A COMPARATIVE STUDY OF THE GROWTH OF WILD OATS (AVENA FATUA L. AND A. LUDOVICIANA DUR.) AND OF CULTIVATED CEREALS WITH VARIED NITROGEN SUPPLY

Growth analysis of wild oats ( Avena fatua and A. ludoviciana ) grown in pots with different levels of nitrogen supply showed many similarities to spring barley, winter oats and winter wheat.
Small differences that could affect competition between wild oats and cereals occurred mainly in the seedlings. Wild oat seedlings were smaller than the corresponding cultivated cereals in total dry weight, total nitrogen content, leaf area and number of shoots. However, very young wild oat plants had higher net assimilation rates than the cultivated cereals and soon caught up and passed them. The difference in net assimilation rate did not persist, and in the later stages of growth differences in dry-matter production depended mainly on differences in leaf area. Another important difference between wild oats and cultivated cereals was that 98–100% of the wild oat seeds and none of the crop seeds were dormant 2 months after harvest.
Ear emergence in wild oats spread over a longer period, the range of ear heights was greater and the tallest ears were taller than in the corresponding cultivated cereals. Assimilation in the ear appeared to account for less of the total dry matter of the plants of wild and cultivated oats than of wheat. The wild oats produced more seeds per plant than the cultivated cereals, but the 1000-grain weight, and hence the total dry weight of seeds, was lower in the weeds than in the crop.
Addition of nitrogen to the soil affected the growth of the wild oats in the same ways as the cultivated cereals; they took up the same amount of nitrogen per plant as winter oats and winter wheat but more than spring barley.
It is concluded that wild oats are most susceptible in the seedling stage to competition from the crop and that nitrogenous fertilizer applied to an infested field is unlikely to alter the balance between the yields of crop and of wild oats.     

SOME EXPERIMENTS AND FIELD OBSERVATIONS ON THE GERMINATION OF WILD OAT (AVENA FATUA AND A. LUDOVICIANA) SEEDS IN SOIL AND THE EMERGENCE OF SEEDLINGS

The distinguishing characters of Avena fatua and A. ludoviciana are described.
Pot experiments and field observations showed that most seeds of A. fatua germinated in spring and a few in autumn; hardly any germinated in summer or winter. Seeds of A. ludoviciana germinated in winter only. The greatest depth of sowing from which seedlings of either species reached the surface was 9 in., but seedlings from this depth were weak and yellow when they first appeared. A. ludoviciana gave more and sturdier seedlings than A. fatua from 6 and 9 in. There was no evidence of induced dormancy in seeds of A. fatua buried at depths down to 20 in. Germination of this species was hastened by monthly cultivation of the soil. The maximum survival of A. fatua was 3 years in pots and slightly longer in the field; seeds of A. ludoviciana in pots survived only 2 years. The two or three seeds of each spikelet of A. ludoviciana germinated in turn, starting with the largest, but the interval between germination of successive seeds varied.
Seedlings from freshly sown seeds of both species were more vigorous than seedlings from seeds which had been buried for a year or more. Germination and subsequent growth of both species took place in soil of pH 4.5 to 7.0 approx.     

Studies in Wild Oat Seed Dormancy: I. THE ROLE OF ETHYLENE IN DORMANCY BREAKAGE AND GERMINATION OF WILD OAT SEEDS (AVENA FATUA L.)

Seed of Avena fatua were shown to exhibit a characteristic loss of dormancy during dry storage at 25 C, whereas similar seed stored at 5 C maintained dormancy. 2-Chloroethylphosphonic acid was shown to increase germination of partly dormant seed imbibed under certain temperature regimes; a similar effect could not be established for fully dormant or fully nondormant seed. Using gas-liquid chromatography, natural ethylene levels were followed during imbibition of fully dormant and nondormant seed. A large peak in production was observed in the period prior to radicle emergence in the case of the nondormant seed. Measurements of ethylene production taken at 15 C, following periods of after-ripening in moist soil at either 5 or 25 C, indicated that endogenous production was unlikely to be a main cause of dormancy breakage in this species. The possibility that endogenous ethylene could play a role in natural dormancy breakage in aged seeds is discussed. The practical possibilities of 2-chloroethylphosphonic acid as a dormancy breaking agent in a field situation are outlined.     

A COMPARISON OF THE GROWTHS OF WILD AND OF CULTIVATED OATS IN MANGANESE-DEFICIENT SOILS

Two species of wild oats, Avena fatua and A. ludoviciana , and two varieties of cultivated oats for comparison, were grown to maturity in pots of manganese-deficient soil with and without added manganese.
A. ludoviciana showed different leaf symptoms of manganese deficiency from A. fatua and the cultivated varieties. In other respects wild and cultivated oats were similar in their responses to the level of manganese supply, though differences were observed in the severity of the effects. These are summarized in Table 6. The relative susceptibility to manganese deficiency of the wild and cultivated oats differed according to the effect considered. The total dry weight at harvest is an integration of all the preceding effects on growth and is therefore presumably the best single criterion for determining susceptibility to manganese deficiency. On the basis of per cent loss of total dry weight at harvest due to lack of manganese, A. fatua is judged less susceptible and A. ludoviciana more susceptible than the two cultivated varieties and no distinction can be made between the latter.
The most interesting differences between wild and cultivated oats in response to the level of manganese supply occurred in seed production. Manganese-deficient wild oats showed a smaller reduction in the number of seeds formed but a greater reduction in the size and manganese content of individual seeds than the cultivated varieties.
Manganese deficiency lowered the percentage of viable seeds and the percentage of dormant seeds produced by both A. fatua and A. ludoviciana.