Plots In Spring Research Articles

Avaliação da regeneração natural em nascentes perturbadas no município de Lavras, MG.

Este trabalho teve como objetivo avaliar a dinâmica da regeneração natural em duas nascentes em processo de recuperação no município de Lavras, MG. Para tanto, foram realizados dois inventários após o isolamento das áreas, nos períodos de Agosto/2005 (18 meses) e Abril/2006 (24 meses). Foram alocadas no total 122 parcelas de 5´5 m (25 m2), sendo 76 na nascente 1 e 46 parcelas na nascente 2. As parcelas foram distribuídas de forma sistemática ao longo de toda a área das nascentes. Todos os indivíduos com altura superior a 0,10 m e DAP (diâmetro a altura do peito) < 5 cm, foram identificados, tendo seus diâmetros e alturas mensuradas. Foram avaliadas a composição florística, a estrutura, e a dinâmica da regeneração natural. Foram amostrados no total 524 indivíduos pertencentes a 24 famílias e 55 espécies. A família Asteraceae se destacou em número de espécies na nascente 1 e as famílias Fabaceae Faboideae, Myrtaceae e Solanaceae na nascente 2. As espécies Baccharis dracunculifolia e Vernonia ferruginea apresentaram os maiores índices de regeneração natural, na nascente 1, enquanto que as espécies Vernonia polyanthes e Nectandra nitidula se destacaram na nascente 2. O maior índice de diversidade foi registrado para a nascente 2 na segunda avaliação, aumentando de 3,324 (primeira avaliação) para 3,384 (segunda avaliação). O índice de similaridade florística encontrado entre as duas nascentes, foi de 20,0 e 18,5% para as avaliações 1 e 2 respectivamente. Durante o período de monitoramento, verificou-se um aumento significativo de 33,33 e 15,8% no número de indivíduos amostrados nas nascentes 1 e 2 respectivamente. O método da regeneração natural apresenta grande potencial para a recuperação da vegetação no entorno das duas nascentes, sendo necessária, no entanto, a adoção de técnicas de controle do capim Brachiaria sp.

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.

Development of Oculimacula yallundae and O. acuformis (eyespot) lesions on stems of winter wheat in relation to thermal time in the UK

Relationships between development of eyespot, caused by Oculimacula yallundae (OY) or O. acuformis (OA) on stems of winter wheat (cv. Avalon), and thermal time (°C days after sowing) were investigated in field experiments in 1985/86, 1986/87 and 1987/88 (two experiments). In all experiments, the incidence and severity of stem eyespot (uninoculated plots, OY‐ and OA‐inoculated plots) were linearly related to accumulated thermal time after sowing. There were ca. 600–800°C days from the time of the first sample when eyespot lesions were recorded on stems to the time when maximum eyespot incidence or severity was recorded. Relationships between stem eyespot incidence or severity and thermal time differed between seasons, with more severe eyespot in 1986/87 and 1987/88 than 1985/86. Both the severity and volume of stem lesions were initially greater in OY‐inoculated plots than OA‐inoculated plots in spring but differences were less by harvest in all seasons. The percentage of plants with stems colonized by OY or OA over all plots (including uninoculated) showed a consistent pattern in 1986/87 and 1987/88 (two experiments), with the percentage colonized by OY greater initially and the percentage colonized by OA gradually increasing with time towards harvest.

Isotopic CO 2 measurements of soil respiration over conventional and no-till plots in fall and spring

