In-Situ Drainage Lysimeters for Field Crops Irrigated With Brackish Water.

Irrigation practices with water containing high levels of salts must satisfy both evapotranspiration and leaching needs. Miscalculation of actual evaporation leads to inefficient use of water and fertilizers resulting in economic losses and groundwater pollution. Such consequences can be minimized by proper irrigation and fertilization scheduling based on in-situ water and solute balances. Lysimeters are accurate research tools for calculating water and solute balances and are used successfully for agricultural research. Low cost in field drainage lysimeters to aid irrigation and fertilization decision making by practitioners could optimize water and fertilizer inputs. When storage is assumed to be negligible, lysimeters are more affordable since weighing is not a requirement. The main challenges for application of such low cost lysimeters include determining: lysimeter size (depth and area), temporal resolution for water and solute balance calculations, and the certainty that the lysimeter is representing field conditions. In order to understand how the lower boundary conditions will affect water and solute balances, numerical and laboratory experiments were conducted using HYDRUS 2D/3D and an automated rotating lysimeter system. In addition, bell peppers were grown in drainage lysimeters having two different depths and three different surface areas in a semi-commercial greenhouse with loamy sand soil. Evapotranspiration (ET) calculated using the drainage lysimeters was compared to ET calculated using weighing lysimeters. The smaller and shallower the lysimeters, the higher the water content in the profile. For these specific conditions, a medium sized (1 m²), shallow (0.3m) lysimeter was found to best represent actual ET and therefore be indicative of the representative elementary volume (REV) for the water and solute balances without yield reduction.  The coefficient of variation (CV) for the chosen REV was lower in comparison to other volumes for weekly measurements. Bigger time resolution led to even lower CV values.