The optimal intensity of P supply for lettuce was investigated in a pot experiment with five soils, six levels of P application (0, 15, 30, 60, 120, 240 ppm) and three times of harvest (2, 3 and 4 weeks after emergence). The P adsorption isotherm for each soil was measured in 0.01 M CaCl2.

All soils responded strongly to P application, the amounts required for maximum growth varying from 120 ppm on a sandy soil to 300 ppm on a moss peat. The differences in requirement were related to the P adsorption by the soil, and on all soils a solution P concentration of about 1 ppm resulted in maximum growth.

The Optimal leaf P concentration in young lettuce was about 0·6%.

Fifteen intervarietal F1hybrids and their parents were evaluated in two field sward trials, representing three levels of management intensity each maintained over a 2-year harvest period. The trials were sown in different years and at different sites. Several hybrids exhibited significant levels of heterosis for total annual dry-matter yield – up to 5–5 % mid-parent and up to 3–6 % higher-parent heterosis. Within individual trials mid-parent heterosis up to 8% was found, while at particular harvests over 25% heterosis was not uncommon. Comparisons made of performance in swards, simulated swards and spaced-plant conditions showed that genetic differences found maximum expression in non-competitive conditions. This was greatly reduced in simulated swards and further suppressed in sown swards in the field. Expression of heterosis was highly specific to the conditions in which it was tested, although the two hybrids most heterotic as spaced plants were also significantly heterotic in field swards.

Pot-culture experiments were made with the rice variety IR-8 on a sandy clay loam soil to study the relative efficiency of urea, urea treated with nitrification inhibitors N-Serve and AM, AM-fertilizer, and slow-release nitrogen fertilizers IBDTJ, oxamide and N-enriched coal. N-enriched coal supplied very little nitrogen to rice and gave no more yield than the control. All other materials were superior to urea. Largest yield of rough rice and nitrogen uptake by rice was obtained with IBDU and AM-fertilizer. Compared with untreated urea IBDU, oxamide, AM-fertilizer and urea treated with N-Serve or AM left larger amounts of mineral-nitrogen in the soil after the harvest. In the case of nitrification inhibitors residual ammoniacal-nitrogen was more at the higher rates of inhibitors.

Ten varieties of field beans, grown in different environments, were analyzed for genotypic stability of their seed yield. The linear responses to the environments were insignificant, but deviations from linearity were highly significant suggesting that the relatively unpredictable component of the genotype x environments interactions was more important in this material than the relatively predictable component. Environmental effects per se were very important in determining differences in mean seed yield. The relatively large deviations from linearity of variety IW may be due to powdery mildew disease. RB 29 was identified as a good yielding and stable variety in the range of environments tested.

Food intake prediction relationships were developed from in vitro dry-matter digestibility determinations on food and resultant faecal material for a number of diets ranging from low quality roughage to high quality irrigated pastures.

The relationship between true digestibility in vitro and in vitro food dry-matter digestibility was curvilinear, although true digestibility of food dry matter in vivo was highly correlated with apparent digestibility of food dry matter in vivo. The latter relationship was linear.

For 122 sheep observations on voluntary dry-matter intake incorporating 11 diet types, introduction of either of the terms, cell-wall concentration in food: cell-wall concentration in the resultant faeces (CWFo/CWFe), or its converse, into conventional faecal index relationships did not increase precision of intake prediction using faecal nitrogen as an indicator substance. However, significant intake prediction relationships using food:faeces cell-wall ratios were generated.

Values for in vitro digestibility of food and resultant faeces dry matter expressed as either a ratio (R) or as a difference (delta) yielded useful prediction relationships. For ‘green’ and for ‘dry’ classifications of the feedstuff's investigated some of these new relationships were either equal to or superior to the predictive efficiency of conventional faecal index relationships.

Reasons are discussed for use of maximum potential in vitro digestibility values for food and faecal dry matter in such relationships in future work rather than a conventional 48 h fermentation.

The skeletons of 34 pigs killed at a number of weights from birth to 120 kg were examined radiographically. Data were also used from radiographs of 83 foetuses of different ages.

