Figure. 1. Evolution in time (days after emergence) of pre-dawn leaf water potential (MPa) of six species grown on loam and clay soils.

Table 3 shows the accumulated evapotranspiration during the crop cycle. In the case of potato, sunflower and sugar beet, the values on clay are significantly lower than those observed on loam. These differences in accumulated evapotranspiration appear (Figure 3) only during a part of the vegetative cycle, when the leaf area attains the maximum value (see paragraph 3.2).

3.2. Soil Type Effect on Growth and Yield

Figure 4 shows the evolution of the leaf area index (LAI) measured in the six species. As for potato, sunflower, and sugar beet, the leaf area measured on clay was significantly lower than that on loam. In contrast, no soil type effect was observed in tomato and maize. As for soybean, the value observed on clay was significantly higher only when LAI attained its maximum value. The observed reduction in accumulated evapotranspiration (Figure3) in potato, sunflower and sugar beet on clay originated from both LAI and stomatal conductance reduction.

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