The application of irrigation depths in irrigated pasture under center pivot machines, in a general way, is accomplished without a pertinent technical criterion, because it should be considered that for any time period, the pasture plots are at different development stages (rotary pasture), presenting different evapotranspiration rates inside the irrigated area. Furthermore, farmers usually apply a single irrigation depth for the whole area. In this study a model was developed for the application of different irrigation depths in each portion of the pivot (pizza shape plots). The model proposed in this study considers: i) the capacity of the pivot-center to apply different water depths in the area; ii) development stage of crop in each plot iii) cattle return period for grazing in-determined plot (pasture cycle fixed); and iv) potential of pasture development during the agronomic year. To compute the crop coefficient (Kc) variable in the model, two methodologies were used: a) constant variation rate of Kc, according to the resting days the portion is submitted and b) sinusoidal variation rate of Kc, according to the resting period. The model was applied for hypothetical pastures conditions under rural areas of Piracicaba and Pereira Barreto municipalities, in the State of São Paulo, Brazil. The model's sensitivity for the irrigation depths applied was observed for the different stages of Tanzania grass development under the center-pivot, according to the variable climatic conditions of each region.
Tanzânia grass; irrigation management; crop coefficient
