Volume 5 Issue 3
Lead scientists: Lisa W. DeVetter (Assistant Professor of Small Fruit Horticulture at WSU-Mt. Vernon), Dave Bryla (Research Horticulturist at USDA-ARS, Corvallis), and Sean Watkinson (Scientific Assistant for the WSU Small Fruit Horticulture Program)
Acknowledgements: Chris Benedict (Whatcom County Extension) and Randy Honcoop (red raspberry grower cooperator in Lynden, WA)
Address Questions to Lisa DeVetter at: lisa.devetter@wsu.edu
Objective
The objective of this study were to evaluate the impact of organic acids on mature and immature (established and establishing, respectively) red raspberry. Please note that organic acids are also commonly known as “humic acids”.
Approach
Mature red raspberry trial
This trial was initiated in 2015 in a four-year old commercial field of ‘Meeker’ red raspberry grown in Whatcom County, Washington. Treatments were applied in a conventionally managed field that was part of a larger trial comparing different fertilizer, cover cropping, and irrigation practices. In this study, four treatments were compared and the experimental design was a completely randomized design with treatments replicated three times. Plots in which the treatments were applied were single-row plots 17 feet in length with treatments applied on both sides of the row. Treatments included: 1) organic acids; 2) brassica seed meals; 3) organic acids plus brassica seed meals; and 3) standard grower management practices (control). The organic acid treatment was a commercial product (22% organic acids). The brassica seed meal was Pescadaro Gold Mustard Meal and was applied annually on the soil surface of the row at 1 ton/acre. This report will focus on the organic acid treatments, which were applied with a pressurized hand-held sprayer. Organic acid treatment application began in April 2015 and the first application was applied in solution with water at 4 gallons/acre. Following this, the organic acid treatments were applied at 2 gallons/acre every other week until Sept. 1, 2015. Nutrient applications were not adjusted in any of the treatments and followed grower management practices. Data collected include estimated yield through yield component analysis, average berry weight, leaf nutrient concentration, and soil chemistry.
Immature red raspberry trial
This trial began in Spring 2014 at the Washington State University Mount Vernon Research and Extension Center located in Mount Vernon, Washington. Six-plant raised-bed plots (2.5 x 10 ft) of ‘Meeker’ and ‘Malahat’ red raspberry were planted Spring 2014. The experimental design was a randomized complete block design replicated five times. Cultivar plots received either an organic acid fertility program or not (OA+/- ; OA was 22% organic acids). These rates were divided into five equal applications, with applications occurring in late May, early June, mid June, late June, and mid July, as per the recommendations of the organic acids manufacturer. The organic acid products were applied simultaneously in a solution of water around the base of each plant and immediately watered in. All plots were fertilized at a rate of 55 lbs. N/acre (18 lbs. granular and 37 lbs. fertigated) in 2014 and 78 lbs. N/acre (60 lbs. granular and 18 lbs. fertigated) in 2015. Plants were irrigated based on volumetric water content, which was approximately three times per week in the summer for 4-6 hours via drip irrigation. Data collected includes primocane height, leaf nutrient concentration, soil chemistry, estimated yield through yield component analysis, and average berry weight. Yield and berry weight data were only collected in 2015, which was the first cropping year for the planting. In Fall 2014, one plant per plot was excavated and biomass of roots, leaves, and canes were determined.
All data were analyzed using RStudio (Version 0.98.1103 – © 2009-2014 RStudio, Inc.). Assumptions of normality and unequal variance were corrected using transformations and data are reported in original units. Statistical significance was declared at P < 0.05.
Summary
In both the mature and immature trials, we observed few effects of the organic acid amendments. This observation was most pronounced in the mature trial, where we saw no differences in estimated yield, berry weight, tissue nutrient concentrations, nor soil chemistry (Tables 1 to 3). It is important to consider that the lack of a response in the mature trial could be due to the fact that plants had a large amount of carbohydrate and nutrient reserves in the tissues from the previous growing seasons and/or because the organic acid treatments were not fertigated and subsequently washed down into the raspberry plant rhizosphere. These results suggest that application of organic acids directly on the soil surface as a spray do not manifest into increased growth and yield for the conditions of the study. We would like to continue experimenting with organic acids in mature red raspberry for at least another year, and time the applications before an irrigation event so to better ensure the product is getting into rhizosphere.
