Location: Forage Seed and Cereal Research Unit
2020 Annual Report
Objectives
The long-term aim of this project is to address strategic, high priority needs of grass seed growers in the Pacific Northwest (PNW) by assessing and developing management practices that simultaneously improve crop productivity and advance soil health. This aim will be met by interrogating research questions that fall into two broad objectives. The first objective is primarily focused on improving crop production by lessening the overall impact of pests, weeds, and pathogens, improving the arability of marginal lands with novel soil amendments, and assessing the impacts of management practices on soil health and fertility. Objective 2 also aims to improve crop productivity by identifying key interactions between genetics, environment, and management (G x E x M). Within this objective, tradeoffs between intensifying production and advancing ecosystem services are quantified and better understood to help farms reach and sustain their potential, including the impact of crop rotation and other management practices on increasing populations of beneficial microbes and improving soil health. Collectively, Objectives 1 and 2 advance our understanding of how G x E x M interactions impact agroecosystem productivity and resilience. For Objective 3, these data will be synthesized and developed into decision-support tools and models to provide growers with concrete strategies for improved land management and cultivation of grass seed cropping systems.
Objective 1: Identify and evaluate management practices that improve crop productivity and crop health or that enhance environmental quality.
- Sub-objective 1A: Identify technologies to reduce priority pests, diseases, and weeds that limit the profitability and sustainability of the cropping system.
- Sub-objective 1B: Assess the environmental and production outcomes from the application of biochar on marginal soils.
- Sub-objective 1C: Determine the effectiveness of crop rotation in reducing populations of weeds, diseases, and invertebrate pests.
Objective 2: Identify and assess key interactions between cropping system, environmental conditions and management practices that influence cropping outcomes and agroecosystem productivity.
- Sub-objective 2A: Evaluate the impact of management practices, including crop rotation, on soil health parameters.
- Sub-objective 2B: Assess the impact of cruciferous crop rotations on plant growth and microbiomes.
Objective 3: Develop knowledge and decision support tools that enable growers to optimize production.
- Sub-objective 3A: Develop and expand decision support tools that provide information about biochar to growers.
- Sub-objective 3B: Develop models and decision aids that improve soil health and improve system productivity by decreasing the yield gap.
- Sub-objective 3C: Develop strategies to reduce priority pests, diseases, and weeds and improve soil health.
Approach
The overall hypothesis of the project is that improved cropping practices in grass seed cropping systems provides simultaneous benefits to soil health and crop productivity. This hypothesis is tested within three objectives and their related subobjectives. In Objective One, we explore methods to reduce the populations of weeds and pests that limit productivity. This research is conducted in laboratory, greenhouse, and field experiments that determine if practices that promote soil health and lessen environmental impacts (application of soil amendments, selective herbicide application, and precision weed management) are detrimental or beneficial to crop yield. In Objective Two, the research aims to determine if conservation practices (cover cropping and reduced tillage) improve soil health, and if soil health can be attributed to improvements in crop yield. These objectives are met with laboratory, greenhouse, and field experiments that assess soil health and identify allelopathic responses mitigated by cover crops. The aim of Objective Three is to synthesize the information gathered in Objectives One and Two, and to create decision support tools that enable growers to optimize production. These tools will be provided to growers as web-based tool kits, models, or agronomic measures used to control pests, pathogens, and weeds, and to apply soil amendments. In general, these approaches aim to identify key interactions between genetics, environment, and management that simultaneously reduce farm inputs and improve ecosystem services by identifying and quantifying tradeoffs.
Progress Report
Seed crops in the Willamette Valley, Oregon, supply seeds for national and global cover crop applications. Ryegrasses, including annual, Italian, and intermediate varieties are a cornerstone of the cover crop market; however, concerns regarding herbicide resistant weeds have emerged. In response to this concern, an herbicide resistant bioassay is being developed to detect the presence of herbicide resistant weeds in seed lots in support of Objective 1. Twelve varieties of annual ryegrass, two of Italian ryegrass and one of intermediate ryegrass, were obtained from different seed certification levels: breeder, foundation, registered, certified and commercial. Initially, method development is focusing on glyphosate, but tests for clethodim, rimsulfuron, and glufosinate are also being developed. Different glyphosate doses and seed testing methods were evaluated, and progress has been made on the identification of an herbicide dose that discriminates between susceptible crops and resistant weeds. In a greenhouse whole plant dose-response experiment, nine varieties were tested for validation purposes. Optimization and expansion of the assay to test more varieties is ongoing.
In support of Sub-objective 1A, roughstalk bluegrass plants were counted for the creation of weed density maps. Although scientists provided the weed density map to the cooperating grower, the grower did not target spray glufosinate. Therefore, the benefits of precision application of herbicide could not be measured but will be assessed in future seasons.
