Jodi L. Johnson-Maynard

Vegetation control on soil organic matter dynamics

Soil organic matter (SOM) formation is one of the least understood steps of the global carbon cycle. An example is uncertainty around the role of plant communities in regulating SOM formation and turnover. Here we took advantage of the highly controlled conditions at the San Dimas lysimeter installation to quantify the influence of oak and pine vegetation on SOM dynamics. SOM turnover rates, estimated using total C and 14C content of litter and physically separable soil fractions, were faster under oak than under pine. In contrast to the rapid turnover for the oak litter (<2 years), the delay in litter incorporation into the mineral soil under pine was a controlling factor of SOM fluxes.

Micro-spectroscopic investigation of selenium-bearing minerals from the Western US Phosphate Resource Area

Mining activities in the US Western Phosphate Resource Area (WPRA) have released Se into the environment. Selenium has several different oxidation states and species, each having varying degrees of solubility, reactivity, and bioavailability. In this study we are investigating the speciation of Se in mine-waste rocks. Selenium speciation was determined using bulk and micro-x-ray absorption spectroscopy (XAS), as well as micro-x-ray fluorescence mapping. Rocks used for bulk-XAS were ground into fine powders. Shale used for micro-XAS was broken along depositional planes to expose unweathered surfaces. The near edge region of the XAS spectra (XANES) for the bulk rock samples revealed multiple oxidation states, with peaks indicative of Se(-II), Se(IV), and Se(+VI) species. Micro-XANES analysis of the shale indicated that three unique Se-bearing species were present. Using the XANES data together with ab initio fitting of the extended x-ray absorption fine structure region of the micro-XAS data (micro-EXAFS) the three Se-bearing species were identified as dzharkenite, a di-selenide carbon compound, and Se-substituted pyrite. Results from this research will allow for a better understanding of the biogeochemical cycling of Se in the WPRA.

Vegetable crop emergence and weed control following amendment with different Brassicaceae seed meals

Brassicaceae seed meals produced through the oil extraction process release biologically active glucosinolate secondary products and may be useful as a part of biological weed control systems. Before meal can be used most efficiently, recommendations for suitable planting dates that maximize weed control but reduce crop injury must be determined. Our objectives were to determine the impact of 1 and 3% (w/w) meal applications of Brassica napus L. (canola), Brassica juncea L. (oriental mustard) and Sinapis alba L. (yellow mustard) on crop emergence and weed biomass in a growth chamber and field study. Results from the growth chamber experiment indicated that lettuce emergence was reduced by at least 75% when planted into 3% S. alba -amended soil earlier than 5 weeks after meal application. After 5 weeks, emergence was not different among treatments. Crop emergence was not reduced by any meal treatment as compared to the no-meal treatment in year 1 of the field study. In year 2, crop emergence in each 1.2-m row was inhibited by all meal treatments and ranged from 16 plants in the 3% B. juncea treatment to 81 plants in the no-meal treatment. The difference between emergence results in year 1 and year 2 is likely due to differing climatic conditions early in the season prior to irrigation, and the method of irrigation used. Redroot pigweed ( Amaranthus retroflexus L.) biomass was 72–93% lower in 1% B. juncea and 3% treatments relative to the no-meal control in the first weed harvest of year 1. These same treatments had 87–99% less common lambsquarters ( Chenopodium album L.) biomass. By the second weed harvest, redroot pigweed biomass in meal treatments (0.02–1.6 g m −2 ) was not different from that in the no-meal treatment (0.97 g m −2 ). Redroot pigweed biomass in 3% B. juncea plots was reduced by 74% relative to the no-meal treatment in the first harvest of year 2. This treatment also reduced common chickweed [ Stellaria media (L.) Vill.] biomass by 99% relative to the 1% meal treatments. While pigweed biomass was reduced by 3% B. juncea in the early part of the season, by the second harvest this same treatment had the greatest pigweed biomass. Despite significant variability between years, 3% B. juncea did provide early season weed control in both years. Repeated meal applications, however, may be necessary to control late season weeds. Inhibition of crop emergence appears to be highly dependent on the amount and distribution of water and needs to be further studied in field settings.

