Figure 1
Real and estimated ratoon sugarcane yield from the1997/1998 to the 2007/2008 season (Paranavaí, Paraná State, Brazil). 1 - Real yield; 2-7 - Estimated yield with models; 2 - Howell & Hiller (1975)HOWELL, T. A.; HILER, E. A. Optimization of water use efficiency under high frequency irrigation. Transactions of the ASAE, Denver, v. 18, n. 5, p. 873-878, 1975.; 3 - Jensen (1968)JENSEN, M. E. Water consumption by agricultural plants. In: KOZLOWSKI, T. T. (Ed.). Water deficits and plant growth. New York: Academic Press, 1968. p. 1-22.; 4 - Minhas et al. (1974)MINHAS, B. S.; PARIKH, K. S.; SRINIVASAN, T. N. Towards the structure of a production function for wheat yields with dated inputs of irrigation water. Water Resource Research, David, v. 10, n. 3, p. 383-393, 1974.; 5 - Doorenbos & Kassam (1979)DOORENBOS, J.; KASSAM, A. H. Yield response to water. Rome: FAO , 1979.; 6 - Stewart et al. (1976)STEWART, J. I.; HAGAN, R. M.; PRUITT, W. O. Production functions and predicted irrigation programs for a principal crop as required for water resources planning and increased water efficiency: final report. Washington, DC: Elsevier, 1976. proposed by Doorenbos & Kassam (1979); 7 - Rao et al. (1988)RAO, N. H.; SARMA, P. B. S.; CHANDER, S. A simple dated water-production function for use in irrigated agriculture. Agricultural Water Management, Austin, v. 13, n. 1, p. 25-32, 1988..
Figure 2
Yield reduction as a function of the ETr/ETc ratio, based on the Jensen (1968)JENSEN, M. E. Water consumption by agricultural plants. In: KOZLOWSKI, T. T. (Ed.). Water deficits and plant growth. New York: Academic Press, 1968. p. 1-22. model, using statistically adjusted coefficients in the development phases I, II and III (Paranavaí, Paraná State, Brazil).