Plots In Autumn Research Articles

Utjecaj obrade tla i malča na strukturu tla, zbijenost i prinos soje u Hrvatskoj

Soil tillage management can have positive and negative short-term effect on agroecosystem. Therefore, searching for optimal tillage management is crucial for the maintenance and improvement of soil functions. The purpose of this study was to analyze the impact of conventional tillage (CT), minimum tillage (MT) and reduced tillage (RT) on Fluvisols in humid environments (Croatia). Under each treatment, subplots with and without straw were applied. The impact was assessed on physical soil properties and soybean (Glycine max (L.) Merr.) yield. Soil bulk density was significantly lower in RT with straw when compared to the other treatments. Straw significantly effected bulk density at 10-20 cm depth. Penetration resistance did not exceed the value of 2.5 MPa on any treatment, it was also significantly reduced on covered plots in Autumn. Soil water content showed higher values in straw treatments at MT and RT. Water stable aggregates percentage were high at straw plots and at MT and RT in addition to CT. Moreover, soybean grain yield was higher in straw plots at RT and MT. It can be recognized in the aspect of short-term results that the MT and RT is an advisable alternative for CT due to its positive impact on soil physical condition and grain yield.

Growth Responses of Boreal Scots Pine, Norway Spruce and Silver Birch Seedlings to Simulated Climate Warming over Three Growing Seasons in a Controlled Field Experiment

We studied the growth responses of boreal Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. Karst.) and silver birch (Betula pendula Roth) seedlings to simulated climate warming of an average of 1.3 °C over the growing season in a controlled field experiment in central Finland. We had six replicate plots for elevated and ambient temperature for each tree species. The warming treatment lasted for the conifers for three growing seasons and for the birch two growing seasons. We measured the height and diameter growth of all the seedlings weekly during the growing season. The shoot and root biomass and their ratios were measured annually in one-third of seedlings harvested from each plot in autumn. After two growing seasons, the height, diameter and shoot biomass were 45%, 19% and 41% larger in silver birch seedlings under the warming treatment, but the root biomass was clearly less affected. After three growing seasons, the height, diameter, shoot and root biomass were under a warming treatment 39, 47, 189 and 113% greater in Scots pine, but the root:shoot ratio 29% lower, respectively. The corresponding responses of Norway spruce to warming were clearly smaller (e.g., shoot biomass 46% higher under a warming treatment). As a comparison, the relative response of height growth in silver birch was after two growing seasons equal to that measured in Scots pine after three growing seasons. Based on our findings, especially silver birch seedlings, but also Scots pine seedlings benefitted from warming, which should be taken into account in forest regeneration in the future.

Persistence of Select Introduced Entomopathogenic Nematodes in the US Southwest as Potential Biological Control for Whitefringed Beetle1 in Alfalfa

Early stand decrease in alfalfa (Medicago sativa L.) throughout New Mexico is increasingly being attributed to root systems damaged by larvae of whitefringed beetle, Naupactus leucoloma Dejean. Entomopathogenic nematodes (Steinernema carpocapsae Weiser, Steinernema feltiae Filipjev, and Heterorhabditis bacteriophora Poinar) effectively control other species that inflict similar damage to alfalfa and other crops, but it is not known if they occur naturally or can persist if released in irrigated semiarid lands. Persistent strains of entomopathogenic nematodes were released in May 2017 by the New Mexico State University Rex E. Kirksey Agricultural Science Center at Tucumcari into an irrigated alfalfa field not known to be infested with whitefringed beetle. Treatments were mixtures of nematode species Steinernema carpocapsae (NY 001) + S. feltiae (NY 04) or S. feltiae (NY 04) + Heterorhabditis bacteriophora (Oswego) in a randomized complete block design with four replications near nontreated check plots. Twenty soil cores were collected per plot in autumn 2017 and 2018 to bioassay for establishment of entomopathogenic nematodes. After inoculation, S. carpocapsae was not found in any sample either year, while H. bacteriophora was found only in 4% of samples from S. feltiae + H. bacteriophora plots in 2017. Similar percentages of S. feltiae were found each year (∼20% of cores in S. feltiae + S. carpocapsae and S. feltiae + H. bacteriophora plots). No entomopathogenic nematode was detected in nontreated check plots, suggesting lack of native entomopathogenic nematodes and lack of spread from treated plots. The multiyear persistence of S. feltiae ‘NY 04' and perhaps H. bacteriophora ‘Oswego’ in the arid Southwestern US was not reported previously. Because entomopathogenic nematodes can control whitefringed beetle and a plethora of other crop pests with similar larval root-feeding behavior on many economic crops, establishing locally adapted sources of entomopathogenic nematodes for widespread distribution would be appropriate.

