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Camelina [Camelina sativa (L.) Crantz] of the Brassicaceae family is a short-season drought- and frost-tolerant oilseed. Camelina has been promoted as an alternative crop for the low-precipitation (

Tillage alters the soil environment and microbial communities responsible for decomposition and nutrient cycling. This study aimed to evaluate the effects of tillage intensity (minimum vs. conventional) on the soil chemical and microbial properties of a winter wheat (Triticum aestivum L.)–fallow rotation in the low-precipitation zone of the Pacific Northwest. Soils collected for 2 yr at two depths from both crop phases (wheat and fallow) were analyzed for pH, nutrient availability, total C and N, fungal and bacterial gene abundance, and enzyme activity related to C, P, and N cycling. All soil variables excluding soil pH were significantly greater in the top 10 cm of the soil. Except for pH and nitrate, all were greater in 2016 than in 2017. Across the full rotation, tillage did not affect any measured parameter. Instead, crop phase influenced several soil chemical properties and arylamidase activity, although the effects were not consistent across depth. Fungal abundance was influenced by tillage intensity but only in the top depth under wheat, indicating a phase-specific effect rather than a change persisting across the entire rotation. Soil enzymes were strongly related to total C, total N, and phosphate across the two soil depths, but effects were inconsistent between depths and across phases. Overall, crop phase and year were stronger drivers of soil chemical and microbial properties than tillage intensity. Short-term (

Improving soil aggregation in the semiarid inland Pacific Northwest (PNW) cropping region can improve water infiltration of its erodible silt loam soils. We compared the individual crop phases of six different crop rotations in plots located in a 200- to 300-mm mean annual precipitation area of the PNW to determine if any crop, sequence of crops, tillage, or combination thereof would result in differences in mean weight diameter or size class distribution (1 mm, 250 μm, 125 μm, 53 μm

Scientists are being called on to measure and predict the effects of soil management and climate change on organic matter and other soil properties. The estimates and predictions generated from current conditions and short-term experiments will only be accurate if our measurement techniques produce data that represent actual soil properties during the period of prediction. Perhaps the least studied aspect of soil sampling is the possibility that the timing of samples might introduce large non-random errors. This study sampled replicated plots every month for 39 mo. Even after removing the measurement variation caused by surface soil bulk density fluctuations, variations in organic N, available P, and pH were always >10% of the mean. Much of the variation appeared to be temporally correlated in a seasonal cycle. In this experiment, with a 1-yr crop rotation, averaging 12 monthly samples allowed differences among soil treatments to be detected that were within 2 to 4% of the mean. When highly accurate estimates are desired, researchers need to consider combining multiple sample timings to overcome temporal variability.

Long-term changes in total soil organic C usually occur gradually. These long-term trends might be obscured by smaller, rapid changes in soil C due to seasonal inputs of plant residues, roots, and exudates, or decomposition of such inputs. Yet there is little, if any, data describing the magnitude of seasonal changes in soil C. If seasonal fluctuations in soil C are substantial, then important implications exist for accurate comparison of soil C between sites, between treatments, and even in the same experimental unit over time. Thirty-nine consecutive monthly soil samples were taken from a field experiment planted every year with winter wheat (Triticum aestivum L.) in the Pacific Northwest, United States. The variation in soil organic C was 14 to 16% of the mean over the 39-mo period in the top 250 kg m⁻² equivalent mass (∼0- to 20-cm depth). Two to eight percent could be identified as a regular seasonal pattern. The no-till management system had the greatest seasonal fluctuation, and the timing of the annual maximum was different from that of the tilled soil management treatments. In the shallower soil layer (∼0–7 cm), total soil organic C varied 12 to 29% in which 4 to 13% could be attributed to a 12-mo seasonal pattern. Given the small magnitude of changes in soil C being measured and modeled in many agricultural and natural systems, soil samples taken at a single point in time are likely to encounter substantial but hidden measurement variability. The variability may be compounded by factors of the timing of sampling in relation to natural soil organic matter cycles and differences in the cycle due to treatment and weather. Sampling plans, which account for seasonal fluctuation and the different fluctuation patterns under different soil situations, will improve measurement accuracy.

