Nutrition of Horticultural Crops Measurements for Irrigation Lincoln Zotarelli Horticultural Sciences Department University of Florida Spring 2015
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)
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
07/0
5
07/1
2
07/1
9
07/2
6
08/0
2
08/0
9
08/1
6
08/2
3
08/3
0
09/0
6
09/1
3
09/2
0
09/2
7
Soil v
olum
etric
wat
er co
nten
t (m
3 m-3
)
0.0
0.1
0.2
0.3
0.4
Rainf
all (m
m)
0
5
10
15
20
25
30
35
40
45
50
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 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.
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
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
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
10
15
20
25
30
35
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00
Tem
pera
ture
(C)
Time (h)
Temperature (°C)
Min Temp (°C) Max Temp (°C)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00
MJ m
-2 h
-1
Time (h)
Solar Radiation RS (MJ m-2 h-1)
0
1
2
3
4
5
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00
m/s
Time (h)
Wind speed Aver Wind Speed (m s-1)
0.28
0.24
0.20
0.16
0.12
0.08
0.04
0.00
0.028
0.024
0.020
0.016
0.012
0.008
0.004
0.00
inch/day inch/h
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/)