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Monitoring changes in soil organic carbon over time is important to many agricultural and environmental goals. Despite decades of measurements, temporal variability in soil carbon measurements has not been studied extensively. In this report, we examine five sets of monthly samples extending up to 3 years each that were collected from field experiments at four locations representative of dryland farming in the Pacific Northwest. The variance from month‐to‐month was 15%–32% of the random error, averaging 20%. This was often greater than the variance between replicate experimental units (2%–42%, averaging 17%). At certain sites, sequential samples were found to be temporally autocorrelated, but no consistent trend patterned on seasonal factors like precipitation was found. This suggests that a single point‐in‐time sample can deviate substantially from the long‐term average soil carbon at the site. We illustrate this problem with the results of repeated soil samples taken from 12 commercial farm fields. We recommend that confidence intervals for soil organic carbon estimates should include variance based on a large population of samples rather than from a single sample set at one timepoint. Core Ideas: Soil organic carbon measurements demonstrate significant variability over time.The variability does not appear to be related to season, rainfall, or temperature.Carbon quantification requires an accounting for temporal variation. [ABSTRACT FROM AUTHOR]

Soil organic carbon was measured after surface application of equal C amounts from various C sources to fallow soil or a winter wheat crop for five consecutive years. Municipal biosolid produced the largest gain, followed by manure and alfalfa (Medicago sativa L.) foliage. Wheat (Triticum aestivum L.) straw, sucrose, and wood sawdust were not different than no addition. These effects were additive to and independent from the effect of fallow soil versus cropped soil. Soil cropped to winter wheat increased in C comparable to the biosolid application or to plots planted to perennial grass. Measurements 4, 6, and 12 years after a return to normal farming practices produced no change in relative or quantitative differences. These results illuminate the durability of above‐ and below‐ground contributions to soil C. Core Ideas: Increased soil organic carbon (SOC) produced by crop roots or amendments is still present 12 years later.The effect of wheat straw and sucrose on SOC was not significant, but biosolids, manure, and alfalfa increased SOC.Five years of wheat or perennial grass produced a substantial gain in SOC compared to fallow. [ABSTRACT FROM AUTHOR]

Core IdeasThe soil water dynamics of 3‐yr winter wheat–camelina–summer fallow and 2‐yr winter wheat–summer fallow rotations were measured for 8 yr.At harvest, there was less soil water after camelina than after winter wheat in the 2‐yr rotation.The water deficit persisted through the 13‐mo fallow period and decreased the yield of 3‐yr vs. 2‐yr winter wheat.Increased cropping intensity may increase risk and variability in dry environments. 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 (<350 mm annually) Mediterranean‐like climate region of the US inland Pacific Northwest, where a monoculture 2‐yr winter wheat (Triticum aestivum L.) (WW)–summer fallow (SF) rotation is widely practiced. An 8‐yr experiment was conducted to compare a 3‐yr WW–camelina–SF rotation with the typical 2‐yr WW–SF rotation to analyze the soil water dynamics of these two crop rotations. Growing spring‐planted camelina reduced soil water content at the beginning of the fallow; this reduction resulted in an average of 21 mm less water at WW planting and a 170 kg ha‐1 reduction in grain yield compared with WW–SF. We show that (i) the deep‐rooted broadleaf weed Russian thistle (Salsola tragus L.) present in camelina most years was the most likely reason for greater in‐crop soil water use than with WW–SF, and (ii) the limited camelina residue was probably responsible for greater evaporative loss during the spring to late summer segment of the fallow. We report the first findings from the Pacific Northwest drylands of greater water use by a cool‐season spring crop versus WW and greater evaporative loss during the summer caused by lack of residue in a minimum‐tillage SF comparison. Here, extending the crop rotation to include camelina was costly in terms of water use, surface soil residue cover, soil water storage during the fallow, and WW grain yield. [ABSTRACT FROM AUTHOR]

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 (<4 yr) tillage intensification does not have a strong influence on the nutrient cycling capacity of soil, although fungal numbers may decline in the Acropped phase.

