Cover Crop Diversity through Evaluation and Increase from Breeder Stocks and Germplasm Repositories

Final report for LS16-270

Project Type: Research and Education
Funds awarded in 2016: $201,249.00
Projected End Date: 09/30/2019
Grant Recipient: University of Florida
Region: Southern
State: Florida
Principal Investigator:
Dr. Carlene Chase
University of Florida
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Project Information

Abstract:

The purpose of this project was to increase the diversity and availability of cover crops adapted to the southeastern United States in general and Florida in particular with the potential to improve soil health, serve as green manure, and suppress weeds and nematodes. The project involved seed increase and evaluation of alternative cover crop germplasm lines of the leguminous cover crops Crotalaria juncea (sunn hemp), C. ochroleuca (slenderleaf rattlebox), Vigna unguiculata (cowpea), and Indigofera hirsuta (hairy indigo) that are not currently commercially available but have the potential for overcoming some of the constraints of existing commercial varieties such as hardseededness and the inability to set seed in Florida. 

The hairy indigo cultivar Flamingo was originally selected for high soft-seededness (low hard-seededness); however, ‘Flamingo’ seed is no longer commercially available. ‘Flamingo’ breeder’s seed is available at the UF-IFAS Forage Breeding and Genetics Lab and at the USDA hairy indigo germplasm collection. Germination tests using these two germplasm sources revealed large genetic variability, i.e. low and high soft-seed levels, present for soft-seededness in the species. The selection and multiplication of those accessions exhibiting high levels of soft-seededness would lead to the development of soft-seeded hairy indigo cultivars. Seed increases are being conducted in the selected soft-seeded lines to allow for field testing (agronomic performance) and nematode resistance in summer 2020.

The sunn hemp cultivar Tropic Sun is unable to consistently set seed within the continental US; whereas the day neutral cultivar ‘AU Golden’, which can set seed, is considered to have low biomass production that may compromise weed suppression. ‘Iron Clay’ cowpea produces hard seed that can cause volunteer plants to emerge in subsequent cash crops. Accessions of slenderleaf rattlebox were identified as nonhosts or poor hosts of the sting nematode but suitability as a cover crop in the US is poorly documented. Therefore, alternative germplasm of sunn hemp (Sanni) and cowpea (US 1136, US 1137, and US 1138) were compared with commercially available cultivars of sunn hemp Tropic Sun and AU Golden and Iron Clay cowpea.  Trials were conducted at the Plant Science Research and Education Unit in Citra, FL and at three organic farms in Gainesville and Hawthorne, FL. A commercially available slenderleaf rattlebox genotype Red Hemp also was evaluated in summer 2017 and compared with a USDA accession PI 274767 in summer 2018.

Sanni and the alternative cowpea germplasm lines provided equivalent or better cover crop biomass accumulation and weed suppression than their respective commercial cultivars. The lower shoot biomass accumulation with Red Hemp and PI 274767 slenderleaf rattlebox genotypes provided less effective weed suppression than cowpea and sunn hemp. Sanni sunn hemp and the three cowpea germplasm lines appear to be viable replacements for ‘Tropic Sun’ and ‘Iron Clay’ cowpea, respectively. Data gathered from the Hawthorne location at our research assessment, field day, and from the collaborator assessments were consistent with our research results. Participants indicated that they are very interested in the sunn hemp germplasm line Sanni and the cowpea germplasm lines: US-1138 and US-1136.

Project Objectives:
  1. Multiply seeds of cover crop species and accessions with high potential for utility but are not currently available to obtain sufficient amounts for replicated field evaluation.
  1. Select for the soft-seed trait in ‘Flamingo’ hairy indigo.
  1. Evaluate on-station and on-farm for ecological services in comparison with commonly available species.
  1. Provide recommendations and make seed available for the most promising species/accessions.

