Showing papers on "Sowing published in 1979"

The biology of ambrosia trifida l.

Abstract: Summary Ambrosia trifida L. is a fast growing annual colonizer of disturbed ground. When present it drastically reduces kinds, numbers and growth of other annuals. Its seedlings emerge before any other annual in early spring. We studied seed germination in relation to temperature, moisture, depth of sowing, and seedling emergence, survivorship and performance of mature plants in relation to time and depth of sowing and seed size. Seeds germinated under a wide range of temperature (8 to 41°C) with an optimum between 10 to 24 °C. Further germination occurred after restratification suggesting germination polymorphism. The seeds also germinated under a wide range of soil moisture conditions (17 to 55 % dry wt) but highest germination occurred at 20 to 33 % soil moisture. Optimum depth of sowing was 2 cm; very little germination occurred very close to soil surface, and some occurred at the 16 cm depth. In the field seedlings emerged from shallow depths first and then from progressively deeper parts of the soil bank. There was positive correlation between seed size and maximum depth from which seeds of this species and those of five other associated annuals emerge. Time required for seedlings to emerge after germination was directly related to depth. Seedlings that emerged first had the highest probability of survival and those that emerged late suffered progressively higher mortality, irrespective of whether late emergence was caused by late germination or deep germination. Among the survivors that reached maturity, plant weight, height, and number of seeds per plant declined with delayed emergence. However, experimental manipulation showed that delayed emergence per se was not the cause of the mortality but rather competition with individuals which emerged earlier. Furthermore, delayed emergence of cohorts in separate plots did not significantly reduce plant height, weight and number of seeds per plant. Thus in the field and within a patch there may be strong selection for early germination and emergence. However, this selection may be opposed by the unpredictability of the time of disturbance, the spatial patchiness of disturbance, and the longevity and induced dormancy of Ambrosia seeds. Compared to its associated annuals, A. trifida has the largest seeds and seedlings, the earliest germination and emergence and a very high photosynthetic rates. These properties give A. trifida a decisive advantage over the other species.

Control of Seed Germination by Abscisic Acid: I. Time Course of Action in Sinapis alba L.

Abstract: The germination process of mustard seeds (Sinapis alba L.) has been characterized by the time courses of water uptake, rupturing of the seed coat (12 hours after sowing), onset of axis growth (18 hours after sowing), and the point of no return, where the seeds lose the ability to survive redesiccation (12 to 24 hours after sowing, depending on embryo part). Abscisic acid (ABA) reversibly arrests embryo development at the brink of radicle growth initiation, inhibiting the water uptake which accompanies embryo growth. Seeds which have been kept dormant by ABA for several days will, after removal of the hormone, rapidly take up water and continue the germination process. Seeds which have been preincubated in water lose the sensitivity to be arrested by ABA after about 12 hours after sowing. This escape from ABA-mediated dormancy is not due to an inactivation of the hormone but to a loss of competence to respond to ABA during the course of germination. The sensitivity to ABA can be restored in these seeds by redrying. It is concluded that a primary action of ABA in inhibiting seed germination is the control of water uptake of the embryo tissues rather than the control of DNA, RNA, or protein syntheses.

Influence of soybean (Glycine max) planting date on velvetleaf (Abutilon theophrasti) competition.

Abstract: A 2-yr study was conducted to determine the influence of early and late soybean [Glycine max (L.) Merr.] planting dates on the competitiveness of velvetleaf (Abutilon theophrasti Medic). Velvetleaf was planted at densities of one plant per 61 and 30 cm of row, and competition ranged from 4 weeks to full season. Soybean planting dates were mid-May and late-June. Velvetleaf emerging with soybeans in mid-May were twice as competitive as those emerging with soybeans planted in late-June. A density of one velvetleaf per 30 cm of row competing full season reduced soybean yields 27% for the early and only 14% for the late planting date. The competitive difference was due to the short-day photoperiodic response of velvetleaf. Although the early growth stages of soybeans are more competitive than those of velvetleaf, 10 weeks after emergence velvetleaf competition reduced soybean growth and development. Velvetleaf does not appear to be a potential major problem in Arkansas for soybeans planted in June due to its photoperiodic response and late season competitiveness. However, the weed could present problems for soybeans planted early, especially when an early maturing variety is used.

