Showing papers on "Growing season published in 1976"

Climatic patterns and the distribution of C4 grasses in North America.

Abstract: A stepwise multiple regression analysis was used in an attempt to correlate statistically the geographic patterns in the abundance of C4 grasses with patterns in climatic variables. The percent of grasses having the C4 pathway was computed for the total grass flora in twenty-seven widely spaced regions of North America. From long-term climatic records seasonal and annual values for solar irradiance, water supply, heat availability, and combinations of these variables were assigned to each of the twentyseven regions. The results of the analysis suggest that high minimum temperatures during the growing season have the strongest correlation with the relative abundance of C4 grass species in a regional flora. It appears that the deleterious effects of low temperatures during growth negate the advantages of possessing the C4 pathway in cooler habitats.

Production and dynamics of experimentally enriched salt marsh vegetation: Belowground biomass1

Abstract: Root growth increased during the early growing season in Spartina alterniflora salt marsh plots. While fertilization with nitrogenous fertilizer did not affect initial growth, a marked decrease in root biomass followed the spring peak particularly where nutrient doses were highest. A sharp reduction in roots occurred in enriched areas covered by Spartina patens, although, as with S. alterniflora, aboveground biomass increased. Roots disappeared during autumn leaving rhizomes as the only part of the plants to overwinter. The maximum standing crop for roots was 0–2 cm deep, for rhizomes 2–5 cm. Net annual underground production was calculated from annual increments in dead matter belowground. Total production, underground and aboveground, exceeds that of any marine vegetation, ranging from 3,900 to 6,600 g m‒2 yr‒1 in S. alterniflora areas and 3,200 to 6,200 g m‒2 yr‒1 in S. patens areas. Fertilization increased production particularly aboveground where dead plant parts are subject to export.

Phosphate absorption: adaptation of tundra graminoids to a low temperature, low phosphorus environment

Abstract: Seasonal changes in phosphate absorption rate were examined in three tundra graminoids growing under natural field conditions and in experimentally heated soils in the field at Barrow, Alaska. Although tundra plants exhibited a high optimum temperature for phosphate absorption similar to that of temperate plants, rates were relatively insensitive to short-term temperature change, suggesting that tundra plants routinely absorb phosphate from cold soil and do not depend upon daily or seasonal increases in soil temperature for phosphate acquisition. Variation in the calculated seasonal course of phosphate absorption resulted more from change in phosphate availability and phosphate status than from temperature acclimation. Absorption capacity was highest early in the growing season when root growth began and then decreased to a level which was maintained well into September, long after aboveground plant parts had senesced. Nearly half of the phosphate acquired by the plants investigated was probably acquired after shoots had begun a net translocation of nutrients belowground for winter storage. Plants acclimatized to a warm, anaerobic, nitrogenrich soil had a higher capacity for phosphate absorption but a lower affinity for phosphate than did control plants growing in cold soil. The applicability of laboratory-derived concepts of nutrient absorption to the seasonal dynamics of these processes in the field is discussed.

Production ecology ofPhragmites communis 1. Relations of two ecotypes to the microclimate and nutrient conditions of habitat

Abstract: The growth rate of stand biomass, the seasonal development of vertical stand structure and accumulation of mineral nutrients were compared in twoPhrogmites ecotypes; the stands occur in two different biotopes, littoral and limosal, situated in the littoral of the Opatovický fishpond in the South Bohemian fishpond basin. Microclimatological data including incoming global radiation were recorded in both biotopes during three growing seasons. The differences in morphological, chemical and production characteristics of the two reed ecotypes were in good relation with the edaphic, hydrochemical and microclimatological characteristics of their biotopes. These differences are reflected in a higher leaf area index, denser stand, higher production parameters and a higher efficiency in the conversion of solar energy in the limosal reed ecotype as compared with the littoral population. The differences in annual production and in energy conversion have not changed within seven growing seasons.

