Soil Water and Chemical Recycling: Impact on Soil Structure and Plant Growth, Study notes of Agricultural engineering

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AGA 105 Crop and Soil Science Chapter 5: Soils Soil • Natural Material Derived from Weathered Rock and Organic Materials • Chemically Active • Supports a Lot of Life within It • Soil’s Quality often Determines Agriculture Development and Sustainability • Needs to Be Protected – Half of Tillable Soil in U.S. Has Lost ¼ of Its Topsoil due to Wind and Water Erosion Soil Functions • Provides Water, Nutrients and Anchorage for Plants • Not Required for Plant Growth • Fig. 5.1, p. 43 Mineral Matter • Solid Portion of Soil Derived from Inorganic or Non-Living Sources • 45% of Soil • Originated from Parent Material – Bedrock (Residual) – Windblown or Water-Deposited Silt or Sand (Transported) Particle Size • Helps Determine Soil Type, Characteristics – Sand – Silt – Clay • The Smaller the Particle Size, the more Reactive It Is in Soil Chemical Reactions Soil Texture • Relative Amounts of Sand, Silt and Clay Determine Soil Texture – Soil Textural Triangle, text p. 44 • Can Affect Size and Number of Soil Pores • Affects Ability of Water to Enter Soil and Be Stored in It • Soil Textural Classes – Coarse = Sands, Loamy Sands and Fine Sandy Loams 1 – Medium = Very Fine Sandy Loams, Loams, Silt Loams, Silts – Moderately Fine = Clay Loams, Sandy Clay Loams, Silty Clay Loams – Fine = Sandy Clays, Silty Clays and Clays Sandy Soils • Advantages – Well-Drained and Easy to Till – Warms up Quickly in Spring • Disadvantages – Low Fertility – Low Capacity to Retain Water and Nutrients • Uses – Crops for Early Market Sandy Loams • Advantages – Most of the Advantages of Sandy Soils plus These Retain Water and Nutrients more Readily • Use – Not as Early to Warm in Spring as Sands, but Still Used Chiefly for Early Market Crops Loams • Relatively Balanced Mix of Sand, Silt and Clay • Fairly Easy to Till, Relatively Fertile • Retain Water and Nutrients fairly Well • Use – Main Season and Later Season Production Clay Loams • Advantages – Usually Good Native Fertility – Retain Water and Nutrients Well and may not Require Side Dressing of Fertilizer • Can Apply all Fertilizer before or at Planting • Disadvantages – Poor Drainage – Warm up Late in Spring – Can Crust over • Use – Can Be Used for Late Crops 2 – Amount of Hold Is Expressed in Bars (mPa) – Since Plants/Atmosphere/Gravity ‘Pull’ Water out of Soil, usually Is Expressed as Negative Bars (mPa) • Soil Moisture Tension (SMT) – Water in Large Pores Is Held with Less Tension than Water in Smaller Pores, because fewer Soil Particles Surround Water in Larger Pores to Exert this Pressure • Easier for Roots to Get Water from Larger Pores than Smaller Pores Soil Water Definitions • Saturated Soil (Saturation Capacity) – All Soil Pores Are Filled with Water – SMT = 0 bars or mPa • Gravitational Water (Free Water) – Water in Saturated Soil that will Quickly Drain away once the Source of Water Input Is Gone • Available Water (Capillary Water) – Water Held in Pore Spaces that Is Available for Plant Uptake after all Gravitational Water Drains away • Field Capacity – When Gravitational Water Is Gone – SMT = 0.3 bar (mPa) • Unavailable Water – As Soil Dries, It Reaches a Point where Plants can no Longer Extract Water from Soil although there Is still Water Tightly Held in Small Pore Spaces • Wilting Point – Name for Soil when the Remaining Water Is Unavailable for Plant Uptake – SMT = 15 bars (mPa) • Plant Water Relations – Water Tension inside a Plant = -1 bar (mPa) – Atmosphere at 99% RH = -1.5 bars (mPa) – Atm at 90% RH = -15 bars (mPa) • Plant Water Relations – Soil Texture will Determine at what % of Water Volume this will Occur in a Particular Soil – See Table 5.1, p. 48 – Fine-Textured Soils Have Higher Volume of Water at Permanent Wilting Point, Higher Amount of Available Water and Higher Field Capacity than Coarse-Textured Soils Soil Air • Essential for Root Growth and Growth of Microbes • Non-Continuous and Non-Uniform Gases 5 – More CO2 and less O2 than Above-Ground Air – Extra CO2 and lower O2 Are Created by Root Respiration and Microbe Decomposition of OM • Plants cannot Take up Water and Nutrients Effectively without Adequate O2 for Roots and Respiration • Good Soil Aeration Needed for Good Root Growth • Poor Aeration Slows Microbial Decomposition as well and Causes more Anaerobic Organisms to Grow – May Produce Compounds Toxic to Plant Roots or other Good Microbes • Conditions that Hurt Aeration – Poor Drainage – Poor Soil Structure due to Salts, Tillage, Compaction • Conditions that Enhance Aeration – Proper Tillage, Leaving Residue, Active Micro- and Macro-Organism Activity, Good Plant Growth Soil Profile • Soil Naturally Occurs in several Layers • How Layers Are Created – Weathering of Mineral Matter – Buildup of OM near the Surface – Leaching Down of Nutrients into the Soil Profile over Time – Vertical Section of Soil to Show the different Layers • A-Horizon – Top Layer, Highest in OM, Main Region of Plant Growth, Also Called Topsoil, May Be only 1 Inch or so Thick or several Feet Thick • B-Horizon – Middle Layer, Usually Has more Clay than A Horizon and Less OM, Also Called Subsoil, Usually several Feet Thick • C-Horizon – Lower Level, Made of Soil Parent Material, Between B Horizon and Bedrock, Has the least amount of Chemical Changes Occurring in It over Time, Can Be Absent in Thin Soils over Shallow Bedrock (many Sites in Ozarks), Can Be many Feet Thick • Erosion by Wind and Water can Remove the A-Horizon • B-Horizon may Be Exposed by Grading or Erosion • B-Horizon usually less Fertile than A-Horizon for Growing Plants • Protecting or Restoring (by Addition of OM) Topsoil Is Essential for Good and Sustainable Crop/Plant Growth Soil Chemistry • Soil Is very Active Chemically – Contains Water and Dissolved Minerals and Nutrients 6 – Fate of Water and Dissolved Compounds • Bind with Soil Particles, Are Taken up by Plants, Acted upon by Microbes • 2 main Factors Affect Soil Nutrient Status and Availability of Nutrients for Plant Uptake – CEC, pH Cation Exchange Capacity • CEC • Ability of Soil Particles (particularly Clay and Humus) to React with Ions in Soil Water Solution – Ions Are Charged Particles – Soil Surfaces on Clay and Humus Have a Net Negative (-) Charge – Dissolved Substances may Have Negative Charge or Positive Charge • - Charge = Anions and + Charge = Cations – The Negative Soil Surfaces Attract Cations and Repel Anions – The Greater the Number of Charged Surfaces Means the Greater the Ability of the Soil Surfaces to Attract and Hold Cations • CEC Is Expressed as Milliequivalents of Negative Charge per 100 Grams of Dry Soil (meq/100 grams) • EC of a Soil Determines how well It can Hold Nutrients for Plant Uptake – Cation Nutrients can Be Held by Soil for Plant Root Uptake • K, Ca, Mg – Anion Nutrients Are not Held by Soil and can Wash down with Gravitational Water • Nitrates – Leaching • When Water Moves Nutrients, Compounds down through Soil (below Root Zone) Soil pH • A Measure of the Acidity or Alkalinity of a Soil • pH Range Is 0-14 – 0 most Acid, 14 most Alkaline, 7 Is Neutral – Soil pH less than 7 = Acid – Soil pH greater than 7 = Alkaline • Most Agronomic Crops Prefer pH of 6.0-7.3 (Neutral to Slightly Acidic) • If pH Is at Extremes—usually not below 4.0 or above 8.0 in most Natural Soil Situations—It Doesn’t Greatly Affect most Crop Growth • Optimum pH Range Provides Greatest Availability of Nutrients in Soil for Plants • Chart of pH Effect on Nutrient Availability: Table 6.2, p. 259 • pH below 6.0 can Reduce Rhizobium Activity • Other Soil Extremes can Affect other Soil Microbes 7 • S, Ca, Mg Are Needed in next Highest Quantity • Micronutrients – Needed in much lower Quantities than Macros – Obtained from the Soil: Fe, Mn, B, Cu, Zn, Mo, Cl, Co • Essential Nutrients – From the Plant’s Standpoint, the Source of Nutrients Is not Important, just Getting the Nutrient in the Right Form Nutrient Mobility in a Plant • Some Nutrients Are Mobile – Available Nutrient in the Plant Moves toward New, Developing Tissue and away from Older Portions – Deficiency Symptoms Show 1st in Older Growth (Base of Plant) – N, P, K, Mg Are Mobile in the Plant • Ca, S, Fe, Zn, Mn, Mo, Cu, B Are Immobile Nutrients Terms Used to Describe Deficiency • Chlorosis Is Yellowing • Interveinal Chlorosis Is Yellowing of Areas between Veins on Leaves • Necrosis Is Browning • Marginal Necrosis Is Browning of Margins of Leaves • Curling, Distorted Leaves • Stunting Deficiencies • Lack of an Element • Antagonisms between Elements/pH • Roots Damaged by Toxins, Pests, Pathogens, Poor Physical Conditions in Soil Excesses • Can Reduce Availability of other Elements • Can Be Directly Toxic • Excess Salts Compete with Plant Tissues for Water, Damage or Kill Roots, may Eventually Damage the Rest of the Plant • Salts that Accumulate in Above-Ground Parts Can also Damage Tissues Corrective Measures • Sometimes can Remedy Plant Damage and Salvage the Crop • Sometimes Irreversible • Grower Needs to ID and Correct Basic Cause of a Problem before Planting Succeeding Crops 10 Nitrogen (N) • Needed the most by Crops • Most Likely to Be Deficient • Is a Mobile Nutrient • Deficiency Symptoms Appear as Uniform Chlorosis, then Necrosis, Older Leaves 1st, Stunted Growth • A Component of Plant Proteins, DNA, Enzymes, Secondary Products • Makes up 40 to 50% of Protoplasm • Microbes Convert Organic Forms of N to Nitrates – Nitrification • Nitrate-N Leaches through Soil Easily • Nitrate can also Be Lost by Conversion Back to N or other N Compounds through Denitrification in Poorly Aerated (Saturated) Soils • Plants can also Take up Ammonium, but usually Present in lower Amounts • Review N Cycle on p. 28 Nitrogen Fertilizers • Most Are Dry, Granular, Inorganic Form – Ammonium Nitrate (33-0-0) – Urea (45-0-0) – Ammonium Sulfate (26-0-0) • Some in Liquid Form from Dissolving Ammonium Nitrate or Urea in Water – 28-0-0 – 32-0-0 • Gaseous Nitrogen – Anhydrous Ammonia (82-0-0) • Converts to Ammonium Ion I Soil and Is Held by Soil Particles until Nitrification Occurs and Is Converted to Nitrate Ammonia • Also Used to Make other Nitrogen Fertilizer Forms Legume Nitrogen • From Nitrogen-Fixing Rhizobium Bacteria Attached to Roots • Nitrogen Fixation – Process of Converting Atmospheric N to Nitrates • Main Means to Provide N to non-Fixing Crops in the Past • Still a Part of Sustainable Agriculture Phosphorus (P) • Needed in lower Quantities in the Plant than N • Component of DNA, Cell Membranes, Proteins, Enzymes, ATP (Main Energy 11 Molecule) • Required for the Synthesis of Carbohydrates and Proteins in the Plant • Concentrated in Regions of Active Plant Growth and Flowers and Fruit • Most of Crop Plant P Used in the 1st Stages of Growth • 75% Used before 25% of Growth of Crop • Mobile Nutrient • Deficiency Symptoms – Purplish Coloring of Older Leaves – Purple Veins in Leaves – Stunted Growth – Poor Root Growth • Sometimes even when Soil P Is Adequate, Temporary Deficiency Symptoms Occur when Weather Is Cold and Wet – Roots Have Difficult Time Getting P from Soil in Cold, Wet Weather Phosphorus Fertilizers • Often Needed in many Soils, especially Sandy, Weathered or Calcareous Soils (Soils with Free Lime, which Have a Higher pH) • P Is Relatively Immobile in the Soil – Leaching not a Problem • Organic Sources – Crop Residues – Animal Wastes • Usually Contain ½ as much P as N – Bone Meal • Inorganic Sources – Still most Common Sources – Derivatives of Rock Phosphate • Superphosphate (0-20-0) Is Made by Treating Rock Phosphate with Sulfuric Acid • Also Contains 25% Sulfur • Treble Superphosphate, Triple Superphosphate (0-45-0) • Made by Treating Rock Phosphate with Phosphoric Acid – Liquid Phosphoric Acid Used to Mix with Liquid Fertilizers Potassium (K) • Plants Take up more K than N but K Is less Likely to Be Deficient • Plants may actually Take up more K than They Need – Luxury Consumption – Not Toxic in Excess Quantity • K Is Essential – PS 12 – Potassium-Magnesium Sulfate (22% Sulfur) Iron (Fe) • Most commonly Deficient of the Micronutrients • Essential for Chlorophyll Synthesis and Electron (Energy) Transfer in Respiration • Immobile in Plant • Deficiency Symptom Is Yellow to White Interveinal Chlorosis on New Growth • Stunting may Occur if Severe Deficiency • Fe Deficiency most common in Calcareous Soils (with Free Lime) and Higher pH Soils • Higher pH, Lime Ties up Fe in Soil even though It may Be Abundant • Need to Use Fe that Is Bound in an Organic Molecule for It to Be Available to Plants or Use Repeated Liquid Foliar Applications – Bound in Organic Molecule = Chelated Iron – Liquid Foliar Applications = Iron Sulfate Zinc (Zn) • 2nd most commonly Deficient Micronutrient • Essential for Enzyme Synthesis, Enzyme Activation and Plant Hormone Synthesis • Immobile in Plant • Deficiency Symptoms – Small Chlorotic Leaves with Rough Margins – Necrotic Spots on New Growth – Rosette-Like New Growth • More common in Sandy, Acid pH Soils, Calcareous Soils, Disturbed Soils (Subsoil on Top) • Can Correct Deficiencies with Zinc Sulfate • Other Nutrients Listed below Are very seldom Deficient in Natural Soils • Deficiencies usually only Exist if an Excess of another Available Nutrient Blocks Uptake of the Micronutrient Manganese (Mn) • Essential for Respiration, PS • Immobile in Plant • Deficiency Symptom – Interveinal Chlorosis on New Growth (similar to Iron Deficiency) • Seldom Deficient Copper (Cu) 15 • Essential for Respiration and for Protein Formation • Immobile in Plant • Deficiency Symptom – Blue-Green, Necrotic Leaves on New Growth • Seldom Deficient Molybdenum (Mo) • Enzyme Activator for N Uptake and Assimilation in Plants • Immobile Nutrient in Plants • Deficiency Symptom – Overall Chlorosis of Leaves, Starting with Newer Growth • Seldom Deficient Boron (B) • Essential for Translocation of Plant Products and Carbohydrate Metabolism • Needed for Cell Wall Formation • Immobile in Plant • Deficiency Symptoms similar to Ca Deficiency – Shorter Spaces between Leaves at Stem Tips – Brittle Growing Points on Plants • Toxicity Symptom – Sometimes can Have too much B and Get Bleaching Color of Plants Chlorine (Cl) • Essential for the 1st Rx of PS • May Be Required for Cell Division in Leaves and Roots • Mobile in the Plant • Deficiency Symptoms – Wilting of Leaf Tips Followed by General Leaf Chlorosis and Necrosis – Leaf Bronzing and Reduced Growth – Roots may Appear Stunted