Nutrition of Horticultural Crops Measurements for Irrigation

Lincoln Zotarelli Horticultural Sciences Department

University of Florida Spring 2015

Principles of plant nutrition • Principle 1. Plants take up 13 essential elements from the

soil in the form of charged particles • Principle 2. The most important element in plant

nutrition is the one that is limiting growth • Principle 3. No correlation exists between PRESENCE in

the soil and AVAILABILITY for uptake • Principle 4. Relative amounts of nutrients are as

important as absolute quantities • Principle 5. Water plays a central role in fertilizer issues,

as a solvent and as a nutrient carrier within and below the root zone

It should be considered:

• Soil properties • Atmospheric conditions • Crop needs • Characteristics of the irrigation

system

http://home.howstuffworks.com/irrigation.htm/printable

Irrigation

Effect of soil texture and soil tension on soil water availability

Kramer and Boyer (1995)

Low water holding capacity: Little water is stored in the root zone.

Florida’s sandy soils

Soil moisture estimation by feel ftp://ftp-fc.sc.egov.usda.gov/MT/www/technical/soilmoist.pdf

Effect of soil texture and soil tension on soil water availability

Actual soil moisture on sandy soils Saturation Field Capacity Wilting Point

VWC > 30% VWC > 0.3 in3/in3

-1 cbar

-0.001 MPa

VWC approx. 12% VWC > 0.12 in3/in3

-10 cbar

-0.01 MPa

VWC approx. 6% VWC > 0.06 in3/in3

-1500 cbar -1.5 MPa

Tensiometers. Changes in moisture in

a porous cup in equilibrium with the soil can be expressed in changes in air pressure inside the cup.

Soil water tension measuring tools

Methodology: Every other week (5 inches deep)

Practical example: Strawberry

More water is applied than what plants use because of leaching, evaporation, inefficient application, and an inadequate ability to assess water requirements on a daily basis.

Time Domain Reflectometry (TDR) The soil dielectric constant is proportional to soil moisture

http://edis.ifas.ufl.edu/ae266

soil volumetric water content in the soil profile

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Soil v

olum

etric

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er co

nten

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3 m-3

)

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all (m

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5 cm15 cm30 cm45 cm60 cmprecipitation (mm)

Strawberry early and total yield. 2009-10 Season.

Irrigation Programs Early Yield Total Yield Volume Frequency gal/100 ft/week (cycles/day) (ton/acre) (ton/acre)

100 1

5.2 23.8 200 5.4 24.9 300 5.2 23.1 100 2 5.4 23.3 200 5.6 25.3 300 5.1 24.1

Significance (P<0.05) NS NS

efficient water use will help strawberry growers to maximize crop production and water savings.

It is difficult to visualize water movement in the soil

Lakeland fine sand:

-<10% WHC -<1% OM

8 hr @2 x 300L/100m/hr Water front: 60 cm

T0-1h T0-2h

T0-4h T0-8h

It should be considered:

• Soil properties • Evapotranspiration and crop needs • Characteristics of the irrigation

system

http://home.howstuffworks.com/irrigation.htm/printable

Irrigation

Evapotranspiration • Water transpired by plants and

the evaporation from soil surface combined.

• Occur simultaneously and there is no easy way of distinguishing between the two processes.

• Normally expressed in millimetres (mm) per unit time.

• ET rates which range from < 0.10 during the winter to over 0.18 inches/day during the summer.

http://www.cimis.water.ca.gov/cimis/infoEtoOverview.jsp

Florida Rainfall & ET (in.)

012345678

JanFeb

MarApr

MayJun

JulAug

SepOct

NovDec

Monthly Potential ET Monthly Rainfall

Crop evapotranspiration under standard conditions (ETc)

• The evaporating demand from crops that are grown in large fields

• Under optimum soil and water • Excellent management and

environmental conditions • And achieve full production under

the given climatic conditions.

http://www.resimsite.com/img196.htm

US Weather Bureau Pan Evaporation Method

• The evaporation rate from pans filled with water is

easily obtained. • In the absence of rain, the amount of water

evaporated during a period (mm/day) corresponds with the decrease in water depth in that period.

• Pans provide a measurement of the integrated effect of radiation, wind, temperature and humidity on the evaporation from an open water surface.

