BASIC CONCEPTS IN SOIL FERTILITY INSTITUTE OF FOOD AND AGRICULTURE FEBRUARY 18, 2015 Sosten Lungu, Ph.D Vermont Technical College

Outline  The Importance of Soil  Soil Physical Properties  Soil Organic Matter  Soil Reaction  N, P and K  Soil Sampling and Testing  Fertilizer/Manure Recommendations

Soil – Life Supporting Layer - Temperature - Gases - Water - Nutrients - Plant Growth

Air 25% Mineral Matter 45% Water 25% Organic Matter 5% SOIL  Definition: Mixture of mineral matter, organic matter, water, and air.  Example:

Physical Properties  Soil texture - Proportion of three sizes of soil particles -

Soil Texture  Texture alone will provide information about: 1) Water flow potential (infiltration and Percolation) 2) Water holding capacity, 3) Fertility potential, 4) Aeration 5) Drainage rate 6) Soil organic matter 7) Warm-up in spring

Soil Texture  Texture alone will provide information about: 8 ) Compaction 9) Resistance to pH change 10) Decomposition of organic matter 11) Suitability for tillage after rain

USDA Textural Triangle

Soil Structure  Arrangement of sand, silt, clay and organic particles  The particles are aggregated to form structural units called PEDS or AGGREGATES

Structure

Why is Soil Structure Important? - Air movement - Water movement - Microbial activities/reproduction - OM accumulation/breakdown - Root development - Leaching of nutrients - Soil erosion

Soil Management  Affects soil structure: - Timber harvest - Grazing - Machinery traffic - Manure application - Erosion - Irrigation

Soil Structure

Degree of Water Movement Structure Water Movement

Penetrometers  Measuring Compaction OIL/photos/May0505a-lr.jpg

Soil Color  Indicator of certain physical and chemical characteristics  Due to humus  Or iron compounds  Anaerobic conditions

Nutrient Pools Soil Organic matter

Soil Organic Matter  Improves soil structure & water holding  Provides CEC  Source of essential plant nutrients - 90 – 98% N and S - 30 – 50% P - Micronutrients

Organic Matter

Stable OM - Complex organic compounds (Humic & Falvic acids, humin - Deposited centuries ago Functions Water sorption CEC Glue Active OM - Less complex non humic substances - Deposited 1-2 years ago Functions Source of energy for MO Aggregation Source of mineralized N, P & S

Fresh Residues  Up to 15% of organic matter is fresh residue (usually <10)  Comprised mainly of litter fall

Decomposing Organic Matter  Plant material is transformed from one organic compound to another mainly by organisms in the soil  Organisms create by-products, wastes, and cell tissue

 SOM can be maintained with:  Proper fertilization  Crop rotations, and tillage practices  Returning crop residues to the soil.

Factors Controlling SOM  1) Texture  2) Climate  3) Management practices Established in 1876 the Morrow Plots are the oldest agronomic experiment fields in the United States. They include the longest-term continuous corn plot in the world. Located near the center of the University of Illinois' Urbana campus. manure, lime and phosphorus (MLP) Morrow Plots – Why the difference in SOM?

Cation Exchange Capacity (CEC)  Positive charge ions (Ca 2+, Mg 2+, K +, Na +, H +, Al 3+, Fe 3+ )  The capacity to hold on to these cations is called CEC  These cations are held by the negative charged clay and organic matter particles

CEC

Why do soils have CEC?  Because clay and OM tend to be negative charged  OM can have 4 to 50 times higher CEC  Negative charge in OM comes from breakdown of organic compounds

Base Saturation (BS)  Important soil property  Defined as percentage of total CEC occupied by Ca2+, Mg2+, K+ and Na+  BS increases with increasing pH

CHEMICAL REACTION SOIL ACIDITY

 Balance between (H+) and (OH-)  Processes that promote soil acidification are:  Production of H ions  Washing away of non-acid cations