Dry matter accumulation and water use relationships in wheat crops

Abstract: In order to better understand crop growth (dry matter accumulation, DM), crop evapotranspiration (Et), and their interrelationships, we studied dryland crops of wheat (Triticum aestivum L. cv. Timgalen) sown at various dates and seeding densities in each of three years at Tamworth, N.S.W. Soil water stress was minimal before anthesis in each year, but in two years substantial stress arose before maturity. DM was increased consistently by increased plant density, and decreased at anthesis and maturity by later sowing. Crop growth rates determined over 2-week intervals around anthesis ranged from 3 to 20 g m-2 d-1, representing a range in efficiency of utilization of intercepted total solar radiation of 0.48 to 2.35%, variation which was adequately explained (R2 = 0.80) by ontogeny (days from anthesis) and Et / Ep ratio (Ep = class A pan evaporation). Et at anthesis, but not at maturity, was increased slightly by higher seedmg density; crop Et was not consistently affected by sowing date. Et / Ep over 2-week periods around anthesis was related to leaf area index, and to a lesser extent to available soil water and Ep (R2 = 0.58). For the period from the first sowing date in June or July until the middle of October, the relationship of total Et to DM production was linear and close each year, but the slope varied from 6.2 g m-2 mm-1 (cold dry year) to 14.0 g m-2 mm-1 (wet year). This variation could be attributed to annual variation in the soil evaporation component of Et, and in the ratio of DM to crop transpiration (= transpiration efficiency, TE). For 2-week periods around anthesis, TE ranged from 2.9 to 5.4 g m-2 mm-1 and was inversely related to Ep (R2 = 0.56). Provided soil evaporation can be allowed for, since it ranged from 18 to 41% of crop Et from sowing to maturity, it is argued that the crop transpirationtranspiration efficiency approach is particularly useful for analysing the growth and water use of dryland wheat.

Periodicity of seedling emergence and seed survival in some umbelliferae

Abstract: (1) Among ten species of Umbelliferae there were differences both in the times of year at which seedlings emerged and in the extent to which seeds survived in cultivated soil. (2) The main time of emergence of Smyrnium olusatrum was in the autumn of sowing, while that of Anthriscus sylvestris, Heracleum sphondylium, Angelica sylvestris, Conopodium majus and Pastinaca sativa was in the following spring. Few viable seeds of these species remained after a year. (3) Seeds of Sison amomum, Conium maculatum and Torilis japonica survived for longer. Sison amomum had autumn and spring peaks of emergence, while Conium maculatum and Torilis japonica were mainly spring-germinating. (4) Maximum emergence of the spring-germinating annual weed Aethusa cynapium occurred in the second or third year, and about one-fifth of the seeds were still viable and dormant after 5 years.

Influence of soil water deficits on root growth of cotton seedlings

Abstract: Cotton (Gossypium hirsutum L. cv. H14) seedlings were raised in soil of differing soil water content in specially designed pots in which the roots had access to freely available water and nutrients located 2.5 cm below the base of the soil core. The time for root emergence from the soil core and the rate of root growth were measured daily from sowing to harvest. The root and shoot dry weight and leaf water potential were measured at the final harvest 16 days after sowing. As soil water content decreased, the root emerged from the soil earlier and the initial rate of root elongation was faster. In spite of the availability of freely available water, the plants in the soil at low water contents had significantly lower leaf water potentials than those in soil at high water contents. The root: shoot ratio increased as the soil water content decreased. This arose from an absolute increase in root weight, with shoot weight not being significantly affected.

Improved growth of white clover in hill grasslands by mycorrhizal inoculation

Abstract: SUMMARY Field trials in a hill grassland area of mid-Wales showed that growth of white clover could be improved by inoculation with selected vesicular-arbuscular (VA) mycorrhizal fungi. After one growing season mycorrhizal inoculation had approximately doubled shoot dry weight, runner number and nodulation at two sites previously improved by adding lime and fertiliser and by replacing the native vegetation mainly with rye-grass and white clover. At a previously unimproved site, limed at the time of planting, mycorrhizal inoculation increased shoot dry weight by up to two and a half times, almost doubled runner formation, and increased nodulation up to five-fold where 90 kg P/ha as basic slag had been applied. Responses to mycorrhiza at this site were smaller with 22-5 kg P/ha as basic slag and were absent where no P was added. After two growing seasons inoculation responses were even more pronounced at this previously unimproved site; where clovers were being overgrown by adjacent native grasses only those given both 90 kg P/ha and mycorrhizal inoculation survived well.

