Managing Salinity in Walnuts. Janet Caprile Farm Advisor UC Cooperative Extension Contra Costa & Alameda Counties

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1 Managing Salinity in Walnuts Janet Caprile Farm Advisor UC Cooperative Extension Contra Costa & Alameda Counties Quad County Walnut Institute Stockton - March 6, 2014

2 Higher Salinity in 2014? Surface waters Reduced runoff -> higher salt load Reduced supply -> use well water Well water Often higher in salts

3 Where do they come from? Salts are found in all irrigation waters Mineralization of soils Fertilizers Manures and composts Salts can accumulate in root zone and damage crops

4 What salts are in the water? Sodium (Na + ) Calcium (Ca 2+ ) Magnesium (Mg 2+ ) Chloride (Cl - ) Sulfate (SO 2-4 ) Bicarbonate (HCO 3- ) Cations Anions Boron (B), Carbonate (CO 3 2- ), Nitrate (NO 3- ), Potassium (K + )

5 How is salinity measured? Electrical Conductivity (EC) ECw = salinity of the water ECe = salinity of the soil The units: ds/m = mmhos/cm us/cm = 1000 x ds/m Total Dissolved Solids (TDS) mg/l = ppm

6 How does salt effect walnuts? 1. Overall salinity EC (ds/m) 2. Specific ion toxicity Sodium (Na) Chloride (Cl) Boron (B)

7 How does salt effect walnuts? Overall salinity High salt restricts osmotic flow uses more energy to exclude salt in the root zone and take in water Symptoms: water stress Less growth Lower yields root membrane Soil water low salt concentration Root cell hi solute concentration

8 The overall osmotic effect is stunting of plant growth salinity Non-stressed crop Salt-stressed crop

9 Tree Salt Tolerance Peach Average Rootzone Salinity (ECe) Maas and Grattan 1999

10 How much salt is too much? Source of Salinity Salt Effects on Yield EC (ds/m) None Increasing Severe Soil/Rootzone (ECe) < >4.8 Irrigation Water (ECw) < >3.2 What does Increasing Effect mean For irrigation water: (assumes full ETc + 15% LF) 1.5 ~ 10% yield reduction 1.9 ~ 25 % yield reduction 2.8 ~ 50% reduction

11 ECw (us/cm) ECw varies over the season Clifton Court /18/10 11/18/10 12/18/10 01/18/11 03/18/11 02/18/11 04/18/11 05/18/11 06/18/11 07/18/11 08/18/11 09/18/11 10/18/11 11/18/11 12/18/11 01/18/12 02/18/12 03/18/12 04/18/12 05/18/12 06/18/12 07/18/12 08/18/12 09/18/12 10/18/12 11/18/12 12/18/12 01/18/13 03/18/13 02/18/13 04/18/13 05/18/13 06/18/13 07/18/13 08/18/13 09/18/13 10/18/13 11/18/13

12 Specific Ion toxicity Boron (B), Chloride (Cl) and sodium (Na)

13 Specific Ion Toxicity (Na, Cl, B) Normal plant nutrients Accumulate in the wood & leaves Interfere with normal cellular processes Reduced photosynthesis Roots can regulate uptake Rootstocks vary in regulation ability

14 Salt Tolerance of Walnut Rootstocks BLACK PARADOX ENGLISH

15 Salt Tolerance of Walnut Rootstocks Leaf Analysis ROOTSTOCK Boron (ppm) Chloride (%) Sodium (ppm) Black 480 b 0.7 c 56 b Paradox 667 a 1.8 b 87 b English 704 a 2.1 a 125 a Excess Level

16 Salt Tolerance of Walnut Rootstocks BLACK ENGLISH PARADOX

17 Salinity Management Apply more water! Leach salts below root zone Apply the full crop water use (ETc) Apply an additional 15-20% leaching fraction Many years the rainfall provides the leaching fraction! More frequent in-season irrigations Keep the upper root zone wetter - it will be easier for the tree to extract water and exclude the salt Apply fertilizer modestly (they are salts!)

18 Salinity distribution in relation to various leaching fractions ET Same irrigation water ECw Soil Depth Low LF 40% 30% 20% High LF 10% ECe

19 Resources UC Drought Management website UC ANR publications Agriculture Salinity & Drainage ($25) Irrigation Water Salinity & Crop Production (free)

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21 Water infiltration Electrical Conductivity (ECw) Low EC -> poor water infiltration Sodium Absorption Ratio (SAR) High SAR -> poor water infiltration SAR = Na + Ca 2+ + Mg 2+ 2 Concentrations are in meq/l

22 35 30 Severe Reduction in Infiltration Slight to Moderate Reduction in Infiltration Sodium Adsorption Ratio No Reduction in Infiltration 5 0 Ideal zone EC of Irrigation W ater (ds/m)

23 How much salt is too much? Salt Effects EC (ds/m) None Increasing Severe Soil (ECe) < >4.8 Water (ECw) < >3.2 What does Increasing Effect mean Soil : every 1 ds/m over 1.5 reduces yield by ~ 20% 2.5 = 20% reduction 3.5 = 40 % reduction 4.5 = 60% reduction

24 Therefore the same average rootzone ECe can result with different ECw s and different LFs. ET ECw = 0.7 ECw = % Soil Depth Low LF 30% 20% High LF 10% ECe

25 Tolerance to ion toxicity is generally controlled by the rootstock Ion Ion excluded by rootstock Sensitive rootstock readily absorbs ion and transports it to the shoot Tolerant rootstock Sensitive rootstock