Graduate Thesis Or Dissertation
 

Effects of Novel Sulfur Applications for pH Management of Calcareous Soil in a New Planting of Organically Grown Northern Highbush Blueberry (Vaccinium corymbosum L.) in the Columbia Basin

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pn89dg222

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  • Organically certified Northern Highbush Blueberry (NHB; Vaccinium corymbosum L.) production in the Columbia Basin region of Oregon and Washington is expanding. Soils in the region are typically calcareous and highly alkaline, often requiring pH adjustment to an ideal range of 4.5–5.5 to support the establishment of the acid-loving, ericaceous crop. Soil pH adjustment is commonly accomplished via incorporation of elemental sulfur (S°), the oxidation of which is mediated by soil borne Thiobacillus bacteria to form the acidifying agent sulfuric acid (H2SO4). In the region’s organic NHB plantings, soil pH management by application of S° is often supplemented by additional acidification of irrigation water by means of a S° burner. The S° burner combusts S° to form sulfur dioxide (SO2) gas, which is then passed through water to form sulfurous acid (H2SO3) which is injected into the irrigation mainline at a controlled rate. Current guidelines for soil S° application methods and adoption of the S° burner are based largely on recommendations developed for the major NHB production regions west of the Cascade Mountain range and have not been locally adapted for the unique climate and pedology faced by NHB growers in the Columbia Basin. The objective of the work described in this thesis was to evaluate novel application techniques of different S° formulations to reduce soil pH to suitable levels in a new 0.24-hectare (Ha) planting of NHB cv. ‘Duke’ in an alkaline, calcareous soil characteristic of the Columbia Basin. The study took place over three growing seasons between Spring 2020 and Fall 2022 at Oregon State University’s Hermiston Agricultural Research and Extension Center (HAREC). We hypothesized that aspects of soil pH, plant performance, and berry production can be optimized through novel S° application techniques. The S° techniques were installed with or without supplemental acidification of irrigation water using an organic-approved S° burner. Soil S° application treatments included: 1) grower standard of applying 1700 kg ·Ha-1 of S° to the soil surface eight months prior to planting; 2) fertigation via the drip irrigation system of micronized S° microparticles over eight weekly applications after planting; 3) soil incorporation of S° prills at a rate of 1700 kg·ha-1 directly before planting without the allowance of the standard fallow period; 4) soil incorporation of dry S° prills at a rate of 1700 kg·ha-1 directly before planting followed by 8 weeks of fertigation with micronized S°; 5) incorporation of S° prills as in the control followed by surface application of S° prills at a rate of in 500 kg·ha-1 in Spring of year two; 6) and micronized S° application directly after planting followed by annual surface application of S° prills at a rate of 500 kg·ha-1 in Spring of year two. Soil pH, the average baseline vale of which was 7.2 before planting, was lower in plots receiving acidified irrigation water than those receiving unacidified water beginning in Fall 2020 (5.66 vs. 6.09), a trend that persisted until the end of the study in Fall 2022 (5.43 vs. 6.05). Average yield was greater in plots receiving acidified water compared the receiving unacidified water over the 2021 and 2022 seasons, producing 21.4% and 15.9% greater berry yields, respectively. These results suggest acidification of irrigation water remains a beneficial soil pH management practice for NHB plantings in the calcareous soils of the Columbia Basin. Soil pH among S° application techniques was similar between the grower standard and those treatments that received soil incorporation of S° directly before planting throughout the course of the study, with berry yield and fresh pruning weights being similar among these treatment groups for 2022 measurements. These findings indicate the grower standard of allowing a fallow period before incorporation of S° prills does not have a significant effect on soil pH adjustment beginning in the first planting year, and does not significantly affect plant biomass accumulation or berry yield beginning in year two of a newly established planting of organically certified NHB. Furthermore, the grower standard of allowing a fallow period prior soil incorporation of S° in an organic planting of NHB does not meaningfully improve soil pH management or overall berry yields during establishment. These findings support a decreased establishment cost for Columbia Basin organic NHB growers, as fields can be brought into production more quickly relative to current standard practices. The results of this study will help to inform region-specific soil pH management recommendations for organic NHB growers in the Columbia Basin, but caution should be taken until more long-term data is available. A second study was conducted to evaluate the applicability of using imaging sensors mounted on small unmanned aerial systems (sUAS) to estimate spectral character and plant height in the established NHB planting described above. This research was conducted during the 2022 growing season. Collection of imagery using a specialized multispectral (MS) sensor mounted on an agricultural survey drone was performed and imagery was processed to generate the common plant performance indices, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Red Edge Index (NDRE). Estimations of plant height from Digital Surface Models (DSM) generated by photogrammetric processing of (Red, Green, Blue) RGB imagery collected using a consumer-grade sUAS was also performed. These imaging outputs were compared against manually collected field measurements of red and infrared light transmittance in leaves, a proxy for leaf chlorophyll content, using a handheld SPAD meter in the case of MS imagery and manual measurements of plant height in the case of the DSM-derived plant height estimations. The objective was to determine if either of these remote-sensing techniques represented a worthwhile improvement in terms of reliability over traditional field measurements. Data consisted of MS imagery, RGB imagery, SPAD measurements, and manual plant height measurements collected within a 48-hour window at four discrete sampling dates (2 Jun, 21 Jun, 19 Jul, and 4 Sep) to facilitate direct comparison of disparate data types. Comparisons were conducted following the 2 x 6 factorial arrangement described above to evaluate if remotely sensed datasets would detect alternative segregation of treatment effects relative to the manual estimations that were already being used in the study. Simple linear regressions were also modeled based on ten unique pairwise combinations of data types on datasets aggregated across all sampling dates and treatment plots. This was done to draw generalized conclusions about the strength of correlation between the metrics being assessed. When viewed within the context of the 2 x 6 factorial design of the original NHB field trial, use of NDVI and NDRE to assess spectral character resulted in segregation of treatment effects, whereas the use of SPAD reading failed to detect any significant difference across all sampling dates. Differences in detected treatment segregation between NDVI and NDRE values indicate the need for further research regarding the relative suitability of these two indices when used as proxies for NHB health. Relative fit of the linear regression models was highest when comparing manual and DSM-derived plant height values (R2 = 0.714), indicating an insufficient degree of correlation between remotely sensed and manually collected plant height estimations based on the specific protocols applied to confidently consider the two datasets interchangeable. Though the relative height estimates of NHB plants from DSM-derived measurements were consistent across all data sets, technical limitations related to low GPS resolution on the consumer-grade sUAS resulted in a tendency to underestimate plant height by 23 cm, on average, when compared to manually-derived values and a high degree of variability between bare-ground elevation estimates collected on different dates (> 5 m difference between sampling dates). These finding contribute to the body of research regarding remote sensing of NHB phenomics using sUAS and aid in determining whether adoption of sUAS-mounted sensors for NHB phenotyping represent a meaningful improvement over traditional field collection methods.
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