Curtis B. Adams

Document Type


Publication Date



Unleached root-zones represent an environmental ideal by eliminating wasteful leaching of nutrients and water. NASA grows plants in space in unleached root-zones, incorporating polymer-coated fertilizer (PCF) into a ceramic media (Turface or Profile). However, lack of growth productivity in space has led to the need for research to improve the nutritional and physical environment of the root-zone, which is the objective of this research. PCF types are diverse in release characteristics and the effects of temperature and substrate water content have not been well characterized. In spite of widespread use, studies on chemical properties and applied studies to verify soil physical models of ceramic media have been limited. We quantified the release rate of three widely-used types of PCF (Polyon, Nutricote, and Osmocote) in water and in sand over a wide range of temperature (5, 15, 20, 30, and 40ºC). Results indicated that substrate water content had a minimal effect on release rates. Nutricote fertilizers were the most consistent in releasing individual nutrients with temperature and over time. Polyon fertilizers had the slowest release rates relative to the manufacturer's specifications, but a relatively linear response to temperature. Osmocote fertilizers rapidly released nutrients at all temperatures. For more efficient PCF use, we present a comprehensive model that couples models to predict plant growth and PCF nutrient release rates. This model is based on phosphorus release, the nutrient found to be limiting to PCF-fertilized plants. The efficacy of the model to accurately predict PCF application rates was verified with a growth trial. In ceramic media, relative media-sorbed nutrient concentrations were highly variable from bag to bag. Excesses of manganese, boron, magnesium, and sulfur in the media induced nutrient imbalances in plant tissues. Rinsing and soaking procedures on the media helped mitigate these nutrient imbalances. Ceramic media also interacted with added fertilizer ions. Copper, phosphorus, and zinc ions were largely removed from solution by these interactions. We also used plants to extract water from root-zones of ceramic media to characterize plant-available water and water supply dynamics. The results suggest that soil physical models may be used to predict plant-available water in ceramic media.