Tree water use and irrigation 1) Consider a rose plant growing in a pot 2) OK, now consider a peach tree growing in a really big pot Peach Lysimeter weight loss over 3 days in May, 1991 100 4.5 66 F, 40% RH Lysimeter weight units 95 90 5.5 70 F, 40% RH 6.0 79 F, 30% RH 85 May 2 May 3 May 4 Date, 1991 1
100 Peach Lysimeter weight loss over 3 days in May, 1991 0.6 Rule #1: trees use a lot of water - Why they do and what happens when they run short we will discuss a little later. Weight units or rate of weight loss 95 90 85 0.4 0.2 0 Rule #2: water comes from the soil and mostly goes into the air - The soil and roots are complex, but for now we will just think of the soil as a reservoir or bank account of water that the plant can draw from. May 2 May 3 May 4 Date, 1991 Rule #1: trees use a lot of water - Why they do and what happens when they run short we will discuss a little later. Rule #2: water comes from the soil and mostly goes into the air - The soil and roots are complex, but for now we will just think of the soil as a reservoir or bank account of water that the plant can draw from. - The air includes the influence of temperature, humidity, sunshine, and wind. Hotter and drier generally means more water loss. Rule #3: We call orchard water loss ET (evapotranspiration) and in CA, use the ET of turfgrass (ET o ) to measure the effects of temperature, sunshine, and wind. ET 0 Reference ET (turf) (From CIMIS) www.cimis.water.ca.gov 2
Example of ET o and ET c for a bean canopy: ET c = ET o K c Canopy establishment (K c increasing) Full canopy (K c stable) Canopy senescence (K c declining) ET (Grass) Loss (inches/day) ET (Beans) Bean Irrigations (Light) (Normal) (Harvest) A couple of useful irrigation related websites Calculating Irrigation Needs for Your Orchard http://www.cimis.water.ca.gov/ Example: Almond orchard in Davis, CA. 12 X24 spacing, 1 microsprinkler per tree at 10 gal per hour (gph). http://www.wateright.org/ Question: how many hours run time per day in mid June (week of 6/14)? 3
ET o K c Tree Row http://www.wateright.org/ (A note at the bottom of the schedule): IMPORTANT! Users ABSOLUTELY need to verify plant health and/or soil moisture level. 4
A tensiometer: one of the many gadgets useful for measuring soil water What is the goal of irrigation management? 1) Supply the evapotranspiration (ET) need of the plant? 2) Keep the soil at an optimal water content? 3) Keep the soil at an optimal water tension? No: Your goal is to get the plant to do what you want it to do! A simple question of resource application: If I apply this much water, now, will I get a beneficial tree response (yield, nut quality, tree growth, etc.) now or later? Forest Gump principle: Stress is as stress does. If you want to know whether a tree is under stress, then irrigate it. If it gives a beneficial response, then it was under stress. If not, it wasn t. Either that, or it was, but there was nothing you could do about it. Almonds after one season s growth (1991, Winters, CA). Irrigated with about 50% of ET 5
Almonds after one season s growth (1991, Winters, CA). Irrigated with about 100% of ET Almonds after one season s growth (1991, Winters, CA). Irrigated with about 300% of ET Forest Gump principle: Stress is as stress does. Overview: plants and water If you want to know whether a tree is under stress, then irrigate it. If it gives a beneficial response, then it was under stress. For young orchards: filling the space quickly has great economic benefits, so growth is a beneficial response. For mature orchards: the space is already filled, so excessive growth is not a beneficial response. So, we need to understand how plants respond to water availability and water stress. 6
2/25/2014 Open stomata on a leaf surface (100 microns) Overview: plants suck Salisbury & Ross, Plant Physiology (1992) 7
2/25/2014 Rule #1: trees suck, big time Open stomata on a leaf surface - The root has to suck harder than the soil in order to get water out of the soil. The trunk harder than the roots, the scaffolds harder than the trunk etc, so the most suction is in the leaves. Rule #2: The suction can become strong enough to suck water right out of the cells - Wilting/flagging. Rule #2: Plants aren t dumb - If there isn t enough water they reduce their demand, but this also means they reduce their production of sugars. One way of reducing demand is to close stomata, but defoliation and reduced vegetative growth are others. (100 microns) Closed stomata on a leaf surface (100 microns) Generalized plant responses to water limited conditions Bradford and Hsiao, 1982, Encyclopedia of Plant Physiology. 12B:263-324. 8
