Palouse Silt Loam Research Articles

Influence of physical crust cover on the wind erodibility of soils in the inland Pacific Northwest, USA

AbstractSoil crusts are especially important for agricultural fields in the inland Pacific Northwest where there is a high wind erosion risk due to exposure of fine erodible soils in fallow croplands. The objective of this study was therefore to evaluate the effect of physical soil crust cover on wind erosion and identify critical soil crust cover amounts to control wind erosion. The effect of crust cover of five loessial soils on wind erosion was tested in a wind tunnel. The results indicated that crust cover appeared to have little influence on soil loss until crust cover was > 30%. Soil loss at this percentage of crust cover was 55.04% to 68.08% lower as compared with a soil surface devoid of crust cover for the five soil types. The relationship between soil loss and crust cover appeared to be nearly a linear function, although an exponential function also provided a good fit to the data. With progressive development of a crust cover, the rate of change in soil loss varied among soil types. From 0 to 100% crust cover, the rate of change in soil loss ranged from −312.8 g m−2 for Palouse silt loam to −1449.1 g m−2 for Warden sandy loam. The rate was not only associated with intrinsic soil erodibility, but also crust stability and abrasion flux. Due to the lower intrinsic soil erodibility and greater crust stability, Palouse silt loam crust was characterized by lower flaking potential and limited abrasion flux relative to the other tested soil types. The Single‐event Wind Erosion Evaluation Program (SWEEP) was used to simulate and identify the effect of crust cover on erosion processes. Differences between simulated and measured soil loss suggest that cracks in soil crusts may affect soil loss and should be incorporated into the SWEEP to expand the model capability for representing crusted soils.

Seasonal Change of WEPP Erodibility Parameters for Two Fallow Plots on a Palouse Silt Loam

Abstract. In cold regions, frozen soil has a significant influence on runoff and water erosion. In the U.S. Inland Pacific Northwest, major erosion events typically occur during winter as frozen soil thaws and exhibits low cohesion. Previous applications of the WEPP (Water Erosion Prediction Project) model to a continuous bare tilled fallow (CBF) runoff plot at the Palouse Conservation Field Station (PCFS) in southeastern Washington State showed that WEPP reproduced the occurrence of the large erosion events, but the amount of sediment yield was either under- or overestimated. The inability of WEPP to reproduce the magnitude of field-observed erosion events at the PCFS suggests the need for an examination of the dynamic changes in soil erosion properties and for improving the representation of such dynamics. The objective of this study was to evaluate the seasonal changes of rill erosion parameters for two CBF runoff plots at the PCFS. Field-observed runoff and erosion events during 1984-1990 were used to estimate WEPP hydraulic and erosion parameters, including soil effective hydraulic conductivity, critical shear stress (I„ c ), and rill erodibility (K r ). The parameters for each event were best-fitted using WEPP single-event simulations to reproduce the observed runoff and sediment yield on both plots. The results suggest that the adjustment factors for I„ c and K r of frozen and thawing soils in the WEPP model could be modified to better describe the changes of these parameters in winter.

Windblown soil crust formation under light rainfall in a semiarid region

Many soils in arid and semi-arid regions of the world are affected by crusting, a process by which a compact layer or thin mantle of consolidated material is formed at the soil surface. Crusts can increase the resiliency of the soil to wind erosion, but characterization of soil crust formation to light precipitation events common to the Columbia Plateau region of the Inland Pacific Northwest is unknown. Our objective was to evaluate the effect of light rainfall events on crust formation of five soil types prominent in the Columbia Plateau. The five soils were Athena silt loam, Palouse silt loam, Ritzville silt loam, Walla Walla silt loam, and Warden sandy loam. Soil crusts were formed in the laboratory using a rainfall simulator that applied water at a rate of 2.5mm h−1 for various durations to achieve a total rainfall application of 0, 0.15, 0.30, 0.60 and 1.0mm. Crust strength was measured by a penetrometer while crust thickness was measured by a ruler. Silt and clay content of the five soils ranged from 23 to 66% and from 9 to 17%, respectively. An increase in crust thickness and strength was observed with an increase in rainfall for all soils. Crust thickness was similar among the soils whereas crust strength varied among soils at any given level of rainfall. For example, crust strength of soils when subject to 0.15–0.60mm of rainfall decreased in order of Walla Walla>Athena and Palouse>Ritzville and Warden. These results are consistent with a decreasing order of clay and silt contents. The strongest crust was formed on Palouse silt loam under the highest rainfall amount. A logarithm relationship adequately described the relationship between crust thickness and rainfall for the five soils (r2=1.00). This relationship over-predicted crust thickness based upon observations in the field, but performed better than the algorithm used by the Wind Erosion Prediction System.