and Thickened near the Root Tips • Deficiency not generally Known in Soil-Grown Plants Cobalt (Co) • Essential for Rhizobium Bacteria on Legume Roots for N Fixation • Not commonly Deficient • Lack of Root Nodules (where Bacteria Live) would Be a Deficiency Symptom Nutrient Interactions • Sometimes when 1 Nutrient Appears to Be Deficient in a Plant, It Is actually 16 because an Excessive Level of another Nutrient Is Preventing the Deficient Nutrient’s Uptake • What if Foliar Analysis Suggests a Nutrient Is Deficient but Soil Analysis Indicates It should Be Sufficient? – Analyze for Suspected Excessive Nutrients before Adding more of the Apparently Deficient Nutrient Excessive Minerals in the Soil • “Salinity” • Excessive Soluble Minerals Are Available in the Soil-Water Solution – Excess Mineral Ions can Limit Water Uptake due to an Increased Soil Affinity to Hold Water – Plants may not Be able to Take up Water Effectively – Excess Available Nutrients may Be Absorbed into the Plant at Toxic Levels • Salinity – Symptoms of Excess Salts in Soils • Plants Wilting even when Soil Is Wet • Salt Crusting on the Soil Surface – Halophytes can Tolerate High Soil Saline Conditions due to Complex Enzyme and Membrane Functions • Ways Halophytes Deal with Excess Salts – Exclude the Salts from Uptake – Excrete Excess through Salt Glands – Store Excess Salts inside Plant Cells • “Sodicity” – When the Excess Salt Is Primarily Sodium – Effects of Excessive Sodium – Destruction of Soil Structure – Reduction of Soil’s Aeration Porosity – Increased Soil Moisture Tension which Reduces the Plant’s Ability to Take up Water • “Saline/Sodic Soil” • Soil Contains both High Soluble Salts and High Sodium • Few Plants can Grow in such Soils • Main Cause of Saline, Sodic or Saline/Sodic Soils – Natural Soil was once Bottom of a Salty Sea – Weathering of Sodium-Containing Rock – Irrigation with Water that Has a High Salt or Sodium Content – Overfertilization with Quick-Release Fertilizers Plant Nutrient Uptake • Nutrients Contact the Roots for Absorption by 1 of 3 Methods (same as for Water Uptake) 17 – Apply Fertilizer at the Time of Seeding – ‘Starter Fertilizer’ – Usually Placed in a Band underneath and next to the Actual Row of Seeding – Enhances Early Seedling Growth – Commonly Done with P and Micronutrients – Can also Apply on the Surface of the Soil, Possibly with Pesticides • Not Called a ‘Starter’ since New Seedlings Don’t Easily Reach Nutrients • Postemergent Application – Applied after the Crop Has Emerged (Germinated) – Most Efficient Means of N Application – Side-Dressing • Applying Fertilizer between Rows • Postemergent Application – Top-Dressing • Applying Fertilizer over all of the Crop when Rows Are too Narrow for Side- Dressing • Requires Rain or Irrigation to Get Nutrients into the Soil • Postemergent Application – Fertigation • Applying Fertilizer through the Irrigation Water • N Is the most Common Nutrient Applied via Fertigation Quick-Release Fertilizer • Nutrients Are Highly Water-Soluble and Enter the Soil Solution as Soon as Rain or Irrigation Move Them into the Water • Most of Nutrient Analysis Available in a very Sort Period of Time Slow-Release Fertilizer • Nutrients Are Released from Fertilizer over a Longer Period of Time • May Be Organic Forms of Nutrients – Animal Wastes – Residues – Composts – Decomposition and Nutrient Release Rate Depend on the Soil Temp • Soil Microbes Work Best in Warm, Moist Soils • Cool and Wet or Cool and Dry Weather Slows Breakdown • May Be Synthetic Forms of Nutrients – Complex Organic Molecules as Plastic- or Sulfur-Coated Pellets – Decomposition may or may