Primordium initiation at the shoot apex in four contrasting varieties of spring wheat in response to sowing date

Abstract: The spring wheat varieties Kolibri, a typical north temperate variety, Pitic 62, a Mexican variety known to respond to vernalization and two selections from the Institute's breeding programme TW 161 and TJB 155 were sown early (2–5 March), during the normal sowing period (27 March) and late (17 April). Primordium initiation was observed until the time of terminal spikelet initiation and the number of leaves and the number of spikelets were analysed in terms of rate and duration of leaf and spikelet primordium initiation. The rate of leaf initiation was affected by time of sowing but not in a systematic way and there were differences between varieties in the way in which the number of leaves changed in response to sowing time. The rate of spikelet initiation increased and the duration decreased with later sowing. There were strong variety × time of sowing interactions. For almost all characters measured, Pitic 62 responded least to time of sowing. Varieties differed in the way in which the number of spikelets per ear responded to time of sowing but in all cases the changes were only small. This waa because the change in the rate of spikelet initiation was almost exactly compensated for by a change in the duration of spikelet initiation. In each variety, the period from terminal spikelet initiation to ear emergence was similar in all sowing treatments and was of similar duration in the main shoot and in the ear-bearing tillers.The number of leaves per shoot on the tillers was less than the number of leaves on the main shoot and the rate of spikelet primordium initiation of the tillers was faster than in the main shoot. These changes tended to synchronize the time of terminal spikelet initiation. Because of the changes in the number of leaves per shoot and the rate of spikelet initiation the number of spikelets borne on the main shoot and the tillers were similar although the growth period of the tillers was shorter than that of the main shoot.

Effect of rust (Phakopsora pachyrhizi) on soybean yield and quality in south-eastern Queensland

Abstract: In a field trial conducted at the University of Queensland Research Farm, Redland Bay in 1976, plots of soybeans were protected from rust, Phakopsora pachyrhizi, with mancozeb sprays for varying periods after sowing. Seed yield losses were 60-70% in the most severely rusted plots. In a glasshouse trial, rust inoculations were commenced at regular intervals during growth, and yield was reduced by 95% in plants inoculated immediately prior to flowering. In both trials, reduced yield was associated with reductions in the number of filled pods per plant, the number of filled seeds per plant and seed weight. The oil but not the protein content of the seed was also reduced in the more severely rusted treatments in the field trial.

The occurrence and control of yellow spot of wheat in north-eastern Australia.

Abstract: Explanations were sought for the increased severity of yellow spot of wheat (Pyrenophora tritici-repentis) in the north-eastern wheat growing areas of Australia. A close association between the severity of yellow spot and stubble management practices was found in a field experiment. There was less disease in plots where stubble had been burned (0.83 lesions per leaf) or burned and cultivated (0.62) than in plots which were mechanically cultivated (2.43) or untreated (11.75). In another study severe yellow spot developed as early as in the second wheat crop in a rotation. Differences in susceptibility to the disease were found among 11 wheat cultivars and lines. Vigorous development of the pathogen occurred on cereal rye and triticale while the fungus was isolated from small lesions on barley and four common grasses. Avoidance of planting wheat into infected wheat stubble, either by crop rotation or removal of surface stubble by incorporation or burning, should provide effective control of the disease in most situations.

Irregular rain cues and the germination and seedling survival of a Panamanian shrub (Hybanthus prunifolius).