Adsorption and Degradation of Ketoprofen in Soils

Ketoprofen, a nonsteroidal anti-inflammatory drug (NSAID), was commonly found in treated wastewater due to its incomplete removal during sewage treatment plant processes. As treated wastewater is increasingly used for landscape irrigation, it is imperative to understand the leaching potential for ketoprofen in receiving soils. In this study, adsorption and degradation experiments were conducted in four U.S. soils with different physicochemical characteristics. Ketoprofen was not strongly adsorbed to the four soils with K(d) values ranging from 1.26 to 8.24 L kg(-1), suggesting its potential to move downward with percolating water. The adsorption was positively related to the soil organic matter (OM) content (R(2) = 0.890). Degradation experiment showed that half-lives (t(1/2)) of ketoprofen were 4.58 d in Arlington sandy loam (ASL, coarse-loamy, mixed, active, thermic Haplic Durixeralfs), 8.04 d in Hanford loamy sand (HLS, coarse-loamy, mixed, superactive, nonacid, thermic Typic Xerorthents), 15.37 d in Imperial silty clay (ISC, fine, semectitc, calcareous, hyperthermic Vertic Torrifluvents), and 27.61 d in Palouse silt loam (PSL) soil (fine-silty, mixed, superactive, mesic Pachic Ultic Haploxerolls), respectively. Degradation of ketoprofen in soils appeared to be influenced by the soil OM content. The prolonged t(1/2) by sterilization indicated that microbial degradation was the dominant pathway for ketoprofen degradation in soils, while photodegradation only contributed a small portion to the ketoprofen degradation. The t(1/2) and K(oc) values were fitted to screening models to predict the leaching potential of ketoprofen in soils. It appeared that relatively high leaching potential of ketoprofen existed in ISC and PSL soils.

Carbon Sequestration in Native Prairie, Perennial Grass, No‐Till, and Cultivated Palouse Silt Loam

Comparative assessments for evaluating soil organic C (SOC) and its characteristics were made at different soil (Palouse silt loam) depths (0–5, 5–10, 10–20, and 0–20 cm) among sites with seven contrasting management histories: conventional inversion tillage (CT) followed by no‐till (NT) for 4 (NT4) and 28 (NT28) yr; bluegrass (Poa pratensis L.) seed production for 9 yr followed by NT for 4 yr (BGNT4); a sequence of 10 yr NT, 3 yr CT, and 1 yr NT (NTR); CT followed by 11 yr perennial grass under the Conservation Reserve Program (CRP); long‐term >100 yr CT; and native prairie (NP). Overall ranking of SOC, particlulate organic C (POC), and microbial biomass C (MBC) at 0 to 20 cm was NP > NTR > NT4 = NT28 > CRP > BGNT4 = CT. Greater SOC, POC, and MBC in NTR than NT28 indicated that tillage rotation could result in more soil C sequestration, primarily by increasing C stocks in 5‐ to 20‐cm depths. The POC was labile in nature as it highly correlated with Cmin (r = 0.69, P < 0.01) and MBC (r = 0.86, P < 0.01) as well as SOC (r = 0.89, P < 0.01). We concluded that: (i) neither NT nor conversion to perennial vegetation would attain the SOC found in NP over 10 to 30 yr; and (ii) medium duration of NT (10 yr) combined with short intervals of CT (3 yr) followed by NT might increase SOC compared with continuous long‐term NT under annual cropping.

