Volume 9 Issue 4
Author: Y. Cai1, F. Takeda2, B. Foote3, C. Zhang4, S. Sankaran4, and L.W. DeVetter1
1Washington State University, Northwestern Washington Research & Extension Center, Mount Vernon, WA
2USDA-ARS, Kearneysville, WV
3Oxbo, Lynden, WA
4Washington State University, Department of Biological Systems Engineering, Pullman, WA
Introduction:
- In the Pacific Northwest, most fresh market blueberries are harvested by hand, but high labor costs and low labor availability are challenges to growers.
- Mechanized over-the-row (OTR) harvesters reduce labor hours and costs, but current OTR harvesters can reduce fresh market quality through bruising.
- Modified OTR harvesters with soft-catch surfaces (SCS) have the potential to harvest blueberry with fruit quality comparable to hand harvest.
- Further research and validation are needed to advance machine harvesting technologies using modified OTR harvesters with SCS for fresh market blueberry with high fruit quality.
Objective:
- Evaluate the impacts of a modified OTR harvester prototype with SCS installed on blueberry harvest efficiency, fresh market quality, and storage.
Research approach:
- On-farm experiments were established in ‘Duke’ and ‘Draper’ fields in Lynden, WA in 2019 with three treatments including hand harvest (hand control; referred to as “hand harvest”), conventional OTR machine harvest (machine control; referred to as “HCS” for hard-catch surfaces), and modified OTR machine harvest with SCS installed in an Oxbo 7440, which was the harvester prototype (referred to as “SCS”). See Figure 1 for an image of the harvester with SCS mounted inside. The HCS machine controls were Korvan 7420 and Oxbo 7420 for ‘Duke’ and ‘Draper’, respectively (Figs. 2 and 3).
- Additional soft cushion sheets were inserted at one transfer point between the bucket elevator and horizontal grading belt for further impact reduction for the experiment with ‘Draper’ (Figure 4).
- Treatments were replicated three times. ‘Duke’ was harvested at 95% blue and packed on the same day. ‘Draper’ was harvested at 85 to 90% blue and packed the next day.
Data collection:
- Harvest efficiency data include in-row ground loss and packout. Packout was obtained from a commercial packing plant.
- Berries were stored at 39° F and 95% humidity for 28 days. Fruit quality measurements were collected after 24 hours and then every 7 days, including firmness, incidence of bruising, and water loss.
- Incidence of bruising or tissue injury was quantified using a digital imaging system. Berries were cut in half prior to image capture in an illuminated box. Pixels of bruised area and total berry area were counted digitally by an algorithm ( Figure 5).
Results:
- Ground loss. There was no difference in ground loss (Table 1) between HCS and SCS among the two cultivars. Hand harvest had the most ground loss due to fruit drop during hand harvest from overly matured berries.
| Treatment | ‘Duke’ (%) | ‘Draper’ (oz) |
|---|---|---|
| HCS | 0.5 az | 6.0 |
| SCS | 0.4 a | 8.5 |
| Hand (control) | 1.4 b | /y |
| p-value | 0.0004 | 0.64 |
Z Means followed by same lower case letter within a column are not statistically different at α=0.05.
Y Means data are not available.
- Commercial packout did not differ by treatment (Table 2). The average packout of ‘Duke’ and ‘Draper’ were 92.6% and 84.6%, respectively.
| Packout (%) | ||
| Treatment | ‘Duke’ | ‘Draper’ |
|---|---|---|
| HCS | 91.8 | 83.7 |
| SCS e/o insertion | 92.7 | 84.2 |
| SCS w/ insertion | /z | 83.0 |
| Hand (control) | 93.2 | 87.5 |
| p-value | 0.14 | 0.26 |
zMeans data not available. The soft-cushion insertion was only tested using ‘Draper’.
- Differences were not detected until day 14 (Table 3). Firmness of hand harvested ‘Duke’ during the first 14-day storage period was numerically highest and statistically highest from day 21 and onward. Firmness of ‘Duke’ harvested by SCS was numerically higher than berries harvested by HCS. There were no differences in firmness of ‘Draper’ among harvest types during the first 14-day storage period and on day 28. ‘Draper’ harvested by SCS with the insertion had the highest firmness on day 21.
| Firmness (g/mm of deflection) | |||||
| Treatment | Day 1 | Day 7 | Day 14 | Day 21 | Day 28 |
|---|---|---|---|---|---|
| ‘Duke’ | |||||
| HCS | 121.0 | 117.6 | 108.3 | 100.5 bz | 89.5 b |
| SCS | 126.5 | 113.3 | 112.0 | 104.4 ab | 92.85 ab |
| Hand (control) | 133.9 | 123.8 | 120.0 | 119.0 a | 103.5 a |
| p-value | 0.09 | 0.06 | 0.10 | 0.03 | 0.03 |
| ‘Draper’ | |||||
| HCS | 192.5 | 192.3 | 182.4 | 151.4 b | 137.7 |
| SCS w/o insertion | 189.5 | 191.4 | 181.5 | 161.9 ab | 139.6 |
| SCS w/ insertion | 183.8 | 192.7 | 192.4 | 175.7 a | 144.5 |
| Hand (control) | 197.9 | 198.9 | 186.8 | 164.9 ab | 136.8 |
| p-value | 0.17 | 0.56 | 0.36 | 0.03 | 0.62 |
- No differences were detected until day 14 (Table 4). There was less bruising in hand harvested ‘Duke’ on day 14 as well as on day 21. Hand harvested ‘Draper’ had less bruising from day 14 and onward. ‘Draper’ harvested with SCS with the insertion had less bruised fruit on day 21 compared to the other machine harvest treatments.
