Ceres Duarte Guedes Cabral de Almeida

Characterization of the microtube emitters used in a novel micro-sprinkler

The microtube is a simple and cheap emitter that was widely used throughout the world in the early days of drip irrigation. Its length can be adjusted according to the pressure distribution along the lateral line and the discharge from the microtube can be adjusted by its length. This not only counters the pressure loss due to pipe friction but also makes it suitable for undulating and hilly conditions, where pressure in the lateral line varies considerably according to the differences in elevation. This is the major problem facing the designer, i.e., emitter flow changes as the acting pressure head changes. In this study, a novel micro-sprinkler system is proposed that uses microtube as the emitter and where the length of the microtube can be varied in response to pressure changes along the lateral to give uniformity of emitter discharges. The objective of this work is to develop and validate empirical and semi-theoretical equations for the emitter hydraulics. Laboratory testing of two microtube emitters of different diameter over a range of pressures and discharges was used in the development of the equations relating pressure and discharge, and pressure and length for these emitters. The equations proposed will be used in the design of the micro-sprinkler system, to determine the length of microtube required to give the nominal discharge for any given pressure. The semi-theoretical approach underlined the importance of accurate measurements of the microtube diameter and the uncertainty in the estimation of the friction factor for these tubes.

Monitoramento da salinidade de águas subterrâneas em várzea cultivada com cana-de-açúcar fertirrigada com vinhaça

This study evaluated potential risk of vinasse to provoke salinity and sodicity in groundwater in a lowland area under sugarcane crop. The research was carried out in Pernambuco State, in the Northeast of Brazil, from December 2010 to September 2011. A georeferenced grid of 81 wells over 7.5 ha (three subareas with 2.5 ha each) under sugarcane crop was monitored. Vinasse was applied at three rates 50, 60 and 65 m³ ha-1 from molasses fermentation. Quality of groundwater was monitored through six samples along period of plant growing. EC, pH, Na+, Ca2+, Mg2+ and SAR were measured. Rate up to 65 m³ ha-1, in lowland areas, for the variables analysed, provided no risk to groundwater for salinity and sodicity, as well as EC and SAR for salinity and sodicity during the experimental stage. This study showed that rainfall provided reduction of salt concentrations in groundwater under monitoring along the time.