Analyzing Early Growth Characteristics and Anchorage Force to Improve Cultivation Tolerance in Carrots

Progress report for GNE19-194

Project Type: Graduate Student
Funds awarded in 2019: $14,683.00
Projected End Date: 10/31/2022
Grant Recipient: University of Maine
Region: Northeast
State: Maine
Graduate Student:
Faculty Advisor:
Dr. Eric Gallandt
University of Maine
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Project Information

Project Objectives:
  1. Examine selected carrot cultivar early growth characteristics in the greenhouse and lab, including shoot height, shoot and root area, root to shoot area ratio, root branching, and shoot and root dry weights using a previously purchased WinRHIZO™ program (Regent Instruments, Québec, Canada).
  2. Determine carrot cultivar root anchorage force in the lab using a previously purchased Alluris® FMI-B150 Force Gauge.
  3. Assess carrot cultivar tolerance to cultivation events by examining crop injury pre- and post-cultivation after use of finger weeders or tine harrows. 
  4. Compare carrot yields across tool treatments and compare to a hand-weeded control treatment.
  5. Perform correlation analyses between carrot early growth characteristics and field experiment results to determine “cultivation tolerance” and determine which growth traits may aid in said tolerance.
Introduction:

The purpose of this project is to help identify traits of carrot cultivars that make them more tolerant to mechanical cultivation. Organic vegetable production in the northeast is growing, but small-seeded crops such as carrot often suffer significant yield and quality losses to weeds because their slow early season growth and size make them less competitive and more prone to injury. Growth characteristics that help a carrot better tolerate cultivation could help direct future plant breeding efforts and help organic vegetable farmers make more informed cultivar selections. 

Cooperators

Click linked name(s) to expand

Research

Materials and methods:

Seven popular commercial carrot cultivars were selected for early growth characteristic screening in 2019 to determine which cultivars and variables to assess in subsequent studies. Nine cultivars were selected in 2020 based on their root and shoot growth to represent a range of carrot growth characteristics. Cultivars were arranged in the greenhouse in a factorial randomized block design with six replications. Each carrot cultivar had four growth stages tested: seed weight, and one, two, and four true leaves. Average seed weight was determined for each cultivar prior to sowing by weighing three samples each of 100 seeds. Anchorage force, biomass, and selected root growth parameters were measured at each stage (Obj. 1-2); for each of the true leaf growth stages two carrots were seeded, one for anchorage force testing and one for analyzing the growth characteristics. Seeds were sown to a depth of 0.63 cm in ConeTainers (Stuewe & Sons, Inc., Tangent, OR) filled with coarse pool sand media using a dibble and watered as necessary. Cones were fertilized once per day using Peter’s Professional 20-20-20 general purpose fertilizer to ensure emergence and growth in the sand media. Cone location in a tray was randomly selected for each cultivar and growth stage and labeled appropriately.

Carrot cultivar tolerance to physical weed control was assessed in a field trial with a factorial arrangement of six cultivars and three physical weed control treatments, using a completely random design with four replications. Physical weed control treatments consisted of cultivation at two-true leaves with finger weeders or tine harrows, and a weed-free control. Plots measured 3.0 m long by 0.5 m wide with two rows of carrots on 50 cm rows sown at a depth of 0.63 cm. Beds were formed using a cultipacker and carrots were sown using a Jang six-row tractor-mounted seeder using recommended seed rollers and calibrations.  

Objective 1. Examine selected carrot cultivar early growth characteristics in the greenhouse and lab, including shoot height, shoot and root area, root to shoot area ratio, root branching, and shoot and root dry weights.

As true leaf growth stages were reached, plant shoot height (cm) was recorded and plants were destructively harvested, carefully washed, and placed in a tray for scanning using the WinRHIZO™ system (Regent Instruments, Québec, Canada) to quantify root and shoot area. Roots and shoots were separated, dried at 65ºC for at least three days in a lab drying oven, and weighed to determine dry root and shoot biomass. Root and shoot area data were pulled from WinRHIZO-generated scan files for analysis.  

 

Objective 2. Determine carrot cultivar root anchorage force.

Additional plants were subjected to anchorage force testing using an Alluris® FMI-B150 Force Gauge. Plants were attached via metal clip at the soil level to the force gauge hook and pulled straight up at a constant speed until all roots had been removed from the soil or the plant stem broke off from the roots. The maximum and average force (Newtons) required to remove a plant from the soil were recorded and data was pulled from the Alluris-generated Excel files for analysis.  

 

Objective 3. Assess carrot cultivar tolerance to cultivation events by examining crop injury pre- and post-cultivation. 

We measured crop mortality from cultivation with either finger weeders or tine harrows by recording the number of carrots pre- and post-cultivation in each of the two rows per plot. Post-cultivation data collection was performed approximately 24 hours after cultivation to ensure desiccation.

 

Objective 4. Compare carrot yields across tool treatments and compare to a hand-weeded control treatment.

Carrots were harvested by hand digging. Each plot was split into four subsampling areas of equal size. Carrots were removed from the soil, dunked in two buckets of water to remove soil, and brought to the farm lab for processing. Subsamples were divided into ‘marketable’ versus ‘unmarketable’ (having major defects). Within each category and subsample, the number of carrots was recorded, as well as total fresh weight in grams. Carrot tops were removed using garden clippers, and carrot root fresh weight was recorded (grams). Carrot yields will be analyzed in JMP 15 Pro and contrasts will be used to compare cultivated treatments to a hand-weeded control treatment to determine any differences.

