Irrigation and Runoff Management Water Quality for Irrigation Soil Salinity and Sodicity Dr. Sharon Benes, Fresno State Franz Niederholzer, UC Farm Advisor fjniederholzer@ucdavis.edu Irrigation and Runoff Management Water Quality for Irrigation Soil Salinity and Sodicity 1
How to measure soil moisture Soil water potential ( in -cbars) or its inverse, *tension (+cbars) or: Soil moisture content ( m or v ) Transpirational Pull moves water into plants and through leaves following the water pressure gradient from small to large pull. 2
Instruments that measure soil water potential ( ) / tension -- tensiometers -- porous block sensors gypsum blocks Watermarks) Tensiometers (soil tension, 0 ~100 cbars) Irrometer Co. Hortau Inc. 3
Porous block sensors, e.g. Watermark (soil tension, 0 - ~200 cbars) Instruments measuring volumetric water content ( v) Neutron probe (access tube, mobile) Capacitance probes -- No access tube: ECH20 -- Access tube, mobile: Diviner -- Access tube, instrument permanently installed, providing continuous monitoring (soil moisture profiles) Enviroscan, Crop Sense (T-tape Int l.) TDR and FDR 4
Neutron probe ( v) Enviroscan -- permanently installed -- continuous monitoring C-probe * w/ telemetry *Same as Enviroscan, but remote access to data 5
Pressure bomb measures plant water status. Irrigation Scheduling Soil moisture sensing and/or Evapotranspiration (ET) estimation, e.g. by CIMIS stations ET = E (evaporation from the soil surface) + T (transpiration (loss of water from plant) 6
Step 1. Irrigation Application Thresholds From Soil Tension Sampling Soil Tension Sand/loamy sand Sandy loam Loam/silt loam Clay loam/clay (entibars) ----------------Depletion of Plant Available Water (%)---------------- 10 0 0 Not fully drained Not fully drained 30 40 25 0 0 50 65 55 10 10 70 75 60 25 20 90 80 65 35 25 110 85 68 40 32 130 87 70 47 38 150 90 73 52 43 170 95 76 55 46 190 98 79 58 49 http://cetehama.ucanr.edu/files/20515.pdf Step 2. How much water to apply? How deep is the root zone? How much water (acre-inch) is 50% of plant available water in each horizon (soil layer)? Add it up Correct for efficiency Apply needed water + efficiency correction 7
CIMIS Weather Station --reference ET (ETo) -- Micrometeorological data -- Temperature -- Wind speed -- Net radiation -- Rain gauge -- other Used to estimate the ET of a well-watered grass under standard conditions Reference (ET o ) from CIMIS Crop coefficient (Kc) specific to the crop & changes as crop cover/canopy s Crop ET (ET c ) estimated as: ET c = ET o x K c * Note: the most effective irrigation scheduling combines soil moisture measurement and calculations of water loss by ET 8
Crop coefficient (Kc) through season. How much water to apply? Et o for the week (or time considered) Kc for crop Et c =Et o X K c Correct for efficiency 9
Water quality for irrigation Soil Salinity and Sodicity 10
Management of Saline & Sodic Soils ANR# 3375 http://anrcatalog.ucdavis.edu FAO #29 http://www.fao.org/docrep/003/t0234e/ T0234E00.HTM Classification of Soils (or water) Salinity (ECe) (ds/m) Sodicity (SAR) ph Physical Condition of Soil Normal <4 <13 <8.5 Normal Saline >4 <13 <8.5 Normal Salinesodic >4 >13 <8.5 Normal Sodic <4 >13 >8.5 Poor 11
Soluble Salt Composition Cations: Sodium, calcium, magnesium Na + Ca 2+ Mg 2+ Anions: Chloride, sulfate, bicarbonate Cl - SO 4 2- HCO 3 - Plus: smaller quantities of potassium & ammonium (cations) & nitrate & carbonate (anions) Commonly analyzed ionic constituents in irrigation water and conversion factor (PPM to meq/l). Symbol PPM / meq per liter* Cations calcium Ca 20 magnesium Mg 12 sodium Na 23 potassium K 39 iron Fe ** manganese Mn ** Anions chloride Cl 35 sulfate SO 4 48 sulfate-sulfur SO 4 -S 16 bicarbonate HCO 3 61 carbonate CO 3 30 nitrate NO 3 62 nitrate-nitrogen NO 3 -N 14 boron B ** 12
Sources of Soluble Salts Soil minerals (marine parent material) Irrigation water Fertilizers & Soil Amendments Shallow ground water ---------------------------------------------------- Climate Low precip and high temps (precip/evap. < 1) Evaporation moves water (& salts) to soil surface, esp. in the presence of shallow GW Texture Westside San Joaquin Valley Soils: Marine sediments (salts, B, Se) 13
Net import of salt to westside SJV in irrigation water = 40 railroad cars daily Effect on Plant Growth Osmotic effect Salts lower the soil water potential more difficult for plants to extract water from the soil. ~Immediate Specific ion effect (Na + or Cl - toxicity) Accumulation over time foliar injury. Less toxicity with calcium and sulfate salts 14
Salinity effects on plants: osmotic Salinity effects on plants: specific ion (Na +, Cl - ) 15
