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Publication #AE456

Evapotranspiration-Based Irrigation for Agriculture: Crop Coefficients of Some Commercial Crops in Florida1

Isaya Kisekka, Kati W. Migliaccio, Michael D. Dukes, Jonathan H. Crane, and Bruce Schaffer2

This article is part of a series on ET-based irrigation scheduling for agriculture. The rest of the series can be found at http://edis.ifas.ufl.edu/topic_series_ET-based_irrigation_scheduling_for_agriculture.

Introduction

Data needed to implement evapotranspiration (ET)-based irrigation scheduling for agricultural crops include crop coefficients (Kc). The Kc is used to estimate the crop water requirement (ETc). This publication identifies typical Kc values for some of the crops commonly grown in Florida. The Kc values listed are only intended for use as guidelines in the absence of locally developed, variety-specific Kc values.

Crop Coefficients (Kc)

The Kc integrates the characteristics of the crop that distinguish it from the reference crop (usually a short, green, well-watered crop that completely shades the ground) used to estimate reference ET (ETo). General guidelines on how to obtain ETo data for most areas in Florida can be found in Evapotranspiration-Based Irrigation for Agriculture: Sources of Evapotranspiration Data for Irrigation Scheduling in Florida at http://edis.ifas.ufl.edu/ae455.

The Kc value changes over the growing period for a crop because of changes in the crop characteristics such as ground cover, crop height, and leaf area. For annual crops, the growth period is divided into four stages (i.e., initial stage, crop development, mid-season stage, and late season stage) and Kc values are calculated based on these stages. The initial stage is the period between the planting date and 10% ground cover. The crop development stage refers to the period from 10% ground cover to the initiation of flowering or full cover. The mid-season stage refers to the period between full crop cover and the start of maturity indicated by the aging, yellowing, browning of leaves or leaf drop. The late season stage covers the period between maturity and harvest or full senescence (advanced aging of leaves). For most perennial crops in Florida, growth continues year-round, and the Kc varies by month based on the phenological stage (bloom, fruit set, fruit development, fruit maturation) of the plant and percentage of the ground shaded by the tree canopy (Allen et al. 1998).

There is minimal information about locally adapted Kc values for most crops grown in Florida. If a scientifically developed Kc for a crop exists that is based on local management practices, variety, and environmental conditions, it should be used to generate ETc for estimating net irrigation water requirement. General information on estimating ETc and net irrigation water requirements can be found in Evapotranspiration-Based Irrigation Scheduling for Agriculture at http://edis.ifas.ufl.edu/ae457. However, if locally developed Kc values do not exist, typical values listed in Table 1 and Table 2 may be used as guidelines for crops commonly grown in Florida.

Conclusion

The Kc values listed in this publication can serve as useful guidelines for areas where locally developed Kc values are not available for specific crops or cultivars. These Kc values can be adjusted to meet local management requirements if necessary.

References

Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. “Crop Evapotranspiration – Guidelines for Computing Crop Water Requirements.” FAO Irrigation and Drainage Paper 56. Rome: Food and Agriculture Organization of the United Nations. http://www.fao.org/docrep/X0490E/x0490e00.htm.

De Azevedo, P.V., B.B. da Silva, and V.P.R. da Silva. 2003. “Water Requirements of Irrigated Mango Orchards in Northeast Brazil.” Agricultural Water Management 58(33): 241–254.

Dukes, M.D., L. Zotarelli, G.D. Liu, and E. H. Simonne. 2012. “Principles and Practices of Irrigation Management for Vegetables.” In The Vegetable Production Guide for Florida. SP170. Gainesville: University of Florida Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/pdffiles/cv/cv10700.pdf.

Fares, A. 2008. Water Management Software to Estimate Crop Irrigation Requirements or Consumptive Use Permitting In Hawaii. Honolulu, HI: Department of Land and Natural Resources. http://hawaii.gov/dlnr/cwrm/publishedreports/PR200808.pdf.

Goenaga, R., and H. Irizarry. 2000. “Yield and Quality of Banana Irrigated from Fractions of Class A Pan Evaporation on an Oxisol.” Agron. J. 92:1008–1012.

Kisekka, I., K.W. Migliaccio, M.D. Dukes, B. Schaffer, J.H. Crane, and K. Morgan. 2009. Evapotranspiration-Based Irrigation for Agriculture: Sources of Evapotranspiration Data for Irrigation Scheduling in Florida. AE455. Gainesville: University of Florida Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/ae455.

Kisekka, I., K.W. Migliaccio, M.D. Dukes, B. Schaffer, and J.H. Crane. 2009. Evapotranspiration-Based Irrigation Scheduling for Agriculture. AE457. Gainesville: University of Florida Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/ae457.

Menzel, C.M., J.H. Oosthuizen, D.J. Roe, and V.J. Doogan. 1995. “Water Deficits at Anthesis Reduce CO2 Assimilation and Yield of Lychee (Litchi chinensis Sonn.) Tree.” J. Tree Physiol. 15: 611–617.

Morgan, K.T., J.M.S. Scholberg, T.A. Obreza, and T.A. Wheaton. 2006. “Size, Biomass, and Nitrogen Relationships with Sweet Orange Tree Growth.” J. Amer. Soc. Hort. Sci. 131(1):149–156.

