This paper discusses factors affecting both field-wide and localized uniformity of injected fertilizers in drip systems. Field-wide uniformity depends on the uniformity of applied water and chemical travel times through the drip system. Field studies have shown substantial travel times along drip lines, with the last 20 percent of the drip line length accounting for 80% of the travel time. Localized uniformity is the uniformity of the fertilizer in the soil around the drip line. The first phase of this project used the HYDRUS-2D computer simulation model to develop distributions of nitrate around the drip line in the soil profile for short fertigation events at the beginning, middle and end of an irrigation cycle; fertigation during the middle 50% of the irrigation; and continuous fertigation during the irrigation for four soil types and four types of drip systems commonly used in California. Results generally showed a high leaching potential for short fertigation events near the beginning of the irrigation.

The second phase of the project involves using the HYDRUS-2D model to develop distributions of nitrate, ammonium, and urea around the drip line for the different fertigation strategies for a silt clay under surface drip irrigation and subsurface drip irrigation. Simulations were conducted over a 28 day time period.