Estimates were made of the age of appearance of various ossification centres and measurements taken of the diaphyseal length and breadth. A chart is given showing the age of appearance of ossification centres. Exponential equations in which the independent variate was time were fitted to both pre- and post-natal linear measurements. These equations were used to calculate the age at which each of the measurements attained a given proportion of the post-natal asymptote. The development of the pig's skeleton is discussed in relation to that of other species. Attention is drawn to the possibility that the uncritical use of accepted terminology such as early and late maturing may tend to obscure an understanding of the manner in which certain components of the skeleton develop.

Results from two trials on spring barley varieties are presented. A factorial fertilizer trial estimated the effects of N, P and K at each of three levels on diastatic power, heat-stable alpha-amylase activity, grain nitrogen content, thousand corn weight and yield in a single variety. This revealed that the main effect of N was the most important source of variation. In a subsequent variety–nitrogen trial seven varieties were tested at each of three levels of N.

In the variety–nitrogen trial, diastatic power was found to be positively correlated with both grain nitrogen content and alpha-amylase activity although these latter two variates were not themselves correlated. These observations were confirmed both within genotypes and within environments, and a hypothesis is advanced in explanation.

The implications of the results for a breeding programme directed towards the production of high-yielding, high-diastase varieties are discussed.

Results of a co-ordinated trial carried out at twenty-one centres indicated that the performance of growing pigs (20–90 kg) can be improved by supplementation of their diet with copper sulphate.

Three levels of copper supplementation were tested, 150, 200 and 250 mg Cu/kg diet. Though significant improvements were recorded on all three levels, the best performance and the highest increase in profitability were obtained with 250 mg Cu/kg diet. With increasing dietary intake of copper, the copper content of the pigs' livers increased markedly.

The melting-point of subcutaneous fat was lower in carcasses of pigs that were given supplementary copper sulphate in their diet.

Drainage lysimeters were used to estimate actual transpiration of a perennial ryegrass sward; this is compared with the calculated values for potential transpiration. Losses to drainage of nitrate nitrogen (NO3–-N) under differing levels of application of nitrogen fertilizer were examined. When 250 kg N/ha were applied annually losses of NO3-N were negligible; when 500 kg N/ha were applied up to 142·9 kg N/ha were lost to drainage. Concentration of NO3-N in the leachate with an application of 250 kg N/ha was low (1–5 ppm); with 500 kg N/ha the concentration ranged from 10 to 109 ppm. Losses of NO3–-N were particularly severe during winter following a dry autumn. When drainage occurred during the growing season losses were minimal.

Concentrations and quantities of K, Ca, Mg, Na, P, Cl and S (as sulphate) leached wore also examined.

Populations of spaced plants of each of the four American upland cotton varieties Deltapine Smooth Leaf, Rex Smooth Leaf, Pope, and Rex and one African upland variety, Bar 7/8, were grown in the 1965–6 wet season at Kimberley Research Station, in the Ord River valley, Western Australia. The number of bolls, boll weight, lint percentage, seed cotton yield, lint yield, micronaire value, mature height, and morphological type were recorded for each plant.

For all varieties the range of each attribute was wide; for example, for a typicalvariety, boll weight ranged from 3·0 to 7·8 g, lint percentage from 30·5 to 43·5%, micronaire value from 3·3 to 5·9 units, and mature height from 78 to 195 cm.

The most variable varieties judged on coefficients of variation were those maintained at the station for the longest period without selection while the most recent accession was the least variable.

Frequency distributions for all attributes in each population departed significantly from normality: the majority showed both significant skewness and kurtosis. Positive skewness shown for the yield parameters seed-cotton yield, lint yield, boll number and boll weight in all varieties suggested there was scope for improvement by selection. Negative skewness for lint percentage was found in three varieties, suggesting previous intense selection for this trait. The coefficient of variation of lint percentage with one variety (Deltapine Smooth Leaf) was considerably less than that recorded 30 years earlier for its predecessor D x PL 11 A.

Covariance adjustments to seed cotton yield of individual plants, based on various hypotheses of the relationship between a plant's yield and that of its neighbours failed to give reductions of consequence in the variability of yield. It was concluded that inter-plant influences were far more complex than the models assumed.

