GROWTH AND SEASONAL COMPOSITION OF NATURAL GRASSLAND IN ZAMBIA

There was a marked increase in basal cover of veld grasses after the first 2 to 3 years of cutting, and this effect continued over a period of 9 years. Short grasses, such as Cynodon dactylon and Heteropogon contortus , increased at the expense of tall tussock grasses, such as Hyparrhenia dissoluta .     

SALINITY EFFECTS ON ROOTS AND TOPS OF BERMUDA GRASS

Bermuda-grass varieties, cut at weekly intervals, differed in salt tolerance when grown in 20 m. eq./l. Hoagland's Solution No. 1 plus 0, 80, 160, 240, and 320. m. eq./l. sodium and calcium chlorides. Weights of above-ground parts decreased while root weight to top weight ratios increased with increased salinity. Highest root weights were obtained at the intermediate to high salt levels.
Explanations proposed for the root-growth stimulation are: maintenance of a high photosynthetic rate despite retardation of top growth, reduced percentage defoliation resulting from top growth retardation or a differential response of tops and roots to growth hormones.     

SEASONAL TILLER POPULATIONS OF GRASS AND GRASSJCLOVER SWARDS WITH AND WITHOUT IRRIGATION

The number of tillers per unit area of pure swards of S23 and S24 perennial ryegrass, S37 cocksfoot, S48 timothy and of a S23 perennial ryegrass/white clover sward, were examined at intervals of 4 weeks during a period of two years. The monthly appearance of new tillers and the death of tillers of S23 and S24 ryegrass and S48 timothy were followed for 15 months. The studies were made with and without irrigation.
The number of tillers varied with season through the year. Tiller numbers increased rapidly in late winter or early spring, and then declined until midsummer. Numbers rose again between June and August. This seasonal pattern of tiller numbers was most marked in ryegrass and timothy and least in cocksfoot. The effect of irrigation on tiller numbers was variable, and usually small in relation to the overall seasonal fluctuations in tiller numbers, but dry soil conditions could delay an increase in tiller numbers between June and August. The relationship between seasonal fluctuations in tiller number and root growth of swards is discussed.     

PATTERNS OF SPRING GROWTH IN SWARDS OF DIFFERENT GRASS VARIETIES

Production of dry matter by swards of ryegrass and cocksfoot varieties in winter and spring is dependent on a number of growth processes, each with different environmental requirements. Growth in the strict sense with the production of new leaves has been found to continue throughout the winter in Aberystwyth, although the rate of production fell very low during periods when the mean air temperature approached freezing, especially in cocksfoot varieties.
Because of the ceiling set by the natural balance between leaf death and leaf formation, net increases in weight of above–ground parts in undefoliated plants may not occur for extended periods during winter. When, however, tiller numbers start to increase, or the ceiling is raised by an increase in size of tillers, dry–weight increases can come about. The extension of leaves and intern odes in spring, measured in terms of sward height, seems to be largely governed by flower initiation. A certain degree of extension was found to be present before this in an Algerian type.
Practical distinctions between early and late types, which are based on flowering dates or sward height, or on parameters influenced by these characters, are not associated with similar differences in production of above–ground parts. These distinctions do not, therefore, permit a completely full and accurate picture to be obtained of winter– and spring–growth potentials in different varieties.     

SEASONAL YIELD AND COMPOSITION OF LUCERNE IN RELATION TO THE TIME OF CUTTING OF FIRST AND SECOND GROWTH

Cutting experiments on the spring growth of a stand of Provence lucerne, the first year of which were described in a previous paper (1), were continued For a second and third season.
The value of taking the first cut at the early bud stage, particularly in an unfavourable season, was confirmed.
No adverse effects were observed in the crop after three seasons of this treatment and yields were satisfactory in the third year.
Similar cutting experiments were made on the second growth of an area of Du Puits lucerne after the spring growth had been cut uniformly at the early bud stage.
The curves for protein and fibre production were similar to those for the first growth but the crop matured more quickly and yields were lower.
No further advantage was observed in cutting the second growth before the flower stage although earlier cutting produced no apparent ill-effect on the plant or upon subsequent yield.     