Isolation and Characterization of Metabolites fromPseudomonas syringae-strain 3366 and their Phytotoxicity Against Certain Weed and Crop Species

Phytotoxic effects of metabolites from a naturally occurring rhizobacterial isolate,Pseudomonas syringaestrain 3366, were determined on downy brome and ‘Hill 81’ winter wheat, along with 10 other weed and crop species. Centrifuged supernatant and concentrated ethyl acetate extracts from aerobic shake cultures of strain 3366 suppressed germination of seeds and reduced root and shoot growth in agar diffusion assays, soil assays, and under field conditions. Generally, root growth was inhibited more than shoot growth. Strain 3366 metabolites applied in soil inhibited all species tested. Crude ethyl acetate extracts in soil inhibited downy brome at concentrations that had little effect on winter wheat. Inhibitory activity was greater in Palouse silt loam (pH 5.8, 3.6% organic matter) than in Shano silt loam (pH 9.0, 0.8% organic matter). Activity of extracted metabolites decreased rapidly in wet soil but remained high in dry soil. Active metabolites were isolated and purified from the ethyl acetate extract using column chromatography, thin-layer chromatography, and crystallization. Chemical analysis revealed the presence of phenazine-1-carboxylic acid, 2-amino phenoxazone, and 2-amino phenol. Activity of these metabolites against downy brome was confirmed in agar assays. Phenazine-1-carboxylic acid, the major identifiable metabolite present in ethyl acetate extracts (20% by weight), inhibited downy brome root growth by 99% at concentrations of 5.7 mg L−1. Production of these metabolites in field soil by live bacteria of strain 3366 was confirmed with thin-layer chromatography.

Relationships between Soil Sulfate‐Sulfur and Seed Yields of Winter Rapeseed

AbstractWinter rapeseed (Brassica napus L.) has a higher S requirement than most currently grown cereals and legumes. The objectives of this study were to (i) determine the effect of S fertilization rates on winter rapeseed yields and oil composition, (ii) establish relationships between winter rapeseed yields and soil SO4‐S levels for three cultivars, and (iii) determine the optimum time and depth of soil sampling for S diagnosis. Field experiments were conducted on a S deficient Latahco silt loam (fine‐silty, mixed, frigid, argiaquic Xeric Argiaboll) and two S deficient Palouse silt loam (fine‐silty, mixed, mesic pachic Ultic Haploxeroll) soils for three growing seasons. Each factorial trial had three cultivars, three S rates, and four replications. Soil samples were collected from all plots to a depth of 120 cm and sectioned into six 15‐cm and one 30‐cm sample in October, April, and June for SO4‐S analysis. Winter rapeseed yield was correlated to soil SO4‐S at different sampling depths. Both ‘Bridger’ and ‘Cascade’ cultivars responded to S; however, no response was observed for ‘Dwarf Essex’. The most significant coefficient of determination values between soil SO4‐S and rapeseed yield (Bridger r = 0.82, P = 0.01; Cascade r = 0.79, P = 0.01) were obtained with a 75‐cm soil sample from the April sampling. By linear plateau regression, critical soil test SO4‐S levels for Bridger and Cascade were 45 and 51 kg SO4‐S ha−1, respectively. This research demonstrates the need to modify current soil sampling for S management in winter rapeseed production to reflect the need for an April sampling to a 75‐cm depth.