Phenological Pattern in the Shortgrass Prairie

Abstract: Data were collected for 1 year on 34 range plant species and for 2 years on six species to describe phenological timing in the shortgrass prairie of northeastern Colorado and also to determine whether there were any distinct groups of plants for which a single species could be used as a phenological indicator. Observations were made in four grazing treatments and two water amendment areas (one with 100 kg/ha mineral N ad'ded). Water amendments altered the phenology of some species, while grazing and nitrogen treatments had no measurable effects on phenology. Standard cooland warm-season classification of plants does not adequately describe the phenological dynamics of the shortgrass prairie. For example, Buchloe dactyloides, a warm-season grass, flowers with Agropyron smithii, a cool-season grass, rather than with Bouteloua gracilis, another warm-season grass. Four general categories of plants having different flowering capacities are recognized: blooming only once very early in the growing season; blooming twice with a summer dormancy period; blooming once during midsummer with blooming delayed during drought; and blooming only once late in the growing season. INTRODUCTION An understanding of phenological progression of plants is basic to understanding the functioning of a grassland ecosystem and is important in sound resource management (Costello, 1939; Lieth and Radford, 1971). Phenology is associated with plant growth rates (Taylor, 1972), nutrient transfer (Sosebee and Wiebe, 1973), thermal requirements (Nuttonson, 1955), plant-water relationships (Blaisdell, 1958) and perhaps even evolutionary change (Leopold, 1961). The objectives of this study were: (1) to describe the phenological progression of a broad spectrum of shortgrass prairie species; (2) to develop an approach for monitoring the phenological progress of the shortgrass prairie plant community by observing a few indicator species, and (3) to compare water treatment and annual weather variation effects as well as any observable differences in phenological state between grazing treatments or fertilization. These measurements, when combined with abiotic and other biotic measurements, will lead to a clearer understanding of the structure and function of the shortgrass prairie ecosystem. SiTE DESCRIPTION The Pawnee Site (intensive research site of the US/IBP Grassland Biome) ig located on the western edge of the USDA Central Plains Experimental Range, approximately 12 km N of Nunn, Colorado, at an elevation of 1652 m. Topography is gentle rolling plains. The major soil types are Ascalon, Vona, Renohill and Shingle, with Ascalon predominating on the sampling areas (Reuss, 1971). Annual precipitation varies from 254 to 381 mm, about 80% occurring from May to

Dynamics of the Root System of Blue Grama

Abstract: Highlight: Field experiments were conducted to determine dynamics of the root system of blue grama (Bouteloua gracilis) during the 19 73 growing season at the US/IBP Pawnee Site in northern Colorado. Differentiation and growth of blue grama roots were recorded in field conditions by means of windows in excavations. Roots began to grow and differentiate a short time before leaf growth was apparent. Desiccation of soil in the mid-growing season resulted in death and subsequent decomposition of 30% to 60% of the newly formed roots., Massive root growth occurred when soil water potential was high near the end of the growing season. Roots were separated into morphological categories by microscopic analysis of soil samples on May 15, near the beginning of the growing season, and on August 9, near the end of it. Young nonsuberized roots, so important in water absorption, were concentrated in regions of the soil profile where soil water potential was high. An empirical model of root growth and development in B.

