Two experiments compared yields of spring barley following barley, oats, beans (Vicia faba), red clover (cut) and (one experiment only) oil-seed rape, and tested effects of trefoil (Medicago lupulina) undersown in the preliminary crops of barley and oats. N fertilizer was applied at two rates to preliminary crops, and four rates to the final crop in each experiment. Barley following barley suffered severely from take-all disease (Gaeumannomyces graminis var. tritici); barley after other crops was little affected. Other recognized soil-borne diseases were unimportant. Barley yielded less after barley than after other crops except where excessive N fertilizer caused lodging. Clover and beans left N residues equivalent to about 88 and 44 kg fertilizer N/ha respectively; undersown trefoil left inconsistent N residues. Couchgrass (Agropyron repens) was more prevalent after barley than after other crops.

During the early period of infestation of winter rape, pollen beetles and seed weevils were mainly feeding and attaining sexual maturity. Before a crop flowered pollen beetles fed on buds but only some of those which they had perforated to obtain pollen dropped off. When flowering started adults obtained pollen from flowers rather than from buds. They laid their eggs in the buds but not in the flowers. Larvae moved from flower to flower up the raceme and caused no damage. Probably many podless stalks have been wrongly attributed to pollen beetle damage.

Overwintered seed weevils caused no damage by feeding on rape pods. New generation seed weevils caused some loss of seed weight and viability when feeding on pods of spring rape; this is probably unimportant on a field scale.

Pollen beetles and seed weevils mated from mid-May until the emergence of new generation adults; these did not mate before hibernating.

The protein contents of plants decline with increasing size and age even when the plants are adequately supplied with nitrogen. The quantitative nature of this decline needs to be defined for use in models for nitrogen response and to improve diagnostic criteria for detecting nitrogen deficiency. For this reason we have considered the use of photosynthate for the synthesis of the organic constituents within a plant and for maintenance purposes. It has led us to deduce that

In (P/P0) = (δβ/a) In (F/F0) – βMG(T–T0),

which in the special case of exponential growth approximates to

In (P/P0) = (δβ/a) In (F/F0),

where P is the critical protein content at time T, F is the total weight of nitrogen-free organic matter at time T, P0 and F0 are the corresponding weights at some initial time T0; δ is a coefficient related to the relative rates of production of protein and the nitrogenfree constituents of plants. β and α. are energy coefficients for the conversion of glucose into protein and nitrogen-free organic matter and MGis the maintenance respiration rate in g of glucose/g of protein/day.

The values for β and α depend on the chemical composition of the crops but for forage crops appear to be about 0·62 and 0·76 respectively over a wide range of temperatures. MG is temperature dependent and experimental evidence suggests that it is about 20 mg of glucose/g of protein/day at 15 °C. Less information is available about δ although when there are ample supplies of nitrogen it is probably near unity.

A theoretical model for the influence of plant size and age on plant protein content was tested against the results of 13 field experiments on vegetable crops grown with high rates of application of N, P and K fertilizers.

For each crop the protein contents of individual plants of similar age (but of different sizes) harvested at regular intervals during growth were found to bear a linear ln-ln relationship to their contents of nitrogen-free organic matter. The slopes of the lines of best fit were almost the same at each harvest date. The intercepts were similar irrespective of harvest date when growth was exponential but showed an approximately linear decline with length of growing period when it was not. These features are in agreement with the theory.

Maintenance respiration rates were deduced by interpreting the data in terms of the theoretical model. The values determined in this way were between 8 and 21 mg of glucose/g of protein/day for the above ground parts of the plant compared with values of between 8 and 87 mg that have been obtained by entirely different methods.

It is concluded that during the exponential phase of growth the critical protein and, thus, nitrogen contents depend primarily on plant size and on the chemical composition of the nitrogen-free organic matter, but that when growth is not exponential plant age and maintenance respiration are also of importance. The models should facilitate the determination of the critical nitrogen contents for crops grown under different conditions.

Heifers and suckled cows in 34 herds were included in a field trial using prostaglandin F2α (PGF2α) to control ovulation. Oestrus was induced by two intramuscular injections of PGF2α 10–12 days apart in 592 animals. Of these, 264 were inseminated once at 80 h and 328 were inseminated twice, at 70 and 88 h, after the second injection of PGF2α. Pregnanoy was confirmed by palpation or by calving without further insemination. After adjustment for independent sources of variation in fertility, estimated true pregnancy rates were 59·6 ± 3·0% for cattle inseminated once, and 61·3 ± 2·7% for those inseminated twice at one oestrus, compared with 66·4 ± 3·2% for 220 animals allowed to cycle normally in the same herds (controls).

In a sub-sample of 538 animals, semen usage was 15% higher for the treated group inseminated once and 107% higher for the group inseminated twice, than for the controls. The breeding season extended over about 80 days for the control groups, and about 30 days for the treated groups.

No side effects attributable to prostaglandin were observed among the treated cattle.

