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The early vegetative growth of Houdeum Iepouinum and Lolium rigidum was studied at three temperatures in a controlled environment cabinet. The seedling growth rate in each species was much more rapid during the period of endosperm availability than after cndospcrm exhaustion. At the temperatures tested (10, 17, and 24C) the relative growth rate of Lolium was greater than that of Houdeum, with a relatively slight difference at 10 and 24, but with a considerable difference at 17. In spite of the superior relative growth rate of Lolium, seedlings of Houdeum were, for a considerable period following emergence, larger in terms of total weight, leaf area, root weight, root depth, and plant height because of the greater seed size. The length of this period of greater size depended on the temperature, being least (c. 26 days) at 17C, when the advantage of Lolium was greatest. The implications of these findings in pasture production in southern Australia, and especially in the competitive relationships of Hordeum and Lolium, are described.

The germination and establishment of Hordeum lepovinum Link and Lolium rigidum Gaud., two Mediterranean annual grasses, were studied under controlled conditions. Results were related to the ecology of these species as pasture plants in southern Australia. Seeds of the two species germinated over a similar range of constant temperatures (8-30C); Hordeum germinated much more rapidly than Lolium at all temperatures. Lolium has a marked requirement for alternating temperatures for maximum germination, while Hovdeum has a weak or nil requirement. Both species withstood prolonged wetting at high temperatures without germinating or losing all viability. Prior soaking and redrying before germination increased the rate of germination of both species. Light rains which fall before the first germinating autumn rains usually wet the seed only for short periods and this further increases the advantage of Hordeum over Lolium in rate of germination. Hordeum germinated and established much more readily on the soil surface than did Lolium, even though Lolium absorbed water more rapidly. The success of Houdeum was due both to its rapidity of germination, which allowed it to establish before the soil surface dried out, and to its ability to germinate at high moisture tensions. Because of these features Hordeum leporinum has the potential to germinate earlier, more rapidly, and more freely than Lolium rigidum in the autumn of the Mediterranean region of southern Australia.

The pattern of absorption and distribution of nitrogen after floret initiation in wheat was examined with the aid of labelled nitrogen with a view to determining the importance of sterile tillers as a source of nitrogen for the fertile parts of the plant. Tertiary tillers were found to be of no importance as direct importers of nitrogen from the growth medium; absorption by these tillers was almost entirely via the roots of the main stem and the primary tillers. In conditions of high nitrogen supply the tertiary tillers continued to receive nitrogen from the main stem and primary tillers, but the tertiary tillers of low nitrogen plants were starved of nitrogen and soon senesced. When the sterile, tertiary tillers died there was a remobilization of most of their nitrogen, apparently to the fertile parts (main stem, primary and some secondary tillers) of the plant, but a small quantity of nitrogen was also lost to the nutrient solution. It is concluded that although sterile, tertiary tillers act as a temporary nutrient reservoir for the fertile plant parts, they are in fact of little or no value and may well be regarded as a useless vestige of perenniality in the wheat plant.

A study was made of the light regime and the growth of clover: (a) in mixed swards with varying proportions of grass; (b) in specially designed cultures in which grass and clover competed for light alone. The growth of the clover showed direct dependence on the level of radiation at the surface of the clover leaf canopy; it was positive when radiation values were above about 60–80 cal/cm⊃;/day but fell to zero or negative rates at lower radiation levels. A relationship is presented between the level of radiation, the leaf area index, and the crop growth rate. It is shown that the optimum leaf area index increases with increasing levels of radiation; and further that as the leaf area index increases, the level of radiation required for maximum growth rate also rises. The implications in agricultural practice are discussed briefly.

Grass-clover swards were grown at four levels of nitrogen to provide a range from extreme clover dominance to extreme grass dominance. Yield, botanical composition, leaf area index, and light density were measured at 3.5 cm vertical intervals in each of the mixed swards throughout the growth period. It was directly demonstrated that the growth of clover in these mixed swards was governed by a series of relationships, namely: (a) Increasing rates of nitrogen application gave increased yields of grass (positive). (b) Increased yields of grass gave higher leaf areas of grass disposed above the clover leaf canopy (positive). (c) Higher leaf areas of grass above the clover reduced the light density at the clover leaf canopy (negative). (d) Reduced light density at the clover leaf canopy caused a reduced growth of the clover (positive). Under conditions of heavy grass growth and of consequent low light density at the clover canopy, the growth of clover not only became slow but eventually was strongly negative, leading to a marked reduction in both the number of clover plants and the yield of clover.