Plant Standing Crop and Productivity Relations in a Scirpus-Equisetum Wetland

Abstract: Plant standing crop and productivity relations were examined for an extensive marsh complex in southern Quebec, Canada. Forty—five 1—m2 plots were sampled for dry weight shoot biomass, species composition, structure (species density, diversity, height), and soil parameters including nutrient concentrations. (Ca, K, Mg, Na, N, P), pH, organic matter, and water depth. Shoot net productivity and decomposition rates were computed for 20—day intervals across the growing season. Relationships between all parameters were examined by principal components analysis. Dominant emergent species included Scirpus fluviatilis, Equisetum fluviatile, Scirpus validus, Phragmites communis, and Eleocharis palustris. For a 150—day interval, shoot net productivity averaged 6.10 g·m(—2) · day(—1) and terminal standing crop was 845 g/m2. Seasonal productivity showed a strong bimodal pattern with peaks in late July (12.90 g°m(—2) · day(—1) and midSeptember 4.73 g°m(—2) · day(—1). Species typical of deep water showed much earlier and higher peak productivity than this general pattern but net shoot productivity as of short duration. Two—thirds of annual litter production was lost by export. Complete decomposition of remaining litter occurred within the next growing season. Temperature and decomposition rate maxima coincided with peak productivity in July and decreased exponentially through October. Among edaphic parameters, soil K had the highest correlation (r = 0.49**) with standing crop while soil N had the highest correlation with shoot net primary production (r = 0.39**). Soil P correlated negatively with all production and soil nutrient parameters except soil Mg levels. It was the only nutrient with a soil concentration maximum in shallow water. Other nutrients attained maximum levels at an intermediate point on the water depth gradient. Maximum litter standing crop occurred at this point, coinciding closely with changes in soil cation levels. While shoot density and standing crop followed these trends, they coincided more closely with changes in soil anion concentrations (nitrogen, hydrogen). Sedimentation and nutrient uptake associated with high stem density and standing crop were shown to be important factors in site enrichment. Shoot net primary productivity and standing crop correlated negatively with all measures of species diversity. Variety and equitability decreased from 8.00 species and 0.96 bits/m2 in Scirpus validus stands of deep water to 2.00 species and .01 bits/m2 in shallow stands of S. fluviatilis. Sparse canopy cover and high levels of disturbance in S. validus stands made possible the coexistence of a rich variety of aquatic life forms not possible under conditions of intense competition typical of S. fluviatilis.

Soil bacterial changes as affected by growing season weather conditions: a field and laboratory study

Abstract: During the 1972 and 1974 growing season, soil bacteria, actinomycetes, moisture and temperature in the top 15 cm of a Wood Mountain loam were monitored regularly under sheltered and unsheltered summer-fallow and cropped conditions. The 1972 temperatures and rainfall were later simulated in the laboratory and their effects on the bacterial population in the Wood Mountain loam, a Sceptre heavy clay, and a Melfort silty clay loam determined. Multiple regression was used to quantify the relationships between the different microbial populations and several selected environmental variables. Microbial change was generally directly proportional to moisture change, the latter being the main factor influencing response. The effect of moisture change was usually dependent on the temperature and/or the initial moisture content prior to the change. Soil microbial populations increased in response to both increases and decreases in temperature. The inverse relationship with temperature appeared to be the result of the ...

Angiosperm production of three Virginia marshes in various salinity and soil nutrient regimes

Abstract: The net aerial angiosperm productivity, salinity, and soil nutrient composition of three Virginia marshes were determined. Oligohaline Ware Creek Marsh and mesohaline Carter Creek Marsh were most productive, 563 and 572 g m−2yr−1, respectively, while euhaline Wachapreague Marsh was least productive, 362 g m−2yr−1. Species in Carter and Ware Creek Marshes were clustered into associations based on salinity tolerance. Nitrogen and phosphorus concentrations ofSpartina alterniflora tissue were high in the spring and decreased as the growing season continued. Soil nutrient concentrations were variable, and trends during the growing season were not discernible. No significant correlations were found between soil and plant nutrient concentrations. Although the empirical data suggests that high soil salinity and low soil nitrogen and phosphorus concentrations limited primary productivity in Wachapreague Marsh, a multiple regression of standing crop on these parameters did not delineate any as the primary factors limiting salt marsh production.

Nutrient turnover studies in alpine ecosystems : I. Phytomass and nutrient relations in four mat communities of the Northern Calcareous Alps.