Abundance and depth stratification of soil arthropods as influenced by tillage regimes in a sandy loam soil

AbstractDifferent tillage regimes can change soil micro‐environmental characteristics, which may influence the distribution and abundance of soil arthropods. In this study, soil arthropods and soil properties under a winter wheat–summer maize cropping system were investigated in different tillage regimes over four seasons at two depths. The tillage treatments included conventional tillage (CT), tillage once a year (T1), tillage every two years (T2) and no‐tillage (NT). The results showed that the primary taxa of soil arthropod were Acarina (65.8%), Collembola (28.5%), Diplura (1.4%) and Coleoptera (1%) over the whole sampling period. The total arthropod density was influenced by tillage treatments and season of sampling. Values for CT plots were significantly greater than those for the NT plots in autumn and spring. In contrast, the Shannon–Wiener diversity index (H’) and the evenness index (J) were relatively higher in CT treatment. The Acarina/Collembola (A/C) ratio was significantly smaller in NT treatment for some sampling seasons as mites were more sensitive to tillage practices. The QBS‐ar index did not show a clear pattern among treatments in this study. Soil arthropods notably showed seasonal variation in depth stratification. Relative to CT, the total soil arthropods in the NT plots tended to concentrate in the upper layer due to soil compaction in the lower layer. The climate conditions and soil physical properties were the main factors affecting the soil arthropod distribution and composition, as the soil chemical and microbial properties did not differ significantly among all tillage treatments.

Effects of deer grazing on soil C and N dynamics in Miscanthus sinensis grassland and Quercus serrata forest in Ashiu research forest, Japan

ABSTRACTTo elucidate the grazing-induced changes in soil nutrient cycling, we compared vegetation and soil C and N dynamics, including inorganic N content and total C and N contents, among four plots: Quercus serrata plots inside and outside of a deer exclusion fence and Miscanthus sinensis plots inside and outside of the fence. A linear model with stepwise procedures was used to assess the effects of vegetation type, deer grazing, and soil layer. In the fenced M. sinensis plot, soil C and N contents were higher than in the other plots in autumn. This is likely because the mass of litter from regenerating herbaceous plants was about three times larger than that from Q. serrata. Regardless of the presence of Q. serrata canopy, soil contents were significantly higher outside the fence than inside during the observation periods, whereas the net nitrification rate showed the opposite trend in the summer. The result indicates that N uptake by herbaceous plants is effective in retaining in the fenced plots. In our study site, the regenerating herbaceous plants, especially M. sinensis, would play a greater key role in C sequestration and retention in the surface soil than do the canopy tree Q. serrata.

Comparative evaluation of insecticide efficacy tests against Drosophila suzukii on grape berries in laboratory, semi-field and field trials

