Water storage in the soil profile under subsurface drip irrigation: Evaluating two installation depths of emitters and two water qualities

Knowledge about soil moisture is essential to maximize irrigation efficiency because it allows the application of water in the proper quantity and at the proper time, thus improving water management. The objective of this study was to evaluate water storage in the soil profile when using a subsurface drip irrigation system at two emitter installation depths (0.20 or 0.40 m) and two water qualities (treated sewage effluent (TSE) and freshwater) in two crop cycles of sugarcane (Saccharum officinarum L.) in Campinas SP (Brazil). The experiment was conducted in the experimental area of FEAGRI-UNICAMP, Campinas-SP, Brazil, adopting a randomized block design (RBD) in a factorial 2 x 2 + 1 with 3 replications. The factors studied included the installation of dripper tube at two depths (0.2 and 0.4 m) and two qualities of water (TSE and freshwater) plus a non-irrigation control. The TDR (time domain reflectometry) technique was used to evaluate the moisture in the soil profile by installing five probes with rods at 0.2 m up to 1.0 m depth. Replacement of the calibration equation provided by the TDR reduced the water depth between the first ratoon and the sugarcane plant and reduced the excess humidity from 0.029 and 0.045 cm(3) to 0.002 and 0.007 cm(3) when the drippers were installed at 0.2 m depth (T2 and T4). The installation of a 0.2 m drip tube proved to be an ideal solution for both environmental management and water use efficiency when using treated sewage effluent. No effect on the water distribution in the soil was observed when comparing the water qualities. For management of subsurface drip irrigation by the water balance in the soil, different layers in the soil profile should be considered to calculate the water depth, using the depth of the drip tube installation as a reference. (C) 2015 Elsevier B.V. All rights reserved.