A Continuous Two-Variable Design Using the Line-Source Concept
Multivariable experiments involving different water salinities are usually conducted using drip irrigation. Preparing the irrigation system to apply these different treatments requires a considerable investment of labor and materials. This study was conducted to examine an alternative irrigation system that is relatively simple and inexpensive, yet produces gradients of two variables. A variation of the line-source irrigation system was tested using water salinity and N levels as variables. The middle line of a triple line-source irrigated using saline water (7.0 dS m−1)> while the two parallel outside lines irrigated using nonsaline water (1.0 dS m−1). A second triple line-source using only nonsaline water was superimposed perpendicularly on the first set. Ammonium nitrate was injected into the middle line. This layout produced linear gradients for both variables (r2=0.99) perpendicular to their source and provided every possible combination of saline water concentrations (7.0−1.0 dS m−1) and N levels (8.1−0.0 mmol L−1). It proved to be a simple yet highly informative system.
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