In semiarid climates, efficient precipitation capture and storage are necessary for successful small grain production. This is especially true in Mediterranean climates dependent on winter precipitation occurring before the most active growth and grain development stages of winter wheat (WW, Triticum aestivum L.). The effects of residue cover and tillage on soil water under annual WW were investigated at Pendleton, OR, on a Walla Walla silt loam soil, (coarse-silty, mixed, superactive, mesic Typic Haploxerolls). These effects were investigated using three treatments in annually cropped WW, (i.e., no fallow year), consisting of no-till (NT), crop residue incorporated with tillage (TI), and crop residue removed before tillage and then returned to the soil surface after tillage (RR). Field data showed that ground cover from crop residue resulted in more soil water from December 24 through May 20 in the driest crop year, 2005, of the 3-yr experiment, but no differences in the two relatively wet crop years 2004 and 2006. The mean soil water in a 105-cm profile when treatment differences occurred were as follows; NT = 187 mm, RR = 168 mm, and TI = 155 mm. The differences were relatively small, however, with NT 31.7 mm more than TI and 19.2 mm more than RR, and RR 12.5 mm more than TI. During normal years these differences could be expected to diminish. This research indicates that tillage practices in the Pacific Northwest have small effect where the land surface is essentially level, but ground cover can play an important role during exceptionally dry years on precipitation capture and storage.

Soil temperature dynamics can provide insights into soil variables which are much more difficult or impossible to measure. We designed an array to measure temperature at precise depth increments. Data was collected to determine if the construction materials influence surface and near-surface temperature estimates during peak insolation. In dry sand, arrays disagreed with a bare reference thermistor at the soil surface by -6 to +5 °C, averaging +0.42 °C. At depths of 1 to 4 cm, the arrays averaged from 3 down to 1 °C warmer during a sunny day, indicating that construction material was conducting heat from the surface at a greater rate than the sand. The average difference between arrays and a reference at 13-cm depth in sand was -0.30 °C (standard deviation = 0.42). Under field conditions in a dry silt loam, the arrays did not show the near-surface daytime bias, and agreed within 1 °C of independent measurements at 2 and 5 cm. The array facilitates multiple measurements of detailed temperature profiles. These measurements are capable of detecting the effect of soil conditions such as tillage, layering, or water content on the flow of heat at a resolution of centimeters.

In semi-arid climates, seed is often sown into soil with inadequate water for rapid germination. Distinguishing between adequate and marginal water can be difficult. Planting decisions become increasingly complicated when one considers possible differences between cultivars. This study was designed to measure the soil water potential limits for rapid, adequate, and marginal germination of winter wheat (Triticum aestivum L.). Laboratory data showed that germination was rapid (3 to 4 d) in soil at water potentials above -1.1 MPa and slower (4 to 5 d) at water potentials that ranged from -1.1 to -1.6 MPa. Below -1.6 MPa, less than half of the experimental units achieved the cut-off criteria of 75% germination with 5-mm radical length within 25 d. Six cultivars varied in time to germination by an average of 0.34 d, and two randomly selected seed lots of each cultivar differed by an average of 0.20 d. We conclude that variation between seed lots may be as important as variation between cultivars when looking for seed with superior germination under marginal soil water contents.

The amount and type of C-containing amendments applied to soil can have an influence on soil organic carbon (SOC) levels. To test the hypothesis that amendment type is more important than amount, we applied 250 g C m⁻² as manure, legume foliage, wheat (Triticum aestivum L.) residue, municipal biosolid, wood sawdust, brassica (Brassica napus L.) residue, composted wheat residue, sucrose, and cotton linters to both fallow soil and an annual winter wheat crop for five consecutive years. After an additional 3.5 yr with no inputs and all plots being fallow, the SOC of biosolid, manure, and wood amended plots were significantly (P < 0.0001) greater than the unamended check. The application of biosolid increased SOC 492 g m⁻², and manure increased SOC 316 g m⁻², over the fallow check plots in the top 300 kg m⁻² of soil (approximately 0–25 cm). The increase in SOC relative to the check ranged from 0 to 39% of the amendment C applied. The SOC content was 482 g m⁻² greater under continuous winter wheat than under fallow. The amendment and wheat crop effects on soil C and N changed little during the 3.5 yr after treatments ended, indicating that decomposition occurred soon after application. Wood sawdust was unique in that it increased SOC even though it was low in N content, and it changed the soil C/N ratio from 12.3 to 13.4. This field research demonstrated that amendments applied at the same C rate can have variable effects on SOC accretion.