Pyroligneous acid (PA) is a byproduct of biochar production that has the potential to control soil-borne phytopathogenic fungi. Progress under Sub-objective 1B confirmed that PA is fungicidal towards Verticillium dahliae at very low concentrations in artificial soils. Moreover, these concentrations are not phytotoxic to target crops, including mint. Ongoing experiments are assessing PA-based amendments to determine if they are able to control disease symptoms.
The strong effect of PA on V. dahliae prompted us to explore whether PA is also detrimental to the growth of other phytopathogenic fungi. To assay this, growth on media amended with PA was compared to that on acetic acid amended (AA) and non-amended media. In all, 17 isolates of phytopathogenic fungi were tested for sensitivity to PA, including species of Pythium, Phytophthora, Fusarium, Rhizoctonia, and Botrytis. Results from these assays indicated that PA inhibits the growth of each of the isolates tested. However, the growth of 16 of the isolates was also inhibited by equivalent amounts of AA. This result suggests that inhibition is likely the result of changes in pH rather than something specific to the PA amendment. In contrast, mycelial growth of F. oxysporum was inhibited specifically by PA. Future studies aim to determine if PA amendments influence the occurrence or development of Fusarium Wilt.
Biochar, a carbon-rich by-product of energy production, has received growing attention as a soil amendment that can improve soil structure, increase yield, and sequester carbon. These impacts are especially evident on marginal soils, including abandoned mine sites and metal-impacted agricultural soils. Progress under Sub-objective 1B was made to determine if biochar aids in the phytostabilization of mine soils. In greenhouse experiments, we observed that biochar, in combination with biosolids, lime, and a biofertilizer (BBLB) produced from a nearby reference site, improved the growth of native grasses in comparison with published best management practices. We also determined that the addition of a BBLB suppressed the growth of autotrophic bacteria that contribute to ecosystem degradation, and increased the diversity but decreased the abundance of soil microbes. The greenhouse study refined the techniques used to implement field studies, which are now ongoing.
Research conducted under Sub-objective 3B facilitated the expansion of the Pacific Northwest Biochar Atlas, an online biochar decision support toolkit. New technologies to produce biochar were demonstrated in conjunction with industrial and federal partners. Several biochars were obtained from these demonstrations, including biochar produced from juniper, grape, apple, and blueberry. Each biochar was characterized for physiochemical properties. We also developed and published several case studies to demonstrate how biochar is being used. These data will ultimately connect regional biochar users and producers by allowing users to identify biochars that ameliorate specific soil deficiencies or that meet other agronomic goals.
Existing research in grass seed cropping systems has shown that conservation farming practices, including reducing tillage and returning residue, have minimal impacts on soil organic matter (SOM) content, despite the fact that producers report improvement in soil health. Progress under Sub-objective 2B assessed the consequences of long-term use of conservation management practices to improve soil health. A pilot project was conducted that surveyed soil health indicators in fields that have been converted from conventional to conservation practices. Working with a single farmer, we compared fields that had been in conservation practices for fewer than five years (“young” fields) to fields that were managed with conservation practices for more than 20 years (“old” fields). Soil health was assessed following the Comprehensive Assessment of Soil Health (CASH) protocols, with additional assessments of microbial community structure and function. Soil health metrics showed significantly higher total organic and active carbon concentrations and a qualitative increase in stable wet aggregates in the population of “old” fields. Our analysis suggested that tillage and crop type significantly influenced microbial community composition, and that arbuscular mycorrhizae were most abundant in no-till annual ryegrass (ARG) fields. The impact of this discovery on production, biogeochemical cycling, and system resilience is being explored; however, the observed increase in carbon content and the changes in the structure and function of the microbial community is potentially important for rethinking the narrative that tillage and residue do not impact the accumulation of SOM or the overall soil health of grass seed cropping systems.
This year, we expanded our focus to characterize how the extremes of management intensity that occur in grass seed cropping systems impact soil health scores. Annually tilled fields used to grow ARG represent the most intensive management practices, while fields used to grow perennial grasses (PG) over 15 years, fall on the opposite side of the intensity spectrum. Intermediate intensity is represented by fields where ARG and PG species are rotated. Natural reference sites on related soil series are also being evaluated. In April 2020, 18 sites across these categories were sampled, and in April 2021 an additional 25 sites will be sampled, to provide a total of 60 fields to complete the soil health survey.
