Two seed components, dark dormant and non-dark dormant, were identified in experiments in which germination and survival of seeds buried in soil were examined. These comprised c. 10–20% and 80–90% of the seed population respectively. About 12% of the dark dormant seeds (1–2% of total seed population) germinated when first buried between 0 and 2 cm depth, and subsequent disturbance of the soil on two occasions caused further germinations. In contrast, all non-dark dormant seed rapidly germinated when buried at 2 cm; however, germination of non-dark dormant seeds decreased progressively as burial depth increased, until at 11 and 14 cm no seed germinated. In one experiment, seed that failed to germinate when buried at 14 cm was found to germinate readily if transferred to a depth of 2 cm without soil disturbance. This indicated that dormancy was enforced, rather than induced, in seeds buried relatively deeply for short periods. In these experiments soil temperature and moisture were favourable for germination, and it is suggested that an unfavourable gaseous environment around deeply buried seeds is the factor enforcing dormancy. The implication of these findings for the persistence of annual ryegrass in the pasture-crop rotation is discussed. _____________________ *Part I, Aust. J. Agric. Res., 28: 81 (1977).

The use of fixed interval or growth stage (crown bud elongation) cutting management for lucerne was studied for cultivars with dormancy characteristics ranging from highly winter-active to winter-dormant. Fixed cutting intervals ranged from 3 to 8 weeks and were imposed on irrigated stands in a subtropical environment. Persistence, dry matter yield, weed yield, nitrogen (N) concentration and yield, and root reserves were measured over a 2-year period. For cultivars from all dormancy classes, persistence was highest with either 5- or 6-weekly cutting, while dry matter yield was maximised with 5-weekly cutting. Nitrogen concentration was highest with 3-weekly cutting but N yield was greatest under 4-weekly cutting. Root reserves were not maintained unless the cutting interval was extended beyond 7 weeks. Growth stage cutting produced equivalent yields and persistence but lower N concentrations and root reserves than the best fixed interval cutting treatment. There was no evidence that cultivars of different dormancy classes require different cutting management to obtain optimum performance. Therefore, a fixed cutting frequency of 5 weeks throughout the year is an acceptable management compromise for all lucerne cultivars, combining high dry matter and N yields with acceptable levels of foliar N and root reserves. Although the more complex management decisions associated with growth stage cutting appear unwarranted, dry matter yield could be maximised by using a flexible cutting schedule which matched cutting interval with growth rate (4 weeks in summer and 7 weeks in winter).

Germination of Lolium rigidum seeds, in the light (12 hr day length) and in the dark, at constant temperatures of 12, 18, and 24°C and an alternating temperature of 24/12" (12112 hr), was studied in freshly harvested seeds and in seeds stored for 18 weeks. In freshly harvested seeds the highest germinability (80%) was recorded at 12' in either light or dark and at 24/12' in the light. After 18 weeks' storage, a germinability of between 95 and 100% was observed at 12" and 24/12" in the dark and at 24' and 24/12' in the light.In another experiment in which seeds from a different source were used, seeds kept in six different environments and recovered at 3-weekly intervals during a 21 week post-harvest period were examined for germinability and germination rate. The six environments were: storage in a room, storage in a 60/15"C temperature cabinet, and four field treatments in which seeds were buried 0 . 2 and 1 . 0 cm under both a bare and a mulched soil surface. Germination was tested in the light and in the dark at an alternating temperature of 24/12". Major increases in seed germinability with age occurred during the first 9 weeks after harvest. The different environments influenced the relationship between seed age and germinability only during the first 9 weeks. Seeds located 0 . 2 cm beneath either a bare or a mulched soil surface during summer germinated at a faster rate than seeds kept in the other environments.These findings are discussed in relation to the germination behaviour of seeds in the field. Ryegrass (Lolium rigidum Gaud.) is a common component of annual pastures in southern Australia. In a ley farming system, a proportion of the seed population can remain ungerminated after the first seasonal rains and during cultivations (McGowan 1970). These seeds may germinate later in crops and create a serious weed problem (Pearce and Quinlivan 1971). Ryegrass infestations as low as 400 plants m-2 can markedly reduce grain yields (Lumb and McPherson 1964).

Germination of Lolium rigidum seeds, in the light (12 hr day length) and in the dark, was studied at constant and alternating (12/12 hr) temperatures in the range 8–35°C. Seeds had after-ripened for 22 weeks. Different constant temperature optima for germinability were found: 27° in light and 11° in dark. Germinability at alternating temperatures in darkness was determined solely by the minimum temperature of the alternation, and there was no response to thermoperiodicity per se. In contrast, light and alternating temperature appeared to interact to increase germinability, although the highest germinability occurred only when the maximum temperature was close to the optimum constant temperature, i.e. about 27°. Germination in both light and dark was most rapid where either the constant or the average temperature of an alternating regime was between 18 and 29°. Below 18° germination rates decreased markedly, and at 8°, rates were one-third of those at 18°. Seeds germinated more slowly in light than in darkness at all temperatures, but the differences were small relative to the effects of low temperatures.In another study, seeds collected from plants naturalized in eight different localities in the cereal belt of Western Australia and subsequently planted together in two contrasting environments were examined for germinability at 24/12°C in light and dark 18 weeks after harvest. Dark germinability differed between seed sources but not between planting sites, and ranged between 78 and 93%. Exposure of germinating seeds to light substantially alleviated dormancy in seeds from all sources.

The yield and plant survival of 23 North American and 5 Australian lucerne lines were assessed at Biloela and Gatton, Queensland, under irrigation over a 40-month period. Total yields ranged from 49 to 72 t/ha at Biloela and from 14 to 47 t/ha at Gatton. The relative performances of lines were similar at each site. The highly winter non-dormant lines were the highest yielding, particularly HS Gen 3 Composite, Matador and CUF 10 1. Semi-dormant lines were generally more productive than nondormant and dormant lines, with Pioneer 581, Falkiner and DeKalb 167 the most productive. Multiple regression analyses showed lucerne yield at both sites to be highly correlated with relative winter dormancy and plant survival. At Gatton, population at establishment, winter dormancy and disease ratings for Phytophthora root rot and anthracnose all influenced survival of lucerne plants, whilst at Biloela establishment population was the only significant factor. The potential commercial impact of lines with reduced winter dormancy and improved resistance to root rot and anthracnose in irrigated stands in south-east Queensland is discussed.