Two clones of perennial ryegrass were planted along the radii of a fan in such a way that any group of four adjacent plants was approximately square, with spacings ranging from 3 to 30 cm. During the first year the amount of regrowth per vegetative plant was found to be related to the area available at the high densities, whereas at low densities there was little change in weight per plant with change in density. At high densities the number of tillers declined following defoliation, but at low densities it increased consistently. In the second year, the ratio of fertile to barren tillers was lower and ear emergence was later at high densities. Results indicated that the performance of the clones differed in each of three stages of regrowth. It appeared that early regrowth was better in the erect clone, but after the first week, and where the canopy remained open, the RGR of the prostrate clone was greater. In a dense sward the crop growth was greater in the erect clone indicating that better use was made of the available light.

In experiments at this Institute in which samples of liver were required for the estimation of mineral content, difficulty had been encountered in obtaining samples reliably, especially in pregnant animals using the technique described by Dick (1944) and Abdellatif (1968). It was decided to investigate the possibility of obtaining liver samples from sheep under direct vision using a laparoscope.

Progenies of randomly chosen plants from spaced plant populations of four American and one African variety of Gossypium hirsutum L. were grown in replicated single-plant plots at Kimberley Research Station in 1967–68 (all varieties) and 1968–9 (two varieties only) to estimate intra-varietal parameters of genetic variability.

Estimates of broad-sense heritability were usually similar when derived from components of variance on either a one- or two-season analysis basis or by parentprogeny regression Heritabilities were in general lowest for lint yield and boll number and highest for lint percentage. Mean value of heritability for lint yield and boll number, considered consistent enough on a varietal and seasonal basis to allow averaging, was about 0·15. Components of variance estimates of heritability on a single environment basis for other attributes ranged as follows: boll weight from 0·05 to 0·56, lint percentage from 0·29 to 0·80, mature height from 0·00 to 0·51, micronaire value from 0·20 to 0·63 and Pressley strength index from 0·05 to 0·56.

Genetic coefficients of variation showed an opposite trend to that for heritability: lint yield and boll-number values were large and lint percentage, micronaire value, and Pressley strength indices small. Expected responses to selection for the top 2·5 % of the population for lint yield and boll number at around 10% were usually higher than for other attributes.

Genotypic and phenotypic correlations were mostly similar but correlations often deviated widely between varieties. Positive lint yield correlations with micronaire value and negative lint yield correlations with Pressley strength index were recorded; these are often undesirable associations for breeding.

The association between the period of maintenance under Ord conditions and variability shown phenotypically in the original populations was not evident from the quantitative inheritance studies. Residual variability following breeding was considered as accounting for the larger portion of the genetic variability.

Eighteen foetal sheep were used to study the relationship between suboptimal growth and linear size of skeletal units, dry weights of representative muscles and muscle histology. Foetuses with suboptimal growth caused by inadequate maternal nutrition and competition with other foetuses showed a decrease in skeletomuscular growth although allometric growth was not affected. A slight correlation (r =0·14, P < 0·005) existed between dry weight of the longissimus dorsi and mean minimum myofibre diameter. On morphological evidence, myofibre hyperplasia was thought to be complete by approximately 80 days gestation in all foetuses. Increases in the number of myofibres crossing mid-length transverse sections of the sartorius occurred after this time but were thought to be due to intrafascicularly terminating myofibres growing in length. Suboptimal muscle growth of foetuses in the latter third of gestation was thought to be associated with an inhibition of growth in length of intrafascicularly terminating myofibres.

Five selected clones of Lolium perenne were selfed and diallel crossed without reciprocals to produce 15 families. These families were grown in a replicated field trial for 2 years at four rates of applied nitrogen – 0, 225, 450 and 675 kg N/ha – per annum. The data recorded included dry-matter yield, number of fertile and sterile tillers per plant, mean dry weight per fertile and sterile tiller and total dry weights of fertile and sterile tillers. Conventional analyses of variance and diallel analyses were applied to the data as well as path analyses, used to examine the interrelationships between yield and the tiller characters.

The main effect of years was significant only for mean dry weights per tiller and dry-matter yield. Increasing the rate of applied nitrogen increased the number of tillers and yields but decreased mean tiller dry weights. Differences between progenies were due to both general and specific combining ability for most characters. Relatively high narrow-sense heritabilities were obtained for the tiller characters although there were differences between the two years.

