Articles
ECOLOGICAL IRRIGATION AND FERTIGATION OF SOIL GROWN PLANTS IN GREENHOUSES
The soil moisture has to be used as a control parameter to prevent loss of water.
Tensiometers were placed in different soil layers (30, 60, 90 and 120 cm) to find out and control the right water quantity for each irrigation event.
Experimental results in the Institute and in many vegetable farms have shown that the continual measuring of soil moisture is a suitable method to optimize the water quantity given.
The water quantity per irrigation cycle has to be reduced in the case of declining moisture tension in deeper soil layers, in case of rising moisture tension it may be increased.
Most soil types (not sandy soil) showed no water loss when a water quantity of 1 to 2 l/m drip irrigation (distance between drippers 30 cm) was given at 90 hPa moisture tension.
However, the small water quantity may lead to problems with water distribution.
At the vegetable institute of the FH Weihenstephan a soft- and hardware system called KLIWADU was developed for controlling irrigation, fertilization and climate in greenhouses.
The amount of nutrients required per day, determined by the horticulturist, is independent of the amount of water required per day.
This software makes it possible to save the information about consumption of nutrients and water as demanded by the authorities and the new German law for using fertilizers.
The nutrient supply to the drip area has to be at the high level of 300 to 500 mg N/1 soil for an economical production during the main growing period although this high level seems to contradict the ecological demands.
Long term experience with cultivation in greenhouses and drip irrigation shows, that fertilization can not follow strict rules because the plant development is influenced by factors such as cultivars, growing period, climate etc., that change all the time.
To optimize the amount of nutrients to be supplied, it is necessary to take regular soil analyses (N-min).
Altogether optimizing irrigation and fertilization brings ecological and economical advantages because of higher yields and less fertilizer and water costs.