Improving the Rotational Value of Field Pea as a Legume Cover Crop.

Final report for GNE18-179

Project Type: Graduate Student
Funds awarded in 2018: $15,000.00
Projected End Date: 08/31/2020
Grant Recipient: University of Vermont
Region: Northeast
State: Vermont
Graduate Student:
Faculty Advisor:
Eric BishopvonWettberg
University of Vermont
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Project Information

Summary:

Cover crops are a great sustainable method to improve yields in agroecosystems. However, minimal effort has gone into improving cover crops as rotational partners. The majority of cover crop research has focused on interspecies comparisons for cover cropping variation with minimal research investigating intraspecies variation. Therefore, to address if variation of cover cropping traits is present within a cover crop, we tested 15 varieties of field pea for cover cropping variation. We measured various cover cropping traits and the effect of the field pea variety on the growth and yield of a subsequently planted crop. We found that varieties of field pea varied in their ability to increase soil C%,  sodium, calcium, and effective CEC, and the yield of the subsequent corn crop. Additionally, minimal difference in the microbial recruitment was observed within field pea. In conclusion, our study illustrates the presence of intraspecies variation for cover cropping traits within field pea. In all, our results suggest that cover crops can be improved as rotational partners to improve the sustainability and profitability of the agroecosystems. 

 

Project Objectives:

The current proposal aims to benefit farmers by improving the rotational value of field pea, a legume cover crop. Therefore, this proposal has three major objectives:

1. Determine the extent of variation of beneficial crop rotational traits (e.g. nitrogen fixation, nutrient mobilization, organic matter deposition) within multiple field pea accessions.

2. Characterize the effect of field pea rotational trait variation on a subsequently grown crop under Northeastern U.S. conditions.

3 Characterize the variability and functional activity of the shifted microbiome communities in the soil/rhizosphere between field pea accessions.

Introduction:

The purpose of this project is to improve the rotational value of field pea (also known as Canadian pea, Pisum sativum var. arvense (L.)) a legume cover crop. In the United States, the acreage of land being cover cropped has rapidly increased over the past five years (CTIC, SARE, & ASTA, 2016). This is due to legume cover crops ability to increase soil fertility and subsequent crop yields at lower costs and environmental risks than fertilizers (Crews and Peoples, 2004; Reckling et al. 2016). Generally, legumes can fix 50 to 150 pounds per acre (lbs/acre) of Nitrogen (N) due to their symbiotic relationship with nitrogen-fixing bacteria (Clark, 2015). In addition to reincorporating N into the soil, legume cover crops can prevent soil erosion, attract and support beneficial insects, mobilize minerals and limiting nutrients, increase soil organic matter, and most importantly, increase the diversity and functional activity of the soil microbiome, which is directly linked with crop health (Berendsen et al. 2012; Clark, 2015; Sare, 2017). Cover crops manipulate microbial soil communities by releasing exudates into the soil to recruit beneficial microorganisms that suppress and protect against pathogens, promote plant growth, and alter plant metabolism (Chavarria et al. 2016; Jacoby et al., 2017; Brennan & Acosta-Martinez, 2017). Therefore, to maintain crop health and increase production, it is crucial for farmers to incorporate legumes into their rotations.

Despite the numerous benefits of cover crops, no single species currently meets all of the needs  (fixing nitrogen, weed and pathogen suppression, promotion of microbial communities, etc.) of farmers. Some legume cover crops have poor establishment rates, and some face disease or other challenges. Additionally, non-legume cover crops, like cereals and forage grasses, provide erosion control, suppress weeds, and add organic matter to the soil, more efficiently than legumes (Clark, 2015). Consequently, farmers use mixtures or “cocktails” of multiple legume and non-legume cover crops to fulfill their needs (Clark, 2015). However, this method requires more time and management leading to increased costs (Clark, 2015). Therefore, there is a clear need to breed for the improvement of rotational value (how well the crop benefits a subsequently grown crop) of legume cover crops to meet farmer’s diverse set of goals at lowered costs to increase farm profitability.

