SUMMARY The influence of season, and certain agronomic treatments (irrigation, nitrogen fertiliser, density of planting and sowing date) on leaf number were analysed in a series of sugar‐beet crops grown during the five seasons 1978‐82. Leaf appearance was a linear function of thermal time (accumulated temperature above 1°C) and could be described by four variables: a) the thermal duration of the seedling establishment phase, d′s; b) the thermal time interval between appearance of each of the early leaves, θe; c) the thermal duration of the early phase of leaf appearance, d'a, and d) the thermal time interval between the appearance of each of the later leaves, θ1. The progression of leaf death could also be described by a thermal time interval, θd. There were only small differences in the number of leaves produced by the eleven crops grown during the five seasons. Such differences as appeared, were largely attributable to changes in d'a and θ1, which were interpreted as responses to increasing competition for mineral nutrients and assimilate at the shoot apex. θe was similar in all crops; 30°Cdays were needed between the appearance of each of the early leaves. Only the early leaves died. Each one was retained by the plant longer than its predecessor. Increasing soil moisture deficit under an unirrigated crop shortened θd and depriving crops of nitrogen lengthened it. It is concluded that small differences in the rates of leaf appearance did not greatly influence the rates at which leaf canopies expanded early in the season, but that the rates of leaf death influenced both the time at which the canopies reached their maximum sizes and the rates at which leaf areas subsequently declined.

SUMMARYThe relationships between the amounts of nitrogen fertilizer applied and taken up by sugarbeet crops and the concentrations of sugar and α-amino-N in the storage root were examined using data obtained from fertilizer-response trials on different soils in the UK and Belgium between 1974 and 1985. On unmanured mineral soils, crop uptakes of N without fertilizer ranged from 65 to 190 kg/ha and increased linearly with the amount of fertilizer N applied. On organic soils or mineral soils that had received large applications of organic manure, crop uptakes of N were very large (295–383 kg/ha) and were not increased by applications of fertilizer N.The amino-N contents of harvested beet increased with crop N uptake. The distributions of crop N to the storage root and of storage-root N to amino-N differed, especially in manured, diseased and drought-affected crops. Greater proportions of crop N were present in the storage roots of manured crops than in conventionally fertilized crops, and more of the storage-root N was present as amino-N in crops affected by virus yellows or drought than in healthy, unstressed crops.The fresh weight concentrations of sugar in the storage root also differed between sites and years but were not consistently reduced by applications of fertilizer N at individual sites. However, when compared across sites, concentrations were negatively correlated with crop N uptakes and the amounts of N in storage roots. This was because particular crops grown on mineral soils with large applications of manure or on organic soils had large N uptakes and exceptionally low concentrations of sugar.The physiological implications of these relationships between N uptake and amino-N and sugar accumulation are discussed.

The influence of season, and certain agronomic treatments (irrigation, nitrogen fertiliser, density of planting and sowing date) on leaf number were analysed in a series of sugar-beet crops grown during the five seasons 1978-82. Leaf appearance was a linear function of thermal time (accumulated temperature above 1 "C) and could be described by four variables: a) the thermal duration of the seedling establishment phase, d's; b) the thermal time interval between appearance of each of the early leaves, Be; c) the thermal duration of the early phase of leaf appearance, d'a, and d) the thermal time interval between the appearance of each of the later leaves, 81. The progression of leaf death could also be described by a thermal time interval, Bd.There were only small differences in the number of leaves produced by the eleven crops grown during the five seasons. Such differences as appeared, were largely attributable to changes in d'a and 81, which were interpreted as responses to increasing competition for mineral nutrients and assimilate at the shoot apex. Be was similar in all crops; 30"Cdays were needed between the appearance of each of the early leaves. Only the early leaves died. Each one was retained by the plant longer than its predecessor. Increasing soil moisture deficit under an unirrigated crop shortened Bd and depriving crops of nitrogen lengthened it. It is concluded that small differences in the rates of leaf appearance did not greatly influence the rates at which leaf canopies expanded early in the season, but that the rates of leaf death influenced both the time at which the canopies reached their maximum sizes and the rates at which leaf areas subsequently declined.