Abstract: Four plots of alpine meadow communities (mats) of the Northern Calcareous Alps are compared with regard to dry substance (DS), N-, P-, and K-content of living and dead overground and total underground phytomass. The Caricetum firmae F (altitude 2,010 m) produces the least green mass but accumulates the highest amount of dead substance (litter). In all parts it has the lowest content of N, P, K. The opposite is the Caricetum ferrugineae C (1,900 m): Small dead mass, but high production of green mass and high content of N and K in the living overground and total underground phytomass. The Nardetum N (1,930 m) is marked by relatively high amounts of P in living and dead parts. The Seslerio-Semperviretum S (2,150 m) is intermediate but with rather low contents of K.In each plot the average total nitrogen found in the underground phytomass is about 200% of the amount found in the living overground phytomass. This suggests a similar relation of living mass in the two components of the total phytomass.The fluctuations in the phytomass throughout the growing season are represented for S. The green mass increase is about 200g DS with about 3 g N/m2. This amount corresponds to the average mineralization supply of N during the growing season as obtained by the field incubation method (3.3 g/m2, in 0-15 cm depth of the soil). In C the average mineralization is lower whereas the green mass production amounts to 300 g DS/m2 with 5.5 g N/m2. This discrepancy supports again our hypothesis of an "internal nitrogen cycle" in the Carex ferruginea community. In F and N we find a lower incorporation of N into the annual green mass production compared with the N mineralized in the upper soil layers (Table 1).Lactate-soluble P and K were as a rule not accumulated in our soil incubation tests. The actual values and their amplitude during the growing season scarcely coincide with the differences of P and K in the green mass.

Patterns of leaf resistance to lodgepole pine transpiration in wyoming

Abstract: Leaf resistance (r_L) of lodgepole pine (Pinus contorta ssp. latifolia [Engelm. ex Wats] Critchfield) was measured with an aspirated porometer at three sites in the Medicine Bow Mountains, Wyoming. In the early part of the growing season all the sites had low leaf resistances (3—5 s/cm) and few significant changes in r_L during the day. Towards the end of the growing season, in August, significant increases in midday leaf resistance occurred at all sites. The greatest increase (to 57 s/cm) was found on the driest site. Smaller increases (to 10—14 s/cm) were measured at a dry—mesic site and a mesic site. The results indicate that stomatal control of transpiration is more important towards the end of the growing season and that the degree of control varies with the soil water regime of the site. The response of r_L to soil H_2O status appears to be nonlinear. When based pressure potential readings were above an upper threshold ( -9 bars) r_L did not increase during the day. Below a lower threshold ( -17 bars) r_L increased significantly. Between the two thresholds, changes in r_L under high light conditions are explained more readily by the interaction between vapor pressure deficit and soil H_2O status than by either factor alone.

A Comparison of Seasonal Primary Production of Mojave Desert Shrubs During Wet and Dry Years

Abstract: Estimates of net primary productivity were made for five major shrub species in the northern Mojave Desert during 2 years of contrasting moisture regimes using harvest and gas exchange techniques. Production increased by 224% (harvest) to 260% (gas exchange) in 1973 over 1972. Production gains varied among species depending on whether the species was favored by the cool, moist spring of 1973. Lycium andersonii and L. pallidum, which have high photosynthetic rates and start growth in the early spring, showed the greatest increases. Larrea tridentata and Krameria parvifolia, species adapted to growing under warmer, drier conditions, exhibited the smallest changes in production. Ambrosia dumosa, which has high photosynthetic rates but responds more favorably to warmer spring temperatures than the Lycium species, had moderate production gains. Reasons for the different estimates obtained by these two methods are discussed. INTRODUCTION The determination of primary productivity in terrestrial ecosystems is a necessary but difficult step in providing information on the basic. energy or carbon input into biological systems. Productivity estimates are important for predictive models of a general nature in ecosystem analysis. In general, two methods have been used for net primary production estimates. The first method is a direct harvest technique in which whole plants or samples are clipped throughout the growing season, dried and weighed, and productivity calculated on dry weight per unit area. The second method involves measuring the total CO2 or carbon exchange per weight of photosynthetic organs, and calculating productivity as carbon or biomass fixed minus respiratory losses. There have been several measurements of net primary production and biomass in deserts made by the harvest and other methods (Burk and Dick-Peddie, 1973; Chew and Chew, 1965; Pearson, 1965; Rodin and Bazilevich, 1967). Measurements of CO2 exchange rates in desert plants have been made in the Negev Desert (Lange et al., 1969) and in the North American deserts (Bamberg et al., 1975; Caldwell, 1972; Patten and Dinger, 1969; Strain, 1969, 1970; Strain and Chase, 1966). Attempts at relating some of these gas exchange rates to production are only now being done. The US/IBP Desert Biome is currently obtaining production estimates from several sites in the western United States. 1 Present address: EG&G Environmental Consultants, 9025 E. Kenyon Avenue, Denver, Colorado 80237. 2 Present address: University of Idaho, Research and Extension Center, Route 1, Kimberly, Idaho 83341.