As the period for field trials on grapevine is limited, we designed a laboratory test system to evaluate the effectiveness of selected insecticides against spotted-wing Drosophila (SWD), Drosophila suzukii, on different types of grape berries all year round. Tests were undertaken during winter and early spring with table grapes of different purchased varieties according to their seasonal availability and with wine grapes from experimental field plots in autumn. In preliminary experiments, we defined parameters for a standard laboratory test system for screening the effectiveness of several formulated insecticides in two different experimental set-ups: i) application before confining adults with berries and ii) application after confining adult D. suzukii with berries. These approaches allowed us to determine the contact activity of the products on adult D. suzukii or the impact on the larval development until the emergence of adult flies. The developed test system is suitable for screening substances with diverse types of activity on different grape types. In a second step, we combined laboratory bioassays with field applications in a semi-field persistence study and lastly we installed a randomized field plot in order to compare the effectiveness of selected insecticides in the laboratory and under field conditions. In all cases, the products Karate Zeon and SpinTor proved most efficacious in their contact mortality or as oviposition deterrents, while Mospilan SG and Coragen exhibited a good larvicidal activity. However, important disagreements occurred for the efficacy of currently authorized insecticides among laboratory, semi-field and practical field applications. The transferability of laboratory results into the field is discussed.

Soil microorganisms at the windthrow plots: the effect of post-disturbance management and the time since disturbance

Abstract: Wind disturbance is a major natural driver of forest dynamics in a large part of Europe and can affect soil properties in different ways and for different time. The present study focuses on the effects of post-disturbance management of windthrow plots in the Tatra Mountains, Slovakia, on soil microorganisms ten years after the disturbance. Their comparison with the microbial characteristics at a new windthrow plot caused by strong wind in 2014 was also carried out. Three research plots differing in the way of their management after the windstorm in 2004 (EXT, salvage plot; FIR, salvage plot affected by fire; NEX, unsalvaged plot) and the plot destroyed by strong wind in May 2014 (REX) were used for study. Ten soil samples were taken from the mineral A-horizon (depth: 0-10 cm) at each plot in autumn 2014. In soil samples, soil chemical and microbial characteristics (microbial biomass C, basal and substrate-induced respiration, N-mineralisation, catalase activity, richness and diversity of soil microbial functional groups based on the Biolog approach) were determined. Ten years after the disturbance we still observed significant differences in microbial characteristics between FIR and the other plots, with higher microbial activity at the FIR, while no significant differences were found among the other plots. The results indicate that at a higher altitude the effect of fire on soil microorganisms is more distinct than removing or not removing of fallen trees and persists even over a decade.

METHODS OF SUPPRESSING COLONIZING SEDGE TO HELP TO ESTABLISH TREE SEEDLINGS IN A NATURAL FOREST

Dense bamboo grasses have delayed the growth of tree seedlings after the wind damage in a natural coniferous forest in deep mountains of Kiso District, Central Japan. After suppression treatment of the bamboo grass, a native sedge Carex oxyandra replaced them and made the growth of tree seedlings worse. The technique to suppress colonized Carex oxyandra is unknown, since this sedge has not ever been a harmful weed to be controlled. Thus, we established first experimental plots for suppressing Carex oxyandraby a herbicide, glyphosate potassium salt solution (Roundup Max load) by normal levels of dilution (control without herbicide, diluted to ×25, ×50 and ×100 volume with water) in May 2010. Next experimental plots with above-normal levels (diluted to ×100, ×200, ×400, ×800, ×1,600 and ×3,200) were established in June 2011. Coverage percentage, plant height of Carex oxyandra and tree seedlings were measured in each plot in autumn up to 2015. As a result, coverage and plant height of Carex oxyandra decreased obviously after a half year in all dilution levels, and the suppressing effect continued during 2 years in the lower dilution from ×25 to ×400. However, withered leaves formed a carpet-like thick mat, which remained several years and was suspected to restrict the germination and growth of tree seedlings. Consequently, the herbicide proved out effective to the sedge for 2 years, but some additional treatment is needed to secure the foundation space for tree seedlings within the mat of withered leaves.

Does White Clover (Trifolium repens) Abundance in Temperate Pastures Determine Sitona obsoletus (Coleoptera: Curculionidae) Larval Populations?

