Oats, clover, beans (Vicia) and maize were tested as ‘break crops’ in three experiments on land cropped frequently with wheat or barley. Barley was used as a ‘no-break’ control treatment. Test crops were winter wheat followed by spring barley; they received N-fertilizer at four rates. After barley wheat had much take-all (Gaeumannomyces graminis var. tritici); all the break crops decreased the take-all effectively and equally. Other soil-borne diseases were unimportant. N-fertilizer required for best yields was less, by 100 kg N/ha after clover and by 50 kg after beans, or maize, than after barley or oats. Best yields after oats, beans, clover were respectively I·O, 1·2, 1·4 t/ha better than after barley. Differences in take-all explain much of these effects. Ploughed-in trefoil did not affect take-all but gave small increases in yield. Percentage N in wheat grain was increased by fertilizer-N; it was greater after barley, maize or clover than after oats. Effects on the following barley, except those of N-fertilizer, were small.

During 3 years a total of ten crops of winter rape and two crops of spring rape were sampled for insect pests and pest damage once or twice a week from the green bud stage to just before harvest. The most common pests were Meligethes aeneusFab., and Ceutorhynchus assimilisPayk.; the former was usually the more numerous, especially on spring rape crops. Ceutorhynchus quadridensPanz. and Dasyneura brassicaeWinn. were less abundant. C. assimilisand M. aeneus immigrated to winter rape crops when temperatures exceeded 15 °C. Maximum infestation of M. aeneus occurred either at the green bud stage, or when flowering began or at full flower depending on temperature; maximum infestation of G. assimilis occurred during flowering, which varied in time from mid to late May. In response to changing temperatures successive waves of immigration sometimes occurred. Immigration to spring rape occurred at green bud stage.

The two methods used for sampling pests, sweep nets and water traps, gave different results. Water trap collections primarily reflected pest flight, and were not necessarily related to the pest population on the crop.

Ovary maturation of M. aeneus occurred between their emergence from hibernation and migration to winter rape. They began laying 3 weeks after their arrival on winter rape but immediately they arrived on spring rape. The proportion of male to female M. aeneus present on crops was variable. C. assimilis fed for 3–4 weeks after their arrival on winter rape before their ovaries developed and they mated.

On both winter and spring rape the number of M. aeneus declined during flowering and that of C. assimilis declined while pods were maturing. Their decline on winter rape was associated with their emigration to new host plants. New generation M. aeneus emerged before winter and spring rape were harvested, and new generation C. assimilis emerged before spring rape but not winter rape was harvested.

The implications of these findings are discussed in relation to pest control.

Electromyographic (EMG) activity, electroencephalographic (EEG) activity, heat production (H), respiration rate (RR), and body temperature (TB) of unacclimatized chickens were measured during periods of light and darkness at ambient temperatures (Ta) between 7·7 and 37·7 °C. The difference between pectoral muscle and abdomen temperature was less than 0·1 °C over the entire temperature range. Body temperature increased (P ≤ O·l) when Ta was above 27·5 °C and was higher in the light than in the dark (P ≤ 0·05). Respiration rate decreased significantly with increasing Ta. The decrease, however, was not as great during the dark (P ≤ 0·05) as during the light period (P s£ 001). Heat production decreased (P ≤ 0·01) with increasing Ta up to Ta = 22·3 °C. There was no significant difference between heat production during the light period and that during the dark period. EMG amplitude declined (P ≤ 0·01) with increasing Ta up to 27·5 °C in the light and 22·3 °C in the dark and was higher (P ≤ 0·05) in the light than in the dark. Mean frequency of EMG activity was independent of light and Ta. The percentage of low-frequency EEG activity in the dark did not change significantly over the entire Ta range, but in the light it decreased as Ta increased above 25·7 °C (P ≤ 0·05). The percentage of high-frequency EEG activity appeared as a mirror image of low-frequency activity. Overall results indicated a thermoneutral zone between 32·2 and 37·7 °C in the light and between 27·5 and 37·7 °C in the dark.

In 1974 and 1975 certified Scottish seed tubers were multiplied at four sites of different altitude which had different mean soil temperatures. The progeny tubers were subsequently grown to produce a ware crop at Wellesbourne in 1975 and 1976. In 1975, the effects of the site of seed production on sprout growth and tuber yield of the ware crop were small though there was an indication of a negative relationship between total tuber yield and the temperature at each site. In 1976 the effect of the site of seed production was more marked. The total sprout length per tuber of both the varieties used was greatest from the hottest site and least from the coolest site. In the field the final yield of both varieties was lowest from the hottest site and greatest from the coolest site of seed production. There was no indication that the effect of the site of seed production on tuber yield occurred as a result of differences in stem density.

