Masters Thesis

Water use Efficiency and Nitrogen use Efficiency in Drip and Deficit Drip Irrigated Sugar Beets (Beta Vulgaris)

Efficient cropping systems emphasize the importance of both water use efficiency (WUE) and nitrogen use efficiency (NUE). One method of increasing WUE and NUE is to implement low-volume irrigation practices. Sugar beet, a resilient crop with a multitude of economical uses, is grown primarily using conventional flood irrigation but has demonstrated improved resource efficiency when grown under drip irrigation. A two-year study (2015-2017) was conducted at two different field sites located in the Central Valley of California and characterized by clay loam (Site A) and sandy loam (Site B) soils. The experimental design was a split-plot with three replications of irrigation regime as the main treatment (Drip 100% of ETc, Drip 70% of ETc, and Flood 100% of ETc) and nitrogen (N) rate as the sub-treatment (0, 112, 168, and 224 kg N ha-1). Best management practices were evaluated based on yield, sucrose yield, above ground biomass (AGB), relative crop water stress index (rCWSI), WUE, and NUE. At both sites, root yields of sugar beets were similar for the 100% drip and flood irrigated treatments. Production under deficit drip (70% of ETc) regimes resulted in the greatest WUE for AGB, yield, and sucrose yield. Sugar beet yields were not significantly influenced by N rates. However, fertilization at the lowest N rate (112 kg N haˉ¹) led to the highest NUE for AGB, yield, sucrose yield, and sucrose production. When assessing NUE based on both total available soil N and applied N, the NUE for sucrose yield showed a generally strong correlation (r2 ≥ 0.74) to total available soil N at both sites. This study is the first investigation of sugar beets cultivated in the spring under deficit drip irrigation in California.

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