Nutrient Management Flashcards
1
Q
Function of Nitrogen
A
Used in synthesis of amino acids, proteins enzymes
Found in chlorophyll (photosynthesis)
ADP, ATP (energy transfer)
2
Q
Function of Phosphorus
A
Important component of energy transfer system (ADP, ATP)
Important to photosynthesis and respiration
Part of cell nuclear material important to cell division
3
Q
Function of Potassium
A
Accelerated growth of meristematic tissue
Regulation of stomata open ring (water loss)
Involved in N and carb metabolism
Catalyze some enzymes
4
Q
Function of Sulfur
A
A component of several amino acids (cystine,cysteine, methionine) which are part of many proteins
Involved in protein synthesis and enzyme activation
Forms flavor compounds in mustard, garlic, and onions
5
Q
How does nutrient need change as plant growth progresses from germination to maturity
A
Plant nutrient demands gradually increase during the seedling stage, rapidly increases during vegetative growth, and decreases again as reproductive growth dominates
6
Q
What is the role of soil solution in supplying nutrients from the soil
A
Plant nutrients dissolved in the soil solution and are made available for plant absorption through the processes of mass flow, diffusion, and roof interception
7
Q
What is the role of cation exchange sites in supplying nutrients from the soil
A
Cation exchange sites located on clay particles and organic matter hold cations and can be released into the soil solution to be readily available to plants
8
Q
What is the role of organic matter in supplying nutrients from the soil
A
Can be a source of nutrients (N, P, K) when decomposed
Holds onto cations by cation exchange and chelation
9
Q
What is the role of soil minerals in supplying nutrients from the soil
A
Dissolved soil minerals can release nutrients into the soil solution
Clays, carbonates, and hydroxides can also retain nutrients by adsorption on their surfaces
10
Q
What is the role of plant residue in supplying plant nutrients from the soil
A
Plant residue contains the essential elements that are returned to the soil system as the plant residue decomposes and rainfall leaches soluble nutrients from the plant residue
11
Q
Describe nutrient mineralization
A
The release of a nutrient when an organic material (SOM, manure, biosolids) is decomposed by soil microorganisms
It is the conversion of a nutrient from organic to inorganic form
12
Q
Describe immobilization
A
When a nutrient is converted from an inorganic to organic form
During decomposition, the nutrient is incorporated into microbial cells and SOM
13
Q
Describe uptake antagonism between ions
A
Two or more ions may compete for plant uptake by various mechanisms
One ion is said to be more antagonistic with regard to the uptake of another ion
14
Q
Describe mass flow
A
Occurs when a nutrient moves to a plant root with the water that is being absorbed by the plant
Important uptake process for N, Ca, Mg
15
Q
Describe Diffusion
A
The movement of a nutrient to a plant root due to a concentration gradient between the soil solution and the root surface. The nutrient concentration is higher in the soil solution than at the root surface so the nutrient moves to the root surface
Important nutrient uptake process go P, K
16
Q
Describe root interception
A
Occurs when a root grows next to a clay or OM surface and absorbs the nutrients.
Usually means the root has grown near a soil colloid and absorbed the nutrients on or near the colloid surface
Usually a minor way nutrients are absorbed
17
Q
How does soil nutrient uptake occur at the root surface
A
Passive (nutrient enters root with water that is being absorbed)
Active processes where the nutrient is moved into the by a molecule or ion termed a carrier
18
Q
Define Cation exchange capacity
A
The amount of positively charged cations that can be held by a given weight of soil
Units are color+charge/kg of soil (equivalent to meq/100 g soil)
19
Q
How does CEC influence nutrient mobility of cations and anions
A
As CEC increases , the mobility of cations decreases as they are held on the cation exchange sites.
Leaching of soluble anions (nitrate, chloride, sulfate) increases as CEC increases.
20
Q
What influences CEC
A
Increases in Clay mineral type (1:1 vs 2:1 clays), organic matter and soil pH generally increase CEC
21
Q
What cations are retained on cation exchange sites
A
Calcium, Magnesium, and Potassium.
Can become immobile.
I’d routine additions of a cation occur, the added cation can change places with Ca, Mg, or K on the CEC releasing them into the soil solution.
22
Q
What forms of Nitrogen are mobile and immobile in the soil
A
Nitrate (NO3-) is mobile
Ammonium (NH4+) is immobile
23
Q
Explain when phosphate is mobile/ immobile in the soil
A
Phosphate is immobile in soil except where P sprouting capacity has been exceeded
24
Q
Is sulfate mobile or immobile in the soi?
