Soil Physical Properties - Soils and Soil Supplements - Lecture Slides, Slides of Biology

Download Soil Physical Properties - Soils and Soil Supplements - Lecture Slides and more Slides Biology in PDF only on Docsity! Unit 2: Soil Physical Properties Docsity.com Unit 2 Objectives • Differences in sand, silt, clay & soil textures • Understand soil structural classes • Importance of soil porosity & aeration • Knowledge of soil color and its importance Docsity.com Docsity.com loam 30/7 sandy clay. Textural Triangle So & FB percent sand Docsity.com Guide to Texture by Feel eainn. atthe place morked "Start ond following the char by cnswerng the questions you determine your soil’s texture. Place same soil. about the size of an ces. waster te modsten it and knead she saal mn v your pal ray oith i abe feels Tmetse wie i | eee ts A Does soal remain in WES YES a ball when squeered?| Is soil poo <li? Ts S031 too wel? ees NO _ NO [--—— No —| Place te bewcen your unmawb and index finger. Gently push the soil with your Uidinhs Bed saibeis 0 anes Gribble S Pdere aonb ise Os eae iit Sewn teidleneses Cot i ribbon extend ower your ides Tnger Uni A Breaks irom ies own weigh. Bs the iobon more than 2.5 cm long? Aaddl more wares and Ts the seil very soft ury again, and mes sticky naw shiny and dots not form a long ribbon witheut breaking? Is the soil sticky, hard Is at Tike a clay but mach setter and mor ns sticky? your bamis, has a shine when rubbed? NO YES YES NO YES NO Does every hand!ul of Dees every handfull of a) vary “Eriny™ soil Feel wery “grably™ oan ee Oe sandy? oa YES NO YES NO Dees the soil fecl very Dees the soil fecl very Ines the soil fecl very sanooth Qike oury? smocah (hike Mowck? smiccdh (like flowcy? VES No WES No YES NO Textural Triangle ¥ The soil bas some sand ‘The soil has some sand ‘The soil has some sand bun ned a io but nea a lor Docsity.com Rock Fragments • % of rock fragments in a soil may be used to help describe a soil texture – <15% by volume: no mention – 15 to 35% by volume: name the dominant kind of rock fragment (ex. Stony loam) – 35 to 60% by volume: add very to the description (ex. Very Stony loam) – >60% by volume: substitute extremely into description (ex. Extremely Stony loam) Docsity.com Soil Structure Soil Structure – arrangement of particles into aggregates Aggregates – secondary units composed of many soil particles held together by organic matter, iron oxides, carbonates, clays, etc. Peds – natural aggregates, vary in water stability (clod is used if soil is broken by artificial means) Docsity.com Soil Structure Fragment – pieces of broken peds Concretion/Shot – mass of precipitation of certain chemical dissolved in percolating waters • Soil Structural Classes – Peds described by three characteristics • Type (shape) • Class (size) • Grade (strength of cohesion) Docsity.com Soil Structure – Classes • Very fine, fine, medium, coarse, very coarse – Grades • Evaluated by distinctness, stability, & strength of the peds – Structureless Soils: no noticeable peds • Noncoherent mass of sand (single grain) • Cohesive mass such as clay soils around here (massive) – Especially found in lowland wet soils Docsity.com Soil Structure – Structured soils • Weak: peds can barely be distinguished • Moderate: peds visible, most can be handled without breaking • Strong: very visible peds, easily handled without breaking – Structure is very important influence on soil properties • What affect might different structures have on soil? – Infiltration of air, fertilizers, & water? Docsity.com Soil Structure • Genesis of Soil Structure – Peds form due to shrink/swell of soil & adhesive materials – Mostly 5/6 sided shapes – Prismatic structure tends to develop early in the genesis of soil w/ vertical cracking – More blocky structure will develop as the soil matures (especially in clay soils) due to horizontal cracking Docsity.com Soil Porosity & Permeability Pore spaces – portion of the soil not occupied by mineral or organic solids – Often referred to as the soil matrix – Typically occupied by: air, water, living roots – Irregular shape, size, & direction to pores – Which soil has the largest/smallest pores? • How does that affect the soil & crops? Docsity.com Soil Porosity & Permeability – Pore sizes are more important than total pore space – Relative amounts of air & water in pores fluctuates • Rain • Deep percolation • Transpiration • Evaporation Docsity.com Soil Air Free oxygen must be available – Required for root growth (respiration) and by soil microbes for organic matter decomposition – Well-aerated soil is best, w/ rapid, continuous gaseous exchange – Factors affecting gas exchange rates • Pore sizes • Pore continuity • Temperature Docsity.com Soil Air • Factors affecting ODR – Pore size – Water filled pores » Diffusion of CO2 gas through water is 10,000x slower through water than air – Depth in the soil » At ~3’ depth, ODR is ½ to ¼ rate of top few in. • So, how does this affect our high-clay soils? – What does is affect? – What makes the problems worse? – What might improve ODR? Docsity.com Soil Air • Oxidation-Reduction Potential (Eh or Redox) – Describes tendency for chemicals in the soil or water to be oxidized – A measure of the availability of O2 in the soil – High redox = O2 is present, low redox = O2 absent – Most plants must have O2 in the soil at root growth • Give an example of a plant that doesn’t Docsity.com Soil Air – Most plants grow best in an oxidized (aerated) soil • Free oxygen is the primary acceptor of electrons in the soil – What does this mean? – More soil nutrients stay/converted soil plant available forms – N is not lost to the atmosphere as much – Plant roots are able to respire Docsity.com Consistence (Strength) Consistence – soil’s response to mechanical forces – Resistance to rupture • Soft/hard when dry • Friable (crumbly), firm, rigid when wet – Plasticity • Tolerate considerable deformation w/out breaking – Stickiness • Ease w/ which the soil is manipulated, or even walked on Docsity.com Soil Color Dark soils absorb more heat than light colored soils – Do you think this helps explain some planting date differences? – Just because they’re dark doesn’t mean they’re warmer • Depends on soil moisture as well Docsity.com Soil Color • Soil Color vs. Soil Properties – White colors – common w/ salts or lime deposits are present – Mottles (rust colors) – soil may have periods of inadequate aeration – Gleying (bluish, grayish, greenish) – subsoils, prolonged periods of waterlogging – Darker colors – higher levels of organic matter Docsity.com Soil Temperature • Avg. summer & winter soil temps @ 3’ rarely differ by more than 9° F • Factors Affecting Soil Temp – How much heat reaches the soil surface • Soil coverings • Plastic mulches • Sun angle • Slope face • Soil Docsity.com Soil Temperature – What happens to the heat in the soil (dissipation) • Amount of heat needed to change soil temp = heat capacity – Greatly affected by soil water content » How? – Thermal conductivity – increases w/ soil-water content increasing, decreases as air-filled pores increase • Moist soils resist temp change, but conduct heat readily • Dry soils change temp faster, but conduct heat poorly – What does this mean for the soil, which is better? Docsity.com Soil Temperature • Living w/ Existing Temps – Maximizing seed germination & growth • Wheat – 40 to 50° F • Corn – 50 to 85° F – When using anhydrous • Apply when soil temp @ 4” is 50° F or less – Reduces N losses – Freeze/thaw • May cause heaving – resulting in death of shallow rooted crops Docsity.com Soil Physical Properties & Engineering • Plasticity Index – difference between liquid limit & plastic limit – Important measures for engineers to be able to understand what the soil will do under various conditions – Helps then understand what moisture needs to be present for effective compacting (make a solid base for roadways, buildings, etc.) Docsity.com Assignment • Assignment 2.1 on WebCT Docsity.com