An empirical model of net photosynthesis for the desert plant Hammada scoparia (Pomel) Iljin

Abstract: An empirical model for describing daily courses of net photosynthesis in Hammada scoparia is being developed. The model is based on the functional relationships, by which various environmental factors affect the photosynthetic activity and which can be measured by experiment in the field. In a sequence of steady-states daily courses of net photosynthesis are predicted during a growing season considering the variability of the physiological states and the capacity for regulative adaptations. The rate of net photosynthesis at a certain date is calculated from the maximal rate of CO2 uptake being expected at that season and from the effects of light, temperature, and air humidity which are scaled from 0 to 1. All factors are connected multiplicatively. The light function accounts for the seasonal changes in the light curve, the temperature function is based on the seasonal shift of the temperature optimum, and the humidity function considers the increasing sensitivity of the stomatal humidity response at increasing water stress. The model is built to be a submodel of a general ecosystem model, where various other submodels (i.e. water stress model, phenology model) are supplied. The present model is tested by predicting daily courses at extreme climatic conditions during the year and by comparing the predicted values of gas exchange with values being measured in an independent experimental procedure. The result shows that the model is able to simulate the natural behaviour of Hammada scoparia during the growing and dry season of a desert habitat. The problems of incorporating the influence of water stress, the interaction of the various factors, and the phenological aspect of the photosynthetic activity is being discussed.

Photosynthate Distribution in Natural Stands of Salt Water Cordgrass1

Abstract: Spartina alterniflora Loisel. is a major grass species of Atlantic coast tidal marshes which contributes heavily to the primary productivity of estuarine ecosystems. As human activity increases in marsh areas, the capability of marsh vegetation to withstand disturbance must be understood and constitute the basis for formulating sound management programs. Toward this end, the seasonal distribution of photoassimilated carbon was studied in S. alterniflora growing under natural conditions. Single culms were exposed to ¹⁴CO₂ at various times during the 1970 and 1971 growing seasons. Plants were harvested 1, 3, and 7 days following exposure to ¹⁴CO₂. subdivided into leaves, culm, rhizomes, and roots; and each portion assayed for ¹⁴C. Assimilate translocation reached a more or less stable distribution pattern within 24 hours. Throughout much of the growing season, most photosynthate was retained in leaf and culm tissue with less than 10% translocated to roots and rhizomes. Only during early autumn was substantial photosynthate translocated into rhizomes. This and seasonal carbohydrate levels within perennial organs indicate that the stability of S. alterniflora stands may be adversely affected by summer disturbance especially defoliation.

Element composition of ryegrass and red clover leaves during a growing season

Abstract: Young ryegrass and red clover leaf blades from clipped swards were sampled for mineral analysis throughout a growing season Only calcium and phosphorus concentrations in ryegrass varied seasonally In red clover during the spring, magnesium levels were lower and nitrogen levels were higher than those in the rest of the growing season The concentrations of Mg, N, K, Fe, Mn, Zn, and Cu did not change seasonally in young ryegrass leaves and none of the elements determined in young leaf blades of red clover showed a seasonal trend

Nutrient turnover studies in Alpine ecosystems : II. Phytomass and nutrient relations in the Caricetum firmae.

