- The knowledge about the intensive agricultural irrigation is very limited, but the use of irrigation is rapidly increasing. As an outcome, the sympathetic ecosystem is accepting modern irrigation that will play an essential function in the present and future for agricultural products. My dissertation will display the modification for investigation of the integration among atmosphere conditions and soil water content, analysis of the stable water isotopes results, fieldwork of experiments, and quantifying unproductive water losses as evaporation ratio from the irrigation designs. This study was covered largely the territories of the Pacific Northwest in the US, in summer over three years, and these farms were alfalfa, corn, potato, and a hazelnut field. My research goal of this academic work that is a study a detailed investigation and analysis of the water lost as evaporation, which is influenced via using various irrigation designs and thus improves agriculture economically. Moreover, this study described the advantages of the isotopic compositions technique that used in this dissertation.
The first section of this dissertation contains an experimental study to assess the influence of irrigation structural configurations on evaporation losses in semiarid agricultural systems by using stable water isotopes. During mid-summer 2017 in eastern Oregon and southeast Washington, we collected soil samples at multiple positions and depths around the central irrigation tower from four different agricultural fields, each with both Mid Elevation Spray Application (MESA) and Low Elevation Spray Application (LESA) configurations. We measured the hydrogen and oxygen stable isotope ratio of soil water at MESA and LESA field locations using H2O liquid–H2O vapor equilibration laser spectroscopy. Though soil moisture contents were similar, the average isotope ratio of soil water under LESA irrigation (δD= -114.5‰, δ18O= -14.5‰) had lower values than under MESA irrigation (δD = -108.2‰, δ18O = -13.1‰). Calculated E/I values demonstrated higher sprinkler and soil water evaporation occurring at the MESA irrigated locations (E/I=16.1 %) compared to the LESA irrigated locations (E/I=9.0 %). We find that LESA systems have lower non-productive water losses than MESA systems and are thereby more efficient users of applied water. Our results suggest that stable water isotopes provide a technique for improving the management of water resources through the assessment of irrigation efficiency.
The second section is included the results of the differences in soil evaporation between row and interrow positions in furrowed agricultural fields. At Hermiston city, Oregon, soil evaporation from the row and interrow positions within potato fields of contrasting irrigation timing (daytime vs nighttime) was estimated based on hydrogen and oxygen isotope ratios. Samples collected throughout the 2016 growing season were measured and used to calculate soil evaporation (E) losses relative to applied irrigation (I). On average, row positions were more enriched in heavy isotopes than interrow positions, indicating that the evaporated fraction of applied irrigation (E/I) depends on the position. Within the day irrigated field the estimated (mean ± standard deviation) E/I ratios determined from both stable isotopes for May, July, and September were 18±8%, 10±3% and 19±5% for row samples and 15±6%, 7±2% and 12±4% for interrow samples. Within the night irrigated field during these same months, the E/I ratios were 13±12%, 16±7% and 13±5% for row samples and 12±7%, 9±2% and 6±2% for interrow samples, respectively. These results reveal that there is more evaporation from the row, as compared with interrow, positions. Therefore, management strategies and practices for water conservation should take into account larger non-productive soil evaporation losses from within rows to minimize evaporative soil water losses.
The third section of our dissertation that is estimating evaporation by using stable water isotope from a hazelnut farm with two designs of drip irrigation. Drip irrigation is often considered an efficient means of water delivery, however how the efficiency changes as more emitted are added to a system is unclear as additional water may be lost to evaporation before it can be taken up by roots. In this study, non-productive soil evaporation losses are estimated based on the hydrogen and oxygen isotope ratios of soil moisture for a hazelnut field in the Willamette Valley of the Pacific Northwest. Soil samples from the hazelnut field under single-line and double-line drip irrigation treatments were collected in summer 2018 at multiple depths from different positions in the tree rows. The stable isotope ratio of soil water in these samples was measured using H2O liquid - H2O Vapor equilibration laser spectroscopy. Our results show average 2H/1H and 18O/16O isotope ratios of the single line with drip irrigation were higher than the double line with drip irrigation. These results suggest that less soil evaporation occurred from the double-line drip irrigation (E/I = 17.33 ±6%) when compared to the single-line treatment (E/I = 20.93 ±6.5%), which also had higher soil moisture levels than the single line with drip irrigation that irrigated during the day. This suggests that increasing the number of drip emitters can lead to an increase in the efficiency of drip irrigation when efficiency is defined as the fraction applied that is used productively by plants.