Management options to impacts of soil salinity Choose more salt tolerant crop (Maas Hoffman tables) Manipulate planting position -- plant on edges of bed for furrow-irrigated -- plant along drip line for drip-irrigated. -- Salinity is lower near the water source Reclaim the soil (leaching) Maas Hoffman Salinity Tolerance Tables 16
Changing planting position to salinity impact Raised bed, furrow-irrigated: plant on shoulders of bed no yes Sprinkler irrigation Leaching: -- Apply extra irrigation water to push salts below the root zone, e.g. pre-plant -- Winter rains 17
Pre-plant leaching in the Imperial Valley Leaching Requirement (LR) LR = minimum amount of water, in excess of irrigation requirement, needed to to leach salts through a water-saturated soil and ensure proper salt balance. Expressed as the fraction* of the water needed to wet the soil (bring to FC) that must be applied additionally. *So LR is a number between 0 and 1. 18
Leaching Requirement LR = EC w X 100 Where: (5 X EC e *) EC w ECw = irrigation water salinity ECe = soil salinity that your crop can tolerate (from MH salinity tolerance tables) Example: irrigating with 1.4 ds/m water, tomato crop requires 36 in. of water, threshold soil salinty (ECe) from MH tables is 2.5 ds/m 1) LR = EC w X 100 (5 X EC e ) EC w = 1.4 X 100 = 0.126 (5 X 2.5) - 1.4 2) Total water needed (AW): AW = ET 1 LR = 36 in. = 41 in. (1040 mm) 1 0.126 19
Colloquial term: alkali Sodicity Problem: sodium disperses clays! Degrades soil structure Dispersed clay particles move with water into soil macropores and clog them. Water penetration slows & sealing (crusting) of soil surface Water ponds; cannot leach to a sufficient depth Poor aeration affects root growth & uptake Sodium Dispersion of Clays Ca 2+ (or O.M.) Na + Calcium (left) overcomes repulsion between negative charges on clays, aggregrating them and building soil structure. Weakly attracted sodium ions (Na+) enlarge the distance between colloids and repulsive forces keep clay particles dispersed. 20
SAR indicates the hazard that soil colloids will disperse. Likelihood of infiltration problems --High SAR greater hazard For a given SAR, dispersion will be greater as the ph s (and less as salinity s) SAR* = [Na+] * *Concs. are in meq/l [Ca ++ + Mg ++ ] * 2 SAR vs. ESP ESP = Exchangeable Sodium Percentage (Ex Na/CEC)*100 Critical value for definition of sodic conditions = 15 ESP used in calculation of Gypsum requirement SAR = Sodium Adsorption Ratio Critical value for definition of sodic conditions = 13 Used in Ayers & Westcott (FAO 29) infiltration hazard determination (graph in next slides) 21
Reclaiming saline-sodic & sodic Soils If SAR > 10-13, soil has excess sodium and susceptible to clay dispersion poor infiltration 1) Establish internal drainage. 2) Replace excess exchangeable sodium with calcium -- gypsum most commonly used -- can use soil sulfur, if free lime (CaCO 3 ) present in soil 3) Leach the displaced sodium. Soil Amendments Inorganic - adjust soil ph or chemistry Lime raise soil ph (for acidic soils) Sulfur lower soil ph (for alkaline soils) or to liberate native Ca Gypsum improve structure/infiltration (sodic soils, or low Ca soils) Organic add nutrients, build soil structure Compost Manure 22
Irrigation Water Quality Ayers & Westcot, FAO Agricultural & Drainage Paper #29 http://www.fao.org/docrep/003/t0234e/t0234e00.htm Irrigation water constituents that pose a clogging risk in irrigation systems Potential problem. Physical suspended solids (clay, etc.) Units None Degree of restriction on use Slight to moderate Severe PPM < 50 50-100 > 100 Chemical iron PPM < 0.1 0.1-1.5 > 1.5 manganese PPM < 0.1 0.1-1.5 > 1.5 bicarbonate meq/liter < 1.0 1.0-4.0 > 4.0 23
Water Quality Guidelines (Salinity & Sodicity) Irrigation water quality guidelines regarding sodium and chloride concentration; values are PPM (= mg/l). Specific ion Sodium No restriction Degree of restriction on use Slight or moderate Trees, vines and other sensitive crops Severe Surface irrigation < 70 70-200 > 200 Sprinkler irrigation < 70 < 70 Vegetables Sprinkler irrigation < 115 115-460 > 460 Chloride Trees, vines and other sensitive crops Surface irrigation < 140 140-350 > 350 Sprinkler irrigation < 100 > 100 Vegetables Sprinkler irrigation < 175 175-700 > 700 24
SAR and salinity (EC w ) influence the infiltrability of water Irrigation water SAR and EC influence infiltration. Likelihood of water infiltration problems Irrigation water SAR unlikely when EC w is more than likely when EC w is less than 0-3 0.6 0.3 3-6 1.0 0.4 6-12 2.0 0.5 12-20 3.0 1.0 20-40 5.0 2.0 25
Water Quality Guidelines (Toxic Ion) 26