Irrigation Water Quality: Understanding Salinity, Evapotranspiration, and Efficiency
Irrigation Water Quality
Poor water quality affects the water-soil-plant relationship.
Salinity and Water Deficit
Salinity can cause water deficits. High salinity reduces water availability for plants. Salinity is related to the osmotic potential.
Sodium and Soil Sodicity
Free sodium (Na) creates a problem called soil sodicity. With sodicity, the soil structure is lost, and infiltration decreases. An example is the dust on roads, where there is almost no infiltration.
To absorb free sodium, use elements like lime or sulfur. However, this improvement takes approximately 4-5 years.
Characteristics Determining Water Quality
- Total concentration of soluble salts (more salts mean less danger of sodicity)
- Relative concentration of sodium
- Concentration of toxic elements (e.g., excess boron is toxic to plants)
- Total soluble solids concentration
- Presence of seeds, weeds, larvae
- Hardness
Water Classification Graph (RAS) (CE)
There are 16 types of water, ranging from the best (C1S1) to the worst (C4S4) quality.
SAR Calculation:
SAR = Na / √((Ca + Mg) / 2)
- No restrictions: C1S1, C2S1, C1S2, C2S2
- With restrictions: C1S3, C2S3, C3S3, C3S2, C3S1
- Very dangerous: C1S4, C2S4, C3S4, C4S4, C4S3, C4S2, C4S1
Evapotranspiration (ETs): Crop Water Requirements
Evapotranspiration depends on weather conditions and geographical areas. It is dependent on having water in the soil. 99% of the water consumed by the plant is through evapotranspiration, and the other 1% is a component of the crop. It is measured in mm/day.
Evapotranspiration is the combined effect of evaporation of water from moist soil and crop transpiration for active growth (this varies from culture to culture).
Transpiration: Loss of water by the plant through the leaf system.
Frequency of Irrigation
Frequency of irrigation = Net irrigation requirement / Evapotranspiration
What goes in equals what goes out plus what is stored (E = S + storage).
Effective Precipitation
Effective precipitation (Pp effective): This is the part of precipitation that is stored in the soil and absorbed by plants.
Actual Evapotranspiration (ETc)
Actual evapotranspiration (ETc): Crop evapotranspiration is the analysis (ETc = ETo x K) and calculated ETc = F (climate, culture), where temperatures = temperature, RH, wind, radiation.
Potential Evapotranspiration (ETo)
Potential evapotranspiration (ETo): The amount of water transpired and evaporated from a short crop, covering all surfaces in an active state of growth with an adequate and continuous supply of water. Can be determined directly (lysimeter) and indirectly or by empirical methods (Penman, radiation, Blaney-Criddle, Turc, etc.).
K-Factor
K-Factor: A factor related to the water, soil, and groundwater relationship. It is called a soil factor and plant factor (K = Ka x Ks x Kc). Ka and Ks are equal to 1, so K = Kc.
Lysimeter
Lysimeter: A small tool where you grow a vegetable crop, using water (average) and drainage to know the evapotranspiration. (A flower pot can be a lysimeter).
Evaporation Pan (Class A Pan)
Evaporation Pan (Class A Pan): It consists of a galvanized iron cylinder with determined dimensions on a wooden platform. It has water inside, which must be measured every day and at the same time. Evapotranspiration is a measure of surface water.
Furthermore, this method is most appropriate in terms of potential evapotranspiration calculation if appropriate measures are taken. It is the most appropriate since the data were taken in the field and not previously housed.
Kc Calculation
Kc is calculated as: determining crop duration, sowing date, and determining the different stages of cultivation.
Drive Efficiency
Efficiency drive: is a function of bypass flow, slope, roughness, hydraulic radius and permeability of channel
EFC = F (Qd, i, n, R, k, nf)
- Qd = flow (+ caual + lost)
- i = slope (+ slope-lost)
- n = roughness (+ rough + lost)
- R = hydraulic radius (+ radio lost)
- K = permeability (+ permeable + lost)
- Nf = groundwater level (+ high water table-lost)
Implementation Efficiency
Efficiency of implementation:
EFapl = (soil moisture, time, volume of irrigation, furrow length, infiltration, hydraulic resistance, hangs soil)
- Soil moisture = more efficient the more humid
- Less time = higher irrigation efficiency
- Flow-flow irrigation efficiency = +
- Path = + log length-efficiency
- Infiltration infiltration-efficiency = +
- Hydraulic resistance strength-efficiency = +
- Soil is pending slope = + + efficient