Small, E., Pocock, T. and Cavers, P. B. 2003. The biology of Canadian weeds. 119. Cannabis sativa L. Can. J. Plant Sci. 83: 217-237. Cannabis sativa has been cultivated for millennia in Eurasia and for centuries in North America, as a source of a textile fibre, oilseed, and intoxicating drugs such as marijuana. Considerable literature is available on the agricultural and biological properties of these basic three cultigens, but relatively little is published on wild-growing plants of the species. Most weedy C. sativa differ from the cultigens in a number of ecological properties, particularly with regard to reproductive biology. The species is the classical example of a "camp follower" that is exceptionally adapted to the habitat conditions around settlements: rich, highly manured, moist soils, and open areas resulting from recent removal or disturbance of the vegetation. In Canada, spontaneous populations have been found in all provinces, but forms that have re-evolved wild adaptations are concentrated along the St. Lawrence and lower Great Lakes. The ruderal plants pose a minor weed problem to agriculture but a major problem to law enforcement, and decades of eradi-cation have exterminated many of the naturalized populations in Canada. With the recent re-authorization of hemp cultivation in Canada, it is inevitable that there will be additional escapes and a reinvigoration of the ruderal phase of the species. Mechanical erad-ication for 2 or 3 yr is effective at destroying populations, and young plants are easily eliminated by herbicide applications. Small, E., Pocock, T. et Cavers, P. B. 2003. Biologie des mauvaises herbes au Canada. 119. Cannabis sativa L. Can. J. Plant Sci. 83: 217-237. On cultive Cannabis sativa L. depuis des millénaires en Eurasie et depuis des siècles en Amérique du Nord pour ses fibres textiles, son huile et la production de drogues comme la marijuana. On a beaucoup écrit sur la biologie et les paramètres agricoles des trois principaux cultigènes, mais relativement peu sur les variétés sauvages de cette plante. La plupart des variétés envahissantes de C. sativa se distinguent des cultigènes par plusieurs propriétés écologiques, surtout au niveau de la reproduction. L'espèce constitue en soi un exemple classique de la « plante colonisatrice », car elle est exceptionnellement bien adap-tée aux conditions souvent associées aux endroits habités : les sols humides et riches en fumure ainsi que les espaces dégagés résultant de l'enlèvement ou de la perturbation de la végétation. Au Canada, on recense des peuplements spontanés dans toutes les provinces, mais aussi des formes sauvages modifiées le long du Saint-Laurent et en bordure des Grands Lacs. Les plantes rudérales ne posent pas énormément de problèmes comme adventices aux agriculteurs, mais sont une véritable source d'ennui pour les forces policières qui ont passé des décennies à lutter contre les peuplements naturels au Canada. La culture du chanvre ayant été de nou-veau autorisée au pays depuis peu, l'espèce s'échappera inévitablement ...

SummaryData from 11 sugar-beet crops grown at different sites, in different years and with some variations in husbandry have been used to re-examine the process of dry-matter partitioning. Two-phase linear models did not describe adequately the distribution of dry matter. There was no evidence of a discontinuity in the partitioning between root and shoot at any point in crop development. It is suggested that, contrary to a recent view, events in the shoot, rather than the storage root, largely determine how dry matter is allocated between growth and sugar storage.

