A flexible computer based irrigation control system
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The project seeks to investigate the possibility of efficient water use in irrigation scheduling systems through the use of a designed flexible computer based irrigation control system. One of the specific objectives of the project was, to develop an irrigation control software program for a drip irrigation system, which will monitor and manage irrigation in the greenhouse. The other specific objectives of the project are to experimental determine the control parameter such as leaf area index, thermal conductance constant Ksh, which are inputs to the developed control program. The final objective of the project was to test the designed control system in a greenhouse. The designed irrigation control system consisted of a combination of hardware, software and electric devices that monitored the plant sap flow variations in a plant via a sap flow gauge, data logger and an interface card. Four voltage signals from the sap flow gauge were sent to the computer via the interface board for computations and control purposes. The processed signals were sent back to the relay card via the same interface board for the actual control of irrigation scheduling. In the control program development phase a software program flowchart was developed followed by the development of actual irrigation control program using Visual Basic 6 enterprise edition (VB6.0) complier. The control program parameters were determined with relative errors as follows, average stem diameter of the rose plant (11.37 0.04mm), the averaged total leaf area (29.25 0.06 ), leaf area index (2.58 0.19), thermal conductance constant (0.846 0.002). The peak stem sap flow rate during the field testing (implementation) period was found to be in the range of 16 - 18 g h-1, corresponding to crop transpiration rates of 0.01-0.03 kg s-1. The current grower system applied 337.4 litres of water for 24 minutes each day of the two field testing days. It was also observed that the designed control system applied less water on both days of implementation, supplying 323.8 and 326.7 litres respectively. The project also reviews the relative suitability of different plant water deficit indicators for specific crop and climatic situations.