Ewe reproductive traits of imported Merino local Ossimi and Barki, their first crosses, backcrosses to Merino and the interbred groups of the backcrosses, were considered in this study. Records of 2168 ewes born from 1960 through 1970 were used in the study; they totalled 6959 records.

Reproductive performance was different in the three purebred groups, with more multiple births but more lamb losses and abortions in Merinos. However, the three groups weaned similar numbers of lambs/ewe run with the rams (0·98). Merino × Ossimi ewes had the best performance, they lambed and weaned 27% more lambs than local Ossimi. They were followed by MB ewes weaning 0·96 lambs/ewe run with the rams. Reproductive performance of the backcross ewes was lower than that of the first cross, but still better than the purebred groups. Inter-breeding of back-crosses reduced their hybrid vigour markedly.

Non-maternal heterosis contributed greatly to the reproductive performance of cross-bred ewes, while the effect of maternal heterosis on reproductive traits was fairly small.

Multiple births showed least heterotic effect.

Teat orders were determined for 76 litters of Large White and Large White × Landrace pigs. Regression analysis within litters revealed a relationship between suckling position and weight both at birth (P<0·01) and at 3 weeks of age (P<0·001), with the heavier piglets tending to occupy the more anterior teats. The correlation coefficients, however, were very small (r = –0·16 and –0·22 respectively). The correlation between birth weight and 3-week weight was much larger (r = +0·47); and a comparison of pairs of litter-mates showed that a difference in birth weight of 0·25 kg or more persisted at 3 weeks in the majority of cases, regardless of which piglet suckled the more anterior teat. Birth weight accounted for much more of the variation in 3-week weight than did teat number, and, when the effect of birth weight had been taken into account, teat number accounted for only an additional 2·3% of the variation. Even so, the anterior teats did appear to confer some advantage which was independent of that of the birth weight of the piglets suckling these teats. From the results of this and other studies it is concluded that there is only a weak relationship between suckling position and weight at birth and 3 weeks. Other unidentified factors are probably of more importance for the within-litter variation in weight gain of suckling pigs.

The development of stable suckling order, the incidence of fighting when suckling, weight gain during the suckling period, and the severity of facial wounding were studied with litters of piglets in which the canine and lateral incisor teeth were either clipped at birth or left intact. Facial wounding was largely confined to litters with unclipped teeth. Severity of wounding correlated with the observed incidence of fighting on the udder (P<0·01); and both wounding and fighting were more common among litters comprising a large number of piglets (P<0·05). When the effect of litter size was taken into account, there were no substantial differences in weight gain to 3 weeks between piglets with high and low scores for facial wounding, nor between clipped and unclipped litters. Piglets which habitually occupied the most anterior or most posterior teats had less facial wounding than middle-suckling piglets, and showed greater consistency in teat choice. No gross differences between clipped and unclipped litters were observed in the development of stable suckling order during the first week of life. It is concluded that the ‘eye’ teeth, although used in disputes over teat choice, have little influence on the frequency of such disputes or on the original development of stable suckling order.

Skin samples were used to evaluate the developing skin follicle population of Cheviot × Dorset Horn cross foetuses. The follicle population was studied from the first appearance of skin follicles (55 days' gestation) to the end of gestation. The pattern of development of primary and secondary follicles is described, and compared with the data available for other breeds. The occurrence of secondary follicle branching, previously confirmed only in the Merino, is described, and the ‘prenatal check’, an important feature of follicle development which had not previously been investigated in prenatal studies, is briefly discussed.

Two experiments were made in successive years in which three frequencies of watering were combined factorially with several rates and methods of applying nitrogen. Soil water content and leaf water potential were measured. The least frequent watering treatment decreased yield and nitrogen applications increased yield. All of the effect of water and most of the effect of nitrogen were associated with changes in the number rather than the weight of bolls. Although the combination of heavy nitrogen with frequent watering caused the crop initially to set fruit more slowly than did heavy nitrogen with infrequent watering, it prolonged flowering and increased the number of fruit ultimately set. Thus yield and the potential duration and cost of insect control were also increased. There were no differences in yield nor rate of setting between the following methods of application of the nitrogen: all applied to the seed bed; split application between the seed bed and side dressing 2 months later; and split application between the seed bed, side dressing, and irrigation water. However, when application was split so that most was applied in the water, the response was not as great. Application of nitrogen combined with frequent watering decreased the weight of the early bolls by decreasing fibre per seed. Nitrogen increased the weight of later bolls by increasing the number and weight of seeds. The practical and physiological implications of these results are discussed and a crop nutritional hypothesis for cotton developed further.

