Nutrient Management and Soil Fertility Flashcards
(39 cards)
1
Q
Practical Nutrient Management
Goals
A
- Cost effective production of high-quality plants
- Efficient use and conservation of nutrient resources
- Maintenance or enhancement of soil quality
- Protection of the environment beyond the soil
2
Q
- Cost effective production of high-quality plants
A
Increasing plant yield, health or appearance is the primary objective of nutrient management for farmers, landscapers, gardeners, or foresters
3
Q
- Efficient use and conservation of nutrient resources
A
Requires renewal or reuse of the resource and nutrient budgeting that reflects a balance between system inputs and outputs.
4
Q
- Maintenance or enhancement of soil quality
A
Loss of nutrients from soil can lead to decreased plant production, and soil degradation resulting from loss of organic matter and erosion.
5
Q
- Protection of the environment beyond the soil
A
Protection of the environment beyond the soil
Excessive nutrient levels in soils most directly impacts water quality, particularly transport of N and P from soil to water.
6
Q
Nutrient Management and Environmental Quality
A
- Most direct environmental impact of nutrients in soil is on water quality
- Principal nutrients that impact water quality are N and P
- Marine and estuarine systems are usually N limited
- Freshwater systems are usually P limited
- Additions of the limiting nutrient causes excessive growth of aquatic plants (seaweed, algae, phytoplankton)
- P at concentrations ≥0.025 mg/L can cause problems
- N as NH3 (ammonia gas) dissolved in water can be directly toxic to fish at 2 mg/L. Drinking water standard for nitrate is 10 mg N/L
- Total loading of water bodies with these nutrients is also an important factor in water quality impacts
7
Q
Nutrient Management Plans
A
- Attempts to balance inputs (fertilizers) and desirable outputs (harvested crops) of nutrients within a production system
- Goals are to:
- Prevent accumulation of nutrients in soils
- Limit nutrient losses (runoff and leaching) to ecologically acceptable levels
- Usually focus on N and P; the two nutrients most likely to cause ecological damage to aquatic systems
- May be voluntary or required by State or Federal statute
- In PA required for “concentrated animal operations (CAO)
- Any farm with >2 AEU per acre of land on which manure can be spread
- Farms with <8 AEU are exempt
- An AEU (animal equivalent unit) is 1,000 lbs of animal live weight
8
Q
Best Management Practices to limit nutrient losses
A
- Buffer strips and riparian zones
- Cover crops
- Conservation tillage
- Forest stand management
9
Q
Nutrient Resources
A
The pool of available nutrients in soil is resupplied from internal and external resources
10
Q
Internal resources
A
- Come from within the ecosystem (e.g. forest, watershed, farm, or suburban home)
- Mineral weathering
- Biological nitrogen fixation
- Atmospheric deposition (comes from outside the ecosystem, but at no energy or economic cost)
- Internal recycling of materials such as animal manures, crop residues, green manures
11
Q
External resources
A
- Are needed when internal resources are inadequate to achieve desired plant production. These are normally purchased nutrients transported to the soil.
- Inorganic fertilizers
- Organic fertilizers (manure, compost, biosolids, food processing residuals, etc)
12
Q
Nutrients from weathering of parent materials
A
- P, K, Ca, and Mg as well as many micronutrients can be supplied from weathering of soil minerals.
- Soil minerals supply negligible amounts of N.
- In natural systems and low productivity systems such weathering may be adequate to supply plant needs together with internal recycling of plant residues.
13
Q
Nutrients from weathering of parent materials
A
- In intensive crop production systems with significant harvest removal, weathering will be inadequate to supply plant needs. Without external inputs reserves of these minerals will be depleted or “mined”.
- Amounts of selected nutrients released by mineral weathering from soil in a humid temperate climate compared with the amounts removed by forest and agricultural harvests.
14
Q
Nutrients from weathering of parent materials
A
P K Ca Mg Amount released or removed (kg/ha)
Weathered from igneous parent material in 50 years
5-25 250-1000 150-1500 50-500
Harvest removal from 50 yr old deciduous bole wood
10-20 60-150 175-250 25-100
Removed by 50 annual harvests of a corn-wheat-soy crop rotation
1200 2000 550 500
15
Q
Recycling Nutrients from Animal Manures
A
- Animals excrete large amounts of the nutrients they consume; on average about 0.75 of the N, 0.8 of the P, and 0.9 of the K.
- There is large variability in manure nutrient content depending on
- Species of animal
- Diet of animal
- Manure moisture content
- Manure handling and processing system
16
Q
Recycling Nutrients from Animal Manures
A
- Manure needs to be analyzed by a laboratory to know the actual nutrient content.
- The balance of nutrients in manures does not match the nutrient balance needed by crops.
- The ratio of P:N in manure is larger than in plant tissue.
- If manures are applied at rates to provide crops with the N they need, the amount of P applied will exceed that needed by the crop.
