1. Medium for Plant growth  provides anchorage  ventilation, soil pores allow CO2, formed through root respiration escape to the atmosphere and O2 to be replenished  absorption and storage of water  temperature modification  supplies nutrients Essential Elements C, H, O - supplied mostly from air and water N, P, K, Ca, Mg, S, Fe, Mn, B, Zn, Cu, Cl, Co, Mo, Ni - supplied by the soil The Functions of Soil

2. Regulator of water supplies There is a growing concern over the quality of the nations water supplies and increasing awareness of the relation between soil and water quality. Remember that almost every drop of water in our river, lakes, estuaries and aquifers has traveled through or over the soil at some point in time.  storage of water  water purification/filtration The Functions of Soil

3. Recycler of raw materials - soil processes take great quantities of organic waste and recycle it to plant available forms. The recycling of plant material (decomposition) returns C in the form of CO2 to the atmosphere. In this capacity, soils play a large role in global cycles and are important to issues such as the Greenhouse Effect. The Functions of Soil

5. Engineering medium Reliable construction requires knowledge of the diversity and variability of soil properties across time and space. The Functions of Soil 4. Habitat for soil organisms  a handful of soil may be home to billons of organisms belonging to a thousand species  soils harbor much of the world's genetic diversity  provides niches

1. Medium for Plant growth  provides anchorage  ventilation, soil pores allow CO2, formed through root respiration escape to the atmosphere and O2 to be replenished  absorption and storage of water  temperature modification  supplies nutrients Essential Elements C, H, O - supplied mostly from air and water N, P, K, Ca, Mg, S, Fe, Mn, B, Zn, Cu, Cl, Co, Mo, Ni - supplied by the soil The Functions of Soil

2. Regulator of water supplies There is a growing concern over the quality of the nations water supplies and increasing awareness of the relation between soil and water quality. Remember that almost every drop of water in our river, lakes, estuaries and aquifers has traveled through or over the soil at some point in time.  storage of water  water purification/filtration The Functions of Soil

3. Recycler of raw materials - soil processes take great quantities of organic waste and recycle it to plant available forms. The recycling of plant material (decomposition) returns C in the form of CO2 to the atmosphere. In this capacity, soils play a large role in global cycles and are important to issues such as the Greenhouse Effect. The Functions of Soil

5. Engineering medium Reliable construction requires knowledge of the diversity and variability of soil properties across time and space. The Functions of Soil 4. Habitat for soil organisms  a handful of soil may be home to billons of organisms belonging to a thousand species  soils harbor much of the world's genetic diversity  provides niches

0.15 × 100 × 100 = 1500 m m3 ×1500 kg/ m3= / = /48 × 100 = × 0.2 = × 1 = = 45 /125 = 0. 36

قرم ز

روشهاي اندازه گيري رطوبت خاک روش هاي اندازه گيري رطوبت خاک بلوک هاي متخلخل وزني نوترون متر تانسيومتر

Mass water content is a ratio of water mass to dry soil mass Example: A moist soil weighs 120 g. when dried the soil weighs 100 g. the water mass was 20 g. Therefore, θm = 20 g water/100 g soil = 0.20 اندازه گيري رطوبت خاک بروش وزني

θmθm 100 × ( وزن خاک خشک / وزن آب) = θvθv 100 × ( حجم خاک خشک / حجم آب) = θvθv =. Bd / wd θmθm dw = θvθv. dS

مثال : نمونه خاكي به جرم 385 گرم را خشك و مشاهده شد كه كه جرم آن به 315 گرم تقليل پيدا مي كند.. اگر وزن مخصوص اين خاك 35/1 گرم بر سانتي متر مكعب باشد مقادير جرمي و حجمي رطوبت را بدست آوريد. 70/315 = × 1.35= رطوبت حجمی 0.22 × 100 = 22 رطوبت جرمي % × 100 = 29.7 طوبت حجمي %

مثال : رطوبت جرمي در خاكي 25/0 است و جرم مخصوص ظاهري 4/1 گرم بر سانتي متر مكعب است. ارتفاع رطوبت در هر متر خاك چقدر است؟ عمق خاك = عمق آب × رطوبت حجمي 1.4 × 0.25 = 0.35 رطوبت حجمي 0.35 × 1000 = 350 mm عمق آب

مثال : مشخصاتي از يک خاک داريم θ m = 18 % θ mfc = 23 % θ mpwp = 9 % Bd= 1.3 gr/cm 3 الف - عمق آب تا عمق 30 سانتيمتري خاک چقدر است؟ θ v = θm × Bd θ v = 0.18 × 1.3 θ v = or 23.4% dw = θv × ds dw = × 30 dw = 7 cm

ب - اگر خاک يکنواخت باشد 8/2 سانتيمتر از آب آبياري چه عمقي از خاک را مرطوب مي کند؟ dw = θv × ds کمبود رطوبت را محاسبه مي کنيم θ m = θmfc – θm ∆ θ m = 0.23 – 0.18 ∆ θ m = 0.05 ∆ θ v = ∆ θm × Bd θ v = 0.05 × 1.3 θ v = ds = dw / θv ds = 2.8 / ds = 43 cm

ج- آب قابل استفاده تا عمق 30 سانتيمتري وقتي رطوبت در ظرفيت زراعي باشد چقدر است؟ dw = θv × ds dw = θm. Bd × ds dw = (θmfc – θmpwp). Bd × ds dw = (0.23 – 0.09) × 1.3 × 30 dw = 5.47 cm

تانسيومتر

کار گذاشتن تانسيومتر سطح خاک عمق خاک خاک نرم

در هر رطوبت وزني ميزان مکش را در تانسيومتر قرائت مي کنيم و يک سري اطلاعات بدست مي آوريم 30% وزني رطوبت مکش 1 بار 20% وزني رطوبت مکش 5 بار 10% وزني رطوبت مکش 10 بار 5 منحني مربوط به اطلاعات را زسم مي کنيم رطوبت مکش

نوترون متر نوترون متر از دو قسمت تشکيل شده است : استوانه اي که در آن منبع نوترون سريع وجود دارد دستگاه شمارش نوترون هاي آهسته که تعداد نوترونهاي آهسته متناسب با رطوبت خاک سنجيده مي شود.