To determine if host plant abundance determined the size of clover root weevil (CRW) Sitona obsoletus larval populations, a study was conducted over 4 years in plots sown in ryegrass (Lolium perenne) (cv. Nui) sown at either 6 or 30 kg/ha and white clover (Trifolium repens) sown at a uniform rate of 8 kg/ha. This provided a range of % white clover content to investigate CRW population establishment and impacts on white clover survival. Larval sampling was carried out in spring (October) when larval densities are near their spring peak at Lincoln (Canterbury, New Zealand) with % clover measured in autumn (April) and spring (September) of each year. Overall, mean larval densities measured in spring 2012–2015 were 310, 38, 59, and 31 larvae m-2, respectively. There was a significant decline in larval populations between 2012 and 2013, but spring populations were relatively uniform thereafter. The mean % white clover measured in autumns of 2012 to 2015 was 17, 10, 3, and 11%, respectively. In comparison, mean spring % white clover from 2012 to 2015, averaged c. 5% each year. Analysis relating spring (October) larval populations to % white clover measured in each plot in autumn (April) found the 2012 larval population to be statistically significantly larger in the ryegrass 6 kg/ha plots than 30 kg/ha plots. Thereafter, sowing rate had no significant effect on larval populations. From 2013 to 2015, spring larval populations had a negative relationship with the previous autumn % white clover with the relationship highly significant for the 2014 data. When CRW larval populations in spring 2013 to 2015 were predicted from the 2013 to 2015 autumn % white clover, respectively, based on their positive relationship in 2012, the predicted densities were substantially larger than those observed. Conversely, when 2015 spring larval data and % clover was regressed against 2012–2014 larval populations, observed densities tended to be higher than predicted, but the numbers came closer to predicted for the 2013 and 2014 populations. These differences are attributed to a CRW population decline that was not accounted by % white clover changes, the CRW decline most likely due to biological control by the Braconid endoparasitoid Microctonus aethiopoides, which showed incremental increases in parasitism between 2012 and 2015, which in 2015 averaged 93%.

Re-introduction of target species into degraded lowland hay meadows: How to manage the crucial first year?

In grassland restoration, the first year after species re-introduction by sowing in former species poor grasslands is a crucial period for the restoration progress. Despite the preparation of the restoration site by ploughing or grubbing, the establishment window is usually open for only a short time period and germination as well as establishment of the sown target species is often hampered by dense vegetation stands and related low above-ground light-availability. However, concepts how to manage freshly sown sites differ widely. In the Elbe lowland plain (Saxony-Anhalt, Germany), we tested the effects of three different cutting treatments (cut once, twice, three times), three nitrogen fertilization treatments (120kgNha−1yr−1, 60kgNha−1yr−1, without fertilization), rolling versus no rolling as well as species-trait affiliation on the establishment of sown target species in a species-poor, grass-dominated hay meadow using a split-split-plot design. Eighteen target species were sown into ploughed and grubbed plots in autumn. In the following year, individuals of each sown species were counted in microplots before the first and after the last cutting date. The treatment effects as well as the species-trait affiliation were tested using generalized linear mixed models and principal component analysis.Cutting three times significantly enhanced the number of established target species compared to cutting once showing the importance of biomass removal after species re-introduction into productive hay meadows. Compared to control plots, the 120kgNha−1yr−1 fertilization led to a lower number of established target species as well as individuals, whereas moderate fertilization did not hamper the establishment success significantly. Rolling did not show a significant effect. In addition, species traits, such as the potential to build large hemirosettes close to the ground, specific leaf area, and species height are good predictors for the establishment success under the different treatments.