Oat straw, timothy straw and two field-cured hays (43·8, 47·3, 52·0 and 56·0% organic matter digestibility (OMD) and 0·56, 0·75, 1·00 and 1·41% N respectively) were fed ad libitum together with 0, 235, 470 and 705 g D.M. of rolled barley to 5-year-old North Country Cheviot wethers in four 4x4 Latin square designs (Expt 1). In an attendant study (Expt 2) of conditions with in the rumen four rumen fistulated wethers were offered daily 0, 200, 400 and 600 g D.M. of rolled barley with ad libitum hay (54·3% OMD, 1·45% N), also following a Latin square design.

The voluntary intake of two of the hays (54·3 and 56·0% OMD) decreased progressively as the barley increased. Intakes of the other roughages were slightly increased when the lowest amount of barley was fed. For each roughage total organic-matter intake and the OMD of the ration increased progressively with increasing amount of barley consumed. No associative effects of barley on the OMD of the roughages were demonstrated. The acid-detergent fibre (ADF) digestibility of diets comprising the highest amount of barley with the oat straw and the field-cured hay of lowest N content were significantly lower than that of the respective all-roughage feeds. In Expt 2 the intake of increasing amounts of barley significantly reduced rumen pH, the molar proportion of acetic acid and the disappearance of hay and hay ADF from terylene bags within the rumen, while volatile fatty acid concentration and the molar proportion of butyric acid increased.

Multiple regressions were obtained relating the change in roughage intake to the amount of barley fed and the digestibility and chemical composition of the roughages. The equation with the least error, explaining 88% of the variation, was Y= 30·561 — 0·615C — 21·453N±3·69, where Y is the change in roughage intake as a percentage of the intake of roughage fed alone, Cis barley intake as g OM/W0·73 and N is the nitrogen content of the roughage.

Several investigations (Shaw & Norton, 1906; Darnell & Copeland, 1936; Kimberley, 1976) have reported no appreciable loss of nutrients of unbroken grain voided by cattle. Although the chemical composition of voided whole grain may be similar to the grain as fed, losses in grain dry matter ranging from 10 to 26% for cereal grains passing through the alimentary tract of steers have been measured (Toland, 1976, 1978a, 6). In one of these studies (Toland, 19786) the disappearance of grain dry matter of whole oats and wheat in nylon bags suspended in the rumen for 48 h was approximately 20 and 35 % respectively. Further analyses of this dry matter remaining in the nylon bags for 48 and 96 h of incubation would indicate which components of the grain were being broken down in rumen fermentation. This report provides information on the differential loss of the fibre and starch components of the grain dry matter from incubation in nylon bags for the two varieties each of oats and wheat and for an additional cereal grain, triticale.

In exploiting to the full the possible advantages of a synchronized oestrus in ewes, the mating management of the ram requires special attention. Previous recommendations (Gordon, 1963) on ram management stated that progestagen-PMSG synchronized ewes should be run with rams at a ram to ewe ratio of 1:10 in the days following treatment. Preliminary work from this laboratory has shown that delaying the introduction of rams until 48 h following sponge withdrawal could improve conception rates significantly (Joyce, 1972). The purpose of the present experiment was to investigate further the effect of time of ram introduction on ewe fertility following oestrous synchronization.

As a nitrogen fertilizer for vegetable production in Britain ammonia has been used mainly for bruasels sprouts (Page, Tatham & Wood, 1974; Page, 1975a; Page, Wood & Case, 1976), and leeks (Page & Williams, 1977). These crops with long growing seasons allow considerable latitude in time of application of the ammonia. Summer and autumn maturing cauliflowers have not only a short growing season, but also have a physiological control of curd formation which appears to be insensitive to nitrogen supply (Salter, 1969; Salter & Fradgley, 1969). They are also usually transplanted into the field, and the root system is therefore restricted for at least part of the growing season. It is therefore desirable to know if the roots would reach the injected nitrogen in time, as, until the ammonia becomes nitrified, nitrogen movement in the soil is small (Page, 19756). Thus, time of application of the ammonia was considered likely to be important.

The practical value of obtaining estimates of general combining ability (GCA) from data accumulated in a breeding programme has been discussed by Gilbert (1967). In this study use has been made of data collected during the course of screening potato breeding material, derived from Solanum vernei Bitt. et Wittm., for resistance to the white potato cyst nematode, Qlobodera pallida (Stone) Mulvey & Stone, to assess the relative contributions of GCA and specific combining ability (SCA) by the procedure described by England (1974) which is based on Gilbert's (1967) method.