Showing papers on "Growing season published in 1973"

Seasonal pattern of net photosynthesis of artemisia tridentata

Abstract: Gas exchange studies were carried out on Artemisia tridenztata during the course of a growing season using microclimatically controlled cuvettes and infrared gas analysis. A definite seasonal pattern of net photosynthesis emerged. This pattern was influenced by the interaction of four major factors: plant water potential, leaf temperature, irradiation, and stage of phenological development. In spring and early summer, when plant water stress was minimal, photosynthesis rate was mainly correlated with leaf temperature and irradiation. During mid and late summer, increased plant water stress and phenological changes assumed at least equal importance with temperature and irradiation in limiting net photosynthesis. Indeed, plant water potential, mainly through its influence on stomatal aperture, r,', was probably the single most important factor influencing assimilation rate of this species on a seasonal basis. However, variations in mesophyll resistance to CO2 flux, rm', in response to temperature, water stress, or phenological changes also were involved. Sagebrush photosynthesis under field conditions was highest in late May and early June, and declined thereafter, minimum rates occurring in August during the driest period. Optimal temperatures for net photosynthesis were higher later in the season, indicating a change in gas exchange capacity more suitable to the warmer temperatures later in the

Changes in Arctic Eriophorum Tussock Communities Following Fire

Abstract: The arctic cottongrass (Eriophorum vaginatum ssp. spissum) tussock community is susceptible to fire even though it has a relatively small aboveground standing crop and the peaty substrate is wet even in years of low precipitation. While burns can be severe enough to kill all aboveground plant parts, differential protection is provided new shoots by tussocks bases, moss mats, and peat. Plant succession following fire was unique in that no new species invaded the area. Growth came principally from root stocks protected by the organic surface. Cottongrass and Carex spp. were the first to show regrowth following a June fire at one site. The role of cottongrass seedlings in colonizing these tussock communities was minor, because few seedlings older than 1 year were found on any of the sites. Epilobium angustifolium ssp.angustifolium and some Calamagrostis canadensis ssp. canadensis originated from seed although most plants of the latter species had long vigorous rootstocks. These plants occurred as minor components in the undisturbed community and increased when fire destroyed the competing species. The charred organic surface, being very dark, absorbed more short wave energy and the active layer depth increased by 35 to 50% in June and as much as 25% by late autumn. The same thermal regime was found in burns several years old. This warmer soil mass, over a longer period of time, was conducive to better growing conditions. Annual plant production had almost recovered after two growing seasons, and nutrient content of the plants was higher in the burned area. This may be due to the greater soil mass available for root exploration, to nutrient release by fire, and to greater microbial activity in the warmer soils. If other tundra communities respond to fire in a similar manner as cottongrass tussock communities, fires may act as a rejuvenating factor, as they do in other biomes

survival of field-grown rhizobia over the dry summer period in Western Australia

Abstract: The survival over summer of field-grown root nodule bacteria was studied in the field and the laboratory during the course of an investigation into a nodulation problem of annual clovers. Dry field soils containing Rhizobium trifolii and R. lupini were subjected to a range of temperatures in the laboratory, the bacteria surviving 6 h exposure to temperatures as high as 80°C. Soil temperatures during summer were recorded at different depths. Populations of rhizobia were estimated at these depths from the end of the growing season (October) to early autumn (April) in plots which had carried dense swards of subterranean clover and Serradella. High populations of R. lupini were maintained in the Serradella plots throughout the summer. Populations of R. trifolii in the subterranean clover plots were initially much lower, and declined with both time and depth. The problem known as ‘second-year clover mortality’ is primarily due to low numbers of clover rhizobia in the soil at the end of the growing season. This situation is aggravated over the long hot dry summer, when there is a further decline in numbers.

