Nutrient management

1
Nutrient management for organic vegetable
production in NC
Part II
http//compost.tamu.edu/demos/palopinto/compost.jp
g
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Good nutrient management begins with routine soil
testing
http//www.gov.sz/Uploads/Images/1806_Sampling.jpg
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• Routine soil testing
• Rapid
• Cheap
• Predictive
• Widely
  applicable

Very different from research analysis of soil
4
History of Soil Testing in North Carolina
http//www.soil.ncsu.edu/about/century/historysoi
ltestingNC.html
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Soil testing starts with collecting a good
sample
http//aggie-turf.tamu.edu/aggieturf2/soilsample/i
mages/sampleprobe.gif
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Collect 5 sub-samples and mix in a clean
bucket
http//www.gov.on.ca/OMAFRA/english/crops/facts/in
fo_soiltestf2.jpg
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• Important soil sampling considerations
• Avoid areas that are clearly not representative
• (old manure piles, eroded knolls)
• Use clean sampling tools
• Collect samples from a depth that is
• appropriate for your soil management system
  
• conventional tillage 6-8
• no-till or lawn 4

8
Sample at the same time every year !
9
Choose a lab and stick with it !
Different labs often use different analytical
and interpretation methods
10
Soil analysis for organic farming S Haneklaus S,
E Schnug, HM Paulsen and I Hagel COMMUNICATIONS
IN SOIL SCIENCE AND PLANT ANALYSIS 36 (1-3)
65-79 2005                 Abstract Organic
farming according to EU 2092/91 aims at closed
nutrient cycles, which means that external
nutrient inputs are kept to a minimum. By
comparison, conventional farming is input
orientated, focusing on high crop productivity.
Soil analytical methods for organic farming
comprise physical, biological, chemical, and
energetic soil tests. The spade diagnosis is an
old field test to obtain "in situ" information
about soil fertility, which has experienced a
renaissance in organic farming. At the laboratory
level, organic farming uses the standard chemical
analytical methods used in conventional
agriculture comprising the determination of
organic matter, humus dynamics, pH, soluble plant
nutrients and reserve fractions. Special
attention is paid to phosphorus, which is
determined in three different extracts (acetic,
lactic, and citric acid) to assess phosphorus
dynamics, which is an indicator of the turnover
of organic matter. Compared with conventional
agriculture, biological methods are of particular
interest in organic farming. Soil biological
methods, such as the release of CO2,
nitrification, dehydrogenase, amylase and.
protease activities, reflect the biological
activity of soils. Problems of biological methods
are the high spatiotemporal variability in
dependence on biotic, pedogenetic, and climatic
conditions and the lack of interpretation schemes
for a transformation into practical
recommendations. The soil chroma test is a method
that aims to analyze energetic processes in
soils. It is a so-called "picture forming" method
and characteristic for the biodynamic school of
organic farming.
Perhaps someday soil tests developed specifically
for organically managed soils will be available
in NC until then
11
http//www.ncagr.com/agronomi/sthome.htm
Soil testing is free in NC !!!!
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5
13
Sampling vegetable crops for tissue analysis
http//www.cahe.nmsu.edu/pubs/_a/a-123.html
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Analytical results
Diagnostic information
http//149.168.222.13/D/2006/PLANTS/Predicti/1000
/PLP00582.PDF
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http//www.ncagr.com/agronomi/saaesd/s394.htm
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Analytical results
Estimated Nutrients available for a single crop
Total nutrient content of DM is adjusted for
moisture and availability
http//149.168.222.13/D/2005/WASTES/Predicti/7000
/WAW06343.PDF
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http//www.ncagr.com/agronomi/ustr.htm0
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Mehlich 3 extractant
The Mehlich 3 extractant was developed by Dr.
Adolph Mehlich to estimate plant availability of
macronutrients and micronutrients in soils with a
wide range of physical and chemical properties.
Adopted by the NCDA soil testing lab in 1981, the
Mehlich 3 extractant has reduced analytical costs
by replacing dual extraction methods.
Reference Mehlich A. 1984. Mehlich-3 soil test
extractant a modification of Mehlich-2
extractant. Commun Soil Sci Plant Anal
15(12)140916. Composition (0.2N CH3COOH
0.25N NH4NO3 0.013N HNO3 0.015N NH4F 0.001M
EDTA)
19
Mehlich 3 extracts are analyzed using an
Inductively Coupled Plasma Atomic Emission
spectrometer
20
Mehlich 3 extract concentrations can be
converted into other formats
21
Become familiar with how your lab expresses
analytical results - the NCDA lab uses an index
system to present results for P2O5, K2O, Mn, Zn,
Cu and S. Ca and Mg are presented as percentages
of CEC.
sufficiency
Crop response
L
M
H
VH
Fertilizer needed
Index
22
Meaningful interpretation of soil test results
requires field calibration
100 yield
50 yield
Soil test P concentration (ppm)
http//www.ipm.iastate.edu/ipm/icm/2003/11-17-2003
/mehlich3.gif
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Results may be accurate but have little meaning
without field calibration
http//www.lamotte.com/
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Relationship between crop yield and soil test K
Response curves are derived from calibration data
response curves do not describe all the
variation in calibration data !