Soils and vegetation are the second largest global carbon reservoir. Carbon storage in soil can be increased by increasing carbon inputs and/or reducing decomposition rates. Reduced tillage practices have the potential to increase soil carbon storage by reducing decomposition of soil organic matter and/or crop residue. Isotope values ( δ 13 C) of soil respiration can help infer the contribution of soil carbon pools to the soil CO 2flux, providing insight into the effects of tillage on residue decomposition. The objectives of this paper were to: (1) measure the isotope signatures of respired CO 2 from conventional tillage and no-till plots; (2) compare and contrast the two treatments in the fall and in the following spring before planting; and (3) compare the δ 13 C of soil respiration of the experimental plots with the surrounding region. Isotope soil CO 2 fluxes were measured using tunable diode laser spectroscopy and micrometeorological methods in a field experiment in Ontario, Canada. Measurements were made in fall following corn (a C4 plant) harvest and again in spring prior to soybean emergence. Data were used to compute the δ 13 C value of respired CO 2 using both the flux ratio and Keeling plot methods. The large concentration footprint prevented the Keeling plots from discerning the treatment effect. In the conventional till plots, the respired δ 13 C value showed a stronger C4 signature ( − 16.7 ± 2.5 ‰ ) compared to the no-till field ( − 20.2 ± 2.7 ‰ ) which had no soil incorporation of above-ground crop residue. This indicates more rapid decomposition of the ‘new’ residue in the conventional tillage treatment. Both treatments showed a decrease in the isotope ratio during the spring measurements ( − 20.6 ± 3.7 ‰ and − 24.2 ± 3.8 ‰ for the conventional and no-till plots, respectively) which shows a depletion of the labile C4 substrate and a shift in respired substrate towards the soil C3 organic matter over the fall to spring period. For the fall, we estimate that 57 and 25% of the CO 2 flux originated from crop residue for the conventional and no-till systems, while in the spring the proportions had decreased to 22 and 0%, respectively.

Comparative Forage Yield of “Poor” Versus “Good” Grass Stands under Different Soil Fertility Regimes in Northeastern Saskatchewan

ABSTRACT Forage yield and its response to fertilizers are affected by the condition of forage stands. A field experiment was conducted on a Gray Luvisol (Typic Croyoboralf) soil at Pathlow in northeastern Saskatchewan, from 2004 to 2006, to determine if low forage yields in “poor” grass stands are due to nutrient deficiencies, other soil properties and/or species composition, and to determine if forage dry matter yield (DMY), protein concentration (PC), and protein yield (PY) in these areas could be improved by fertilization. The four fertilizer treatments: no fertilizer—nil, plus three combinations of increasing amounts of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) fertilizers (i.e., 45 kg N + 10 kg P + 12.5 kg K + 5 kg S ha−1; 90 kg N + 20 kg P + 25 kg K + 10 kg S ha−1; and 135 kg N + 30 kg P + 37.5 kg K + 15 kg S ha−1) were applied annually to the same plots in early spring of 2004 and 2005. The lower forage yield in “poor” compared to “good” grass stand areas was most likely due to differences in plant species composition, although other factors such as soil fertility and compaction may have also contributed to lower DMY. There was a significant response of DMY, PC, and PY to applied N, P, K, and S fertilizers in both “good” and “poor” grass stands in both years. The DMY, PC, and PY in the first year (2004) continued to increase up to the highest fertilizer rate used in this study, but in the second year (2005) there was no increase in total DMY in both grass stands, and in PC and PY in “good” grass stand with application of fertilizer blend beyond the 90 kg N + 20 kg P + 25 kg K + 10 kg S ha−1 rate. Fertilizer application for two years also increased the proportion of smooth bromegrass in both stands, indicating that proper nutrient management may increase the proportion of smooth bromegrass (high yielding grass species) in the “poor” growth area, thereby improving forage yields. Overall, the findings indicate that forage yields and quality in “poor” grass stand areas can be improved considerably by applying fertilizer nutrients that are lacking in the soil. Also, the significant responses observed in the “good” grass stand areas suggest that these regions of the field can also benefit from additional fertilization.

Prescribed fire and grazing effects on carbon dynamics in a northern mixed-grass prairie

Rangelands are complex systems that occupy more than 50% of the land area in the world. Carbon cycling on rangelands is generally understood, but details concerning agricultural management practices of prescribed fire and grazing are not well defined. Field experiments were conducted on northern mixed-grass prairie in eastern Montana with undisturbed, burned, and grazed treatments established in 2003. Designated plots were burned during the dormant season (December) in 2003. Grazing occurred in 2004 and 2005, removing 45–50% of then currently available leaf area. Responses were evaluated monthly from April to October of 2004 and 2005. Abiotic measurements included: precipitation, soil water content, photosynthetically active solar radiation, and temperatures of soil and leaves. Biotic responses were: standing crop, leaf area, root mass to a soil depth of 30 cm, and CO 2 fluxes above the mixed-grass prairie canopy and bare soil. Moisture available to the northern mixed-grass prairie system at this location was the primary identifiable factor that either directly or indirectly controlled much of the CO 2 flux. Treatment effects on seasonal changes in soil water content were consistent across years, with grazed and undisturbed plots being similar. Burned plots had less soil water content than grazed or undisturbed plots in late spring and early summer with soil water content becoming similar across all treatments in late summer and into autumn. Despite differences in soil water content, CO 2 fluxes above either burned or undisturbed plots were dynamically similar. However, peak CO 2 flux of grazed plots was shifted one month earlier in 2004 and was decreased in 2005, relative to the undisturbed and burned plots. Over the course of this experiment, cumulative CO 2 flux on the grazed plots was 72% of that on the burned and undisturbed plots. Depending on conditions during the growing season, C removed from northern mixed-grass prairie rangeland may not be re-sequestered during the growing season immediately post-burning. We conclude that the studied ecosystem is unlikely to sequester considerable C, irrespective of imposed agricultural practices, due to the relatively low CO 2 flux and the small magnitude of treatment observed.