Assessment of biological nitrogen fixation in grassland and associated sites

Abstract: The extent of nitrogen fixation in native grassland on clay soil was measured using the C2H2 reduction assay Undisturbed soil cores incubated in microcanopies in the field indicated fixation rates of 2 kg N/ha per season Less nitrogen fixation activity was found in associated cultivated soils Other sites on different soil associations were found capable of fixing 1 kg·N/ha or less per growing season The fixation by several legumes and nodulated nonlegumes ranged up to 18 μg/cm2 h

Establishment of Early Successional Plant Populations on Forest and Prairie Soil

Abstract: Seed germination and plant community development on adjacent forest and prairie soils (Typic Hapludalf and Typic Halplaquoll) were studied to elucidate the causes of variation in plant community composition during the first growing season after crop harvest. The number of plant individuals in July on the forest soil was three times larger than on the prairie soil. Abutilon theophrasti, Chenopodium album, Polygonum pensylvanicum, and Setaria faberii occurred in large numbers on the forest soil but were considerably less important on the prairie soil. Ipomoea hederacea predominated on the prairie soil. The seed load after abandonment on the forest soil was larger than on the prairie soil both before and after overwintering. Total numbers of plants that reached maturity were significantly higher (at the 5% level) on the forest soil than on the prairie soil. Population levels were generally constant throughout the growing season. Diversity peaked in June and was higher on the prairie soil than on the forest soil throughout the growing season. Germination of Ambrosia artemisiifolia, Lactuca scariola, and Polygonum was enhanced by moist soil conditions, whereas germination of Amaranthus hybridus was higher under dry soil conditions. Lactuca and Polygonum were the most sensitive to water stress and Abutilon and Setaria the most tolerant. It appears that the kinds and numbers of plants that become established in an abandoned field are a function of the number of germinable seeds present in the soil and the seed—soil water relationships. Of the soil parameters that may control seed germination, there is strong evidence to suggest that soil moisture the extreme upper portion of the profile is the major factor.

Rainfall interception in mixed grass prairie

Abstract: A model has been built that permits calculation of both gross and net interception loss from mixed grass prairie. This model has been applied to two complete growing seasons for which the net interception losses were calculated to be 14 and 22%. Under arid conditions losses may be significant, particularly when much dead vegetation is present.

Fascicle Density and Needle Growth Responses of Red Pine to Water Supply Over Two Seasons

Abstract: The ontogeny of terminal growth in red pine (Pinus resinosa Ait.) suggests that the growing season in Michigan be divided into three 2—month periods: April—May,June—July, and August—September. It is during the middle period that mitotic activity at the shoot apex initiates dwarf shoot primordia in the bud for the subsequent season's foliage; thus, preconditioning one year has a strong effect on next year's growth. Water was applied to or withheld from the soil under 23—year—old trees in various combinations of the 2—month periods over two growing seasons. All effects of drought were greatest on the terminal shoot of the main stem, diminishing on terminals of branches with distance from the apex, and disappearing at the base of the crown. Shoot extension was governed equally by conditions of the middle period of the previous year and of the early period of the current year. Each year fascicle density was regulated only by water conditions of the early period of the current year, regardless of preconditioning. Spacing of needles on shoots depended on elongation of the stem internodes between dwarf shoots, and was independent of the number of fascicles. Number of fascicles per shoot was governed only by conditions of June—July of the previous year, with drought during this period reducing the number of 30%. Length of needles was related to two factors: the number of fascicles produced per shoot and the water treatment of the period during which needles elongated. Thus when the water supply of the middle of the previous year was deficient, fewer but longer needles were produced currently; when water during the middle of the current year was deficient, needles were reduced in length by about 30%. It is concluded that the interaction of two seasons' water supply are usually compensative, rarely additive. The average net effect on foliage production is along—term, year—to—year stability in photosynthetic potential for red pine.

Comparative Photosynthesis of Quebec and California Ecotypes of Typha Latifolia

Abstract: Photosynthesis and transpiration were examined in detached leaves of broad—leaved cattail (Typha latifolia L.) ecotypes from a long growing season continental climate in California's central valley and a short growing season continental in northwestern Quebec when grown under identical conditions. The principal difference between the ecotypes were (a) greater temperature dependence of net photosynthesis in the Quebec ecotype, particularly when young leaves were compared, (b) a decline in temperature dependence of Quebec leaves as they aged, but not of California leaves, (c) a downward shift in the photosynthetic temperature curve when California plants were transferred to cooler growing conditions, while the curve was stable in Quebec plants, (d) an increase in photosynthetic rate at the optimum temperature when Quebec plants were transferred to cooler conditions, but a decline in California plants, (e) a more phenotypically plastic acclimation response in the California ecotype, and(f) greater sensitivity to photosynthesis inhibition by high oxygen in Quebec leaves. Differences in net assimilation rates were less than would be expected from previous studies of other species.

