Research at Pendleton

Pendleton Long-term Experiments (LTEP)

LTEP is located 15 km northeast of Pendleton, in the northeastern corner of Oregon at the Columbia Basin Agricultural Research Center (CBARC), which is administered by the Oregon State University Agricultural Experiment Station. The Columbia Plateau Conservation Research Center, administered by USDA-ARS, is immediately adjacent. Research facilities are shared jointly by the staff of both agencies. All research activities at LTEP are presently monitored by an oversight committee consisting of five members from Oregon and one each from Washington and Idaho.

The research center is located in the Columbia Plateau physiographic province between the Cascade and Rocky Mountains at an elevation of 455 m. The climate is semi-arid, but partially influenced by maritime winds from the Pacific Ocean. Winters are cool and wet, and summers are hot and dry. Annual precipitation averages 420 mm, with nearly 70% falling between 1 September and 1 April. Average temperature is 10°C, but ranges from -1°C in January to 21°C in July. LTEP is located on a gently sloping landscape, with slopes ranging from 0 to 5%. Soils are coarse silty mixed mesic Typic Haploxerolls (Walla Walla silt loam) that developed from loess deposits overlying basalt. Virgin vegetation was a shrub-grassland or sagebrush-grassland steppe, with Idaho fescue (Festuca idahoensis) and Sandberg bluegrass (Agropyron spicatum) as the dominant species. Drier landscapes had lesser amounts of sagebrush (Artemesia tridentata) and wetter areas low-growing shrubs (Symphiocarpos albus). Downy brome (Bromus tectorum L.) was an early invader after land was broken for cultivation. The area was first broken for cultivation in the mid 1880s, and was farmed for about 50 years when the research center was established in 1929.

Several long-term experiments have been established at LTEP (Table 1). Their design, history, and published data will be briefly summarized below. More detailed information, including detailed management histories and plot maps, is available in Rasmussen and Smiley (1997) and an on-line publication

Table 1. Long-term experiments at Pendleton, Oregon.



Year initiated

Perennial grassland



Continuous cereal

Fertility (N), crop, tillage


Residue management

Fertility (N, manure, pea vine), burning



Tillage, fertility (N)



Tillage, fertility (N, liming)


No-till wheat

Fertility (N)


Moro Long-Term Experiments

Tillage, crop rotations



Perennial Grassland.  

The perennial grassland site (46 m by 109 m) contains no experimental variables but has been maintained since 1931. The site is intended to approximate a near-virgin grassland and serves as a baseline for evaluating changes in other experiments. It is periodically reseeded with introduced grass selections, occasionally fertilized, and infrequently irrigated. The dominant grass species are bluebunch wheatgrass (Agropyron spicatum var. ‘Secar’) with lesser amounts of Idaho fescue (Festuca idahoensis var. ‘Joseph’). Weeds are controlled as needed. It was grazed occasionally until 1985 but has not been grazed since, although vegetation is sometimes clipped during or after summer growth.

Above-ground productivity was measured in 2004 for the first time since renovation. Species counts were initiated in 2004. Soil is sampled every 5 and 10 years and analyzed for nutrients and SOM. Soil samples for nutrient analysis are taken at 30-cm intervals down to restricting zone and at 10-cm interval in the first 30 cm root zone for SOM determinations.


Continuous Cereal.

The continuous cereal experiment was begun in 1931 to determine the feasibility of annual cropping of winter wheat in this low rainfall region. In 1982 it was modified to include three cereals: winter wheat, spring wheat, and spring barley. Each of these cropping treatments is replicated eight times (12 m by 27 m plots). Plots were split again in 1996 to include a N fertilization treatment. The continuous cereal experiment evaluates the effect of tillage (CT and no-till, NT) and fertility (unfertilized and fertilized) on soil and crop productivity. It was hypothesized that intensifying crop production by growing a crop every year would maintain or increase SOM and fertilization would replenish nutrients usually supplied through mineralization during fallow. The objectives are…

The CTNT experiment was initiated to determine the feasibility of annual cropping in the 400 mm precipitation region around Pendleton. Results indicate that CT maintained SOM in the 10 to 20-cm zone (where residues are buried) at the same levels as SOM in 1931 but depleted SOM in the 0 to 10-cm zone (Fig 2) (Machado et al., 2006). This leaves the top soil susceptible to wind and water erosion. To this end, a NT continuous cereal LTE was initiated on land that was under wheat-fallow.