Milled barley straw, either untreated or treated with 70 g of NaOH/kg straw was supplemented with four levels of urea, namely 0, 6, 12 or 18 g/kg and fed ad libitum to young sheep. For the untreated straw, dry-matter intakes were (g/day) 423, 451, 441 and 463, while the digestibility of organic matter was 458, 467, 490 and 483 g/kg, respectively. For the treated straw, the intakes of dry matter were 355, 402, 531 and 567 g/day and the digestibility of organic matter was 423, 480, 589 and 628 g/kg respectively.

The different responses to urea supplementation of treated and untreated straw are discussed in relation to a new system of estimating protein requirements for ruminants put forward by the Agricultural Research Council.

Diploid and tetraploid perennial ryegrass (Lolium perenne L.) cultivars were compared sown alone and in mixtures, with and without cattle treading for 4 years after the year of sowing. Data were also obtained on the survival of tetraploid ryegrass in mixtures under farm conditions.

The overall effect of treading was not large but annual yield of dry matter was reduced by cattle treading every year (mean 9%). Sheep grazing and treading also reduced yield below that of cut plots. The reduction depended on the sampling date and varied from 40% to nil. In two instances treading increased yield.

Interactions between cultivars/mixtures and treading occurred in 22% of the occasions when treading influenced yield. In the first harvest year the tetraploid Reveille was more resistant to treading than the diploid S. 24. In older swards (3rd and 4th harvest year) the situation was reversed. The occurrence of cultivar/mixtures × treading interactions and the effect of mixing diploid and tetraploid ryegrass on resistance to treading were unpredictable.

The evidence from the main trial and the farm survey showed that tetraploid ryegrass could persist for at least 3 years after the seeding year when exposed to periods of high stock density. In addition, in mixtures there was no initial domination of the sward by either component when cut or when subjected to severe treading. In the third harvest year of the experiment the proportion of tetraploid ryegrass decreased considerably. Total yield of the mixtures was not significantly different from that of pure swards of the components though seasonal distribution of yield could be modified. The contribution of tetraploid ryegrass to swards up to 4 years old was in proportion to the percentage of tetraploid in the seeds mixture. Evidence from both the experiment and farm survey demonstrates that it is possible to exploit advantages claimed for tetraploids in mixtures for three harvest years without detrimental effect on sward performance.

The response to dietary inclusion of NaCl or NaHC03 at 42 and 60 g/kg (18 g Na/kg) respectively was examined in relation to rumen fermentation and the flow of nutrients to the duodenum of calves.

Measurements were made with four calves on each diet at 8 and 11 weeks of age: weaning having taken place at 5 weeks of age.

Osmotic pressure, pH, total VFA concentration and molar proportions of VFA were not significantly affected by the treatments imposed. Rumen dilution rate was increased by 28% on the NaHCO3 diet compared with the other two diets but this difference failed to achieve statistical significance. Mean duodenal flows of organic matter, modified acid detergent fibre and total amino acids were 0·52, 0·72 and 1·25 of the respective dietary intakes and were not significantly affected by the treatments imposed. NaHCO3, however, significantly increased the supply of α-linked glucose polymer to the small intestine (15% of dietary intake) compared with the control (4%) and NaCl (6%) diets. The results demonstrated that NaCl and NaHCO3 had small effects upon the digestion within the rumen of young calves with specific reference to flow of nutrients to the proximal duodenum. It is suggested that the stimulatory effect of NaHC03 on food intake and performance of calves may be attributable to an increase in rumen buffering capacity, and some indication of an increase in the fractional outflow rate of water and possibly particulate matter from the rumen.

The triple test cross analysis (Kearsey & Jinks, 1968; Jinks & Perkins, 1970) was used to detect and estimate the additive, dominance and epistatic components of genetic variation for four metric traits, namely, final plant height, number of spikelets per spike, 100-kernel weight and yield per plant, in the first backcross populations of four wheat crosses (Norteno 67 α Moti, Sonalika α Moti, Kalyan Sona α Sonalika and Kalyan Sona × NP 876). Epistasis was a more important component of variation for final plant height and yield per plant than for number of spikelets per spike and 100-kernel weight. On the other hand, the additive component was highly significant for all four characters in all eight backcrosses.

Sesamum phyllody is a serious disease of sesame (Sesamum orientale L.). The disease is mainly spread by the leaf–hopper vector Orosius albicinctus Distant (Ghauri, 1966). The biology and bionomics of the hopper was worked out by Bindra & Singh (1970). The relative fecundity–cum–fertility and longevity of the hopper on the diseased and healthy plants were studied to supplement the existing information.

With the development of effective methods of oestrus synchronization (Gordon, 1975), it is now possible to breed ewes at most times of the year. Encouraging conception rates have been reported following insemination (Colas & Brice, 1970; Colas et al. 1973; Gordon, 1975). A major disadvantage with the technique is the need to inseminate ewes twice at 10–14 h intervals. Because of the anatomy of the ovine cervix, it is not possible to deposit semen in the uterus as in the bovine. The present experiment was designed to compare a single or double insemination with natural service. Two types of inseminating gun were employed in an effort to deposit semen deep in the cervical folds.