- With repeated applications soil P levels gradually build up which also increases the likelihood of soil P transport to water systems
17
Q
Practical Utilization of Organic Nutrient Sources
A
- Application rates are usually based on supplying needed N for plant production.
- Most N in organic sources is organic N and thus not available to plants until it has been mineralized. The rate of net mineralization depends on soil environmental factors (moisture, temperature, aeration) as well as characteristics of the organic material added (C:N ratio and types of organic compounds in the material).
- Manures and fresh green plant material tend to mineralize more rapidly than partially stabilized materials such as compost or digested sewage sludge or highly lignified high C:N ratio material such as straw or sawdust.
- Small amounts of N in organic sources are present as NH4+ and NO3- which is immediately available to plants.
18
Q
Practical Utilization of Organic Nutrient Sources
A
- Organic materials will continue to mineralize N for several years following application. This supply of N should be considered for at least 2 years beyond the year of application.
- Expected N mineralization rates from various organic nutrient sources in humid temperate region climate and medium textured soil. Value is the percentage of remaining organic N that will be mineralized.
19
Q
Practical Utilization of Organic Nutrient Sources
A
Organic N mineralization (%) Source 1st yr 2nd yr 3rd yr Poultry floor litter 50 15 8 Dairy manure (fresh solid) 35 18 9 Swine manure (lagoon liquid) 50 15 8 Anaerobically digested sewage sludge 20 8 4 Compost, mature and well stabilized 10 5 3
20
Q
Recycling Nutrients from Animal Manures
A
Manure needs to be analyzed by a laboratory to know the actual nutrient content.
Animal type Units N P2O5 K2O
Dairy lb/ton 10 4 8
Beef lb/ton 11 7 10
Swine lb/1000 gal 40 35 15
Poultry (layer) lb/ton 37 55 31
21
Q
Recycling Nutrients from Animal Manures
A
- The balance of nutrients in manures does not match the nutrient balance needed by crops.
- The ratio of P:N in manure is larger than in plant tissue.
- If manures are applied at rates to provide crops with the N they need, the amount of P applied will exceed that needed by the crop.
- With repeated applications soil P levels gradually build up which also increases the likelihood of soil P transport to water systems.
22
Q
Inorganic Commercial Fertilizers
A
- P and K fertilizers are primarily obtained by mining geologic deposits.
- Salt beds are the primary source of K fertilizer
- Apatite rock deposits are the primary source of P. Because apatite is extremely insoluble it must be treated with acid to produce a readily soluble P fertilizer.
- N2 gas in the atmosphere is the primary source of N fertilizer
- In an energy intensive process at high temperature and pressure N2 fixed by reaction with hydrogen from natural gas to produce NH3 (the Haber-Bosch process, 1913)
- NH3 can be used directly as fertilizer (anhydrous ammonia) or can be further processed into other N fertilizers such as urea [CO(NH2)2], or ammonium nitrate (NH4NO3).
23
Q
Inorganic Commercial Fertilizers
A
- Many fertilizers contain more than one nutrient element either by blending carriers or by forming molecules with more than one nutrient such as ammonium phosphate (NH4H2PO4) or potassium nitrate (KNO3).
- Inorganic fertilizers can be precisely formulated to contain known quantities of macro and micronutrients. Manufacturers are required to label and guarantee the nutrient content of fertilizers.
24
Q
Composition of Inorganic Fertilizers
A
- Nutrients in fertilizers can be supplied by many different carriers or chemical compounds. These compounds have different characteristics that, along with cost, should be considered in deciding which material to use.
- Salt Hazard Fertilizer compounds that are very soluble salts are readily available to plants, but can cause salt injury to plants (especially germinating seeds and young seedlings). Such compounds include: ammonium nitrate, sodium nitrate, potassium nitrate, and potassium chloride.
- Acid forming potential Compounds containing ammonium or elemental sulfur generate acidity when they are oxidized.
- Volatilization Anhydrous ammonia (a gas) and urea (converted to ammonia) can be lost from soil by volatilization.
25
Forms of Fertilizer
- Commercial fertilizers are available as
- Dry, flowable materials (pellets or prills)
- Liquid solutions or suspensions
- Pressurized (liquified) gas (anhydrous ammonia)
-Most fertilizers today are sold in bulk form. In the USA about 50% of sales are bulk solids, 40% liquids, and 10% bagged.
26
Fertilizer Grade
- The percentage of nutrients in fertilizer are reported in the order N-P-K as
- Total N
- Available P2O5
- Soluble K2O
- Thus the fertilizer on the upper right contains
- 15% total N
- 0% available P2O5
- 15% soluble K2O
- The fertilizer on the lower right contains
- 24% total N
- 6% available P2O5
- 12% soluble K2O
27
Fertilizer Grade
- Fertilizer recommendations and soil test results are often reported as elemental P and K, but fertilizer grade is always given on the oxide basis.
- To convert between oxide and elemental values
- Multiply P by 2.29 to convert to P2O5
- Multiply P2O5 by 0.437 to convert to P
- Multiply K by 1.2 to convert to K2O
- Multiply K2O by 0.83 to convert to K
- How much elemental P or K is in the bag if it is a 25 lb bag?
