Soil Electrical Conductivity: Managing Salts for Sustained High Yields
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Managing salts: Why you should care more Mismanagement of salt applied during irrigation ultimately reduces production—drastically in many cases. Irrigating incorrectly also increases water cost and the energy used to apply it. Understanding the salt balance in the soil and knowing the leaching fraction, or the amount of extra irrigation water that must be applied to maintain acceptable root zone salinity is critical to every irrigation manager’s success. Yet monitoring soil salinity is often poorly understood. Measure EC for consistently high crop yields In this webinar, world-renowned soil physicist Dr. Gaylon Campbell teaches the fundamentals of measuring soil electrical conductivity (EC) and how to use a tool that few people think about—but is absolutely essential for maintaining crop yield and profit. Learn: - The sources of salt in irrigated agriculture - How and why salt affects plants - How salt in soil is measured - How common measurements are related to the amount of salt in soil - How salt affects various plant species - How to perform the calculations needed to know how much water to apply for a given water quality
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Soil Electrical Conductivity: Managing Salts for Sustained High Yields
- 2. SOIL ELECTRICAL CONDUCTIVITY MANAGING SALTS FOR SUSTAINED HIGH YIELDS Gaylon S. Campbell, PhD METER Group, Inc. USA
- 3. THE COST OF SALT IN IRRIGATED AGRICULTURE • Sins of past management practices • Threats to the future • Cost in lost production
- 4. GOLDILOCKS PRINCIPLE Stirzaker’s Goldilocks Principle • Root zone water content - Too fast • Salt in groundwater and rivers - Too slow • Salt concentration near the bottom of the root zone - Just right
- 5. THE PROBLEM • Salts are in all irrigation water • Salts and water enter soil • Water leaves, but salts remain
- 6. ADDITIONAL SALT SOURCES • Fertilizer is applied to crops, some stays • Groundwater also contains salt • Water and salts flow upward from shallow water tables • Water leaves, but salts stay
- 7. HIGH SALT CONCENTRATIONS STRESS PLANTS • Salt concentrates as the soil dries • Total water potential of soil depends on: – Salt concentration (osmotic potential) – Soil matric potential
- 8. CROP SENSITIVITY TO SALT Sensitive Moderately Sensitive Moderately Tolerant Tolerant almond alfalfa olive barley apple broccoli red beet Bermuda grass avocado cabbage ryegrass cotton bean corn safflower date palm carrot cucumber soybean sugar beet grapefruit grape wheat lemon lettuce wheatgrass okra peanut wildrye onion potato orange radish peach rice plum sugarcane strawberry tomato
- 9. CLASSIFICATION OF SALT SENSITIVITY Sensitive Moderately Sensitive Tolerant Sensitive Moderately Sensitive Tolerant Sensitive Moderately Sensitive Tolerant
- 10. SALT CONCENTRATION VS. EC AND OSMOTIC POTENTIAL • Salt in water increases its EC • Salt decreases water availability to plants – More negative osmotic potential
- 11. THREE MEASURES OF EC • Bulk (ECb) – EC measured by in situ sensors • Pore water or soil solution (ECw) – What the plant “sees” • Saturation extract (ECe) – Saturate the soil with distilled water, extract the water, and measure its EC – Directly proportional to the salt content of the soil TEROS 12 Water content, EC, & temp
- 12. 𝑘𝑘𝑔𝑔𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 3 × 𝑚𝑚𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 3 𝑚𝑚𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 3 = 𝑘𝑘𝑔𝑔𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 3 ECw (=ECe at sat.) Water content Salt content × = SATURATION EXTRACT EC (ECE) FUNDAMENTAL PROPERTY OF SOIL
- 13. PROCESSES THAT AFFECT SALT IN SOIL • Redistribution – Water moving to deeper soil depths – Water and salt content change together • Evapotranspiration – Water evaporating from the soil or plant – Water content changes, but salt content stays constant
- 16. WHY IS SOIL EC LOWER THAN WATER EC? Water Saturated Soil Field Capacity 1.Cross section for flow is smaller in soil 2.Flow path is longer in soil ECb = ECw ECb = ECw/3 ECb = ECw/10
- 17. RELATING ECW TO ECB • Pore water EC will always be greater than ECb • At low water content, the multiplier is very large • Water content must be known to determine ECw from ECb • Texture doesn’t play a big role in the relationship • ECe = ECw * saturation VWC
- 18. MAINTAINING SOIL PRODUCTIVITY LEACHING FRACTION • Defined as the ratio of drainage water to applied water – LF = Dd/Di • Can use it to compute drainage required for a particular irrigation water quality – LF = ECi/ECe • If ECi = 0.3 dS/m, and ECe = 3 dS/m, then LF = 0.1 – 10% of the water would need to drain to maintain productivity
- 19. EC OF NATURAL WATERS WESTERN USA River EC (dS/m) Columbia (Wenatchee) 0.15 Snake (Minidoka) 0.41 Sacramento (Tisdale) 0.16 Rio Grande (El Paso) 1.16 Pecos (Carlsbad) 3.21 Colorado (Yuma) 1.06
- 20. THE TOOLS ES-2 Water EC & temp ZL6 Data logger connected to ZENTRA Cloud TEROS 12 Soil water EC & temp
- 21. WHAT WE CAN DO • TEROS 12 measures water content and bulk EC (ECb) • ZENTRA Cloud converts that to pore water EC (ECw) • Water content * ECw = saturation extract EC (ECe) • ECe at bottom of root zone is Stirzaker’s Goldilocks measurement • Gives: – Crop suitability – Crop loss from salinity – Leaching fraction (with irrigation water EC) • ECi = 0.3, ECe = 3, LF = 0.4/4 = 0.1 Sensitive Moderately Sensitive Tolerant
- 22. EC DATA UNDER WHEAT GRACE, IDAHO
- 23. CONCLUSIONS • Mismanagement of salt in irrigated agriculture is costly • Monitoring the saturation extract EC at the bottom of the root zone is “just right” as a long-term management tool for irrigated agriculture • METER has the tools to provide the right measurements for modern irrigators to choose the right crops and manage water sustainably
- 24. QUESTIONS