If stress is as stress does, then how do you measure Some suggested measures of stress: stress in time for an appropriate irrigation response? Type Measurement Advantages and disadvantages Direct (plant) Indirect ET (calculated) Soil moisture WYND ET (measured) Sap flow Growth (trunk, stem, fruit, etc.) Canopy temperature Canopy spectra Water tension (water potential) Relatively simple math, but only gets you in the ballpark. Good for planning ahead. Exhibits a lot of spatial variability which sensor is correct? Easy, if you trust you neighbors judgment. A relatively new technology. Need to know how much ET to expect in order to interpret the data. Gives relative values, so you need to know how much flow to expect in order to interpret the data. Gives relative values, so you need to know how much growth to expect in order to interpret the data. Gives relative values, so you need to know what temperature to expect in order to interpret the data. Gives relative values, so you need to know what readings to expect in order to interpret the data. Absolute values can be interpreted, but not reliably automated at the present time, so you need to go to the orchard, collect and keep track of data. 7 6 Relation of plant transpiration to soil water content in field corn (1962) 7 6 Relation of plant transpiration to soil water content in field corn (1962) Plant ET (mm/day) 5 4 3 2 Medium day Plant ET (mm/day) 5 4 3 2 Medium day 1 1 Humid day 0 20 25 30 35 (PWP) (FC) Soil Volumetric Water Content (%) 0 20 25 30 35 (PWP) (FC) Soil Volumetric Water Content (%) Denmead and Shaw (1962) Availability of soil water to plants as affected by soil moisture content and meteorological conditions. Agron. J. 54: 385-390 Denmead and Shaw (1962) Availability of soil water to plants as affected by soil moisture content and meteorological conditions. Agron. J. 54: 385-390 9
Plant ET (mm/day) Relation of plant transpiration to soil water content in field corn (1962) 7 6 Dry day 5 4 Medium day 3 2 Humid day 1 Pressure chamber method for measuring water stress Like measuring the blood pressure of the plant 0 20 25 30 35 (PWP) (FC) Soil Volumetric Water Content (%) Denmead and Shaw (1962) Availability of soil water to plants as affected by soil moisture content and meteorological conditions. Agron. J. 54: 385-390 Stem Water Potential (SWP) 10
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Resources to help with the pressure chamber (NOTE ON UNITS: -10 BARS = -1 MPa = -145 psi) 12
Almonds, one seasons growth: Dry treatment: average SWP about -15 bars(-1.5 MPa) Almonds, one seasons growth: Medium treatment: average SWP about -12 bars (-1.2 MPa) Almonds, one seasons growth: Wet treatment: average SWP about -8 bars (-0.8 MPa) Baseline values of midday SWP (Bar) under various air temperature and RH conditions for Prune and Almond Air Air RH (%) Temperature (F) 20 40 60 70-6.5-5.9-5.3 80-7.5-6.6-5.8 90-8.7-7.6-6.4 100-10.4-8.8-7.2 110-12.6-10.4-8.3 13
Stem Water Potential (Bar) 0-5 -10-15 -20-25 Almond Irrigation Experiment WINTERS, CA TREATMENT WET MED DRY (Baseline) JUNE JULY AUGUST SEPT OCT Date, 1991 Stomartal conductance (mmol m -2 s -1 ) Midday SWP (MPa) 0-1 -2-3 600 500 400 300 200 100 0 Midday SWP Almond irrigation study Midday stomatal opening (conductance, g s ) TREATMENT (BASELINE) MAY JUNE JULY AUGUST SEPTEMBER OCTOBER Date, 1993 WET MEDIUM DRY TREATMENT WET MEDIUM DRY Stomatal conductance (mmol m -2 s -1 ) Trunk cross-sectional area (cm 2 ) 400 300 200 100 60 50 40 30 20 10 Average midday g s and SWP, 1993 Almond irrigation study Tree size (trunk cross-section), 1993, and SWP (1991 1993) SYMBOL TREATMENT WET MED DRY -2.0-1.5-1.0-0.5 Average midday SWP (MPa) Relative Water Use (Actual Kc/Model Kc) Johnson et al. 2005. Peach ET response to SWP in a lysimeter 1.4 1.2 1 0.8 0.6 y = 0.0557x + 1.3538 R 2 = 0.8107 0.4-15 -10-5 0 SWP (Bar) 14
Walnut canopy development effects Using water stress to set terminal buds in cherry Percent Terminal Bud Set Stem Water Potential (MPa) 0-1 -2-3 100 80 60 40 20 0 SWP % Set APR (Mahaleb) Early Stress (Colt) Early Stress Mid- Stress MAY JUNE JULY AUGUST SEPT Date, 1992 Mid- Stress Control Control Resources to help with the pressure chamber New baseline website: http://informatics.plantsciences.ucdavis.edu/brooke_jacobs/index.php Resources to help with the pressure chamber New baseline website: http://informatics.plantsciences.ucdavis.edu/brooke_jacobs/index.php 15
So many responses, so little time RDI: Regulated Deficit Irrigation Concept: Mild to moderate levels of water stress, at the correct time, may benefit horticultural crop production or quality, or at least save water without reducing production or quality. Bradford and Hsiao, 1982, Encyclopedia of Plant Physiology. 12B:263-324. Almond hull split Proposed benefits of RDI for almonds during hull split: 1) Speed up Hull Split 2) Reduce Hull rot 3) Reduce Sticktights (Improve Harvestability) 4) Save Water SWP recommendation: -14 to -18 bars during hull split 16
