Overseeding novel forages in Oregon as a model for enhancing perennial grass pastures in the Pacific Northwest

This two-year project will be implemented in representative pasture-based livestock farming systems across various climatic zones of Oregon. The farm locations include Lakeview, SE Oregon, Union, NE Oregon (desert highland), Willamette Valley, NW Oregon (high rainfall, oceanic climate), and SW Oregon (Mediterranean climate). The project will consist of agro-ecological characterization studies, replicated on-farm trials, and training components. Site-specific technology assessment and refinement will be accomplished through multi-location, adaptive, on-farm trials. The field studies will investigate the influence of introduced pastures species, agronomic management practices, and grazing strategies on agricultural productivity and water use efficiency. The project-led interventions will be compared with conventional pasture farming practices. On-farm studies will include comparison of several grasses, deep rooting-perennial legumes, self-regenerating annual clovers, and pasture herbs for their nutrient utilization potentials under high and low inputs of irrigation and fertility management in several agroecoregions across Oregon. The overall goal of this proposal is to improve pasture production, nutritive value, and resource use efficiency through overseeding legumes and herbs with high bioactive compounds into grass-dominated pastures located in key agroecological zones of Oregon.

Objectives are to:

1. Quantify the persistence and yield of pasture grasses, herbs, perennial and self-regenerating annual pasture legumes incorporated into grass-dominated pastures in both rainfed and irrigated production systems for higher animal production, extended grazing season, agronomic and ecological benefits (e.g. biological N₂ fixation, nectar source for pollinators).
2. Investigate the effect of soil amendments (lime, N, B and Mo) in legume production and biological N2 fixation potentials.
3. Compare the bio-economic efficiency (cost-benefit analyses) of overseeding forbs in grass- dominated pastures with control pastures.

Location 1. Desert highland areas: Overseeding perennial grasses, legumes and herbs in irrigated pastures.

Irrigated systems in Lake and Union Counties are utilized for grazing or hay production, since primary agricultural products of the county are beef cattle and hay production (USDA Census of Agriculture, 2017). Irrigated systems provide consistent water application for growing livestock forages on the deeper soils in the county. However, over time, soil nutrients have been depleted and perennial forage species declined in quantity and quality. The common mode of operation is to till the existing pasture and establish a new one.  However, this is an expensive strategy with no profit realized until the second year.  Our project site is on pasture, currently dominated by Kentucky bluegrass (Poa pratensis L.) which has formed a thatch layer, affecting water infiltration. In addition, due to it is physiological dormancy in mid-summer, irrigation is ineffective for producing feed for half of the growing season.  As irrigation cost is high, other strategies for increasing pasture productivity need to be employed.

Hypothesis: Summer forage production can be greatly increased through incorporating legume and forb species, also improving the forage quality and water use efficiency in irrigated pasture systems.

On-farm studies will be undertaken in 2 farms in Lake County and one farm in Union County in each farm.  We will divide the field into three pasture plots and overseed either a simple mixture of (2 species) orchardgrass (Dactylics glomerata L.)-birdsfoot trefoil (Lotus corniculatus L.) (Treatment 1) or a diverse mixture (6 species) composed of orchardgrass, festulolium (×Festulolium Asch. & Graebn.), chicory, plantain, white clover (Trifolium repens L.) and birdsfoot trefoil (Treatment 2) into the existing grass-dominated pastures in June 2021. One subplot that will not be overdrilled will serve as the control (Treatment 3). These species were selected based on our initial success in our ongoing WSARE Farmer/Rancher Project (ID:602381). Each pasture plot will be split into 3 subplots and applied Nitrogen at either (i) 50 kg/ha, (ii)), 100 kg/ha or (iii) no N application (control) to assess their effects on pasture production, nutritive value and biological N₂ fixation. All legume seeds will be inoculated with the appropriate rhizobia. All plots will be fertilized based on soil test results.

Prior to planting, the site will be grazed to 5 cm to provide light and effective irrigation for germinating seedlings. Following the establishment of the overseeded plants, pasture will be grazed in late summer.  We will collect data on seasonal pasture biomass yields, forage nutritional quality, grazing days, water use efficiency, soil quality, and cost of production.  For the grazed pastures, growth will be measured between each grazing cycle. Prior to drying in an oven (65 °C) to constant weight, sub–samples will be sorted into botanical fractions. Samples will be analyzed for their nutritive value. A well-mixed bulk sample will be ground in a Wiley mill with a 1-mm stainless steel sieve (Thomas/Wiley) for chemical analyses using Association of Official Analytical Chemists methods (AOAC, 2016).