Importance of Soil pH  Availability of essential plant nutrients  Influences chemical reactions  Activity of microorganisms  Solubility (toxicity) of non-essential elements  Performance/carryover of some herbicides

SOIL pH and Nutrient Availability

POOLS OF SOIL ACIDITY  Active acidity  Salt-replaceable acidity  Residual acidity

Active acidity  Free hydrogen ions in soil solution  Very small part of total acidity in soil  Takes <1/3 lb/acre limestone to neutralize

Exchangeable Acidity  Amount of acid cations (Al and H) on the CEC  Common in soils that have a low base saturation

Residual (Reserve) Acidity  H ions and Al ions chemically bound to organic matter and clay  Estimated by buffer pH  This is what limestone must neutralize when acid soils are limed in order to increase pH

Residual (Reserve)  Soils with large CEC can hold large amount of acidity  These soils are highly buffered  Require large amounts of lime to increase soil pH

How do Soils Become Acidic?  Carbonic and other organic acids  Accumulation of organic matter

How Soils Become Acidic?  Oxidation of Nitrogen  Oxidation of S  Acids in precipitation (acid rain)  Plant uptake of cations

How Soils Become Acidic?  Clay and Oxide Minerals  Soluble salts - Mineral weathering - Addition of manure

ROLE OF Al 3+ IN SOIL ACIDITY  Aluminum is highly toxic to most organisms  Al 3+ ions splits water molecules into H + and OH - ions

Al Hydrolysis in Soils  Al 3+ + H 2 O = Al(OH) 2+ + H +  Al(OH) 2+ + H 2 O = Al(OH) H +  Al(OH) H 2 O = Al(OH) H +  Al(OH) H 2 O = Al(OH) H +

Aluminum Toxicity  Occurs in soils with high Al minerals  Al minerals dissolves in soil solution at pH < 5.4

Effects of Al 3+  Interferes with cell division in roots  Inhibits nodule initiation  Makes P unavailable to plants

Al Toxicity  Increases cell wall rigidity  Interferes with uptake of water and nutrients  Decreases root respiration  Interferes enzymes governing deposition of sugars

Correcting Soil Acidity

What is a Liming Material?  Material containing Ca and/or Mg compounds capable of neutralizing soil acidity

Amount of Lime to add Depends on:  Quality of Lime  Soil buffer Capacity  Desired pH range

Lime Quality  Two properties of Lime govern its quality: 1. Chemical Purity 2. Fineness

Chemical Purity  Expressed as Calcium Carbonate Equivalent (CCE)  CCE is acid neutralizing capacity of a liming material expressed as a weight percentage of CC  Pure CC is the standard against which other liming materials are measured

Agricultural Liming Materials

Fineness  Particle size  Reaction rate depends on surface area  Reaction rate increases with decreasing particle size

How Lime Neutralizes Soil Acidity

Liming Reactions

Nutrition Plant nutrients

Essential Plant Nutrients

Nitrogen  Most frequent deficient nutrient in non legumes  Most soils need inorganic and or organic N sources

Nitrogen Cycle

The N Cycle  N = 78 % in atmosphere  Plants cannot directly metabolize N directly into protein  Must be converted to plant available N

N Conversion  Symbiotic microbes on legume roots  Free living non-symbiotic microbes  Atmospheric electric discharges  Manufacture of synthetic N fertilizers

Forms of Nitrogen  Urea  CO(NH 2 ) 2  Ammonia  NH 3 (gas)  Ammonium  NH 4  Nitrate  NO 3  Nitrite  NO 2  Atmospheric Dinitrogen  N 2 (gas)  Organic N

Forms of N in Plants  Plants contain 1 – 6 % N by weight  Plants absorb N both as ammonium ( NH 4 + ) or Nitrate (NO 3 - )

Function of N  Formation of proteins  Nucleic acids (DNA, RNA)  Component of energy transfer compounds (ATP and ADP)  Integral part of chlorophyll

Visual Deficient Symptoms  Yellowing on leaves/leaf veins  Loss of protein N in older leaves