Slash burning, faunal composition, and nutrient dynamics in a Eucalyptus grandis plantation in South AfricaThis article is one of a selection of papers published in the Special Forum on Towards Sustainable Forestry — The Living Soil: Soil Biodiversity and Ecosystem Function.

The sustainability of exotic commercial plantations is dependent on the conservation of soil nutrients, especially on the ancient, leached soils of the tropics, particularly when limited fertilization is practiced. In Eucalyptus grandis W. Hill ex Maid. plantations in South Africa, the site is usually burned following harvest and prior to replanting, potentially causing a disruption of soil faunal function and losses of nutrients associated with burning and removal of slash residues. The aim was to study the effect of fire on nutrient dynamics and invertebrate faunal composition. The in situ nitrogen and phosphorus mineralization rates and invertebrate faunal composition were measured in six randomly located plots — three burned and three unburned — prior to and after a low-intensity fire. Results indicate that within the burned plots, phosphorus availability was enhanced 10-fold within the first month following the fire. Invertebrate faunal diversity was low both prior to and after burning, with ants constituting the highest number. Invertebrate faunal composition was more markedly influenced by season than by the fire, with millipedes present in the majority of plots in spring and ants dominating in summer.

Runoff, sediment, nitrogen, and phosphorus losses from agricultural land converted to sweetgum and switchgrass bioenergy feedstock production in north Alabama

Abstract Renewable energy sources such as bioenergy crops have significant potential as alternatives to fossil fuels. Potential environmental problems arising from soil sediment and nutrient losses in runoff water from bioenergy crops need to be evaluated in order to determine the sustainability and overall feasibility of implementing bioenergy development strategies. This paper discusses runoff, sediment, N, and total P losses from agricultural land (continuous cotton (Gossypium hirsutum L.)) converted to short-rotation sweetgum (Liquidamber styraciflua L.) plantations with and without fescue (Festuca elatior L.) and switchgrass (Panicum virgatum L.) bioenergy crops, compared to corn (Zea mays L.), on a Decatur silt loam soil in north Alabama, from 1995 to 1999. Runoff volume was significantly correlated to total rainfall and sediment yield in each year, but treatment differences were not significant. Sweetgum plots produced the highest mean sediment yield of up to 800 kg ha−1compared to corn and switchgrass plots, which averaged less than 200 kg ha−1. Runoff NH4+ N losses averaged over treatments and years for spring season (3.1 kg ha−1) were three to five times those for summer, fall, and winter seasons. Runoff NO3− N for no-till corn and switchgrass plots in spring and summer were five to ten times that for sweetgum plots. No-till corn and switchgrass treatments had 2.4 and 2.1 kg ha−1 average runoff total P, respectively, which were two to three times that for sweetgum treatments. Growing sweetgum with a fescue cover crop provides significantly lower risk of water pollution from sediment, runoff NH4+ N, and NO3− N.

Application of an emulsifiable mixture of 1,3-dichloropropene and chloropicrin against root knot nematodes and soilborne fungi for greenhouse tomatoes in Italy