Cooperators

Click linked name(s) to expand
  • Dr. Marilyn (Mickie) Swisher
  • Dr. Esteban Rios

Research

Materials and methods:

Objective 1. Multiply seeds of cover crop species and accessions with high potential for utility but are not currently available to obtain sufficient amounts for replicated field evaluation

In September 2016, 2 accessions of sunn hemp (PI 391567 – Sanni, PI 426626 – T’ai-yang-ma) and 2 accessions of slenderleaf rattlebox (PI 543869, PI 274767) were obtained from the USDA-ARS in Griffin, GA and were sent to Puerto Rico for seed increase. The sunn hemp germplasm lines were selected based on our prior work that showed that these lines were capable of setting seed in Florida. The slenderleaf rattlebox accessions were selected due to their effectiveness for root-knot nematode and sting nematode suppression. 

The cowpea germplasm lines US-1136, US-1137, and US-1138 obtained from Dr. Brian Ward at Clemson University were planted at Rosie’s Organic Farm in summer 2017 for seed multiplication. The harvested seeds were used for on-station and on-farm trials in summer 2018 and to distribute to interested farmers during a field day planned to coincide with the summer 2018 trials. Additional cowpea seed was received from Dr. Ward in December 2018 that will be used for further seed increase and distribution to interested stakeholders.

Seeds of sunn hemp (Sanni and T’ai-yang-ma) and slenderleaf rattlebox (PI 274767 and PI 543869) were again requested from USDA, Griffin, GA for seed increase in Florida in Summer 2017. Twenty-five seeds of each accession were planted at University of Florida, IFAS Plant Science Research and Education Unit, Citra, FL. Seed set of Sanni and Tai-yang-ma was sporadic and seed yield was low. The C. ochroleuca accession PI 274767 resulted in more prolific seed production than PI 543869 with 1 lb and 1.5 g of seeds, respectively.  

A quarter pound of Sanni seeds from the previous year’s multiplication (in Puerto Rico) and about 35 seeds of Tai-yang-ma harvested from Citra were sent to Dr. Elide Valencia at University of Puerto Rico for multiplication in Fall 2017. This yielded over 5 pounds of Sanni seeds and a quarter pound of Tai-yang-ma seeds.

Seeds of the cowpea germplasm lines US1136, US1137 and US1138 and sunn hemp germplasm lines Sanni and T’ai-yang-ma were planted in isolated plots in summer 2019 for seed increase in certified organic acreage at the Plant Science Research and Education Unit. Seeds will be harvested and threshed in Fall 2019.

Objective 2. Select for the soft-seed trait in ‘Flamingo’ hairy indigo

Breeder ‘Flamingo’ seed was used as the base population to reduce hard-seededness in hairy indigo. Germination tests have been performed in 43 genotypes, including plants selected from ‘Flamingo’, USDA plant introductions and a wild check collected in Alachua county. In order to reduce bias due to seed source and seed age, seed stocks were increased in a greenhouse at the UF/IFAS Forage Breeding and Genetics Lab during the Summer/Fall 2018, and Summer/Fall 2019.  Seed was harvested, dried at room temperature, threshed and placed for germination in petri dishes. A randomized complete block design with three replications was used for germination tests, and 20 seeds were evaluated on moist germination paper in petri dishes, and the entire study was repeated twice. Seeds were assessed for germination at 3 and 7 days after planting and seeds that had not geminated were considered to be hard-seeded. Data were analyzed using ANOVA followed by Tukey Test at a 5% level of significance.

Objective 3. Evaluate on-station and on-farm for ecological services in comparison with commonly available species

First-year field evaluations of cover crops sunn hemp, slenderleaf rattlebox, and (cowpea) were conducted in Summer 2017 at the UF/IFAS Plant Science Research and Education Unit, Citra, FL. The performance of the sunn hemp accession Sanni was evaluated in comparison with the commercially available sunn hemp cultivars Tropic Sun and AU Golden; and the three cowpea germplasm lines (US-1136, US-1137 and US-1138) were compared to ‘Iron Clay’ cowpea. A commercially available slenderleaf rattlebox cultivar Red Hemp was also assessed. Cover crop growth and weed and nematode suppression were evaluated.

First-year field evaluations of cover crops sunn hemp, slenderleaf rattlebox, cowpea were conducted in Summer 2017 at the UF/IFAS Plant Science Research and Education Unit (PSREU), Citra, FL. The performance of the sunn hemp accession Sanni was evaluated in comparison with the commercially available sunn hemp cultivars Tropic Sun and AU Golden; and the three cowpea germplasm lines (US-1136, US-1137 and US-1138) were compared to ‘Iron Clay’ cowpea. A commercially available slenderleaf rattlebox cultivar Red Hemp was also assessed. Cover crop growth and weed and nematode suppression were evaluated.