Deforestation effects on soil moisture, streamflow, and water balance in the central Appalachians

Abstract: Soil moisture, precipitation, and streamflow were measured on three watersheds in West Virginia, two deforested and one forested. Water content of barren soil always exceeded that of forest soil throughout the growing season and especially in dry weather. Streamflow increased 10 inches annually on the watersheds that were cleared, most of the increase occurring between July and October. Higher soil moisture was accompanied by large instantaneous peak flows during small storms in the growing season but this peak effect was minor in large stoms and in all storms during the dormant season. With precipitation, streamflow, interception losses, and soil-moisture change estimated to comparable levels of precision, the water balance equation was solved for transpiration with sufiicient sensitivity to demonstrate the effects of tree leaf growth. After tree leaves were fully grown, calculated evaporative losses from the forested watershed somewhat exceeded potential rates as long as unmeasured runoff (leakage) was disre arded. With all components of the water balance quantified, including leakage, estimated soil-moisture loss by transpiration was at rates close to potential. Estimated leakage seemed consistent with observed stream behavior.

Primary Productivity and Microenvironment in an Ambrosia-dominated Old Field

Abstract: Aboveground primary production in a field dominated by Ambrosia artemisiifolia in southeastern Illinois was 630 + 168 g m-2 in 1968 and 595 + 142 g m-2 in 1969. During the 1st year productivity for the entire growing seasorn was 7.8 g m-2 dayand 14.4 g mr2 dayfor a short period during the growing season. Efficiency of aboveground net primary production was 1.3 % between plowing of the field and peak, standing, aboveground biomass of the plant community in mid-August. Efficiency was a high 2.6% during a short period of the growing season when productivity was maximal. Comparisons with other data on primary production of 1-year and 2-year fields in several areas of the eastern deciduous forest biome show that the southeastern Illinois fields are significantly more productive and more efficient. This suggests that generalizations concerning community organization in young successional ecosystems require further investigation.

Variations in the albedo of wheat and barley crops

Abstract: The albedo of wheat and barley crops was measured during the course of two successive growing seasons, one of which was exceedingly wet (1966) and the other abnormally dry (1967) at Derrimut, Victoria, Australia.

Soil Moisture Patterns on Two Chained Pinyon-Juniper Sites In Utah.

Abstract: Highlight: Soil moisture patterns were studied under chaining-with-windrowing, chaining-with-debris-in-place, and natural woodland at one site each in both southwestern and southeastern Utah. Results of the study indicate the greatest moisture accumulation occurred under the debris-in-place treatment (as compared to woodland controls), during the first 6 months of each year at Milford and regardless of season at Blanding. The woodland had the least soil moisture throughout most of each year. Most moisture flux took place in the upper 60to 90-cm of soil profile, with only minor changes occurring at greater depths. Differences in soil moisture patterns have been attributed to changes in microclimates due to chaining, different rooting depths and length of growing season, mulching effect of litter on the debris-in-place treatment, and possible differences in snow accumulation. Variation in vegetation density on the chained treatments did not influence soil moisture patterns. There was no evidence of deep seepage on any chaining treatment at either site.

Seasonal, Daily, and Hourly Growth of Height and Radius in Norway Spruce

Abstract: Daily height increment of trees was measured throughout two growing seasons as was 2-day radial increment of 212 of the same trees in the second season. The relationships between phenological variables and total growth, and the effect of environment on short term growth were assessed. Inferences taken from the latter data were tested on seedlings under more controlled conditions in the laboratory. The arbitrarily defined dates of initiation and cessation of growth, and the grand period growth rates were read from the growth curves. The respective simple r2 values between these variables and height growth were 0.10, 0.40, and 0.71, and r2 for the multiple regression of height growth and these variables was 0.94; for radial growth these values were 0.07, 0.56, 0.64, and 0.94. Length of the growing season and grand period growth rate were positively correlated. Dates of growth initiation and growth cessation were also positively correlated.Daily height growth varied considerably, depending strongly on temper...