Late summer planting of winter wheat (Triticum aestivum L.) into tilled fallow is necessary for production of maximum yield in many areas of the low precipitation (<30 cm, annual) zone of the inland Pacific Northwest region of the United States. Farmers plant deep to reach moisture adequate for germination and emergence. The coleoptile of deep‐planted wheat remains underground. The first leaf protrudes through the tip of the coleoptile and usually emerges about 10 to 12 d after planting. Emergence may be jeopardized by below‐surface buckling of the first leaf. Buckling of the first leaf occurs when its exerted force cannot overcome the density or strength of overlying soil. Small, single‐point load cells were used to measure force exerted by the first leaf of one semidwarf cultivar ('Norwest 553') and two standard‐height cultivars ('Farnum' and 'Finley') as they emerged from a deep planting depth (100 mm) in a small containerized volume of soil. The average maximum before‐buckling emergence force (BBEF) of Norwest 553 and Finley was 12.2 and 11.6 g, respectively. The corresponding value for Farnum (10.9 g) was statistically similar to the BBEF of Finley and less than that of Norwest 553. The measured difference between Farnum and Norwest 553 may be a consequence of variation in coleoptile diameter. Maximum diameter measurements of 1.6 to 1.7 mm were made near the base and in the middle of the Norwest 553 coleoptile. New knowledge generated from this research can be used to make decisions about the focus of future investigations that deal with poorly understood mechanisms responsible for emergence of wheat from deep planting depths. [ABSTRACT FROM AUTHOR]

Interest in soil organic carbon (SOC) levels is focused on both soil quality and sequestering carbon from the atmosphere. Farmers have developed minimum tillage systems and no-till systems. This study carefully measured SOC at three sites where long-term, randomized, replicated studies compared minimum tillage and no-till rotations in the low-precipitation inland Pacific Northwest, USA. To overcome seasonal, annual, and rotational effects, a soil sample was taken from each plot monthly for three years. The top 250 kg m-2 dry soil mass (representing the 0- to 20-cm depth) from each core was analyzed for SOC. Averages of monthly samples revealed the tilled treatment had 7.21 g kg-1 of SOC compared to 7.04 for the no-till treatment (p < 0.004). Examining variation month-to-month, 93% of sample variation was due to sample date, and 7% due to blocks (replications) within sites. Of 77 individual site-by-date samples, only six produced significant t-tests (p < 0.05) but SOC differences were 46–31 in favor of tillage and those 46 had larger differences. Power calculations estimated 34–100 samples would be required to detect a relative difference of 5% given the data's standard deviation. Soil water and soil temperature to 30 cm was measured at the time of sampling, and while no-till more often had greater water, temperature differences were inconsistent. We conclude that no-till did not result in more soil carbon in these systems and judicious tillage is an option for sustainable production. • Measurements over three years revealed significantly more C with tillage. • Variance in measurements was due to date of sampling, not spatial variability. • Surface soil moisture tended to be greater in no-till, except during fallow. • Soil temperatures were not consistently greater or less with no-till. [ABSTRACT FROM AUTHOR]

Creation of a dry soil mulch to maintain near-surface moisture in dry environments is an ancient practice that is still used in many regions of the world for timely establishment of crops after long fallow. Before availability of herbicides, the first tillage during fallow was timed to kill weeds, but now the optimum timing for tillage depends only on the interplay of evaporation and infiltration of rain. The goal is to maximize total root zone water storage and seed-zone water at seeding time. Our objective was to measure the effect of delaying soil mulch creation progressively later in the spring and summer on weed-free fallow for winter wheat (Triticum aestivum L.) in the Mediterranean inland Pacific Northwest drylands of the United States. Over a period of six years and a total of 12 site-years, four to seven tillage timings were compared to an untilled treatment. Soil water was measured at seeding time in the seed zone and total root zone. Seed-zone water and total stored water produced by different tillage timings was surprisingly constant, with few statistically significant or substantial differences. On average, only 2% of stored water was lost in the top 1.0 m of soil over 80 days during the hot, dry period towards the end of fallow. Responses to late spring rain could be seen, and tillage near the end of June (early summer) often produced maximum soil water content. • Tillage during fallow reduced both evaporation and infiltration of water. • Tillage improved seed-zone water at the end of arid fallow. • Delayed tillage facilitated soil storage of rain. • Peak seeding-time moisture at 21 cm was most often experienced with tillage in June. [ABSTRACT FROM AUTHOR]