In Summer 2018 at the University of Florida, second-year evaluations of cover crop seeds of sunn hemp, slenderleaf rattlebox, and cowpea were conducted at PSREU, Citra, FL and three commercial organic farms located in northcentral Florida. Performance of sunn hemp accession Sanni and three cowpea germplasm lines (US1136, US1137 and US1138) were evaluated in comparison to the commercially available cultivars of sunn hemp (‘Tropic Sun’ and ‘AU Golden’) and cowpea (‘Iron clay’), respectively. A commercially available slenderleaf rattlebox variety Red Hemp and an accession from the USDA-ARS in Griffin, GA (PI 274767) were also assessed. Data were collected on cover crop biomass, weed biomass, leaf area index (LAI), photosynthetically active radiation (PAR) penetrating the cover crop canopy, nematode suppression, and C:N ratio.

Objective 4. Provide recommendations and make seed available for the most promising species/accessions

This objective focused on making seed available to interested stakeholders and disseminating results. Recommendations for use of the new germplasm will be developed based on the performance of the cover crops and will be included in a refereed journal publication and subsequently a University of Florida factsheet. Small amounts of seed of recommended accessions were made at the field day in 2018 and will also be distributed at the Southern SAWG conference in January 2020 to growers interested in evaluating the cover crops and/or propagating the seeds for their own use. Seed distribution will be in response to requests on the weblog (described below).

Research results and discussion:

Objective 1. Multiply seeds of cover crop species and accessions with high potential for utility but are not currently available to obtain sufficient amounts for replicated field evaluation

Multiplication of cowpea germplasm US-1136, US-1137, and US-1138 was prolific at Rosie’s Organic Farm in 2017. Sufficient seed was produced to allow for 1 on-station and 3 on-farm trials in summer 2018 and for distribution of seed samples to farmers. Sanni sunn hemp multiplied in Puerto Rico will also be adequate for evaluation in the 4 trials. However, multiplication of Tai-yang-ma sunn hemp and 2 accessions C. ochroleuca was much less successful.

During seed increase in 2019, rainfall in September while cowpea pods were drying in the field prior to harvest resulted in fungal growth on pods and seeds of US1136, US1137 and US1138 cowpeas. After harvest and threshing of pods, seeds will be treated with an approved seed sanitizer for organic seeds. In addition to sharing seeds with interested stakeholders, seeds will be used to conduct a study in summer 2020 aimed at developing seeding rate recommendations for the cowpea germplasm lines.

Objective 2. Select for the soft-seed trait in ‘Flamingo’ hairy indigo

Germination tests run for 7 days revealed that hard-seededness ranged from 30% to 100% in our hairy indigo population after two germination experiments (Figure 1)  As expected, the naturalized population collected in Alachua (HI-Alachua) had 89% hard-seed. Several accessions from the USDA and Flamingo selections had higher hard-seed percentages than the wild check. On the contrary, 3 genotypes had lower than 50% hard-seededness, including plants selected from the original Flamingo breeder’s seed stock. Seedlings from these genotypes have been transplanted and they are being grown for seed production increases during the Summer/Fall 2019. A second run of germination tests was conducted exhibiting consistent seed germination and soft/hard seededness. Plants exhibiting low hard-seed levels (less than 50%) are being grown for seed increases. Field testing for the soft-seeded lines will be performed in summer 2020, and plants will be evaluated uniform morphological traits, agronomic performance, and for root-knot nematode resistance.