Results after only 6 years indicate that NT was reversing 73 years of SOM depletion that occurred under CT. The increase in SOM was significantly more in the top 0-10 cm zone. We would like to continue this experiment and determine how long it will take to restore SOM levels to 1931 levels and beyond and determine the effects of SOM increase on soil quality and crop productivity.


Residue Management.

The crop residue experiment is the most comprehensive of the long-term experiments at Pendleton. It was originally initiated to evaluate the effect of different soil amendments (based on farmer practices in the 1930’s) on soil and crop productivity under the wheat-fallow system. The hypothesis was that application of N would alleviate detrimental effects caused by burning of crop residues and also could replace the use of pea vine and manure in wheat production. The objective of the experiment was to determine the effects of N application, burning, and pea vine and manure application on soil chemical and physical properties, SOM, and soil productivity under the traditional wheat-fallow system using conventional tillage (CT). The experimental design is an ordered block consisting of nine treatments and two replications. The experiment contains duplicate sets of treatments that are offset by one year so that data can be obtained annually. Plot sizes are 12 m by 40 m.

Results from this experiment indicated that all other treatments except the manure treatment depleted SOM (Fig 1) (Rasmussen and Ronde, 1988b; Rasmussen and Collins, 1991; Rasmussen and Parton, 1994; Rasmussen et al., 1980, 1995, 1998a,b). Soil organic matter consists of decomposed plant materials rich in carbon (C) that improve soil structure and increase nutrient storage and water holding capacity. In agricultural lands, tillage, fertility, crop rotations, and cropping intensity influence the rate at which C is added to or removed from soil (Franzluebbers, 2004). The wheat-fallow system depletes SOM because one crop is grown in two years and CT, which is practiced under this system, exacerbates SOM loss and CO2 emission by enhancing oxidation of buried crop residues. On the basis of CR results and other related local and regional studies, some LTEs were modified and new LTEs were initiated to reduce or arrest the depletion of SOM. In the CR experiment, SOM continues to decrease in treatments that resemble farmer practices except in the manure treatment. How the soil microbial community has been affected is not clear. We hypothesize that the manure treatment will have the greatest microbial diversity and biomass compared to other treatments. To this end, we would like to continue this experiment to determine the point of equilibrium in C sequestration and depletion for each treatment and how soil microbial community and soil quality will be affected.



The Tillage-Fertility experiment evaluates tillage and nitrogen treatments on crop and soil productivity under the wheat-fallow cropping system. It was hypothesized that reduced tillage that partially buries crop residues and reduces SOM oxidation, together with high N rates that will increase plant biomass and SOM, will improve the productivity of the wheat-fallow system. The experimental design is a randomized block split-plot with three replications. Main plots consist of three primary tillage systems (moldboard plow, offset disk, and subsurface sweep) and subplots (6 m by 40 m) of six fertility levels. These plots are fallow during every other year.

 Results indicate that SOM increased with increase in N and was higher in the stubble mulch tillage treatments (sweep and disc) than moldboard plow treatments. But there were no differences in SOM between sweep and the disc treatments (Rasmussen and Rohde. 1988b). We now propose to change the disc treatment to a no-tillage treatment. Although SOM increased with increase in N under reduced tillage, SOM levels were still lower than under annual cropping (Rasmussen and Smiley, 1997). Based on these results we hypothesize that no-till will increase SOM more than the sweep and plow but may need more N to produce the same yields due to increased N immobilization during the initial years. More and more growers are changing to no-till and this change would make the TF LTE more relevant to current trends in agriculture.