25
Weather often regulates crop productivity more
than nutrient input rates in high
productivity systems
http//www.fertilizer.org/ifa/publicat/PDF/2005_ag
_frankfurt_lammel_slides.pdf
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Equations can be derived to predict input rates
from index values
27
Index 50
P2O5 and K20 recommendations for different crops
25 different equations are used to calculate P2O5
and K2O recommendations in NC
28
Equation s for converting indices into input
rates
29
N is normally a limiting nutrient
Potential N uptake by
wheat
pasture
Mineralized soil N
Jenkinson
30
Why doesnt the NCDA lab test for N ???
Total soil N is also a poor predictor of seasonal
availability of N
Preseason mineral N is a poor predictor of
seasonal availability of N
31
http//res2.agr.ca/stjean/publication/bulletin/nit
rogen-azote_e.pdf
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Recommendations
Analytical results
So what do the numbers mean ???
33
Soil class Each soil sample is classified as
mineral (MIN), mineral-organic (M-O), or organic
(ORG). These classifications are based on the
humic matter percent (HM) and weight/volume
ratio (W/V). Target pH values differ between soil
classes 6.06.5 for MIN soils, 5.5 for M-O
soils, and 5.0 for ORG soils. Mineral soils
require a higher pH to minimize aluminum
toxicity. A lower pH can be maintained in M-O and
ORG soils without detrimental effects to crop
production.
34
Weight/volume ratio (W/V) The weight/volume
ratio, expressed in g/cm³, is used to classify
the samples soil class. For example, a very
sandy soil may have a W/V of 1.50 g/cm³, whereas
an organic soil may have a W/V as low as 0.5
g/cm³. Soils high in clay fall within these two
extremes. W/V is generally inversely related to
cation exchange capacity (CEC) that is, soils
with a high W/V generally have a low CEC.
35
Cation exchange capacity (CEC) The cation
exchange capacity is measured in meq/100 cm³ and
is determined by summation of the extractable
calcium, magnesium, potassium, sodium and
exchangeable acidity (Ac). The CEC of North
Carolina soils ranges from lt 2.0 meq/100 cm³ for
very sandy soils to gt 25 meq/100 cm³ for some
clay and organic soils. Cation nutrients are
less subject to leaching in soils with higher
CECs. CEC values are relatively stable but will
respond to changes in soil pH, organic matter,
and clay content.
36
Base Saturation base saturation is a way
of describing the extent to which a soils CEC is
occupied by non-acid cations (i.e. Ca2, Mg2, K
and Na). Soils with similar mineralogy have a
fairly consistent relationship between pH and
base saturation.
http//faculty.plattsburgh.edu/robert.fuller/3702
0Files/Week7Soil20Acidity,Liming/aaStart8.htm
37
Exchangeable acidity (Ac) Ac is measured using a
pH 6.6 buffer method and represents the quantity
of exchangeable acid cations (i.e. meq H and
Al3 / 100 cm³) that should be considered when
calculating lime recommendations. Lime
recommendation Ac target pH current pH
6.6
current pH
38
Humic matter (HM) The HM is measured
colorimetrically following soil extraction using
a dilute NaOH solution and is reported in g/100³.
The HM represents the chemically active organic
matter that is most relevant to herbicide
adsorption. On average, the HM is slightly less
than half of the total OM but the relationship
between HM and OM is not consistent. The HM
changes very little with management.
39
Phosphorus Potassium (P-I, K-I) Mehlich 3
extractable phosphorus and potassium
concentrations are reported as P-I and K-I
values. When P-I and K-I values are low, a large
yield response to the addition of P and K is
likely. Medium index levels indicate that a
moderate response to the addition of P and K is
likely. High index levels indicate that a
positive crop response to the addition of P and K
is unlikely.
40
Clay content affects the relationship between
soil test P and optimal P input rate
Finer textured soils have lower sufficiency
levels of extractable P than sandy soils
Current NCDA recommendations do not adjust for
texture related variation in P response
clay
clay
clay
100 yield
clay
(Lins, 1987)
41
Relative increase in P-I per unit of P2O5 added
to NC soils with variable clay content
0.80
0.65
Soils with more clay have more P- buffering
capacity
0.5
?P-I / P2O5 added
0.35
0.20
Adapted from Cox (1994)
42
Calcium (Ca ) Mehlich 3 extractable calcium is
reported as a percentage of the soils CEC. For
example, if the Ca is 62, then 62 of the soils
negative charge is balanced by Ca2. At target pH
levels, calcium is rarely limiting to crop yield.
Peanuts are an exception. Gypsum (CaSO4) is
routinely applied as a source of supplemental
Ca. Calcium determination is essential to
calculate the CEC and to evaluate the
relationship between Ca, Mg, and K.
