Lecture 13a Soil Fertility NPK

1
Lecture 13aSoil Fertility N-P-K

• The study of supplying plant nutrients from the
  soil.
• Understanding CEC is the single most important
  concept in understanding soil fertility.
• Nutrient analysis of the soil determines the
  potential of the soil for supplying N,P,K, Ca,
  Mg, S, plus micronutrients to plants during the
  growing season.
• Nutrients become available through organic matter
  decomposition, chemical weathering of minerals,
  airborne additions, and fertilizers.

2
Fertilizers
Fertilizer Plant

• Manufactured fertilizers have been used for over
  a 100 years.
• The numbers on a bag of fertilizer--"10-5-5",
  guaranteed chemical analysis. These numbers
  indicate the bag of fertilizer contains 10 N,
  5 P2O5, and 5 K2O. These numbers--"10-5-5
  the fertilizer grade.
• Fertilizer ratio is the relative proportion of
  primary nutrients (N-P2O5-K2O) in a fertilizer
  grade, divided by the highest common divisor in
  this example, 10 52, so the ratio of this
  fertilizer is 2-1-1.

3

• For phosphorus and potassium, the chemical
  analysis is given in the oxide form.
• This is the way the nutrients were first thought
  to be absorbed by the plant and is still used
  today to express the analysis of fertilizer.
• For a grade of 18-24-12 elemental analysis 18-
  10.5 - 10
• The elemental analysis can usually be found on
  the bag near the fertilizer grade.
• To convert from the elemental analysis to the
  chemical analysis for phosphorous and potassium
  fertilizers, use this formula
• P2O5 x .44 P
• K2O x .83 K

4
Converting P2O5 K2O (oxide from) into P and K
(elemental form)

• P2O5 x .44 P
• P x 2.29P2O5
• K2Ox.83K
• K x 1.2K2O
• For Example A 30 pound sack of fertilizer (25 -
  5 - 5) , is applied to your garden.
• The amount of N applied.25 x 307.5 lbs N
• amount of P205 applied.05 x 301.5 lbs P.44 x
  1.50.66 lbs P
• amount of K20 applied.05 x 301.5 lbs K.83 x
  1.51.245 lbs.K

5

• Dyad If you apply a 14 lb sack of 22-3-14 how
  many pounds of N, P2O5, and K2O did you apply?
• N 14 x .22 3.08
• P2O5 14x .03 0.42
• K2O 14 x .14 1.96

6
Soil Fertility

• Nitrogen Fertilizer - management of Nitrogen
  requires an understanding of the Nitrogen Cycle.
  
• Nitrogen is dynamic in the soil and forms of N
  will change depending on the soil conditions.

Reed Palm N Def on left
7
Nitrogen

• NH4 and NO3- forms taken up by plants
• Loss of N can occur 1) leaching of NO3- , 2)
  volatilization of NH4 to NH3 (high pH soils),
  
• 3) immobilization by plant or microbe uptake,
  
• 4) Denitrification

8
Nitrogen Cycle
9
(No Transcript)
10
Fertilizer Nitrogen

• Nitrogen fertilizer should be added to the soil
  when the crop will use it, adding excess N will
  cause losses that may harm the environment.
• Keep N P out of water bodies by only applying
  it to soils that need the nutrients.
• Nitrogen is expensive and using only what the
  crop needs for adequate growth is important

Wheat with N response
11
N Fertilizer Rate and Application

• Rate of N application is the management practice
  that most influences nitrate concentrations in
  the tile drainage water.
• Reducing the N rate by 33 ( to 80 lbs N) from
  the recommended 120-lb N rate for corn after
  soybeans decreased the nitrate-N concentration in
  the subsurface, drainage water by
• 2.6 mg/L (14)
• and decreased corn yield by 25 bu/A (16).

http//www.ewg.org/reports/deadzone/top10.php
12

• On the other hand, increasing the N rate by 33
  above the fall-applied 120-lb rate, increased
  nitrate-N concentration by 4.3 mg/L (23) but
  increased yield only 9 bu/A (6).
• Time of application studies showed nitrate-N
  losses from a corn-soybean rotation to be ranked
• fall N gt split(fall and spring) N gt spring N
  fall N with a nitrification inhibitor.
• From G. Randall,2004

U.S. Geological Survey, 1993 26-38.
13
Alfalfa and grass CRP effectively filter tile
drain water
Randall et al., 1997
14
Nitrogen Pollution from Manure
15
Nitrogen soil testing

• NO3- Mobile nutrient
• In drier areas use a fall or spring nitrate-N
  soil test.
• In humid areas, use spring nitrate-N test or
  table value based on previous crop and organic
  matter.
• The amount of rain after the soil test may
  determine if the NO3- tested for has been leached
  below the root zone.

