Master of Science (MS)
Plant, Environmental Management and Soil Sciences
Overirrigating container crops can lead to increased nutrient leaching and negatively impact water quality. Leaching is implemented to reduce substrate salinity. “Leaching fraction” (effluent volume/irrigation volume) has been described by best management practices to monitor irrigation efficiency. Recommendations and methods for controlling leaching fraction can greatly vary. Therefore, two studies were conducted to test the accuracy of attaining targeted leaching fractions compared to the accuracy of leaching targeted percentages of container capacity. In the first study, the effects of container size and substrate moisture content were tested on each method. Three container sizes of pine bark substrate at three moisture deficits were irrigated to achieve targeted leaching fractions of 0%, 20%, 40%, and 60% of applied irrigation. After leaching, effluent was collected and actual leaching fractions were calculated. Actual leaching fractions were higher than treatment targets, and varied according to substrate moisture content. When irrigation and effluent volumes were compared to container capacity, a linear relationship (R2>92%) was found between percent container capacity leached at irrigation termination and actual percent of container capacity leached, regardless of substrate moisture and container size. Salt concentrations were measured on effluent samples collected from volumetric intervals during leaching, and were higher in initial samples. In the second study, effects of rooting and time on container capacity, particle size distribution, and the accuracy of leaching based on container capacity were investigated. Taxodium distichum liners planted into 10.4L containers were sampled at three time intervals during growth for container capacity, and were irrigated until a proportion of container capacity (0%, 10%, 30%, or 50%) had leached. After leaching, effluent was collected and actual percentage of container capacity leached was calculated. Significant changes were seen in container capacity and rooting by the end of the growth period; however, leaching based upon container capacity retained high accuracy. Controlling container effluent as a percent of container capacity is accurate despite changes in container size, moisture deficit, container capacity, and rooting, and not only provides a more streamlined approach for container salt removal, but also a method to account for irrigation volumes that could improve irrigation efficiency during container production.
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Thiessen, Maureen, "Use of Effluent Volumes to Control Leaching in Nursery Container Crops With Tipping Bucket Sensors" (2012). LSU Master's Theses. 3289.