Evaluate sorghum and sorghum-sudangrass hybrids as soil builders and microbial enhancer crops in the tropic.

Progress report for GW20-212

Project Type: Graduate Student
Funds awarded in 2020: $25,000.00
Projected End Date: 08/31/2022
Grant Recipient: University of Hawaii
Region: Western
State: Hawaii
Graduate Student:
Major Professor:
Dr. Koon-Hui Wang
University of Hawaii
Major Professor:
Dr. Amjad Ahmad
University of Hawaii at Manoa
Roshan Paudel
University of Hawaii
Joshua Silva
University of Hawaii at Manoa, College of Tropical Agriculture a
Philip Waisen
University of Hawaii
Expand All

Project Information

Summary:

Cover crops play important roles in maintaining soil health. This project focuses on identifying a cover crop that have additional benefits besides soil erosion control including disease suppression, and water conservation. In particular, I would like to devote my Ph.D. dissertation into evaluating the multi-facet benefits of sorghum and sorghum-sudangrass hybrids (I hear by refer this as SSgH) for their potential in suppressing plant-parasitic nematodes and soil borne fungi, while contributing to increase soil organic matter that will lead to soil moisture retention. This is the first year of my Ph.D. program. Although I am partially funded by other projects of my adviser, I do not have sufficient funding to carry out multiple components of the soil health assays for SSgH. I am proposing to work with researchers, two edible crop extension agents and three local farmers with different farming operations. I aim to evaluate SSgH as a viable tropical cover crop for their 1) soil building and water conservation properties; 2) plant growth enhancement potential following a no-till SSgH cover cropping practice, and 3) ability to enhance beneficial soil microbiome that are associated with various soil health improvement properties. While PI Wang had been demonstrating the great benefits of another tropical cover crop, sunn hemp, for soil health management, this project come in critical now as sunn hemp is suffering from soilborne fusarium disease throughout Hawaii. By collaborating with extension agents, we also will work with a new farmers training program in Hawaii to reach out to wider audience.

Project Objectives:

The overall goal of this project is to identify sorghum and sorghum-sudangrass hybrids that are most efficient in tropical climate for suppressing soil-borne pathogens, improving soil water holding properties and enhancing soil microbiome that can contribute to better soil nutrient cycling and ecosystem functioning. Under a no-till cover cropping system, this healthy soil microbiome would not be disturbed and can help to increase soil organic matter faster. These would improve soil aggregates, water infiltration, thus a better water conservation. Specific objectives of this project are:

  1. Evaluate sorghum/sorghum-sudangrass hybrids for soil building and water conservation properties in a no-till farming eggplant agroecosystem (by Paudel, Wang, Silva)
  2. Evaluate eggplant growth and soil-borne disease suppression following no-till planting of different sorghum/sorghum-sudangrass hybrids (by Paudel, Ahmad).
  3. Identify sorghum/sorghum-sudangrass hybrids with distinct microbiome that are associated with good water conservation properties, soil-borne disease suppression and nutrient cycling (by Paudel, Wang, Waisen)

This project will be carried out over a 2-year period at three locations, one at Poamoho Experiment Station, University of Hawaii, the others at Kahumana Farm, an organic farm advocate for permaculture, and Tolentino Farm, a family farm at Waianae. The best outcome of this study will also be demonstrated at a conventional leafy green farm that is always challenged by soil-borne fungal disease problem (Owen Kaneshiro Farm). Detail of measurable outcomes of each objective are listed in Materials and Methods section below. Field days will be organized by the PI and the collaborative extension agents who are also our co-PIs multiple times a year to update findings to local farmers in Hawaii, in particular to new farmers under GoFarm Hawaii New Farmers training program as well as clients of CTAHR Sustainable and Organic Agriculture Program (SOAP). We aim to provide more incentive for farmers to practice no-till cover cropping in Hawaii.

Timeline:

Activities / Milestones

2020

2021

2022

F

W

Sp

Su

F

W

Sp

Su

 

Objective 1

 

 

 

 

 

 

 

 

Conduct field experiment to evaluate nine different sorghum/sorghum-sudangrass hybrids for soil health and water conservation.

