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Titre : Influence of Irrigation with Brackish Groundwater and Ro Concentrate on Pecan Growth and Physiology, and Soil Physical, Chemical, Microbial, and Thermal Properties

Auteur : Ben Ali, Akram R

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) Plant and Environment Science 2021

Résumé partiel
Water scarcity has become a salient problem in southern New Mexico. A combination of drought and a decrease in surface water for irrigation encouraged to search for other sources of water. Desalination of brackish groundwater (BGW) using reverse osmosis (RO) results in highly salty water or RO concentrate. The objectives of this two-year greenhouse study were to evaluate impacts of irrigation with RO concentrate and BGW on (1) physical and thermal soil properties, and evapotranspiration (ET) rate of pecan (Carya illinoinensis (Wangenh.) K. Koch) irrigated with BGW and RO concentrate (Chapter 1), (2) on soil microbial composition in pecan rhizospheres using microbial phospholipids fatty acids (PLFA) biomarkers as indicators (Chapter 2), and (3) on pecan growth and physiological parameters. Three treatments with four replications were prepared and irrigated with the same volume of control water (EC = 0.8 ds/m), BGW (EC = 4 ds/m), and RO concentrate (EC = 8.0 ds/m). Soil physical properties determined were texture, moisture content, bulk density, hydraulic conductivity, and moisture retention. Thermal properties measured were conductivity, diffusivity, resistivity, and heat capacity. ET and leaching fractions (LF) were determined using water balance. Significant differences were found between the treatments on thermal conductivity, diffusivity, resistivity, and heat capacity (P<0.05). Irrigation with BGW and RO increased soil thermal conductivity because soil moisture was higher in pots irrigated with BGW and RO than in control. Increases in heat capacity with increasing irrigation water salinity were the most pronounced. Pecan irrigated with RO concentrate had the lowest ET among irrigation treatments. Electrical conductivity (EC), pH, and organic matter (OM%) of the soil samples were measured from each pot. PLFA biomarkers for the microbial community were determined. For two seasons, gram-positive bacteria were found to be dominant while gram-negative bacteria disappeared in the second season. PLFAs biomarkers of fungi were found with all three treatments in the first season ; however, they appeared only with BGW in the second season. Actinomycetes were recorded in the first season while they were not seen in the second season.

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