Number of Microorganisms in the Soil Cultivated with Legume-Grass Mixtures Supplied with Phytohormones and Nitrogen

The study concerned the number of microorganisms colonizing the humus layer and under plough soil from the cultivation of perennial ryegrass mixtures with red clover, which were fed by biostimulant based on the phytohormones and different doses of nitrogen. Nitrogen was applied at four levels-control (no nitrogen), 50, 100 and 150 kg N∙ha-1, biostimulant in two combinations - with and without preparation. Soil material to assess the size of individual groups of microorganisms was collected from each experimental plot in autumn 2010 from the humus (0-20 cm) and under plough layers (20-40 cm). The analysis of soil samples for a total number of bacteria, actinomycetes and fungi was conducted at the Department of Agricultural Microbiology IUNG-PIB in Pulawy. Results of studies have shown that more colonies of bacteria, actinomycetes and fungi were colonized the humus horizon. Biostimulant application in this cultivation led to a decrease of the total number of colonies of the all soil microorganisms groups but improved the ratio of bacteria to fungi. Increasing doses of mineral nitrogen by the limiting of the bacteria number and intensive development of soil fungi, helped to narrow the B/F ratio.

Effects of a winter or spring sowing date on soil nitrogen utilisation and yield of barley following a forage crop of red clover, lucerne or hybrid ryegrass

An experiment tested the hypothesis that the yield and nitrogen content of a spring-cultivated barley (Hordeum vulgare) crop (cv. Riviera) would be higher than for a winter-cultivated barley crop (cv. Pearl) when following 3-year-old swards of either red clover (Trifolium pratense), lucerne (Medicago sativa) or hybrid ryegrass (Lolium hybridicum) maintained and harvested for silage. Four replicate, 15m×15m plots of red clover, lucerne, hybrid ryegrass receiving 250kgNha−1annum−1 (250-N HRG) or hybrid ryegrass receiving 0Nha−1annum−1 (Zero-N HRG) were sown on 2 September 2002. On 13 October 2004 and 17 March 2005, half of each plot was ploughed and sown with either winter or spring barley, respectively. Barley was harvested as whole-crop at the dough stage. Soil samples were collected from all plots in autumn 2004, spring 2005 and autumn 2005 for soil mineral N (SMN) analyses and ceramic cups were used to assess nitrate leaching from red clover plots. The grain DM yield of barley was higher when cultivating winter barley compared with spring barley when sown following Zero-N ryegrass (P<0.05), whereas the grain DM yield was higher when cultivating spring barley compared with winter barley when sown following legumes (P<0.05). In autumn 2005, following harvest of the barley crops, SMN and soil nitrate-N was higher in soils cultivated the previous autumn compared with soils cultivated in spring 2005 (P<0.001). SMN was higher (P<0.05) in red clover plots than Zero-N HRG plots, but there were no differences in SMN among the other treatments (P>0.05). The total N leached from red clover plots was higher from winter-cultivated barley plots (57kgNha−1) compared with spring cultivated barley plots (35kgNha−1) (P<0.01). Overall, the results showed that the best practice to optimise the recovery of SMN by a subsequent cereal crop following legumes in this study was to cultivate and sow barley in spring rather than in autumn whereas, when sowing cereals after ryegrass, the best use of SMN was obtained when cereals were sown in the autumn compared with the spring.

The development of lucerne root morphology traits under high initial stand density within a seven year period

The root system of plants is generally regarded as a factor, which is in relation to important agronomic and ecological characteristics. The aim of this study was to investigate the effect of high initial stand density on the reduction in development of lucerne root morphology traits and how long-term this effect would be. In spring 2003, a field experiment with six lucerne entries in randomized blocks was established. Broadcast sowing was used and the seeding rate was 5000 germinated seeds per m2. In 2003&amp;ndash;2009, the plants were sampled in each plot in autumn; the average depth of sampling was 0.2 m. The stand density reached an average value of 860 plants per m2 in the autumn of the seeding year and this strongly reduced the root weight, tap-root diameter, position and number of lateral roots. The subsequent decrease of stand density to 57 plants/m2 in 2009 was not linear but it was extremely quick from the 1st to 2nd year and, by contrast, it was extremely slow in the last three years. It indicates that older plants with larger tap-root diameter probably have a higher persistency. All evaluated root traits were developed slowly, nevertheless, they reached common values during a seven year period. The intensity of the relation of stand density to root weight or tap-root diameter increased over time whilst it decreased to the ratio of root-branched plants. Results suggest that an assessment of density in samples should be recommended for the varieties evaluation in case of irregularly-spaced plants because the differences in root morphology among varieties could be caused by the differences in density among the varieties. It is possible to conclude that lucerne stands under higher initial density provided a strongly reduced speed of root development with an impact on important agronomic traits connected with root morphology.

