Intelligent Drip Irrigation Control System Based On Crop Evapotranspiration Model

Drip irrigation technology can accurately control irrigation water, puting the water and nutrients into the the soil directly, so it is widely used in the agricultural production. But now the drip irrigation systems are almostly according to the experience control, it is difficult to control the precise need of crop, meantime, the modern automatic drip systems is very expensive, the irrigation users of normal and small can hardly to bear it.In order to the problem, a set of intelligent drip irrigation control system had been designed, which calculate the crop evapotranspiration model as the amount of irrigation. The system used humidity and temperature sensor to measure temperature and humidity difference, utilized Bowen ratio-energy balance method to calculate crop evapotranspiration, and converted the evapotranspiration to amount of irrigation. Finally, the switching time of the electromagnetic valve was controlled with the single-chip microcomputer by making program. At the same time, the contrast tests had been finished to verify the Bowen ratio-calculating value and real-weighing value, the results showed that both two have basicly the same trend, and the curve relevance achieved to R2=0.9672.The main content of this paper was as follows:1. An decision-making model was established to control water amount, which used Bowen ratio-energy balance method measuring the difference of air temperature, humidity and net radiation value, then it was suitable to calculated the crop evapotranspiration during this period, through the value can derive the crop water amount, adding the moisture that crops lost precisely.2. The intelligent irrigation controller systerm was designed, which included the following six parts:power supply module, data acquisition conversion module, microprocessor control module, LCD display module, human-computer interaction module and output driver module. The signals was collected by the temperature and humidity sensors and photoconductive resistance translated into the corresponding digital signals to the microcontroller though A/D transformation, these digital signals could be calculated by irrigation decision-making model into evapotranspiration, and then displayed to the LCD screen. Microprocessor coverted the evapotranspiration into the irrigation time, through the driver circuit controlling open and close of electromagnetic valve, achieving precise irrigation. The systerm provided users two modes:manual and automatic. In the manual mode, users could set any time to irrigate, in another mode, the systerm irrigated by precise theoretical calculations.3. The drip irrigation uniformity test was designed to show that, under no conditions did the droping arrows have the good water uniformity, the relative error of the first group range is1.68%-9.73%, the relative error of the second group range is0.48%-8.56%, the relative error of the third group range is0.65%-3.59%. As it can be seen, the error of the third group is minimum, so its uniformity is best, the average relative error is1.57%, and the error of the first group is the maximum, the average relative error is5.75%. According to three experiments overall, absolute value of relative error of drip irrigation uniformity were all within10%, basicly accorded with uniformity condition need, so it can be used as the criterion to calculation the whole water amount of cucumber.4. The contrast test of actual crop were completed, through the analysis of daily change of evapotranspiration and influence of environmental factors on the evapotranspiration, it can be seen that the basic trend of drip irrigation amount began to increase from eight a.m. until noon12(reach the largest), and then with the value of net radiation declining, the drip irrigation amount decreased until the evening did not need to drip irrigation, compared with temperature humidity, the net radiation is the main factors which affecting crop evapotranspiration change. On this basis, the contrast tests had been finished to verify the Bowen ratio calculating value and real weighing value, the results showed that both the two have basicly the same trend, and the curve relevance achieved to R2=0.9672,it also illustrated that the bowen method can be used to measure the evapotranspiration value, and can be used as the drip irrigation model of crop in the precise irrigation of greenhouse canopy.