Showing papers on "Growing season published in 1994"

Woody plant regeneration in four floodplain forests

Abstract: Between 1987 and 1990, we estimated seedfall and recorded age, growth, and survival of 10 933 tree and vine seedlings growing in the understories of four bottom- land hardwood forests in South Carolina. The forests differed in flood frequency, soils, and vegetation structure but had a number of woody plant species in common. Several demographic processes were consistent for all four forests as well as for flood- plain forests described in other published studies. Smaller seeded species had larger numbers of seeds dispersed, germinants, and established seedlings. Seed size, however, was not clearly related to seedling survival. Published rankings of shade and flood tolerances were also unrelated to survival, at least during the first growing season after germination. Seedling survival rates were least during the first growing season and greater in subsequent years. Within a growing season, early germinants had greater survival. For some species, survival was negatively related to basal area of neighboring conspecific adult trees. Some aspects of the regeneration process were more site specific. Within species, seedfall densities relative to adult tree abundance differed across forests by an order of magnitude. First-year seedling mortality rates were significantly affected by site and site x species interactions. Mortality in subsequent years was also significantly affected by site. Although the role of flooding in site-specific mortality was not clear, small elevation changes within flooded sites were correlated with changes in germination and survival for some species.

Growth responses of four sub-Arctic dwarf shrubs to simulated environmental change

Abstract: Vegetative responses of Empetrum hermaphroditum, Vaccinium vitis-idaea, V. uliginosum and V. myrtillus to environmental change (temperature (T), water (W) and fertilizer (F)) were investigated in a factorial field perturbation study in sub-Arctic Sweden over two growing seasons (1991 and 1992). Total above-ground biomass was largely unresponsive to the perturbations due to dilution of current season's growth by material produced in previous years. The mass of shoot material produced in 1991, increased in response to F within 11 weeks of the start of the experiment in the two evergreen species (V. vitis-idaea and E. hermaphroditum), but not in the only deciduous species (V. uliginosum) measured that year (...)

Effect of Crop Density on Weed Interference in Maize

Abstract: Development of an integrated weed management system requires detailed information on crop-weed interactions, including the impact of the relative competitive ability of the crop during serious phases of development on weed growth. The objective of this study was to quantify effects of maize (Zea mays L.) plant density on weed interference in maize throughout the growing season. Experiments were carried out during 1990, 1991, and 1992 at the Elora Research Station, Elora, ON, on a London loam (Aquic Hapludalf) soil that had been tile drained. Maize was grown at three plant densities (4, 7, and 10 plants m −2 ) under three weed pressures. Weed pressures were established by varying the weedfree period after maize planting: all season (weed free), planting to 5to 7-leaf stage of maize (medium weed pressure), and planting to 3- to 4-leaf stage of maize (high weed pressure) [...]

Changes in Vegetation and Soil Fertility along a Predictable Snowmelt Gradient in the Mosquito Range, Colorado, U. S. A.

Abstract: Changes in edaphic conditions and vegetation along snowmelt gradients are well known in many alpine areas, but very few studies have used multivariate techniques to document these changes at a microgeographic scale and to measure predictability of snowmelt patterns. This paper describes concordant changes in microenvironmental factors and plant species abundances among >200 evenly spaced microsites in a large alpine snowbed in the Mosquito Range, Colorado. The snowmelt gradient was highly consistent: averaged over all microsites, the mean date of snowmelt varied by only 1 wk from 1989 to 1992, and relative date of snowmelt among microsites was highly predictable (R2 > 90% among years). Soil in later melting microsites had reduced organic content, water content, nitrogen, phosphorous, and acidity. Total soil nitrogen and water content decreased through the growing season, while pH increased significantly. Species richness and total vegetation cover were significantly greater in early melting microsites, and soil disturbance by pocket gophers and erosion peaked in moderately latemelting areas. Canonical correspondence analysis (CCA) showed that microgeographic changes in the plant community were associated with four environmental factors: snowmelt date, rock cover, soil disturbance, and soil organic content. Plant species that are common in the vegetation surrounding the snowbed tended to decrease in abundance in later melting snowbed sites. Other species attained peak abundance in the less productive late melting sites, and a few appeared to be associated with soil disturbance. Plant community differences between paired sampling units (quadrats) were determined more by differences in their snowmelt date than by their spatial separation, suggesting that plant species distributions along this alpine gradient are determined principally by ecological interactions and physiological tolerances, rather than by historical accident and limited dispersal.