Ultimately, the improvement of the rotational value of legume cover crops will further enhance soil quality, soil microbial diversity, and functional activity, which will increase the productivity of fields, ensuring farm profitability and food security. Additionally, increased soil fertility and pathogen suppression will reduce the need for fertilizers and other agricultural inputs, lessening the amount of these chemicals in agricultural runoff and dampening the detrimental impacts of runoff on the environment. In all, the rotational improvement of legume cover crops will benefit farmers, improve agriculture sustainability, and help conserve environmental health.

Research

Materials and methods:

Field Site: The experiment took place at the University of Vermont’s’ Horticulture Research and Education Center located at 65 Green Mountain Drive, South Burlington, VT 05403 (Appendix, Figure 1).

Field pea material: 15 field pea accessions were used in this experiment (Appendix, Figure 2A). All accessions were requested from the USDA NPGS and then amplified in Burlington, Vermont. Eight of the accessions are wild material from Georgia. The other accessions are cultivated lines originating in the United States. The use of wild material that has not undergone the genetic bottlenecks of domestication and breeding provided more genetic variation to this experiment.

Objective 1: Determine the extent of variation of beneficial crop rotational traits (e.g. nitrogen fixation, nutrient mobilization, organic matter deposition) within multiple field pea accessions.

Experiment 1: Testing for variation of rotational traits: nitrogen fixation, nutrient and mineral mobilization, and organic matter deposition.

To test for variation of rotational traits, 15 field pea accessions and two controls (no cover crop and no cover crop with fertilizer) were grown or administered in a randomized block design in one continuous field (Appendix, Figure 2). There was four replicates of each accession and control, for a total of 92 2m2 plots. Before the field pea was planted, “pre-planting” soil core samples approximately 30 cm (or 12 inches) deep were taken from the direct center of each plot using a 5-inch diameter hand-held auger. Once soil samples were collected, 50 field peas were hand sown in each plot and grown for 40 days. 50 plants in each plot simulated the recommended field pea density of 180 lbs/ac (NDSU, 2002, Stepanovic, 2017). Two days before field pea harvesting, “post-planting” soil samples were taken using the same methods as listed previously. Soil samples were only collected from the center of plots to avoid edge effects of neighboring plots. All soil samples (182 soil samples) were sent to the University of Vermont Agricultural and Environmental Testing Laboratory where they tested for pH, organic matter, available nitrate, phosphorus, potassium, aluminum, boron, calcium, copper, iron, magnesium, manganese, sulfur, and zinc.

A two-way repeated-measures analysis of variance (ANOVA) test with a Tukey’s honestly significant difference (HSD) post hoc test was used to analyze the measurements reported by the testing laboratory. The two factors used in the analysis were accession and block. The analysis determined if there is variation in rotational traits in field pea and if this variation is due to genetic variation or placement in the field.

Objective 2. Characterize the effect of field pea rotational trait variation on a subsequently grown crop under Northeastern U.S. conditions.

Experiment 2: How is the subsequently grown corn affected by the genetic variation of the previously planted field pea?

To test how the variation of rotational traits in field pea affects a subsequently grown crop, a nutrient-intensive (“heavy feeder”) subsequent crop of corn was sown. Due to the late planting in June, the early sweet corn variety “Sugar Buns” was used. “Sugar Buns” is an early maturing corn that is harvestable 70 days after sowing. The corn was hand-planted according to the manufacturer’s specification, of 2 seeds a foot (30.48 cm) in rows 36 inches (91.44 cm) apart. Fertilizer was added to the previously specified “no cover crop with fertilizer” control plots according to the recommendations from the UVM soil testing laboratory. Thirty-five days after sowing, chlorophyll content was recorded using a SPAD 502 Plus Chlorophyll Meter. The youngest fully developed leaf of the three plants closest to the center of each plot was sampled. Once the corn was ready to be harvested, plant height, dry aboveground biomass, and yield was measured for the same three plants. Plants closest to the direct center of the plot was only sampled to avoid edge effects from neighboring plots.