×

 

 

 

×

 

 

 

Objective 2

 

 

 

 

 

 

 

 

Experiment: Conduct field experiment to evaluate the growth and disease suppression of eggplant following the sorghum/sorghum-sudangrass termination.

 

×

×

×

 

×

×

×

Objective 3

 

 

 

 

 

 

 

 

Experiment: Identify microbiome associated with good water conservation properties using bioinformatics and statistical analysis.

×

 

 

 

×

 

 

 

Field day 1: Demonstrate the growth and performance of eggplant under different cover crop treatments.

 

×

 

 

 

×

 

 

Field day 2: Demonstrate the effect of the best sorghum/sorghum-sudangrass hybrid on soil properties and water conservation.

 

 

 

 

×

 

 

 

Farmers’ evaluation during field days and guest lectures.

 

×

×

 

×

×

 

×

Data analysis and manuscript writing

 

 

×

 

×

 

×

×

 

Cooperators

Click linked name(s) to expand
  • Owen Kaneshiro - Producer
  • Lito Tolentino - Producer
  • Christian Zuckerman - Producer

Research

Materials and methods:

Objective 1

Two greenhouse pot experiments were conducted to screen SSgH varieties that are most suppressive against M. incognita. The first greenhouse trial was conducted on March 27, 2020. Eleven SSgH varieties tested included ‘Elite Brown Mid Rib’, ‘Bundle King’, ‘Monster II’, ‘Big Kahuna Plus’, ‘Cow Vittles II’, ‘512×14’, ‘Latte BMR’, ‘535×14’, ‘Latte’, ‘NX 4264’, and ’NX-D-61’. Sunn hemp (Crotalaria juncea) was included as a positive control, and a no amendment was included as a negative control. The second trial conducted on June 8, 2020, was a repeat of the first trial with an additional sudangrass variety, ‘Piper’ and forage sorghum ‘EBMR’. All SSgH were grown in the field at Magoon Teaching Facility, University of Hawaii at Manoa. SSgH shoot biomass was collected at 1, 2, and 3 months after planting and brought back to the laboratory to set up the greenhouse pot trials. Fresh SSgH shoot tissues were chopped into small pieces of 1 cm consistency prior to amending into the soil at 1% (w/w) dry weight equivalent. Each pot consisted of 103 g dry weight of sterile sand: soil mix (1:1 v/v). Sterile soil was an autoclaved Wahiawa soil (Tro-peptic Eutrustox, clayey, kaolinitic, isohyperthermic soil) collected from Poamoho Experiment Station. Shoot tissues and sterile soil were placed in a plastic bag and thoroughly mixed before transferring into each pot. The experiment was arranged in a 12×3 (amendment × plant age) factorial design with 4 replications on a greenhouse bench. A 5-week-old ‘Hirayama’ kai choi seedlings were transplanted into each pot and 220 J2/plant were inoculated on the same day. Root penetration by the nematodes was observed 1 month after soil amendment by staining a 0.3 g subsample of roots using acid fuchsin (Byrd et al., 1983). Stained roots were observed under a dissecting microscope (Leica Microsystems Company, Wetzlar, Germany) to quantify the number of J2, J3-4, and females per sample.

A field trial was conducted on May 28, 2020, at Poamoho Experiment Station, Waialua, HI (21°33′08.3”N 158°06′08.4”W) to compare the SSgH varieties for their potential to improve soil health. Soil at the test site was a Wahiawa Soil Series, Oxisol, Tropeptic Eutrustox clayey, kaolinitic, isohyperthermic with 18.6% sand, 37.7% silt, 43.7% clay and pH 6.7. Seven SSgH varieties with an assortment of allelopathic effects against root-knot nematodes penetration and development based on the greenhouse experiment results, SSgH types with high sugar content or high biomass production were selected for the field trial. A bare ground (BG) tilled plot was included as a control. Each SSgH variety was seeded at 56 kg seeds/ha in 3.6 × 1.2-m2 plots. Experimental plots were arranged in a randomized complete block design (RCBD) with 4 replications. Cover crops were drip irrigated for 2.5 months and terminated in a no-till system using a flail mower operated by BCS walk-behind tractor (Model 853, BCS America, LLC, Portland, OR). The mower had a plastic flap to contain the flailed tissues. Prior to the termination of SSgH, the biomass from each plot was estimated using three 0.1-m2 quadrants. Each plot was 0.5 m away from the adjacent rows, with a 1.5-m bare ground area between plots in a row. A total of 32 plots were established. Six-week-old ‘Shikou’ eggplant seedlings were transplanted with minimal disturbance to the soil. Each plot had 7 eggplant seedlings planted at 0.5 m spacing between plants in a zigzag pattern in plot. Eggplants were fertilized using Sustane 8-2-4 organic fertilizer (Sustane Natural Fertilizer, Inc., Cannon Falls, MN) at a rate of 73 kg N/ha. The experiment was terminated at 4.5 months after eggplant transplanting.

Soil samples were collected systematically from 4 spots per plot in a zigzag pattern from the top 10-cm of soil using a GroundShark shovel (Forestry Suppliers Inc., Jackson, Mississippi). Soil cores from each plot were composited in a plastic bag and transported to the laboratory for nematode extraction and soil nutrient analysis. Soil samples were collected 2 weeks after cover crop termination, and at 3 months after eggplant planting. Soil samples were submitted to Agricultural Diagnostic Services Center (ADSC) of the University of Hawaii, Honolulu, Hawaii to analyze for total C and N content using LECO TruSpec CN (LECO Corporation, Saint Joseph, MI). FieldScout TDR 100 Soil Moisture Meter (Spectrum Technologies,  Inc., Aurora, IL) was used to measure volumetric soil moistures twice during the eggplant growing season with 12-cm rods at the rhizosphere from 3 randomly selected spots per plot. Soil from each plot was measured for infiltration rate at 2 months after growing sorghum and 3 months after eggplant planting using a double-ring infiltration method (Fares et al., 2008).

Objective 2

Soil samples were collected as described in objective 1 at the initiation of the experiment, and at monthly intervals thereafter from cover crop to eggplant growing seasons. All soil samples were sieved through a 0.5 cm2 mesh screen and homogenized before sub-sampling 250 cm3 soil for nematode extraction using elutriation and centrifugal floatation method (Jenkins, 1964; Byrd et al., 1976; Barker, 1985). All nematodes extracted were identified to the genus level wherever possible, counted under an inverted microscope (Leica DMIL, Leica Microsystems Company, Wetzlar, Germany), and assigned to trophic groups (algivores, bacterivores, fungivores, herbivores, omnivores, or predators) based on categorization of Yeates et al. (1993). Nematode richness was calculated as the total number of different taxa recorded per sample. Simpson’s index of dominance was calculated using λ = Σ (pi)2, where pi is the proportion of each of the i genera present, and Simpson’s index of diversity was calculated as 1/λ (Simpson, 1949). The fungivore to fungivore and bacterivore ratio (F/F+B) was calculated to characterize the decomposition and mineralization pathways (Freckman and Ettema, 1993). Maturity index (MI) of free-living nematodes was calculated as Σ (pi ci), where pi is the proportion of the taxon, and ci is the c-p rating of taxon i according to the 1 to 5 c-p scale (Bongers and Bongers, 1998). Enrichment index (EI) and Structure index (SI) was calculated as EI = 100 × [e/(e+b)] and SI = 100 × [s/(s+b)] where e, s, and b are the abundance of nematodes in guilds representing enrichment (e = Ba1 and Fu2 guilds, where Ba1 = guild of bacterivores with c-p value of 1, Fu2 = fungivores with c-p value of 2), structure (s = Ba3-Ba5, Fu3-Fu5, Om3-Om5, Ca2-Ca5 guilds, where Om = omnivores, Ca = carnivores), and basal (b = Ba2 and Fu2 guilds) food web components, respectively. The channel index (CI) was calculated as CI = 100 × [0.8Fu2/ (3.2Ba1+ 0.8Fu2)] (Ferris et al., 2001).

Following the termination of the SSgH, eggplant plant height was monitored at 2-month intervals after transplanting. Eggplant fruits were harvested from 4 plants per plot beginning at 2 months after planting, and weekly thereafter. Numbers of fruits and fruit weight per plot were recorded. Fruits were sorted to marketable and unmarketable categories. Unmarketable fruits were due to thrips damage. At the end of the experiment, around 4.5 months after transplanting, three plants from each plot were uprooted, washed, weighted, and rated for root-gall index (RGI) based on a 0-10 scale according to Netscher and Sikora (1990).

Objective 3

A soil sample was collected from the rhizosphere of SSgH or eggplants at 3 plants/plot at 2-week after SSgH termination, and 2 months after eggplant planting for PLFA analysis. To obtain rhizosphere soil, roots were dug out and shaken in a bucket to remove major soil clogs and collect rhizosphere soil by screening through a 0.5-cm2 mesh metal sieve. A 10 g subsample from the composited rhizosphere soil was placed in a 14-ml Falcon tube (cat. No. 352059, Becton Dickinson, Lakes, NJ) and immediately stored in a cooler packed with dry ice. Soil samples were transported to the laboratory and stored at -80◦C (PHCBI, cat. No. MDF-DU702VHA-PA, PHC corporation, Wood Dale, IL) before shipping to Microbial ID Laboratory (MIDI Inc., Newark, DE) for PLFA analysis. Based on PLFA, total and relative (%) microbial biomass of G+ bacteria, G- bacteria, actinomyces, arbuscular mycorrhizae (AMF), non-AMF, and protozoa were estimated. 

All parameters collected were subjected to Canonical Correspondence Analysis (CCA) using CANOCO for Windows 4.5 (ter Braak and Smilauer, 2002) to deduce relationships between eggplant yield, nematode suppression, soil water conservation, soil health indicators, Solvita respiration rates, and PLFA microbial biomass.

Research results and discussion:

Objective 1

1.  In Trial I, energy sorghum ‘NX2’ was most suppressive (P ≤ 0.05) to M. incognita female development for all three ages of sorghum biomass amended compared to the no amendment control. Sorghum-sudangrass hybrid ‘LA’ was suppressive to M. incognita when using 1- and 2-month-old tissue, however, it could not suppress the number of females when using 3-month-old biomass.

2. In Trial II, ‘NX2’ and ‘LA’ were again found to be most suppressive to M. incognita infection and lead to lower number of females compared to the control.

3. Interestingly, ‘NX2’ and ‘LA’ suppressed the number of females more effectively than sunn hemp amendment.

4. Results from both trials showed a clear trend of decrease in the allelopathic effect of SSgH against M. incognita as the age of the biomass increase.

5. Soil carbon was significantly higher (P ≤ 0.05) in ‘NX2’ sorghum compared to the bare ground control at 2.5 months after planting SSgH cover crop, however this effect dissipated at 3 months after eggplant planting, soil carbon was not different (P > 0.05) among SSgH varieties. 

6. Energy sorghum ‘NX2’ and forage sorghum ‘BKP’ had higher (P ≤ 0.05) soil respiration rates compared to the bare ground control. However, water infiltration rate though highly variable, was not different among treatments.

 

Objective 2

1. Whereas SSgH treatment did not affect the abundance of reniform nematodes, population density of root-knot nematodes was numerically lowest in the bare ground (BG) control but statistically lower in ‘CV’ than BG. The abundance of root-knot nematode increased by most SSgH treatments was only occurring towards the end of the eggplant growing cycle.

2. Abundance of bacterivorous nematodes was increased by ‘512’ (P ≤ 0.05), whereas omnivorous nematodes was increased by ‘NX2’, ‘BKP’, ‘BK’ and ‘512’ (P ≤ 0.05) compared to BG. In general, all SSgH treatments increased abundance of omnivorous nematodes compared to BG numerically.

3. In terms of nematode community indices, SSgH treatments only affected richness and CI significantly. All SSgH treatments increased nematode richness compared to BG (P ≤ 0.05) except for ‘CV’ and ‘BKP’. There was also a trend that all SSgH increased CI compared to BG but this was most significant in ‘BK’, ‘BKP’ and ‘NX2’ (P ≤ 0.05). Though not significant, all SSgH also increased SI compared to the BG.

4. Eggplant height recorded at 5 weeks after transplanting was not significantly different (P > 0.05) among treatments. Eggplant fruit weight was numerically higher in all SSgH treatments compared to BG control, though it was not significantly different (P > 0.05). Significant differences were detected for eggplant fruit number and root weight. A higher (P ≤ 0.05) fruit number was observed in ‘CV’ plots. Root weight was increased (P ≤ 0.05) by ‘BK’ sorghum and all SSgH treatments had a higher root weight than BG control. On the other hand, there were no significant differences (P > 0.05) among treatments for root-gall formation. 

Objective 3

1. At the time of SSgH cover crop termination, total phospholipid fatty acids (TPLFA) indicating microbial biomass was increased (P ≤ 0.05) by 6 SSgH treatments excluding ‘NX1’ sorghum. Among the SSgH, ‘LA’ and ‘NX2’ showed the most promising results with 92% and 60% higher microbial biomass, respectively, than the BG control. Energy sorghum ‘NX2’ significantly increased populations of non-arbuscular mycorrhizal fungi and eukaryotes compared to BG control.

2. Three months after eggplant planting, ‘LA’ still increase (P ≤ 0.05) microbial biomass with 87% more than the control plot. Although not statistically significant, ‘CV’ and ‘NX2’ showed a 45% and 38% increase in microbial biomass, respectively, compared to bare ground.

3. Canonical Correspondence Analysis (CCA) at the time of termination of SSgH cover crop showed that most of the soil health indicators including total microbial biomass, soil microbial respiration rates, soil moisture, soil carbon, nematode enrichment index, maturity index, structure index, and abundance of omnivorous nematodes were negatively related to the abundance of plant-parasitic nematodes and reniform nematodes. At 3 months after eggplant planting, a negative relationship between root-gall index on eggplant with the above-mentioned soil health indicators was observed.

Participation Summary
2 Farmers participating in research

Educational & Outreach Activities

6 Curricula, factsheets or educational tools

Participation Summary:

88 Farmers
83 Ag professionals participated
Education/outreach description:

Workshops/field days

  1. Ecological & Sustainable Nematode Management. NRCS Conversations on Soil Health: Nematode Management and Cover Crops (Adobe Acrobat on-line event), June 17, 2021 (75 participants-NRCS Staff), Organized by Rachel Seman-Varner, Ph.D. 
  2. Integrating cover crops and organic fertilizers into your nutrient management regime to meet your farm’s soil health goals. Hawaii Women Farmer’s Network: Soil Health Workshop Four-Part Series. Kahumana Organic Farm, June 15, 2021 (12 participants), organized by India Clark, Oahu Resource Conservation and Development Council.
  3. The science behind cover cropping. Oahu County Cooperative Extension’s Research in the Garden Series. Urban Garden Center, May 27, 2021. Organized by J. Sugano (30 participants). A cover crop field day was conducted at the Urban garden center, in collaboration with CTAHR extension agents .The advantage of growing sorghum/sorghum-sudangrass hybrids (SSgH) was demonstrated through a series of activities including a soil slaking test to compare no-till cover crop vs tilled plots and a simulation rainfall test to compare the infiltration rate of 3  SSgH varieties against a bare ground control. Participants were encouraged and involved in performing each of these activities. In addition, a written copy of the benefits of SSgH cover cropping along with our recent research finding was made available to all participants.  Seeds of best-performing sorghum ‘NX-D-61 was distributed to the attendees. 
  4. GoFarm Hawaii New Farmers Training Program: Sustainable nematode and other pest management in agroecosystems through cover cropping or biological derived products (12 participants, Farm Coach: Eric Hanssen; March 24, 2021; 12 participants, Farm Coach: Jay Bost).

  5. Soil Health Lecture. Together We Farm Online Learning Platform. Oahu Oahu ACA.tovuti.io (Jan-March, 2021).
  6. Virtual soil health and IPM Mini-Conference. A presentation on ‘Which sorghum/sorghum-sudangrass hybrids have higher allelopathic toxicity against soil-borne pests’ was delivered to farmers and agricultural professionals through zoom on Aug 4, 2020 (30 participants).  

Presentations

1. Paudel, R. and K. -H. Wang. 2021. University of Hawaii Plant Sciences Symposium, “Management of plant-parasitic nematodes and soil health using sorghum/sorghum-sudangrass hybrids as a cover crop”.

2. Paudel, R. and K. -H. Wang., and Waisen, P. 2020. Society of Nematologists virtual meeting, “Management of plant-parasitic nematodes and soil health using sorghum/sorghum-sudangrass hybrids as a cover crop”.

Extension videos

Two videos were created and uploaded to the PIs YouTube channel.

1.  https://www.youtube.com/watch?v=XrdYbhQnVAc

This video demonstrates the importance of soil health management as the foundation of Plant Health Management. Keeping the ground cover 24/7 is important in 1) reducing soil erosion thus maintaining soils for crop roots to grow, 2) preventing water runoff and pollution, 3) maximizing water infiltration to conserve water and mitigate drought problems in crop production, and 4) sustaining soil organisms that are crucial for soil nutrient cycling.

2. https://www.youtube.com/watch?v=hbCSWttx8_A

This video showcases the multipurpose of sorghum as a cover crop in terms of suppressing plant-parasitic nematodes, adding soil carbon, improving water conservation and microbial activities in a vegetable agroecosystem in Hawaii.

Journal article

A manuscript entitled ‘Exploiting the innate potential of sorghum/sorghum-sudangrass cover crops to improve microbial profile that can  lead to suppression of plant-parasitic nematodes’ has been submitted to a special issue “Interactions between the rhizosphere microbiome and plant-parasitic nematodes) in MDPI-Microorganisms Journal.

Project Outcomes

2 Grants received that built upon this project
Did this project contribute to a larger project?:
Yes
4 New working collaborations
Knowledge Gained:

During the course of the first year of this project, we learned that no-till practice to terminate sorghum/sorghum-sudangrass hybrids (SSgH) as cover crops can improve soil edaphic factors (soil moisture content, soil organic matter), soil health indicators mostly just the abundance of omnivorous nematodes, and soil microbial profiles (Gram negative, Gram positive bacteria, arbuscular mycorrhizal fungi, saprophytic fungi, protists etc) in the soil within one cropping cycle, but it fails to suppress plant-parasitic nematodes (PPN) in the subsequent cash crops like eggplant. We learned that it is important to partially incorporate SSgH residues into the soil to achieve PPN suppression. Thus, we are working on a strip-till cover cropping system with SSgH to further evaluate this cover crop. 

We also improve our skill to evaluate soil health by conducting soil microbial profile assay using HPLC of phospholipid fatty acid (PLFA) from soil microorganisms through collaboration with a commercial lab, Microbial ID Lab (https://microbialid.com/).  We learn that although the PLFA assay provided different results from nematode community analysis, all these parameters draw a more complete pictures on what is happening in the soil following cover cropping practices. These assays are not meant to substitute each other rather provide a more rigorous interpretation of soil health conditions. 

We further expand our collaboration to a greater group of farmers/agriculture professional that are interested in cover crop and soil health management. My advisor secured two more grants (NIFA OREI and NRCS CIG) related to the use of SSgH or other cover crop mix using similar soil health assay tools we developed from this project.  Knowing the potential of some of these SSgH varieties tested, we now can provide more information for our local cover crop seed companies and their clients on what variety of sorghum to use as a cover crop. We also learn that there are increasing interest of farmers in Hawaii to use cover crops in particular those farmers that we interact with through GoFarm Hawaii New Farmers’ training program. 

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.