Nitrogen Use by Northern‐Adapted Barley Genotypes Under No‐Till

AbstractNo‐till planting can restrict the growth and productivity of spring grains in the U.S. Pacific Northwest. Cooler soil temperatures, compared to conventional tillage, may contribute to lower productivity. Therefore, genotypes bred in cold climates may better adapt to notill management. Eleven spring barley (Hordeum vulgare L.) genotypes were evaluated for N content and dry matter accumulation under direct drilling at 45 and 90 kg N ha−1. These genotypes originated in the Pacific Northwest (PNW) or the Northern European (Nordic) countries Denmark, Finland, and Sweden. The Nordic genotypes were developed under cooler, wetter soil conditions than the PNW genotypes, and were therefore predicted to be better adapted to no‐till management. Barley was drilled into stubble of spring cereals in a Palouse silt loam (fine‐silty, mixed mesic Pachic Ultic Haploxeroll). The Finnish genotypes, HJA Potra, HJA 80201, and HJA 78003, generally had greater above‐ground dry matter and N content than the domestic genotypes prior to anthesis. These differences were not sustained through rain filling, however, and PNW genotypes accumulated more N and dry matter per unit area by maturity. Steptoe was the only genotype that consistently absorbed N during grain filling, while many genotypes exhibited net N losses. Nitrogen remobilization and N harvest index tended to be greater in 6‐row genotypes compared to 2‐row genotypes. The PNW genotypes generally outyielded the Nordic genotypes with the exception of ‘Nordal’. Nevertheless, if the physiological traits of the Nurdic genotypes associated with efficient N uptake during cold soil conditions could be incorporated into an existing PNW genotype, improved N use efficiency may be obtainable.

Nitrogen Effects on Yield and Malting Quality of Barley Genotypes under No‐Till

AbstractConservation practices, such as reduced tillage and improved fertilizer use, are desirable from an environmental perspective and may yield economic benefits if production and quality are not impaired. This study was conducted to determine the effects of two N fertilization levels, 45 and 90 kg ha−1 (50 and 100% of normal grower rates), on yield and malting quality of spring barley (Hordeum vulgare L.) under no‐till management. The study was conducted in 1986 and 1987 on a Palouse silt loam (fine‐silty, mixed mesic Pachic Ultic Haploxeroll). Seven Nordic (Europe) genotypes were compared with four U.S. Pacific Northwest (PNW) cultivars. The higher N level increased grain yield across genotypes in both years (17% in 1986, 5% in 1987), reduced the percentage of plump kernels (4%) in 1987, and did not affect test weight, 1000‐kernel weight, or percentage of thin kernels. All Nordic genotypes yielded less than the PNW cultivars except the Danish cultivar Nordal. Higher N increased total malt protein (7%) in both years and soluble malt protein (7%) in 1986. Higher N also significantly increased a‐amylase (25%) and diastatic power (15%) in the malt, while malt extract was unaffected. Significant genotypic differences existed for all agronomic and malting parameters examined. Under no‐till, HJA 78003 was the only Nordic genotype that produced good quality malt, equaling the three PNW malting cutlivars under no‐till. The higher N rate produced slightly better yield and quality than the reduced rate. Therefore, reducing the N rate to half the normal grower rate (90‐45 kg ha−1) would probably not be recommended under these test conditions. Overall, the PNW cultivars tested outperformed the Nordic genotypes both in yield and malting quality. However, Nordal and HJA 78003 could prove useful in PNW barley breeding programs.

The effect of N placement on grass weeds and winter wheat responses in three tillage systems

Field studies were conducted for three seasons (1978–1979, 1979–1980 and 1981–1982) on a Palouse silt loam near Pullman, Washington, to compare the effects of broadcast and deep banding of nitrogen (N) fertilizer beneath winter wheat ( Triticum aestivum L.) seed on N uptake and dry matter production of downy brome ( Bromus tectorum L.) and jointed goatgrass ( Aegilops cylindrica Host.), and on N uptake, dry matter production and grain yields of winter wheat. Three tillage systems were used: conventional tillage; shallow roto-tilling, or no-tillage prior to planting. Rates of N were 0, 65, 130 and 190 kg N ha −1 as ammonium nitrate. Additional plots were maintained free of weeds at the 130 kg N ha −1 rate. In 1983–1984, deep banding of the fertilizer between rows in a paired-row configuration was compared to surface-broadcast N fertilizer using N rates of 0, 45, 90 and 135 kg N ha −1. There were no significant differences between broadcast and deep-band application of N on grass weed N uptake or dry matter production with mold-board plowed or no-tillage, but there was greater weed growth with surface-broadcast N with shallow roto-tilling. Wheat N uptake, growth and grain yields were consistently higher with band-applied N compared to broadcast N. The yield response to banding N was the same with or without the presence of grass weeds.