Chlorophyll meter evaluation for nitrogen management in corn

Abstract: Precise nitrogen (N) fertilizer management in corn requires accurate and timely analysis of plant tissue N status throughout the growing season. Chlorophyll meter readings (CMR) were compared to la...

Consequences of habitat heterogeneity for availability of nutrients in a dry tropical forest.

Abstract: 1 This study evaluates the consequences of habitat heterogeneity in terms of patchy availability of nutrients in a dry tropical forest. The forest floor was characterized by the presence of topographic depressions; litter accumulation in these troughs gives rise to patchy microsites which are different in appearance from the adjoining non-patchy milieu (flats). 2 Litter mass and decomposition were significantly greater in the troughs than in the flats. Decomposition of 95% of the leaf litter needed 488 days in the troughs compared to 576 days in the flats. 3 Troughs were characterized by higher levels of microbial biomass and available nutrient pool. N-mineralization rates were also higher in the troughs. C, N and P concentrations in microbial biomass were positively correlated with N-mineralization rate when data for flats and troughs were pooled. The study indicated that immobilization and release of nutrients occurred in different parts of the year. 4 Fine roots were concentrated in the troughs with the net fine root production of 488 g m -1 compared to 218 g m -1 in the flats. Fine root biomass was positively correlated with the concentrations of mineral N and available P in the troughs. N-mineralization explained 46-63% variability in fine root biomass in the microsites. 5 The troughs supported greater herbaceous shoot biomass, particularly in the rainy season, thus preventing leaching by immobilizing excess nutrients. Herbaceous shoot biomass was positively correlated with N-mineralization and mineral N throughout the growing season and across the fertility gradient. 6 Troughs, which accumulated litter and trapped the nutrients in the dynamic microbial biomass, were characterized by higher amounts or organic C, total and mineral N, available P and nutrient supply potential. These areas attracted fine roots to support tree growth, compensated for nutrient limitation and sustained a fairly high level of net primary production in otherwise nutrient poor, leached, impoverished and shallow soil milieu.

Rhizosphere carbon fluxes in field-grown spring wheat : model calculations based on 14C partitioning after pulse-labelling

Abstract: Knowledge on the quantity and dynamics of rhizodeposition under ecologically realistic conditions may elucidate various aspects of soil organic matter dynamics Data from a field experiment with 14C pulse-labelling of spring wheat at different development stages, were used to estimate rhizosphere carbon fluxes Not only the flux of C to the roots was assessed but also the fluxes of organic and inorganic release of root-derived material C fluxes were calculated from curves fitted to data on shoot and root biomass and to data on 14C distribution at different development stages The 14C distribution curves were extrapolated from the first labelling date (elongation stage) down to crop emergence and from the last labelling date (dough ripening stage) up to crop harvest, using different extrapolation procedures The results show that while the maximum shoot growth rate occurred around ear emergence, the flux of C to the roots had a maximum around tillering Over the entire growing season, shoot growth amounted to 5730 kg Cha−1 and 2310 ± 90 kg C ha−1 was translocated belowground Of this 920± 150 kg C ha−1 was lost in root respiration and 500 ±120 kg C ha−1 was released as young photosynthate rhizodeposits, which are defined as organic materials released from the roots within 19 days after assimilation Root growth amounted to 940 ±40 kg C ha−1, of which, however, 370 ±40 kg C ha−1 was lost again through root decay Root turnover during the growing season, defined as root decay divided by root growth, was therefore 37–42% Most of the organic input to soil (56–64%) occurred through rhizodeposition, while 36–44% was comprised in root biomass at crop harvest The model used for the calculation of the carbon fluxes is discussed

