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Questions and Answers
Considering the relationships between soil volume components, which scenario would result in the highest porosity?
Considering the relationships between soil volume components, which scenario would result in the highest porosity?
- High volume of soil particles ($V_s$) with minimal air ($V_a$) and water ($V_w$).
- High volumes of air ($V_a$) and water ($V_w$) with a low volume of soil particles ($V_s$). (correct)
- Equal distribution of air ($V_a$), water ($V_w$), and soil particles ($V_s$).
- Predominantly water ($V_w$) with trace amounts of air ($V_a$) and soil particles ($V_s$).
A soil sample has a dry weight of 800 g and a total volume of 500 $cm^3$. If the particle density is 2.65 g/$cm^3$, what can be inferred regarding the soil's pore space and its potential impact on water infiltration?
A soil sample has a dry weight of 800 g and a total volume of 500 $cm^3$. If the particle density is 2.65 g/$cm^3$, what can be inferred regarding the soil's pore space and its potential impact on water infiltration?
- High pore space, potentially leading to excessive water infiltration.
- Adequate pore space, allowing moderate water infiltration.
- Insufficient information to determine pore space or water infiltration potential.
- Low pore space, hindering water infiltration. (correct)
Under what conditions would the apparent specific gravity ($A_s$) of a soil be approximately equal to its real specific gravity ($R_s$)?
Under what conditions would the apparent specific gravity ($A_s$) of a soil be approximately equal to its real specific gravity ($R_s$)?
- When the porosity of the soil approaches zero. (correct)
- When the soil is completely saturated.
- When the soil is completely dry and devoid of organic matter.
- When the bulk density of the soil equals the density of pure water.
A farmer is considering two irrigation methods: applying 5 cm of water using a high-efficiency drip system or applying the same amount using flood irrigation. How would the depth of water present in the soil ($d_w$) differ between these methods, assuming equal soil characteristics and root zone depth?
A farmer is considering two irrigation methods: applying 5 cm of water using a high-efficiency drip system or applying the same amount using flood irrigation. How would the depth of water present in the soil ($d_w$) differ between these methods, assuming equal soil characteristics and root zone depth?
Given two soils, one with a high clay content and another with a high sand content, how would their infiltration rates typically compare under similar conditions, and what implications would this have for irrigation management?
Given two soils, one with a high clay content and another with a high sand content, how would their infiltration rates typically compare under similar conditions, and what implications would this have for irrigation management?
A soil has a field capacity of 28% and a permanent wilting point of 12%. If the readily available moisture (RAM) is approximately 75% of the available moisture, what percentage of the total soil moisture is considered readily available for plant uptake?
A soil has a field capacity of 28% and a permanent wilting point of 12%. If the readily available moisture (RAM) is approximately 75% of the available moisture, what percentage of the total soil moisture is considered readily available for plant uptake?
What is the primary distinction between water conveyance efficiency and water application efficiency in irrigation systems, and why is understanding this distinction important for effective water management?
What is the primary distinction between water conveyance efficiency and water application efficiency in irrigation systems, and why is understanding this distinction important for effective water management?
A farmer is deciding between furrow irrigation and sprinkler irrigation for a field with varied topography. What key factor related to the field's topography should most influence this decision, and why?
A farmer is deciding between furrow irrigation and sprinkler irrigation for a field with varied topography. What key factor related to the field's topography should most influence this decision, and why?
In the context of irrigation canal design, how does the diversion water requirement differ from the farm water requirement, and what considerations are essential when calculating each?
In the context of irrigation canal design, how does the diversion water requirement differ from the farm water requirement, and what considerations are essential when calculating each?
When designing a sprinkler irrigation system for a sloped field, what considerations must be taken into account regarding the pressure or head ($H_n$) required at the junction of the lateral and the water main?
When designing a sprinkler irrigation system for a sloped field, what considerations must be taken into account regarding the pressure or head ($H_n$) required at the junction of the lateral and the water main?
Flashcards
Irrigation
Irrigation
Applying water to soil to aid plant growth, supplementing rainfall through man-made systems.
Drainage
Drainage
Removing surplus water from soil to improve growing conditions.
Soil Texture
Soil Texture
Proportion of sand, silt, and clay particles in soil.