Soil microbial communities are sensitive to carbon amendments and largely control the decomposition and accumulation of soil organic matter. In this study, we evaluated whether the type of carbon amendment applied to wheat-cropped or fallow soil imparted lasting effects on the microbial community with detectable differences in activity, population size, or community structure after a period of seven years post-amendment. The microbial communities from the top 10 cm of soil were analyzed for activity related to C-cycling (glucosidase, galactosidase), P-cycling (acid phosphatase), S-cycling (arylsulfatase), and N-cycling (β-glucosaminidase, arylamidase), in addition to fungal and bacterial abundance and structure. The amendments were applied at similar carbon rates for five years under annual wheat or continuous fallow and included cotton linters, sucrose, wheat residue, composted wheat residue, brassica residue, wood sawdust, alfalfa feed pellets, manure, biosolid and a no treatment control. Two crops, brassica and grass, were in the fallow treatments. The majority of the communities in the amended soils were not distinguishable from the no-treatment control. For amendments and crops that produced changes, significant differences in the population size and community structure were observable for fungi but not bacteria. Wood, sugar, and grass cropping produced the most pronounced effects on enzyme activity, fungal abundance and structure. Overall, the species of the planted crop had a significant effect on the soil enzyme activity and population size of fungi, with the greatest values under grass compared to wheat or brassica. The microbial communities were differentially affected by C source amendments in which the persistency of change and the aspect of the community affected (i.e. function, size, structure, kingdom) were dependent on amendment type. [ABSTRACT FROM AUTHOR]

Formation of soil organic C (SOC) is influenced by inputs. We applied organic amendments for five consecutive years at 250 g C m-2 yr-1. Seven years after the applications ended, the effects of biosolids and manure on SOC were greater than alfalfa (Medicago sativa L.), wood, wheat (Triticum aestivum L.) residue, sucrose, brassica residue, cotton (Gossypium hirsutum L.), wheat compost, or the unamended check. Soil C increases ranged from 3 to 49% of C applied and had changed little in the previous 28 mo. Plots sown to continuous winter wheat during the period of amendment had 10% more SOC than plots that had been fallow, an effect more than twice as large as most amendments. This suggests that the contribution of roots to SOC was more important than aboveground crop residues. The effect of amendments on SOC was highly correlated to their initial P content. In addition, for a similar available soil P and soil S content, SOC was significantly greater where wheat or perennial grass was grown. Wood caused an increase in the C/N ratio that persisted >3.5 yr but almost disappeared by the seventh year. This study indicated that continuous cropping or the addition of animal waste or municipal biosolids had the greatest impact on the formation of SOC, and this positive effect remained stable for many years after the end of the continuous treatment applications. [ABSTRACT FROM AUTHOR]

Formation of soil organic C (SOC) is influenced by inputs. We applied organic amendments for five consecutive years at 250 g C m-2 yr-1. Seven years after the applications ended, the effects of biosolids and manure on SOC were greater than alfalfa (Medicago sativa L.), wood, wheat (Triticum aestivum L.) residue, sucrose, brassica residue, cotton (Gossypium hirsutum L.), wheat compost, or the unamended check. Soil C increases ranged from 3 to 49% of C applied and had changed little in the previous 28 mo. Plots sown to continuous winter wheat during the period of amendment had 10% more SOC than plots that had been fallow, an effect more than twice as large as most amendments. This suggests that the contribution of roots to SOC was more important than aboveground crop residues. The effect of amendments on SOC was highly correlated to their initial P content. In addition, for a similar available soil P and soil S content, SOC was significantly greater where wheat or perennial grass was grown. Wood caused an increase in the C/N ratio that persisted >3.5 yr but almost disappeared by the seventh year. This study indicated that continuous cropping or the addition of animal waste or municipal biosolids had the greatest impact on the formation of SOC, and this positive effect remained stable for many years after the end of the continuous treatment applications. [ABSTRACT FROM AUTHOR]