大豆成苗期抗旱性与根系生长的关系

选择抗旱性强、中、弱的大豆品种各5个,在试验室条件下研究成苗期抗旱性与根系生长、胚轴伸长的关系。结果表明:抗旱性强的品种发根早,主根长,侧根数量多,侧根总长度长,胚轴长,成苗率高。在干旱条件下的趋势更为明显。     

THE GROWTH AND DEVELOPMENT OF SOME GRASS SPECIES UNDER COMPETITIVE STRESS

Three experiments were carried out in a semi-controlled glasshouse environment to determine the response of individual plants to competition; (i) between seedlings of different species, (ii) between seedlings derived from seeds of differing sizes within a species, and (iii) between seedlings and established plants.
Differences were detected in seedling competitive ability between species and between plants derived from differing seed sizes. In associations of species of very high and very low competitive ability the differences in competitive ability were accentuated by an increase in plant density.
Established plants of Phalaris coerulescens were less aggressive to seedlings growing in close proximity than were plants of Lolium rigidum and H1 ryegrass. Despite the early death of established swards of L. rigidum , and the consequent removal of competitive stress, there was no rapid increase in the growth and development of seedlings in these swards. Possible mechanisms causing this effect are discussed.
There was evidence of a specific relationship between the species of the established sward and the seedling species, in particular seedlings of HI ryegrass were particularly susceptible to competition from established plants of their own species.
Dry weight per plant, tiller production, rate of leaf appearance and leaf size were ail affected by competition between seedlings; however, tiller production was generally more severely affected than rate of leaf appearance and leaf size.
Dry weight per plant, tiller production, seedling height, number of leaves per tiller and number of seeds per seedling were all affected by competition from established plants.     

THE GROWTH AND DEVELOPMENT OF SOME GRASS SPECIES UNDER COMPETITIVE STRESS

Two pot experiments were carried out in a semi-controlled environment to examine the response of individual plants to competitive stress in simple systems incorporating varying cutting frequencies and soil–nitrogen levels. A third experiment was set up outdoors to examine the effect of competition on individuals in an association, on the association as a whole, and to extend the controlled environment studies to a more complex model involving micro-plots.
Phalaris coerulescens , although its seedlings possessed a high competitive ability, showed a dramatic decline in competitive ability in later stages of the association, this decline being associated with extensive floral development. In micro–plots the effect of competition was so severe as to prevent the expression of seasonal growth characteristics by P. coerulescens .
Considerable inter-specific differences existed in the response to competition of leaf-area production per tiller during periods of regrowth.
Whilst P. coerulescens remained highly productive and maintained a dense tiller population in monocultures, its tiller regeneration following flowering was severely suppressed in competition with vegetative plants of HI ryegrass or Festuca arundinacea .
The number of heads produced per plant, head length and time of head emergence were all affected by competitive stress, the former response being a reflection of the relative competitive abilities at the time of floral initiation. The response of the latter two characters reflected the decline in competitive ability which occurred during later stages of the growth and development of P. coerulescens .     

GRASS GROWTH IN MID-SUMMER: A RE-INTERPRETATION OF PUBLISHED DATA*

In a recent paper by Anslow it was concluded that there was no significant relationship between Leaf-area Index, light interception and growth rate in a perennial ryegrass sward. The author further concluded that higher growth rates would not be obtained by attention to this relationship. The data presented by Anslow are re-examined in this paper and the results of the analysis showed that: (a) recovery growth of the swards followed a sigmoid pattern of growth, (b) at low values of LAI growth rate was low and maximum growth rate was attained when most of the visible light was intercepted by leaves, and (c) the relationship between yield and LAI was linear, indicating that leaf-area increase after defoliation also followed a sigmoid pattern. These results are discussed in relation to Anslow's interpretation.     

VARIATION IN YIELD, MATURITY TYPE, WINTER GREENNESS AND SENSITIVITY TO CUTTING OF HILL GRASS SPECIES

Two experiments are described in which data were collected on yield, floral characteristics and winter greenness of a number of indigenous hill grass species. Differential cutting treatments, besides affecting total yield, affected yield and floral vigour in the subsequent year. Differences in sensitivity to cutting were present among the species. The date at which the grasses were last cut in autumn affected their winter greenness though responses differed among species. The significance of these results in relation to performance and management of hill pastures is discussed.     