16
Nitrogen Credits

• Once the amount of N needed for the plant is
  determined -
• N credits need to be taken for
• Previous crop
• Previous manure applications or sludge
• 2nd year after alfalfa

17

• THUS it becomes important to give N - CREDITS for
  previous management activities.
• legumes, manure or other organic additions with
  low CN ratios are adding N to the soil
• Thus this organic N needs to be counted into the
  total N available for crop growth
• And thus reduce the need for fertilizer N.

Cow Manure
Green Manure
18
Price of N

• 2005 2006 2007 2009
• NH3 .254/lb N .314/lb N .41/lb N .47
• Urea - .294/lb N .404/lb N
  .45/lb N .59
• P2O5 - .244/lb P .244/lb P
• K2O - .144/lb K .224/lb K

19
P - Fertility

• Phosphorus is low in total amount in the soil and
  low in solubility and is readily fixed by Fe and
  Al at low pH and Ca at high pH.
• H2PO4- and HPO4-- forms taken up by plants
• P Fertilizer is made from rock phosphate
• Rock phosphate mines are in Florida South
  Carolina

20
Phosphorus Fertility

• To control P availability
• 1) control pH (lime acid soils)
• 2) Place fertilizer in bands near the seed,
• 3) Maintain organic matter levels for P release
  and to avoid P tie-up by microorganisms.

Root
Fertilizer
21
Soybean Yields with P fertilizer

• _______________________Yield bu/acre___
• Lbs P fertilizer added Waseca Lamber.
• 0 31 27
• 23 33 29
• 46 35 30
• 69 36 30
• 92 37 32

Ridge Till Soybeans
22
P

• Soil test for P (Bray pHlt7.4 of soil)
• 0-5 ppm very low
• 6-10 ppm LOW
• 11-15 ppm med
• 16-20 ppm high
• gt 21 ppm very high
• No reason to have
  soil test gt 21
• environmental problems
  when P gt16
• ppm x 2 lbs/acre

P deficient tomato
23
Soil P

• Crops need more P than is dissolved in the soil
  solution at any one time, therefore, this P in
  the solution phase must be replenished many times
  during the growing season.
• The ability of a soil to maintain adequate levels
  of phosphorus in the solution phase is the key to
  the plant available P status of the soil. The
  solid phase P is both organic and inorganic

P deficiency reduces root growth
Solid P Phase Solution Phase Root Hair
24
John P. Crumrine
25

26
(No Transcript)
27
Potassium Fertility (Potash)

• Potassium (K) is a problem on
• acid soils,
• soils with low CEC
• soils with irrigation or high rainfall where
  leaching can readily occur.
• Potassium can be stored in the soil from one year
  to the next
• K is not a pollutant - even if leached from soil,
  K does not cause environmental problems.

K deficient corn
28
K

• Different crops have different K requirements
• Soil test
• 0-40 ppm very low
  40 80 ppm low 80 120 ppm medium
  120 160 ppm high
• gt 160 ppm very high
• ( gt 160 no K needed)

K deficient soybeans
29
Potassium
Feldspar Mineral

• Potassium is found in minerals like
  feldspars and
  micas (90 of Soil K)
• K is fixed inside of clay minerals ( 9 of soil
  K)
• K is on the soil exchange sites ( 1)
• K is in the soil solution (0.1)
• Annual K Recommended for 160 bu corn yield goal
• Soil Test CEC
• 10 20
  30
• 50 130 150
  170
• 150 90 110
  130
• 250 50 70
  90
• _______________________________________

30
Ca, Mg

• Calcium and Mg - when soils are low in Ca, Mg,
  they have a pH problem and by adding lime or
  dolomite the pH and Ca, Mg problem is corrected.
  
• On some acid, sandy soils Mg deficiency on corn
  has been noted. 15 lbs as a starter or 75 lbs
  broadcast corrected the problem.

Magnesium deficiency on corn
31
S

• Sulfur - Most soils in Mn would not respond to
  additions of Sulfur because of adequate levels
  and atmospheric deposition.
• However, on sandy soils in NE Minnesota yields
  have increased with 25 lbs/Acre to Alfalfa, Corn
  and Small grains.

32
Sample Fertilizer Problem- For your notes

• Nutrient Analysis - N - P - K N -P2O5 - K2O
• P .44 x P205 K K20 x .83
• If you apply 25 lbs of P205 how much elemental P
  did you apply, 25 x .44 11 lbs P
• Fertilizer Bag 20 - 5 - 10
• 20 N, 5 P20,
  10 K20
• If you apply 50 lbs of fertilizer you put on ?
• .20x50 10 lbs N,
• .05 x 50 2.5 lbs P205 and 1.1 lbs of P,
• .1 x 50 5 lbs K20 and 4.15 lbs K.