5-9-02 % Hull Split, Carmel variety (East/West difference similar in all varieties) WEST (gravel) EAST (silt) East (Average SWP = -8.4 bars) West (Average SWP = -14.1 bars) Date, 2000 10 Aug 16 Aug 22 Aug 31 Aug 6 Sep 14 Sep 0% 0% 5% 13% 32% 40% 4% 23% 60% 83% 85% 91% Problems with uneven hull split timing: - Uncertain timing for hull split spray - Irrigation management problems - Uneven/delayed harvest Starting in 2001, under RDI (east soil), hull split was the same for east and west soils Corning location irrigation summary (RDI) 2001 2003 Date Jul 13 Jul 20 Jul 27 Aug 1 Aug 13 East (silt) 2% 20% 45% 70% 100% West (gravel) 2% 25% 55% 75% 100% Date Jul 29 Aug 7 Aug 15 Aug 22 East (silt) 29% 95% 100% 100% West (gravel) 29% 88% 100% 100% Soil Water applied 2002 2003 2004 Cutoff date Water applied Cutoff date Water applied Very long cutoff/cutback OK on East (silt) soil Cutback date East (silt) 24 10-Jul 14 1-Jul 18 7-Jun West (gravel) 40 25-Aug 41 4-Sep 36 16-Sep ETc 43 40 42 17
5-9-02 WEST (gravel) EAST (silt) West side story Some unfortunate west side trees growing the east side 5-9-02 (Almonds) EXPERIMENTAL PLOT Wy - Wyo loam (East) AvA - Arbuckle gravely loam (West) 18
Four year yield summary (lbs. nutmeats per acre) 4000 Lbs. nutmeats/acre Lassen Land co. (Orland, CA) RDI study Nutmeat yields, 2004-2007 2001 2002 2003 2004 3000 Treatment (2 sites) (7 sites) (7 sites) (7 sites) Grower 2,400 3,170 2,860 2,650 2000 RDI 2,430 3,080 2,660 2,680 1000 CONTROL RDI 0 2004 2005 2006 2007 YEAR Benefits of RDI (mild stress) for almonds during hull split: 1) Speed up Hull Split (use water as a management tool) 2) Reduce Hull rot 3) Reduce Sticktights (Improve Harvestability) 4) Save Water 5) No negative impact on yield Benefits of RDI in Prunes: 1) Increase fruit sugar concentration 2) Decrease fruit water content and drying costs 3) Increase flower density and yield 4) Save Water 19
15 Bartlett pear, fruit soluble solids Bartlett pear, fruit size 200 14 180 IRRIGATION TREATMENT WET Fruit Soluble Solids (%) 13 12 11 10 IRRIGATION TREATMENT WET MED DRY (NW) DRY (SE) 2.0 1.5 1.0 0.5 Mean fruit size (g) 160 140 120 100 80 MED DRY (NW) DRY (SE) 2.0 1.5 1.0 0.5 SWP (MPa), June August, 1994 SWP (MPa), June August, 1994 Drought Study in almonds, 2009 Main questions: 1) How much water does it take for an almond tree to survive? 2) Will application of small amounts of water (5, 10 ) over the season help? Drought Study in almonds, 2009 Treatments applied: Irrigation Treatment Target Canopy modification None 3) Is there a critical level of tree water stress that is necessary to cause tree death or dieback? Location: Nickels soils lab, Arbuckle, CA Single line drip irrigation system (restricted root zone expected) Gravel soil, WHC about 1 /foot Previously demonstrated root water uptake only to about 3 Should be a good place to cause water stress! 0 (rain fed) 5" in-season 10" in-season Control (100% ETc, 40?) 50% reduction once SWP reaches -15 bars 50% reduction + Kaolin spray None Kaolin spray None Kaolin spray None 20
July 21, 2009 Control tree - 9.8 bars SWP July 21, 2009 10 tree - 25 bars SWP July 21, 2009 0 tree - 39 bars SWP July 21, 2009 0 tree - 54 bars SWP 21
This tree had reached -63 bars (913 psi) on July 14, 2009, and by July 28 was completely defoliated. This tree had reached -63 bars (913 psi) on July 14, 2009, and by July 28 was completely defoliated. However, neither it nor any other tree died! Drought Study in almonds, 2009 Yield: The biggest reduction occurred in the year following the stress (i.e. carryover effect) Yield (pounds nutmeats/acre) CONTROL STRESS (BAR) -40 Around -60 Complete defoliation Year 22
Late season water stress in peach: doubled fruit 23
Normal floral meristem development Floral meristem developed under water stress Recap: 1) Trees use a lot of water (ET c ). 2) Water use increases because of canopy growth (until the orchard canopy has filled it s space), and increases or decreases following the weather (ET o ). 3) A ballpark value for irrigation requirement is ET c = K c Et o. 4) Plants have to suck to get their water (SWP). 5) If trees are at baseline SWP, then soil water is not limiting. 6) Stress is as stress does: there are some beneficial plant responses to stress, but most stress responses cause a reduced plant productivity (yield). 7) Severe stress may not kill the tree, but typically will involve both within-season as well as strong carryover effects. Sorry, but there were many issues that were not covered, including such diverse elements as: irrigation system design, salinity effects, flooding stress, root physiology, etc 24