One criteria that may be applied in water management consists in irrigating whenever a pre-fixed water depth (h1) is completely depleted from the soil. Therefore, the necessary irrigation depth (h1n) to replenish the soil profile to field capacity will be always larger or equal to hi. This paper investigates the relevance of this percentage of additional irrigation depth (%h a) by simulating the irrigation occurrence through water balance technique for several values of hi in Ribeirão Preto, State of São Paulo, Brazil. The relative frequency of h1n was compared to hi and %h a calculated. The results showed that %h a was more important than something else when: 1) hi was small or 2) values of evapotranspiration were high; and 3) the probability level adopted in a project. Figures are presented to help in the calculation of %h a.
irrigation depth; irrigation design; water balance