Abstract: Seeds of the Panamanian shrub, Hybanthus prunifolius (Schult.) Schulze (Violaceae) are dispersed at different times in different years ((March to June) and are exposed to the irregular rainfall of the dry season in some years. Fluctuations in soil moisture in the dry season represent suboptimal conditions for germination and seedling survival. There are no mechanisms to prevent germination prior to the arrival of consistent rains in the wet season. Among three natural cohorts of seeds followed in two years, the cohort experiencing the longest time from sowing to consistent rains had the highest germination, but it also had the longest time lag from sowing to, beginning of germination, longest germination period, and lowest survival of seedlings 3 months after sowing. Seeds were also induced experimentally to germinate under 14 different moisture patterns. The patterns encompassed 1) varying lengths of moisture before a dry period, 2) inconsistent moisture, and 3) varying lengths of dryness prior to any moisture. Mortality of seeds by fungal infection occurred if the wet period was delayed. But germination was less affected by fluctuations than was seedling survival. Length of the first wet period and frequency of occurrence of the wet period both affected germination levels. Survival and development of seedlings was influenced by the number of days exposed to dry conditions and by the stage of development at the beginning of the dry period. Young seedlings suffered attrition due to drought stress, and older seedlings died from fungal attack. Results from field and experimental sowing of seeds both indicate that this perennial species has minimal defense against germination when conditions are suboptimal for seedling survival. Undoubtedly there is more recruitment in some years than in others.

Seed dispersal in relation to the domestication of Middle East Legumes

Abstract: Modification of seed dispersal was perhaps one of the most important steps towards domestication of seed crops. Among the legumes of the Middle East, four patterns of such modification can be distinguished in the process of domestication. The initial stage of domestication of lentil, pea and grass pea was apparently due to a single mutation in a major gene that prevented pod dehiscente. In chick pea the domesticated type was formed by accumulation of several mutations in minor genes that reduced the amount of pod dropping and shattering. From a seed dispersal point of view, fenugreek was preadapted to cultivation since the wild species do not shatter their seeds. In the bitter vetch and common vetch partial seed shattering apparently was tolerable and desirable under cultivation since the seed served merely for sowing the next year crop.

The effect of soil water potential, temperature and seeding depth on seedling emergence of wheat

Abstract: Daily emergence counts were made on Canthatch wheat (Triticum aestivum L.) grown in five soil types, at four soil temperatures and three water potentials and planted at five different depths. Regardless of soil type, soil water potential or depth of planting, 50% emergence generally occurred within a week at 19.4 and 26.7 °C, and within 2 wk at 12.2 °C, but it took up to 6 wk at 5 °C. The heat sum required to attain 50% seedling emergence did not increase significantly with decreasing soil water potentials, but the minimum temperature for emergence dropped from 1.3 to 0.2 °C as the water potential decreased from −⅓ to −10 bar. It was suggested that the seedlings compensated for the increased water stress by lowering their minimum temperature requirements. Increasing the planting depth not only increased the heat requirement for emergence, but it also increased the variability of emergence, especially at low temperatures. Practical aspects concerning planting dates and depths were considered.

Agronomic studies on Vigna spp. in south-eastern Queensland. I. Phenological response of cultivars to sowing date

Abstract: Phenological development of 16 cultivars from four Vigna species (V. radiata, green gram; V. mungo, black gram; V. angularis, adzuki bean; V. umbellata, rice bean) was studied over a range of 17 weekly sowing dates at Lawes in south-eastern Queensland. Cultivar and sowing date effects on phenology were large. In all cultivars, the rate of development during pre-flowering was associated negatively with mean day length and positively with mean maximum and/or mean minimum temperature. Cultivars differed in sensitivity to both photoperiod and temperature. Genetic lateness of flowering among cultivars was associated positively with increasing sensitivity to day length and negatively with the latitude of cultivar source. In the grams, early-flowering cultivars showed response to maximum temperatures, while the later-flowering lines responded to minimum temperatures. Rate of development in all four species during the reproductive phase was largely independent of cultivar and sowing date, per se, but rather appeared to depend on the day length and temperature regimes prevailing subsequent to the onset of flowering. The reproductive period in all species was shortest for those cultivar x sowing date combinations which commenced flowering in early autumn. Where flowering occurred in midsummer, i.e. for early sowings and for early cultivars, the reproductive period was extended as a consequence of prolonged flowering in response to the longer prevailing day lengths. As the date of flowering was delayed into mid or late autumn, the reproductive phase was extended owing to slower pod maturation rates in response to cooler prevailing temperatures. The implications of these responses on adaptation and agronomic utilization of these species are discussed.