Reconciling Social and Biological Needs in an Endangered Ecosystem: the Palouse as a Model for Bioregional Planning

The Palouse region of southeastern Washington State and an adjacent portion of northern Idaho is a working landscape dominated by agricultural production, with less than 1% of the original bunchgrass prairie remaining. Government agencies and conservation groups have begun efforts to conserve Palouse prairie remnants, but they lack critical information about attitudes and perceptions among local landowners toward biological conservation. Knowledge about the location and condition of native biological communities also remains sparse. Using a bioregional approach, we integrated data collected through biological surveys and social interviews to investigate relationships between biologically and socially meaningful aspects of the landscape. We combined GIS layers of participant-identified meaningful places with maps of native biological communities to identify the overlap between these data sets. We used these maps and interview narratives to interpret how stakeholder perceptions of the landscape corresponded with patterns of native biodiversity. We found several prominent landscape features on the Palouse that supported diverse biological communities and were important to stakeholders for multiple reasons. These places may be expedient focal points for conservation efforts. However, the many small prairie remnants on the Palouse, although ecologically important, were mostly unidentified by participants in this study and thus warrant a different conservation approach. These findings will assist government agencies and conservation groups in crafting conservation strategies that consider stakeholder perceptions and their connection with the Palouse landscape. This study also demonstrates how GIS tools can link biological and social data sets to aid conservation efforts on private land.

Modification of soil structural and hydraulic properties after 50 years of imposed chaparral and pine vegetation

Although biotic communities have long been recognized as important factors in soil development, especially of A horizons, few studies have addressed their influence on soil physical properties in nonagricultural settings. A biosequence of 50-year-old soils supporting near monocultures of Coulter pine (Pinus coulteri), scrub oak (Quercus dumosa), and chamise (Adenostoma fasciculatum) was used to determine the relative influence of vegetation type and associated soil organisms on the development of soil structural characteristics and water flow. Total porosity ranged from a high of 51% in the heavily worm-worked A horizon under oak to a low of 39% within the 35- to 50-cm depth under pine, where earthworms were absent. Macroporosity (pores with diameters >300 Am) was highest in the A horizon under oak (15.6%) and lowest under pine (9.5%). Saturated hydraulic conductivity of surface soils ranged from 10.8 cm h � 1 under oak to 3.2 cm h � 1 under pine. Soil under chamise, which had fewer earthworms than that under oak, had Ksat and bulk density values intermediate between oak and pine. Root and macrofauna distributions suggest that roots are the dominant factor in the development of macroporosity under pine, while earthworms have had the greatest effect under oak. Porosity has increased at an average rate of 0.22% per year in the 0- to 7-cm depth under oak (from 41% to 56%), but has not been significantly altered within the same depth under pine. Below the 7-cm depth, porosity values are similar for each vegetation type and the original parent material. Available water capacity (AWC) within the first 0to 7-cm depth has increased from the original values (about 0.11 m 3 m � 3 ) to 0.17 m 3 m � 3 under oak, 0.16 m 3 m � 3 under chamise, and 0.13 m 3 m � 3 under pine. The data show that the presence of

PHYSICAL AND HYDRAULIC PROPERTIES OF WEATHERED GRANITIC ROCK IN SOUTHERN CALIFORNIA

Weathered granitic rock is a material with properties intermediate between soil and hard rock. It retains structural features of the hard rock, including joint fractures, but also has porosity generated as a result of weathering of primary minerals, clay formation, and root invasion. This study evaluated the physical and hydraulic properties of moderately and highly weathered granitic rock (class 5 and 6, respectively, of the classification scheme of Clayton and Arnold (1972)) in the San Jacinto Mountains of southern California. Class 5 and 6 samples exhibited comparable bulk densities (approximately 1.94 g cm−3), porosities (27%), and particle size distributions. Saturated hydraulic conductivities were also similar for both weathering classes (approximately 5.5 cm h−1). Water retention data indicate that about 50% of the water held at saturation is drained at −100 cm head. Effective pore size distributions calculated from water retention data indicate that 25% of the total porosity was associated with pores >100 μm in diameter.

Ionic Thiocyanate (SCN - ) Production, Fate, and Phytotoxicity in Soil Amended with Brassicaceae Seed Meals

Brassicaceae seed meals produce ionic thiocyanate (SCN (-)), a bioherbicidal compound. This study determined the fate of SCN (-) in a field soil amended with seed meals of Sinapis alba, Brassica juncea, and Brassica napus and quantified crop phytotoxicity by monitoring carrot ( Daucus carota) emergence. Meals were applied at 1 or 2 t ha (-1), and soils were sampled to 35 cm for SCN (-). Maximum SCN (-) (211 micromol kg (-1) of soil) was measured at 5 days in 0-5 cm samples from plots amended with S. alba meal at 2 t ha (-1). Less than 30 micromol of SCN (-) kg (-1) of soil was measured at soil depths below 15 cm. At 44 days, SCN (-) was <15 micromol kg (-1) of soil in all treatments. Emergence inhibition of carrots seeded 15-36 days after meal amendment was found only in S. alba treatments. The rapid decrease of SCN (-) concentrations in Brassicaceae meal-amended soil indicates limited potential for off-site environmental impacts.