The wheat-pea rotation experiment, initiated in 1963, evaluates the timing and severity of tillage operations on the soil and wheat and pea productivity. Given the decline in SOM under wheat-fallow, it was hypothesized that annual cropping using wheat and peas in rotation under reduced tillage would improve soil productivity compared to the annual mono-cropping of wheat under conventional tillage. Legumes allow for grassy weed control and supply N. Timing of tillage was thought to be critical to soil moisture conservation and it was hypothesized that spring tillage would increase available soil moisture and increase yields. The objective of the experiment was to determine effects of four different tillage treatments on soil quality and productivity in a wheat-legume crop rotation. The experimental design is a randomized block with four replications. Each replication contains eight, 7 m by 37 m plots (duplicates of the four tillage treatments to allow yearly data collection for wheat and peas). In 1976 lime was applied to the west half of each plot.

Results indicate spring plowing has consistently produced the highest yields of both peas and wheat compared to fall plowing because of increased water storage. This was primarily because standing stubble increased over-winter snow entrapment, reduced evaporation and increased water infiltration before being plowed in the spring. Given these results it was later hypothesized that introducing no-till would improve SOM content that increases soil water retention and produce higher yields than the spring plow treatment. In 1996 it was decided to change the sweep treatment to a NT treatment. It takes about 3 to 5 years for soil properties of these soils to change under no-till. So far we have about 7 yrs of data after making that change and we plan to continue this experiment for another 10 yrs or more. We started measuring SOM in this experiment in 1995 and every 5 yrs thereafter. Continuing this experiment for 10 or more years might allow this system to reach steady state and provide us the opportunity to determine the effects of these treatments on SOM and crop productivity. The effects of these treatments on soil microbial community changes have not been documented.


No-Till Wheat.

The no-till wheat experiment was initiated in 1982 to compare the effects of the traditional winter wheat-fallow system under CT with chemical fallow under NT on C sequestration and N requirements. It was hypothesized that eliminating CT (moldboard plowing), which buries crop residues and enhances residue decomposition, will reduce SOM depletion and improve soil productivity. Furthermore, under the traditional system, buried crop residue supplied mineralized N and reduced N applications. It was hypothesized that under NT chemical fallow, higher N application will be required to compensate for reduced N availability than under the traditional wheat-fallow system. To determine N requirement for these soils under NT system, a fertility component (different N levels) was included. The overall objectives of this experiment are to define the N response curve of winter wheat in a NT wheat-fallow system and to estimate soil contribution to N and C sequestration. Modifications made in 1997 offered an opportunity to make comparisons between new and established NT systems. Since the fall of 1997, the overall experiment has consisted of three different components: (1) a 20-year-old NT management system, with five N levels; (2) new treatments incorporating a 5-year-old NT management system, also with five N levels; and (3) another 5-year-old addition utilizing CT, with only two N levels. The experiment was designed so that half the plots are cropped and half are fallow in any given year, with the subsequent year cropping system reversed, thus allowing yield data to be taken every year.



Posters from American Society of Agronomy Meeting in Seattle November 2004. S. Machado, S. E. Petrie, and K.E. Rhinhart, Oregon State University.

Agricultural and Economic Comparison of Annual-Cropped Conventional Tillage and No-tillage. I. Winter Wheat

Agricultural and Economic Comparison of Annual-Cropped Conventional Tillage and No-tillage. II. Spring Wheat

Agricultural and Economic Comparison of Annual-Cropped Conventional Tillage and No-tillage. III. Spring Barley

Long-Term Continuous Annual Cropping in the Pacific Northwest (PNW): Tillage and Fertilizer Effects on Grain Yield and Profitability of Winter Wheat, Spring Wheat, and Spring Barley