not Be Affected by Temp • Some Are Broken Down Chemically, without Microbe Aid Tillage and Seedbed Preparation • Tillage Is the Mechanical Turning or Stirring of the Soil 20 • Requires ½ of the Engine Power Used on Farms • Can Be Beneficial – Improve Soil Structure – Loosen Soil for New Plant Growth (Seedbed Preparation) • Increase Soil T° • Increase Soil Aeration – Weed Control Is a 1° Reason for Tillage – Disease Control – Turn Residue Underground to Aid in Decomposition – Incorporate Fertilizers or Pesticides • Can Be Harmful – Destroy Soil Structure – Harm Crop Roots – Aid in Soil Erosion • Can Be Harmful – Creation of a ‘Plow Pan’ or ‘Tillage Pan’ Zone of Compacted Soil just below the Area where the Tillage Implements can Turn the Soil • Ways to Reduce Compaction – Reduce # of Tillage Operations – Avoid Tillage when Soil Is Wet – Avoid Running over the same Tracks when Repeat Going over the Field – Can Use Deep Chisel Plow to Break up a Pan but Could Develop a Deeper Pan if other Factors Have not Been Reduced Tillage Implements • Primary Tillage – To Incorporate Crop Residue and Kill Existing Weeds after Harvest of a Crop – Moldboard Plow and Offset (Tandem) Disk Are Common 1° Tillage Implements • Moldboard Plow can Turn under 100% of Residue • Disks can Turn under 40 to 50% of Residue • Secondary Tillage – Other Tillage Operations Done to the Soil prior to Seeding or Between-Row Cultivation after the Crop Is in and up – All Implements other than Moldboard Plow might Be Used for 2° Tillage – Implement Selection Depends on various Factors • Crop • Crop Age • Level of Surface Residue Desired • Conventional Tillage – Using 1° and 2° Tillage Implements and Practices • Conservation Tillage, Minimum Tillage – To Reduce Soil Erosion 21 – Using Limited Tillage that Minimized Disturbance of the Soil Surface Residue • No-Tillage – Only Uses Planting Equipment to Disturb the Soil Surface – No other Soil Preparation Tillage Is Performed • Benefits of Conservation, Minimum or No-Till Practices – Reduced Soil Erosion – Good Soil Structure if Soil Is not Worked when Wet – Less Fuel, Labor and Equipment Costs for Planting • Not a Lot of Tillage Done before, during and after the Crop • Disadvantages of Conservation, Minimum or No-Till Practices – Greater Weed Problems • More Spent on Herbicides (Weed Killer Chemicals) – Slower Slow Drying and Warming in the Spring Raised Beds • Typically 3 to 8 Inches Higher than Normal Field Level • Can Be Produced using Commercially Available Bed Shapers or Disk Hillers • ‘Rotovators’ Rototill and Shape Beds Weedy Soils • Control Weeds Before Planting – Repeated Tilling to Destroy Weeds as They Emerge – Application of Non-Selective, Short-Residual Herbicide (Glyphosate) • Control Weeds Before Planting – Cover Crops that Are Tilled into Soil – Plastic Mulches to Smother and Heat Kill Weeds and Some Seed • Control of Weeds After Planting – Use Weed Barrier Fabric in Perennial Beds, Usually Topped with Mulch for Appearance – Organic Mulches 2 to 3 Inches Thick in Annual Beds • Control of Weeds after Planting – Use Pre-Emergence Herbicides (Dacthal, Preen, Surflan, Ronstar) to Control Annual Grasses and Broad Leaves Before They Emerge from the Soil • Must Be Applied Before Weeds Are Up • Pre-Emergence Herbicide + Mulch Is Great 2-Step Weed Control Practice • Some Pre-Emergence Herbicides Must Be Applied again in Midsummer to Maintain Weed Suppression (Read and Follow Herbicide Label) • Use Post-Emergence Herbicide (Poast, Ornamec) to Control Grassy Weeds such as Bermudagrass – Avoid Use of Grass-Killing Herbicides in Beds Planted with Ornamental Grasses • Hoeing 22