nitrate.
rest probably due to the clay.
This will supply approximately 120 pounds of N, 30 pounds of
• Low potassium indicates that this soil has probably not received high
phosphate, and 210 pounds of potash.
levels of manures recently.
• There was no test done for nitrogen, but given the field’s history of
Recommendations for organic producers:
continuous corn and little manure, there is probably a need for nitro-
1. Apply 2 tons per acre of rock phosphate (to meet P needs) or about 5
gen. A low amount of active organic matter that could have supplied
to 8 tons of poultry manure (which would meet both phosphorus and
nitrogen for crops is indicated by the history (the lack of rotation to
nitrogen needs), or a combination of the two (1 ton rock phosphate and
perennial legume forages and lack of manure use) and the moderate
3 to 4 tons of poultry manure).
percent of organic matter (considering that it is a clay soil).
2. Apply 400 pounds of potassium sulfate per acre broadcast preplant. (If
poultry manure is used to meet phosphorus and nitrogen needs, use
General recommendations:
only 200 to 300 pounds of potassium sulfate per acre.)
1. This field should probably be rotated to a perennial forage crop.
3. Use manure with care. Although the application of uncomposted
2. Phosphorus and potassium are needed—probably around 30 pounds
manure is al owed by organic-certifying organizations, there are restric-
of phosphate and 200 or more pounds of potash applied broadcast,
tions. For example, four months may be needed between application
preplant, if a forage crop is to be grown. If corn will be grown again, all
of uncomposted manure and either harvest of crops with edible por-
of the phosphate and 30 to 40 pounds of the potash can be applied
tions in contact with soil or planting of crops that accumulate nitrate,
as starter fertilizer at planting. Although magnesium, at about 3% of
such as leafy greens or beets. A three-month period may be needed
the effective CEC, would be considered low by relying exclusively on
between uncomposted manure application and harvest of other food
a basic cation saturation ratio system recommendation, there is little
crops.
likelihood of an increase in crop yield or quality by adding magnesium.
246
Building SoilS for Better CropS: SuStainaBle Soil ManageMent
chAPter 21 getting the Most FroM routine soil tests
—SOIL TEST #4—
(Alabama)
Soil Test #4 Report Summary*
MEASUREMENT
LBS/ACRE
PPM
Soil Test CATEGORY
Recommendation SUMMARY
P
102
51
very high
none
Field name: River A
K
166
83
high
none
Sample date: October
Mg
264
132
high
none
Soil type: sandy loam
Ca
1,158
579
none
Manure added: none
Cropping history:
pH
6.5
no lime needed
continuous cotton
CEC
4.2 me/100g
Crop to be grown: cotton
OM
not requested
use legume cover crops,
consider crop rotation
N
no N soil test
70–100 lbs N/acre
*All nutrient needs were determined using the Mehlich 1 solution (see table 21.3B).
Note: ppm = parts per million; P = phosphorus; K = potassium; Mg = magnesium; Ca = calcium; OM = organic matter; me = milliequivalent; PSNT = pre-sidedress nitrate test; N = nitrogen.
What can we tell about soil #4 based on the soil test?
Recommendations for organic producer:
• With a pH of 6.5, this soil does not need any lime.
1. Although poultry or dairy manure can meet the crops’ needs, that
• Phosphorus is very high, and potassium and magnesium are sufficient.
means applying phosphorus on an already high-P soil. If there is no
• Magnesium is high, compared with calcium (Mg occupies over 26% of
possibility of growing an overwinter legume cover crop (see recom-
the CEC).
mendation #2), about 15 to 20 tons of bedded dairy manure (wet
• The low CEC at pH 6.5 indicates that the organic matter content is
weight) should be sufficient. Another option for supplying some of
probably around 1–1.5%.
the crops’ need for N without adding more P is to use Chilean nitrate
until good rotations with legume cover crops are established.
General recommendations:
2. If time permits, plant a high-N-producing legume cover crop, such as
1. No phosphate, potash, magnesium, or lime is needed.
hairy vetch or crimson clover, to provide nitrogen to cash crops.
2. Nitrogen should be applied, probably in a split application totaling
3. Develop a good rotation so that all the needed nitrogen will be sup-
about 70 to 100 pounds N per acre.
plied to nonlegumes between the rotation crops and cover crops.
3. This field should be rotated to other crops and cover crops used
4. Although the application of uncomposted manure is al owed by
regularly.
organic-certifying organizations, there are restrictions when growing
food crops. Check with the person doing your certification to find out
what restrictions apply to cotton.