The progenies achieved their yield through different combinations of tiller characters, some having large numbers of fertile tillers with medium dry weights and others having numerous sterile tillers with high dry weights. Although there was inconsistency in the interrelationships between characters, number of tillers was always more important in determining yield than mean dry weight per tiller.

The results are discussed in relation to the predictive value of tiller characters on yields and the implications for breeding programmes.

Red blood cell electrolyte levels and haemoglobin types have been determined in flocks of Peppin Merino sheep genetically different for clean fleece weight and crimp frequency. The flocks selected for high clean fleece weight or low crimp frequency had significantly higher mean erythrocyte potassium levels than did those flocks selected for low clean fleece weight or high crimp frequency, this difference was apparent in both haemoglobin AB and BB types. Erythrocyte potassium concentration was not correlated with either clean fleece weight or crimp frequency within flocks. The high clean fleece weight flock had a significantly higher gene frequency for high potassium than did the low clean fleece weight flock, while the high crimp frequency flock had a lower haemoglobin B gene frequency than the low crimp frequency flock.

Response to selection primarily for lint yield among spaced plant populations of four American and one African variety of Gossypium hirsutum L., established in 1965—6 at Kimberley Research Station, was studied in three experiments conducted between 1966 and 1970.

In the first experiment, in which single-hill micro-plots of 3–5 plants per hill were used, the mean lint yield of progenies was larger than predicted from single plant heritabilities. In the second experiment, in which single-row plots were used, response to selection for lint yield was generally less than expected. In the third experiment, in which three-row plots were used, response to selection for lint yield was again less than expected and less than manifested in the second experiment. However, in all experiments responses to selection for lint percentage, lint quality properties, and height were close to expectations while some individual progenies substantially out-yielded their unselected parents.

The progressive decline in response to selection for lint yield from the first to thethird experiment, and the discrepancies between the actual responses and the expected responses for lint yield in all experiments, were interpreted mainly on a basis of intergenotypic competitive effects differing in sympathy with plot size and plant disposition.

It was concluded that the objective methods of selection practised were successful when judged on plant breeding criteria. It was also concluded that intra-varietal selection is an important technique by which genetic improvement can be achieved at regional breeding centres with limited resources.

Swayback disease of lambs occurs widely in Britain, its incidence varying from year to year, but is usually most severe in lambs born in March and April after a mild winter. It is known to be related to a copper deficiency in both the ewe and the lamb, but not all copper-deficient owes give birth to swayback lambs. The disease can be effectively prevented by administering copper compounds to ewes in susceptible flocks at mid-pregnancy (Allcroft, Clegg & Uvarov, 1959).

Experiments were carried out to measure the components of canopy structure (on young spaced seedlings), their heritabilities and relationship to sward yield in the F1 generation of a diallel cross between six ryegrass populations.

Considerable differences existed between parent populations in both leaf length and tiller angle, but little difference existed in leaf angle. All the components of canopy structure were highly heritable, tiller angle, leaf length and leaf rigidity showing narrow sense heritabilities greater than 0·75.

There were large differences in yield between F1 families, moreover, when (a) Lolium perenne families, (6) L. multiflorum families and (c) L. perenne x L. mvltiflorum families were considered separately, leaf length and a composite character derived from leaf length and tiller angle (all measured on young spaced seedlings) were closely related to yield under sward conditions.

The plant breeding implications of these results are discussed.

During 3 years, three groups of 20 Scottish half-bred ewes were grazed on perennial ryegrass, white clover or red clover. During this period the two legumes were oestrogenic, in terms of teat-length extension of wethers, but the perennial ryegrass was not. The white clover was only markedly oestrogenic when there was a high proportion of diseased leaves. The mean litter size and lambing percentage of the ewes grazed on red clover was significantly reduced. White clover, although it was oestrogenic, had no effect on mean litter size or lambing percentage. The mean litter size of the ewes on the perennial ryegrass was 2·35, 2·30 and 2·24, on the white clover was 2·20, 2·33 and 2·23 and on the red clover was 1middot;60, 1·67 and 1·78 for the three lambings. Lambing percentage of the ewes on the perennial ryegrass was 175, 225 and 218, on the white clover was 210, 222 and 189, and on the red clover was 160, 128 and 118 for the three lambings. The lambing date of the ewes grazing on the red clover was significantly later at the third lambing.