Objective 3. Evaluate on-station and on-farm for ecological services in comparison with commonly available species

In summer 2017, the results indicated that ‘Tropic Sun’ produced significantly higher shoot biomass than ‘AU Golden’ by 8 weeks after planting (WAP); however, the shoot biomass of Sanni was not significantly different from ‘Tropic Sun’ (Table 1). Among cowpea germplasm lines, only US-1138 produced significantly more biomass than the commercial cultivar Iron Clay. Weed suppression in terms of biomass and density was not statistically different among sunn hemp cultivars by 8 WAP (Table 2). Broadleaf weed density with US-1138 cowpea was significantly lower than with ‘Iron Clay’ by 8 WAP and may account for the lower total weed biomass with US 1138 than with ‘Iron Clay’ (Table 2 and 3). Slenderleaf rattlebox had low shoot biomass accumulation that was comparable to ‘Iron Clay’ with correspondingly low weed suppression Tables (1-3). At 4 weeks after planting, Sanni had the lowest photosynthetically active radiation (PAR) penetrating the canopy, which was not significantly different from ‘Tropic Sun’ and US-1137 (Table 4).

For the trials conducted in summer 2018, results showed that total shoot biomass produced by Sanni, ‘Tropic Sun’ and ‘AU Golden’ did not differ significantly at any of the four locations. A significant difference in total weed biomass was observed at only one farm where Sanni resulted in less grass biomass production than the commercial cultivars. This contributed to lower total weed biomass production in Sanni than the commercial sunn hemp cultivars. The three cowpea germplasm lines produced similar or greater shoot biomass than ‘Iron Clay’ and suppressed total weed biomass as effectively as or better than ‘Iron Clay’. The PAR results indicated increased canopy closure over time that may partially explain the lower total weed biomass and densities with the cover crop treatments compared to the weedy control at eight weeks after planting. No significant difference in shoot biomass accumulation and weed suppression was observed with the slenderleaf rattlebox germplasm lines. Shoot biomass production with slenderleaf rattlebox was comparable to cowpea and lower than sunn hemp. Thus, slenderleaf rattlebox may be an alternative to sunn hemp where lower biomass and less fibrous residue is preferred. However, additional work to optimize slenderleaf rattlebox seeding rates will be needed. No proliferation of root-knot nematodes and ring nematodes was observed with any of the crops evaluated. The C:N ratios ranged between 14-16 for sunn hemp genotypes and 10-13 for cowpea and slenderleaf rattlebox genotypes for the on-station trial and two of the farms. However, the C:N ratios at the third organic farm tended to be higher than the other locations and ranged from 14 with Red Hemp and US 1136 to 20 with Sanni. The equivalent or better performance of the alternative germplasm lines indicate that the Sanni sunn hemp germplasm line and the US 1136, US 1137 and US 1138 cowpea germplasm lines are suitable replacements for the commercial cultivars in Florida.

Objective 4. Provide recommendations and make seed available for the most promising species/accessions

In summer 2019, seed of US1136, US1137 and US1138 were planted for seed increase and were harvested in October 2019. The seed will be used in 2020 in a study to determine optimal seeding rates for maximizing shoot biomass and weed suppression. The results of the study conducted in 2018 to address objective 3 were reported in a poster at the Southern Cover Crops Council in Auburn, AL (July 16-17, 2019) and as an oral presentation at the American Society for Horticultural Science meeting in Las Vegas, NV (July 21-25, 2019):

  • Sharma, S. and C.A. Chase. Addressing some constraints of ‘Tropic Sun’ sunn hemp and ‘Iron Clay’ cowpea. Southern Cover Crops Conference. Auburn, AL. July 16-17, 2019.SCCC poster_Sharma and Chase
  • Sharma, S., C.A. Chase, M.E. Swisher, and K. Sattanno. 2019. Comparison of alternative germplasm and commercial cover crops for improved traits and utility in Florida. HortScience 54(9) Supplement: S128.ASHS Abstract 2019 HortScience

A manuscript also has been prepared that will be submitted to a refereed journal for publication in 2020. Distribution of small amounts of US1136, US1137 and US1138 cowpea seeds was done at the field day in summer 2018 and to a non profit organization in Gainesville, FL. More seed distribution is planned for a workshop on cover crops by Dr. Chase and one of the cooperating growers at the Southern SAWG conference in January 2020.  

 

Table 1. Cover crop biomass accumulation at four and eight weeks after planting.