A
Immobile
25
When are cations mobile/immobile in the soil?
When on exchange sites, Ca, Mg, and K are immobile.
When cations are in the soil solution they are mobile
26
Describe how texture affects nutrient uptake
The more clay in a soil, the more likely there will be available nutrients.
Leaching of nutrients increases as souls become more sandy because sandy soils have larger pores allowing fewer water movement and have a small cation and anion exchange capacity
27
Describe how structure affects nutrient uptake
Soil structures that create large pores will increase the potential for nutrient losses through leaching
Lack of structure can lead to increases in runoff and erosion
28
Describe how drainage/aeration affect nutrient uptake
If drainage is poor, anaerobic conditions may occur, causing increased solubility in Iron and Manganese and the loss of nitrate by denitrification
Nutrient losses are associated with excessive drainage
29
Describe how moisture affects nutrient uptake
Adequate soil moisture is important for nutrients that move to roots by diffusion (P)
Adequate moisture favors decomposition of and release of N,P, and S from the material undergoing decomp.
As soil moisture decreases, insoluble compounds containing nutrients often form.
30
Describe how soil pH affects nutrient uptake
Soil pH affects the availability of most nutrients due to physical (leaching/volatilization), chemical (adsorption/desorption/precipitation), and biological processes (mineralization/immobilization) that change with pH
Extremes in soil pH can alter absorption of nutrients by roots by changing root metabolism
31
Describe how temperature affects nutrient uptake
The influence of temperature can be through plant metabolism where a min/optimum/max temperature for nutrient uptake exists and can change with plant growth and development
Temperature can also affect the rate of decomposition of organic material
32
Describe how ammonium fixation by clay affects the fate of N in soil
Some 2:1 clay minerals that contain negative charge in the tetrahedral layer near the surface of the clay can fix the ammonium ion rendering it unavailable for plant uptake
Slow release of this ammonium ion occurs over long Time periods
33
Describe how ammonification affect the fate of N in soil
Ammonification converts organic N to ammonium by microorganisms as they decompose OM and release ammonium into the soil
34
Describe the process of nitrification
Ammonium is oxidized to nitrite (NO2-) by microorganisms. Requires water, hydrogen ions, and energy for microorganisms
Nitrite is oxidized to nitrate by soil microorganisms. Requires oxygen and produces energy for microorganisms.
35
What affects the rate of ntrification
Soil temp (below 50degF), soil pH below 5 and above 8, and low soil moisture decreases nitrification
36
What is Volatilization?
The conversion of ammonium to ammonia gas.
37
What conditions favor volatilization?
High temp (ammonia is less soluble in water)
High soil pH (more ammonium concerted to ammonia)
Low soil CEC (less ammonium adsorbed by soil colloids)
Moist/wet soil (favors formation of ammonia)
Windy weather (increases ammonia gradient from soil to atmosphere)
Large amounts of surface residue (prevents ammonium adsorption)
38
When does denitrification occur
When soils are waterlogged /flooded
Soil microorganisms will use nitrate for metabolism when oxygen is depleted from the soil
39
What are the products of denitrification
Gaseous dinitrogen (N2) and gaseous oxides of nitrogen that move to the atmosphere
40
What conditions favor denitrification?
Nitrate present
Oxygen absent
Organic compounds are available as an energy source
Near Neutral pH
Warm soil temp
41
When does immobilization occur?
When Nitrogen poor (C:N ration >20) organic materials such as wheat area/sawdust are applied to soil and soil microorganisms remove large amounts of inorganic N from the soil during decomposition
42
How does immobilization affect the mobility of Soil N
It immobilizes N until it can be mineralized when the microbial cells decompose
43
Describe how leaching affects the fate of N in soil
Leaching of nitrate is a major loss mechanism that is most likely to occur when soil nitrate levels are high and/or water movement through the soil is rapid
44
What is symbiotic fixation
A mutually beneficial process where a legume supplies energy to a microorganism (Rhizobium sp.) that uses that energy and the enzyme, nitrogenase, to convert N2 in the atmosphere to ammonium for the legume in the legume nodule.
45
What can cause a reduction in rhizobia
Acidic soils
Soils low in fertility
Soils with poor physical condition
Where the legume has not been grown for a number of years
46
How does plant uptake affect the fate of soil N?