Estimating corn yield response models to predict impacts of climate change

Abstract: observations on solar radiation, an essential determinant of crop yield. A corn yield response model for Illinois crop reporting districts is estimated using field data. Weather variables are timed to crop growth stages to allow use of the model if climate change shifts dates of the crop growing season. Solar radiation is included. Results show this model is superior to conventionally specified models in explaining yield variation in Illinois corn.

Growth of Thuja plicata seedlings along a light gradient

Abstract: To improve understanding of light – growth response relationships in western red cedar, seedlings were grown on three environmentally comparable sites representing nearly optimum growth conditions for the species in coastal British Columbia. On each site, the seedlings were planted on transects extending from a clearcut to the interior of an adjacent old-growth stand. After three growing seasons, seedling mortality, vigour, growth characters, and foliar nutrients were compared across five light classes and between study sites using analysis of variance and related to the percentage of above-canopy light available to each seedling using regression analysis. Three-year mortality was ≤ 27%, and most mortality (≥ 85%) occurred at ≤ 20% of above-canopy light. Seedling growth improved consistently with increasing light; however, the actual growth response at > 40% of above-canopy light varied with study site. The pattern of variation in the growth characters suggested that planted seedlings were able to acclima...

Nematodes as indicators of enhanced microbiological activity in a Scottish organic farming system

Abstract: . The presence of spring barley plants increased the numbers of nematodes, particularly of plant-feeders, compared with fallow plots in a Scottish organic farming system. The addition of farmyard manure (FYM) had no detectable effect on nematode populations but poultry manure (PM) caused a considerable increase. The application of PM also altered the types of nematode present and favoured bacterial-feeders and rhabditids in particular. These changes suggest that PM causes shortterm (within a growing season) increases in microbiological activity and nutrient cycling, whereas FYM is more likely to bring about long-term changes.

CO2 exchange in the Hudson Bay lowlands: Community characteristics and multispectral reflectance properties

Abstract: Net ecosystem CO2 exchange was measured during the 1990 growing season (June to August) along a transect starting 10 km inland from James Bay and extending 100 km interior to Kinosheo Lake, Ontario. Sites were chosen in three distinct areas: a coastal fen, an interior fen, and a bog. For the most productive sites in the bog, net daily uptake rates reached a maximum of 2.5 g C-CO2 m(exp -2)/d with an area-weighted exchange of 0.3 g C-CO2 m(exp -2)/d near midsummer. This site was estimated to be a net carbon source of 9 g C-CO2 m(exp -2) to the atmosphere over a 153-day growing season. The interior fen was less productive on a daily basis with a net maximum uptake of 0.5 g C-CO2 m(exp -2)/d and with corresponding area-weighted uptake of 0.1 g C-CO2 m(exp -2)/d during midsummer. Early and late season release of carbon to the atmosphere resulted in a net loss of 21 g C-CO2 m(exp -2) over the growing season from this site. The coastal fen was the most productive site with uptake rates peaking near 1.7 g C-CO2 m(exp -2)/d which corresponded to an area-weighted uptake of 0.8 g C-CO2 m(exp -2)/d during midsummer and an estimated net uptake of 6 g C-CO2 m(exp -2) for the growing season. Associated with net CO2 exchange measurements, multispectral reflectance properties of the sites were measured over the growing season using portable radiometers. These properties were related to exchange rates with the goal of examining the potential for satellite remote sensing to monitor biosphere/atmosphere CO2 exchange in this biome. The normalized difference vegetation index (NDVI) computed from surface reflectance was correlated with net CO2 exchange for all sites with the exception of areas with large proportions of Sphagnum moss cover. These mosses have greater near-infrared reflectance than typical surrounding vegetation and may require special adjustment for regional exchange/remote sensing applications.

