摘要：

In order to investigate the effect of soil water tension (SWT) on the nitrate content and yield of lettuce, an experimental field was established on a clay loam soil in Southern Greece. Scheduling irrigation by tensiometers and/or porous blocks, water was applied in each of the four treatments when the SWT reached ‐30, ‐60, or ‐100 kPa, respectively. The fourth treatment was irrigated by using local plant and soil criteria. Lettuce fresh yield was increased as SWT was increased with maximum fresh wt at the SWT of‐30 kPa. The highest water‐use efficiency was obtained at the SWT of ‐100 kPa. The nitrate content in the external leaves was about 3.5 to 4 times higher than the content in the heart leaves of lettuce. Furthermore, the nitrate content from ‐30 to ‐100 kPa treatment was decreased 26% for the external and 23% for the heart leaves in dry matter and 22% and 19% in fresh matter, respectively. The total nitrogen (N) of the external leaves was decreased with decreasing soil water potential and remained constant in the heart leaves.

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