Over supply of Nitrogen: 1. Excessive vegetation 2. May cause lodging 3. Delay plant maturity 4. Plants may be more susceptible to disease. 5. Can cause nitrate poisoning in cattle grazing forages

Nitrogen Cycle  Mineralization  Immobilization  Nitrification  Denitrification  Nitrogen Fixation

Mineralization

 It is a two step process: 1. Aminization 2. Ammonification

Aminization

Ammonification

 Ammonium (NH4+) produced is subject to several fates - Nitrification - Absorbed by plants - Immobilization

C:N Ratio Effects on Mineralization  Important in planning crop rotations  MO need a ratio of 24:1(16 for energy and 8 for maintenance)  If alfalfa hay (C:N 25:1) is added, No excess N left over

C:N Ratio of different materials:  Topsoil10:1  Alfalfa13:1  Rotted manure20:1  Cornstalks60:1  Grain straw80:1  Coal124:1  Oak200:1  Spruce1000:1

Immobilization  The opposite of mineralization  Happens when nitrogen is limiting in the environment  Nitrogen limitation is governed by C/N ratio  C/N typical for soil microbial biomass is 20  C/N < 20  Mineralization  C/N > 20  Immobilization

Nitrification NH 4 +  NO 2 -  NO 3 - ammonium nitrite nitrate Nitrosomonas NH 4 +  NO energy Nitrobacter NO 2 -  NO energy

Soil Conditions Favoring Nitrification  Rapid in well-aerated, warm, moist soils  Supply of Ammonium  Population of bacteria  Soil pH (5 -9)

Ammonia Volatilization Urea: CO(NH 2 ) 2  NH 3 +CO 2 + H 2 O urea soil enzymes & H 2 O - Most volatilization when:   coarse or sandy-textured soils   low clay and low organic matter (which adsorb NH 4 + )   dry alkaline surface

Denitrification Gaseous loss of N upon N reduction + e - + e - + e - + e - NO 3 -  NO 2 -  NO  N 2 O  N 2 nitric nitrous oxide oxide

Denitrification (cont’d) * Microorganisms responsible: facultative anaerobes - prefer O 2 but will use N for a terminal e - acceptor mostly heterotrophic - use organic-C for energy source

Denitrification (cont’d) * Denitrification enhanced by: low O 2 (flooding) high O.M. (energy source) high NO 3 -

Nitrogen Fixation N 2  (organisms)  NH 4 + * Symbiotic relation between bacteria and plants: - legumes + - rhizobium

What is Rhizobia?  Bacteria that fix N in association with plants  Rhizobia are specific to host plant  There are 6 genera of bacteria that fix N 1. Rhizobium 2. Bradyrhizobium 3. Sinorhizobium 4. Azorhizobium 5. Allorhizobium 6. Azorhizobium

Process: Rhizobium nodule

(b) Process: C from plant photosynthesis  N from fixation of N 2   symbiosis   symbiosis Rhizobium organic-C N2N2N2N2 organic-N

Quantity of N Fixed 4 Depends on the following: 1. Soil pH 2. Photosynthesis 3. Management - Water - Nutrients - Weeds - pests

Benefits of Legumes  Economics: - N captured by legumes due to use of inoculants costing $2.00/acre - N fertilizer costing $87.00/acre  Environment

N Fixation Comparisons Industrial N FixationBiological Nitrogen Fixation Need 2 metric tons of coal/ton of NH 3 Coordination of 23 genes to fix 165 – 450 lbs N/acre/yr Pressure atm.Ambient pressure Temp – 500 CAmbient temperatures Natural gas is the feedstock for H Energy comes from oxidation of organic C Unsustainable systemSustainable system

Industrial N Fixation

Inorganic N Fertilizers  Anhydrous ammonia (82% N)  Urea (45-46% N)  Ammonium Nitrate (33-34% N)  Urea-ammonium nitrate (28-32% N)