Soil Structure
Soil Structure
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Porosity
Porosity
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Bulk Density
Bulk Density
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Water Conveyance Efficiency
Water Conveyance Efficiency
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Evapotranspiration
Evapotranspiration
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Communal Irrigation System (CIS)
Communal Irrigation System (CIS)
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Interception or Cross-slope System
Interception or Cross-slope System
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Study Notes
Introduction to Farm Irrigation and Drainage
- Irrigation is the process of applying water to soil to facilitate plant growth where rainfall is insufficient
- It involves controlled water application via man-made systems
- Drainage is the removal of excess water from the soil to promote favorable conditions for crop growth
Objective of Farm Irrigation and Drainage
- Knowledge of farm irrigation and drainage helps understand the relationship between crops, irrigation amount, and timing
Basic Soil and Water Relations
- In a soil system:
- VT = Va + Vw + Vs, where:
- VT = total volume
- Va = volume of air
- Vw = volume of water
- Vs = volume of solid particles
- Vv = Va + Vw
- WT = Wa + Ww + Ws, where:
- WT = total weight
- Wa = weight of air (negligible, assumed 0)
- Ww = weight of water
- Ws = weight of solids
- VT = Va + Vw + Vs, where:
Soil System Properties Defined
- Soil Texture: relative proportion of sand, silt, and clay
- Soil Structure: arrangement of soil particles into units or peds
- Porosity (n): ratio of void volume to total soil volume (unitless)
- n = Vv/VT = (Va + Vw)/VT = Vs/VT
- Moisture Contents (unitless):
- Dry weight basis (mcw): ratio of water weight to dry soil weight
- Volume basis (mcv): ratio of water volume to total soil volume
- mcv = Vw/VT
- Densities (g/cm3, kg/m3):
- Bulk density (ρB): ratio of dry soil weight to total soil volume
- ρB = Ws/VT
- Particle density (ρP): ratio of dry soil weight to soil particle volume
- ρP = Ws/Vs
- Bulk density (ρB): ratio of dry soil weight to total soil volume
- Specific Gravities (unitless):
- Apparent Specific Gravity (As): ratio of soil bulk density to water density; also the ratio of soil weight to the weight of water
- As= ρB/ρw = Ws/ρwVT
- Real Specific Gravity (Rs): ratio of particle density to water density; also the ratio of soil weight to the weight of water
- Rs = ρP/ρw = Ws/ρwVs
- Apparent Specific Gravity (As): ratio of soil bulk density to water density; also the ratio of soil weight to the weight of water
- Depth of water (mm, cm, m, inch):
- Present in soil (dw): equivalent depth of water in the soil. dw = mcv x D, or dw = mcw x As x D
- D: depth of crop root zone or soil column
- Needed (dwn): to increase moisture content from initial (mci) to final (mcf) value
- dwn = (mcvf – mcvi) x D
- dwn = (mcwf - mcwi) x As x D
- mcvf: final soil volumetric moisture content
- mcvi: initial soil volumetric moisture content
- mcwf: final soil moisture content on dry weight basis
- mcwi: initial soil volumetric on dry weight basis
- Present in soil (dw): equivalent depth of water in the soil. dw = mcv x D, or dw = mcw x As x D
Volume of Irrigation Water
- The volume of water must be applied to increase soil moisture content from an initial to a final value (units: liters, cm3, m3)
- Equation:
- Viw = dwn x A
- A: area of land for consideration
- Notes: Density of water pw = 1 g/cm3 or 1,000 kg/m3. mcv = mcw x As
- As = Rs (1 - n)
Infiltration Rate
- The time rate at which water percolates into the soil (empirical equations):
- Lewis-Kostiakov Equation:
- F = ctα
- ft = dF/dt = αctα-1
- F: cumulative infiltration (mm)
- t: cumulative time
- c, α: constants
- ft: instantaneous infiltration (mm/hr or mm/min)
- Horton's Equation:
- ft = fc + (f0 - fc)e-kt
- ft: instantaneous infiltration at time t
- fc: final or ultimate constant infiltration capacity
- f0: initial infiltration rate at the beginning of rain or a chosen moment constant
- Philip's Method:
- F = st1/2 + At
- ft = dF/dt = (s t-1/2)/2 + A
- F: cumulative infiltration (mm)
- ft: instantaneous infiltration (mm/hr or mm/min)
- s: soil sorptivity
- A: soil parameter depending on the ability of the soil to transmit water
- Lewis-Kostiakov Equation:
Intake Rate and Permeability
- Intake Rate - the rate of infiltration from a furrow into the soil.
- Permeability is the velocity of flow into soil caused by a unit hydraulic gradient, where the driving force equals one kilogram of water per kilogram.
Soil Moisture Constants
- Saturation Point: soil profile holds the maximum water when all pore spaces are filled.