A mixture of 1,3-dicloropropene 60.5% w/w and chloropicrin 33.3% w/w (Telone C35 EC) may be registered in Italy for soil drip fumigation. Five experiments on greenhouse tomatoes in Northern, Central and Southern Italy compared the effectiveness of this mixture in comparison with methyl bromide to find the optimum application rate in soils infested by Fusarium oxysporum f.sp. lycopersici, F. oxysporum f.sp. radicis lycopersici, Sclerotium rolfsii, Meloidogyne javanica and M. incognita. Its efficacy against F. oxysporum f.sp. radicis lycopersici and M. incognita was confirmed when applied to soils at 100, 200, 300 and 400 l ha −1 (132.4, 268.4, 402.6 and 536.8 kg ha −1) under gas-tight films with 15–45 mm of application water (900–1200 mg Telone C35 EC l −1). In sandy soils, with slight F. radicis lycopersici infections and with heavy nematode ( M. incognita) attacks, the mixture, drip applied at 900 mg l −1 during late summer (fumigation: late summer; transplant: late-summer/autumn; last harvest: early spring), performed well up to 132.4 kg ha −1 (100 l ha −1). In sandy loam soils with slight F. radicis lycopersici infections and severe infections of F. lycopersici and galling nematodes ( M. javanica), 268.4 kg ha −1 (200 l ha −1) of the mixture applied at 900 mg l −1 as a drip provided yields similar to those of methyl bromide treated plots both in spring and summer cycles. In sandy loam soils, the diseases ( F. lycopersici, F. radicis lycopersici) were controlled at rates ⩾268.4 kg ha −1 (containing 90 kg ha −1 of chloropicrin), but the mixture was ineffective against Sclerotium rolfsii occasionally observed in sandy loam soils. In both sandy and sandy loam soils, no significant relationships were found between the rates of mixture applied (132.4, 268.4, 402.6 and 536.8 kg ha −1) and the degree of nematode infestation.

Oviposition site preferences by Helicoverpa armigera (Lepidoptera: Noctuidae): effect of season and density on distribution of eggs on plants

In an attempt to improve field sampling of the African bollworm, Helicoverpa armigera (Hübner), oviposition behaviour of the pest on tomato plants was investigated. From limited studies conducted in the past, variation in oviposition sites preferences by H. armigera is thought to be seasonally related. This phenomenon has been hypothesized as being associated with seasonal variation in leaf nutritional composition. To further our understanding of the oviposition behaviour of the pest, field studies were conducted to determine oviposition site preferences, the effects of season and infestation density on the distribution of eggs on tomato plant parts. Experimental tomato crops were grown on replicated plots in spring (August to November) and in summer (February to April). Oviposition behaviour was determined by weekly sampling for eggs on tomato crops grown during the above seasons. The second and third compound leaves from the terminal bud and flower clusters at the third inter-node were the most preferred egg laying sites. Chi-square tests indicated that significantly higher percentages of eggs (P < 0.01) were laid on flower clusters in summer compared to spring. As infestation densities increased from low to high, significantly higher proportions of eggs (P < 0.01) were deposited on flower clusters but this relationship was only observed during the first year.