 

Objective 5. Determine whether carrot early growth characteristics are related to “cultivation tolerance” and determine which growth traits may aid in said tolerance.

Using JMP 15 Pro, early growth data including root and shoot biomass, root and shoot area, and shoot height will be correlated with crop mortality and carrot yield data from the field trial. This analysis will be used to determine if meaningful relationships exist between root and shoot morphology and crop mortality from mechanical cultivation. Based on this analysis, a “cultivation tolerance” table will be developed to help inform plant breeders and farmers about cultivar tolerances to physical weed control.

Research results and discussion:

The greenhouse trial was completed from July-September, and the field trial from July to October. Due to the late start the data from this year is currently being analyzed, and final results are expected to be written up by spring. Below are tables and figures of data that has been summarized to date. Pictures from this year are also attached for reference.

Obj. 1-2-

Table 1. Greenhouse Trial Analysis of Variance results using JMP at α = 0.05. 

Source 

Shoot Ht 

Shoot Area 

Shoot Mass 

Root Area 

Root Mass 

Root:Shoot 

Max AF 

Avg AF

 

----------------------p-value---------------------- 

 

Cultivar (C) 

<0.0001

<0.0001

0.019

0.0054

0.007

0.779

0.687

0.0008

Growth Stage (G) 

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

0.136

0.975

<0.0001

C x G 

0.490

0.0588

0.0583

0.563

0.006

0.651

0.907

0.0216

Block 

0.775

0.119

0.511

0.396

0.298

0.712

0.385

0.496

Figure 1. Mean root area (cm2) by cultivar category, separated by true leaf growth stage. Error bars represent standard error of the mean.

Figure 2. Mean shoot area (cm2) by cultivar category, separated by true leaf growth stage. Error bars represent standard error of the mean.

Obj. 3-5-

Table 2. Mean ±SE for crop mortality and in-row weed control efficacy by cultivar. Data is averaged across weed control treatments.

Cultivar

Crop Mortality

Weed Control Efficacy

 

---------------%---------------

Bolero

10.23±3.32

68.48±5.02

Yellowstone

23.69±5.49

78.11±1.19

Dragon

16.90±2.38

65.52±4.23

SFF

10.79±1.47

38.38±4.43

NB1

12.71±2.42

35.50±3.32

NB2

17.21±4.23

44.80±4.89

 

Table 2. Mean ±SE marketable versus unmarketable crop yield variables. Data is averaged across weed control treatments.

Cultivar

Marketable Crop Count

Marketable Total Fresh Wt.

Marketable Root Fresh Wt.

Unmarketable Crop Count

Unmarketable Total Fresh Wt.

Unmarketable Root Fresh Wt.

 

 

--------g m-2--------

 

--------g m-2--------

Bolero

17±2

1586±145

1205±112

4±1

160±21

110±14

Yellowstone

14±2

1419±166

823±95

5±1

252±44

139±26

Dragon

17±1

2275±178

1580±122

5±1

265±31

175±21

SFF

17±2

1058±115

865±94

6±1

253±46

204±37

NB1

21±1

1023±68

828±57

5±1

162±20

126±16

NB2

5±1

445±39

341±31

2±1

248±28

186±22

Figure 3. Mean crop mortality by cultivar category and weed control treatment. Error bars represent standard error of the mean.

Figure 4. Mean marketable total crop fresh weight (g/m2) by cultivar category and weed control treatment. Error bars represent standard error of the mean.

Figure 5. Mean total hand-weeding labor (hours/acre) to achieve weed-free conditions for each weed control treatment. All treatments were hand weeded at one true leaf. Finger weeder and tine harrow treatments were hand weeded once 14 days after cultivation. The hand-weeding only treatment was weeded every 14 days for a total of three times after the initial hand weeding event.

 

Summary points to date-

Greenhouse (Obj. 1-2)-

  • No cultivar differences detected at first true leaf, but cultivars diverge in growth allocation thereafter.
  • “Top” category appears to put more growth allocation into shoot height after first true leaf.
  • Once fourth true leaf is reached, Bolero has biggest root and shoot area and mass.
  • “Bottom category” has lowest shoot and root area and mass at four true leaves- these cultivars tend to have slower emergence and put resources into roots and shoots equally.

Field (Obj. 3-5)-

  • “Top” category prioritizes shoot growth first, but this resulted in greater crop mortality from tine harrows, which have more contact with carrot tops than finger weeders.
  • Yield differences still need to be analyzed. Marketable total crop fresh weight graphs show a general trend of yields being similar across weeding treatments, but tine harrowing may reduce yield in cultivars which prioritize shoot growth early in the season while cultivars that put resources equally into root and shoot growth may be able to recover well after damage from PWC.
  • Total hand weeding time (hours/acre) appears to be higher for the hand-weeding control group, as expected, while hand weeding time is lower for the tine harrow treatment. The tine harrow is likely killing more weeds but comes with the tradeoff of greater crop loss.

Pictures-

Participation Summary

Project Outcomes

Knowledge Gained:

Data collection began for this project in July 2020. During the duration of the experiment and data collection, my knowledge about carrot production and my skills in their production drastically changed. It is one thing to read literature and talk to farmers about their experience growing carrots, it is another thing to be the one in charge of every aspect of the production. I was in charge of everything from purchasing seed, to bed prep, planting, weeding, irrigating, and harvesting. I now have a much greater appreciation for the work that goes into growing carrots, and this further reinforces why the need for this research is so important for organic farmers. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.