Irrigation and Drainage Flashcards
Knowledge on farm irrigation and drainage will equip the individual with the understanding of the relation between crops and the amount and timing of both irrigation and drainage.
the relative proportion of primary particles (sand, silt and clay) in the soil
Soil Texture
the arrangements of primary particles in the soil into units or peds
Soil Structure
the ratio of the void volume to the total soil volume (unitless)
Porosity (n)
the ratio of the weight of water to the dry weight of the soil
Moisture content on a dry weight basis (mcw)
the ratio of the volume of water to the total soil volume
Moisture content on a volume basis or volumetric moisture content (mcv)
the ratio of the dry weight of the soil to the total soil volume
Bulk density
the ratio of the dry weight of the soil to the volume of the soil particles
Particle density
– ratio of the bulk density of the soil with the density of water; it is the ratio of the weight of soil to the weight of water with volume equal to the total soil volume
Apparent Specific Gravity (As)
ratio of the particle density of the soil with the density of water; it is the ratio of the weight of soil to the weight of water with volume equal to the volume of the soil particles alone
Real Specific Gravity (Rs)
the equivalent depth of water in the soil at a given condition
Depth of water present in the soil
Requred to increase the moisture content from an initial value (mci) to a final value (mcf)
Depth of water needed
volume of water to be applied to increase a the soil moisture content from an initial to final value (units: liters, cm3, m3)
Volume of irrigation water (Viw)
Value of the density of water, ρw
1 g/cm3 or 1,000 kg/m3
the time rate at which water will percolate into the soil and can be expressed in terms of the following empirical equations
Infiltration Rate
the amount of water the soil profile will hold when all its pore spaces are filled up with water
Saturation Point
(1) the amount of water a soil profile will hold against drainage by gravity at a specified time (usually from 24 to 48 hours) after a thorough wetting. (2) the moisture content of the soil when gravitational water has been removed (after irrigation by flooding). It is usually determined few days after irrigation. The soil moisture tension at this point is normally between 1/10 to 1/3 atmosphere.
Field Capacity
the soil moisture content when plants permanently wilt. The soil moisture tension at this point is about 15 atmospheres. Permanent wilting percentage can be estimated by dividing the field capacity by a factor ranging form 2.0 top 2.4, with the value higher for soils with higher silt content.
Permanent Wilting Point (or wilting coefficient)
the difference in moisture content of the soil between field capacity and the permanent wilting point.
Available Moisture (AM)
that portion of the available moisture that is most easily extracted by plants; this is approximately 75% of the available moisture.
Readily Available Moisture (RAM)
the ratio between the water delivered to the farm and the water diverted from a river or reservoir expressed in percent.
Water Conveyance Efficiency
the ratio between water stored in the soil root zone during irrigation and the water delivered to the farm expressed in percent.
Water Application Efficiency
the ratio of water beneficially used on the project, farm or field to the amount of water delivered to the farm expressed in percent.
Water-use Efficiency
the ratio of water stored in the root zone during the irrigation to the water needed in the root zone prior to irrigation, expressed in percent.
Water Storage Efficiency
the ratio of the normal consumptive use of water to the net amount of water depleted from the root zone soil.
Consumptive Use Efficiency
- the power theoretically required to lift a given quantity of water each second to specified height.
Water horsepower
water horsepower divided by pump efficiency, in decimal.
Brake Horsepower
- the difference in elevation of the water surface in a pond, lake, or river from which pumped water is taken, and the water surface of the discharge canal into which the water flows from a submerged discharged pipe. In pumping from groundwater source, static head is the difference in elevation between the water surface in the well and the water surface of the discharged canal.
Static Head
the sum of total static head, pressure head, velocity head and friction head.
Total Dynamic Head
(in a well) is the difference in elevation between the groundwater table and the water surface at the well when pumping.
Drawdown