POTENTIAL OF A CORN STARCH-BASED BIODEGRADABLE PLASTIC FILM FOR SOIL SOLARIZATION

In temperate regions soil solarization with plastic films represents a valuable alternative to the use of methyl bromide for the control of soil borne diseases. However, large quantities of wastes are derived by plastic materials used for solar heating, whose inappropriate management could affect negatively the whole agro-ecosystem. Use of biodegradable films, which spontaneously start up a degradation process after their soil application, could represent a potential solution to these disposal problems. Greenhouse and open field experiments were undertaken in 2002 and 2003 in Southern Italy with the aim to assess the effect of soil solarization with a corn starch-based biodegradable plastic film on soil temperature, root-knot nematode (Melodogyne spp.) and weed control and crop yield, in comparison with EVA and LDPE plastic films. Mechanical and spectroradiometrical properties of the films were also studied. Use of biodegradable films resulted effective, particularly in greenhouse, for the control of nematodes and weeds improving yield and quality of melon fruits. INTRODUCTION Soil solarization is widely applied as an effective alternative to the use of chemicals for the control of soil phytoparasitic nematodes and weeds (Katan, 1981). However, the disposal of the large amounts of wastes deriving by the massive application of plastic materials in agriculture is more and more a serious environmental problem to solve. A possible solution could be represented by the use of innovative materials, such as biodegradable films, that spontaneously start up a degradation process after their application (Castronuovo, 2003). Nevertheless, technical performances of these films should be verified, more specifically if their mechanical and spectroradiometrical properties are comparable to those of traditional materials. Therefore, greenhouse and open field experiments were undertaken in southern Italy in 2002 and 2003 in order to verify the effectiveness of a corn starch based biodegradable film for solarization against phytoparasitic nematodes and weeds, in relation to its mechanical and spectroradiometrical properties. MATERIALS AND METHODS Three solarizing films, a corn starch-based biodegradable milky coloured film (40 μm thick) and two traditional transparent films (LDPE 50 μm; EVA 35 μm) were examined. Mechanical and spectroradiometrical characteristics of the films were determined at 15 days intervals during solarization using a computerized press (Galdabini PMA 10) and two spectrophotometer, working in UV-VIS-NIR (Jasco V-570) and IR (Jasco FT/IR-430), respectively. Mechanical measurements were determined by tensile (UNI 8422) and tearing (UNI 9563) strength tests, in order to obtain values of ultimate tensile strength, percentage stretch at break and tearing strength resistance (Manera et al., 2003). Proc. VI IS on Chemical and Non-Chemical Soil and Substrate Disinfestation Ed. A. Vanachter Acta Hort. 698, ISHS 2005 202 After laboratory tests the plastic films were used in two solarization trials in 2002 and 2003, either in metal and plastic tunnel greenhouse (LDPE 200 μm) and in open field in the Experimental Farm Pantanello at Metaponto (40°20’N; 16°48’E; 10 m a.s.l.). In both years, solarization treatment was applied from July 13 to September 13 on 30 m plots, after rotavation and irrigation of the soil. Plots were arranged according to a randomized block design with three replications for each treatment. During solarization soil temperatures were monitored at 10 and 30 cm depth every 30 min by precision probes (PT 100) and a CR10x data logger. Moreover, for each film the number of hours above 40°C, assumed as the minimum effective temperature on soil pathogens, was also calculated. Melon (Cucumis melo L. var. reticulatus Naud. cv. ‘Drake F1’) was cultivated in experimental plots in spring (March – July) 2003, either in greenhouse and in open field, with the aim to verify the yield response of a vegetable crop to the solarization treatment. In each plot, number and weight of marketable fruit were recorded on a 16 m area (eight plants) and soluble solids (°Brix) and pulp dry matter content were determined on ten fruits. Moreover, root-knot nematode M. javanica gall index was determined on eight plants of each plot, according to a 0-5 scale (Di Vito et al., 1979) and weeds from a 2 m sample area were counted and weighed. Data were subjected to analysis of variance and means separated by Duncan’s Multiple Range Test.

Responses of a Remnant California Native Bunchgrass Population to Grazing, Burning and Climatic Variation

This study examined the interactive effects of grazing intensity and burning on a remnant population of the California native bunchgrass Nassella pulchra. We measured growth, reproduction and mortality of permanently marked bunchgrasses and measured bunchgrass seedling recruitment and density in permanent quadrats. We burned half of the treatment plots in late spring 1998. Grazing treatments were implemented in 1998, 1999 and 2000 at four different intensities: ungrazed, light rotational grazing (31% average biomass removal), heavy rotational grazing (42% average biomass removal), and continuously grazed. Both burning and grazing affected the bunchgrass population. Bunchgrass mortality was 10% higher in burned vs. unburned plots but was not significantly different among grazing treatments. Seedling density was 100% higher in burned vs. unburned plots 2 years after the burn, however seedling densities never attained preburn levels. Seedling densities did not differ significantly among grazing treatments, but grazing reduced the height and reproduction of the mature bunchgrasses. Adult bunchgrass density did not differ significantly in any of the treatments but experienced a five-fold decrease over the 4 years of the experiment. Although the continuous grazing treatment reduced the number of culms produced per plant by 75% from the baseline year, the effect on culm production in the continuous grazing treatment was not consistently greater than the rotational grazing treatments. The interaction of grazing and burning had no significant impacts on the N. pulchra populations except on the diameter of adult bunchgrasses which was highest in the lightly grazed, unburned treatments 2 years following the burn. All response variables except bunchgrass height followed a similar pattern in time over the 4 years of the experiment regardless of treatment, peaking in 1998 and then declining in 1999 and 2000. We believe the above average rainfall and below average temperatures experienced late in the growing season in 1998 provided conditions that favored the native bunchgrasses. Overall, we found few interactive effects of grazing and burning but the separate treatments did affect bunchgrass growth, reproduction and mortality, and these effects were modulated by the ubiquitous effects of climatic fluctuations.