In the immature trial, we observed increased primocane growth with organic acid treatments in both years of the trial, excluding ‘Malahat’ in 2014 (Table 4). Biomass of roots, leaves, and canes were also numerically greater from plants treated with organic acids, particularly for ‘Meeker’ (Figures 1 and 3). Plants treated with organic acids also appeared to produce more fine roots (Figures 2 and 4). However, we observed no differences in estimated yield nor berry weight during the first cropping year of the immature trial. It is important to note that this planting was weak compared to commercial standards, despite adequate mineral nutrition and irrigation. We attribute the weak planting to be due to the high temperatures experienced in 2015. Additionally, we observed few differences in tissue nutrient concentrations and soil chemistry (Tables 5 to 8).
Data resulting from these trials combined with our observations indicate organic acid amendments can increase cane growth and biomass in new plantings, as well as increase production of fine roots. These effects may be advantageous in soils of poor quality or with high soilborne disease pressure. Yet, these impacts were not associated with increases in fruit production under the conditions of our experiments. We would like to continue experimenting with organic acids in red raspberry, particularly in a controlled greenhouse environment and in modified trials with mature red raspberry where organic acids are directly irrigated into the rhizosphere after application.
*Please note – The name of the organic acids products are intentionally excluded in this report at the request of the manufacture.
Results
Mature Red Raspberry
Table 1. Estimated yields and berry weight of ‘Meeker’ red raspberry treated with brassica seed meal and organic acid amendments, 2015.
Table 2. Tissue nutrient content of ‘Meeker’ red raspberry treated with brassica seed meal and organic acid amendments, 2015.
*Treatment codes, with BSM = brassica seed meal, OA = organic acids, OABSM = organic acids + brassica seed meal, and STD = standard grower practice (control).
**Significance, with NS = not significant.
Table 3. Soil chemistry analyses of soils grown with ‘Meeker’ red raspberry treated with brassica seed meal and organic acid amendments, 2015.
*Treatment codes, with BSM = brassica seed meal, OA = organic acids, OABSM = organic acids + brassica seed meal, and STD = standard grower practice (control).
**Significance, with NS = not significant.
Immature Red Raspberry
Table 4. Primocane height, estimated yield, and berry size of ‘Meeker’ and ‘Malahat’ red raspberry treated with organic acids (OA), 2014 and 2015. Note that the first cropping season for this planting was 2015, so only yield data from 2015 is presented.
*Significance at P < 0.05 and NS denotes not significant.
Table 5. Tissue nutrient content of ‘Meeker’ and ‘Malahat’ red raspberry treated with organic acids (OA), 2014.
*Significance at P < 0.05 and NS denotes not significant.
Table 6. Tissue nutrient content of ‘Meeker’ and ‘Malahat’ red raspberry treated with organic acids (OA), 2015.
*Significance at P < 0.05 and NS denotes not significant.
Tissue 7. Soil chemistry analyses of soils grown with ‘Meeker’ and ‘Malahat’ red raspberry treated with organic acid (OA) amendments, 2014. Cultivars are combined.
*Significance at P < 0.05 and NS denotes not significant.
Table 8. Soil chemistry analyses of soils grown with ‘Meeker’ and ‘Malahat’ red raspberry treated with organic (OA) amendments, 2015. Cultivars were combined.
*Significance at P < 0.05 and NS denotes not significant.
Figure 1. Biomass of ‘Meeker’ red raspberry treated with and without organic acids, 2014. Orange is treated, yellow is untreated (control).
Figure 2. Roots of ‘Meeker’ red raspberry treated with or without organic acid (OA) amendments, 2014. Left is treated, right is untreated (control). Photo courtesy of Sean Watkinson.
Figure 3. Biomass of ‘Malahat’ red raspberry treated with and without organic acids, 2014. Orange is treated, yellow is untreated (control).
Figure 4. Roots of ‘Malahat’ red raspberry treated with or without organic acid (OA) amendments, 2014. Left is treated, right is untreated (control). Photo courtesy of Sean Watkinson.