Class A pan • Is circular, 120.7 cm in diameter and 25 cm deep. • Made of galvanized iron (22 gauge) or Monel metal (0.8 mm). • Is mounted on a wooden open frame platform which is 15 cm

above ground level.

Class A pan

• Pans should be protected by fences to keep animals from drinking.

• It must be located in the center of a 20 x 20 m2 actively growing grassy area.

Ep from Class A evaporation pan

How reference ET is calculated

ETo = reference evapotranspiration rate (mm d-1), T = mean air temperature (oC), u2 = wind speed (m s-1) at 2 m above the ground. es

o = mean saturated vapor pressure (kPa) computed as the mean eo at the daily minimum and maximum air temperature (oC), ea = mean daily ambient vapor pressure (kPa) and Δ= slope of the saturated vapor pressure curve [ δeo/ δT, where eo = saturated vapor pressure (kPa) and Rn = net radiation flux (MJ m-2 d-1), G = sensible heat flux into the soil (MJ m-2d-1), γ = psychrometric constant(kPa oC-1), and Ea = vapor transport of flux (mm d-1).

Evapotranspiration during the day

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21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00

Time (h)

Evapotranspiration (inches)

ET0 (mm h-1)

ET0 cum(mm h-1)

inch/h inch/day

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ture

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Temperature (°C)

Min Temp (°C) Max Temp (°C)

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m/s

Time (h)

Wind speed Aver Wind Speed (m s-1)

0.28

0.24

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0.00

inch/day inch/h

FAWN weather stations

Crop coefficient: Kc

Crop water use (ETc) is related to ETo by a crop coefficient (Kc) which is the ratio of ETc to the reference value Eto Crop water requirement = Reference evapotranspiration x Crop coefficient

• ET provides reference measure of water use based on plant water demand

• Scalable for specific crop, growth stage, climate, and season of year

• ETc = ETo * Kc

Crop Evapotranspiration

• Table 7 pg 25

Vegetable Production Handbook for Florida: Chapter 3: Principles and Practices of Irrigation Management for Vegetables.

Crop water requirements: water needs for evapotranspiration (ET) and plant growth, and depend on crop development and climatic factors. Irrigation requirements: determined by crop water requirements, but also by the characteristics of the irrigation system, management practices and the soil characteristics.

Crop water requirements and irrigation system water requirements

Sample calculation: Overhead irrigation

• We grow potato with a center-pivot • Our pan indicated= 24-hr ETo of 0.32 inch • The Kc of potato = 0.70 • We can calculate ETc as: ETc = Kc x Ep ETc = 0.70 x 0.32 = 0.224 inch We will apply 0.224 x 27,150 = 6082 gallons/acre

Sample calculation: Drip-irrigated crops

• We grow peppers on 6-ft centers

• Our pan indicates 0.20 in 24-hr Ep

• We need to convert vertical amounts of water into gallons/100ft.

• How?

http://www.hort.purdue.edu/ext/senior/vegetabl/pepper1.htm

Example: PEPPER LBF for 6-foot centers: 43,560 ft2/6 = 7,260 LBF /acre

Lateral water movement from the drip line is about 8 inches on each side

The total wetted width in the bed is then 16 inches or 1.33 feet

The wetted area of the field: 1.33 ft every 6 ft or 22% of the field

The total irrigated area is then only (7,260 ft)*(1.33 ft)= 9,583 sq ft 1 acre inch = 27,150 gallons of water

So, 0.1 inch of water applied over the entire field corresponds to 2,715 gallons

We only wet 22% of the field

Hence, 0.1 inch applied via drip corresponds to 597 gallons

http://www.hort.purdue.edu/ext/senior/vegetabl/pepper1.htm

Sample calculation: Drip-irrigated crops

• We need to convert vertical amounts of water into gallons/100ft.

• How? • ETc= Kc x ETo x Fraction of wetted acre-inch • ETc = 1.25 x 0.20 x 27,150 x 0.22 = 1,493 gallons/Acre = 1,493/72.60 = 21 gal/100ft • If overhead: ETc = 1.25 x 0.20 x 27,150 = 6,687 gallons/Acre

References • Food and Agriculture Org. (FAO) Pub.56

http://www.fao.org/docrep/X0490E/x0490e00.htm

• VPH –Chapter 8, pp. 33-40 • BMP manual, BMPs 36 to 48, pp. 136 • FAWN

http://fawn.ifas.ufl.edu/)