Post-fire, seasonal and annual dynamics of the ectomycorrhizal community in a Quercus ilex L. forest over a 3-year period

Two study plots, burned and control, were established in autumn 1998 in a Quercus ilex forest located in northern Spain, part of which had been affected by a low intensity fire in 1994. Soil samples for ectomycorrhizae (ECM) were taken over a 3-year period in each study plot in spring, summer, autumn and winter. ECM morphotypes were identified and the relative abundance of each morphotype in each soil sample calculated, along with species richness, Shannon diversity index and percentage of mycorrhization in each soil sample. The relative abundance of certain ECM morphotypes differed between burned and control plots, and the percentage of mycorrhizal tips was significantly lower in the burned than in the control plot. Nevertheless, there were no significant differences in the diversity, species richness or species composition of the ECM community in the burned and control plots. The dominant ECM morphotypes in both stands were Cenococcum geophilum and several thelephoroid fungi. Sphaerosporella brunnea and Pisolithus tinctorius thrived especially in the burned plot, whereas three ectomycorrhizal morphotypes assigned to the genus Hebeloma were especially abundant in the control plot. There was no significant variation in the relative abundance of the ECM morphotypes between seasons, but ECM community species richness was highest in autumn and lowest in summer. The percentage of mycorrhizal tips reached a maximum in winter, with its minimum in autumn. Collection of samples over the 3-year period also enabled us to detect a significant increase in percentage of ECM colonisation in the burned stand over time.

Carbon Dioxide and Nitrous Oxide Emissions following Fall and Spring Applications of Pig Slurry to an Agricultural Soil

In Québec, most pig slurry is applied to agricultural soils in the spring and fall. A study was initiated to compare the impact of the contrasting spring and fall weather conditions on CO2 and N2O emissions, and on the transformation of pig slurry C and N in a loamy soil cropped to maize (Zea mays L.). Treatments were approximately 200 kg total N ha−1 either as a spring (SPRING) or fall (FALL) application of pig slurry, and 150 kg N ha−1 as NH4NO3 (control). Fluxes of CO2 and N2O, and soil O2, CO2, N2O, NH4+, NO3−, extractable C and microbial biomass C (MBC) contents were measured 50 times over a 1‐yr period. Fluxes of N2O were generally low during the experiment but were greatly increased in recently manured soils when soil O2 concentration fell below 0.20 mol mol−1 Soil was warm and well‐aerated following spring slurry application. Under these conditions, slurry NH4–N was rapidly nitrified and high N2O emissions attributed to denitrification occurred when soil was rewetted by abundant rainfall. For the fall applied slurry, wet and cool conditions limited net nitrification and resulted in little accumulation of NO3–N, thus limiting potential for subsequent denitrification and N2O emissions. Cumulated N2O emissions during the experiment represented 1.74, 2.73, and 1.14% of added N in the FALL, SPRING, and NH4NO3 plots, respectively. Fluxes of CO2 and cumulated CO2–C losses were also greater for SPRING than for FALL application. Our results clearly show that the impacts of the timing of animal manure application on N2O emissions cannot be generalized, but will vary between years in response to interactions between crop, climatic, and soil factors.

Seed bank dynamics in tall‐tussock grasslands along an altitudinal gradient

Abstract. We studied the germinable soil seed bank of tall‐tussock grasslands along an altitudinal gradient in the mountains of central Argentina. We selected 10 sampling plots at three altitudinal levels (1200 m, 1600 m and 2200 m). We assessed the composition of the established vegetation and took ten compound soil samples (0 ‐ 5 cm depth) at each plot in autumn and spring. The soil samples were sieved, chilled, and incubated in a glasshouse to assess the composition of the seed bank. The similarity between the composition of the seed bank flora and that of the established vegetation was low throughout the gradient. Most species did not change their seed bank strategy along the gradient. Seed bank richness and density increased with altitude. Most species had a persistent seed bank at all altitudinal levels, and the proportion of such species increased with altitude. These results suggest that a cold climate directly and/or indirectly favours the formation of seed banks and seed persistence in the soil.