The productivity of rainfed winter wheat (WW, Triticum aestivum L.) depends on the efficient capture and storage of precipitation. In the semi-arid Pacific Northwest (PNW), USA, soil water is managed through a 14-mo fallow period to establish wheat before winter and maximize growth potential the following spring. The effects of soil management on soil water storage were investigated on a Walla Walla silt loam soil (coarse-silty, mixed, superactive, mesic Typic Haploxerolls). The treatments were untilled chemical fallow (CF), versus a one-pass undercutter fallow (UF) in 2-yr WW-fallow rotations. These were compared with an annually cropped no-till WW (ANT). Measured from 2007 through 2014, CF had significantly more soil water than UF. Annually cropped no-till WW had less soil water than CF or UF for the duration of the research. These results were not relected in precipitation capture efficiency. Annualized crop yield was significantly greater in ANT than in CF or UF, which were not significantly different. This resulted in water-use efficiency (WUE) being 30% greater in ANT than CF or UF. Unlike reports from drier zones of the PNW, it appears that CF and even annual wheat production may be ways to maximize WUE by wheat. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A tillage-based winter wheat ( Triticum aestivum L.)-summer fallow rotation is practiced on 1.56 million cropland hectares in the low-precipitation (<300 mm annual) region of the Inland Pacific Northwest of the United States (PNW). Farmers use deep-furrow drills with rows spaced 40–45-cm apart to plant winter wheat (WW) as deep as 20 cm below the soil surface to reach moisture in summer fallow (SF). Conservation tillage methods have been successfully developed that preserve ample residue during SF to control wind erosion, but existing drills cannot pass through heavy residue without plugging; thus farmers are reluctant to adopt conservation-tillage practices. We conducted field experiments over 3 years at three sites using the same number of seeds row −1 (8 site years) and same number of seeds ha −1 (3 site years) with row spacing of 40, 45, 50, 55, 60, and 80 cm and measured effects on grain yield, grain yield components, straw production, and weed dynamics. With same number of seeds row −1 (seeding rate declined as row spacing widened) the highest average grain and straw yield was achieved with the 40 and 45-cm spacing with gradual decline as row spacing widened due to fewer spikes unit area −1 (SPU) and despite increased kernels spike −1 (KPS). Kernel weight (KW) was not a factor. With same number of seeds ha −1 (more seeds row −1 as row spacing widened) there were no overall differences in SPU, KPS, KW, and straw production among treatments and only a slight grain yield reduction at the two widest spacing treatments. Weeds were not an agronomic problem with any spacing treatment due to timely and effective in-crop herbicide application although weed dry biomass did increase slightly as row spacing widened. Our research suggests that row spacing for WW production in the dryland PNW can be widened to at least 50 cm and most likely 55 cm to facilitate conservation-tillage farming with equal grain and straw production compared to narrower row spacing currently used by farmers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Farmers in the low-precipitation (<300 mm annual) region of the Inland Pacific Northwest of the USA practice summer fallow to produce winter wheat [Triticum aestivum L.) in a 2-yr rotation. No-till fallow (NTF) is ideal for wind erosion control but is not widely practiced because of seed-zone soil drying during the summer, whereas adequate seed-zone water for germination and emergence of deep-sown winter wheat can generally be retained with tilled fallow (TF). Successful establishment of winter wheat from late August- early September planting is critical for optimum grain yield potential. A 6-yr field study was conducted to determine if accumulations of surface residue under long-term NTF might eventually be enough to substitute for TF in conserving seed-zone water over summer. Averaged over the 6 yr, residue rates of 1500, 6000, and 10 500 kg ha-1 (1X, 4x, and 7x rates, respectively) on NTF produced incrementally greater seed-zone water but were not capable of conserving as much as TF. Total root zone (0-180 cm) over-summer water loss was greatest in the 1X NTF whereas there were no significant differences in the 4x and 7x NTF versus TF. Average precipitation storage efficiency ranged from 33% for 1 x NTF to 40% for TF. We conclude that for the low-precipitation winter wheat-summer fallow region of the Inland Pacific Northwest: (i) Cumulative water loss during the summer from NTF generally exceeds that of TF; (ii) there is more extensive and deeper over-summer drying of the seed-zone layer with NTF than with TF; (iii) increased quantities of surface residue in NTF slow the rate of evaporative loss from late-summer rains, and (iv) large quantities of surface residue from April through August will marginally enhance total-profile and seed-zone water in NTF, but will not retain adequate seed-zone water for early establishment of winter wheat except sometimes during years of exceptionally high precipitation or when substantial rain occurs in mid-to-late August. [ABSTRACT FROM AUTHOR]