Nutrition Phosphorus

Functions of P in Plants  Energy storage and transfer  Essential element in DNA and RNA that contain the genetic code of the plant  Associated with increased root growth  Adequate P increases straw strength in cereals and increases N 2 -fixation capacity of legumes

P Deficiency - Stunted - Foliage dark purplish to bluish green

The Phosphorus Cycle Solution P Crop Harvest Crop Harvest Manure P Fertilizer P Crop Residue Crop Residue Labile Stable Organic P Labile Inorganic P Stable From: Livestock and Poultry Environmental Stewardship Leaching

Pathways for P Loss from Soils

Forms of Soil P  Solution P - Orthophosphate (HPO 4 2- and H 2 PO 4 - ) - The two species of orthophosphate are determined by solution pH

P Cycle  Chemical forms - Organic P - Ca inorganic P - Fe/Al inorganic P

Organic P  Mineralization and immobilization - Similar processes to N - C/P ratios of 300:1 – net immobilization - 200:1 net mineralization

Inorganic P or Fixed P  Precipitation by Al, Fe, and Ca - Fe 3+ + H 2 PO H 2 O = 2H + + Fe(OH) 2 H 2 PO 4 - Al 3+ + H 2 PO H 2 O = 2H + + Al(OH) 2 H 2 PO 4 - Ca 2+ + H 2 PO H 2 O = 2H + + Ca(OH) 2 H 2 PO 4

Solubility of Inorganic P  Depends on - Soil pH - Aeration

Factors Influencing inorganic P Fixation - Clay content - Type of clay - Organic matter - Time and Temperature - Flooding

P Best Management Practices 1. Soil testing and sound recommendations 2. Determine available P credits 3. P placement

Dietary ManipulationManure Treatment Less Available P in Manure Agronomic Application Rates Erosion Control Buffer Strips Improved Water Quality

Potassium  Absorbed as K+ ion  Unique nutrient – not part of any plant compound  Exists in plat sap

The Potassium Cycle

K in primary mineral structure Unavailable (90-98% of all soil K) K in nonexchangeable positions of secondary minerals Slowly available - fixed K is not easily exchangeable - In equilibrium with more available forms K in exchangeable form on soil colloid surfaces Readily available (1-2% of all soil K) -90% of readily available K ions soluble in water Readily available - Subject to leaching - Equilibrium with exchangeable form Availability of Potassium Forms

Functions of K in Plants  Activates 80 different enzymes  Lowers osmotic potential in cells  Essential in photosynthesis, protein synthesis  N fixation, starch formation  Translocation of sugars  Helps plants adapt to environmental stress

Functions of K in Plants  It enhances fruit size, color in fruits/vegetables  Involved in ATP synthesis  Strengthens stems  Balances other nutrients

Visual Deficiency Symptoms  White spots on the leaf edges in alfalfa  Visual symptoms appear in lower leaves first  Weakening of the straw

Factors affecting K Availability  Clay mineral and CEC  Soil moisture  Soil temperature  Soil Aeration  Soil pH

Sources of K  Organic K – manures  Inorganic K

SOIL TESTING Fertility

Soil Testing  Provides index of nutrient availability  Predict probability of obtaining a response to fertilizer or lime  Basis to provide recommendations

Philosophies of Soil Testing 1. Maintenance approach – apply adequate amount of nutrients to replace nutrients removed - This method does not the capacity of soils to supply nutrients - This approach can lead to over-fertilization

Philosophies of Soil Testing  Cation saturation ratio – based on proposition that an ideal soil has 65% exchangeable Ca, 10% Mg, 5% K and 20% H - This philosophy is not valid across soil types - It does not consider N, P, S or micronutrients

Philosophies of Soil Testing  Sufficiency level approach – based on long term calibration of soil tests with field yield response data - This method gives nutrient levels - Low, Medium, Optimum, High, Excessive

Steps in Soil Testing Soil Sampling Soil Analysis Calibration/Correlation Recommendations