Microwave seed sensor for field seed planter

Abstract: A seed planting apparatus comprises a mobile planting machine to be connected to a tractor or similar vehicle, and having a seed hopper for containing a supply of seeds to be planted. A seed outlet on the hopper feeds a seed dispensing apparatus for delivering seeds to the ground to be planted. A microwave seed sensing apparatus is disposed in a path of travel for seeds discharged from the hopper for detecting the seeds and producing an observable indication to the operator of the presence of seeds in the path of travel. The seed planting apparatus may also include magnetic seed treatment apparatus. The microwave sensing apparatus may therefore be connected in a control circuit for actuating the magnetic field in response to the presence of seeds and for producing an indication to an operator of the passage of seeds.

Effect of time of sowing on wheat phenology in South Australia

Abstract: Relations between the growth intervals in wheat and meteorological variables were defined from time-of-sowing field experiments. The major factors affecting the duration of each interval were the date of sowing, the day-degrees of maximum air temperature and daylength. Equations to predict the number of days in a growth interval were tested against measurements made in other wheat growing districts. The relations between day-degrees of maximum air temperature and sowing date gave best predictions of the growth intervals in various districts. The data have application for estimating flowering dates and potential yield, and for estimating harvest dates,

Factors influencing the development of primary dormancy in wild oat seeds

Abstract: Germination in response to gibberellic acid was used as an assay for wild oat seed dormancy. In growth chamber studies removal of glumes, a 5 °C reduction in night temperature (20 °C day/15 °C night vs. constant 20 °C), and a shorter photoperiod (12 vs. 18 h) during the period following panicle emergence reduced subsequent germination (increased dormancy) of mature seeds. Dormancy of field-grown wild oat seeds increased with increasing seed maturity and was affected by planting location and associated crop.

Effects of inoculation and fertilizer n levels on n2 fixation and yields of soybeans in ontario

Abstract: Soybeans (Glycine max (L.) Merrill) often do not give yield responses to added fertilizer nitrogen (N) because high soil N levels inhibit fixation of atmospheric N2. Yield responses to N fertilizer applied at planting usually indicate that N2 fixation is less than optimal. The effects of inoculation with Rhizobium japonicum, and fertilizer N levels, on soybean N2(C2H2) fixation and seed yields in Ontario were investigated in ’ 1976 and 1977. Three locations were used each year, representing areas where soybeans had been grown for many years (Ridgetown), for only a few years (Elora), or not at all (Woodstock). Treatments were (a) Uninoculated + 0 N, (b–e) Inoculated + 0, 50, 100 or 200 kg N/ha. Results indicated that inoculation increased seed yields only when soybeans were introduced into new areas. Fertilizer N applications at planting time did not increase yields in areas where soybeans had been grown several times previously, indicating that N2 fixation could support maximum yields. Nodule number and m...

The effect of planting density, inorganic nitrogen fertilizer and supplementary carbon dioxide on yield of Vicia faba L.

Abstract: Vicia faba cv. Minden was planted at densities ranging from 6 to 98 plants/m2. Nitrogen was applied to the soil as split dressings or as a foliar spray. CO2 concentration in the canopy was increased in some plots to 0·22% for 3 weeks during the early pod-filling stage.Yield and number of seeds per plant varied inversely with plant spacing between 9 and 98 plants/m2. Mean seed weight increased up to 13 plants/m2 and then remained constant between 13 and 98 plants/m2. Yield/ha was unaffected by plant density above 18 plants/m2.Application of 200 kg N/ha as ‘Nitro-Chalk’ (mixture of NH4NO3 and CaCO3) to the soil as split dressings did not affect yield or its components but 80 kg N/ha as urea applied in four foliar sprays increased yield by 361 kg/ha (8·6%). Recovery of the labelled nitrogen in the grain varied from 28% when applied during vegetative growth to 8% when applied in the reproductive phase and 15% in the foliar spray.The highest yield (5·12 t/ha) was obtained by supplementary CO2. The results suggest that there is no advantage in applying fertilizer nitrogen to well-nodulated spring beans.

Effects of Planting Date and Soil Water on Infestation of Sunflower by Larvae of Cylindrocopturus adspersus

Abstract: Plant population had no significant effect on the infesation level of Cylindrocopturus adspersus (LeConte) larvae infesting the stalks of cultivated sunflower under dryland conditions. However, the mean number of larvae per plant was significantly (5% level) reduced by both delayed planting dates and reduced preplant soil water. Delayed planting dates also significantly reduced the avg number of larvae per plant and percentage infestation in irrigated sunflower. Application of insecticide to control adults reduced the number of larvae infesting stalks of irrigated sunflower, reduced plant lodging, and resulted in significant (5% level) increases in both the quantity and the quality of seeds produced in plants that did not lodge.