A 2-yr winter wheat (Triticum aestivum L.)-fallow rotation continues to be the most common cropping system in much of the US. 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 tilage, it will be necessary to characterize spring water storage plus the potential for end-of-summer water storage for each soil type. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A 4-yr study was conducted in a dry Mediterranean region of the Inland Pacific Northwest USA (PNW) to measure winter wheat (WW) (Triticum aestivum L.) stubble height and orientation effects on overwinter precipitation capture in the soil and subsequent water retention during ensuing dry summer months. The stubble was left standing and undisturbed during the 13-mo fallow periods. Stubble-height treatments were:(i) short (8 cm), (ii) medium (25 cm), and (iii) tall (75 cm). An additional treatment: (iv) mow tall stubble in mid-June, was included in the final two years. Soil water measurements were obtained at the beginning, middle, and end of fallow in 15-cm increments to a depth of 180 cm. Additionally, seed-zone water content was measured at the end of fallow in 2-cm increments to a depth of 26 cm. Near-surface soil temperature was measured from June-August. On average, tall- and medium-height stubble captured 34 and 32 mm (p = 0.002) more overwinter precipitation, respectively, than short stubble and these values were particularly pronounced (91 and 79 mm greater than short stubble) during a winter of heavy snow drifting. However, from mid-April until late August, the tall stubble lost an average of 91 mm of soil water compared to 70 and 59 mm in the medium and short stubble treatments (p < 0.001). Mowing tall stubble in mid-June before the hot, dry summer did not improved water retention. Continuous soil temperatures at 3, 7, 15, 25, and 40-cm depths measured electronically from June-August were coolest with the short, mowed, medium, and tall stubble, respectively, with frequent significant differences of > 1 °C among treatments. We speculate that soil in the tall treatment was warmest and lost the most over-summer water because all stubble was standing and offered less soil shading than the other treatments. At the end of fallow, medium and tall stubble averaged 14 and 8 mm greater soil water, respectively, than the short treatment (p = 0.027). Short stubble was a disadvantage for overwinter precipitation capture but was equal or better than the other treatments for retaining soil water from April to late August; presumably because this treatment had the most residue lying flat on the soil surface for shading. These findings offer opportunity to improve current models for soil water dynamics during fallow by incorporating stubble height. For combined soil water retention and farm management factors, medium-height WW stubble is the best fallow option for farmers in the PNW drylands. • Wheat stubble height effects on overwinter precipitation capture and over-summer soil water loss during 13-mo-long fallow periods were measured over four years in a dry Mediterranean climate. • Tall (75 cm) and medium (25 cm) height stubble captured significantly more overwinter precipitation in the soil than short (8 cm) stubble. These differences were most pronounced during two winters of drifting snow. • Soil temperatures at 3, 7, 15, 25, and 40-cm depths from June-August were warmest with the tall, medium, mowed, and short stubble, respectively. • At the end of the fallow periods, tall and medium treatments were equal for soil water retention and greater than with short stubble. Mowing tall stubble in mid-June at the onset of warm, dry summer month did not benefit soil water retention. • For combined precipitation capture and soil water retention as well as farm management factors, medium-height stubble is the best fallow option for wheat farmers in the US Pacific Northwest drylands. [ABSTRACT FROM AUTHOR]

Abstract: Reduced tillage methods for field crop production result in less disruption of soil structure and often increased amounts of crop residue maintained on the soil surface. The combination of these two factors produces increased surface soil aggregation. This study was conducted in the field and within pots to determine whether surface residue by itself improves soil aggregation within a short period of time. The soil was a silt loam loess deposit in the Pacific Northwest, USA, where summers are hot and dry, and most precipitation (420mm) is received during the mild winters. Two pot studies were conducted over winter, one under a shelter with controlled irrigations (183mm), and the other outdoors receiving natural precipitation (77mm). In both pot studies 640gm−2 wheat (Triticum aestivum L.) residue was either placed on the surface of the soil or thoroughly mixed into the soil. The field study was conducted on plots where, for the past 7 years, wheat crop residues were either incorporated through chisel/disk tillage or removed before tillage and replaced on the surface after tillage. The field study included plots where wheat was grown with no tillage. In the pots, there was no significant effect due to residue treatment on aggregate mean weight diameter, measured monthly for 4 winter months. This was true despite dissolved organic carbon being leached from the surface residue. In the 7-year-old field plots, replacing residues on the surface resulted in slightly greater mean weight diameter of aggregates at 5–10cm depth compared to the mixed residue treatment. The no-till plots had significantly greater mean weight diameter at 0–5cm depth than either tilled treatment. Our conclusion is that surface residue by itself failed to increase aggregation of tilled surface soil within the first rainy season after tillage. [Copyright &y& Elsevier]