At an elevation of 2040 ft on the southern tablelands of Kew South Wales, seed production by swards of subterranean clover was apparently governed by mininnnn temperatures (frequency and intensity of frosts) during the flowering period. The aggregate deficit of the daily minimum temperature below 40°F in the 21 days from the commencement of flowering showed a high correlation with seed production per unit area in four successive seasons. Spring frosts account for the altitudinal limit of about 4000 ft to which subterranean clover grows in the alps of south-eastern Australia. Lateness of flowering has specific survival value at high altitudes in this region and in such areas as the high parts of the plateau of Spain. On the average 92 per cent. of the seed crop germinated in the year following its production, with 6.3 per cent. in the second year, and with falling values to 0.07 per cent. in the fifth year. Germination thereafter was nil or negligible. The early-flowering variety Dwalganup appeared to show a genetic difference in the persistence of more of its seed into the second and subsequent years. There was a regular seasonal pattern of seed germination, with the peak of germination occurring in the late summer and autumn. The "carry over" of seed into the second and subsequent years, and the germination peak in the autumn, have each considerable ecological significance.

Two field studies conducted in the Mediterranean type environment of Adelaide, South Australia, are described. The first experiment was designed to assess the effects of defective summer grazing by young sheep upon current and lifetime productivity, while the second sought to define the nature of the nutritional deficiencies of the mature herbage of sown pastures in terms of energy and protein respectively. The results show that the mature herbage of the sown pastures under study was deficient in both protein and energy. However, the retarded growth resulting from grazing this herbage appeared to be of no permanent significance in average to well-grown wether weaners; summer periods of defective nutrition did not affect ultimate size nor influence subsequent productivity.

A new technique is described for the study of the interaction between competition for light and competition for a nutrient or for water. The technique was applied in a study of the competition between two grasses for light and for nitrogen. The aggressor species showed a negative interaction in the effect of the two modes of competition; it was slightly reduced in yield by competition for either factor alone, but when competition for both factors was operative, it achieved almost the same yield as in the absence of competition. The effect of the two modes of competition on the suppressed species showed a positive interaction; the depression in yield when there was competition for both factors greatly exceeded the sum of the effects of competition for the separate factors. An analysis is made of the nature of competition for one or more factors. Competition for even a single factor involves interaction between direct and indirect effects; when competition occurs for two factors, it leads to multiple interactions between two groups of effects and thus greatly intensifies the effects of competition for either factor operating alone.

An experiment was conducted to study the growth of subterranean clover (Trifolium subterraneum L.) sown at different densities; the control swards were not defoliated while others were subjected to a single defoliation at various dates. During the final month the rate of dry matter production (tops only) increased to a maximum when the leaf area index (the ratio of the area of the leaves to the area of the ground surface - L.A.I.) was about 4-5, falling by about 30 per cent. as the L.A.I. increased to 8.7. The rate of leaf production was greatest at about L.A.I. 4-5, falling to zero at L.A.I. 8.7. Climatic conditions during the growing season influenced the relationship of L.A.I. to growth; as conditions became more favorable the values of the optimum LA.1. for growth and of the ceiling L.,4.1. progressively rose. Irrespective of the density, all swards tended towards a common ceiling L.A.I. and yield by the end of the season. The effect of defoliation depended on the L.A.I. at which defoliation occurred, on the value to which the L.A.I. was reduced, and on current climatic conditions. If swards near the ceiling L.A.I. were defoliated, total dry matter production was slightly increased and there was a great increase in leaf production. On the other hand, defoliation of swards from about the optimum L.A.I. to very low L.A.I. values led to a substantial reduction in both dry matter and leaf production. It is suggested that all these effects depend on the light relationships within the sward and their influence on the balance of photosynthesis and respiration. Pasture at the optimum L.A.I. will give greater production than swards of lower or higher L.A.I.; defoliation can give greatly increased leaf production, unless L.A.I. is reduced to very low values.