Impact of Tasmanian blue gum belts and kikuyu-based pasture on sheep production and groundwater recharge in south-western Western Australia

The effect of Tasmanian blue gum (Eucalyptus globulus) belts and kikuyu (Pennisetum clandestinum) grass on livestock production and groundwater recharge was studied in the high rainfall zone (&gt;600 mm/year) of south-western Western Australia from 1998 to 2001. The objective was to identify optimum combinations of tree belts and pasture for sustainable livestock production and the prevention of secondary salinisation. Treatments were annual pasture, in competition with trees at different orientations (east, west and south), kikuyu pasture in competition with trees at one orientation (west), compared with pasture in the absence of tree competition. Plots had 0, 20 or 36% of their area within 10 m of the tree belt where tree–pasture competition would be expected. Plots (0.48 ha) were stocked with Merino wether hoggets at 12 DSE/ha on annual pastures and 14 DSE/ha on kikuyu pastures. Additional sheep were placed on plots in spring and the annual pasture was destocked in autumn.Within the growing season, herbage mass was similar across both control treatments as a result of varying stock numbers. However, in summer and autumn the kikuyu control contained between 350 and 4900 kg DM/ha more herbage than the corresponding annual pasture. While both pastures accumulated similar amounts of herbage in 1998 and 2000, kikuyu accumulated more in 1999 (11 900 v. 9800 kg DM/ha) as a result of summer rain. Competition from tree belts significantly reduced adjacent annual pasture herbage accumulation (16% average reduction), although there was no difference among the levels of competition. Trees did not significantly affect adjacent kikuyu pasture herbage accumulation. Both carrying capacity and clean wool production per hectare were significantly higher on kikuyu pasture in 1999 and 2000. Tree competition also significantly reduced the carrying capacity of neighbouring annual and kikuyu pasture by an average of 10%. Clean wool production per hectare was significantly lower on annual pasture in combination with trees (11% reduction on average), but there was less effect of competition on kikuyu pasture. The kikuyu pasture used 115, 57 and 132 mm more water than the annual pasture in 1999, 2000 and 2001, respectively. The soil water deficit beneath the trees exceeded that below both control pastures by between 297 and 442 mm.Although the addition of tree belts to annual pasture provided substantial reductions in groundwater recharge, producers would also have to accept losses in livestock production. While kikuyu alone provided significant increases in livestock production and substantial reductions in groundwater recharge, the best compromise was kikuyu in combination with tree belts.

Seed bank dynamics in tall-tussock grasslands along an altitudinal gradient

We studied the germinable soil seed bank of tall- tussock grasslands along an altitudinal gradient in the moun- tains of central Argentina. We selected 10 sampling plots at three altitudinal levels (1200 m, 1600 m and 2200 m). We assessed the composition of the established vegetation and took ten compound soil samples (0 - 5 cm depth) at each plot in autumn and spring. The soil samples were sieved, chilled, and incubated in a glasshouse to assess the composition of the seed bank. The similarity between the composition of the seed bank flora and that of the established vegetation was low throughout the gradient. Most species did not change their seed bank strategy along the gradient. Seed bank richness and density increased with altitude. Most species had a persistent seed bank at all altitudinal levels, and the proportion of such species increased with altitude. These results suggest that a cold climate directly and/or indirectly favours the formation of seed banks and seed persistence in the soil.

Effect of defoliation height and redefoliation interval on regrowth and survival of perennial ryegrass (Lolium perenne) in subtropical dairy pastures

