Water Relations

Water management• Citrus trees water-conserving plants

• Root hydraulic conductivity (Lp) is low

• Lp is positively correlated with root temperature

(Fig 4.1)

• Young leaves are more likely to wilt than mature leaves

• High VPD leads to decrease in stomatal conductance and reduce water loss from the leaf.

Water Stress

• As temp. increases and RH decreases during the day, VPD increases

• SC, transpiration and NCA increases (Fig 5.3)

• Mid morning- Mid day: maximum SC, NCA

• > 30C reduce SC and reduce RuBisco activity

• Water stress is greatest in high VPD

Water Stress• Manifestation: cessation of growth, leaf wilting or

decrease in stomatal conductance (SC), net CO2 assimilation (NCA) or root conductivity.

• Rootstocks: high in Carrizo than rough lemon

Irrigation

• 3-4 acre feet of water is needed on average / year.

–acre foot = 325,851 gal• Too much water

–O2 depletion

–Phytophthora• Temp. of water is important• Internal drainage is needed

Irrigation• Need to know water holding capacity

–amount /irrigation–Frequency of irrigation

• How to know when the trees needs water

–look at soil moisture status–look at status of water

•Pressure bomb–Estimate ET

•Use pan

Guidelines for estimating soil moisture level by “feel” Contd.

% ofmoistureremaining

Sandy loam Sandyclayloam

Clay loams

25 Dry, will not forma ball whensqueezed

Crumblybut forma ball

soil issomewhatpliable

Guidelines for estimating soil moisture level by “feel” Contd.

% ofmoistureremaining

Sandy loam Sandyclayloam

Clay loams

25-50 will not holdtogether whensqueezed butballs underpressure.

Somewhatpliable

Ribbons out butnot easily.Forms a ball.

Guidelines for estimating soil moisture level by “feel”

% ofmoistureremaining

Sandy loam Sandyclayloam

Clayloams

50-75 Forms a ballthat breaks

verypliable.Slickfeeling.

Ribbonsout veryeasilybetween fingers.Slickfeeling.Contd.

Guidelines for estimating soil moisture level by “feel”

% ofmoistureremaining

Sandy loam Sandyclayloam

Clayloams

75-(Fieldcapacity)

Soil ball leavesa wet outlineon a hand butno free watercan besqueezed out.

Same Same

Contd.

Irrigation• Need to know water holding capacity

–amount /irrigation–Frequency of irrigation

• How to know when the trees needs water

–look at soil moisture status–look at status of water

•Pressure bomb–Estimate ET

•Use pan

Water Use (inches/day) Grapefruit, Navels,Valencia, Pineappleorange

‘Marrs’Orange

Summer (June- Sept.) 0.17 0.14 - 0.16

Spring (March - May &Fall & Oct. - Nov.)

0.10 - 0.16 0.08 - 0.13

Winter (Dec. - Feb.) 0.05-0.08 0.05 - 0.07 1 inch / acre =27, 158 gal of water, Weigand & Swanson, 1982 &Swietlik, 1992.

Evapotranspiration (ET)

ET = Class A X 0.7 X A X 27,158

Class A Pan = Daily evaporation from Class A pan in inches.

A = Area covered by one tree (in acres)

ET = Daily water use in gal / tree.

1 Acre =43,560 sg.ft

Factors to consider when deciding irrigation system

• Source of water

• Topography of grove

–Flood irrigation• high volume needed, good leaching, but

enhances phytophthora

• In young orchards (first 2 years) 12 % of the water amount used for flood irrigation

• Soil water capacity

Factors to consider when deciding irrigation system

• Water quality

–should the orchard be established?