Effects of companion crops and their management on the undersown forage seedling environment

Abstract: Effects of companion crops, oats, barley, and wheat on light and soil moisture available to the undersown forage species, alfalfa, birdsfoot trefoil, timothy, and bromegrass, are reported. Early in the growing season, barley intercepted the highest percentage of both visible light and light energy, whereas at the end of the season, weeds growing where forage seedlings had been established without a companion crop intercepted a greater amount of light than companion crops undersown with a forage crop. Seedlings growing under companion crops managed as simulated pasture received the greatest amount of light. Soil moisture percentages were higher where forage seedlings were established without a companion crop. Forage yields reflected a greater advantage from improved moisture during establishment than from light penetration.

Radionuclide Tracer Analysis of Trophic Relationships in an Old-Field Ecosystem

Abstract: Wild radish (Raphanus raphanistrum) and ragweed (Ambrosia artemisiifolia), the dominant producers during initial succession in an old field, were labeled with 32P in several trophic—transfer studies. Feeding relationships were determined by correlating the population dynamics and 32P uptake by consumer species with the phenological changes in producer components and isotope distribution in plant tissues. The relative magnitude of consumer pathways was estimated by using trophic—transfer indices. The first year of old—field succession was characterized by rapid phenological changes in plant—organ availability with related shifts in consumer trophic relationships. The food web of wild radish, the early summer dominant producer, changed rapidly over time resulting in successive pulses of leaf, pollen, and seed feeders. Grasshoppers were the major leaf feeders. Aphids consumed internal juices within stems while flea beetles were concentrated and feeding solely on nutrient—rich seed tissue. Leafhoppers and tarnished plant bugs also consumed internal fluids during wild radish development. The high densities and consumption by plant bugs and aphids, the major consumers of wild radish, resulted in a low food—web diversity for wild radish. Predator—prey relationships during early summer were governed mainly by the aphid infestation. Young ragweed plants and the litter and seed crop of wild radish were major food—web bases in midsummer. Generalized herbivores such as grasshoppers and crickets utilized radish seeds and ragweed tissue during this period. A second phase of specialized feeders entered the old field as ragweed became available. Food—web diversity was highest at this time when many species were present and at low densities. Ragweed was the dominant producer late in the growing season. Some herbivores utilized ragweed leaves while several species of plant bugs became abundant and were consuming the nutrient—rich fluids being channeled into pollen tissue. Plant bugs were the major ragweed herbivores. The importance of these plant bugs resulted in a decline in food—web diversity near the end of the growing season. Most consumers decreased in numbers and 32P activity as ragweed died back in September. Ragweed litter, however, supported crickets and other components of the detrital food web over the fall season. Wild radish and ragweed were the major food—web bases during the first year of succession. Over 90% of the arthropods sampled in the old field were food—web components of these producers. Many of these consumers were specialists and sucking forms which peaked in density and 32P activity as nutrient—rich fluids were entering their specific food sources. The synchronal occurrence of consumer population peaks and successive nutrient pulses in host—plant organs thus appears to maximize the energy utilization by these consumers while minimizing interspecific competition for sites of trophic transfer. Little foliar damage was evident for wild radish or ragweed because of the importance of herbivores with sucking mouthparts. Tracer studies were thus critical in evaluating the role of both producers as food—web bases. The similarity of results in two replicate studies confirmed the repeatability and accuracy of tracer techniques for trophic—transfer analysis. However, temporal aspects of food—web structure should be considered in future studies where rapid changes in plant phenology are present.

Crop Responses to No-till Management Practices on Hilly Terrain 1

Abstract: Management practices are needed that will permit economic crop production in hilly terrain without excessive soil and water losses. Field studies were conducted over a 3-year period to determine the effects of two rates of atrazine on yield of corn (Zea mays L.) sod planted in orchardgrass (Dactylis glomerata L.) for 2 years and to determine the residual effect of atrazine on germination and growth of 16 agricultural plant species the third year. Atrazine at 2.2 and 4.5 kg/ha was applied at planting time for sod-planted corn and compared with two different methods of growing corn using conventional tillage. Regrowth of orchardgrass in sod-planted treatments was measured following harvest of corn. Temperature and soil water measurements were made in sod-planted and conventionally-tilled corn over a 2-year period. Silage and grain yields were significantly higher from sod-planted corn than from conventionally tilled corn. No soil losses were noted in areas where corn was sod-planted as compared to heavy losses in conventionally-tilled corn. Soil temperatures in no-till corn averaged about 10 C less than under conventional tillage methods, with significantly higher amounts of available soil water present in no-till plots than in conventionally-tilled plots throughout the growing season. Residual studies with 16 different plant species indicated very little detrimental effect from residual atrazine after 2 years of application. Growth of many plant species was significantly higher following application of atrazine.

