This article is part of a series on ET-based irrigation scheduling for agriculture. The rest of the series can be found at https://edis.ifas.ufl.edu/topic_series_ET-based_irrigation_scheduling_for_agriculture.
The crop coefficient (Kc) is one of the most important variables in the estimation of irrigation water needs for a specific crop. Kc integrates crop properties, related to the plant phenological stage, plus the effects of soil evaporation in one value. Usually, Kc values are estimated in controlled conditions related to the crop type, phenological stage, soil moisture, crop health, and crop management practices. However, these controlled estimations are not possible to reproduce in the field due to timing and management restrictions. 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 Coefficient (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 https://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 field data exist for a crop related to 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 https://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.
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.
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. https://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. https://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. https://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.
Typical crop coefficients (Kc) for perennial crops commonly grown in Florida.
Typical crop coefficients (Kc) at various growth stages for annual crops commonly grown in Florida.