Graduate Thesis Or Dissertation
 

Evaluating Alternative Soil Amendments for Organic Northern Highbush Blueberry Cultivation in Sub-Optimal Soils

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9593v374q

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  • Escalating demand for organic blueberries has driven a significant expansion of northern highbush blueberry (NHB; Vaccinium corymbosum L.) production area. This expansion is particularly pronounced in regions of the Pacific Northwest where native soil conditions are sub-optimal for NHB, notably east of the Cascade Mountain Range of Oregon and Washington, known as the Columbia Basin. Soils within the Columbia Basin present formidable challenges, characterized as calcareous, highly alkaline, with low organic matter. In contrast, the optimal conditions for NHB require well-drained, acidic soils, with high organic matter content. Current grower practices in this region include incorporating woodchips, sawdust, or compost into the soil prior to planting. Additionally, growers often incorporate additional fertilizers at planting that can minimize nitrogen immobilization, as well as manage soil pH by applying elemental sulfur, which is often supplemented by the further acidification of irrigation water by means of a sulfur burner. While these practices are commonly used in this region, they raise production costs and have yet to be scientifically assessed. Moreover, current amendments are becoming more expensive and less available. For this reason, growers are looking for alternative options for organic NHB in this region. The goal of the work contained within this thesis was to identify alternative soil amendments that could effectively enhance soil chemical parameters, plant growth, and berry yield during the establishment period. The aim was to provide practical options and recommendations for the current cultivation challenges of organic NHB in environments with sub-optimal soil conditions. To address these challenges, we conducted two experiments, a 12-week glasshouse study and a two-year field study. In our glasshouse study, we evaluated various locally available organic materials as potential soil amendments to support NHB plant growth. This region's ubiquitous wine grape, apple, and cherry tree industries are a large source of organic matter waste that is often burned or sent to landfills. Past studies supported commercial biochar as a beneficial NHB amendment, which guided our experimental treatments that consisted of woodchips (commercial standard), grape pomace, commercial biochar, and biochar derived from conifer (Pinophyta), apple (Malus domestica), and cherry (Prunus avium) trees. Biochar from regionally sourced cherry and apple wood was created on-site and compared to commercial biochar to assess the practicality for growers to process their own at a reduced cost. These materials were tested alone or co-composted with grape (Vitis vinifera) pomace. The mixed conifer biochar emerged as a promising soil amendment for NHB cultivation in the Columbia Basin, demonstrating comparable plant growth to current organic amendments. Additionally, we found that biochars and woodchips co-composted with grape pomace performed better than when used alone. These initial results show promise to improve soil conditions while reducing organic input expenses, but multi-year validation in a representative field setting is needed. Our greenhouse study findings provided insight into treatments evaluated in the subsequent 2-year field study. Due to subpar performance in NHB growth by biochars produced from cherry or apple wood, we proceeded with treatment combinations of a mixed conifer commercial biochar and grape pomace. The field trial was initiated in 2021 in the eastern Oregon region of the Columbia Basin. Four soil amendments, including biochar, grape pomace compost, biochar + grape pomace co-composted, and woodchips (grower standard control), were evaluated in combination with two placement techniques (incorporated and band applied) in a new planting of ‘Draper’ NHB. The treatment with incorporated grape pomace compost increased organic matter content, cation exchange capacity, and availability of N, P, and K in the soil compared to band applications but had no consistent effect on plant growth. However, both the band applied biochar + compost blend and compost incorporated treatments surpassed the control in terms of pruning weight during both years of the study. Furthermore, leaf area was at least 53% greater in the compost incorporated treatment than in any other treatment. Although it was not statistically different, the band applied biochar + compost blend treatment also exhibited the highest percent fruit bud set and 48% greater yield than the control. Overall, amending the soil with biochar and compost shows promise for alternative soil amendments to enhance plant growth, mineral nutrition, and fruit production in organic plantings of NHB.
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  • The work within this thesis was partially funded by the USDA National Needs Fellowship (award# 2021-38420-34064).
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