Potential Benefits of Humic Acids on Yield and Fruit Quality in Highbush Blueberry

Goals / Objectives
Evaluate the effects of humic acids on 1) shoot and root growth, 2) yield, 3) fruit quality (berry size, firmness, Brix, titratable acidity), 4) leaf nutrient status, 5) soil chemical, physical, and biological properties (pH, nutrients, organic matter content, infiltration, bulk density, water holding capacity, and soil microbial activity), 6) mycorrhizal fungal colonization, and 7) incidence of Phytophthora root rot in a mature planting of highbush blueberry.

Project Methods
The research will be conducted in a mature 0.6-acre field of ¿Bluecrop¿ blueberry established at the Oregon State University Lewis-Brown Horticulture Research Farm in Corvallis, Oregon. Treatments will be arranged in a split-plot design with six replicates. The main plots will include a combination of two irrigation methods, microsprinklers (to simulate sprinklers) and drip (two laterals per row), each with and without potassium phosphite for root rot control. The subplots will include 1) humic acids (22% humic acids + ammonium sulfate fertilizer), 2) humic acids nutrient management program (12.5% humic acids + NPK+Zn fertilizers), 3) a control for the humic acids treatment (ammonium sulfate fertilizer only) and 4) a control for the humic acids nutrient management program treatment (NPK+Zn fertilizers only). A total of 165 lbs/acre of N will be applied to each treatment per year using a triple-split application (April, May, and June) of granular fertilizer banded on each side of the row in the sprinkler plots and weekly fertigation (mid April to late July) with liquid fertilizer through the irrigation system in the drip plots. Humic acids will also be banded using a sprayer every 2 weeks (sprinklers) or applied weekly by fertigation (drip). Shoot growth will be measured each season by counting the total number of new whips produced on each plant and measuring cane length weekly. Root production will be quantified on one plant per plot during two major peaks in root growth, which, based on our minirhizotron work in blueberry, is at approx. 2 weeks before the fruit begin ripening and 2 weeks after harvest. To avoid excessive disturbance to the roots and soil, different plants in the plots will be selected for root sampling on each sampling date. Roots will be carefully washed from each core in 10-cm depth increments, cleaned with tweezers, scanned using a flatbed scanner, and analyzed for total root length. The roots will also be analyzed for mycorrhizal colonization and Phytopthora infection on each collection date. Ripe fruit will be hand-harvested three or four times per summer and weighed to determine the total marketable yield in each treatment plot. A subsample of fruit will be also weighed and counted to determine average berry weight, and diameter and firmness of each berry will be measured using a firmness tester. The berries will then be frozen and later analyzed for soluble solids and titratable acidity. Leaf samples will be collected in early-August each year and analyzed for nitrogen (N) and other nutrients. Soil samples will be collected each fall and analyzed for extractable nutrients, organic matter, N, and soil pH and EC. Water infiltration will be measured using a single ring falling-head procedure. Bulk density will be measured on cores collected using a hammer-driven core sampler. The cores will also be measured for water holding capacity and then incubated to determine soil microbial activity. Amendment #3 adds funds to continue the current research objectives and will be used to collect and process field samples, conduct data analyses, present results at grower meetings and field days, and prepare research for publication.