Longevity and productivity of leaves of a cultivated annual, glycine max merrill. i. longevity of leaves in relation to density and sowing time

Abstract: Summary A life-table approach has been applied to the leaf population of the soybean plant (Glycine max Merrill) in order to determine leaf longevity, a basic factor in production of dry matter. Longevity of leaves was determined at various heights on the stems of plants grown at three densities at three different sowing times. In general, longevity increases with the height of the leaf on the stem, but the uppermost leaves have short lives due to frost-damage. In the plants sown earlier than the standard sowing time the lowest leaves fell very rapidly as a result of physiological ageing. It was concluded that, at the densities examined, density does not show a generalized relationship with leaf longevity. At the lower nodes, most leaves fell due to physiological ageing, but those at the higher nodes suffered from noxious insects. Two typhoons had little influence on leaf longevity.

Effect of time of sowing on Argentine stem weevil (Hyperodes bonariensis Kuschel) damage in autumn-sown Tama ryegrass

Abstract: A field trial is described which tested the laboratory observation that Argentine stem weevil appears to go into a state of facultative diapause during winter. Tama ryegrass was sown in an area of heavy weevil infestation on 23.1.78, 15.2.78, and 8.3.78. The crop that emerged from the 23.1.78 sowing was severely damaged by adult feeding and larval mining. The subsequent sowings showed sharp reductions in damage. This result supports the concept that the end of egg-laying is photoperiodically controlled and therefore predictable. By interpolation it can be estimated that this event occurs at the end of the first week of March. A corresponding sharp reduction in adult feeding suggests that the jotensiey of adult feeding damage declines rapidly after egg-laying because of reduced metabolic demand. Chlorpyrifos and phorate were used to estimate damage and were not tested as control measures themselves. Since egg-laying declines rapidly at a known time, the timing of sowing of short rotation ryegrass ...

Problems in tree replacement. III.* The effects of cultural practices and soil fumigation on root-lesion nematodes and on the growth of apple replants

Abstract: The growth of replant apple trees cv. Delicious was much less in field plots after a mixture of cover crops, including rye cv. Black Winter and lupin cv. New Zealand Blue, had been grown for 16 months than where the land had been left to volunteer weeds or kept free of plant growth. In a subsequent glasshouse experiment, growing rye or blue lupin in old orchard soil before planting apple seedlings caused severe stunting. In a field trial, soil fumigation with dichloropropene-dichloropropane (DD) before planting increased the first season's shoot growth of apple trees cv. Delicious after rye cv. Black Winter by 79% and after lupin cv. New Zealand Blue by 60%. Trees grew well after prairie grass cv. Priebe or oats cv. Saia, increases due to fumigation being 4.0 and 4.5% respectively. In a glasshouse experiment rye and blue lupin were shown to be much better hosts for the root-lesion nematode Pratylenchus penetrans than prairie grass or oats. A survey of Queensland apple orchards indicated that Pratylenchus penetvans and another species previously identified as Pratylenchus coffeae often occurred together. In a glasshouse experiment the addition of large numbers of P. penetrans to soil severely stunted apple seedlings cv. Granny Smith, whereas the other Pratylenchus species had little effect. ________________ *Part II, J. Aust. Inst. Agric. Sci., 20: 234 (1954).

Agronomic studies on Vigna spp. in south-eastern Queensland. II. Vegetative and reproductive response of cultivars to sowing date

