An automatic control device for negative pressure irrigation for continuous low-rate water supply at constant soil wetting

In order to achieve automatic pressure regulating and promote the field application of negative pressure irrigation, an automatic negative pressure control device based on a single-chip microcomputer was developed for regulating and recording data automatically. The results of laboratory and field tests showed that the pressure adjustment precision was 0.45%, 1.79%, 1.99% and 0.84% respectively. In a field test, the water infiltration rates were decreased from 7.20-9.72 mm d(-1) on the first day to 1.6-2.5 mm d(-1) in the following 30 d, the soil moisture content was the largest around the emitter for 0.24-0.27 g g(-1) and lowest in the margin for about 0.07-0.08 g g(-1) at different negative pressure. Both laboratory and in-field measurements demonstrated that the device functioned well in signal acquisition, data conversion, processing, transmission, storage and control. The result showed the device could supply a low-rate water continuously and keep soil wetted. It needed more than 10 d obtain soil moisture conditions suitable for crop growth in the field, thus it is advised that a positive pressure should be applied in the initial to generate a stable water distribution, and then adopt a suitable negative pressure to meet crop water requirements. The study confirmed the potential of the device to be used for regulating pressure and recording data accurately in the laboratory and field experiment, and helped ensure future research of similar irrigation systems in the field. (c) 2021 IAgrE. Published by Elsevier Ltd. All rights reserved.