Evaluation of intact soil-core microcosms for determining potential impacts on nutrient dynamics by genetically engineered microorganisms

Nutrient export from intact soil-core microcosms in leachate or by plant uptake was evaluated as a means to assess the ecosystem impacts from the environmental release of genetically modified root-colonizing bacteria. Intact cores of two soil types, a Burbank sandy loam and a Palouse silt loam, were excavated for use as microcosms, seeded with corn and wheat, respectively, and inoculated with Azospirillum lipoferum transposon Tn5 mutants. Microcosms were leached at 33 d and 67 d after seeding and the leachate analyzed for sulfate, phosphate, ammonium, nitrite, nitrate, dissolved organic carbon and inorganic carbon. Statistically significant differences in leachate nutrient concentrations between treatments were due to differences in soil types, rather than inoculation with the bacteria. The high variation in the concentrations of nutrients in the leachates from replicate microcosms, attributed to real field variation, suggest that the measurement of nutrient export in leachate from microcosms may not be a sensitive indicator of ecosystem impacts. One exception was dissolved organic carbon (and total carbon). A statistically significant difference (p ≥ 0.05) was observed between the microcosms receiving live inoculum and those receiving heat-killed cells for leachate organic carbon concentration. Plant uptake of N, P, S, B, Cu, Fe, Mg, Mn and Zn was not affected by inoculation but the coefficients of variation were considerably lower than for the leachate analyses. It is suggested that, although the leaching of organic carbon from microcosms may be used as a holistic indicator of ecosystem impacts from the release of genetically engineered microorganisms (GEMs), measurements of plant assimilation of nutrients and specific rates of microbial transformation of nutrients may provide more sensitive effects end points.

Evaluation of Factors Affecting Emergence of Winter Wheat Planted with Seed‐Banded Nitrogen Fertilizers

AbstractNitrogen use efficiency by cereal crops may be increased by the placement of fertilizer with the seed; however, high N concentrations often cause injury and reduce both germination and emergence. Two studies were conducted under controlled greenhouse conditions to evaluate factors affecting emergence of winter wheat (Triticum aestivum L.) planted with seed‐banded N fertilizers. Soil from the Ap horizon of a Palouse silt loam (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) was used in both studies. Two N materials (ammonium nitrate and urea) were banded with the winter wheat seed (‘Stephens’) at N rates of 0, 11, 22, 33, 44, 55, and 66 kg ha−1, and placed in soils at soil matric potentials of −0.15, −0.25, and −0.35 MPa. The tolerance of five winter wheat cultivars ‘Daws’, ‘Hill 81’, ‘Nugaines’, ‘Peck’, and Stephens to sulfur‐coated urea (SCU) materials SCU‐10, SCU‐20, and SCU‐30 was evaluated in a separate study. Nitrogen rates of 0, 50, 100, and 150 kg ha−1 were used at a soil matric potential of −0.20 MPa. In the first study significant N source × water potential (P < 0.0003) and water potential × N rate (P < 0.0001) interactions were observed. In the second study, significant N source × N rate × cultivar (P < 0.0001), N source × N rate (P < 0.0001), and N source × cultivar (P < 0.0001) interactions were found. The N source, N application rate, soil‐water potential, and winter wheat cultivar main effects were all significant for winter wheat emergence. Ammonium nitrate reduced winter wheat emergence 5 to 26% less than urea when comparable quantities of N were placed with the seed. Winter wheat emergence decreased as soil‐water potential decreased (became more negative). These studies demonstrated how the evaluated factors are interrelated with regard to winter wheat emergence. Consequently, guidelines routinely used for seed‐banded N fertilization that only consider N application rate should be modified to also consider N source and soil moisture.