247
Building SoilS for Better CropS: SuStainaBle Soil ManageMent
chAPter 21 getting the Most FroM routine soil tests
—SOIL TEST #5—
(Semiarid Great Plains)
Soil Test #5 Report Summary*
MEASUREMENT
LBS/ACRE
PPM
Soil Test CATEGORY
Recommendation SUMMARY
P
14
7
low
20–40 lbs P2O5
Field name: Hill
K
716
358
very high
none
Sample date: April
Mg
340
170
high
none
Soil type: silt loam
Ca
not determined
none
Manure added: none indicated
pH
8.1
no lime needed
Cropping history: not indicated
Crop to be grown: corn
CEC
not determined
OM
1.8%
use legume cover crops, consider
rotation to other crops that produce
large amounts of residues
N
5.8 ppm
170 lbs N/acre
*K and Mg extracted by neutral ammonium acetate, P by the Olsen solution (see table 21.3D).
Note: ppm = parts per million; P = phosphorus; K = potassium; Mg = magnesium; Ca = calcium; OM = organic matter; me = milliequivalent; PSNT = pre-sidedress nitrate test; N = nitrogen.
What can we tell about soil #5 based on the soil test?
Recommendations for organic producers:
• The pH of 8.1 indicates that this soil is most likely calcareous.
1. Because rock phosphate is so insoluble in high-pH soils, it would be
• Phosphorus is low, there is sufficient magnesium, and potassium is
a poor choice for adding P. Poultry manure (about 6 tons per acre) or
very high.
dairy manure (about 25 tons wet weight per acre) can be used to meet
• Although calcium was not determined, there will be plenty in a calcar-
the crop’s needs for both N and P. However, that means applying more
eous soil.
P than is needed, plus a lot of potash (which is already at very high
• The organic matter at 1.8% is low for a silt loam soil.
levels). Fish meal might be a good source of N and P without adding K.
• The nitrogen test indicates a low amount of residual nitrate (table
2. A long-term strategy needs to be developed to build soil organic
21.4B), and, given the low organic matter level, a low amount of N
matter—better rotations, use of cover crops, and importing organic
mineralization is expected.
residues onto the farm.
3. Use manure with care. Although the application of uncomposted
General recommendations:
manure is al owed by organic-certifying organizations, there are
1. No potash, magnesium, or lime is needed.
restrictions. For example, three months may be needed between
2. About 170 pounds of N per acre should be applied. Because of the low
application of uncomposted manure and either harvest of root crops
amount of leaching in this region, most can be applied preplant, with
or planting of crops that accumulate nitrate, such as leafy greens or
perhaps 30 pounds as a starter (applied at planting). Using 300 pounds
beets. A two-month period may be needed between uncomposted
per acre of a 10-10-0 starter would supply all P needs (see recommen-
manure application and harvest of other food crops.
dation #3) as well as provide some N near the developing seedling.
Broadcasting and incorporating 300 pounds of urea or 420 pounds of
ammonium nitrate will provide 140 pounds of N.
3. About 20 to 40 pounds of phosphate is needed per acre. Apply the
lower rate as a starter, because localized placement results in more
efficient use by the plant. If phosphate is broadcast, apply at the
40-pound rate.
4. The organic matter level of this soil should be increased. This field
should be rotated to other crops and cover crops used regularly.
248
Building SoilS for Better CropS: SuStainaBle Soil ManageMent
chAPter 21 getting the Most FroM routine soil tests
ADJUSTINg A SOIl TEST REcOMMENDATION
table 21.5. If you don’t test your soil annually, and the
Specific recommendations must be tailored to the crops
recommendations you receive are only for the current
you want to grow, as well as other characteristics of
year, you need to figure out what to apply the next year
the particular soil, climate, and cropping system. Most
or two, until the soil is tested again.
soil test reports use information that you supply about
No single recommendation, based only on the soil
manure use and previous crops to adapt a general rec-
test, makes sense for all situations. For example, your
ommendation for your situation. However, once you feel
gut might tell you that a test is too low (and fertilizer
comfortable with interpreting soil tests, you may also
recommendations are too high). Let’s say that although
want to adjust the recommendations for a particular
you broadcast 100 pounds N per acre before plant-
need. What happens if you decide to apply manure after
ing, a high rate of N fertilizer is recommended by the
you sent in the form along with the soil sample? Also,
in-season nitrate test (PSNT), even though there wasn’t
you usually don’t get credit for the nitrogen produced by
enough rainfall to leach out nitrate or cause much loss
legume cover crops because most forms don’t even ask
by denitrification. In that case, you might not want to
about their use. The amount of available nutrients from
apply the full amount recommended.