A two-way repeated-measures ANOVA test with a Tukey’s HSD post hoc test was used to analyze chlorophyll content, plant height, dry aboveground biomass, and yield, with accession and block as the two factors. The analysis determined if there is variation in corn performance and if this variation is due to genetic variation of the previously planted field pea or the location of the corn in the field.

Objective 3: Characterize the variability and functional activity of the shifted microbiome communities in the soil/rhizosphere between field pea accessions.

Experiment 3: Extracting microbial DNA from soil samples, sequencing 16s rRNA, and analyzing the sequences for diversity and functional activity.

To test for microbial community shifts in the soil, microbial DNA was extracted from pre-planting soil samples and rhizosphere samples. A small portion, ~10 g, of the pre-planting soil samples was separated and stored at -80C. The rhizosphere is the soil still attached to the roots after the plant has been uprooted. Rhizosphere microbial samples were collected two days before the field pea is harvested. The center-most field pea plant in each plot was uprooted and the soil still clinging to the roots was removed and collected in the field and stored at -80C. The centermost field pea plant was sampled to avoid edge effect of neighboring plots.184 DNA samples (92 pre-planting, 92 rhizosphere samples) were extracted from all soil samples using the QIAGEN DNeasy PowerSoil Kit.

DNA extracts were sent to LC Science, a biotechnology sequencing company. Samples were processed for DNA library preparation in order to sequence 16s rRNA. Specifically, Phusion polymerase was used to amplify the 16s rRNA region of the DNA samples for 25-25 PCR cycles. After a single cycle of PCR, sequencing adapters and barcodes was added to each sample before further amplification. After amplification, an Illumina cBot system was used to generate clusters for sequencing using a next-generation MiSeq sequencer. Sequencing data was “cleaned” by trimming the barcodes and adapters, merging paired ends reads into single sequence tags, excluding tags with more than 5% ambiguous bases, and lastly excluding tags with more than 20% of low-quality bases (a Phred Score of < 10). The clean data, which is usually 300-400 bp in length, was then analyzed for operational taxonomic units (OTU) (analogous to species identification for microbial groups) using CD-HIT, a nucleotide clustering, and comparison program. To determine an OTU, the sequence similarity had to be greater than 97% within clusters. In addition to OTUs, LC Science provided species accumulation curves, alpha diversity, Shannon index (H), Simpson index, Chao1 index, rank-abundance curves, beta diversity, and a principal coordinate analysis (PCA). These analyses provided a measure of microbial diversity and species abundances for each submitted soil sample. In addition to diversity analysis, LC Science determined the taxa of the OTUs, by mapping each OTUs’ representative tag in the Ribosomal Database Project (RDP, version 11.3), Greengeens Database, and the NCBI 16S Microbial Database. 

Research results and discussion:

1. Determine the extent of variation of beneficial crop rotational traits (e.g. nitrogen fixation, nutrient mobilization, organic matter deposition) within multiple field pea accessions.

Accessions varied significantly in crop rotational traits for  soil calcium ( P = 0.013), magnesium (P = 0.002), manganese (P = 0.016), sodium (P = 0.007), effective CEC ( P = 0.012), and %C (P = < .001). This indicates phenotypic and genetic variation for rotational traits within pea.  

2. Characterize the effect of field pea rotational trait variation on a subsequently grown crop under Northeastern U.S. conditions.

Cob weight was significantly different between accessions (P = 0.021), with accessions W6 26154 PSP (wild) and PI 577142 (domesticated) increasing cob weights the most. This indicated phenotypic and genetic variation for increasing subsequent crop yields within pea. 

3 Characterize the variability and functional activity of the shifted microbiome communities in the soil/rhizosphere between field pea accessions.

Αlpha (α)-diversity (richness, evenness, Simpson’s, Fisher) and β-diversity (Bray-Curtis dissimilarity) measurements for accession were non-significant. Indicating similarly recruited microbes.  However, despite a lack of significant difference in community composition, significant differential abundances were found between history groups versus control for 5 phyla, with Firmicutes (P = <0.001) and Patescibacteria  ( P = <0.001) enriched in pea, and Chloroflexi (tP = <0.001), Gemmatimonadetes (P = <0.001), and WPS-2 P = <0.001) enriched in control plots. Indicating that pea as whole recruit specific microbes. 