43
Magnesium (Mg) Magnesium is also reported as a
percentage of the soils CEC. Multiplying Mg by
the CEC gives you the amount of Mg present in
meq/100 cm³. The following guidelines are useful
in evaluating the Mg status of a soil If a soil
contains more than 0.5 meq Mg/100 cm³, Mg
application is not necessary. If a soil contains
less than 0.5 meq Mg/100 cm³ but more than 0.25
meq Mg/100 cm³ and Mg is greater than 10, Mg
application is not necessary. If a soil contains
less than 0.5 meq Mg /100 cm³ and Mg is less
than 10, most crops will benefit from additional
Mg. If a soil contains less than 0.25 meq/100
cm³, most crops will benefit from additional Mg.
44
Manganese (Mn-I, Mn-AI) Mehlich 3 extractable
manganese concentrations are converted into 2
types of index values. Mn-I is a general
indicator of the level of Mn in soil. Mn-AI is an
availability index which accounts for pH effects
on Mn availability. If two crops are entered on
the sample submission form, Mn-AI(1) is the
manganese availability index for the first crop
and Mn-AI(2) applies to the second crop. Mn-AI
values decrease as soil pH increases. The need
for manganese is evaluated for all crops on the
basis of response similar to corn and soybeans.
Values above 25 are considered sufficient for
most crops if the pH is below 6.0.
45
Zinc (Zn-I, Zn-AI)
Mehlich 3 extractable Zn concentrations are
converted into 2 types of index values. Zn-I is a
general indicator of the level of Zn in soil. A
zinc-availability index (Zn- AI) is also
calculated as follows 1.0 Zn-I for mineral
soils, 1.25 Zn-I for mineral-organic soils, and
1.66 Zn-I for organic soils. Fertilization
with zinc is recommended if the Zn-availability
index (Zn-AI) is 25 or below for specific crops
that have shown a response to Zn. The current
recommendation for Zn is 6.0 lb/acre broadcast or
3.0 lb/acre banded. A potential zinc toxicity is
indicated whenever a Z appears under Zn in the
Recommendations section of your report. The Z
alerts the grower that the Zn-I is greater than
2000. The critical toxic level for Zn is 3000 for
most crops. Peanuts are very sensitive to zinc,
so growers are alerted when Zn-I 300 or 500
(critical toxic level).
46
Copper (Cu-I) Mehlich 3 extractable Cu
concentrations are converted into Cu-I, an
indicator of plant availability of copper.
Adjustments for pH effects on availability are
not made as they are for Mn and
Zn. Fertilization with copper is recommended if
the Cu-I value is 25 or below for specific crops
that have been shown to respond to fertilization.
Uniform broadcasting and thorough incorporation
contribute to optimum Cu availability. A
potential Cu toxicity is indicated whenever a C
appears under Cu in the recommendations section
of your report. The C alerts the grower that the
Cu-I is greater than 2000. The critical toxic
level for Cu is 3000.
47
Sulfur (S-I) A value for S-I is given, but no
rate for sulfur application is recommended. S is
rarely lacking in Piedmont or Mountain soils due
to their clay content. Under normal growing
conditions, S is also sufficient on organic
soils. S, however, does leach readily from very
sandy soils. It accumulates in the subsoil where
it is still available for crop use. Therefore,
the S content in the plow layer alone is not a
good indicator of the S status in the soil. If
the S-I for the plow layer of deep sandy soils is
less than 25, however, there is a high
probability that S should be included in the
fertilizer. A rate of 2025 lb of S per acre
should satisfy most crop requirements.
48
Sodium (Na) Na values greater than 0.4 meq /
100 cm³ may interfere with plant uptake of
calcium, magnesium, and potassium and also
adversely affect soil structure.
49
Diagnostic Soil
Testing Problem soil samples are handled
separately from the routine samples. In addition
to the routine analyses, levels of nitrate
nitrogen (NO3-N), ammonium nitrogen (NH4-N) and
soluble salts (SS-I) may be determined. Problem
soil sample test results are reviewed by an
agronomist. The agronomist makes appropriate
comments regarding the cause of the problem and
any recommended treatment. Plant analysis, in
conjunction with a diagnostic soil test, is the
best way to ascertain a nutrient problem. It is
also wise to collect soil and plant samples from
both good and bad areas for comparison
purposes. Soil and plant samples from the same
vicinity should be labeled the same to facilitate
comparison.
50
Nutrient balancing concepts Nutrients interact
in plant and soil systems. Some important
nutrient interactions include ammonium-calcium,
phosphorus-iron, phosphorus-copper,
phosphorus-zinc, and potassium-magnesium-calcium.
Some consultants and private labs place great
emphasis on base cation ratios. Typical target
ratios 65-75 Ca 10-15 Mg 2-5 K Very
little research indicates that specific cation
ratios are critical for vegetable crops (or any
other crops) in the southeastern US. However,
keep in mind that Ca is the cheapest non-acid
cation, excessive levels of Mg and K interfere
with crop uptake of Ca, and adequate Ca is
important for crop quality.
Nutrient interactions and proper nutrient balance
need to be considered in relation to nutrient
supply i.e. the availability of nutrients in
the soil. Nutrient supply is important because
recommended nutrient ratios" in soil or plant
tissue are possible when nutrients are deficient
or excessively high.