Tillage differentially affects the capture rate of pitfall traps for three species of carabid beetles

The influence of tillage, gender, and microclimate on capture rates of pitfall traps for the beetles Poecilus scitulus LeConte, Poecilus lucublandus (Say), and Pterostichus melanarius Illiger (Coleoptera: Carabidae) were assessed in mark–release–recapture experiments in spring pea and spring wheat. Experiments were conducted during June, July, and August of 2003 in the Palouse region of northern Idaho, USA. Rates of capture in pitfall traps for the three carabid species were differentially affected by crop‐tillage systems. Capture rates for P. scitulus and P. lucublandus were higher in no‐till (NT) than in conventional tillage (CT) peas, whereas capture rates for P. scitulus and Pt. melanarius were higher in CT than in NT wheat. Ground‐level temperatures and relative humidity (r.h.) differed little among tillage systems. Nevertheless, capture rates were generally positively correlated with ground‐level temperature and negatively correlated with r.h., with correlations more often significant in NT than in CT systems. The response of the thermophilic Poecilus spp. to temperature provides a possible mechanistic explanation for capture rate patterns in legumes during June, but not in other months for peas or any month in wheat during the experiments. Movement impedance due to residue could explain lower capture rates of P. scitulus and Pt. melanarius in NT than in CT spring wheat. These results suggest that researchers using pitfall trapping for carabid populations should take into account potential capture biases their treatments can introduce.

Changes in soil solution chemistry of Andisols following invasion by bracken fern

Disturbed areas within the Grand Fir Mosaic (GFM) ecosystem of northern Idaho show little to no natural conifer regeneration. Clear-cut sites are invaded quickly by bracken fern successional communities and seem to be in an arrested state of secondary succession. This study compared the soil solution composition of Andisols supporting bracken fern successional communities with undisturbed forest to determine the effects of shifts in vegetation communities. Treatment areas included undisturbed forest, a 30-year-old bracken fern glade (clear-cut in 1965), and a natural bracken fern glade estimated to be centuries old. The natural bracken fern glade was divided into subplots, one of which has been weeded 2 to 3 times each growing season since 1988. Soil solution was collected in porous ceramic cup lysimeters at 12- and 25-cm depths. Samples were collected from May to July in 1994 and 1995. Solutions were analyzed for pH, Al, and dissolved organic carbon (DOC). The soil solution pH in the 30-year-old glade was consistently lower than in the other sites throughout the sampling period, and the 30-year-old glade was the only site to periodically register below pH 5. The natural bracken fern glade that had been weeded was more similar to the undisturbed forest, suggesting that bracken fern biomass does have an acidifying effect on soil solution. The highest Al concentration recorded was 1.6 mg/L in the 30-year-old glade, whereas in the undisturbed forest Al was often below the detection limit. Aluminum and DOC were found to be positively related, with r values of 0.533 and 0.824 for 1994 and 1995, respectively. These results indicate that bracken fern does have an acidifying effect on soil solution. Aluminum concentrations were lower than reported toxic levels for other conifer species and were correlated with DOC. These two findings suggest that Al toxicity may not be a major factor contributing to the lack of conifer regeneration within the GFM.

Impact of Climate Change Adaptation Strategies on Winter Wheat and Cropping System Performance across Precipitation Gradients in the Inland Pacific Northwest, USA

Ecological instability and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems, particularly those threatened by projected climate change. Crop intensification, diversification, reduced tillage, and variable N management are among strategies proposed to mitigate and adapt to climate shifts in the inland Pacific Northwest (iPNW). Our objectives were to assess these strategies across iPNW agroecological zones and time for their impacts on 1) winter wheat (Triticum aestivum L.) productivity, 2) crop sequence productivity and 3) N fertilizer use efficiency. Region-wide analysis indicated that WW yields increased with increasing annual precipitation, prior to maximizing at 520 mm yr-1 and subsequently declining when annual precipitation was not adjusted for available soil water holding capacity. While fallow periods were effective at mitigating low nitrogen (N) fertilization efficiencies under low precipitation, efficiencies declined as annual precipitation exceeded 500 mm yr-1. Variability in the response of WW yields to annual precipitation and N fertilization among locations and within sites supports precision N management implementation across the region. In years receiving less than 350 mm precipitation yr-1, WW yields declined when preceded by crops rather than summer fallow. Nevertheless, WW yields were greater when preceded by pulses and oilseeds rather than wheat across a range of yield potentials, and when under conservation tillage practices at low yield potentials. Despite the yield penalty associated with eliminating fallow prior to WW, cropping system level productivity was not affected by intensification, diversification, or conservation tillage. However, increased fertilizer N inputs, lower fertilizer N use efficiencies, and more yield variance may offset and limit the economic feasibility of intensified and diversified cropping systems.