Cover Crop

4 WAP

8 WAP

 

Biomass (kg/ha)

Sanniz

    724 a

    3534 ab

AU Goldenz

    419 bc

    2801 b

Tropic Sunz

    548 ba

    3922 a

US-1136y

    178 cd

    1423 cde

US-1137y

    412 bc

    1636 dc

US-1138y

    333 bc

    1768 c

Iron Clayy

    279 c

      741 de

Slenderleaf rattleboxx

      10 d

      462 e

P-value

< 0.0001

< 0.0001

z Crotalaria juncea; y Vigna unguiculata; x Crotalaria ochroleuca

 

Table 2. Weed biomass in response to cover crop at 4 and 8 weeks after planting (WAP).

Cover Crop

4 WAP

 

8 WAP

Broadleaf

Grass

Sedge

Total

 

Broadleaf

Grass

Sedge

Total

 

Shoot biomass (kg/ha)

Sanniz

152

   175 a

318

    646 a

 

    244 cd

257

495

     996 c

AU Goldenz

123

   136 ab

194

    453 bc

 

    392 bc

267

352

   1011 c

Tropic Sunz

114

   116 abc

234

    465 abc

 

    375 bcd

280

444

   1099 bc

US-1136y

137

   139 ab

252

    527 ab

 

    324 bcd

402

504

   1231 abc

US-1137y

114

   124 ab

163

    401 bc

 

    317 cd

413

372

   1102 bc

US-1138y

100

   133 ab

300

    533 ab

 

    207 d

162

569

     938 c

Iron Clayy

116

     42 c

145

    303 c

 

    503 ab

226

802

   1531 ab

Slenderleaf rattleboxx

180

     81 bc

169

    430 bc

 

    595 a

394

691

   1680 a

P-value

0.67

0.049

0.22

0.04

 

0.0012

0.15

0.26

0.02

z Crotalaria juncea; y Vigna unguiculata; x Crotalaria ochroleuca

 

Table 3. Weed density in response to cover crop at 4 and 8 weeks after planting (WAP).

Cover Crop

4 WAP

 

8 WAP

Broadleaf

Grass

Sedge

Total

 

Broadleaf

Grass

Sedge

Total

 

 

Plants/m2

Sanniz

249

54

146

450

 

   158 bc

69

148

   376 abc

AU Goldenz

215

50

104

370

 

   206 ab

72

113

   391 abc

Tropic Sunz

203

88

182

473

 

   173 ab

68

138

   379 abc

US-1136y

194

64

137

395

 

   144 bc

80

117

   341 bc

US-1137y

188

73

109

371

 

   128 bc

68

142

   338 bc

US-1138y

173

79

219

472

 

     83 c

46

154

   284 c

Iron Clayy

169

46

156

371

 

   181 ab

62

208

   451 ab

Slenderleaf rattleboxx

215

54

100

369

 

   246 a

80

185

   511 a

P-value

0.92

0.28

0.17

0.43

 

0.017

0.88

0.5

0.05

z Crotalaria juncea; y Vigna unguiculata; x Crotalaria ochroleuca

 

Table 4. Photosynthetically active radiation penetrating the cover crop canopies at 2, 4, 6 and 8 weeks after planting (WAP).

Cover crop

2 WAP

4 WAP

6 WAP

8 WAP

 

%

Sanniz

    87 d

     49 d

65

    51 bcd

AU Goldenz

    92 bc

     75 bc

63

    55 abc

Tropic Sunz

    91 bcd

     63 cd

66

    49 d

US-1136y

    93 abc

     71 bc

64

    54 abcd

US-1137y

    91 bcd

     61 cd

63

    56 ab

US-1138y

    89 cd

     68 bc

63

    54 abcd

Iron Clayy

    95 ab

     83 ab

65

    50 cd

Slenderleaf rattleboxx

    97 a

     91 a

64

    58 a

P-value

0.0011

<0.0001

0.12

       0.012

z Crotalaria juncea; y Vigna unguiculata; x Crotalaria ochroleuca

Participation Summary
3 Farmers participating in research

Education

Educational approach:

The education and outreach component of our project utilizes four methodologies: (1) an on-farm field day, (2) a virtual field day, (3) a website and blog for the project, (4) and an in-service training session for county faculty and other technical advisors in the Florida SARE Program’s on-line webinar. Our approach was designed for two potentially distinct target audiences of growers. Some growers in Florida and the Southeast Region have prior experience using cover crops, quite extensive experience in some cases. Others have little or no experience. We proposed that these groups are likely to find different aspects of our research of interest. Therefore, we have been collecting information about previous experience with cover crops during the on-farm and virtual field days.

