Quality of center pivot irrigation controlled by tensiometers

Abstract

The irrigation quality was evaluated for a center pivot winter bean (Phaseolus vulgaris, L) crop in a Typic Hapludox of the county of Guaíra (SP), Brazil (20° 27'30"S, 48°19'30"W, 495m). Criteria used for this evaluation were the crop water use efficiency and the irrigation "effectivity", the latter being assessed by the water application efficiency, the water distribution uniformity on the soil surface and the soil water storage efficiency. The irrigation monitoring was done by means of 20 sets of two tensiometers (15 and 30 cm soil depths) installed at each 15 m on a 300 m transect along the radial direction of the pivot, and 60 rain/irrigation gages installed at each 5 m on the same transect. The irrigation control was done by means of the 15 cm-soil depth tensiometers. The minimum matric potential value used to define the irrigation timing was -0,06 MPa and the water depth to be applied by the pivot was calculated taking into account the value of -0,008 MPa for the soil at field capacity. Results showed that irrigations were of high quality since high values of water application efficiency (80%) and water distribution uniformity coefficients (94% and 91%) were obtained, the same occurring with the soil water storage (95%) and crop water use (0,8 kg/m³) efficiencies.