Optimization of irrigation in open-air vegetable cultivation in Lower Bavaria | Continuation project "Radar-based weather forecasts for efficient and water-saving irrigation of horticultural crops in Agriculture and Horticulture" (RADOLAN)
As part of the research project "Optimization of irrigation in open field vegetable cultivation", practical trials on irrigation control were carried out mainly in Lower Bavaria. The aim of the project, which was funded by the Bavarian State Ministry of Food, Agriculture and Forestry, was to find suitable instruments for controlling the irrigation of open field vegetables. The possible control and monitoring systems were used and tested both in overhead irrigation and in drip irrigation systems. From 2010 to 2013, the focus was mainly on sensor-based systems; in 2014 and 2015, the focus was on climatic model calculations and improving their application.
Overall, it can be seen that the farms handle irrigation very differently and decisions are made according to horticultural instinct and intuition. Due to the pump technology used, complete automation is currently not possible, especially in Lower Bavaria, and is not desired by the users. For this reason, the project was primarily designed to support the gardener or farmer in making decisions regarding the time and quantity of irrigation. In addition to the irrigation control system, the water distribution system must also be regularly checked for accuracy with regard to water distribution. Ongoing extensions and changes can have a significant impact on the hydraulics and therefore the water distribution accuracy. Furthermore, the operating pressure required for the system must be maintained. In particular, it must be checked that this is also achieved at the critical end points.
One way to control irrigation using objective criteria is to use soil moisture sensors. These can provide valuable information regarding both the time of irrigation and the amount of water. In addition to the familiar tensiometers, which in the simplest case have to be read by hand, watermark sensors and sensors for measuring the volumetric water content are also suitable for controlling irrigation and monitoring water movement. With the volumetric measuring principle, it should be noted that instead of the absolute value, which can vary greatly from sensor to sensor and is also very dependent on the type of soil, the relative value or the changes are used as a decision-making aid. Tensiometers ran empty during the test phase due to persistently high water tensions (>800 hPa) and therefore had to be checked and refilled frequently.
Manual meter reading is very time-consuming and only meaningful if it is carried out regularly and without gaps. Internet-based systems are available from around €1500 with automatic data transmission, depending on the configuration and equipment. Although these systems require a certain amount of installation and maintenance, they offer maximum convenience in terms of data recording and processing. If the data cannot be evaluated immediately during the season, a follow-up analysis can also provide a considerable amount of information. A possible configuration is shown in Figure 4 in the right-hand column under "Weblinks". In addition to recording the soil moisture, it is essential to record the irrigation quantities (time, water quantity). Further optimization can only be achieved with this information. Another way of controlling irrigation according to objective criteria is the Geisenheim method. The irrigation time is calculated on the basis of natural precipitation and evaporation values according to Penman and a correction factor adapted to the condition of the plants and their development. Depending on the soil type or usable field capacity of the soil, the irrigation time is adapted to the water storage capacity of the soil. The disadvantage of the high work and maintenance effort (data entry, maintenance and recording of natural precipitation), which is frequently mentioned by practitioners and trial participants, is to be remedied by a further research project, again in the Lower Bavaria growing region and in the Kitzingen area.
Final project report
The detailed report on this project can be found in the right-hand column under "Weblinks".