THE GROWTH AND DEVELOPMENT OF SOME GRASS SPECIES UNDER COMPETITIVE STRESS

Two experiments were set up in a semi-controlled glasshouse environment to determine the nature of the competitive stress, and the characters associated with competitive ability, during the seedling growth of some grass species. Over a period from sowing until the attainment of a relatively stable tiller population root competition was almost entirely responsible for the suppression of Festuca arundinacea in association with H1 ryegrass at two densities. In contrast, root and shoot competition were of equal importance in bringing about the suppression of Phalaris coerulescens in association with H1 ryegrass, an effect which only occurred at the high density.
Differences in the patterns of root growth of the species and populations are discussed in relation to differences in their competitive abilities.
It is suggested that the rate and extent of nodal root production are closely associated with seedling competitive ability.     

草甸黑土中大豆根系及其活性的动态分布

采用钢丝网框架剖面法，在不同生育阶段分别测定了大豆根系干重和根系活性在草甸黑土中的动态分布。结果表明：大豆根系在草甸黑土中呈浅层分布状态，平均80％以上分布在3～18cm土层内，20cm以下根量锐减。水平分布是以主根为中心随距离加大根重减少，随生育时期的推移根重分布比例逐渐外移。高活性根区与根冠密集区变化一致，随侧根的生长逐渐远离主根，其水平分布区间是，V3期距主根5～10cm、R5期已移至13～40cm；垂直分布为两层，分别在5～17cm和30cm以下土层内。     

A COMPARISON OF THE REACTION OF DIFFERENT GRASS SPECIES TO FERTILIZER NITROGEN AND TO GROWTH IN ASSOCIATION WITH WHITE CLOVER

Seven species or varieties of grass, and a mixture of 3 of them, were sown in pure swards and treated with 4 levels of nitrogenous fertilizer (0,17·5, 35 and 70lb N per acre per cut). Each species, and the mixture, was also sown with white clover. The experiment was cut 4 or 5 times per year. The effect of fertilizer on the yield of each grass was compared with the effect of clover on the yield of the grass/clover swards. Mean annual yields showed an approximately linear response to N; there was a small but significant fall in response to the highest level of N. Response among the species ranged from 20 to 30 Ib of dry matter per Ib N applied for the intermediate level of fertilizer and from 14 to 23 Ib for the final increment of fertilizer.
S37 cocksfoot, S48 timothy, S24 ryegrass, and a mixture of these grasses, were high yielding and responded well to fertilizer N; Irish ryegrass and Agrostis tenuis were less productive and gave poorer responses to N. S215 meadow fescue and S23 ryegrass were intermediate in yield and response.
There were no significant differences between the annual yields of the 8 grass/clover mixtures; the yields of the grass and clover components of each mixture were inversely related. The effect of clover on the yield of the grass/clover mixtures was estimated to be equivalent to the effect of an annual application of 205 lb N per acre to Agrostis tenuis and 120 lb N to S48 timothy. The fluctuations in annual yields were greater with grass/ clover mixtures than with grass swards receiving N.
The yields of grasses when sown with clover were in similar order to their yields when sown pure; but whereas the latter tended to fall from year to year, the yields of the grass components of mixtures (except Irish ryegrass) did not.     

INTER-VARIETY VARIATION IN RHODES GRASS (CHLORIS GA YANA KUNTH)

The characters in 25 varieties of Rhodes grass introduced from Africa have been studied with a view to improving on Australian Commercial. Only the diploid Katambora and a tetraploid variety from Kenya appeared to possess a higher yield potential than Commercial. Sixty per cent of the varieties are tetraploid, the rest diploid. A degree of association occurred between the level of ploidy and some Rhodes grass characters.
Although Rhodes grass appears to be xenogamous, all the critical evidence points to an apodictic form of reproduction. Viable caryopses were extracted from harvested "seed" and the percentage of florets setting caryopses was low. Rhodes grass caryopses germinate fairly well and have a higher resistance than usual to irradiation by gamma rays.     

不同熟期和结荚习性大豆品种的固氮活性差异及其遗传变异

不同熟期大豆品种固氮活性为中热组>中早熟组>早熟组。不同结荚习性大豆品种的固氮活性为无限结荚习性>亚有限性结荚习性。以方差分析估算的大豆固氮活性的广义遗传力平均为42.21％,其中中熟组大豆品种为52.01％,无限结荚习性大豆品种为51.10％。