- Field Capacity:
- The amount of water a soil profile can hold against gravity after a thorough wetting, typically measured 24-48 hours after
- The moisture content of the soil when gravitational water has been removed
- Soil moisture tension ranges from 1/10 to 1/3 atmosphere.
- Permanent Wilting Point (or wilting coefficient):
- Soil moisture content at which plants permanently wilt
- Soil moisture tension is about 15 atmospheres
- Permanent wilting percentage estimated by dividing field capacity by a factor between 2.0 to 2.4, value higher for soils with higher silt
- Available Moisture (AM): difference in moisture content between field capacity and permanent wilting point.
- Readily Available Moisture (RAM): portion of available moisture easily extracted by plants; approximately 75% of available moisture.
- Computation of Moisture Content:
- mc: amount of moisture present in the soil
- mc = FC – (% AM used) x (FC – PWP)
- mc = PWP + (% AM retained) x (FC – PWP)
- mc: amount of moisture present in the soil
Irrigation Efficiencies
- Water Conveyance Efficiency: ratio (%) of water delivered to the farm to water diverted from source
- Water Application Efficiency: ratio (%) of water stored in root zone during irrigation to water delivered to the farm
- Water-use Efficiency: ratio of water beneficially used on the project, farm, or field to the amount delivered (expressed in percent)
- Water Storage Efficiency: ratio (%) of water stored in the root zone during irrigation to the water needed in the root zone prior to irrigation
- Consumptive Use Efficiency: ratio of normal consumptive use of water to the net amount of water depleted from the root zone soil
Pump Irrigation Key Concepts
- Water horsepower: power to lift a given quantity of water each second to specific height.
- Brake Horsepower: equals water horsepower divided by pump efficiency.
- Static Head:
- Elevation difference between water surface at intake and discharge in open systems
- In groundwater, it's between the water surface in the well and the discharge canal
- Total Dynamic Head: sum of static head, pressure head, velocity head and friction head.
- Drawdown: elevation difference between the groundwater table and the water inside the well during pumping.
- Characteristic Curve: interrelations between speed, head discharge and horsepower of pump.
- Specific Speed expresses the relationship between speed (rpm), discharge (gpm), and head (feet).
Irrigation Principles
- Evapotranspiration: sum of transpiration and water evaporated from soil or plant surfaces, equivalent to consumptive use.
- Transpiration: process where water vapor escapes from living plants and Enters the atmosphere.
- Canal Capacity:
- Dependable stream flow divided by diversion water requirement
- Formula: service area(ha) = dependable streamflow (m³/s) / diversionwaterrequirement (m³/s ha)
- Canal Capacity (Q): dictated by total area canal serves and the area water requirement
- Formula: Q (m³/s) = area (ha) x water requirement (m³/s-ha)
Leaching Requirement
- Fraction of irrigation water that must be leached to control soil's salinity
- LR = Ddw / (Diw + Drw) = EC(iw + rw) / ECdw
Where:
- Ddw = depth of drainage water
- Diw = depth of irrigation water
- Drw = depth of rain water
- EC(iw+rw) = weighted average electrical conductivity of irrigation and rain water
- EC(iw + rw) = (Diw x ECiw + Drw x ECrw)/(Diw + Drw)
- ECiw - electrical conductivity of irrigation water
- ECiw- electrical conductivity of rain water
- ECdw- electrical conductivity of drainage water
Crop Water and Irrigation Water Requirement
-
Crop Water Requirement (CWR) is the amount of water needed for both consumptive and non-consumptive demands during the entire growth.
- Non-consumptive uses depend of crop , soil, climate, techniques including seepage and percolation losses
- Seepage is the lateral movement of water along the soil
- Percolation is the downward flow.
- Consumptive uses include evapotranspiration ie. evaporation and transpiration lumped together
- Non-consumptive uses depend of crop , soil, climate, techniques including seepage and percolation losses
-
Irrigation Water Requirement (IWR) is the amount of water needed to be applied to the field as irrigation, calculated as:
- IWR = CWR - ER
- ER is the effective rainfall.