2021 - 2022  Adjusted materials and methods

LAKEVIEW (John Shine):  One ranch in Lake County (Willow Springs Ranch, Keith Barnhart) was removed from this project as the producer decided to put his land up for sale and not pursue any research activities. The other ranching operation  (KV Bar Ranch, John Shine) is very engaged in this project.  To that cause, we implanted this project on a 15 acre field, containing 2 soil types - a silt loam (majority = 70% of the area) and a clay loam, both running in an east-west direction.  This field is flood irrigated and was chosen due to water reliability in the extreme drought year of 2021.  The field is sod heavy due to rhizomatous plant activity of Kentucky bluegrass and heavy white clover.  Overseeding was accomplished with a Great Plains 12 foot wide, no till drill.  Legumes were appropriately innoculated and seed boxes were calibrated.  Field was split with the simple mix overseeded in the east half of the field, and the diverse mix overeeded in the west half.  Fields were fertilized north to south in two replicated strips against seeding treatments.  Fertilizer rates were:  F1 = 25 kg. nitrogen (N)/hectare and F2 = 50 kg. N/ hectare at 21% N in ammonium sulfate  (F1 = 119 kg/hectare and 238 kg/hectare of ammonium sulfate fertilizer).  Forage was sampled for biomass and quality by Clipping 1/4 meter frames randomly in each treatment.  

In 2023, the same area was sampled with quarter meter frames but only samples by fertilizer treatment were taken because forage growth was extremely poor due to a cold spring and the forage diverse mix we planted looked just like the simple mix.  Only grass and some white clover was up, and the white clover was too short to clip.

UNION COUNTY:  (John Sheehy and Eastern Oregon Agricultural Research Station (EOARC)):  

Soil tests from 2021 show alkaline fields in producer Sheehy's field with a very suitable neutral pH at the EOARC field and levels of nitrogen and phosphorus at both sites

EOARC alfalfa field was treated with a glyphosate application at 16 oz./acre.  Evaluation of overseeding was through density counts of emerged plants.  This was done with a 2x2 ft. quadrat (4 sq ft. = 0.37 sq. meter) and replicated 5 times per site.

On June 21, 2022, forage was clipped using a 2 by 2 square meter frame and weights were taken by forage species in the mix.

Location 2. Willamette Valley dryland sheep farm evaluation of self-regenerating annual legumes in a rainfed sheep farm.

Early to late maturing  subterranean clover and balansa clover cultivars will be over-drilled into existing pastures on a dryland sheep farm located in the Willamette Valley, Oregon, in the fall of 2021. We will divide the field into four pasture plots and overseed either early maturing subterranean and balansa clover mix (Treatment 1), or mid-maturing subterranean and balansa clover mix (Treatment 2), or late maturing subterranean and balansa clover mix (Treatment 3) into the existing grass-dominated pastures in each block. One subplot that will not be overdrilled will serve as the control (Treatment 4). Each pasture plot will be split into 4 subplots and applied either (1) lime (2 t/ha), (2) micronutrients (boron and molybdenum), (3) lime and micronutrients, or (0) no lime or micronutrient application (control) to assess their effects on seed yield ( for persistence of annual legumes) and biological N₂ fixation. The rates for the micronutrients will be determined based on soil test results. The seasonal forage production and self-regenerating potential (persistence) of these legumes will be monitored under the current management practices of these farms. Herbage growth rates of each pasture combination will be measured at each grazing cycle. All plots will be fertilized based on soil test results and recommendations of the Western Oregon and Western Washington Pasture Fertilizer Guide (http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/20636/fg63-e.pdf).

For the grazed pastures, growth will be measured inside 1-m² grazing exclosure cages. Prior to drying in an oven (65 °C) to constant weight, sub–samples will be sorted into botanical fractions. Samples will be analyzed for their nutritive value, including nitrogen and fiber determinations. For the quantification of the persistence of annual clover, seedlings of subterranean and balansa clover will be counted in two randomly placed quadrats in each plot containing these legumes in the fall of 2021, 2022 and 2023. Following summer grazing each year, 15 randomly selected soil cores will be collected to monitor the soil seed bank in each annual legume-containing plot. These soil cores will be bulked and washed through mesh sieves to remove soil; the retained legume seeds will be counted. Number of flowers and seeds per m² will be quantified for balansa clover. During the peak growing season, we will investigate the root nodule development of legumes by randomly digging three legume plants of each species in each treatment. The nodules then will be scored and recorded. [Score of nodulation 0 (no nodule) to 5 (full of healthy pink nodules)]

2021 - 2022 Adjusted Materials and Methods

JUNCTION CITY (Cody Wood)

Fields were fertilized accordingly before planting, with the addition of lime to the micronutrient (MN) plot.  MN application consisted of boron and molybdenum which were applied in MN plots consisting of 10 X 5 meters on March 16, 2022.  Table 2e reflects clover seedling counts within the entire pasture.

Although it was not listed in the original proposal, we have included another farm in the northern part of Willamette Valley (CCR Portland), thanks to the support of Saddlebutte Ag by providing the seeds.