A 2-yr winter wheat (Triticum aestivum L.)―faflow rotation continues to be the most common cropping system in much of the U.S. Pacific Northwest. The sustainability of soils in the region depends on our ability to halt or greatly reduce wind and water erosion. An incomplete understanding of how tilled summer fallow preserves seed-zone moisture for timely fall crop establishment has slowed efforts to optimize tillage techniques for creating profitable and erosion-resistant systems. This 2-yr study created a series of soil mulches at two sites representing major soils in the region. It was found that timing and depth of mulch creation had consistent effects at all four site-years. Tillage performed in mid-June to depths of 10 and 15 cm preserved up to 0.01 kg kg ―1 greater water content than no or 5-cm tillage, an amount of water that can make substantial differences in the germination of winter wheat. The later or shallower tillage treatments produced water contents similar to zero tillage below the 15-cm depth. Temperature profiles at 1-cm resolution demonstrated different shapes under different mulch treatments, which may prove useful in making quick mulch performance comparisons in the field. To optimize the timing and depth of summer fallow tillage, it will be necessary to characterize spring water storage plus the potential for end-of-summer water storage for each soil type.

This study compared linear depth from the soil surface vs. equivalent sample mass for interpreting soil water content and concentration data. Our first experiment sampled soils that differed only in surface bulk density. A second experiment compared different soil sampling tools. In both cases, analysis by mass instead of depth corrected water content discrepancies caused by bulk density or sample compaction differences. In a third experiment, samples collected from an on-farm test resulted in many significant differences in soil moisture between tillage practices for linear depth data that did not exist when analyzed using equivalent sample mass. When it is important to avoid confounding bulk density, depth from the surface, or sampling method with quantitative measurements, sampling by mass instead of volume is more accurate and precise than many quantitative methods currently in use, and represents an important advance in our ability to make comparative measurements across time, treatments, locations, and equipment.

Mixed solid-water-gas media such as soil can supply water to a dry object as both liquid and vapor. Modelers and agricultural engineers have commonly assumed liquid transport dominates imbibition by seed. This study tests the hypothesis that vapor is the major source of water for imbibition under normal soil moisture conditions. Water uptake was measured under varying degrees of seed-soil contact. Wheat (Triticum aestivum L.) seeds were suspended in holes in blocks of moist soil (average water potential -0.16 MPa). Hole diameter varied from 13 to 0 mm (no hole), so that the distance between the moist soil and the seed varied from a maximum of 5 mm to intimate seed-soil contact. The amount of water absorbed by seed in 24 h increased from 15 to 17 mg seed -1 as seed-soil contact increased from none to maximum contact, indicating that at least 85% of the water absorbed by seed in intimate seed-soil contact could be attributed to vapor alone. Reevaluation of the role of vapor transport should result in improved multiphase transport models in soil and other media.

Measurement of soil bulk density and volumetric water content in small (≤2-cm) depth increments is tedious and time consuming. Most methods require compositing several subsamples to control measurement error, and few are feasible with loose, dry soils. We developed and tested a sampler that uses an electric linear actuator to push an intact soil core out of the sampling tube. The soil core is maintained in an upright position and protected from fracturing by remaining inside the tube until sectioned with a cutting saw. Precise length increments and flat cuts are easily obtained, even in loose soils. Compared with existing incremental sampling technology developed 30 yr ago, the electric sampler reduced sample variability by half. The electric sampler requires only 7 min to collect a 26-cm core and section it into 2-cm increments, compared with 20 min per core with the older sampler.