Soil Sampling  The most critical step -1 lb of soil is often used to represent million lbs

How to Take a Soil Sample  Do not sample from wet areas, eroded banks, bare spots, near trees, livestock watering areas  Sampled areas must have the same soil texture and management  Take a minimum of 20 to 30 random samples on 10 acres or less

How deep to sample  In permanent hay fields, sample from 2 – 8 inches deep  For no till fields, take two samples

When to sample  Can be taken at any time of the year  Do not take samples if the soil is wet or frozen  Do not take samples shortly after fertilizer or lime application  The best time is spring or fall

How often to Soil test  Frequency of soil testing depends on: - Crop grown - Previous fertilization rates - Timing of lime application - In general, every 3- years

Soil Fertility Report  pH  Lime requirement  Cation exchange cap. & exch. cations  Available P  Inorganic N (NO 3, NH 4 )  Organic matter  Available micronutrients  Reactive Aluminum

Other Soil Tests  Pre sidedress soil Nitrate test (Corn)  Corn Stalk Nitrogen Test

Adding Nutrients Manure

Manure Basics  What is Manure?  Urine, feces  Waste feed  Parlor water

Nutrient Value of Manure  Test manure annually  Collect sample before application  Freeze sample immediately

Manure Basics  How Much Manure Does a cow produce in a day? A week? A Month? A Year?

How Much Manure?  Typical Dairy Cow:  148 lbs/day (18 gal)  1036 lbs/week (124 gal)  4440 lbs/month (531 gal)  lbs/year (6460 gal) Does not include youngstock, other wastes

Rule of Thumb #1  One cow plus replacement plus wastewater = 10,000 gal/year

What is in manure?  Nutrients  Nitrogen, Phosphorus, Potassium  Micro nutrients Whatever the cow eats that does not become milk or meat becomes manure. If it’s in the feed, it’s in the manure.

Dairy Diet and Runoff  Manure from 2 rations applied  1.28 and 0.48% P (rec is )  Runoff was 4x higher for high P diet  Same lbs P applied  Runoff was 10x higher when manure rates were the same. Ebeling et al, 2001

Dairy Diet Impacts  Ave P in dairy ration is 0.47% Gunderson, Keuning & Erb, 2001  NRC Recommendation is % P  Higher rates are due to belief that lower P reduces reproductive efficiency.

The Manure Paradox Crops use N:P:K in a 3:1:2 ratio Dairy manure is a 1:1:2 ratio (available) Meet the crop’s N need = excess P Meet the crop’s P need = buy N fert

Corn Nutrient Need vs. Manure Nutrient Supply Following a Nitrogen Strategy lb/acre

Manure Application Rates Nitrogen Strategy  Maximum rates  P and K in excess of crop need  Efficient with time and labor  Preferred when land is limited

Corn Nutrient Need vs. Manure Nutrient Supply Following a Phosphorus Strategy lb/acre

Manure Application Rates Phosphorus Strategy  Low rates  Need supplemental nitrogen  Increased time and labor  Need adequate acreage

Economics $0.20/lb) 100 Cow Dairy Alfalfa N =$ 1,200 ( lbs N/a) Manure N =$ 1,320 (22 3 lbs N/ton) Total On-Farm N =$ 2,520

Economics (P 2 O $0.25/lb; K 2 $0.13/lb) 100 Cow Dairy Manure P 2 O 5 =$ 1,650 (22 3 lbs P 2 O 5 /ton) Manure K 2 O =$ 2,288 (22 8 lbs K 2 O/ton) Total Manure P & K 2 O =$ 3,938

If You Are Going To Use Manure as a Fertilizer… Treat It Like A Fertilizer!

Challenges of the Future:  Dairy Trends  Management: More cows, fewer farms.  Realization by farmers that manure management requires a cash investment  Manure’s Internet IPO: Lots of ideas now, lots of broken ideas coming in a few years. Easiest to use / most farm-profitable techniques will remain.