McMINNVILLE (Catherine Johnson) - The 80 acre field is of mixed terrain (2% - 30% slopes) Soil tests show 5 different soil types, with the majority of soils as a silty loam.  Soils were sampled on the entire, 8 acre  “steep” field (containing the micronutrient (MN) plots) and entire field “below” parents’ house (planted with birdsfoot trefoil (BFT)).  Lime was applied at 2T/acre to TMT 1 and 3 of micronutrient plot.  Slugs were baited with Feroxx^TM  at 11.2 kg/ha. with Wizzer spinners.  During first attempted seedling counts, it was noted that all species had some germination but small size deterred successful identification.  MN application was initially adjusted and applied in two field applications.  Fields were rotationally grazed, beginning in late March.  Twelve cages were placed on the micronutrient plots, 3 per treatment

Location 3. Cattle farms in SW Oregon.

Hypothesis: Novel, deep-rooting perennial legumes and early-mid maturing annual clovers will provide a persistent and high quality forage in grass-dominated pastures and extend grazing season while reducing the input requirement for soil fertility.

These dryland cattle farms are located on flat and hill sites in SW, Oregon where average annual precipitation is 18.35 inches. These farms have both open and wooded pastures under white oak trees (Quercus alba). Most pastures predominantly contain annual grass and legume species. Medusahead (Taeniatherum caput-medusae) and foxtail barley grass (Hordeum jubatum) are major, highly problematic weed species. A visit to the farms and discussions with farmers in the field on October 12, 2020, prompted an idea to test a number of grass, legume and herb species for preliminary assessment for their persistence and production in the region. In replicated small plots (2 × 2 m), early and mid-maturing subterranean clover, balansa clover chicory aberlasting [a hybrid between white clover and Caucasian clover (Trifolium ambiguum L.), bigleaf trefoil (Lotus pedunculatus L.), alfalfa (Medicago sativa L.) and strawberry clover (Trifolium fragiferum L.) are currently being tested on three farms.

To increase the legume content of the pastures, we will investigate the persistence and productivity of a number of annual and perennial legumes in mixed pasture plots. Pasture mixtures containing either deep-rooted perennial legumes (birdsfoot trefoil, bigleaf trefoil, strawberry clover, aberlasting clover) (Treatment 1) or self-regenerating annual legumes (subterranean and balansa clovers) (Treatment 2) will be overseeded into a grass-dominated open and wooded pastures in both flat and hill sites in fall 2021 A diverse mixtures containing the species in both treatments will be planted in Treatment 3. Each pasture combination will include orchardgrass and a novel endophyte tall fescue (Festuca arundinacea L.), chicory, and plantain. Each pasture plot will be split into 4 subplots and applied either (i) lime (2 t/ha), (ii) micronutrients (boron, molybdenum), (iii) lime and micronutrients or (iv) no lime or micronutrient application (control) to assess their effects on biological N₂ fixation. The same pasture and plant sampling procedure as described for Location 2 will be followed in the trials to be established in SW Oregon.  All legume seeds will be inoculated with the appropriate rhizobia at planting. All plots will be fertilized based on soil test results and recommendations of the Western Oregon and Western Washington Pasture Fertilizer Guide.

2021 - 2022 Adjusted Materials and Methods

We included  Bob's farm in Klamath falls in place of Keith Barnhart who experienced a shortage of water due to drought conditions and couldn't conduct the trial.

KLAMATH FALLS (Bob Buchanan)

Pastures were grazed in 2021, prior to overseeding with the simple and diverse mixes at 1/2 inch depth.  No fertilizer was applied in 2021.  For establishment evaluation, seedling count, forage biomass and forage quality were evaluated. Pasture samples were clipped in the field within a quarter meter frame and sent in for laboratory analysis of forage quality.  For the seedling count, samples were weighed, then a representative handful was taken, from which plants were counted

CENTRAL POINT  (Lynn Gladman)

A previous soil test shows a loam soil, slightly acidic soil lacking sufficient nitrogen, phosphorus and potassium.  Micronutrient plots for this project are contained within the main large pasture.  Seedling counts were done within a 0.01 m² grid on the balansa and subclover.

Location 4.  Coastal areas with moderate climate and grass dominated pastures have areas of waterlogged soils and some low pH areas that would benefit from additional forage varieties that could establish in these areas.    

Five on farm trial areas were established in the fall of 2023.  Each area had a footprint of 18.3m. x 18.3 m. within which 24 small plots (3.04m. x 3.66m.)  were broadcast seeded with a hand held crank seeder with one forage species each. Livestock were used to trample broadcast seeds into the trial plots for a maximum of 24 hours after seeding and then excluded by fencing from the plots.

Table 2a lists the 24 forage species within individual plots replicated over 5 farms.  Pastures were all flat with full sun exposure.  Livestock grazing was diverse and is captured by farm in Table 2b.  Site 4 will be re-seeded in the spring of 2024 due to seedling failure of all species at that site.  Table 8 presents data averaged across three farms and across all harvest dates in addition to average crude protein content per species.  

Table 1. Summary of research activities in 2021-2024 in Oregon by date, region, and location

E. OR = Eastern Oregon; S.W. OR = Southwest Oregon; W.V. OR = Willamette Valley, Oregon

Table 2a.  Forage varieties planted by broadcast seeding in five farms in the coastal area of Oregon, September 2023

Table 2b.  Livestock use and seeding date by farm site in the coastal region of Oregon, 2023