ISHS Acta Horticulturae 449: II International Symposium on Irrigation of Horticultural Crops
IRRIGATION SCHEDULING OF VEGETABLES TO INCREASE THE EFFECTIVITY OF THE USE OF WATER IN RESPECT TO ECOLOGICAL ASPECTS USING LETTUCE IN OPEN FIELD CONDITIONS AS AN EXAMPLE |
| Authors: | P.J. Paschold, K.H. Zengerle |
| Keywords: | Lactuca sativa L. var. Capitata, Time Domain Reflectometry (TDR), tensiometers, soil humidity, climatic water balance |
| Abstract:
The "Geisenheim Method" of irrigation timing based on the uses of daily climatic data in form of the modified Penman equation. The reference crop evapotranspiration (ETo) is multiplied by plant coefficients (kc) to determine when it is necessary to start irrigation. These "kc" factors have been determined in lysimeters and in field experiments for numerous vegetables. During the vegetation period this factor has to be changed three or four times depending on the stage of development of the vegetable. In current experiments these factors are being evaluated in respect to ecological aspects and, where possible, made more precise. The method will be demonstrated in a three-year long investigation in open field conditions using lettuce as an example. To irrigate the experimental surfaces a computer controlled linear-move irrigation system was used. Irrigation with according to the Geisenheim Method (GS) was compared with the same method using reduced kc values (GS x 0.6). In further experimental variants irrigation was controlled on the basis of soil water tension determination using tensiometers with thresholds of 200 and 500 hPa. Comparative measurements with tensiometers and TDR probes showed that both methods can give rise to horticulturally and ecologically functional irrigation. The use of the Geisenheim method made high yields possible without increasing the risk of nutrient leaching. On the basis of these long-term investigations in Geisenheim, irrigation recommendations for the most important crops have been issued to growers twice a week for the past few years. | |
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