Soil, Water and plant relationships

Question 1

Soil Water

Answer 1

soil supporting the structure of the plants
to sustain life
provides a cooling mechanism to maintain a favorable temperature
all the plants have optimal moisture regime

Question 2

Water movement through soil
Infiltration
Permeability of soil

Answer 2

1.infiltration
It is the flow water molecules from the soil through surface to the lower soil structures.
It depends upon the soil structure, moisture content and surface condition, degree of inclination of the soil and plant cover

2.Permeability of soil
property of the soil to transmit water through the soil.
depends upon the soil structure, presence of plant roots, reaction of base exchange and changes in the termperature of the soil

Question 3

Soil Water Classification

Answer 3

1. Gravitational water(excess or surplus water) water that flows through the interstices of the soil structure at gravity pull of 0 to 0.1 atm, this water is not available to the plants.
2. Capillary water( water of cohesion)- it is the water available to the plants after the cessation of downward movement of water at a atmospheric tension of 0.1 to 15 atm. This is water supplies the largest moisture needed by the plants. however the plants do not have access to the water at atmospheric tension of 15 to 30 atm.
3. Hydroscopic water( water of adhesion or hydration) it is the water that is in non liquid form, immobile and not available to the plants. it is a thin film held at 30-10000 atmospheric tension, only when the soil is overn dry it absrobs the exposed saturated water vapour.

Question 4

1. Field capacity
2. permanent wilting point
3. air dried soil
4. oven dried soil

Answer 4

1. field capacity- it the percentages or the property of the soil to retain water against the gravitational force when provided with adequate drainage. soil contains the greatest amount of water available to the soil.
2. permanent wilting point- refers to the water content in the soil at which the plants do not get enough water to meet the demand of transpiration and wilt permanently.
3. air dried soil- when the soil is dried in air under the shade(1000 atm). water is not available to the plants.
4. oven dried soil- when the soil is dried in the oven at 105 degree Celsius at 10000 atm until the sample loses no more water.

Question 5

1. water of crystallization- it is the water held by the mineral soil at atm of 10000.
2. available water
3. non available water

Answer 5

1. it is the water held by the mineral soil at atm of 10000.
2. it is the water between field capacity and the wilting point at a tension of 0.1 to 0.33 to 15 atm which is available to the plants.
3. it occurs at two levels- when the water is beyond the level field capacity held at 0.1 atm( gravitational water) and water content below the level of permanent wilting point.(Hydroscopic water).

Question 6

what are the properties of typical soil for water retention?

Answer 6

it has soil air, soil wedges with macro and micro pores.

Question 7

Soil water retention

what are the characteristics of the soil that influences the water retention .

Answer 7

1. size and amount of pores
   2.structure of the soil
   3.amount and nature of organic and inorganic water coloidal matters
   4, quantity of exchangeable cations
   greater the soil interface and pore space better the the degree of soil water retention.
   fine soil retain more water than Coase soils

Question 8

illustrate and explain the soil-water retention relationship.

Answer 8

the soil water decreases as the tension increases therefore at higher tension the soil water content is low

Question 9

1. how does the soil holds water?
2. maximum water holding capacity
3. determination of water holding capacity?

Answer 9

soil holds the water in two ways
surface tension- it holds as thin film of water on the surface of the individual soil particles
capillary storage - water is stored in the pores of the soil

2.it the water content in the soil when the total pores in the soil are completely filled by water. It is determined by the total numbers of pores present in the soil

3. the water available for the plant growth lies in the moisture range between the field capacity and the permanent wilting point(0.1 to 15 atm)
   moisture at field capacity denotes 100%
   moisture at wilting point is 0%
   expressed in inches per foot or cm per metre depth.

Question 10

water available capacity formula

Answer 10

A.W.C=(F.C-P.W.P)x A.S.G x D
A.W.C-available water capacity
F.C-field capacity
P.W.P=permanent wilting point
A.S.G-  bulk density
D-root depth

Question 11

soil water measurement

importance

Answer 11

proper scheduling of irrigation
estimate amount of water required for irrigation
methods are employed depending on the situation such as
rapidity and accuracy wanted
convenience and availability pf equipment

Question 12

Soil water measurement methods

Answer 12

Gravimetric method
Tensiometric method
Feel or appearance method
electrical resistance method
suction plate apparatus method
pressures plate and pressure membrane plate method
neutron scattering method
immersion method
dielectric method
thermal conductivity method
colorimetric method
chemical method
penetrometric method
air permeability method

Question 13

explain the mechanism of water absorption by plants

Answer 13

plants absorbs water mainly through the root hairs. The roots hairs are in contact with the thin film of water around the soil particles. The cells of the root hairs have permeable cell wall around the vacuole which is semi permeable. As the soil solution is weaker as compared to the solution in the cell sap osmosis occurs therefore water is absorbed through the root hairs. The cells become more turgid losing their osmotic pressure . the cells in the cortex have higher causing the diffusion of water from the root to the cortical cells. gradually the water diffuses deeper into the cortical cells until it reaches the endodermis cells of the roots. this forces the water into the xylem tubes through the passage cells .

Question 14

Water absorption by roots

Answer 14

a young growing tip or cap is the zone of maximum meristematic activity - region of rapid celli elongation, cell differentiation and maturation. swift absorption of water through younger part of the roots immediately basal to the meristematic region. its the area where the root hairs grow extensively. root hairs are protuberance of epidermal cells which large absorbing surface.

Question 15

Pathways of water movement in roots

Answer 15

Apoplast pathway- movement of the water is mainly through the cell membrane without involving any other membrane. majority of water moves through this apoplast pathway.

Symplast pathway. the movement of water from cell to cell through plasmdesmata. plasmodesmata forms a network of cytpplasm connecting cells with one other. The casparian strip separates the cortex and the endodermis membrane. Its composed of wax like substance known as suberin which blocks the entry of water through the cell wall of the endodermis.therefore water is forced through the cell membrane of different cells leading to tansmenbrane pathway.

Transmembrane pathway- water crosses through the plasma membrane entering and exiting through cells. its passes through both the pathways symplast and apoplast .water crosses the tonoplast entering the center vacuole as part of transmembrane pathway.

Question 16

Factors affecting water absorption

Answer 16

atmospheric factor- the rate of transpiration is more when there is high temperature, low humidity, high solar radiation, high winds.

plant factor- root growth, nature of root system,(old young, fibrous and tap root system,
distribution of roots- deep and spreading root have more access to water
soil temperature and soil aeration

soil factor
water available
hydraulic conductivity of soil
soil temperature 
soil aeration
concentration of soil solution.

Question 17

Water absorption processes

Answer 17

Active process-water absorption takes place due to the activities present in the roots. With the help of energy in the form of ATP which is synthesized as a result of respiration in the cells of the roots. the absorption of water takes place against the concentration gradient. the water is absorbed by the roots even when concentration of the cell sap is less than that of the soil water.

Passive process- This absorption takes place by osmosis. when the concentration of the cell sap is greater than that of soil water. Water is absorbed when the transpiration is high or the soil is dry. due to high transpiration rate water is removed and creates water deficit in the cells of transpiring cells reducing the turgor pressure. Due to that effect suction force is extended to the roots xylem. it pulls water from the surrounding to make the water deficit.