The seasonal pattern of CO2 exchange of Festuca rubra L. in a montane meadow community in Northern Germany.

Abstract: Completely climatized cuvettes were used to follow the CO2 gas exchange of red fescue (Festuca rubra L.), growing on a fertilized and an unfertilized plot, during a growing season from May through October. Objective of the study was to determine the effect of environmental factors on the seasonal CO2 gas exchange.Gas exchange rates were calculated on the basis of leaf dry weight, surface area and chlorophyll content. Photosynthetic rates differed between the fertilized and unfertilized plants when based on leaf dry weight or leaf surface area but were similar when based on chlorophyll.Multiple regression analysis was used to related photosynthetic rates to radiation, temperature, water vapor concentration difference, chlorophyll content and time. A cubic regression equation based on daily radiation alone explained 85% of the variation for the fertilized plants and 87% of the variation for the unfertilized plants.During the growing season the unfertilized plants had a continual decline in their photosynthetic rates. The fertilized plants had high photosynthetic rates in the spring and in the fall.Light response curves indicated greater photosynthetic rates at light saturation as well as in the light limited portion of the light response curve for the fertilized plants. Photosynthetic rates of the fertilized plants were generally depressed during periods of warm temperature and high light intensity in June and July.Photosynthetic rates declined at temperatures above 24°C. The decline was greater for the more mesomorphic fertilized plants. A similar response was noted to increasing water vapor difference, although it was difficult to separate from the temperature effect. Maximum photosynthetic rates were found between 14°C and 22°C, although there was considerable variation in the maximum rates.The effects of cutting (mowing) on the gas exchange were difficult to determine due to the interaction of the environmental factors.Chlorophyll content showed significant correlation with photosynthetic rates.

Irrigation of Field Crops

Abstract: The successful production of field crops in arid regions is entirely dependent on the use of a sound irrigation program based on a knowledge of the effect of soil-moisture stress on the plant at different stages of its development. This is particularly critical when the crop is grown during that period of the year when there is no rainfall, or when rainfall anticipated during the growing season is not forthcoming.

Pepper Plant Response to Irrigation Water Quality and Timing of Leaching

Abstract: When saline water is used for irrigation, leaching may be required if the level of salt accumulation in the root zone is expected to exceed the salt tolerance level of the crop. Under steady state conditions, leaching requirements depend mainly on the salinity level of the irrigation water (Ci) and on the tolerance of the crop to salinity (Cd) (United States Salinity Laboratory Staff, 1954). In the process of salt build-up in the soil, it may however be possible or even desirable, to reach, temporarily, levels of salinity higher than the specified tolerance level of the crop. It has been shown by many workers that, under conditions of changing salinity with time or with depth, the effective salinity is a weighted mean salinity (Shalhevet, 1970). Consequently, it may be possible to allow considerable accumulation of salts during the growing season, without causing undue damage to the crop, before leaching is required.

Studies on some deep sandy soils in Cape York Peninsula, North Queensland. 2. Plant nutrient status

Abstract: The nutrient status of the deep siliceous sands which cover an extensive area in Cape York Peninsula has been studied in glasshouse and field experiments. Using Townsville stylo (Stylosanthes humilis) as a test legume, the soils were found to be extremely deficient in P and S, and moderately so in Zn, Cu, and K. Responses to Mo were found on most of the eight soils tested in the glasshouse but these were not confirmed at the field site in either of the two growing seasons. There was little response to Ca (lime) in spite of the very low levels of total and exchangeable Ca in these soils. Suggested reasons for this are the known tolerance of tropical legumes to low Ca supply and the fact that exchangeable Ca, although low, represented a fairly high percentage of the total exchange capacity. Levels of total N in these soils were also very low and the native grasses were able to absorb only 15 kg N ha-1 in an entire growing season. Two samples of rock phosphate (from north-western Queensland and Christmas Island) were found to be very poor alternatives to superphosphate, at least in the first season. In spite of the extreme infertility of these soils, very high levels of pasture production (> 10,000 kg of Townsville sty10 ha-1) could be achieved in well-fertilized pastures.