Educational & Outreach Activities

2 Consultations
3 On-farm demonstrations
1 Online trainings
5 Webinars / talks / presentations
2 Workshop field days

Participation Summary

8 Farmers
6 Ag professionals participated
Education/outreach description:

The Information Dissemination and Outreach Activities included:

  1. An on-farm field day
  2. A virtual field day
  3. A website and blog for the project
  4. A research assessment
  5. Poster and oral presentations at conferences

In August 2018, we hosted a research assessment and field day at one of the on-farm trials. Over the course of the on-farm trials we completed collaborator assessments and interviews with two of the three on-farm trial participants. After the on-farm trials were completed we created a virtual field day (VFD) assessment that we launched via Qualtrics. To date, twelve participants have completed the online assessment. The VFD assessment allows participants to assess our field research virtually. This allowed us to reach participants who could not attend our on-farm research assessment and field day. Thus, the VFD allowed us to gather more data about our field research from Florida farmers. Data gathered at the research assessment, field day, and from the collaborator assessments indicate that our participants are very interested in the sunn hemp cultivar: Sanni and the cowpea accession lines: US-1138 and US-1136. We are in our final data collection stage for the VFD and will analyze the data in November 2019. We currently have a project webpage at https://floridafoodandag.com/new-home/cover-crop-diversity-through-evaluation-and-increase-from-breeder-stocks-and-germplasm-repositories-southern-sare-research-education-grant that is updated regularly. We will submit an abstract in November to present our findings at the 2020 Southern Sustainable Agriculture Working Group (SSAWG) Conference. We will submit a journal article for publication about these findings and will host an in-service training webinar about this project and our findings in conjunction with the Florida SARE Program webinar series in Spring of 2020.

Research Assessment and Field Day

The research assessment and field day allowed for information dissemination of our study of three sunn hemp (SH) accessions (AU Golden, Sanni, and Tropic Sun), four cowpea (C) accessions (Iron Clay, US-1136, US-1137, US-1138), and two slenderleaf rattlebox (SR) accessions (PI-274767 and Red Hemp) at four locations. Six farmers and/or agricultural service providers with experience using cover crops participated in a field research assessment at one of our test sites in Hawthorne, FL, at the end of the growing season in summer 2018. Participants completed an individual written assessment that included specific observations in the research plots such as plant vigor, weed suppression, canopy cover, biomass accumulation, and any other positive or negative effects observed. After completing the individual observations, a researcher led a structured discussion in which the participants shared their observations and provided recommendations for the research as a group. 

We also hosted a field day at the same location where we distributed a comprehensive list of key advantages, potential problems, and potential barriers to the adoption of our research. Each participant scored the degree to which each of those factors either encourages or discourages him/her from using cover crops using a scalar response of 1 (very encouraging) to 5 (very discouraging).

After completing the individual assessments in the research plots, each participant was given two green stickers and two red stickers to vote for the two cover crops that showed the most potential for weed suppression (green stickers) and the two cover crops that show the least potential for weed suppression (red stickers). The three cover crops identified as having the most potential to suppress weeds were US-1138 (C), US-1136 (C), and Sanni (SH). The three cover crops identified as having the least potential to suppress weeds were the weedy control (no cover crop planted), PI-274767 (SR), and red hemp (SR).

We then asked the participants to identify the desirable traits of the most promising cover crops in our experiment and the undesirable traits of the least promising cover crops in our experiment.  The table below presents a summary of their comments.

Desirable Traits Undesirable Traits
   Weed suppression    Poor germination
   Reducing new weed seeds    Poor stand establishment
   Not becoming a weed in subsequent seasons  
   Not a nematode host plant/does not increase nematode pressure  
   High nitrogen fixation  
   High biomass accumulation  
   Low seed cost  
   Does not deplete soil moisture   
   

After reviewing their observation forms and the group discussion notes, the participants ranked from best to worst the performance of the cover crops within each species. Not all participants ranked each cover crop so we calculated the average score based on the number of participants that ranked each of the cover crops. None of the participants ranked the slenderleaf rattlebox accessions due to poor performance overall.  The most highly ranked accessions were US-1138 (C), US-1136 (C), and Sanni (SH).  The table below presents a summary of the rankings and scores for each accession.