The uptake and distribution of N were examined in a series of sugar-beet crops grown on different sites (Broom's Barn, Suffolk and Trefloyne, Dyfed) or with 0 (N o ) or 125 kg N/ha (N m ) between 1978 and 1982. Depletion of soil N was followed in some years.Initial rates of N uptake in spring for the N 126 crops at Broom's Barn ranged from 2-3 kg/ha per day in 1980 to 5-8 kg/ha per day in 1981 and 1982 and at Trefloyne from 4-7 kg/ha per day in 1980 to 5-4 kg/ha per day in 1979. The initial phase of N uptake in N o crops was shorter and at Broom's Barn the rate ranged from 1-6 kg/ha per day in 1979 to 5-1 kg/ha per day in 1982. Crops with high initial uptake rates had somewhat greater shoot N concentrations. There was no relation between the initial uptake rates or the total N uptake and the amounts of mineral N in the soil at the start of rapid growth in June. Simulations of early crop growth coupled with analysis of changes in the total N in the crop-plus-soil system showed that the rate of N uptake by the N 125 crops was regulated by crop demand for N as determined by growth rate in 4 of the years and by soil supply in the 5th. The analysis of the crop-plus-soil N also showed that substantial losses of N occurred when the crop was actively growing in June and July in 1979 and 1980 due to excessive rainfall following early irrigations. There were serious consequences for N uptake, N concentration in developing leaves and the overall growth of these crops.N uptake rates in autumn ranged from no net uptake in 1979 and 1980 to 0-6 kg/ha per day in the other 3 years at Broom's Barn and 1-0 kg/ha per day at Trefloyne. Large amounts of N were remobilized from the shoot to sustain the growth of the storage root in years when uptakes from the soil in autumn were small. Remobilized N represented 80, 50 and 30 % of the net increase in storage-root N between the end of August and harvest in 1979, 1980 and 1981 respectively. The amounts remobilized from shoots ranged from 8 to 18 kg N/ha and may therefore also represent a source of amino-N impurities in harvested beet. An analysis of N in individual leaves showed that remobilized N probably originated from leaf protein and that remobilization started at full expansion rather than at the onset of leaf senescence, which was often many weeks later. INTRODUCTION8 U g a r b e e t i m P r o v e s vield > excessive use has deleterious effects on the quality of the harvested beet Greater use of nitrogen fertilizer has been a major that make the crop less profitable for both grower factor in increasing yields of British arable crops, and processor. In particular, beet given too much During the past 30 years, rates applied to cereals fertilizer N contains smaller concentrations of sugar have increased five-fold and those to potatoes and higher concentrations of a-amino nitrogen three-fold, whereas applications to sugar beet have compounds, both of which decrease the efficiency only doubled (Cooke, 1972). Nevertheless, there is of sucrose extraction. concern within the sugar industry...

SUMMARY The increase of leaf area index (L) was examined in a series of sugar‐beet crops grown on different sites (Broom's Barn, Suffolk and Trefloyne, Dyfed) or with different husbandry treatments (sowing dates and nitrogen rates) between 1978 and 1982. The development of L could be described as a function of thermal time using three parameters; DE, which was essentially an estimate of the thermal time required for crop establishment, and rHL and DL, the thermal rate and duration, respectively, of the increase of L. Variations in DE between seasons and with sowing date were small, but significant; they were attributed to factors affecting the condition of the seedbed. There were much larger variations in rHL, especially between seasons, sites and crops given different rates of nitrogen fertiliser, and there was a strong negative relationship between rHL and DL. Much of the variation in rHL was associated with differences in the concentrations of nitrogen in the lamina dry matter. Faster rates for rHL at Trefloyne than at Broom's Barn, and in the crop grown in 1982 as compared with other years, were also partly attributable to particularly warm conditions during the early development of some of the larger, faster‐growing leaves within the canopy. The wider application of the relationships established from these experiments was tested with data from a series of crops grown on other sites between 1960 and 1962. The relationships held particularly well for beet grown on soils with high water‐holding capacity but not for those on soils of low water‐holding capacity.

The physiological and morphological factors necessary for efficient accumulation of sucrose in sugar beet (Beta vulgaris L.) are considered in relation to potential uses of plant growth regulators to modify the anatomy of storage roots so as to increase sucrose content and yield . The percentage of sucrose in root fresh and dry matter is closely related to root structure . Sugar beet, mangold and chard are three sub-species of Beta vulgaris that differ considerably in their anatomy, assimilate partitioning, sucrose concentration and root dry matter yield . The concentrations of indole-3-acetic acid (IAA), abscisic acid (ABA) and cytokinins were measured during the growth of the storage root in each of these cultivars . Correlations were found between the phytohormone levels and the formation of secondary cambia and their subsequent cell division and expansion activity .