Planting Date and Temperature Effects on Germination, Emergence, and Seed Yield of Chickpea

AbstractCommercial production of chickpea (Cicer arietinum L.) in the Palouse region of northern Idaho and eastern Washington was initiated in 1981. Since the cool springs and short growing season of this area limit the adaptation of chickpea, field and laboratory studies evaluating 10 chickpea lines were conducted to optimize the planting date of this new pulse crop. Laboratory germination and radicle elongation of the 10 lines at 5, 13, and 20 °C were compared to field emergence and seedling growth at Moscow, ID, on a Palouse silt loam (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) during 1982 and 1984. The 10 lines were also planted in late April, early May, and late May to determine the effect of planting date on yield components and seed yield. Greatest germination and radicle elongation of all 10 lines occurred at 20 °C. At 5 °C, less than half of the seed germinated within 7 d, and radicle elongation was less than 4% of that observed at 20 °C. The 10 lines did not differ in their ability to germinate under cold conditions in the laboratory. Under field conditions of 1984, the Desi lines with pigmented testa showed a higher percentage of emergence than the non‐pigmented Kabuli lines. Seedling dry weight accumulation was most rapid in the large seeded Kabuli seedlings and slowest in the smaller seeded Desi seedlings. Planting in late April produced higher seed yields than planting in late May (34 and 5% in 1982 and 1984, respectively). However, seedling emergence was slower at the early planting date. These results indicate that chickpea grown in areas with cool climates such as northern Idaho should be planted in the early spring when average soil temperatures exceed 13 °C to insure optimum seed yield.

Influence of methanol and hexane on soil adsorption of atrazine

The increasing frequency of chemically contaminated groundwater, occurring as a result of improperly managed waste disposal or accidental spills, presents a need for research on the fate of chemical mixtures in the soil. The batch equilibration technique was used to measure adsorption of 14C ring-labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) for a Palouse silt loam (Pachic Ultic Haploxeroll) and a Pembroke silty clay loam (Typic Paleudalf). The solution phase consisted of mixtures of methanol-water and hexane-water containing up to 33.3 % organic solvent by volume. Aqueous solubility limited atrazine concentrations to 100 μmol L−1 except for an additional isotherm determined in 33.3 methanol-water at up to 1542 μmol L−1 The Freundlich adsorption coefficient indicated that the Palouse adsorbed more atrazine than the Pembroke with K values of 4.95 and 0.54, respectively. Both soils showed a significant decrease in K as the percentage methanol increased. Adsorption isotherms from a 33. 3 methanol-water system were of the Freundlich type for atrazine concentrations of 0.25 to 1542 μmol L−1. In the hexane-water systems, K decreased as the fraction of hexane increased and the Pembroke soil adsorbed less atrazine than the Palouse soil. These results suggest that the introduction of nonaqueous solvents such as methanol and hexane decreased adsorption and increased the potential for atrazine mobility.

Influence of Soil Water Potential and Seed-Banded Sulfur-Coated Urea on Spring Barley Emergence