Farm and Diversion Water Requirement
-
Farm Water Requirement (FWR): From tertiary canal to field losses are incurred
- Computated with application (ea) efficiency in consideration
- ea = Qin / Qout = (water entering canal) / (water entering canal + S + P + E)
- Qin = water entering tertiary canal. Qout = water exiting tertiary canal or water entering field -S = seepage losses. P = percolation losses. E is evaporation losses
- ea = Qin / Qout = (water entering canal) / (water entering canal + S + P + E)
- The design farm water requirement can be computed with the equation: FWR = IWR / ea
- Computated with application (ea) efficiency in consideration
-
Diversion Water Requirement (DWR): To account for conveyance losses from the main system to the tertiary canals, the DWR consideres conveyance efficiency - ec = Qin / Qout = (water entering main canal) / (water entering main canal + S + P + E) - Qout is water exiting the secondary canal, or the water entering the tertiary channel - S = seepage losses, P= percolation losses, E = evaporation losses
- DWR = FWR / ec
Modes and Methods of Irrigation
-
Modes of Irrigation:
- National Irrigation Systems (NIS): large service areas, managed by government
- Communal Irrigation Systems (CIS): managed by farmers' groups
- Shallow Tubewell Irrigation Systems (STW): Individual owned/operated pipes set in ground to extract ground water used for irrigation
-
Methods of Irrigation:
- Overhead: moistens soil similarly to rainfall:
- Watering can: simplest, for small plots with accessible water source
- Hose pipe: requires piped water system with sufficient pressure
- Sprinkler irrigation: uses pressurized water through nozzles.
- Furrows: wets the soil for uniform slopes
- Furrow irrigation: water runs through small channels or furrows
- Corrugation irrigation: small rills or corrugations used for closely spaced crops
- Overhead: moistens soil similarly to rainfall:
Flooding & Drip or Trickle Irrigation
-
Flooding, which wets the entire land surface:
- Ordinary flooding: uses field ditches, but has low efficiency
- Border-strip flooding: fields divided into strips, water advances in a thin sheet
- Level-border or basin irrigation: uses level plots surrounded by dikes
- Contour-ditch irrigation: controls flooding from field by contour ditches
-
Drip or Trickle Irrigation directs water to plant base :
- Emitters discharge 1 to 8 liters per hour delivered via pipelines usually laid on the soil surface or buried
- Has highly efficient water utilization, but it is a very expensive method.
Sub Irrigation and Sprinklers
- Sub-irrigation supplies water from soil underneath, keeps root zone free of excess water
- Sprinklers need head computations for a Sprinkler Irrigation System. Calculated as:
- Hn = Ho + Hf ± He + Hrp
- where
- Hn = pressure/head required at the junction of the lateral and main
- Ho = nozzle pressure at the farthest end of the line
- Hfl = friction head loss in the lateral
- He = elevation difference between the junction with the main and the farthest sprinkler on the lateral
- Hrp = riser height
- The elevation term is negative if located downhill and positive if located uphill.
- where
- Hn = Ho + Hf ± He + Hrp
Friction Head Loss and Pump Head
-
for main lines Hfm = (KsLQ^1.9) / (D^4.9 *statichead (4.10x10^6 )) , where:
- Hfm is the total friction loss (m)
- Ks Scobey’s coefficient of retardation. L length of pipe. Q total discharge in L/s. D in mm
- table is provided for laterals
-
Pump head must determined (total H)
- Ht = Hn + Hfm + Hj + Hs
Drainage
- Drainage: removal of excess water in the soil to create conditions suitable for plant growth.
- improves soil structure
- the productivity of soils
- facilitates early plowing and planting
- lengthens the crop growing season
- increases the depth of root zone soil thereby provides more available soil moisture and food
- improves soil ventilation
- increases water infiltration into soils
- favors growth of soil bacteria
- leaches excess salts from the soil
- Sources/Causes of Excess Water:
- Rainfall, high water table, over-irrigation, runoff/seepage from adjacent farms
- Components of a Drainage System:
- Field drainage system, secondary drains or laterals, outfall, and recipient water
Drainage System Types
- Types of Surface Field Drainage System or Open Drains:
- Bedding: furrows drain to collection ditches. Soil type determines bed width
- Random Ditch: For areas too deep to fill via land leveling
- Interception or Cross-slope: ditches constructed across the slope
- Diversion or Parallel Ditch: suitable on flat soils with depressions
Tile Drains and Impermeable Layers
- Layout of Tile-Drain System or Closed Drains
- Natural System: for small valleys in rolling topography
- Gridiron Layout: for entire areas
- Herringbone Pattern: Submain in depression, laterals join alternately
- Double-main System: use if bottom of depression is wide.
- Intercepting Drain: for hillside drainage
- Arrangement to avoid trees: keep drains away from trees
- Drain Depths and Spacing: for soil underlain by impermeable soil in which groundwater flows horizontally
- R for sandy soils over clay is used to determine flow of drain where ground level table water level is above a drain above the surface
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Description
Learn the basics of farm irrigation and drainage, including the importance of water application and removal for crop growth. Understand soil and water relations, including the components of a soil system and soil texture. Also, explore the key objective of farm irrigation and drainage.