Sunn Hemp Averaged Score (Out of 3 points)
   Sanni 3
   Tropic Sun 2
   AU Golden 1
Cowpea  
   US-1136 3.25
   US-1137 3.25
   US-1138 2.00
   Iron Clay 1.50

 

The research assessment participants then listed areas of cover crop research that could potentially be addressed by a breeding program. The table below presents a summary of the suggestions.

Future Areas of Research
   Earliness of cover crop production before cash crop planting in spring (day length issue for late planted winter cover crops)
   Nematode resistance (root knot, sting, stubby root)
   Compatibility and benefits of cover crop mixes
   Greater nitrogen production
   Tonnage per acre estimates
   Seed cost, availability and supply, and re-seeding potential
   Regional seed production to reduce freight cost and match local environment
   Enhancing effectiveness of winter legumes in poor sandy soil

 

After exploring our research plots on their own, three of the six field day participants ranked the advantages, disadvantages, and barriers to adopting our research using a scalar response of 1 (very encouraging) to 5 (very discouraging). The top three factors identified that encourage farmers to use cover crops are suppressing weeds (1), attracting beneficial insects (1), and increasing cropping system biodiversity (1).  The top three factors identified that discourage farmers from using cover crops are timing the termination of the cover crop with the cash crop cycle (3), timing the establishment of the cover crop with the cash crop cycle (3), and difficulty dealing with cover crop residue when preparing to install plastic mulch (3).

All of the participants were most interested in the sunn hemp accessions, Sanni and Tropic Sun, and two of the cowpea accessions, US-1136 and US-1138.  None of the participants liked the performance of the slenderleaf rattlebox accessions and all but one participant recommended we discontinue studying them.

Poster and Oral Presentations

Cheng, I., S. Sharma, C. Chase, Y. Lopez, and E. Rios. Breeding hairy indigo (Indigofera hirsuta) for soft-seededness. Third Annual University of Florida Plant Science Symposium, Gainesville, FL. January 22-23, 2019. (Poster) Cheng et al. 2019

Sattanno, K., S. Sharma, C. A., Chase, , M. E. Swisher. 2018. Increasing cover crop diversity in Florida. Professional Agriculture Workers’ Conference, Tuskegee, AL. December 2-4, 2018. (Poster) Sattanno et al. 2018

Sharma, S. and C.A. Chase. Addressing some constraints of ‘Tropic Sun’ sunn hemp and ‘Iron Clay’ cowpea. Southern Cover Crops Conference. Auburn, AL. July 16-17, 2019. (Poster) Sharma and Chase 2019

Sharma, S. and C.A. Chase. Cover crop diversity through evaluation and increase from breeder stocks and germplasm repositories. SARE Our Farms, Our Future Conference. St. Louis, April 3-5, 2018. (Poster) Sharma and Chase 2018

Sharma, S., C.A. Chase, M.E. Swisher, and K. Sattanno. Comparison of alternative germplasm and commercial cover crops for improved traits and utility in Florida. American Society for Horticultural Science Annual Conference. Las Vegas, NV. July 21-25, 2019. (Oral Presentation)

Outreach in Progress

An in-service training session for county faculty and other technical advisors will be conducted in the Florida SARE program’s on-line webinar series. A manuscript based on objective 3 has been prepared that will be submitted to a refereed journal for publication in 2020. Once this is published a University of Florida fact sheet will be prepared for the EDIS platform. A second manuscript is planned that will be based on the results of the virtual field day. A workshop presentation and a poster are scheduled for the Southern SAWG conference in January 2020.

Learning Outcomes

7 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • The purpose of the research assessment and field day was to gain insight from participants about how they perceived the cover crop research conducted by personnel from the University of Florida. We explained to participants that the research was aimed at increasing the diversity and availability of cover crops adapted to the southeastern United States and Florida in particular, with the potential to improve soil health, serve as green manure, and suppress weeds and plant-pathogenic nematodes. We also indicated that although there are commercially available leguminous cover crops that provide these agroecosystem services, the number of commercially available varieties is limited and most exhibit constraints that may be avoided by use of germplasm that is not currently available commercially.