Plant responses to selective grazing by bison: interactions between light, herbivory and water stress

Abstract: Two abundant tallgrass prairie forb species, Ambrosia psilostachya and Vernonia baldwinii, are commonly found intact in patches where the grasses have been selectively grazed by bison. Microclimatic patterns and physiological responses of these forbs were measured in grazed and ungrazed patches. These experiments demonstrated that bison herbivory indirectly enhanced water availability and productivity of forbs growing in grazed patches. This was due primarily to the reduction in transpiring grass leaf area in grazed patches and an increase in light availability. In grazed patches, incident light at forb mid-canopy height was 53% greater than ungrazed sites at midseason and soil temperatures were always warmer (e.g., 10°C at 5 cm), perhaps enabling forbs to initiate growth earlier in the spring. Enhanced leaf xylem pressure potential and stomatal conductance in plants in grazed areas were most evident when water availability was low (i.e., late in the growing season and over short-term dry periods characteristic of the tallgrass prairie environment). Relative to individuals in ungrazed areas, end-of-season biomass of A. psilostachya was 40% greater and reproductive biomass and head number of V. baldwinii was 45% and 40% greater, respectively, in plants in grazed patches. A favorable growing environment maintained in grazed patches during periods of water limitation enhances carbon gain in forbs leading to increased biomass and potential fitness.

Effect of elevated CO2 on carbon and nitrogen distribution within a tree (Castanea sativa Mill.) — soil system

Abstract: Two-year-old sweet chestnut trees were grown outside in normal or double CO2 atmospheric concentration. In spring and in autumn of two growing seasons, a six day labelling pulse of14C labelled CO2 was used to follow the carbon assimilation and distribution in the plant-soil system. Doubling atmospheric CO2 had a significant effect on the tree net carbon uptake. A large proportion of the additional C uptake was ‘lost’ through the root system. This suggests that increased C uptake under elevated CO2 conditions increases C cycling without necessarily increasing C storage in the plant. Total root derived material represented a significant amount of the ‘extra-assimilated’ carbon due to the CO2 treatment and was strongly correlated with the phenological stage of the tree. Increasing root rhizodeposition led to a stimulation of microbial activity, particularly near the end of the growing season. When plant rhizodeposition was expressed as a function of the root dry weight, the effect of increasing CO2 resulted in a higher root activity. The C to N ratios were significantly higher for trees grown under elevated CO2 except for the fine root compartment. An evaluation of the plant-soil system nitrogen dynamics showed, during the second season of CO2 treatment, a decrease of soil N mineralization rate and total N uptake for trees grown at elevated CO2 levels.

The significance of internal nutrient cycling in branches for growth and reproduction of Rhododendron lapponicum.

Abstract: The significance of internal nitrogen and phosphorus cycling for growth and reproduction was evaluated for the evergreen dwarf shrub Rhododendron lapponicum in a subarctic environment. The evaluation was made by analysing the seasonal dynamics of branch nitrogen and phosphorus pools and studying the effects of experimentally depleting the resources available from one-year-old leaves. Resource depletion was induced by shading the old foliage or removing it entirely. Responses were measured as growth and changes in nutrient pools (N and P) in new vegetative and reproductive parts. Non-reproductive branches maintained relatively constant resource levels over the growing season (...)