Effects of Late‐Season Ethephon Applications on Cold Tolerance Parameters of Four Bermudagrass Cultivars

Winter injury of bermudagrass (Cynodon spp.) is a problem across the U.S. transition zone. In an attempt to hasten the onset of autumn senescence and improve cold acclimation, ethephon (3.6 kg a.i. ha−1) was applied three times at 3‐wk intervals beginning on 15 August in 2001 and 2002. Cultivars examined were ‘Riviera’, ‘Midiron’, ‘Princess‐77’, and ‘Tifway’. Tifway exhibited greatest autumn color retention in both years. Ethephon promoted early autumn senescence as indicated by yellowing of the leaves and reduced turfgrass color during ratings in both years. Plant samples removed from plots in autumn and winter were exposed to controlled temperatures to determine those which were lethal to 50% of the material's greenup potential (LT50). Ethephon treatment did not affect freeze tolerance. Freeze tolerance of cultivars differed following seasonal acclimation. The LT50 results were: Midiron &lt; Riviera &lt; Tifway &lt; Princess‐77. In both years greenup results were: Riviera ≥ Midiron &gt; Tifway &gt; Princess‐77. Ethephon treatment slowed greenup in both years. Measurements of proline and linolenic acid levels revealed that Midiron &gt; Riviera &gt; Tifway &gt; Princess‐77. Ethephon treatment did not affect linolenic acid levels; however, it negatively affected proline concentrations in Midiron and Riviera. Since ethephon had little or deleterious effects on bermudagrass cold tolerance, it should not be considered as a strategy to improve winter survival in the transition zone.

Effect of urease and nitrification inhibitors on N transformation, gaseous emissions of ammonia and nitrous oxide, pasture yield and N uptake in grazed pasture system

Nitrogen (N) losses via nitrate (NO 3 −) leaching, ammonia (NH 3) volatilization and nitrous oxide (N 2O) emissions from grazed pastures in New Zealand are one of the major contributors to environmental degradation. The use of N inhibitors (urease and nitrification inhibitors) may have a role in mitigating these N losses. A one-year field experiment was conducted on a permanent dairy-grazed pasture site at Massey University, Palmerston North, New Zealand to quantify these N losses and to assess the effect of N inhibitors in reducing such losses during May 2005–2006. Cow urine at 600 kg N ha −1 rate with or without urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) or (trade name “Agrotain”) (3 L ha −1), nitrification inhibitor dicyandiamide (DCD) (7 kg ha −1) and the use of double inhibitor (DI) containing a combination of both Agrotain and DCD (3:7) were applied to field plots in autumn, spring and summer. Pasture production, NH 3 and N 2O fluxes, soil mineral N concentrations, microbial biomass C and N, and soil pH were measured following the application of treatments during each season. All measured parameters, except soil microbial biomass C and N, were influenced by the added inhibitors during the three seasons. Agrotain reduced NH 3 emissions over urine alone by 29%, 93% and 31% in autumn, spring and summer respectively but had little effect on N 2O emission. DCD reduced N 2O emission over urine alone by 52%, 39% and 16% in autumn, spring and summer respectively but increased NH 3 emission by 56%, 9% and 17% over urine alone during those three seasons. The double inhibitor reduced NH 3 by 14%, 78% and 9% and N 2O emissions by 37%, 67% and 28% over urine alone in autumn, spring and summer respectively. The double inhibitor also increased pasture dry matter by 10%, 11% and 8% and N uptake by the 17%, 28% and 10% over urine alone during autumn, spring and summer respectively. Changes in soil mineral N and pH suggested a delay in urine-N hydrolysis with Agrotain, and reduced nitrification with DCD. The combination of Agrotain and DCD was more effective in reducing both NH 3 and N 2O emissions, improving pasture production, controlling urea hydrolysis and retaining N in NH 4 + form. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses if losses are associated with urine and improve pasture production in intensively grazed systems.