Abstract: Vegetative and reproductive growth of 16 cultivars from four Vigna spp. (V. radiata, green gram; V. mungo, black gram; V. angularis, adzuki bean; and V. umbellata, rice bean) were studied over a range of sowing dates at Lawes in south-eastern Queensland. Seed yield and total dry matter (DM) at maturity were highest in the black grams, and lowest in the adzuki beans. Within species, vegetative development was generally higher in the later-maturing cultivars, but the same was not true for seed yield. Harvest index was negatively associated with cultivar maturity in the grams and adzuki beans. All cultivars showed substantial response to sowing date, with highest total DM and seed yield for December sowings. Delayed sowings reduced growth such that for late February sowings, total DM at maturity and seed yields were generally less than one-tenth of the maximum. Harvest index revealed an optimum type response to sowing date, with highest values for late December/early January sowings. Phenological response per se was not a useful predictor of the effect of sowing date on yield or total DM for any of the 16 cultivars, since in all cases growth rates varied substantially with sowing date, apparently in response to temperature. The linear form of the Arrhenius equation relating mean growth rate and mean prevailing temperature provided an excellent description of the response of both yield and total DM accumulation rates over sowing dates for all cultivars. Among cultivars, there was a significant correlation between the slope of the Arrhenius plots (k values) for seed yield and total DM accumulation, implying similar relative temperature sensitivity for both growth processes. For the 16 cultivars tested, the absolute magnitude of the k values for both seed yield and total DM accumulation was significantly negatively correlated with the latitude from which the cultivars were introduced, which implied greater temperature sensitivity for cultivars from the tropics. Some implications of these responses on cultivar adaptation and cultural practices are discussed.

A comparative study of establishment of plantago coronopus l. from seeds sown randomly and in clumps

Abstract: Summary This paper reports the results of a study of the establishment of Plantago coronopus L. seeds in the field. Seeds were introduced at a range of densities into plots with intact vegetation, and plots from which the vegetation was removed. Seeds were also sown in a variety of clump sizes on to non-vegetated plots. The aim of this experiment was to determine whether the density-dependent germination patterns exhibited by this species in laboratory experiments could also be observed in the field. All treatments exhibited similar patterns of seedling recruitment although different conditions of planting showed quantitatively different responses. During the first 4 weeks after sowing there was rapid seedling recruitment followed by mortality which balanced this recruitment. Eight weeks after sowing, seedling densities were not significantly different from the starting densities in any of the treatments. In particular, the chance of a seed forming an established seedling was not increased when seeds were sown in clumps, thus calling into doubt the ecological benefits of density-dependent germination responses which have been proposed in previous laboratory studies of the phenomenon. Factors influencing germination and establishment were investigated by means of an autocorrelation matrix. Recruitment of seedlings into the population appears to be limited by the number of adult and seedling plants already present in the population.

The effect of time of sowing on the incidence of subterranean clover red leaf virus infection in broad bean (Vicia faba).

Abstract: SUMMARY Yield losses in broad beans due to subterranean clover red leaf virus (SCRLV) in 1972/73 were 21, 30, 61 and 8% in plots sown in May, July, September and November respectively. The variations in yield loss resulted from differing levels of virus infection during periods in which harvestable pods were set because further pod set virtually ceased after symptoms of infection became apparent. The increases in infection were paralleled by increases in the infestation of Aulacorthum solani the aphid vector of SCRLV. Yield losses were greatest in the September-sown plots because the plants emerged at the commencement of the spring peak of aphid flight and were least in the November-sown plots which emerged after the peak of aphid flight had declined. However, potential yields decreased with deferment of sowing time and recorded yields were greatest from May-sown plots. Yield losses due to SCRLV in 1973/74 were 79 and 91% for plots sown in May and September respectively. These larger yield losses resulted from an earlier and more rapid colonisation of plants by A. solani than in the previous year. Choice of May as sowing date would not have controlled the disease satisfactorily in 1973/74 but would have been practical in the previous season when colonisation by A. solani was delayed so that little infection with SCRLV occurred before pod set had ceased.

“Starter nitrogen”; fertilization in soybean culture 1

Abstract: Proponents of the “starter nitrogen”; concept believe that a small amount of nitrogen fertilizer stimulates early vegetative growth of soybeans, thereby facilitating cultivation and weed control. To evaluate this concept, soybean leaf area, plant height, fresh weight, and yield were measured over three growing seasons. Growth parameters were measured at weekly intervals during the 7 weeks following planting of ‘Bragg’ soybeans (Glycine max (L.) Merr.) which had received 0, 16.8, and 50.4 kg N ha‐1 banded pre‐plant into the soil. The analysis, a multiple linear regression maximum R2 (multiple correlation coefficient) improvement procedure, showed that starter nitrogen did not significantly (.05) influence leaf area, plant height, fresh weight, or yield of Bragg soybeans.