Plant uptake removes both ammonium and nitrate from the soil. Loss from the soil system is temporary except for the nitrogen contained in the harvested portion of the crop. Nitrogen in the part of the crop that is returned to the soil enters the soil system as decomposition proceeds
47
How does pH affect symbiotic nitrogen fixation
N fixation declines as soils become more acidic (little N fixation occurs below 5)
48
How does moisture affect symbiotic N fixation?
N fixation declines as soil moisture decreases and then abruptly stops at low soil water content
49
How does the available N level affect symbiotic N fixation?
As soil N from other sources increase, N fixation decreases
50
How does the presence of correct rhizobium species affect symbiotic N fixation
The correct rhizobium species is needed for a legume to be infected and fix atmospheric N2
51
How does the availability of phosphorus, Sulfur, molybdenum, and cobalt affect symbiotic N fixation?
P is needed to provide energy for symbiotic N fixation
S is important for protein synthesis
Molybdenum is part of the nitrogenase enzyme
Cobalt is a Co factor in an enzyme needed for N fixation and nodule growth
(N fixation is reduced If any of these nutrients is limiting)
52
How does fixation affect the fate of Soil P?
P fixation reduces soil solution P concentration, plant available P, and P mobility
53
What is P fixation?
A combination of P sorption by soil minerals (Fe/Al oxides and kaolinite clay)
P precipitation as calcium phosphates at high pH
Fe/Al phosphates at low pH
54
How does pH affect the fate of soil P?
Plant available P is generally highest over a pH range of 5.5-7
At a pH below or above, P in the soil solution is reduced due to increased fixation
55
How does mineralization affect the fate of soil P?
When soil OM is decomposed/mineralized by soil microbes, inorganic P is released to the soil
A portion is typically fixed
56
How does soil erosion affect the fate of Soil P?
When runoff leads to soil erosion, both fixed and soluble P are transported to surface waters
57
How does soluble P transport affect the fate of soil P?
When fertilizers, manures, or other materials containing soluble P are applied to soil, run of can transport that soluble P to surface waters
58
How does the method of previous nutrient applications affect soil sampling methods
The method of application (broadcast, banded, injected, side-dress) and degree of subsequent mixing with the soil during incorporation (tillage, land leveling) will impact the uniformity of a nutrient spatially and with soil depth
59
How does nutrient stratification affect soil sampling methods
Soil should be sampled at a uniform depth, depending on what nutrients are being looked at (is subsoil needed) and what is recommended by the soil lab
60
How does within-field soil and crop variability affect soil sampling methods
Uniform field samples can be done with 25-30 cores per field and thoroughly mixed. In non-uniform fields, fields can be gridded and 8-10 samples taken for a composite in an area of about 3 ft from grid point. Soil test values are then plotted over the field to identify areas in need of fertilization
61
How does the nutrients to be analyzed affect soil sampling methods
Depth of soil sampling can vary depending on nutrients tested
A soil core 1-2 ft can be used to measure residual nitrate in certain cropping systems
One inch core can be used to measure soil P that may move to surface water in runoff
Routine soil tests use a 4-6 in depth
62
How does predictive vs diagnostic soil sampling after the soil sampling method
Predictive soil sampling is used in routine soil test procedures and whole field or grid samples are taken. The results are used to make fertilizer and lime recommendations.
Diagnostics soil samples are used to characterize and improve problem soils. Soil samples are taken from areas in a field where crop growth is poor and where crop growth is good. Soil test data are compared to determine differences between the poor and good crop growth areas
63
How does root zone depth affect the soil sampling method?
Many plant root stems extend feet into the soil, but often most roots are found in the first 4-6 in. This is the depth routine soil samples are taken unless there is a good reason to sample deeper.
64
Differentiate grid, zone, and whole field soil sampling approaches
Whole field- a composite soil sample is collected for the entire field and an average soil test value is used to make recommendations
Grid- a uniform grid is used over the entire field and samples collected at each point on the grid. Accounts for spatial differences due to soil and past management which is then used to make recommendations
Zone- recognizes parts of the field that have been managed similarly and samples collected from each zone. Recommendations are then made for each zone
65
Describe how to use plant tissue analysis for problem solving/ diagnosis, nutrient program monitoring, and in season nutrient management
Plant tissue analysis is used to determine if a plant contains sufficient, deficient, or toxic amounts of a nutrient/element. Diagnosis may result in a recommendation to improve current crop or changes that should be made for future crops.
Analysis can be used to follow concentration of nutrients throughout growing season to determine if sufficient amounts were present over the entire season.
