خصائص التربة وعلاقتها بالمياه

Soil Properties and Their Relationship to Water

• Soil is a complex mixture of solid components (mineral and organic matter) and spaces filled with liquid and gas.
• The spaces between soil particles contain microorganisms (bacteria, fungi, protozoa, insects, and small animals).
• Minerals are the main component of most soils, formed by weathering.
• Organic matter usually makes up less than 5% of soil volume, except in topsoil or organic soils.
• In temperate and semi-arid regions, organic matter content is low due to limited plant cover.
• Clay is the dominant mineral component in these regions, while sand is more prevalent in areas near river basins and deserts.
• Iron and aluminum oxides are common in addition to clay.
• Pore spaces vary between 30-60% and depend on water content; full with water when saturated, filled with air in dry conditions.
• The water content of 40-60% of porosity is typically the field capacity in cultivated land.
• Living plant roots and microorganisms are present in the root zone.
• These organisms decompose organic matter, release nitrogen and other minerals, which are then reabsorbed by the roots.
• Roots consume oxygen and release carbon dioxide, influencing the air in the root zone.

Soil Properties and Their Relationship to Water (cont.)

• Soil texture (particle size distribution) affects soil structure (arrangement of particles).
• Types and amounts of exchangeable ions.
• Amount and characteristics of organic matter in the soil.
• Type of clay minerals and their properties.

Soil and Plant Nutrition

• Plants obtain all nutrients (except carbon) from the soil.
• While over 60 elements are vital for plant growth, only hydrogen (H), oxygen (O), nitrogen (N), and carbon (C) can readily move through the atmosphere.
• Nutrients like phosphorus (P), magnesium (Mg), potassium (K), molybdenum (Mo), calcium (Ca), sulfur (S), and chlorine (Cl) must be present in the soil near plant roots for uptake.
• Nutrient movement in soil is often limited to a few micrometers, except when carried by soil water (soil solution).
• Plant roots must extend extensively to access these nutrients.

Soil and Water Relationship

• Soil is a heterogeneous mixture of solids, liquids, and gases.
• Soil solution is the direct source of nutrients for terrestrial plant roots.
• Soil solution is generally dilute, so soil's ability to supply nutrients is crucial.
• Nutrient release from solid soil components occurs via:
• Mineral and organic matter dissolution.
• Dissolution of sparingly soluble salts.
• Ion exchange (especially cation exchange) between exchange complex and soil solution.

Soil Water Characteristics

• Soil water occupies pore spaces.
• Soil water affects soil aeration and plant growth.
• Agricultural soil is the top layer of Earth's surface suitable for plant growth, characterized by:
• Adequate depth to cover roots.
• Loose enough to allow water and air movement.
• Ability to retain moisture needed by plants.

Soil Physical Properties

• Soil texture: proportions of sand, silt, and clay.
• Indicates the coarseness or fineness of soil particles.
• Determined via laboratory mechanical analysis.
• Clayey soils are "smooth", sandy soils are "rough", and mixed soils are "medium" or "mixed".
• Soil texture does not determine fertility or salinity, but does affect water-holding capacity and aeration.
• Soil structure: arrangement of primary soil particles into aggregates.
• Affects water movement and infiltration rates, aeration, and soil temperature.

Soil Density

• Bulk density (A): the mass per unit volume of undisturbed soil.
• Influenced by soil texture and structure.
• Important for determining moisture parameters and irrigation needs.
• Bulk density is higher for clayey or silty soils and lower for sandy soils (1-1.6 g/cm³ for clayey/silty soils, 1.2-1.8 g/cm³ for sandy soils).
• Real density (R): the mass per unit volume of solid soil particles.
• Varies based on the mineral composition.
• Organic matter's presence usually decreases real density.

Soil Porosity and Permeability

• Soil porosity (n): proportion of pore space to total soil volume (35-55%).
• Sandy soils typically have lower porosity than clayey soils.
• Soil permeability (k): rate of water movement through soil pores due to gravity.
• Dependent on soil texture and structure, and other factors.

Soil Moisture Characteristics

• Field capacity: maximum water content after excess gravitational water drains (0.1-3.0 bars).
• Reached in 2-4 days after irrigation, depending on soil type.
• Represents the maximum water available to plants.
• Wilting point- point where plants start to wilt (permanent and temporary).

Soil Water Classification

• Total available water (TAW): water held between field capacity and wilting point.
• Useful water: water accessible to plants without significant effort.
• Available water = TAW x Extraction Ratio (Ea)
• Extraction Ratio usually ranges between 35-75%.
• Gravitational water: water beyond field capacity, percolates downwards.

Nutrients Role in Plant Growth

• Carbon (C), hydrogen (H), and oxygen (O): constituents of carbohydrates, proteins, and fats, comprising most of a plant's structure.
• Water (H₂O) accounts for >80% of a plant's fresh weight and >90% of its dry weight.
• Nitrogen (N): crucial for vegetative growth. Rich N levels produce dark green leaves but excessive amounts can lead to lodging, delayed maturation, and reduced fruit yield.
• Phosphorus (P): involved in cell division and energy transfer (photosynthesis).
• Potassium (K): involved in respiration and photosynthesis, though its precise mechanism is not fully understood.

Essential Nutrients and Deficiency Symptoms

• Plants obtain essential nutrients from the soil solution.
• Nutrient deficiencies can show up differently throughout the plant.
• Nutrient deficiencies manifest as specific symptoms (depending on the element).

استكشاف خصائص التربة المختلفة وكيف تؤثر على وجود المياه فيها. تتحدث هذا الاختبار عن مكونات التربة، مدى وجود المادة العضوية، والعوامل التي تؤثر على نسبة الماء في التربة. تعرف على العلاقة بين التركيب المعدني للتربة وإمدادات المياه.