legume cover crops and from manures is indicated in
Another example: A low potassium level in a soil
Table 21.3
Soil Test Categories for Various Extracting Solutions
A. Modified Morgan’s Solution (Vermont)
C. Mehlich 3 Solution (North Carolina)*
Category
Very
Low
Low
Optimum
High
Excessive
Category
Very
Low
Low
Optimum
High
Excessive
Probability of
Probability of
response to
Very
response to
Very
added nutrient
High
High
Low
Very
Low
added nutrient
High
High
Low
Very
Low
Available P (ppm)
0–2
2.1–4.0
4.1–7
7.1–20
Available P (ppm)
0–12
13–25
26–50
51–125
>125
K (ppm)
0–50
51–100
101–130
131–160
>160
K (ppm)
0–43
44–87
88–174
>174
Mg (ppm)
0–35
36–50
51–100
>100
Mg (ppm)**
0–25
>25
B. Mehlich 1 Solution (Alabama)*
*From Hanlon (1998).
**Percent of CEC is also a consideration.
Category
Very
Low
Low
Optimum
High
Excessive
Probability of
D. Neutral Ammonium Acetate Solution for K and Mg and
response to
Very
Olsen or Bray-1 for P (Nebraska [P and K], Minnesota [Mg])
added nutrient
High
High
Low
Very
Low
Available P (ppm)
0–6
7–12
13–25
26–50
>50
Category
Very
Low
Low
Optimum
High
Excessive
K (ppm)
0–22
23–45
46–90
>90
Probability of
Very
Mg (ppm)**
0–25
>25
response to
added nutrient
High
High
Low
Very
Low
Ca for tomatoes
(ppm)***
0–150 151–250
>250
P (Olson, ppm)
0–3
4–10
11–16
17–20
>20
*From Hanlon (1998).
P (Bray-1, ppm)
0–5
6–15
16–24
25–30
>30
**For corn, legumes, and vegetables on soils with CECs greater than 4.6 me/100g.
K (ppm)
0–40
41–74
75–124
125–150
>150
***For corn, legumes, and vegetables on soils with CECs from 4.6 to 9.0 me/100g.
Mg (ppm)
0–50
51–100
>101
249
Building SoilS for Better CropS: SuStainaBle Soil ManageMent
chAPter 21 getting the Most FroM routine soil tests
Table 21.4
Soil Test Categories for Nitrogen Tests
A. Pre-Sidedress Nitrate Test (PSNT)*
B. Deep (4-ft) Nitrate Test (Nebraska)
Category
Very
Low
Low
Optimum
High
Excessive
Category
Very
Low
Low
Optimum
High
Excessive
Probability of
Probability of
response to
Very
response to
Very
added nutrient
High
High
Low
Very
Low
added nutrient
High
High
Low
Very
Low
Nitrate-N (ppm)
0–10
11–22
23–28
29–35
>35
Nitrate-N (ppm)
0–6
7–15
15–18
19–25
>25
*Soil sample taken to 1 foot when corn is 6–12 inches tal .
test (let’s say around 40 ppm) will certainly mean that
developed for soils and cropping systems in your home
you should apply potassium. But how much should you
state or region. It also is an indication that you may need
use? When and how should you apply it? The answer
to modify a recommendation for your specific situation.
to these two questions might be quite different on a
low organic matter, sandy soil where high amounts of
MAKINg ADJUSTMENTS TO
rainfall normally occur during the growing season (in
FERTIlIZER APPlIcATION RATES
which case, potassium may leach out if applied the pre-
If information about cropping history, cover crops, and
vious fall or early spring) versus a high organic matter,
manure use is not provided to the soil testing laboratory,
clay loam soil that has a higher CEC and will hold on to
the report containing the fertilizer recommendation can-
potassium added in the fall. This is the type of situation
not take those factors into account. Below is an example
that dictates using labs whose recommendations are
of how you can modify the report’s recommendations:
Table 21.5
Worksheet for Adjusting Fertilizer Recommendations
Amounts of Available Nutrients from
Manures and Legume Cover Crops
N
P O
K O
2 5
2
Soil test recommentation (lbs/acre)
120
<