Sulfur-coated urea (SCU) has been proposed as an alternate N source for use in small grain production in northern Idaho. Both the N release rate of sulfur-coated urea (SCU) and plant seedling emergence are affected by soil matric potential. Two studies were conducted under greenhouse conditions to determine the effects of banding SCU in direct contact with spring barley (Hordeum vulgare L., cv. Advance) at different soil matric potentials. Soil from the Ap horizon of a Palouse silt loam (fine-silty, mixed, mesic Pachic Ultic Haploxeroll) was collected for this study. Three SCU materials with varied release rates (SCU-10, SCU-20 and SCU-30) were banded with the barley seed at N rates of 0, 34, 67, 101 and 134 kg ha⁻¹ and soil matric potentials of −0.1, −0.2, −0.35 and −0.65 MPa. An additional study in which SCU-20 and SCU-30 were applied at N rates of 0, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250 and 275 kg ha⁻¹ at −0.15 MPa was also conducted. For each SCU material there was a significant interaction of N rate with water potential. The SCU-10 (slowest release rate) material had minor adverse effects on seedling emergence at all N rates (above 0 kg ha⁻¹) and soil matric potentials evaluated. At the −0.65 MPa matric potential emergence was reduced at 67, 101 and 134 kg N ha⁻¹ when SCU-20 and SCU-30 served as N sources. The SCU-30 material reduced spring barley emergence to a greater extent than the SCU-20 material. As single parameters both water potential and N application rate had a significant effect on spring barley emergence. With soil moisture conditions that are typical in the spring in Idaho (-0.15 MPa), it appears that both SCU-20 and SCU-30 can be used as pop-up fertilizers for spring barley production without adversely affecting yield.

Effects of Phosphorus and Acidity on Levels of Silica Extracted from a Palouse Silt Loam

AbstractConcentrations of Si found in soil solutions are affected both by soil pH and by P availability. Consequently, it was hypothesized that the heavy local use of NH4‐based N fertilizers and of P fertilizers could greatly affect the Si chemistry of soils from the Palouse area of northern Idaho. The objectives of this study were to evaluate the effects of P and acidity on concentrations of Si in water extracts from Palouse silt loam (fine‐silty, mixed, mesic, Pachic Ultic Haploxerolls) soils and to correlate observed effects with possible mechanisms responsible for Si solubility, Soil samples were equilibrated with acid and with P for periods of 0.2 to 150 d in 0.02 M CaCl2 solutions. Increased acidity and the presence of P were both found to increase the concentrations of Si in solution above control levels. These data appear to be additive, suggesting that the mechanisms responsible for increasing solution Si levels for the respective treatments are different. It is postulated that acidity increases Si concentrations in solution by directly affecting the solubility of compounds containing Si, and that P oxyanions compete directly with Si compounds for specific sorption sites.

Influence of Tillage on Phenology and Carbohydrate Metabolism of Spring Wheat1

AbstractNo‐tillage systems help reduce soil erosion, yet crop growth is often adversely affected by the presence of surface residue. The specific effects of no‐tillage systems on phenological events of spring wheat (Triticum aestivumL.) have been poorly characterized. A field study was conducted on a Palouse silt loam (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) during 1983 and 1984 to examine the growth and development of four spring wheat cultivars grown under conventional (fall plow and spring disk) and no‐tillage (direct drilling) tillage systems. Throughout the two growing seasons, leaf and tiller production, tiller abortion, and soil moisture were monitored while leaf area, leaf weight, and stem weight were determined at weekly intervals in 1983. The length of the second leaf on the main stem, rate of leaf production, and rate of tiller production were reduced in plants grown in no‐tillage compared with conventional tillage. Except for the cultivar ‘Waverly’, tiller production was reduced by no‐tillage but tiller abortion was not. More soil water was available throughout the season in the no‐tillage plots, yet the plants grown in no‐tillage tended to be smaller than conventionally grown plants. Total nonstructural carbohydrates in the lower stem‐crown area at 12 days after anthesis were not affected by tillage treatment, and all cultivars had used most of this stored carbohydrate by physiological maturity. Overall, these results indicated that stresses that occur early in seedling development under no‐tillage reduced early growth and the plants were unable to overcome these effects prior to maturity. However, cultivars differed in tolerance to these early stresses. Thus, it should be possible to develop spring wheat cultivars for growth under no‐tillage.

