At each irrigation, water was supplied in excess of about 20% for restoring field capacity. Irrigation water was supplied simultaneously to the two lysimeter series (5 lysimeters containing clay soil, and 5 with loam) whenever the accumulated daily evaporation of the class "A" pan, located in the standard agro-meteorological station nearby the lysimeter set-up, had attained the threshold of about 65 mm. In the Mediterranean region, actual crop evapotranspiration is systematically lower than the class "A" evaporation (see the review published by Rana and Katerji, 2000). If evaporation and evapotranspiration were the same, 65 mm correspond to 34% of the total amount of the available soil water for clay and to 40 % for loam. Under these soil water conditions, crops can be considered well-watered (Tardieu and Katerji, 1991). This hypothesis was tested by measuring the plant water status during the growth cycle.

2.2. Crops

Table 2 presents the crops grown during 6 seasons, the cultivars, and the reference publications with detailed information concerning crop density and fertilization. The table shows that the crops grew in different seasons: sugar beet from late autumn to early summer, potato in spring, and maize, sunflower, tomato, and soy-bean in summer. For each crop the cultivar, the sowing date, the plant density and the fertilization were the same in this study.

Table 2. Crop, variety, growth period, final density (plant m-2), and reference

Potato (Solanum tuberosum L.)



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