Can also be used to fine tune fertilizer recommendations
66
What is the formula to convert fertilizer analysis from elemental to oxide form?
N stays the same
```
%P2O5= 2.3*%P
%K2O= 1.2*%K
```
67
What is the formula to convert fertilizer analysis from oxide to elemental form?
N stays the same
%P= 0.44*%P2O5
%K= 0.83*%K2O
68
What is the procedure for taking a fertilizer recommendation and calculating the fertilizer/manure application rate
1) concert soil test value to oxide basis
(Either % it lbs/acre)
2) Compute fertilizer needed by dividing lb/ac by the lb of nutrient in 100 lb fertilizer
69
What needs to be taken into consideration for manures when calculating application rate?
Percentage of nutrient available during the cropping season
Conversion into a wet basis
70
Describe various nutrient placement methods
Injection- application of liquid or gaseous fertilizer in a zone beneath the soil surface
Surface broadcast- fertilizer is uniformly applied to the soil surface
Broadcast incorporated fertilization- plowing/dishing the soil after broadcasting to incorporate fertilizer
Band (starter)- fertilizer is placed slightly below or to the side of the seed, below the seed, or between rows.
Fertigation- the application of dissolved or suspended fertilizer by injection into an irrigation system
Foliar- small amounts of fertilizer applied in liquid form to a growing crop
Side-dress- fertilizer applied on or below the soil surface for a growing crop (usually a row crop)
Top-dress- fertilizer is broadcasted onto a growing crop (small grains/forages)
Seed placed- fertilizer is applied to the seed prior to planting
71
Describe the relationship between soil pH and the hydrogen ion activity in water
As soil pH decreases, Hydrogen increases, causing the soil to become more acidic
As soil pH increases, Hydrogen decreases, causing soil to become more basic or alkaline
The concentration of hydroxyl ions (OH-) increases when the concentration of Hydrogen ions decrease
72
Define buffer pH
A buffer is a solution that contains weak acids, bases, and salts that cause that solution to resist a change in pH
73
What types of acidity contribute
| To total soil acidity
Salt replaceable acidity- acidity that can be removed by an unbuffered salt solution
Residual acidity- acidity that reacts with a buffer
Lime needs are largely based on residual acidity because of its larger prevalence in the soil than salt replaceable acidity.
74
Describe the long-term change in soil pH from applying nitrate vs ammonium fertilizer
Soil pH will decrease if a process or practice adds hydrogen ions to a soil, with decreases being more pronounced in poorly buffered soils. Use of ammoniacal fertilizer produces hydrogen ions during first step of nitrification.
Soil pH will increase if a process/practice adds bases or basic cations to soil. Since nitrate fertilizers contain basic cations (Ca, K) Thur continues use can increase pH. Increase will be more pronounced in poorly buffered soils.
75
What determines buffer pH
Amount and type of clay minerals, OM content.
Soil texture can be good indicator of buffer pH (clay texture- higher buffer pH, sandy texture-lower buffer pH)
76
How does soil pH affect nutrient availability?
Soil pH affects nutrient availability by changing the form of the nutrient in soil.
Soil pH that favors formation of insoluble compounds or incorporation of nutrients into organic matter reduces availability
Soil pH that favors high nutrient solubility can decrease availability of rainfall is sufficient to leach nutrients from the root zone
77
Reason for decreases availability of ammonium and nitrate ions at low and high pH
Rescued OM decamp for both
78
Reason for decreases availability of phosphate ions at low and high pH
Low pH- insoluble iron and aluminum phosphates form
High pH- insoluble calcium phosphates form
79
Reason for decreases availability of potassium ions at low and high pH
Low pH-Cation exchange with Al3+, H+, and leaching
High pH- cation exchange with Ca2+, Mg 2+, and leaching
80
Reason for decreases availability of calcium ions at low and high pH
Low pH- cation exchange with Al3+, H+, and leaching
81
What plant available forms of nutrients leach from the soil at normal pH?
Nitrate
sulfate
boric acid/borate ion
chloride ion
Ferrous (Fe2+)
Manganous ion (Mn2+)
Molybdate ion(MoO4^2-)
82
Reason for decreases availability of copper ions at low and high pH
High pH- insoluble compounds form
83
Reason for decreases availability of primarily ferrous ion (Fe2+) ions at low and high pH
High pH- insoluble compounds form
84
Reason for decreases availability of manganous ions at low and high pH
Insoluble compounds form
85
Reason for decreases availability of molybdate ions at low and high pH
Insoluble compounds form
86
Reason for decreases availability of zinc ions at low and high pH
Insoluble compounds form
87
What is the effective calcium carbonate equivalence?