A further investigation has been made on soils examined by Donald and Williams (1955) in a survey of the influence of superphosphate and subterranean clover (Trifolium subterraneum L.) on podzolic soils formed on granodiorite in the Crookwell district of New South Wales. The soil organic matter was found to have approximately constant proportions of carbon, nitrogen, sulphur, and phosphorus in the ratio 155 : 10 : 1.4 : 0.68, and it is suggested that the rate of build-up of soil organic matter under the clover pastures may have been limited by the amounts of sulphur supplied in the superphosphate top-dressings. The soil organic matter was found to have a cation-exchange capacity a t pH 7.0 of about 220 m-equiv./100 g, and increases in soil organic matter have led to substantial increases in the cation-exchange capacity of the soil. About 75 per cent. of the total cation-exchange capacity of the unimproved soils was due to organic matter while, in the most improved soils, this figure approached 90 per cent. The increases in cation-exchange capacity included increases in exchangeable hydrogen and were accompanied by decreases in soil pH. There were increases equivalent to 6.5 lb of exchangeable potassium, 25.5 Ib of exchangeable calcium, and 5.2 lb of exchangeable magnesium per acre in the surface 4 in. of soil for each hundredweight of superphosphate applied per acre. Increases in soil organic matter also resulted in increases in the field capacity which may reflect improvements in soil structure. Results indicate that heavier rates of superphosphate application would increase the rate of fertility build-up.

An experiment was undertaken with wheat (cv. Insignia 49) to study the effects of interplant competition on dry matter and grain production. Crops ranging in density from 1.4 to 1078 plants per sq. metre were established, and light intensity and growth measurements were made within the crop. Four sequential stages in the growth of the crop were recognized, namely: A period in which there was no interplant competition at any density. A period in which the crop growth rate showed a curvilinear relationship to the leaf area index and a linear relationship to light interception. A period when the weight of ears (early dough stage) showed a linear relationship to an expression involving the weight of green leaf in an earlier period and the percentage survival of tillers. A period of grain filling and ripening in which some further relative changes in ear and grain weight occurred. It is suggested that the application of this type of analysis to the reaction of different genotypes to crowding may add to an understanding of crop performance.

A survey was made of the influence of the use of superphosphate and subterranean clover (Trifolium subterraneum L.) on podzolic soils formed on granodiorite in the Crookwell district of New South Wales (average rainfall, 32.7 in. per annum). Forty-four paddocks were sampled; they varied from untreated native pasture to paddocks which had been for 26 years continuously under clover and which had received a total of 13 cwt of superphosphate per acre. In all instances there had been no cultivation during treatment, and the land use mas uniformly one of sheep raising, principally for wool but with some emphasis on fat lamb production on highly improved pastures. Criteria used in this study were the changes in yield and botanical composition of the pasture, changes or trends in the chemical composition of the 0-4 in. depth of soil, and the yield of oats produced by each of the soils in pot culture with varying superimposed applications of phosphorus, sulphur, and nitrogen. The native pasture species disappear under the competition by subterranean clover, which gives a fourfold increase in the yield of pasture. Within the limits of experimental error, the phosphorus and sulphur applied as superphosphate, even that applied many years previously, can be accounted for in the surface 4 in. of soil. Losses by removal in wool and carcases are small. The added phosphorus is present in approximately equal amounts as organic phosphorus and readily extractable inorganic phosphorus. The applied sulphur appears to become a part of the organic complex. Eighty-five pounds of nitrogen has been added in the surface 4 in. of soil by rhizobial activity for each hundredweight of superphosphate applied per acre. Initially the most acute deficiencies affecting plant growth on these soils are those of phosphorus and nitrogen, with a less pronounced deficiency of sulphur. After a period of several years of superphosphate and clover, each of these deficiencies is much reduced, the order of the intensity of deficiencies then being nitrogen, sulphur, and phosphorus. Soil pH falls with superphosphate application at the rate of about 0.06 units per hundredweight of fertilizer per acre, but may reach an equilibrium value at about 5.1. This could be due to the increase in exchange capacity of the soil as a result of the increase in organic matter. A field experiment on two sites also indicated the increase in fertility under subterranean clover pasture and demonstrated the capacity of the improved soils to produce a satisfactory field crop of oats.