    Our objective was for farmers and agricultural service providers to actively learn about our research by evaluating the cover crops at the cooperating farm and identify for themselves the potential benefits and limitations of our research with the overall goal of improving the sustainability of horticultural crop production in Florida.

    All of the participants were most interested in the sunn hemp accessions, Sanni and Tropic Sun, and two of the cowpea accessions, US-1136 and US-1138. None of the participants liked the performance of the slenderleaf rattlebox accessions and all but one participant recommended we discontinue studying them.

Project Outcomes

Project outcomes:

We gathered a large pool (43 different populations) of hairy indigo accessions from the UF-IFAS Forage Breeding and Genetics Lab and from the USDA germplasm collection. We grew the plants under greenhouse conditions to produce seed under the same environmental conditions, and then performed two rounds of germination tests to determine levels of soft-seededness in those plants. Plants exhibiting low hard-seed levels (<50% hard-seed) have been selected and seed production increases are being conducted in order to tests the performance of those plants under field conditions. These plants exhibiting high soft-seed levels will be used for cultivar development.

There is an increased interest in using warm-season legumes as cover crops and as a feed source for livestock to reduce nitrogen inputs into agricultural systems. The development of a hairy indigo cultivar with reduced occurrence of hard seeds would provide another tool for producers who are exploring options to diversify their production systems. A hairy indigo cultivar with high soft-seed levels would facilitate uniform seed germination at planting and it will reduce the likelihood of becoming a weed in subsequent crops.

Equivalent or better performance of the alternative germplasm lines of sunn hemp and cowpea indicate that Sanni, US 1136, US 1137 and US 1138 are suitable replacements for the commercial cultivars in Florida. The advantage of Sanni is that unlike ‘Tropic Sun’, seed production is possible in the Florida. Sunn hemp seed production within the continental US would eliminate the need for seed importation and improve availability and possibly reduce the cost of sunn hemp cover crop seed. The use of the alternative cowpea germplasm will allow for the same agroecosystem services as ‘Iron Clay’ without the problem of volunteer plants due to hard-seededness.

The results of this research will address key barriers to the adoption of sunn hemp and cowpea cover crops. We also have increased our knowledge of the utility of slenderleaf rattlebox and have increased our seed availability to allow for additional research with this species. Additionally, the development of a softseeded hairy indigo cultivar along with appropriate outreach will elevate this species from its current forage and weedy status. Growers already using warm-season cover crops will be able to increase the sustainability of their cropping systems by having at their disposal a greater diversity of cover crops. Those growers who are not currently using cover crops whose barriers to adoption are addressed by this project will realize enhanced agroecosystem sustainability through reduction in their off-farm nitrogen input requirement, improved soil health, and systems that are more resilient to pests. Growers who grow warm-season legumes as a seed crop may also benefit from greater economic sustainability by adopting sunn hemp as a seed crop.

Recommendations:

The hairy indigo part of the project is delayed due to changes in leadership. Dr. Patricio Munoz was originally in charge of completing this specific objective for our project. However, Dr. Munoz is no longer with the Agronomy Department at the University of Florida. He is currently the blueberry breeder in the Horticultural Sciences Department and thus no longer has responsibility for breeding activities that involve cover crops. Dr. Esteban Rios replaced Dr. Munoz as Assistant Professor of Forage Breeding and Dr. Rios has taken over the duties of Dr. Munoz, and the responsibility for this specific objective since Spring 2018.

We compared the cowpea germplasm lines on the basis of an equal number of seed per unit area since the lines and ‘Iron Clay’ vary in seed size. The next step would be to evaluate the lines at 4 or 5 seeding rates to determine an optimal seeding rate for each line. It will also be necessary to promote the lines to seed companies in an effort to develop the lines into commercially available cover crop. The poor performance of slenderleaf rattlebox appears to be due to slow early growth. This may be overcome by use of a higher seed rate, selecting for more vigorous plants or utilizing in bicultures and polycultures with complementary species.

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.