Optimizing Irrigation Water Supply in a Young Citrus Orchard

摘要

Morocco is a country with arid-to-semi arid climate and some of the best citrus is produced in areas with very limited water resources. In all cases, irrigation of citrus orchards is quasi permanent. Several research projects are directed to water use efficiency and water economy. Irrigation monitoring was studied in a ' Nules' Clementine grove budded on Citrus macrophylla. Trees were planted at 1. 5m×5 m spacing and have one dripline with 2 drippers/tree, and a flow of 2. 31/hour/emitter. A complete block design experiment (with 6 blocks) was undertaken using 4 treatments based on an ' f' value representing the percentage of water used from the soil and available water reserve when an irrigation is applied. Four doses were thus defined: 1.05, 1. 6, 2. 1 and 2. 6 mm/application corresponding to an 'f factor of 10%, 15%, 20% and 25%. In practice, irrigation is made when cumulated daily evapotranspiration (ETc, calculated using ETo×Kc) reached one of these predefined dose values. ETo is the reference evaporation according to PenmanMonteith and Kc the cultural coefficient. Measurements concerned parameters of the soil-plant-atmosphere continuum. Between June 2007 and May 2008, cumulative water application reached 300mm. Observations and measurements were made from January to June 2008. During this period, application of 172mm was made in 162 interventions when the lowest dose of 1. 05 mm was used and in 65 interventions when the highest dose of 2. 6mm was applied. ETo values were less than 4mm/day in January-February and between 4 and 6mm/day in May-June. Results indicated that at high doses, soil water tension was always < 10cbars at 25cm depth, and in the range of 20 - 30 cbars at 50cm depth. Low doses gave tensions of 10 - 15 cbars in the shallow soil horizon, and values of 15 -20 cbars in deeper soil profiles. Root growth attained 50cm in depth and roots were also found in between the drippers indicating a comfortable soil water situation for the tree. Vegetative growth was similar for the four regimes. Soil water was also monitored by FDR sensors and fluctuations in tree -trunk diameter were monitored by LVDT probes. Good correlation was obtained between LVDT data and air temperature and relative humidity.