Inflorescence and seed production were studied in swards of varying 5 density of two annual Mediterranean pasture plants, Trifolium subterraneum L. and Lolium rigidum Gaud., each in pure culture. While the maximum level of dry matter production, achieved at moderate densities, was maintained at all higher densities, seed production showed a peak at moderate densities and thereafter a progressive decline. The greatest number of inflorescences was produced at densities exceeding those of peak seed production. Although the most widely spaced plants had the greatest numbers of inflorescences and seeds per plant, they had smaller seeds and fewer seeds per inflorescence than did substantially denser swards, apparently owing to intense intra-plant (inter-inflorescence) competition at the widest spacings. It is suggested that the results can be explained in terms of the changing competitive relationships between and within the plants of the sward at the times of initiation of flower primordia, of floral development, and of seed production. Dense swards give most of the attributes needed in the use of these plants for grazing purposes; for seed multiplication swards of moderate densities give the highest yields of seed per unit area.

A series of experiments was conducted to examine the influence of density, stage of growth, and fertility level on intra-specific competition among annual pasture plants. At sowing there is a linear relationship between density and yield (weight of embryos or embryo + endosperm per unit area). Competition is evident in dense populations shortly after germination and thereafter becomes operative progressively in populations of lower and lower density. Because of the extreme reduction in growth rate in dense swards later in the season and the high growth rate in sparse swards, the sparse sward tends to approach the more dense sward in its final yield. Final yield of dry matter is constant from moderate to high densities. There is no reduction in dry matter per unit area even in extremely dense swards. This maximum yield of dry matter for the environment is controlled by some factor of the environment. It is considered that nitrogen was the factor in two of the experiments here reported and light in the third. The significance of light in competition in pastures is discussed. Practical applications of these findings are discussed.

Pre-soaking seed in a sodium molybdate solution was compared with the direct application of sodium molybdate to the soil as a means of preventing deficiency of molybdenum. Subterranean clover, which was used as the test plant, was grown in a molybdenum deficient soil in pot culture for this study. Pre-soaking in 0.1 per cent. or 1 per cent. sodium molybdate was fully effective in promoting normal growth. The soil and seed treatments were equally effective in promoting yield response at all levels of application examined. At levels of application in excess of the requirements for maximum yield, pre-soaking gave a higher molybdenum content of the tops than did equivalent soil applications. At all levels of application, pre-soaking gave a higher nitrogen content than that resulting from the soil application of molybdenum.

A study was conducted at Adelaide of the ignitability of monospecific swards of four Mediterranean annual pasture plants under windless conditions throughout the normal field desiccation of the swards in the spring. For any individual species the ignitability depended almost wholly on the percentage of water or the very closely correlated percentage of dead herbage. Atmospheric conditions had no measurable influence on ignitability during desiccation. Trifolium subterraneum was much less ignitable at any particular level of moisture content than were the grasses. Lolium rigidum was more inflammable early in the desiccation process than was Hordeum leporinum of equal water content, presumably due to the greater continuity of dry leaf; but H. leporinum was ignitable much earlier in the spring because it matured and dried sooner than did L. rigidum. In the case of the grasses, only those firebrands that fell to or near the soil surface started a fire, whereas the more compact sward of T. subterraneum, when sufficiently dry, lit readily at the upper surface.

The growth and water content of annual swards were examined in a Mediterranean environment under three lengths of season (attained by extension of the natural season by irrigation), and under two defoliation treatments. Swards attained their maximum percentage water (about 800-950 per cent of the dry matter) in late July or early August. Maximum dry matter yields were attained two months later, when the percentage water had fallen to 150-400 per cent. The swards were dead and dry about 50 days after maximum yield. Earlier commencement of the growing season (18 days) doubled the winter production, delayed desiccation, in the spring and gave heavier dry herbage in the following summer. Extension of the season in the spring gave little response by undefoliated swards, but a considerable response by defoliated swards ; it failed to prevent the maturation and desiccation of these annual pasture plants. Autumn irrigation gave a greater return of dry matter per inch of water than did spring irrigation. The influence of these practices on pasture growth and summer fuel production is discussed.