AGRI 608 UNIT 2
is the pathway of water moving from soil through the plant-animals to the atmosphere. It is a concept recognizing that the field with all of its components (soil, plant, animals and the ambient atmosphere taken together) constitute a physically integrated, dynamic system in which the various flow processes involving energy and matter occur simultaneously and independently like links in the chain. This continuum hypothesis characterizes the state of water in different components of the SPAC as expression of the energy level or water potential of each.
The Soil-Plant-Atmosphere Continuum (SPAC)
is used for transpiration carrier of nutrients from the soil to green plant tissues.
Water
Water forms over ___ of the plant body by green or fresh weight basis.
90%
Plants can synthesis food through __& only in the presence of water in their system.
photosynthesis
is essential in hydraulic process in the plant.
Water
Importance of Water
nutrients are absorb by plants in their ionic form
Universal Solvent
Importance of Water
during water uptake in plants
Nutrient Carrier
Importance of Water
heat energy absorbed by the soil may cause the soil temperature to rise
Stabilizes the soil temperature
Importance of Water
cell division particularly cell enlargement and cell turgor
For growth
Importance of Water
1. Universal Solvent
2. Nutrient carrier
3. Nutrient in itself
4. Stabilizes the soil temperature
5. For the physiological functions of plants
6. For growth
Major Functions of Water in the Plants
gases, minerals and other solutes may enter the cell
Solvent
Major Functions of Water in the Plants
may act as reactant in hydrolysis and photosynthesis
Reagent
Major Functions of Water in the Plants
cells would collapse with the loss of water
Maintain turgidity of the cells
1. Major component of the protoplasm
2. Solvent
3. Reagent
4. Maintain turgidity of the cells
5.Stabilizes the temperature of the plant at physiological level
Major Functions of Water in the Plants
Properties of Water
moment a chemical property which is an indication of the turning force which a given field could insert in a molecule
High dipole moment
Properties of Water
is a measure of its ability to reduce the intensity of an external electric field. Ability to store energy
High dielectric constant
Properties of Water
the amount of heat that is necessary to raise the temperature of 1 gram of water by 1°C.
High specific heat
Properties of Water
amount of energy necessary to change the water from liquid to vapor form
high heat of vegetation
Properties of Water
is a physical phenomenon at liquid-air interface
High surface tension
1. Ability to form hydrogen bond
2. Liquid at ordinary room temperature
3. High dipole moment
4. High dielectric constant
5. High specific heat
6. High heat of vegetation
7. High surface tension
Properties of Water
___ is a substrate for plants to grow in. ____ provides support, nutrients, and a network of water and air to the plant's roots. Plants can grow without ___ , but they will need structures to support them, the correct amount of water and air to their roots, and ample nutrients.
Soil
includes the following:
1. The capacity of the soil to hold water and still be well-drained;
2. The flow characteristics of water in the soil;
3. The physical properties of the soil matrix, including the organic matter content, soil depth, soil texture and soil structure
4. Chemical properties including the translocation and concentration of soluble salts and nutrients due to the movement, use and evaporation of the soil water.
The soil characteristics that are of particular importance to irrigated agriculture
Soil texture and structure influence the intermolecular forces and suction of water in unsaturated soils. These forces can be quite substantial and include the capillary and attractive forces resulting from the close contact of soil particles. Soil structure greatly influences the porosity and distribution of pore sizes, and thereby the permeability of the soils to air, water and roots, which is as important to crop growth as an adequate supply of nutrients.
Irrigation practices are influence by the degree of root proliferation since the water supply available to the plant is limited to the soil volume explored in the crops root system. Different crops have different root growth patterns, hence different moisture extraction pattern. A shallow-rooted crop will require more frequent irrigation than will a deep-wide-rooted crop in the same soil.
Physical Properties of Soil
The proportion of the different sizes of particles making up a soil determines its texture. The primary soil texture sizes, as measured by the effective particle diameter, are designed by textural groups as gravel, sand, silt and clay. In general, sandy soils are classed as coarse-textured soils, loam soils as medium-textured, and clay soils as fine-textured.
Soil Texture
high water-holding capacity, low intake rate
Clay
medium level
Silt
low water-holding capacity, high intake rate
Sand
the time rate at which water will percolate into the soil
Infiltration rate
infiltration occurs under a particular soil surface configuration
The capacity of the soil to retain moisture will influence factors such as soil aeration ( the amount of air in the soil after irrigation), the amount of water available for crop use and hence the necessary amount and timing of irrigation and how much water remain in the soil as sensitive crop begin to wilt but more drought tolerant crop can continue to grow.
Intake rate
Soil structure refers to the grouping or arrangement of the soil particles. It describes the gross, overall combination or arrangement of the primary soil separates into secondary grouping called aggregates.. The particles of coarse-grained soils tend to function as individuals, while the aggregated particles of fine-textured soils tend to form granules. The size and shape of these particle groups and their stability is defined as the soil structure.
Structure signifies shape, size, arrangement and durability of aggregates in their natural occurrence.
Soil Structure
Structure signifies shape, size, arrangement and durability of aggregates in their natural occurrence. It reflects the internal soil architecture which include pore spaces. From the agronomic standpoint, soil structure affects plant growth through its influence on the following:
1. infiltration
2. percolation
3. retention of water and
4. mechanical impedance to root growth
Fundamentally ________ is developed by wetting and drying, freezing and thawing, and combination of these conditions.
soil structure
The primary function of _________ in the soil is to add stability to soil aggregates and serve as cushion against the effects of tillage.
organic matter
The existence of _____ assures a desirable soil structure. Favorable soil structure is recognized as the key to soil fertility.
granules
1. Very Fine 2. Fine 3. Medium 4. Coarse 5. Very Coarse
Classes
Types:
Includes rounded complexes that lie loosely and are readily shaken apart. Characteristics of many surface soils especially those with high in organic matter and are especially prominent in grassland. The only type of aggregation that are commonly influenced by practical method of soil management.
1. Spheroidal ( granular and crumb)
Types:
Aggregates are arranged in relatively thin horizontal plates, leaflets or lenses.
Platelike (Platy)
Types:
Characterized by vertically oriented aggregates or pillars which vary in length with different soils.
Prismlike (Prismatic and columnar subtype)
Types:
The original aggregates had been reduced to blocks, irregularly six-faced, with their three dimensions more or less equal.
Blocklike (Blocky and sub-angular blocky type)
Since ______ can influence infiltration, or the intake rate of the soil it thereby affects the design and selection of the farm irrigation system. The intake rate of the soil can be a controlling factor in length of runs and sizes of borders for surface irrigation methods, as well as the permissible application rates for sprinkler and trickle systems to prevent run-off and erosion.
Soil Structure
A favorable structure implies that the soil has:
its pore spaces dominated by the medium and large pores;
Relatively high porosity
Relatively high porosity its pore spaces dominated by the medium and large pores;
high hydraulic conductivity and air permeability with aggregates of medium and large sizes;
that the above condition persist or are stable after the action of water and/or manipulation of soil.
A favorable structure implies that the soil has:
Particle density ( ρp ) is the dry weight of the soil per unit volume of the soil solids alone.
Particle Density and Real Specific Gravity
Bulk density (ρb ) refers to the ratio of the mass of dry soil or dry weight of soil to its bulk or total volume.
Bulk Density and Apparent Specific Gravity