Fluxes of nitrous oxide and methane from nitrogen-amended soils in a Colorado alpine ecosystem

Abstract: In order to determine the effect of increased nitrogen inputs on fluxed of N2O and CH4 from alpine soils, we measured fluxes of these gases from fertilized and unfertilized soils in wet and dry alpine meadows. In the dry meadow, the addition of nitrogen resulted in a 22-fold increase in N2O emissions, while in the wet meadow, we observed a 45-fold increase in N2O emission rates. CH4 uptake in the dry meadow was reduced 52% by fertilization; however, net CH4 production occurred in all the wet meadow plots and emission rates were not significantly affected by fertilization. Net nitrification rates in the dry meadow were higher in fertilized plots than in non-fertilized plots throughout the growing season; net mineralization rates in fertilized dry meadow pots were higher than those in non-fertilized plots during the latter half of the growing season.

Crop coefficients for irrigating cotton in the presence of groundwater

Abstract: A cotton crop coefficient was modified to account for the contribution of shallow groundwater to crop water use. The data used in the modification were developed using weighing column lysimeters. The percentage groundwater contribution to crop water use, expressed as a function of growing degree days for several salinities and two water table depths, was used in the regression analysis. Use of the modified coefficient was demonstrated by scheduling a subsurface drip irrigation system installed in an area with shallow saline groundwater. Use of the modified crop coefficient resulted in 25% of the cotton water requirement being extracted from shallow groundwater with a salinity of 5 dS m-1 without any adverse effects on vegetative plant growth and yield. Groundwater depth dropped from 1.2 to 2.2 m during the growing season.

Seed Production of Wiregrass in Central Florida Following Growing-Season Prescribed Burns

Abstract: Wiregrass (Aristida stricta Michx.) is a major species in the long leaf pine (Pinus palustris Mill.) sandhills areas of central Florida, providing a major portion of the fuel for the recurring ground fires necessary to maintain the community. Growing season burning promotes flower and seed production. The objective of this study was to assess the seed production potential of wiregrass following prescribed burns from May through August. Four longleaf wiregrass sites were prescribed burned, one each in May, June, July, and August. Information on bunch size, bunch density, seed stalk density, seed density, and seed germination were collected. The four sites differed significantly in the density of wiregrass bunches, average bunch size, wiregrass cover and seed viability. The density of seed stalks was fairly consistent across sites. Viable seed production was lowest on the June burned site and highest on the July burned site. The study shows good quantities of seed are comparatively easy to produce with growing season bums.

Growth and yield responses of almond (Prunus amygdalus) to trickle irrigation

Abstract: Growth and yield responses of developing almond trees (Prunus amygdalus, Ruby cultivar) to a range of trickle irrigation amounts were determined in 1985 through 1987 (the fifth through seventh year after planting) at the University of California's West Side Field Station in the semi-arid San Joaquin Valley. The treatments consisted of six levels of irrigation, ranging from 50 through 175% of the estimated crop evapotranspiration (ETc), applied to a clean-cultivated orchard using a line source trickle irrigation system with 6 emitters per tree. ETc was estimated as grass reference evapotranspiration (ET0) times a crop coefficient with adjustments based upon shaded area of trees and period during the growing season. Differential irrigation experiments prior to 1984 on the trees used in this study significantly influenced the initial trunk cross-section area and canopy size in the 50% ETc treatment and 125% ETc treatment. In these cases, treatment effects must be identified as relative effects rather than absolute. The soil of the experimental field was a Panoche clay loam (nonacid, thermic, Typic Torriorthents). The mean increase in trunk cross-sectional area for the 3-year period was a positive linear function (r 2 = 0.98) of total amounts of applied water. With increases in water application above the 50% ETc treatment, nut retention with respect to flower and fertile nut counts after flowering, was increased approximately 10%. In 1985 and 1987, the nut meat yields and mean kernel weights increased significantly with increasing water application from 50% to 150% ETc. Particularly in the higher water application treatments, crop consumptive use was difficult to quantify due to uncertainty in estimates of deep percolation and soil water uptake. Maintenance of leaf water potentials higher than −2.3 MPa during early nut development (March through May) and greater than −2.5 MPa the remainder of the irrigation season (through August) were positively correlated with sustained higher vegetative growth rates and higher nut yields.