Effect of herbaceous vegetation on survival and growth of trees planted on coal-mine spoils

Abstract: Establishing both trees and herbaceous vegetation is often desirable in the reclamation of strip-mine spoil banks. To study the effect of herbaceous competition with trees, grass alone and grass with legumes were sown concurrently with the planting of four tree species on coal-mine spoils in southeastern Kentucky. After three growing seasons, the herbaceous vegetation, which had produced about 95% ground cover, did not significantly affect the survival of trees, but greatly suppressed their growth. However, in the fourth and fifth growing seasons, the growth of trees in the plots dominated by the legume exceeded the growth in plots with grass only and without herbaceous competition. Tree growth was suppressed the most by a cover of grass alone.

Seasonal changes in the growth rate of duckweed community (Lemnetum gibbae)

Abstract: Seasonal changes in the growth rate of duckweeds—Lemna minor L. andL. gibba L. associated in the communityLemnetum gibbae (W. Koch 1954)Miyawaki etTx. 1960—were investigated at the Podzamecký fishpond at Průhonice near Praha, during the growing season of 1969. Initial and final dry weight values (W1 andW2) of selected samples of the duckweed community were assessed at weekly intervals. The relative growth rate (RGR) was calculated from the dry weight increments, and correlated with water temperature, mean air temperature and sunshine duration. A linear regression equation was fitted to describe the dependence ofRGR on these factors.

The effect of time of sowing and harvesting on growth, yield and nitrogen fertilizer requirement of sugar beet: I. Yield and nitrogen uptake at harvest

Abstract: Four field experiments (1968–71) investigated the effect of changing the length of the growing period on the nitrogen fertilizer requirement of sugar beet. The crop was sown on three occasions (March–May), harvested on three occasions (September–December) and given four amounts of fertilizer (0–225 kg N/ha). Plant samples were analysed at several stages of growth (1969–71) in an attempt to predict the amount of nitrogen fertilizer needed for maximum sugar yield and also at the end of the season to determine the nitrogen uptake. Increasing the length of the growing period increased sugar yield greatly but the amount of nitrogen fertilizer needed for maximum sugar yield was unchanged. The crop given the largest dressing of nitrogen and with the longest growing period contained most total nitrogen, but in every experiment, giving more than 75 kg N/ha neither increased nor decreased the sugar yield significantly. As a result of the small variations in nitrogen requirement, the plant analyses during the growing season were of little value in predicting the needs of the crop.

Diurnal Variations of Water in Developing Secondary Stem Tissues of Eucalypt Trees

Abstract: ZAHNER1 has stated that living cambial tissues must be under moderate to severe water stress almost daily during the growing season because of the great tensile forces which develop in the adjacent mature xylem. We have studied diurnal water variations within the developing tissues of tree stems.

Dry matter content of apical and basal portions of Russet Burbank potatoes

Abstract: Studies were made over a 4-year period of some factors affecting the dry matter content of the apical and basal portions of growing Russet Burbank potatoes. The greatest difference between portions was obtained from tubers of the normally irrigated plots of 1969. The amounts in the two portions in 1970 were nearly equal throughout the growing season. The major differences between the 2 years was a slightly cooler June and warmer maximum temperatures in July of the 1970 growing season. Moisture stress, particularly, early in the stage of tuber development (1972 season) caused a switch in amount of dry matter in the apical and; basal portions. Stress later in the development stage (1969 season) did not cause a switch. Fertility level was not as influential as moisture stress in affecting the ratio of dry matter in the two ends, whether under stress or normal moisture conditions.

Utility of a simple soil water budget model in agronomic research. 1. Effects of plant density, time of sowing and fallow water on available soil water under spring wheat

Abstract: A simple soil water budget model was used to estimate weekly changes in available soil water as affected by plant density, time of sowing and level of available fallow water for spring wheat cultivars grown on a black earth in northern New South Wales. Estimated values of available water were mostly within ±10 mm of observed values (ranging from 50-270 mm) obtained at four intervals during the growing season. The results are discussed in relation to both the interpretation of agronomic field experiments and use of the model in regions where conserved fallow water contributes significantly to cereal production.