The fast neutrons are emitted in all directions, where they collide with atoms in the soil. Through repeated collisions, they are scattered and some lose part of their energy. As the energy is lost, the neutrons are slowed to a speed of about 1.7 miles per second. Neutrons that have been slowed are said to be "thermalized" and are called "slow neutrons." The neutron detector in the neutron moisture meter is designed to ignore fast neutrons and count only thermalized or slow neutrons. The average energy in a collision with another atom is much greater with atoms of low atomic weight than in collisions involving heavier atoms. Hydrogen is the only element with a low atomic weight that is found in significant amounts in typical soils. Hydrogen found in soils is almost entirely in the form of water. The occurrence of hydrogen in water allows for the use of the neutron probe to measure soil water content.

θ v = Rs / Rstd × b-j رطوبت شمارش در خاک Rs شمارش در پارافين Rstd ضريب واسنجي b, j

بلوک گچي الکترود اهم متر

سطح خاک عمق خاک

مقاومت به اهم رطوبت در هر رطوبت وزني مقاومت را در بلوک گچي قرائت مي کنيم و يک سري اطلاعات بدست مي آوريم 30% وزني رطوبت 100 اهم 20% وزني رطوبت 100 اهم 10% وزني رطوبت 500 اهم منحني مربوط به اطلاعات را زسم مي کنيم

کالسکه

1. Size - extremely small 2. Surface area - very large 3. Surface charge (a) most soils = electronegative charge dominates (b) results in ion (cation) adsorption Colloidal Properties

1. Layer silicate clays Types of Colloids

(a) highly weathered soils & coatings (b) some have structure, others poorly structured (c) examples: gibbsite, Al(OH)3; goethite, FeOOH 3-Allophane and other amorphous minerals 2- Hydrous oxides of Fe and Al

(a) highly charged (pH dependant) (b) phenolic and carboxyl OH groups 4. Organic colloids

(a) arid region soils = "basic" cations Ca+2, Mg+2, K+, Na+ (b) humid region soils = "acidic" cations as well Ca+2, Mg+2, H+ and Al+3 (c) strength of adsorption Al+3> Ca+2 = Mg+2 > K+ = NH4+ > Na+ Adsorbed cations

بخش معدني خاک کاني هاي ثانويه(رس) کاني هاي اوليه(شن و سيلت) ساختمان کاني هاي اوليه : O و Si به عنوان سازند گان 75% وزن پوسته ي زمين اساس ساختاري کاني ها مي باشند. مجموعه ي 4اکسيژن و يک سيلسيم يک چهار وجهي بنام تتراهيدرون را به وجود مي آورند.

Si O SiO 4-

O/Si= 4/1 O/Si= 2/1

انواع کاني هاي ثانويه اکسيد هاي مختلف هماتيت گيسبايت حاصل از حاصل از رسوبات شيميايي رسوبات شيميايي پيريتپيريت کربنات کلسبم کاني سيليکاتي کائوليت مونت موريلونيت ايليتايليت ورمي کوليت

C. Layer Silicate Clay Structure- basic building blocks 1. Tetrahedron - SiO4 Sharing of O or OH groups = sheets and unit layers (a) tetrahedral sheet

2. Octahedron - Al(OH)6 octahedral sheet

Tetrahedral and octahedral sheets are often drawn as shown below

1:1 Type Minerals 1. Mostly, kaolinite

Unit layers H-bonded together  "fixed lattice type" no interlayer activity no shrink-swell only external surface 3. Well crystallized (a) little isomorphous substitution low cation adsorption (b) larger particle size (  m) - hexagonal shaped

Type Minerals 1. Expanding lattice (a) Smectite group (mostly, montmorillonite)

(b) Freely expanding  water in interlayer = large shrink-swell  adsorbed cations in interlayer - offset the isomorphous substitution  large internal surface (c) Poorly crystallized  small size  isomorphous substitution = large cation adsorption

Vermiculite ¯ similar to smectites except Al+3 for Si+4 in tetrahedral layer ¯ interlayer ions are more structured (Mg+2 + H2O) = limited expansion ¯ large cation adsorption

Non-expanding lattice (a) Fine-grained micas or illite Al+3 and K+ substitute for Si+4 (tetrahedral sheet) u weathering at edges = release of K+ - very limited expansion - medium cation adsorption - limited internal surface - properties between kaolinite and vermiculite

Chlorites u Mg-octahedral sheet replace K+ of illite u properties similar to illite

Summary of Properties Surface Area (m 2 /g) Interlayer Cation Size (  m) ExternalInternalSpacing (nm)Sorption Kaolinite Smectite< Vermiculite Illite Humuscoatings

Clay Genesis and Distribution 1. Stages of weathering (a) alkali metals and alkaline earths dissolve (Na+, K+, Ca+2, Mg+2) (b) Si dissolves and leaches (c) continual reforming of new clay minerals Clays reflect weathering processes Young, weakly weathered soils = fine-grained mica, chlorite, vermiculite Intermediate weathering = vermiculite, smectite, kaolinite Strong weathering = kaolinite, hydrous oxides