A cut plot study was undertaken on the subtropical north coast of New South Wales, Australia, to determine the effect of defoliation height and redefoliation interval on dry matter yield and persistence of perennial ryegrass (Lolium perenne L.) pastures. The pasture was established on 7 April 1998 and plots were irrigated to replace evapotranspiration loss. The study was a completely randomised block design with plots of 2 by 1 m and treatments replicated 3 times. In winter (commencing 13 July) plots were defoliated to 20, 50 or 120 mm stubble height and either not redefoliated or redefoliated at 3, 6 or 3 and 6 days after initial defoliation. In spring (commencing 28 October) plots were redefoliated as for winter but only to 50 mm stubble height. After imposition of the redefoliation treatments, the plots were allowed to regrow until the non-redefoliated treatments had regrown 3 new leaves per tiller (subsequently referred to as a regrowth cycle) and then again defoliated (regrowth cycle 1). Plots cut in winter were then halved with one half (A plots) continuing to be subject to the redefoliation treatment for 4 more regrowth cycles until regrowth cycle 1 in spring was completed on 24 November, while the other half (B plots) were a carryover comparison of redefoliation treatment in regrowth cycle 1. Both A and B plots continued to be subjected to the same defoliation height treatments as imposed in regrowth cycle 1. From 24 November to 30 March 1999, plots were defoliated at 50 mm height each time 3 new leaves per tiller had regrown.Plots defoliated to 20 or 50 mm height during regrowth cycle 1 in winter yielded 21% more dry matter than plots cut to 120 mm height while redefoliation at 6 or 3 and at 6 days produced 14% less dry matter than plots not redefoliated or redefoliated at 3 days. Continued redefoliation at 6 days (comparison within A plots) reduced dry matter yield by 63% compared with no redefoliation or redefoliation at 3 days, but only in plots defoliated to 20 or 50 mm height.Plant density in the autumn (March 1999) of the year after establishment was positively related to defoliation height over regrowth cycles 1–5 of the previous year (35, 55 or 77 plants/m2 for plots defoliated at 20, 50 or 120�mm, respectively). Plant density of plots not redefoliated or redefoliated at 3 days over regrowth cycles 1–5 was 63% higher (70 plants/m2) than for the other treatment combination (43 plants/m2) at P = 0.07 level of significance.Plants cut to 20 or 50 mm stubble height at the commencement of regrowth cycle 1 in winter had a stubble water-soluble carbohydrate content of 5.2%, decreasing to 2.3% at day 6 post-defoliation. The water-soluble carbohydrate content of plants cut to 120 mm were initially higher at 8% and fell to only 6.4% by day 6.The redefoliation treatments imposed in this study were designed to simulate the regrazing of regrowth shoots in an extended grazing bout at various defoliation heights. The results confirm the negative effects of redefoliation, at 6 days in the winter to spring period, on both dry matter yield and plant survival over the subsequent summer in the subtropics. In contrast to winter, redefoliation in late spring had no effect on dry matter yield or plant density. The results also indicate a compromise between the benefits of more lax grazing for persistence and harder grazing for pasture utilisation.

Seasonal fluctuations and long-term persistence of pathogenic populations of Agrobacterium spp. in soils.

Short- and long-term persistence of pathogenic (i.e., tumor forming) agrobacteria in soil was investigated in six nursery plots with a history of high crown gall incidence. No pathogenic Agrobacterium strains were isolated in soil samples taken in fall and winter in any plots, but such strains were isolated from both bulk soils and weed rhizospheres (over 0.5 x 10(5) pathogenic CFU/g of bulk soil or rhizosphere) in three out of six plots in spring and summer. PCR amplifications of a vir sequence from DNA extracted from soil confirmed the presence of Ti plasmids in summer and their absence in fall and winter. The results indicate that strains that harbor a Ti plasmid had an unforeseen positive fitness versus Ti plasmid-free strains in soil and rhizosphere in spring and summer in spite of the apparent absence of tumor, and hence of opines. The gain of fitness occurred during a bloom of all cultivable agrobacteria observed only in conducive soils. An evolution of the pathogenic population was recorded during a 4-year period in one particularly conducive soil. In 1990, the pathogenic population in this soil consisted of only biovar 1 strains harboring both octopine- and nopaline-type Ti plasmids. In 1994, it consisted of only nopaline-type Ti plasmids equally distributed among biovar 1 and 2 strains. These results suggest that nopaline-type Ti plasmids conferred a better survival ability than octopine-type Ti plasmids to biovar 2 agrobacteria under the present field conditions.

Damage potential of Argentine stem weevil in Lincoln dairy pasture: has biological control by Microctonus hyperodae altered the balance?

To measure the impact of biological control of Argentine stem weevil, Listronotus bonariensis (ASW) by Microctonus hyperodae in dairy pasture, a research site was established in the autumn of 1997 on a dairy farm near Lincoln, where the parasitoid had been present since 1994. Existing pasture was killed with glyphosate and four ryegrass cultivar treatments consisting of three perennial (Nui, Embassy, Vedette) and one hybrid mixture (Marsden/Greenstone), each containing either low or high levels of Neotyphodium lolii endophyte, were sown by direct drilling. A third main plot treatment was low endophyte plus insecticide. Between 1997 and 1999, seasonal pasture production was measured in all plots. Herbage composition was also measured in all plots for the first 2 years but only in the Nui treatments in 1999. ASW adult and larval densities, larval damage to ryegrass, parasitism by M. hyperodae and ryegrass tiller density were measured on Nui plots in spring and again in summer, coinciding with periods of peak ASW egg laying and larval development. Between 1997 and 2000, ASW adult densities in Nui were highest in the first summer (26 January 1998) following establishment. Thereafter, densities did not rise above c. 60 ASW/m2. Densities of adults, larvae, levels of larval damage to ryegrass, and parasitism by M. hyperodae were significantly higher in summer than spring (P