ISHS Acta Horticulturae 559: V International Symposium on Protected Cultivation in Mild Winter Climates: Current Trends for Suistainable Technologies
IRRIGATION SCHEDULING FOR PLASTIC GREENHOUSE MELON CROPS BASED ON HISTORICAL REFERENCE EVAPOTRANSPIRATION DATA |
| Authors: | M.D. Fernández, S. Bonachela, F. Orgaz, E. Fereres |
| Keywords: | Cucumis melo, crop evapotranspiration, irrigation scheduling, plastic greenhouse |
| Abstract:
In coastal areas of Almería (south-eastern Spain), approximately 30000 ha of greenhouse crops are cultivated for intensive horticultural production. Given the limited water resources of the region, optimising irrigation efficiency is necessary. Currently, irrigation scheduling is based mostly on farmers experience, and the amount of water applied to the same (each) crop varies considerably. The main objective of this work was to analyse whether historical crop evapotranspiration could be used to improve irrigation scheduling of horticultural crops. Actual crop evapotranspiration (ETc) was estimated as the product of actual values of reference crop evapotranspiration (ETo) and crop coefficients (Kc). A "class A" evaporative pan, located in the centre of a grass plot within a typical greenhouse, was used to determine ETo, and the pan coefficient was experimentally measured. Kc was calculated from leaf area index (LAI) values. A simple model was used to estimate LAI as a function of thermal time, and actual temperature values were used to calculate thermal time. During the whole 1993/94 growing season, estimated ETc values of a melon crop were close to measured ETc values. The mean absolute error was 0.2 mm d-1. Historical daily values of reference evapotranspiration (EToh) were calculated as the average of daily reference evapotranspiration (ETo) values from a data set of 14 years. Historical daily values of crop coefficient (Kch) were determined from LAI values. Average temperature values from a data set of 11 years were used to calculate thermal time and to estimate LAI values. The use of ETh for irrigation scheduling was theoretically studied by using a simple water balance model applied to a range of representative soil types in a melon crop. For three planting dates in each of 11 cropping seasons, both ETh and ETc values were used to calculate the amount of irrigation water. When ETh was lower than ETc the soil water was depleted, and cumulative soil water deficits were quantified. In general, soil water deficits were not detected when ETh was used for schedule the irrigation. The use of ETh is a simple method for estimating crop water requirements within a greenhouse, and could be easily adopted by farmers. | |
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