A Comparison of Inter- and Intraspecific Interference on Broom Snakeweed (Gutierrezia sarothrae) Seedling Growth

AbstractBroom snakeweed (snakeweed) is a native range shrub found throughout semiarid rangelands of the western United States, which increases and dominates plant communities after disturbances such as overgrazing, drought, or wildfire. The objective of this study was to compare the ability of selected grass species and prostrate kochia to restrict establishment and growth of snakeweed seedlings in potted-plant and replicated field studies within two sagebrush ecological sites. In the potted-plant studies, single snakeweed seedlings were grown with seedlings (seedling neighbor study) and established plants (established neighbor study) of three cool-season grasses (crested, pubescent, and bluebunch wheatgrass), prostrate kochia, and snakeweed at increasing densities (1, 3, 5 plants/pot). Interference from crested wheatgrass in the seedling neighbor study, and both crested and bluebunch wheatgrass in the established neighbor study, induced the greatest mortality of snakeweed seedlings, and snakeweed growth was suppressed more by interspecific (grass) than intraspecific (snakeweed) neighbors in both potted-plant studies. Snakeweed establishment was also evaluated at two field sites: Howell and Nephi, UT. Snakeweed and downy brome were controlled by picloram (0.25 kg ae/ha) and glyphosate (1.5 kg ae/ha), then three native and three introduced grasses were drill-seeded, and prostrate kochia was dribble-seeded in replicated plots (3 m by 15 m) at both sites in October 2003. Snakeweed seedlings were transplanted into seeded plots and a bare ground control plot in autumn 2004. Snakeweed mortality was greatest (73%) in crested wheatgrass plots at Howell, but there were few differences among species treatments at Nephi. Of the snakeweed seedlings that survived, there was relatively little growth in any of the seeded plots compared to those in the bare ground control plots. These results indicate that seeded cool-season grasses interfered with and reduced establishment of snakeweed seedlings.

Vegetation development on deposit soils starting at different seasons

Permanent plots were created in different seasons (autumn and spring) and filled with two substrates: nutrient-rich topsoil and nutrient-poor ruderal soil (n = 5 for each treatment). My objectives were to assess the influence of starting season on initial species composition, whether differences at the start cause divergent or convergent pathways of succession and which mechanisms are operating during vegetation development. Mean species richness (number of species per plot) and mean total cover of herb layer differed significantly between substrates and changed significantly during 10 year succession, but there were no significant differences with respect to starting season. However, seasonal as well as substrate effects were evident for particular dominant species and for the pattern of successional sequences. When succession on topsoil plots started in spring, first summer annuals dominated, then monocarpic and polycarpic perennial herbs, then herbaceous perennials together with woody perennials, and at the end of the decade woody perennials. When succession started in autumn, polycarpic perennial herbs dominated from the beginning, and then were replaced by woody perennials in the second half of the decade. On ruderal soil, there was a less rapid but continuous increase of polycarpic perennial herbs and woody species, both on spring and on autumn plots, whereas short-lived plants were more abundant in the first years and then decreased. Species turnover was very high from the first to the second year for all treatments (except topsoil plots starting in autumn), but slowed down during succession. Priority effects due to starting season caused high dissimilarity at the start on the nutrient-rich substrate, but convergent succession towards the end of the first decade. The main mechanisms during early succession on the nutrient-rich topsoil were tolerance based on different life-history traits and inhibition due to reduced light availability. There was no evidence for obligate facilitation. However, an indirect facilitative effect by annuals, which slowed the development of herbaceous perennials down, and thus facilitated growth of woody species, could be seen on topsoil when succession started in spring.