A measure of the effectiveness of a given lime material
=effectiveness*CCE
The greater the ECCE of a liming material, the greater the acid neutralizing ability per ton of material
88
What is the effectiveness of liming material
The fineness of a lining material
89
What is the Calcium Carbonate Equivalence of a liming material?
A measure of the chemical purity of a liming material
Also the neutralizing power off liming material— the acid neutralizing ability by Wright compared to pure calcium carbonate
90
How does fineness affect liming and how is it measure?
Affects the rate at which the liming material will react with soil acidity
Finer particles rest quicker, courser particles may react over a long period of time. If lime particles are too course, they may not react with soil sufficiently to increase pH.
Fineness is measured by mesh size of a screen. The larger the mesh number, the finer the particle size of the lime
91
What is the formula for calculating ECCE?
(%CCE/100)*1/2(%passing 10 mesh+ % passing 50 mesh)
92
What factors impact calculating lime application rates to meet liming requirement
Effectiveness of liming material as compared to a typical lime source
Crop being grown (determines target pH)
How much the pH of a soil will change for a given addition of lime
93
How do you determine how much the pH of a soil will change for a given addition of lime?
A test of soil pH and previous knowledge of the amount of lime needed to increase soil pH a given amount (slope of buffer curve) or the amount of lime needed to increase percent base saturation to an acceptable level (slope of base saturation vs pH curve)
Test of soil pH in water plus soil pH in a buffer solution (pH in buffer is a measure of the slope of the buffer curve)
A test of soil pH and some other soil property related to the slope of the buffer curve (exchangeable Ca or measure of soil CEC occupied by base forming cations)
94
How does calcitic and dolomitic lime affect soil pH
It increase soil pH
95
How does elemental S affect soil pH
Decreases soil pH due to its oxidation to sulfuric acid by soil microorganisms
96
How does alum (Al2(SO4)3*2H2O) affect soil pH
It dissolves in water, forming insoluble aluminum hydroxide and sulfuric acid, and decreases soil pH
97
How does ammonium in ammonium sulfate affect soil pH
Decrease soil pH
It’s oxidized by soil microorganisms releasing hydrogen ions
98
How does Gypsum (CaSO4*2H2O) affect soil pH
Does not directly affect soil pH unless Ca ions replace H or Al on soil cation exchange complex and the H or Al is leached, in which case soil pH increases.
99
How does Potassium nitrate affect soil pH
It can increase pH much like gypsum
100
How does ammonium nitrate affect soil pH
Acidifies soil much like ammonium sulfate
101
What are the 5 steps to adaptive management
Current nutrient inputs, crop yield and quality, and profits are quantified
A change in nutrient management that has potential to improve profits while protecting the environment is identified
A change in nutrient management is implemented
The results of the change (profits, inputs, yield, and quality) are assessed
Nutrient management is adjusted based on that assessment
102
How does crop rotation impact crop nutrient needs?
Fertilizer of one crop may also provide sufficient fertilizer for other crops in rotation
The portion of a crop returned to the soil can increase/decrease the need for a nutrient by a succeeding crop
103
Describe factors involved in P loss assessment at field scale
P source, P transport, rainfall, and best management practices
Special factors include soil test P, P fertilization method, rate, and timing, distance to surface waters, rainfall, runoff, and erosion, and crop harvest
104
Describe factors involved in N loss assessment at field scale
Crop harvest, ammonia volatilization, leaching nitrate to groundwater or loss via tile drains, and dentrification
Other factors include runoff of nitrate to surface water and erosion of soil OM; distance to surface water ; N fertilization method, rate, and timing; rainfall, runoff, and erosion
Each factor is quantified during assessment
105
Describe when to use N-based or P-based recommendations for manure/biosolids application
1) a P-index is determined for a given field (integrates factors involved in P losses) and the amount of manure/biosolid that can be applied is a function of that P-index value. If value is low enough, manure/biosolid application rates cab be N-based
If applications are based on crop P needs, then much smaller amounts are applied and supplemental N fertilization must be added for adequate crop growth unless the crop grown is a legume
Timing of application should be taken into consideration because much more P is contributed to runoff when recently applied rather than applied earlier. (Don’t want to apply during high rain seasons)