Progress was made under Sub-objective 2B. Cruciferous species produce a suite of well-known allelopathic compounds that alter the soil microbiome, including glucosinolates and isothiocyanates (ITC). ITCs alleviate pathogen pressure in several cropping systems. The ability of ITCs to positively select for beneficial microbes, including plant growth promoting rhizobacteria, is not well understood and has not been studied in seed cropping systems. Growers have reported higher yields in fields post-brassica rotation and when volunteer brassicas emerge in recently planted stands. To understand whether brassica species improve the growth of seed crops due to ITC production, a bacterial biosensor that detects the presence of ITCs was optimized. This biosensor has been shown to detect ITCs at biologically relevant concentrations in a dose-dependent manner. The biosensor detected ITCs in seed, sprout, and leaves of brassicas, but not in crops that do not produce ITCs. ITCs were also detected in two different brassica-based seed meals used as field amendments to suppress weeds and disease. Greenhouse experiments deploying the biosensor to detect ITC in brassica-planted and seed meal-amended soils and the impact of these ITC on the growth of ARG are ongoing. Should ITCs promote the growth of ARG, we will determine if those effects are best realized through crop rotations or through intercropping with ryegrass and cruciferous crops.
Plant growth-promoting bacteria (PGPB) are often applied as biofertilizers. Pseudomonas spp. are well recognized PGPB. A group of P. fluorescens strains has been isolated from grass roots in the Willamette Valley and appears to be endemic to the region. One of these strains, WH6, has also been shown to have PGP activity on woody trees. Endemism to the Willamette Valley and known PGP activity suggests that the WH6 group may facilitate plant growth in grass seed cropping systems and that its abundance in fields result in higher yields. In support of Sub-objective 2B, a quantitative method for detecting the WH6 group of bacteria in soils was developed and used to test whether plant yields correlate with amounts of WH6 in the soil. In laboratory experiments, treatment of seedlings with WH6 resulted in thicker roots compared to controls. A preliminary greenhouse study showed that WH6-treated plants grew more densely, more quickly and developed flowering stems earlier than control plants. In addition, the ratio of above to below ground growth was significantly higher in the WH6-treated plants. These preliminary findings support the idea that the WH6 group of P. fluorescens is a PGPB endemic to grass-growing regions and deserves further study.
Accomplishments
1. A bacterial biosensor detects isothiocyanates in soil to promote the use of seed meal. Seed meal produced from canola and mustard can reduce pathogen pressure and suppress the germination of weeds by releasing glucosinolates (GCS) and isothiocyantes (ITCs) into the soil. However, the widespread use of canola and mustard-based seed meals is hampered because off-target effects also suppress the germination of crop plants. Furthermore, methods that detect residual GCS and ITCs are expensive and time consuming. Scientists in Corvallis, Oregon, developed a biosensor that detects biologically relevant concentrations of GCS and ITCs in soil. This technology is being developed into a method that can rapidly screen soils for the presence of ITCs, allowing growers to determine when it is safe to replant fields after the application of seed meals.
Review Publications
Phillips, C.L., Light, S.E., Lindsley, A., Wanzek, T.A., Meyer, K.M., Trippe, K.M. 2020. Preliminary evaluation of a decision support tool for biochar amendment. Biochar. 2:93-105. https://doi.org/10.1007/s42773-020-00037-3.
Kharel, G., Sacko, O., Feng, X., Morris, J., Phillips, C.L., Trippe, K.M., Kumar, S., Lee, J. 2019. Biochar surface oxygenation by ozonization for super high cation exchange capacity. ACS Sustainable Chemistry & Engineering. 7(19):16410-16418. https://doi.org/10.1021/acssuschemeng.9b03536.
Phillips, C.L., Light, S.E., Gollany, H.T., Chiu, S., Wanzek, T.A., Meyer, K.M., Trippe, K.M. 2020. Can biochar conserve water in Oregon agricultural soils? Soil and Tillage Research. 198. https://doi.org/10.1016/j.still.2019.104525.
Garcia-Jaramillo, M.N., Trippe, K.M., Helmus, R., Knicker, H.E., Cox, L., Hermosin, M.C., Parsons, J.R., Kalbitz, K. 2019. An examination of the role of biochar and biochar water-extractable substances on the sorption of ionizable herbicides in rice paddy soils. Journal of Environmental Management. 706. https://doi.org/10.1016/j.scitotenv.2019.135682.
Phillips, C.L., Meyer, K.M., Trippe, K.M. 2020. Biochar application method affects soil moisture and seedling establishment. Geoderma. 375. https://doi.org/10.1016/j.geoderma.2020.114457.
Soong, J., Phillips, C.L., Ledna, C., Koven, C.D., Tom, M. 2020. CMIP5 models predict rapid and deep soil warming over the 21st century. Journal of Geophysical Research-Biogeosciences. 125(2). https://doi.org/10.1029/2019JG005266.
Sales, B.K., Bryla, D.R., Trippe, K.M., Weiland, G.E., Scagel, C.F., Strik, B.C., Sullivan, D.M. 2020. Amending sandy soil with a softwood biochar promotes plant growth and root colonization by mycorrhizal fungi in highbush blueberry. HortScience. 55(3):353-361. https://doi.org/10.21273/HORTSCI14542-19.
Phillips, C.L. 2020. How much will soils warm? Journal of Geophysical Research-Biogeosciences. 125(7). https://doi.org/10.1029/2020JG005668.