Abstract: 1. A plot of the Caricetum firmae in the Northern Calcareous Alps (at 2,160 m above sea level) was investigated during the growing season 1973 with regard to dry matter, nitrogen, phosphorus, and potassium content of overground and underground phytomass, including accumulated litter. 2. Compared to another habitat of the same community at 2,010 m a.s.l., the overground phytomass in the state of maximum development (ca.250 g per m2) and the store of nutrients (4 g N, 0.25 g P and 2.4 g K per m2) are nealy, the same, but the primary production is less (ca. 100 g as against ca. 160 g per m2). 3. The accumulation of litter in relation to the annual overground production is nearly 30:1. 4. The content of N, P, and K in the predominant species Carex firma and Dryas octopetala ranks near the inferior limit known for terrestrial plants. The minimum values are attained in the state of maximum development (mid-August). 5. The mineralization of N amounts to about 2 g per m2 during the growing season and thus exceeds the quantity that enters into the overground production. The maximum mineralization is found 5 to 10 cm under the soil surface. In this layer most of the fine roots are concentrated. 6. The lactate-soluble content of P and K in the soil averages ca. 0.3 or 1.5 per m2 and decreases from the beginning to the height of the growing season by ca. 0.35 or 0.5 g per m2 with a slight increase toward the end. In the field incubation experiments losses of P and K, interpreted as microbial incorporation, prevailed during the growing season. It was hardly possible to determine evident relations between the fluctuations of P and K in the soil and those in the phytomass. 7. The Caricetum firmae ranks between the "typical arctic tundra" and the "dwarf-shrub tundra" with regard to the obtained data on phytomass, primary production, and nutrients, except for the underground production which seems to be remarkably higher.

Shortening of growing season in the US corn belt

Abstract: I ATTEMPT here to relate the gradual and oscillatory temperature drop in the Northern Hemisphere to a shortening of the length of the growing season in the US corn belt.

Vegetation Death and Its Importance in Primary Production Measurements

Abstract: Annual net aerial primary production (NAPP) was determined by two methods on two abandoned pastures of contrasting vegetation composition in southern Ontario, Canada. Summing the maximum biomass of each individual species gave NAPP values, 84% and 49% respectively, of those obtained when indirect determinations of vegetation death were made during the growing season as well as changes in standing crop of live material.

Field experiments with simulated acid rain in forest ecosystems. I. Soil and vegetation characteristics, experimental design and equipment

Abstract: Effects of simulated acid rain on tree growth, ground cover vegetation and on chemical and biological properties of the soil are studied at two sites in Southern Norway. The experiments are established in young plantations of Norway Spruce, Lodgepole pine, Scots pine and birch, and also in a mature stand of Scots pine. Field plot size ranges from 15 to 625 m/sup 2/ and the number of replicates from 3 to 10. During the growing season 25 or 50 mm/month of simulated rain is applied. Rain with pH levels ranging from 6 to 2 is obtained by adding sulphuric acid to well water. Unwatered and limed plots are included in the experiments. Most irrigation equipment has been specially constructed.

The temperature of the soil under a barley crop

Abstract: Summary Continuous records of soil temperature were collected at 1, 5, and 20 cm depth, throughout the growing season, under crops of barley in the east of Scotland. The values obtained were considerably lower than the temperatures normally employed in laboratory studies of temperate cereal roots. The resulting hazards in extrapolating from the laboratory to the field are briefly discussed.

A Revised Method for Determining Phosphate-Phosphorus Levels in Sugarbeet Leaf Petioles

Abstract: Knowledge of plant nutrient status during the growing season can be valuable. Early detection of a deficiency sometimes allows it to be correc­ ted that same growing season. Plant analysis also aids in planning the fer­ tilization program the following year. Johnson and Ulrich (4)3 developed a test to determine the status of P in the growing sugar beet. They found that the amount of acetic acid soluble PO; in the leaf petiole material provided a reliable measure of P status . They have established that a concentration of 750 ppm PO; -P repre­ sents the "critical level. "

A phytosociological study of weed communities on the southwestern Coastal Plain of North Carolina

Abstract: The vegetation of cultivated, fallow and ‘old’ fields of Scotland County, N.C. was both randomly and subjectively sampled throughout the growing season of 1973. Releves were placed in each of the above management units, and the data collected in this releve analysis were sorted into phytosociological charts, with the aid of the digital computer.