33

• If you need 85 lbs of N for Corn how many lbs of
  this fertilizer(20-5-10) do you need?
• 85/.20 425 lbs fertilizer
• How many lbs of elemental K will you apply with
  the 85 lbs of N.
• 425 x .1 42.5 lbs K20 and 42.5 x .8335.275
  lb.K

34
Micronutrients

• Iron - Fe
• Boron - B
• Zinc - Zn
• Copper - Cu
• Molybdenum - Mo
• Chlorine Cl
• Manganese - Mn
• Cobalt Co
• Nickel-

grape leaf symptoms of boron deficiency
right boron toxicity)

• Reasons why use of micronutrients has increased
  in recent years
• Increased knowledge of their role in plant
  nutrition, deficiency symptoms in plants, and
  behavior in soil.
• Higher crop yields which have increased
  micronutrient needs.
• Improved analytical methods, resulting in more
  soil tests and improved fertilizer
  recommendations.
• Improved sources of micronutrient fertilizers and
  methods of incorporation into other fertilizers.
• Land-shaping practices, such as terracing or land
  leveling for irrigation, which remove topsoil
  containing organic matter, often associated with
  most of the available micronutrient supply.
• (Reference The Fertilizer Handbook / The
  Fertilizer Institute - pp 91-92)

35
Role of Micronutrients

• Boron is believed to be involved in carbohydrate
  transport in plants it also assists in metabolic
  regulation .
• Chlorine is necessary for osmosis and ionic
  balance it also plays a role in photosynthesis.
• Zinc participates in chlorophyll formation, and
  also activates many enzymes
• Copper is a component of some enzymes and of
  vitamin A.
• Iron is essential for chlorophyll synthesis,
  which is why an iron deficiency results in
  chlorosis.
• Manganese activates some important enzymes
  involved in chlorophyll formation
• Molybdenum is used by plants to reduce nitrates
  into usable forms
• Cobalt is thought to be an important catalyst in
  nitrogen fixation. It may need to be added to
  some soils before seeding legumes.
• Nickel has only recently been shown to be an
  essential nutrient for plants. Ni-deficient
  conditions, barley plants fail to produce viable
  grain because of a disruption of the normal
  grain-filling and maturation processes.

36
Micronutrients

• Correcting pH problems for most soils will
  correct micronutrient deficiencies
• Most common deficiency is Iron on alkaline soils
  for those plants that like acid conditions.

Fe Deficiency on rhododendron,
Fe deficiency on pin oak
37
Nutrient Management

• Need to manage nutrients
• Plant growth
• Feed the world
• Economic
• Aesthetic
• Environmental
• N in drinking water
• Hypoxia Gulf of Mexico
• Eutrophication of fresh waters

Jubilees (oxygen-deficient waters) occur in
coastal areas around the world, as a result of
excessive nutrients (particularly nitrogen)
flowing from rivers into oceans.
38
Justus von Liebigs Law of Minimum

• Plant production can be no greater than that
  level allowed by the growth factor present in the
  lowest amount relative to the optimum amount for
  that factor

39
Tools for detecting nutrient deficiency

• 1) Tissue testing -involves a complete and
  detailed laboratory analysis of nutrient elements
  in the plant leaves. This is a very accurate way
  of assessing how much nutrient the plant has
  actually taken up from the soil.
• Recommendations are made on the basis of these
  test results
• Backed by research
• Dependent on plant growth stage and plant part.

40
Soil testing

• Collecting a soil sample to determine the current
  nutrient status of the soil.

41
Soil Sampling
42
Sufficiency Method of Nutrient Needs

• Uses soil testing to predict fertilizer needs.
• Based on green house and field research.
• Two phased process
• Correlation
• Calibration
• Soil test is truly a predictive tool.
• Gives soil credit for its nutrient providing
  ability.

43
Correlation

• Process used to determine if
• a soil nutrient, as extracted by a soil test,
• and crop response to added nutrient, are so
  related that one directly implies the other.
• process of selecting the best soil test for the
  soils of the area.

44
Correlation - process

• Exploratory fertilization trial
• Greenhouse a controlled environment with soil
  homogeneity.
• Trials in field with selected soils.

45
Correlation - process

• Cate-Nelson method
• Determine percentage yield values for each
  fertilizer rate trial.
• Determine soil test values for nutrient being
  studied.
• Plot percentage yield vs soil test value.

46
Soil test categories
47
Improving soil fertility the 'green' way

• Importance of expanding the use of agricultural
  production methods that are both agronomically
  and economically
  sustainable.

Legume intercropped with maize in Wenchi, Ghana,
Africa
48
What is the earth showing us?
The End