Transmittance of Winterhardiness in Segregated Populations of Peas1

Winterhardiness in Pisum sativum (L.) was evaluated in segregated populations derived from crossing the cultivars ‘Melrose’ (hardy) and ‘Romack’ (intermediate) to ‘Garfield’ (nonhardy). The reciprocal backcrosses and the F2 generations were advanced by single seed descent to derive F5 lines. The F5 lines derived from these six populations and the parental lines were evaluated for winter survival and winter injury at Moscow, Idaho, during the winter of 1982—1983 on a Palouse silt loam (finesilty, mixed, mesic pachic Ultic Haploxeroll). The three populations derived from the cross between Melrose and Garfield were also evaluated for survival and freezing injury in the laboratory. Increasing the dosage of the more hardy parent increased the number of winter‐hardy lines recovered. In populations with 75% of their genetic background from the more hardy parent, approximately half the F5 lines had greater than 70% survival in the field. Percent survival and injury score in the field were significantly correlated (r = 0.80 and r = 0.82; both at the 0.01 level) for both crosses. Screening in the laboratory at −7°C was more closely correlated with the field evaluation than results obtained at either −4° or −10°C. Recovery of lines with the same level of winterhardiness as either parent from populations with less than 50 lines suggests that as few as three or four genes or linkage groups could be responsible for winterhardiness in the pea lines evaluated. Winter survival in Pisum was found to be associated with the genes which produce pigmented hilum (Pl) on Chromosome VI and pigmented seed coat (A) on Chromosome I, suggesting that genes which condition winterhardiness are linked to these genes.

Seed Yield of Austrian Winter Field Peas Intercropped with Winter Cereals1

AbstractIntercropping has improved the production of annual food grasses and legumes in several warm‐season areas of the world. Winter cereals intercropped with winter peas may improve winter pea yields in many cool‐season areas. The primary objective of this study was to compare seed yield of winter peas in mono‐ and intercropped culture in northern Idaho. Winter peas (Pisum sativumspp. arvenseL. Poir) were intercropped with either winter wheat (Triticum aestivumL.) or winter barley (Hordeum vulgareL.) on a Tilma silt loam (fine, mixed, mesic Xeric Argialboll) in 1980–1981 and on a Palouse silt loam (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) in 1981–1982. Winter peas and winter cereals were planted either alone or in mixtures containing 25, 50, or 75% winter peas. Seeding rates of 67 and 90 kg ha−1were used for both monocrops and intercrops. All trials were conducted in fields that had been fallowed for 1 yr prior to planting the intercropping studies. Winter peas in mixtures with 25% winter cereals produced seed yields equal to or 27% greater than (P< 0.05) monocropped winter peas. Winter cereal yields were reduced an average of 60% (P< 0.05) when mixed with 25% winter peas (20 winter pea plants m−2). Monocropped winter wheat and winter barley produced higher seed yields than intercrops and monocrop winter peas under adequate N conditions, but winter peas produced higher seed yields than intercrops or monocrop winter cereals when N was partially limiting in the spring due to water logging. Seeding rate had no influence on seed yield but did increase plant populations of each species. Winter peas were compatible with winter cereals in both planting and grain harvesting requirements and pea seed can be easily separated from harvested mixtures.

The effect of available carbon and nitrogen in straw on soil and ash aggregation and acetic acid production

Aerobically decomposed straws containing various contents of available C and N were tested for resultant aggregating effect on Mt. St. Helen's ash and Palouse silt loam. Aggregation decreased when straw N content increased in the range 0.25–1.09% w/w. These results suggest that microbial extra-cellular products are very important for stabilizing soils. Microbial production of acetic acid, which can be phytotoxic to wheat plant seedlings, was greatest initially from the 1.09% N w/w straw. After the first three days of aerobic decomposition, acetic acid production was not linked to the straw N content. The potential of barley and wheat straw to serve as a substrate for acetic acid production was greater than that of the remains of the flowering heads (chaff). However, the chaff might pack more tightly than the straw in the field, which would increase effectively its acetic acid concentration over that of the straw.