Nutrient concentration of corn as effected by poultry manure

Abstract: The elemental composition of corn was evaluated during the 1973 growing season in an experiment with various rates of poultry manure. In general, the nutrient concentration of plant tissue reflected poultry manure applications with the exception of Mg which declined and Ca, Fe and Na which appeared to be largely unaffected. The elemental concentrations in the corn tissue were not in a toxic range however, the nutrient balance was changed by poultry manure application. Sampling of corn early in the growing season can be quite valuable with respect to predicting nutrient concentration of more mature corn for Mg, Mn, B and Zn, but it leaves much to be desired for the other elements tested.

Effect of Temperature and Depth of Burial on the Persistence of Seed of Avena fatua L. In Western Australia

Abstract: Two wild species of Avena predominate in the temperate south-west region of Western Australia; A. fatua L. is a major weed of cereal crops, while A. barbata Pott ex Link is found mainly on vacant, undisturbed land and in pastures (Paterson 1976). These habitat preferences may be due largely to the differing seed germination characteristics of the two species (Paterson 1974). A. fatua has considerable seed dormancy; less than 4000 of each seed crop germinates with the following opening rains and a further 10-30% germinates later in the season. In contrast, almost complete germination of A. barbata occurs with the opening rains and pre-sowing cultivation virtually eliminates this species in a cereal crop. The dormancy of A. fatua seed is known to continue through the following growing season regardless of soil temperatures (Paterson 1974). Banting (1962) and Forbes (1963), in Canada and England respectively, stated that a minimum of five years of continuous pasture is required before the number of viable seeds in the soil falls to a level where resulting plants do not constitute a weed problem in a subsequent cereal crop. Thurston (1966) in England and Quail & Carter (1969) in Eastern Australia believe that a much shorter period, possibly only one to two years, is equally effective. This paper reports on a study of the long-term persistence of A. fatua in Western Australia and the effect of temperature and depth of seed burial on persistence.

Emergence, seedling development and survival of native and exotic grasses on a sandy red earth in South-Western Queensland.

Abstract: The growth and development of eight perennial grasses, from sowing until flowering, was studied in the field on a sandy red earth near Charleville, south-western Queensland. They included four species native to this soil, Thyridolepis mitchelliuna, Aristida armata, Digitaria ammophila and Monachather paradoxa, and four exotic species Cenchrus ciliuris cv. Biloela, Anthephora pubescens, Eragrostis curvula and Schmidtia bulbosa. Cenchrus ciliaris, A. pubescens and S. bulbosa emerged much more promptly than the other species and much less viable seed was left in the soil after the fist germination event. The native species tillered and flowered earlier than the exotic grasses and survived better under adverse growing conditions. Average survival at the end of the first growing season, during which good seasonal conditions pre- vailed, was 30% of the emergent seedlings. Schmidtia bulbosa performed best within the exotic group and this was associated with early tillering and earlier flowering. The exotic species needed at least a four month growing season before they flowered under field conditions compared with two months or less for the native grasses. However this disadvantage was offset somewhat by their greater dry matter yield at this stage of development.

Performance of Five Warm-season Perennial Grasses Grown in Southern Mississippi

Abstract: Increased interest in summer forage production in southern Mississippi prompted this study, comparing the performance of five perennial grasses. Plots of ‘Coastal,’ ‘Alicia,’ ‘Coastcross-1,’ and Common bermudagrass (Cynodon dactylon L. Pers.) plus ‘Pensacola’ bahiagrass (Paspalum notatum Flugge) were harvested monthly during the 1973 growing season and at 2 and 4-week intervals during 1974. Parameters measured were dry matter yield, digestible dry matter, and crude protein. Results show Alicia and Coastcross-1 bermudagrass exhibited vigorous 1st-year growth, but performance decreased during the 2nd year, especially of Alicia. Common also decreased in forage production in the 2nd year. Coastal maintained approximately the same level of growth both years, and bahiagrass increased in total yield during the second growing season.