| Percent bruising area (%) | |||||
| Treatment | Day 1 | Day 7 | Day 14 | Day 21 | Day 28 |
|---|---|---|---|---|---|
| ‘Duke’ | |||||
| HCS | 64.0 | 73.9 | 77.9 az | 76.4 a | 79.8 |
| SCS | 61.2 | 71.8 | 71.2 ab | 73.9 a | 79.4 |
| Hand (control) | 56.6 | 67.4 | 69.1 b | 69.3 b | 69.9 |
| p-value | 0.08 | 0.27 | 0.02 | 0.02 | 0.08 |
| ‘Draper’ | |||||
| HCS | 33.0 | 26.0 | 31.8 a | 40.6 a | 50.8 a |
| SCS w/o insertion | 33.0 | 27.9 | 33.2 a | 42.8 a | 54.9 a |
| SCS w insertion | 31.8 | 27.5 | 33.3 a | 30.5 b | 50.4 a |
| Hand (control) | 27.3 | 21.2 | 22.8 b | 23.9 b | 36.8 b |
| p-value | 0.15 | 0.14 | 0.0007 | 0.0004 | 0.006 |
ZMeans followed by same lower case letter within a column are not statistically different at α=0.05.
A p-value of less than 0.05 indicates statistical significance.
- Water loss. Water loss was the same in ‘Duke’ across all treatments during the storage period, but was highest in ‘Draper’ on day 28 when harvested using SCS without the insertion (Table 5). The high water loss among ‘Draper’ fruit harvested using the SCS may be potentially due to edge effects as these plots were on the furthest side of the field with higher light exposure, leading to increase softness that could exacerbate water loss in storage.
| Percent bruising area (%) | ||||
| Treatment | Day 7 | Day 14 | Day 21 | Day 28 |
|---|---|---|---|---|
| ‘Duke’ | ||||
| HCS | 2.4 | 5.0 | 6.0 | 8.3 |
| SCS | 1.9 | 4.1 | 5.7 | 7.7 |
| Hand (control) | 2.2 | 4.5 | 5.7 | 7.2 |
| p-value | 0.27 | 0.10 | 0.93 | 0.58 |
| ‘Draper’ | ||||
| HCS | 1.6 | 2.9 | 4.5 | 6.1 az |
| SCS w/o insertion | 1.9 | 4.7 | 6.4 | 8.2 b |
| SCS w insertion | 1.7 | 3.2 | 5.0 | 6.5 ab |
| Hand (control) | 1.7 | 3.3 | 4.7 | 6.0 a |
| p-value | 0.20 | 0.08 | 0.07 | 0.05 |
ZMeans followed by same lower case letter within a column are not statistically different at α=0.05.
A p-value of less than 0.05 indicates statistical significance.
Take-aways from 2019 and next steps
- No harvest efficiency losses were observed between HCS and SCS when installed in OTR harvesters.
- Hand harvested berries have higher firmness and less bruising than machine harvested berries during a 28-day storage period. However, SCS moderately improved firmness in ‘Duke’ relative to HCS during storage.
- The soft cushion insertion between the bucket elevator and horizontal grading belt improved firmness and reduced bruising in ‘Draper’ during storage, but installation will need to be optimized for improved harvesting in the field as fruit sometimes got stuck with the insertion.
- The lack of more significant differences between harvester types is likely due to fruit getting over-mature relative to most fresh market operations that begin harvesting at 50-60% blue. Our fields were harvested at >85% blue, which is standard for machine harvesting for processed markets. Harvest timing for fresh market operations should be earlier to increase firmness and postharvest longevity while reducing the incidence of bruising. Earlier picking times with OTR prototypes with SCS will need to focus on selectivity so ripe berries are harvested and immature (green) fruit is left behind for continued development.
- Overall, SCS can improve firmness and reduce bruising without sacrificing harvest efficiency compared to conventional OTR harvesters with HCS. The additional of soft materials at the transfer belt has potential to further improve postharvest fruit quality.
- The experiment will be repeated in summer 2020.
- We are also studying machine harvest intervals using modified OTR harvesters and impacts on fruit quality.
- Remember, machine harvesting high quality fruit for fresh market doesn’t rely solely on machine engineering, but several other interconnected factors (Figure 6).
Acknowledgements:
Thank you to Sean Watkinson, Huan Zhang, Amit Bhasin, Qianwen Lu and Brenda Janeth Madrid Martinez for field support. Great thanks to Scott Korthuis, Kathryn Vanweerdhuizen and Clayton Polinder from Oxbo for providing harvester and technical support. We also appreciate cooperating farms and packing plants for helping in harvest and packing. At last, we would like to acknowledge our funding sources as following:
