Showing papers on "Growing season published in 1974"

Phenological Events and Their Environmental Triggers in Mojave Desert Ecosystems

Abstract: Phenological events in Mojave desert systems are triggered by heavy rains (>25 mm [1 in]) The most predictable and consequential of these is a regional rain between late September and early December This rainfall event is usually the precursor of successful vegetative and reproductive growth of shrubs the next spring, and is usually necessary for all growth phenomena of herbaceous perennials and winter annuals during the following winter and spring For most plant components in most years, the growing season is synchronized within the autumn—winter—spring period, and the relative biological success each spring is dependent upon the occurrence or failure of occurrence of events of the preceding autumn Under certain conditions rainfall during other seasons may trigger growth and reproduction of the primary producers and permit at least moderate or local successes every season The relationships are stated in a flow diagram for the rainfall and phenological events, as documented for 13 yr in the Mojave desert of southern Nevada

Stability in relation to nutrient enrichment in arthropod consumers of old-field successional ecosystems'

Abstract: Two adjacent, abandoned hayfields in central New York State were subjected to nutrient enrichment perturbation by means of a single application of 10-10-10 N, P, K fertilizer early in the growing season of 1970. Aboveground arthropod herbivores and carni- vores were monitored with respect to net productivity (dB/dt) and diversity for one growing season (1970) in the younger field (6 yr old), and for two growing seasons (1970 and 1971) in the older field (17 and 18 yr old). Sampling of arthropods was done with a gasoline- powered suction sampler between 1200 and 1600 h, twice weekly. Stability of the old-field arthropods was defined as resistance to change imposed by external (fertilizer) perturbation and was measured in terms of (1) magnitude (amplitude of deflection from ground state, (2) rate of initial response to perturbation, and (3) rate of damping or return to ground state. The degree of deflection from ground state was determined by com- paring fertilized (treated) plots with unfertilized (control) plots in each field. During the first growing season the older, more species-rich field was less stable with respect to magnitude and rate of productivity deflection than the younger, less species-rich field at both arthropod consumer levels. In addition, the magnitude of productivity deflection from ground state was lower in the carnivore level than in the herbivore trophic level. By the second growing season, the productivity of the arthropod consumers in the treated plots of the older field had not yet returned to control levels. The productivity of arthropod herbivores in the older field exhibited a relatively lower magnitude of response in 1971 than in 1970, while the arthropod carnivores in the older field exhibited a significantly greater difference from ground state in 1971 than in 1970. It was concluded that (1) the magnitude of deflection caused by the enrichment perturba- tion was decreased up the trophic levels from the herbivore to the carnivore level, (2) the rate of response to perturbation decreased up the trophic levels, and (3) although in control plots diversity increased and productivity decreased with increasing successional age for both trophic levels, stability was not positively related to either higher diversity or to increasing age in either consumer trophic level in this old-field successional ecosystem.

Carbon dioxide evolution from virgin and cultivated soil as affected by management practices and climate

Abstract: Soil respiration during the growing season was calculated from CO2 profiles in a heavy clay soil under native grass and on cultivated plots. Soil respiration of the native grass plots was correlated with moisture content and temperature of the surface soil. However, the correlation accounted for only ⅓ of the observed variation in soil respiration and could not explain the large difference between two growing seasons. Addition of mineral N decreased soil respiration and irrigation increased it. Total soil respiration on the cultivated plots was higher than on the native grassland. On the wheat plots, soil respiration was significantly correlated with soil moisture but not with temperature; the reverse was true for the fallowed plots. Soil respiration between 1 May and 1 September on the native grassland was highly correlated with rainfall and the number of days with rain in excess of 5 mm. It was concluded that the number of wetting and drying cycles in the soil was mainly responsible for the annual varia...

The natural regulation of buffalo populations in East Africa: The food supply as a regulating factor, and competition*

Abstract: Summary Evidence is presented to show that both the quality and quantity of food available to a buffalo population falls below the minimum maintenance requirements of that population at certain times of the year. In the Serengeti grasslands there was a shortage of the only good quality component, grass leaf, in the dry season, with the result that the animals consumed an increasing proportion of poor quality food such as grass stem. By the end of the dry season the diet had dropped in quality below the minimum maintenance level. In areas such as Mt. Meru where there was a more continuous growing season, the high density of animals kept the standing crop of leaf at a low level. During the cooler dry season the growth of leaf became insufficient in quantity for the maintenance requirements of the population. These two quite different situations suggested that food shortage was a more general phenomenon in eastern Africa. Various measurements of feeding behaviour were made. Total grazing time per 24 h did not differ between seasons but ruminating time may have increased as the season became drier and could have been a response to the more fibrous food. Analysis for cycles of activity showed that there was more temporal organization during the dry season. These changes in activity cycles appeared to be related to the increase in energy expenditure produced by heat stress and sweating. Old animals with poor teeth did not compensate for the poor food supply by changing their feeding behaviour. There was a positive relationship between annual rainfall and mean crude density in different areas of eastern Africa, indicating that regulation was taking place. Since rainfall determined the amount of available food, it could have operated through the food supply. On a finer scale it was found that the extent of the preferred riverine habitats was also related to density. Thus rainfall, the extent of riverine habitat and perhaps soil moisture were three limiting factors that determined mean density and all could have taken effect through the food supply. As a result of initial selective grazing the amount of available leaf declined as the dry season progressed to the extent that by the end of the season the proportion of this component in the diet fell to a very low level. The impact of the population on its limited food supply indicated that intra-specific competition was acting as the cause of regulation. Measurements of wildebeest eating the same food in the same habitats as buffalo showed that inter-specific competition was also taking place. A small proportion (7“) of the wildebeest population could have reduced the buffalo population by approximately 18o,‘, from its potential population size. The buffalo population in the Serengeti was regulated by adult mortality which was caused by undernutrition as a result of food shortage. This food shortage was caused by intra- and inter-specific competition. The effect of predation and disease was to hasten the response of the population to changes in the food supply. The limiting factors determining the mean level of the available food were, amongst others, rainfall, soil moisture and the extent of the preferred riverine habitat. The effect of interspecific competition could result in a complex regulation of populations through their food supply. There appears to be no foundation for hypotheses which invoke over-utilization or damage as a consequence of regulation through food.

High-alpine environments and primary production on the Rock and Pillar Range, Central Otago, New Zealand

Abstract: Cushion and herbfield communities, characteristic of the Central Otago high-alpine zone, are subjected to severe environments : persistent strong winds, low air and soil temperatures with many freeze-thaw cycles during the 5-month growing season, and moist frost-active soils. Sites in herbfield experience somewhat higher temperatures and lighter winds, and have deeper soils with greater profile development and higher organic content than cushion sites. Compared with alpine communities of similar physiognomy from the Northern Hemisphere, the snow-free season is very long, about 6 months, and plants grow, at least intermittently, throughout much of this period. Annual net above-ground production of herbfield (208–255 g m−2) is about twice that of cushion vegetation (126 g m−2) where very high stem densities compensate for the extremely small production of individual stems. Annual productivity is somewhat higher than for many physiognomically similar communities overseas but the longer growing seaso...

Functions to Predict Optimal Irrigation Programs

Abstract: Davis, Calif., programming dates and depths of irrigations are based on comparison of the estimated sequence of maximum evapotranspiration rates (ET m a x rates) throughout the season with the sequence of actual ET rates expected if no irrigation is given. The difference constitutes an expected sequence of ET deficits which carefully programmed irrigations may alleviate fully or in part. ET m a x depend on the sequence of leaf canopy development and on evaporative conditions at the site being planned for. ET actual rates (unirrigated) depend on the sequence of root system development, available soil water in storage at planting time, and growing season rainfall. Time relationships of corn leaf canopy and root system development researched at Davis, Calif., are combined with irrigation planning site measurements of climate, soil, and soil water content to estimate the sequence of ET deficits. Measurement of actual irrigation operational efficiency completes the needed information.

Belowground productivity of two cool desert communities.

Abstract: A new technique based upon the dilution of C 14 /C 12 ratios in structural carbon of root systems during the course of the growing season was used to evaluate belowground turnover or productivity of two cool desert communities in northern Utah, USA. This technique provides a measure of turnover of the root system of established perennial plant communities avoiding many of the disadvantages of other techniques. Adjacent communities dominated by Atriplex confertifolia and Ceratoides lanata both exhibited belowground productivity values exceeding aboveground production by three-fold. The greater belowground turnover of the Atriplex-dominated community may be a factor contributing to the maintenance of a greater quantity of aboveground biomass and prolonged periods of active photosynthesis during the driest portions of the year when Ceratoides becomes largely photosynthetically inactive.

Seasonal changes in the productivity, caloric content, and chemical composition of a population of salt-marsh cord-grass (Spartina alterniflora)

Abstract: During the 1972 growing season, the productivity of a short form and a tall form ofSpartina alterniflora was studied by the harvest method in the vicinity of the Rutgers Marine Sciences Center on Great Bay near Tuckerton, New Jersey. The aboveground biomass of living and dead grass was determined and subsamples were analyzed for caloric equivalents, ash, nitrogen, crude protein, crude fiber, ether extract, and nitrogen free extract. S. alterniflora had peak standing crops of 1,592 g/m2 for tall form and 592 g/m2 for short form. Standing crops of crude fiber, ether extract, nitrogen free extract, and caloric values are a function of dry matter production while nitrogen components seem to be influenced by some other factor. Seventy percent of the crude protein was present in early summer at a time when dry weight was less than 50% of its maximum value. The data indicate that the amount of nitrogen that the plant accumulates in its aboveground parts early in the growing season is directly related to the peak of dry matter standing crop. The early spring accumulation of nitrogen may act to offset shortages at the peak of the growing season. The chemical composition of litter and soil samples suggests that biological breakdown of plant material occurs at the soil surface.

Primary production and life history of Carex lacustris

Abstract: Seasonal changes in aboveground and belowground standing crop and primary production in a Carex lacustris wetland were determined and related to the basic life history of this species. There was a seasonal minimum of 180 g/m2 green material aboveground frozen in the ice in winter and a maximum of 1037 g/m2 in summer (early August). Seasonal aboveground production based on quadrat data and based on the difference between maximum and minimum standing crop is estimated to be 857 g/m2 per year, maximum daily production 15 g/m2 per day. A second estimate, also based on quadrat data but taking into account the very high shoot mortality during the growing season, was determined. Seasonal aboveground production then is 1580 g/m2 per year, maximum daily production is 20.3 g/m2 per day. Belowground standing crop was 387 g/m2 in winter but then declined to an average summer low of 226 g/m2. Belowground standing crop increased during autumn and, by October 7, a value equal to the previous winter's value was reached. ...

Propagation of smooth cordgrass, Spartina alterniflora , from seed in North Carolina

Abstract: Spartina alterniflora Loisel, produces large quantities of viable seed, particularly when stands are vigorous and relatively young. Excellent germination occurred when seeds were harvested as near the shattering stage as possible, stored in burlap sheets at 2–3 C for 1 month, and submerged in estuarine or sea water at 2–3 C until seeding the following spring. Direct seeding from April until early June is an effective method of establishing new stands ofS. alterniflora on dredge spoil in protected areas. The elevational range over which seedlings can be expected to survive is limited to the upper 20–50% of that occupied by natural stands in a given area. Complete cover is achieved the first growing season and the above-ground standing crop produced from seed in one growing season can exceed that produced from transplants and may approach that of long-established marshes.

The relationship between standing crop in sedge meadows and summer temperature

Abstract: A major focus of ecology today, as indicated by the activities of the International Biological Program, is upon various aspects of ecosystem productivity. In order that productivity may be estimated over broader areas than can be encompassed by direct measurement, it is desirable that indirect methods (cf. Lieth 1965) be devised whereby easily measured environmental variables can be used to predict either productivity itself, or quantities such as standing crop which, for unexploited vegetation of similar life form, are closely related to productivity. Brylinsky & Mann (1973) have shown recently that energy-related variables, particularly mean air temperature, length of growing season, and latitude, are excellent global predictors of freshwater phytoplankton productivity, which itself is highly correlated with phytoplankton biomass. Bray & Gorham (1964) have likewise demonstrated a strong correlation between worldwide forest litterfall, a reflection of forest productivity, and latitude, which integrates the influence of insolation, temperature, and length of growing season. The sedge meadows with which this paper deals are of much less importance than forests and freshwaters, but they do constitute a common feature of northern and midlatitude landscapes. Hence it is of value to point out that the magnitude of their standing crop, measured over a wide range of habitats, is closely related to summer temperature. This energy-related environmental variable may therefore be used in broad-scale studies to estimate approximate standing crops for sedge meadows where actual data are lacking but where data for monthly mean temperatures are readily available.

Distribution of photo-assimilated 14 carbon in the root system of a shortgrass priarie

Abstract: Shortgrass prairie plots (0· 5 m 2 ) dominated by Bouteloua gracilis were labelled by liberating 14CO 2 from a Na 2 14 CO 3 solution inside polyethylene tents on 26 May, 12 July, and 13 September 1972. Three days after labelling, roots were sampled to a depth of 60 cm in 5-cm segments. Functional and non-functional roots were separated through autoradiography. Functional roots were combusted in a micro-bomb, and the CO 2 released was absorbed in alkali. An aliquot of this solution was radio-assayed in a liquid scintillation counter in order to assess the specific activity of roots of different depths at different times in the growing season. About 62% of the roots receive the label, and there is an indication that with the advance of the growing season there is increasingly more storage of assimilates in the roots of upper depths. The roots of deeper layers are mostly replenished during the early part of the growing season.

Natural Selection at the Enzyme Level

Abstract: Population samples of the broad-leaved cattail (Typha latifolia L.) from different types of climate could be ordered by three properties of malate dehydrogenase in a pattern clearly related to climatic origin. The three properties measured are activation energy, thermostability, and activity level. Populations are differentiated into three groups by ordination: (1) populations from long growing season, maritime sites, (2) populations from summer hot, continental sites, and (8) populations from short growing season, montane sites.

Variation in Australian and European Collections of Trifolium glomeratum L. and the Provisional Distribution of the Species in Southern Australia

Abstract: Seventy-four lines of Trifolium glomeratum L. from a wide range of Australian and European environments were grown in a glasshouse at Canberra. Time to flower, growth habit, leaf markings, stipule colour, floret colour and dry matter production varied among collections, and within some lines. Numbers of flowers per plant, leaf: stem ratio, and dry matter yields were correlated with days to flower. The variation within the European collection was similar to that within the Australian collection. Time of flowering has probably been important in natural selection in this species, since the date of flowering at Canberra was strongly correlated with date of the end of the growing season (defined by effective rainfall) at the collection site of each ecotype. A survey during 1970 through New South Wales, Victoria and South Australia showed the western limit of spread of T. glomeratum to be through Garah, Burren Junction, Coonamble, Euabalong,Booligal, Moulamein, Beulah, Lake Hindmarsh, Mannum and Jamestown. Extrapolation of climatic restrictions to Western Australia indicated that the species could exist west of Lake Biddy, and possibly north and east to Geraldton and Esperance. The distribution appears to be controlled by the shortest length of growing season in which the species can germinate, grow, and set viable seed.

Effect of Plant-Available Stored Soil Moisture on Corn Yields. I. Constant Climatic Conditions1

Abstract: Agronomists have long been interested in how variation in soils and climate are related to crop yields. An experiment was conducted to quantify the effect of weekly plant available stored soil moisture (PASSM) during 10 weeks of the growing season on corn (Zea mays L.) yield under constant and variable climatic conditions. The objective of this study was to determine how soils, varying in the amount of water supplied to corn, affect corn yield under constant climatic conditions. Plot yields from four Illinois locations (farms) for 3 years (1969–1971) were correlated with weekly PASSM, rooting depth, and available water-holding capacity in the rooting zone. Experimental plots had high fertility and management levels. Approximately six sites to various depths to a root-restricting glacial till or natric horizon, giving a wide range in independent variables, were established at each location. The PASSM values were calculated from weekly gravimetric moisture samples that were adjusted for rooting depth, bulk density, and 1/3 and 15 bar water retentions. The PASSM values were summed by a method similar to Fisher's polynomial technique as previously modified. The average R² value of quadratic regression calculated for each year location was 58%. Above average PASSM was most beneficial either during tasseling or grain-filling stages depending on the season. Quadratic regressions for each year-location were calculated using rooting depth and available water-holding capacity instead of weekly PASSM as the treatment variable, with average R² values of 73 and 71%, respectively. The effect of each centimeter of rooting depth or available water-holding capacity, as estimated from linear regression coefficients, varied considerably with the favorableness of the season. The lower precision of the weekly PASSM models, when compared with the rooting depth and available water-holding capacity models was due to weekly sampling variation and possibly water movement above and below the soil surface. It was concluded that with adequate fertility and a high level of management, the potential of a soil to produce corn was largely determined by the soil's capacity to store and supply water.

The epidemiology of common root rot in Manitou wheat: disease progression during the growing season

Abstract: Common root rot in Triticum aestivum cultivar Manitou caused primarily by Cochliobolus sativus was followed during plant development in 1969, 1970, and 1971 at Matador, Saskatchewan. Plants were sa...

Effects of growing season soil temperature, moisture, and nh4-n on soil nitrogen

Abstract: Wood Mountain loam was wetted with water or (NH4)2SO4 solution to provide a factorial combination among three moisture and three NH4-N levels. Samples in polyethylene bags were incubated at 2.5-cm depths in fallow, and in an incubator that simulated the diurnal patterns of temperature fluctuation recorded in the field. During the growing season, treatments were sampled regularly for moisture, NO3− and exchangeable NH4-N. Similar determinations were made on in situ samples taken in fallow Wood Mountain loam. The incubator simulated the effects of growing season temperatures on soil N transformations satisfactorily. Pronounced increases or decreases in temperature led to flushes in N mineralization. However, in the 1972 growing season, temperature was suboptimal and temperature changes were generally small. Consequently, when a stepwise multiple regression technique was used to analyze the data, neither ammonification nor nitrification showed a quantitative relationship to temperature. Comparison of the nit...

A dynamic model for the effects of soil and weather conditions on nitrogen response

Abstract: A dynamic model was derived to predict crop response to nitrogen fertilizer under different soil and weather conditions. It combined formulae representing existing principles about important processes such as leaching of nitrate through soil and nitrate uptake by plant roots. Starting values were given for the initial plant weight and its nitrogen content and parameters were included for the crop's growth and rooting characteristics under optimum growing conditions. For each day the model re-calculated the distribution of water, nitrate and roots down the soil profile and the increment of growth. The validity of the model was tested by using it to forecast the effects of different weather conditions and cultural practices on the nitrogen responses of a test crop, lettuce, when grown in experiments that were entirely independent of those used to obtain parameter values for the model. It successfully predicted the effects on the general shape of the response curve of the distribution of rainfall during the growing season, the age of the plant, the depth of fertilizer incorporation and the application of the nitrogen partly as a top dressing instead of entirely as a base dressing. The model was used to develop a strategy for nitrogen fertilizer practice for lettuce in the U.K. which was found to be broadly in agreement with the results of fertilizer experiments on grower's holdings.

Nitrogen needs of wheat. 1. Grain yield in relation to soil nitrogen and other factors

Abstract: A four year study of the relations between wheat yields and various edaphic, cultural and climatic factors in the wheat belt of southern New South Wales indicated that seasonal rainfall was the major source of yield variation. A regression equation involving pre-sowing (January to April) and growing season (May to September) rain, soil nitrate nitrogen concentration (0-30 cm), average annual rainfall, sowing time and weed density proved to be the most useful function for predicting yield (R2 = 0.613). Equations relating expected grain yields to soil nitrate nitrogen concentrations were derived for a combination of average annual rainfall and pre-sowing and growing season rainfall conditions. These show that, under optimum rainfall conditions, soil nitrate levels would restrict yields on most farms, wherever nitrate concentrations in the surface 30 cm fell below 20 p.p.m.

Survival and growth in Scots pine ( Pinus silvestris L.)

Abstract: Genotype — environment interaction has been investigated in Scots pine provenance experimental series, laid out during 1952–1955 in Sweden. Results obtained from six experimental plantations in the county of Norrbotten during a period of 20 years (including 1970) are the subject of discussion. The genecological variation of climatic hardiness, survival and growth — rate are shown graphically and in statistical analyses. Response of seed sources to the transfer of populations from their native habitats to the experimental sites has been analysed. The changed length of the growing season in connection with the transfer of populations is taken as the criterion of climatic differences on natural habitats and experimental sites.

Field measurements of photosynthesis and leaf growth rates of three alpine plant species

Abstract: Leaf photosynthetic measurements using a portable 14CO2 field system were carried out and leaf relative growth rates, Rl, were determined at different leaf positions of three alpine plant species throughout the growing season. Initially there was a period of high RI associated with a period of high or increasing photosynthetic activity. Following this stage was a long period of no net change in length of the living leaf with photosynthetic activity eventually exhibiting a steady decrease. The final ontogenetic stage was a period of negative Rs denoting leaf senescence which was associated with a marked decline in leaf CO2 uptake. Ontogenetic timing of these alpine species is geared with the surge and decline of individual leaf photosynthetic activity so that one to several leaves operating at near maximal photosynthetic capacity for existing conditions are always maintained during the growing season for each plant.

Ecological Effects of Weather Modification: Effect of Late Snowmelt on Festuca idahoensis Elmer Meadows

Abstract: Diversity, cover and productivity of Festuca idahoensis meadows become progressively lower as one moves: (1) from deep-soil to shallow-soil sites, or (2) from sites that melt out in mid-May to sites that melt in late May or early June. Changes in species composition are also obvious on late melting sites. Changes associated with different melt dates are probably due to the shorter growing season of the late melting sites. Winter weather modification programs are expected to add snow, postpone melt, shorten the growing season and degrade these meadows in proportion to the amount of snow they add. Especially if the snow is deposited in drifts, the 10-15% increases in snowfall probably achievable will have small effects on the "target area" while returns to the "service area" might be considerable.

Carbohydrate and Lipid Contents of Celmisia Plants in Alpine Snowbank and Herbfield Communities on Rock and Pillar Range, New Zealand

Abstract: Carbohydrate and lipid cycles in relation to plant phenology were examined in alpine snowbank and herbfield populations of Celmisia haastii var. tomentosa, C. prorepens and C. viscosa on Rock and Pillar Range, New Zealand. Major periods of carbohydrate build-up and depletion were observed in roots, stems and evergreen leaves during the growing season. Depletion generally occurred during flowering scape elongation, flowering, a late February-early March burst of vegetative growth and overwintering. Although carbohydrates accumulated in some tissues to near seasonal maxima at the onset of winter snow cover, they dropped during the winter to near seasonal minima. Thus, the species do not retain large amounts of carbohydrate reserves over winter, and major periods of growth and flowering are not sustained by carbohydrate reserves from previous growing seasons. Lipid levels in the evergreen leaves were remarkably high. Maximal observed percentages were 6.6, 14.6 and 20.3% in the three species, respectively. Lipid percentages decreased during flowering scape elongation-early flowering in C. viscosa, and possibly during flowering and the February-March growth period in C. haastii. Lipid percentages increased markedly during the winter in C. prorepens. The evergreen leaves may serve as overwinter storage sites for lipids in C. prorepens and C. viscosa. INTRODUCTION Arctic and alpine environments of the Northern Hemisphere have short, cool growing seasons of only a few weeks duration (Bliss, 1956). Plants adapted to these environments must complete their vegetative growth and set seed during these few weeks of favorable weather. Consequently, spring bursts of rapid vegetative growth and flowering characterize most tundra species. This rapid growth must depend on translocation and utilization of stored reserves from the previous growing season as well as current photosynthate (Fonda and Bliss, 1966; Mooney and Billings, 1960, 1961; Russell, 1940, 1948). In perennial species, the depleted reserves must be replenished later in the growing season for use the following year. These reserves are usually stored as carbohydrates in stems and roots, although lipids may also be important reserves in old leaves and stems of evergreen alpine species (Bliss and Mark, 1965; Hadley and Bliss, 1964). In contrast, New Zealand alpine environments have long growing seasons which often exceed 5 months; however, temperatures are favorable for plant growth for only short periods throughout those prolonged seasons (Bliss 1969; Mark,. 1965; Mark and Bliss, 1970). Consequently, vegetative growth is slow and intermittent over 2-4 months (Bliss, 1969). The objective of the present study is to examine energy reserves in

Measurement of aeration, respiration rate and oxygen diffusion in soil during the growth of cotton in a rhizotron

Abstract: Gaseous diffusion experiments were conducted in soil below cotton plants in a rhizotron throughout a growing season. Buried oxygen transducers permitted the estimation of transient-state oxygen diffusion coefficients after soil sterilization with methyl bromide at the end of the season. This provided a relationship between soil air-filled porosity and oxygen diffusion coefficient which was applied in calculations of soil respiratory activity at steady state earlier in the season. These values varied with root density throughout the season. Transient-state values for respiratory activity were different from steady-state values at similar times, even when allowance was made for continual loss of water by transpiration during the transient state. Possible reasons for such differences are discussed, and the utility of the technique for field studies is outlined.

Grain sorghum -high yield, satisfactory protein content or both?

Abstract: Negative correlations have been found to exist between yield and grain protein concentration in grain sorghum, and the problem of low protein levels appears to be associated particularly with high-yielding hybrid cultivars . .Solution culture experiments with the hybrid Texas 610 showed that the effects of nitrogen deficiency oli grain yield are are greatest when the deficiency occurs early in the growing season; the magnitude of the effect .. ranking: pre-head. initiation_;> initiation to anthesis>post-anthesis. By contrast large and consistent effects of nitrogen deficiency on grain protein concentration were observed only when the deficiency was imposed between anthesis and maturity. In the field, nitrogen supply was shown to. have large effects on both yield0.8 to 9.2 tonnes/ha and on grain protein concentrations (6.6 to 18. 9o/o), low yields being associated with exhaustion of plant available nitrogen during the early part of the season, and low protein concentrations with nitrogen shortage during the latter part of the season. It is concluded that the desired objectives of high yield and satisfactory grain protein concentrations can be achieved if care is taken to ensure that adequate nitrogen is available to the crop throughout the growing season up to and including the grain filling stage.

Energy budget measurements over three cover types in eastern Arizona

Abstract: Three years of continuous records of net radiation Rn were taken over a pine forest, a cienega, and a clear-cut opening. Seasonal patterns of the portion of Rn going into evapotranspiration ET were determined for these cover types by energy budget measurements in the Bowen ratio equation. By using the average daily Rn over two summer periods (May to June and July to September) and the mean ratios of ET to Rn, ET for the three cover types for the growing season was estimated at 19.4 in. for the forest, 15.3 in. for the clear-cut opening and 13.2 in. for the cienega. Weighting these amounts by the extent of the type resulted in a watershed average ET of 18.4 in. for the growing season.