Four rates of nitrogen fertilizer, three dates for the last application of water, and two varieties were combined factorially in two experiments in successive years. Leaf water potential was measured. There were large yield responses to water and nitrogen; in both cases the response in number of bolls was relatively twice as great as that in boll weight. Because one effect of nitrogen was to prolong the setting of bolls, which required continued watering for its full expression, there was an interaction between the nitrogen and water treatments which affected number of bolls, and thus yield. Deltapine 16 yielded more than Acala 1517BRI and responded more to nitrogen than did Acala 1517BRI. Heavy nitrogen rates decreased the initial rates of boll setting of Acala. Weekly picks of open bolls showed that, with early cessation of water and with the lightest rate of nitrogen, the boll weight decreased in the fourth and subsequent picks. This effect of nitrogen was more marked in Acala. These responses were analysed into the components of boll weight and are discussed in relation to the timing of the development of the bolls in order to explore the physiological implications. Nitrogen and water delayed harvest by prolonging effective flowering, by increasing boll maturation period, and by increasing the number of defoliant sprays required.

Two methods of analysis of variance of experiments involving diallel arrangements of binary mixtures and monocultures where the former are each represented by a linear replacement series (de Wit, 1960) to detect mean quadratic and quartic patterns among the monocultures and different mixture types, and array differences with respect to linear, quadratic, cubic and quartic effects are given. These are applied to data from an experiment on Italian ryegrass where the four varieties 1145 and S. 22 (diploid), IG2 and Tetila (tetraploid) are mixed in the proportions 75:25, 50:50 and 25:75.

Significant mean quadratic effects for D.M. yield at certain harvests are due to higher yields from monocultures than mixtures, and a mean quartic effect at one harvest reflects a lower yield from 75:25 mixtures than 50:50 mixtures or monocultures. Array differences for linear and quadratic effects are largely a property of the ploidy contrast. Specific mixture effects were recognized for two varietal combinations, mixtures between the two tetraploid varieties showing some yield depression, and those between the two commercial varieties (RvP and Tetila) a considerable increase. No meaningful significant effects were detected for in vitro digestibility.

Further analysis of total D.M. yield by means of the regression of array covariance (Wr) on to array variance (Vr) show, as expected, a closer relationship of Wr and Vr with the non-recurrent component at a frequency of 75% than at 50% or 25%, but the significant departure of the slope from unity is interpreted as evidence that no reliable information as to the relative competitive abilities of the varieties can be obtained from these statistics. Examination of the de Wit replacement graphs strongly suggests a ranking of competitive ability which accords with the known morphology of the varieties.

In North West Pembrokeshire, sulphur was determined in soils sampled at 268 sites, and in pasture plants sampled at 172 sites. The sulphur contents of the topsoils ranged from 199 to 3392 mg/kg, with a mean of 710 mg/kg; and the S contents of the subsoils from 115 to 1344 mg/kg, with a mean of 356 mg/kg. Sulphur was concentrated in soils containing much organic matter. There was no clear relationship between plant and soil sulphur contents, though soil drainage influenced both. Poorly drained soils were richer in S than well-drained soils, whereas herbage on poorly drained soils accumulated less S than herbage growing on well-drained soils. Herbage S contents ranged from 0·180 to 0·560%, with a mean of 0·310%. If other factors, e.g. soil N, are not limiting, 14% of the herbage sampled in Pembrokeshire had less than the critical S level recommended by other workers for maximum dry matter yield.

The proportions of bacterial and dietary protein entering the duodenum of sheep fed fresh herbage were assessed using 2,6-diaminopimelic acid as a marker. The herbages fed were Lolium perenne L., ‘Grasslands Ruanui’ perennial ryegrass; L. (perenne × multiflorum), ‘Grasslands Manawa’ short-rotation ryegrass; Trifolium repens L., ‘Grasslands 4700’ white clover.

The dietary protein degraded in the stomach was approximately 70% for all herbages. The bacterial contribution to protein entering the duodenum was 43·1, 57·1 and 52·9% for Ruanui, Manawa and white clover respectively. Protein entering the duodenum contained only a small amount of protozoal protein.

Bacterial protein synthesis in the stomach was different for all three herbages, averaging 16·2, 30·7 and 19·8 g/100 g organic matter apparently digested for Ruanui, Manawa and white clover respectively. It is suggested that the micro-organisms digesting Manawa synthesized protein more efficiently.

Two obstacles to achieving diets which maximize farm profits are discussed: (1) the continuing inability to predict reliably the response of animals to a diet with any given composition, and (2) batch-to-batch variation in the true nutrient content of a diet with a fixed nominalcontent. With the aid of simple practical examples it is demonstrated that diet recommendations can be more sensitive than might be expected to the type of function used to predict response, and that variation in dietary nutrient content may reduce farm profits (though the size of the reduction is not clear because of (1) above).