Research conclusions:

1. Determine the extent of variation of beneficial crop rotational traits (e.g. nitrogen fixation, nutrient mobilization, organic matter deposition) within multiple field pea accessions.

Field pea accessions did vary in beneficial crop rotation traits such as nutrient mobilization, organic matter deposition, soil C%, and soil N%. 

2. Characterize the effect of field pea rotational trait variation on a subsequently grown crop under Northeastern U.S. conditions.

Field pea accessions did vary in their ability to increase subsequent crop yields, with a wild pea variety increasing yields the most. 

3 Characterize the variability and functional activity of the shifted microbiome communities in the soil/rhizosphere between field pea accessions.

Field pea accessions did recruit similar microbial communities, with similar alpha and beta diversity. However, when looking at specific genus or phyla there were differences in abundances for beneficial microbes versus control plots. 

Participation Summary

Education & Outreach Activities and Participation Summary

4 Journal articles
1 On-farm demonstrations
1 Published press articles, newsletters
4 Webinars / talks / presentations
1 Workshop field days

Participation Summary

30 Farmers
20 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

We presented our research to farmers at the 2019 Research Open House at the University of Vermont Horticulture Research & Education Center and the 2020 NOFA VT Conference. 

We presented our research to scientists at the 2019 Emerging Opportunities for Pulse Production:
Genomics, Phenomics, and Integrated Pest Management Conference,
the 2019 Botany Conference, and at the Dissertation defense of Edward Marques. 

Articles published or in preparation with the support of this grant include: 

Marques, E., Kur, A., Bueno, E., von Wettberg, E. J. B. (2020) Defining and improving the
“Rotational Value” and “Intercropping Value” of a crop using a plant-soil feedbacks approach.
Crop Science. 60(5): 2195-2203. https://doi.org/10.1002/csc2.20200

Coyne, C.J., Kumar, S, von Wettberg, E.J.B, Marques E. Berger, J.D., Redden, R.J., Ellis
T.H.N., Brus, J., Zablatzká, L., Smýkal, P. (2020) Potential and limits of exploitation of crop
wild relatives for pea, lentil, and chickpea improvement.
Legume Science.
2:e36. https://doi.org/10.1002/leg3.36

Marques, E. (2020) Increasing the Agronomic and Economic Value of Chickpea and Pea. Graduate
College Dissertations and Theses
. 1232. https://scholarworks.uvm.edu/graddis/1232

Marques, E., and von Wettberg E. J. B. A next-generation cover crop: assessing the variation of
cover cropping traits present in field pea. Manuscript in Review
.

 

Project Outcomes

20 Farmers reporting change in knowledge, attitudes, skills and/or awareness
4 Grants applied for that built upon this project
2 Grants received that built upon this project
$32,075.00 Dollar amount of grants received that built upon this project
10 New working collaborations
Project outcomes:

I believe the research collected from this project opens up a new avenue for increasing the sustainability and profitability of agriculture. We showed that genotypes differ in rotational traits, illustrating the possibility of breeding more effective cover crops and rotational partners that may potentially increase the sustainability and profitability of farms. Additionally, our research shows the importance of wild relatives as a reservoir of phenotypic diversity for crop improvement efforts. This further strengthens the argument for the enhanced conservation of these plants. 

Knowledge Gained:

This grant has allowed me and my advisor to become more knowledgeable and aware of agriculture and sustainability. It also brought on collaborative efforts with local farms that would have otherwise not occurred. 

As a result of this grant, my career and research direction has changed with me wanting to become an Extension Agent or a researcher for the USDA. 

The research generated by this grant was used in numerous successfully funded grant applications that are currently ongoing. 

Assessment of Project Approach and Areas of Further Study:

A challenge/limitation of this study was that it was only replicated at a single farming site with a limited number of varieties. This design limits our ability to extrapolate our claims to other environments. However, this limitation was necessary given the time and financial effort it took to implement at a single farm. Potentially, in the future, reducing the number of accessions and increasing the number of farming sites may have been a better approach to better support our claims. 

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.