SCOPE OF PROBLEM SALINITY MANAGEMENT PROBEMS COMMONPLACE IN ARIDLAND SOILS. Important Considerations

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1 SALINITY MANAGEMENT Charles A. Sanchez Yuma Agricultural Center The University of Arizona SCOPE OF PROBLEM Approximately 1/3 of all land worldwide or 70 million ha are made up of saline soils. In the United States approximately 5 million ha in the 17 western states are saline soils. One proposed cause for the decline of the Hohokam civilization in Central Arizona is soil salinization of the Gila River Valley PROBEMS COMMONPLACE IN ARIDLAND SOILS 1. Salinity 2. Sodicity 3. High soil ph (free carbonates) 4. Soil physical problems Important Considerations I. Soil II. Crop(s) III. Irrigation Water IV. Management Page 1

2 I. Soil A. Define Soil Characteristics 1. Chemical Properties 2. Physical Properties Salinity Characterization Electrical conductance in a solution is proportional to solute concentration Therefore,electrical conductivity of saturated soil paste extracts is used to characterize soil salinity. TDS (mg/l)=ec (ds/m) x 640 OP (bars)=ec (ds/m) x 0.36 Saline Soil A non-sodic soil containing sufficient quantities of soluble salts to adversely affect the growth of most crop plants EC > 4.0 ds/m Salinity Effects 1. Osmotic effects 2. Specific Toxicities 3. Nutritional imbalances Page 2

3 SODIUM STATUS OF SOIL 1. Exchangeable sodium percentage (ESP) 2. Exchangeable sodium ratio (ESR) [NaX]/[CaX + MgX] 3. Sodium absorption ratio (SAR) [Na]/[(Ca + Mg)/2] 0.5 Sodic Soil Contains sufficient exchangeable sodium to adversely affect soil structure and crop production. ESP > 15 SAR > 15 Sodic Soils -Dispersed soil particles -Low hydraulic conductivity Soil pore clogging Soil colloid swelling -High soil ph (>9.0) -Dispersed organic matter (black alkali) -Na toxicities Page 3

4 Clay Soils Sensitive to Na ESP of 5 to 10% May reduce infiltration Particularly with good quality water II. Crops to be grown Relative Yield ( % ) Lettuce Cotton Soil Salinity (ds/m) 1. Water Quality 2. Irrigation method IRRIGATION Water Quality EC SAR Presence of toxic ions Cl, B, Na Page 4

5 Bicarbonate Hazard Excess HCO 3 - causes precipitation of CaCO 3 thus increasing the Na hazard (SAR) of irrigation water Calcium Carbonate Precipitation 1. High bicarbonate Ca HCO 3 - > CaCO 3 + H 2 CO 3 >H 2 O + CO 2 2.Ammoniated water NH 3 + H 2 O > NH 4 OH NH 4 OH > NH 4 + OH OH- + HCO 3 > CO 3-2 +H 2 O Ca ++ + CO 3-2 > CaCO 3(s) Page 5

6 LEACHING REQUIRMENT LR=D dw /D iw =EC iw /EC dw Effective use of leaching for management requires drainage Internal drainage-tillage, amendments External drainage-open drains, tile drains The average leaching requirement is attained for most surface irrigation scenarios if drainage is not impeded EC of sprinkler water can increase 4 to 5% inside field and up to 21% on field edges Page 6

7 Soil Amendments and Water Treatments Soil application of amendments are used for initial reclamation and long-term maintenance of soil quality. Rates are often large and based on economics. Water treatments are generally intended to alter the chemistry of irrigation water so that no further degradation in soil quality will occur. Rates used for water treatment are usually small and based on solubility and stoichiometry. Reclamation of Sodium Affected Soil 1. Exchange of sodium H 2 SO 4 + CaCO 3 >Ca +SO 4 +H 2 O +CO 2 Ca NaX > CaX + Na 2. Leach out Na Gypsum (Soil Application) -Primarily serves as Ca source -exchangeable with Na -Serves to flocculate soil particles -bunching of particles together to form stable aggregates -improves soil tilth Response of Lettuce to Gypsum Gypsum Rate (kg/ha) Stat. Marketable Yield (Mg/ha) L* Sulfuric Acid (Soil Application) Forms Gypsum in soils with free carbonates Ca replaces sodium Broadcast application does not reduce ph significantly Directed application can cause ph reduction in localized zone Page 7

8 Water Treatment 1. Control CaCO 3 precipitation. 2. Reduce sodium hazard of water. 3. Reduce ammonia volatilization. 4. Improve water infiltration. Spatial Variability Salts are not uniform across fields Page 8

9 RESULTS SALT MAPPER gps antenna EM 38-DD Comparison of Resolution between Grid and EM 38-DD methods EM 38-DD data (ESAP) estimated an average salinity in 0-30 cm depth as 5.05 ds/m. Grid data estimate for same depth ds/m. Note that grid method did not capture majority of elevated levels on the east side of the field and underestimated average was 4.09 salinity by about 1 ds/m. Computer platformgps control box Retractable Tube EM 38-DD Data and cm depths Page 9