ppm total salts

200-400 Excellent

400-600 good

600-800 fair

1000 + plant something else

Water Quality Considerations• Total Soluble Salts: 1000 ppm -1.5 dS/m

1200 ppm -1.8 dS/m

• Boron Concentrations: 0.5 -0.75 ppm

• Chloirde: < 350 ppm

• Sodium Adsorption Rates (SAR): <8

Water Quality ConsiderationsRio Grande River

• Total Soluble Salts: 770 ppm -1.2 dS/m

• Boron Concentrations: Trace

• Chloride: 160 - 180 ppm

• Sodium Adsorption Rates (SAR): 3- 4

Factors to consider when deciding irrigation system

• Method

–Furrow • Need flat grove and uniform soil

• permanent furrows vs cultivation

• length

• slope

• labor intensive

Factors to consider when deciding irrigation system

–Sprinklers• permanent

• high vol… ground level or overheardOver head- requires good water qualitycan cool treeswashes trees (dust vs mites)

• Drag line systemspashing water vs phytophthora

Factors to consider when deciding irrigation system

–Drip System (low volume sprinkler)

–Problems• Salts build up… need winter rains to leach

• Soil type vs soil mass wet vs # needed / tree

• minimize weed growth

• Drip- when trees are small

• microjet -once trees are large

Microirrigation• Microsprinklers Drip

– 10 % of the amount of water used in young orchards

– 80% of the amount of water used in mature orchards

• Strip Irrigation– 50 % saving of water in young orchards

compared to flood

– Possibility of strip irrigating mature orchards as well

Scheduling Flood Irrigation (winter)

• Trees will extract water mostly from the top 4 ft layer.

• 1 ft of soil holds 2” of available water.

• Irrigations are scheduled when 60% of available water is depleted from the soil.

• 1 Irrigation supplies 6” water

Scheduling Flood Irrigation winter (contd.)

• with 60 % depletion of available water

• 1 ft of soil can hold 2” X 0.6=1.2‘‘ of water

• 6’’ irrigation will wet 6/1.2 = 5 ft of soil

• 20 % of water percolates below the root system

winter

• In winter, grapefruit orchard uses 0.08“ of water / day.

• with 60% depletion, then there is 4 ft X 1.2“ = 4.8 of water to be used before the next scheduled irrigation.

• 4.8 “/0.08 = 60 days is the interval between irrigations.

Summer

• In summer, grapefruit orchard uses 0.18“ of water / day.

• with 60% depletion, then there is 4 ft X 1.2“ = 4.8 of water to be used before the next scheduled irrigation.

• 4.8“/0.18 = 27 days is the interval between irrigations.

Summer (Contd.)

• with 60 % depletion of available water

• 1 ft of soil can hold 2” X 0.6=1.2‘‘ of water

• 6’’ irrigation will wet 6/1.2 = 5 ft of soil

• 20 % of water percolates below the root system

Scheduling Drip Irrigation

INT = S X AW X 0.623

IrS = Soil water storage capacity at 25 %

depletion in inches

Aw = area wetted with emmitters (sq. ft /tree)

Ir = Irrigation amount (gal / tree / day)

Soil water storage capacity at 25 % water depletion

Depth of the rootingzone (ft)

Storage capacity (inches)

1.0 0.4

1.5 0.6

2.0 0.8

3.0 1.2

4.0 1.6

Tree Canopy Diameter (ft)

Month 2-3 4-6 8 10 18Jan. 0.5 0.7 1.5 2.6 4Feb. 0.6 0.8 1.8 3.3 5March 0.9 1.2 2.7 4.8 8April 1.1 1.5 3.5 6.1 10May 1.3 1.8 3.9 7.0 11June 1.3 1.8 4.1 7.2 11

Contd.

Daily water needs of drip- irrigated citrus trees

Tree Canopy Diameter (ft)

Month 2-3 4-6 8 10 18July 1.5 2.1 4.7 8.3 13Aug. 1.5 2.1 4.7 8.3 13Sept. 1.1 1.5 3.3 5.9 9Oct. 0.9 1.2 2.7 4.8 8Nov. 0.6 0.9 2.0 3.5 6Dec. 0.5 0.7 1.5 2.6 4

Daily water needs of drip- irrigated citrus trees

Tons /Acre

Age Year Drip Flood7 1980 7.0a 8.7 a

8 1981 28.6a 24.7b

9 1982 18.1b 21.8a

Spacing 14 X 24 (129 trees /Acre)

Ruby Red on Mercedes Clay