Tables

Table 1. 

Typical crop coefficients (Kc) for perennial crops commonly grown in Florida.

Month

Avocado1

Banana1

Carambola2

Citrus3

Guava4

Lychee5

Mango6

January

0.70

1.00

1.00

0.79

0.80

0.40

0.60

February

0.70

1.00

1.00

0.86

0.80

0.40

0.50

March

0.86

1.10

1.15

0.93

0.80

0.90

0.45

April

0.86

1.20

1.20

0.97

0.85

1.2

0.45

May

0.98

1.20

1.20

1.03

0.90

1.2

0.50

June

0.98

1.25

1.20

1.05

1.00

0.85

0.50

July

0.98

1.25

1.15

1.05

1.00

0.85

0.60

August

0.98

1.25

1.15

1.03

1.00

0.40

0.80

September

0.86

1.10

1.20

1.00

1.00

0.40

0.80

October

0.86

1.10

1.20

0.95

0.85

0.40

0.70

November

0.70

1.00

1.10

0.87

0.80

0.40

0.70

December

0.70

1.00

1.10

0.79

0.80

0.40

0.60

Note: These are only intended for use as guidelines in the absence of locally developed Kc values and may be modified to suit local growing environments and management practices.

1Time averaged Kc values for non-stressed, well-watered crops in a subhumid climate (minimum relative humidity approximately 45% and average wind speed of 2 m/s at a height of 2 m) (Allen et al. 1998). The Kc values have been listed by month to correspond to different phenological stages of plant development. Banana values for summer months are based on Goenaga and Irizarry (2000) conducted under Puerto Rican conditions. Avocado values include considerations from current research at the Tropical Research and Education Center (Personal communication, J.H. Crane and K.W. Migliaccio, 2009).

2Carambola Kc is based on the phenology of plants growing in the South Florida conditions (Personal communication, J.H. Crane, 2008).

3Citrus Kc is based on recommendations by Morgan et al. (2006). More information about citrus irrigation scheduling can be obtained from Improving Citrus Nitrogen Uptake Efficiency: Effective Irrigation Scheduling (http://edis.ifas.ufl.edu/ss467).

4Guava Kc values are taken from a report by Fares (2008) for Hawaiian conditions latitude of about 21o N and longitude 157o W. Kc values in the table have been listed by month to reflect the guava season in South Florida (May to October). More information can be obtained at http://treephys.oxfordjournals.org/cgi/reprint/15/9/611 .

5Lychee Kc values are based on work by Menzel et al. (1995) and were determined in a lychee orchard in subtropical South Africa using an evaporation pan. More information on the study can be obtained at http://treephys.oxfordjournals.org/cgi/reprint/15/9/611 .

6Mango Kc values were obtained from De Azevedo et al. (2003) in a study at Petrolina in northeastern Brazil. Mango orchard ETc was measured using Bowen ratio and soil water balance methods. Kc values in the table have been listed by month to reflect the mango season in South Florida (May to October).

Table 2. 

Typical crop coefficients (Kc) at various growth stages for annual crops commonly grown in Florida.

Crop

Initial Stage

Mid-stage

Late-stage

Tomatoes7

0.4

0.9

0.75

Squash1

 

0.95

0.75

Green pepper1

 

1.05

0.9

Green beans1

0.5

1.05

0.9

Cucumber7

0.27a–0.47b

0.95

0.9

Cabbage7

0.27a–0.47b

1.05

0.95

Potatoes1

 

1.15

0.75

Sweet potatoes7

0.27a–0.47b

1.1

0.7

Carrots7

0.27a–0.47b

1.05

0.75

Okra7

0.27a–0.47b

1.0

0.9

Strawberries7

0.27a–0.47b

0.5

0.6

Sweet corn7

0.27a–0.47b

1.1

1.0

Note: These are only intended for use as guidelines in the absence of locally developed Kc values and may be modified to suit local growing environments and management practices.

1Time averaged Kc values for non-stressed, well-watered crops in a subhumid climate (minimum relative humidity approximately 45% and average wind speed of 2 m/s at a height of 2 m) (Allen et al. 1998).

7Kc values are from Vegetable Production Guide for Florida (SP170), “Principles and Practices of Irrigation Management for Vegetables.” More information about this publication can be found at http://edis.ifas.ufl.edu/topic_hs_vegetable_production_guide_for_florida_(sp170).

7a represents small row spacing (high population densities).

7b represents wide row spacing (low population densities).

Footnotes

1.

This document is AE456, one of a series of the Department of Agricultural and Biological Engineering, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date January 2010. Revised February 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Isaya Kisekka, graduate student, Department of Agricultural and Biological Engineering, Tropical Research and Education Center, Homestead FL; Kati W. Migliaccio, associate professor, Department of Agricultural and Biological Engineering, Tropical Research and Education Center, Homestead, FL; Michael D. Dukes, interim chair, Environmental Horticulture Department, and professor, Department of Agricultural and Biological Engineering; Jonathan H. Crane, professor, Department of Horticultural Sciences, Tropical Research and Education Center, Homestead, FL; Bruce Schaffer, professor, Department of Horticultural Sciences, Tropical Research and Education Center, Homestead, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.


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