Abstract: Water erosion and runoff can be severe due to poor infiltration through frozen soil in the dryland wheat (Triticum aestivum L.) production region of the inland Pacific Northwest (PNW), USA. For more than 70 years, farmers and researchers have used various methods of subsoiling to reduce runoff and erosion and to improve infiltration and soil moisture storage. The practice and equipment have evolved from chiseling continuous open channels across hillslopes to the rotary subsoiler that pits the soil. Farmers often subsoil wheat stubble after harvest, but do not employ this practice on newly planted winter wheat fields. These fields are especially vulnerable to erosion because of meager residue cover after a year of fallow. A 6-year field study was conducted in eastern Washington to determine the effect of rotary subsoiling in newly planted winter wheat on over-winter water storage, erosion, infiltration, and grain yield. There were two treatments, rotary subsoiling and control. The rotary subsoiler created one 40cm-deep pit with 4L capacity every 0.7m2. Natural precipitation did not cause rill erosion in either treatment because of mild winters during the study period. Net change in water stored over winter was significantly (P <0.05) improved with rotary subsoiling compared to the control in 2 of 6 years. Grain yield was not affected by treatments in any year or when averaged over years. In 2003, we simulated rainfall for approximately 3h at a rate of 18mm/h on both subsoiled and control plots to determine runoff and erosion responses on frozen soils. Rotary subsoiling reduced runoff (P <0.01) by 38%. Rotary subsoiling also significantly reduced erosion (P <0.01) during the 20–45min period after runoff had begun. The total quantities of eroded soils were 1.3 and 3.4Mg/ha for the subsoiled and control treatments, respectively, with inter-rill the dominant erosion process. The average infiltration rate for the control treatment (3.3mm/h) was half of the rate for the subsoiled treatment (6.6mm/h), at the end of the 3h simulation. Rotary subsoiling of newly-planted winter wheat can increase soil moisture stored over-winter and reduce runoff and soil loss on frozen soils, but the benefit of this practice for increasing grain yield has not been proven. [Copyright &y& Elsevier]

Abstract: Seventy years of different management treatments have produced significant differences in runoff, erosion, and ponded infiltration rate in a winter wheat (Triticum aestivum L.)–summer fallow experiment in OR, USA. We tested the hypothesis that differences in infiltration are due to changes in soil structure related to treatment-induced biological changes. All plots received the same tillage (plow and summer rod-weeding). Manure (containing 111kgNha−1), pea (Pisum sativum L.), vine (containing 34kgNha−1), or N additions of 0, 45 and 90kgha−1 were treatment variables with burning of residue as an additional factor within N-treatments. We measured soil organic C and N, water stability of whole soil, water stable aggregates, percolation through soil columns, glomalin, soil-aggregating basidiomycetes, earthworm populations, and dry sieve aggregate fractions. Infiltration was correlated (r =0.67–0.95) to C, N, stability of whole soil, percolation, and glomalin. Basidiomycete extracellular carbohydrate assay values and earthworm populations did not follow soil C concentration, but appeared to be more sensitive to residue burning and to the addition of pea vine residue and manure. Dry sieve fractions were not well correlated to the other variables. Burning reduced (p &#60;0.05) water stability of whole soil, total glomalin, basidiomycetes, and earthworm counts. It also reduced dry aggregates of 0.5–2.0mm size, but neither burning nor N fertilizer affected total C or total N or ponded infiltration rate. Water stability of whole soil and of 1–2-mm aggregates was greater at 45kgNha−1 than in the 0 and 90kgNha−1 treatments. Zero N fertilizer produced significantly greater 0.5–2.0mm dry aggregate fractions. We conclude that differences in infiltration measured in the field are related to relatively small differences in aggregate stability, but not closely related to N or residue burning treatments. The lack of an effect of N fertilizer or residue burning on total C and N, along with the excellent correlation between glomalin and total C (r =0.99) and total N (r =0.98), indicates that the major pool of soil carbon may be dependent on arbuscular mycorrhizal fungi. [Copyright &y& Elsevier]

Investigates role of vapor transport on water transfer from soil to seed. Assumption that liquid transport dominates water imbibition by seeds; Comparison of water gain and germination for wheat seed.