- P = 25 x 0.06 x 0.437 = 0.66 lb
- K = 25 x 0.12 x 0.83 = 2.49 lb
28
Concept of Limiting Factor
Justus von Liebig, a German chemist developed the concept that plant growth can be no greater than that allowed by the nutrient present in the lowest amount relative to plant needs.
29
Fertilizer Interaction
- The concept of the law of the minimum is often observed in crop fertilizer responses.
- In the figure at right, when increasing amounts of N fertilizer were added, crop response was small
- When a constant amount of P fertilizer was added, the crop growth response to increasing amounts of N fertilizer was much greater
30
How much fertilizer to apply
- Fertilizer application rates should always be based on reasonable crop yield goals and soil testing.
- N fertilizer recommendations are based on expected crop yield for a given region and soil type. Such information can be obtained from Cooperative Extension services.
- P, K, Ca, and Mg should be based on soil testing and recommendations for the crop being grown.
- Application of fertilizer in excess of recommended rates will be a waste of time and money, could adversely affect crop yields, and could increase the likelihood of nutrients being transported from soil to surface or ground water.
31
Fertilizer Application Methods
- Broadcasting
| - Localized Placement
32
Broadcasting
| Fertilizer Application Methods
Fertilizer is uniformly spread over the entire soil surface which may be followed by incorporation into the soil.
-Most economical means for application of large volumes of fertilizer over large areas of soil
- Appropriate when the goal is to increase soil fertility levels over a long period of time.
- Appropriate for close growing vegetation (pastures, hay crops, range land, turf grass, forests)
- Decreased fertilizer use efficiency for nutrients that are strongly bound to the soil (P, Mn, Zn)
33
Localized Placement
| Fertilizer Application Methods
- Plants can easily obtain their entire nutrient need from a concentrated localized source in contact with only a small fraction of the rooting volume.
- Localized placement concentrates nutrients in a small volume of soil and minimized the amount of fertilizer that might be fixed by the soil in unavailable forms.
- Localized placement increases the concentration of nutrients in the soil solution at the root surface and greatly enhances uptake by roots.
- Localized placement is especially effective for starter fertilizer applications made when soils are cool in the spring and for plants that grow rapidly with a big demand for nutrients early in the growing season.
- Localized placement can be accomplished by placing fertilizer in bands (can also be done with liquid fertilizers, manure slurries, and sewage sludge).
- For starter fertilizers it is important that the band not be placed with the seed since salts and acids could injure the plant. Best results are usually obtained with placement 5 cm below and 5 cm to the side of the seed.
34
Diagnostic Tools for Soil Fertility Assessment
- Systematically record field observations and history
- Date, location in the field, weather conditions, symptom observed
- Include information from land owner or manager; first occurrence of the problem, management history
- Map of symptom distribution
- Look at spatial distribution of problem, is there a pattern or correlation with other soil factors?
- Carefully examine individual plants, plant leaves and roots for deficiency symptoms, and other possible problems such as insect or herbicide damage; flooding, aeration, or drought damage
- Measure differences in plant growth and yield
35
Plant tissue analysis
- Plant tissues are collected and analyzed for total concentrations of specific plant nutrients
- Critical points of plant tissue analysis and interpretation
- The correct plant part be sampled (leaf, stalk or stem, fruit or grain)
- The correct growth stage be sampled
- Recognize that concentration of one nutrient may be affected by another
- Recognize that poor plant growth due to factors not related to plant nutrition can affect plant tissue concentrations of nutrients
36
Soil testing
- Relies on chemical extraction methods that will accurately mimic plant nutrient availability over a growing season
- Three important phases of the soil testing process
1. Obtaining a representative sample of the soil
2. Chemically analyzing the sample
3. Interpreting the analytical results to make soil fertility management recommendations
37
Sampling
- Separate fields or area of concern into smaller sampling areas based on
- Observable differences in soil characteristics
- Observable differences in plant growth performance
- Known differences in management history
- Obtain several soil cores from within the sampling area and combine and mix to obtain a single composite sample.
- Normally combine 15 – 20 cores to make one composite sample
- Sampling area should normally not be larger than about 10 ha
- Sampling depth depends on soil management practices and type of analysis to be performed on the sample
- Time of year to sample. Good practice is to sample every year or two at the same time of year.
38
Soil analysis
Chemical extractants are designed to dissolve from soils the portion of a nutrient that corresponds to the fraction that will become plant available during the course of a growing season
39
Soil analysis
- Soil tests (extractants) designed for use in one region may not be reliable or useful in another region with different soils and climate
- Soil tests (extractants) results need to be correlated with field experiments in order to make a meaningful recommendation
- Soil test results are indicators of nutrient availability, they are not quantitative measures of nutrients present.
- Field experiments relate crop yield to a wide range of soil test levels and to changes in soil test level achieved by various levels of fertilizer additions
- This is done on a range of soil types in a given region