Differences in the diversity of oribatid mite communities in forests and agrosystems lands

A field study was conducted in the province of Burgos (Castile, NW of Spain) to assess the role and influence of the different anthropic use of soil on the oribatid mite communities (Acari, Oribatida). Soil samples from 20 representative soil sites of the Castilian upland steppes, with cultured, pastureland or forest soil uses, were taken in spring and autumn 2000. Thereafter, soil samples were analysed in terms of their mesofaunal biodiversity, measured using the real and relative diversity of the oribatid mite communities. Collected individuals were identified to species level, being altogether 111 Oribatid species. Results from communities' ordination analysis showed clear gradients based on community variables. One of these was defined by plots with high values of diversity and species richness which correspond to the less anthropic natural soils, mainly oak forest. In contrast, the most anthropic agrosystems soils, including extensive cereal crops, most of them receiving only mineral fertilisation or having human management, were placed in opposite gradients. Differences in biodiversity between crop lands and natural soils were also confirmed by ANOVA. The seasonality, measured in terms of difference between spring and autumn plots, played a minimum role in explaining differences of diversity. Nevertheless autumn diversity values were slightly higher than those of spring, except for crops.

Bite rates in Rocky Mountain bighorn sheep (Ovis canadensis): effects of season, age, sex and reproductive status

We investigated the effects of vegetation biomass, crude protein content of consumed forage, age, sex and reproductive status on bite rates in Rocky Mountain bighorn sheep. We expected higher bite rates and vigilance in lactating females with young and higher bite rates in young growing individuals, than in non- reproducing females or rams. Lactating ewes had higher bite rates than yeld ewes and than subadult or adult rams. Subadult rams had higher bite rates than adult rams or yeld ewes. On recently burned grassland in spring, however, rams had a higher bite rate than adult females, while the contrary was true on control plots and on the burned plots in autumn. Bite rates declined for both ewes and rams from April to September and varied from year to year. While rams of different ages had significantly different bite rates, there was no effect of age on bite rates for ewes. There was no correlation between bite rates and available total biomass or biomass of live vegetation, or the numbers of steps taken while foraging for either ewes or rams. Adult rams had a lower vigilance rate than adult ewes, and vigilance decreased with increasing bite rates for all sheep. Bite rates in bighorn sheep vary greatly according to age, season and vegetation structure. An increase in bite rates during the forage growing season may compensate for higher energy demands during lactation and growth. There is a potential trade-off between foraging and vigilance as vigilance decreased with increasing bite rates.

Effects of Season of Burning on the Microenvironment of Fescue Prairie in Central Saskatchewan

The microenvironmental effects of spring, summer and autumn burns were investigated for a small area of fescue prairie in Saskatchewan over two growing seasons. Maximum fire temperature in all burns exceeded 300°C at a height of 5-10 cm in the canopy. At a depth of 1 cm in the soil, temperature increased to 40°C during the summer burn, but was unaffected by burns at other seasons. Spring-burned grasses recovered to the same height as the unburned control plot by the end of the first summer. Grass height was similar in all plots by the end of the second growing season, but aboveground biomass in all burned plots was about half that of the control. Graminoid leaf area index at the end of the second growing season ranged from 0.65 in the control plot to 0.27 in the autumn burn. Surface albedos dropped to about 0.03 immediately after burning and took about 3 months to return to the pre-burn values near 0.20. By mid-June of the second year, albedos were similar in all plots. Soil temperatures at 50 cm depth in the burned plots were higher than in the control during the first summer and lower during the winter. The greatest winter snowpack (73 mm water equivalent) accumulated in the control, compared to 48, 35 and 25 mm in the spring, summer and autumn burned plots, respectively. In the first growing season the greatest demand for water occurred in the spring plot followed by the summer, control and autumn plots. In the second season water demand did not differ significantly among plots, reflecting the similarities in plant cover. The microenvironmental effects of a single burning episode in fescue prairie disappear rather quickly, so that there is little long-term impact on the vegetation.