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 mm to collect a 26-cm core and section it into 2-cm increments, compared with 20 mm per core with the older sampler. [ABSTRACT FROM AUTHOR]

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, <53 μm) of water soluble aggregates. Diversification and intensification of crop rotations under minimum tillage showed statistically significant and positive changes to soil aggregation compared to the winter wheat (Triticum aestivum L.)–fallow rotation typical of this region; however, the effect was crop-specific and of minor practical consequence. Ethiopian mustard (Brassica carinata) produced soil aggregates with a larger mean weight diameter and more 1-mm class aggregates than winter wheat. The latter effect was the result of two highly aggregated samples collected in separate years. In the wheat-fallow rotation, there were significantly (P < 0.05) more 250-μm sized aggregates and fewer small class aggregates (53 μm and <53 μm) under minimum tillage than under conventional tillage. While crop diversification may not substantially improve soil structure as measured by water-stable aggregates, the reduction of tillage can reduce the amount of small size aggregates which are known to impede water infiltration and increase erodibility. [ABSTRACT FROM AUTHOR]

Meeting the goals set by the Energy Independence and Security Act requires evaluation of all potential feedstock sources including arid and semi-arid portions of the western United States (U.S.). The objective of this study was to assess the lignocellulosic feedstock potential in stream buffers of the inland Pacific Northwest. A 3-yr (2010-2012) experiment was conducted at two sites within each of the three precipitation zones (low, mid, and high). At each site, barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), alfalfa (Medicago sativa L., cultivar Ladak), tall wheatgrass (Agropyron elongatum Podp. cultivar Alkar) (TWG), and a mix of alfalfa and tall wheatgrass (MIX) were planted in a randomized complete block experimental design. Productivity followed precipitation; in the high and mid precipitation zones, the MIX and TWG treatments showed potential production of 3,079±262 l ha-1 and 3,062±235 l ha-1. Productivity in the low zone was inadequate or unreliable as a source of feedstocks. A geographic information system was then used to identify the area available for stream buffers with soil resources that matched the experimental results within each precipitation zone. In 3.7×106 ha of dryland cropland, 44 656 ha (1.5%) available within the mid and high precipitation zones is capable of producing 147 million liters of ethanol. This potential contribution is 0.3% of the lignocellulosic ethanol production expected by the year 2022. Though not a substantial contribution, the added benefit of producing energy for on-farm consumption might provide an additional incentive for landowners and managers to install conservation buffers. [ABSTRACT FROM AUTHOR]

Rainfed experiments operated continuously for up to 84 years in semiarid eastern Oregon are among the oldest agronomic trials in North America. Disease incidence and severity had been quantified visually but quantification of inoculum density had not been attempted. Natural inoculum of 17 fungal and nematode pathogens were quantified for each of 2 years on eight trials using DNA extracts from soil. Crop type, tillage, rotation, soil fertility, year, and their interactions had large effects on the pathogens. Fusarium culmorum and Pratylenchus thornei were more dominant than F. pseudograminearum and P. neglectus where spring crops were grown, and the opposite species dominances occurred where winter wheat was the only crop. Bipolaris sorokiniana and Phoma pinodella were restricted to the presence of spring cereals and pulse crops, respectively. communities in Helgardia spp. occurred in winter wheat-fallow rotations but not in annual winter wheat. Gaeumannomyces graminis var. tritici was more prevalent in cultivated than noncultivated soils and the opposite generally occurred for Rhizoctonia solani AG-8. Densities of Pythium spp. clade F were high but were also influenced by treatments. Significant treatment effects and interactions were more prevalent in two long-standing (>50-year) annually cropped experiments (29%) than two long-standing 2-year wheatfallow rotations (14%). Associations among pathogens occurred mostly in an 84-year-old annual cereals experiment. This survey provided guidance for research on dynamics of root-infecting pathogens of rainfed field crops and identified two pathogens (Drechslera tritici-repentis and P. pinodella) not previously identified at the location. [ABSTRACT FROM AUTHOR]