The aim of the present investigation was to determine the effect of adding urea to a diet based on ground maize and dried sugar-beet pulp (2/1) on the composition of duodenal content and diet digestibility in calves.

Two bull calves (140 kg) were provided with duodenal fistulae and pair fed the ration alone or with 1·2% urea in a cross-over design. Lucerne hay was also given. The difference in intake of nitrogen between the two diets was 18·4 g/day.

The results obtained showed negligible differences between the diets in the amounts of dry matter, organic matter and energy disappearing both before and after the duodenum. Digestibility of nitrogen was greater with the urea-containing diet.

Although some of the added urea (25%) was apparently lost from the forestomach, the duodenal digesta contained 13·7 g N/day more with the diet containing urea. Of this a minimum of 6·5 g was in the form of amino acid-N and only 0·4 g as ammonia-N. All the amino acids determined were present in increased amounts but lysine and isoleucine showed smaller relative increases than the other amino acids.

From these results and calculations based on measurements of 2,6-diaminopimelic acid it is suggested that the extra protein in the duodenal content derives from both more efficient bacterial protein synthesis in relation to energy expended and decreased degradation of plant protein in the rumen.

Wool growth rates were estimated in Merino ewes differing in their red blood cell concentrations of reduced glutathione ([GSHRBC]). Over a 42-day wool growth period, sheep with low [GSHRBC] maintained significantly higher rates of wool growth. Red blood cell concentrations of K+, ([K+RBC]), [GSHRBC] and estimated gene frequencies for the low [GSHRBC] and high [K+RBC] genes were determined in flocks of Merino ewes bred for high or low clean fleece weight. The high fleece weight flock had a significantly lower [GSHRBC] and higher gene frequency for the low [GSHRBC] allele than the low fleece weight flock. The high fleece weight flock also had a significantly higher [K+RBC] and a higher gene frequency for the high [K+RBC] allele than did the low fleece weight flock.

A substantial loss in yield usually occurs when oilseed rape is sown later than mid-September. Field experiments in 1972–3 tested whether this is because all plants, irrespective of size, initiate inflorescences during the winter, thus restricting the eventual size of the leaf canopy and the yield potential of late-sown plants, which are still very small when the change to the reproductive phase occurs.

Sowing a standard winter variety, Victor, from mid-August to mid-October resulted in initiation occurring from late October to February. When sown after mid-September yields were proportional to plant size at initiation. The winter was mild, and in colder conditions earlier sowing may be required to enable plants to reach a critical size before initiation takes place. When sown in August plants were very large but yield was not improved. A study of the development of the pod canopy showed that the extra yield potential was not realized because heavy losses of pods and seeds occurred, particularly in the more shaded positions.

When a range of winter varieties, chosen to contrast the timing of phasic development, was sown on two dates yield was proportional to the interval between sowing and initiation, particularly when late sown, presumably because late initiators were able to lay the foundation of a more substantial root and shoot system. This has implications for plant breeding programmes because the low erucic acid varieties currently being grown initiate inflorescences early. When spring types were sown in mid-October they formed floral initials very early, and gave particularly small and weak plants, with a low yield. Winter types sown in March did initiate flowers and produce large plants, but yields were no better than spring types as flowering and ripening were irregular and late, the cold requirement for initiation being only marginally fulfilled.

Tubers of Dioscorea rotundata yam obtained from the same harvest were stored at room temperature (25–30 °C). After storage for various durations, tuber samples were taken and used as planting material. The number of days to sprouting, for head pieces and non-head pieces alike, decreased with increasing storage time up to 159 days. Heads sprouted earlier than non-heads. The number of days to formation of new tubers also decreased with increasing storage age of the parent tuber up to 226 days. The interval from sprouting to tubering was constant up to 106 days of storage, decreased rapidly between 106 and 226 days, and thereafter remained constant. The implications of these results for off-season yam production are discussed.

March-born non-cyclic Suffolk × Galway ewe lambs were treated with progestagen pessaries while being either fed fresh-cut grass ad libitum, or restricted to 50% of appetite and at pessary removal half of the animals on each nutritional treatment received either 600 i.u. or 300 i.u. PMS. Averaged over both levels of PMS, 97·5% of the lambs showed oestrus when fed ad libitum but only 67·5% of those on restricted feeding responded. When feed intake was not restricted there were no differences due to PMS level but when feed intake was restricted the higher dose level of PMS resulted in a greater percentage showing oestrus and a significantly higher ovulation rate. The dose level of PMS had no effect on the time of oestrous onset but restricted feeding resulted in delayed onset and poor synchronization of oestrus. Duration of oestrus was greatest for lambs fed ad libitum given 600 i.u. PMS and least for those on restricted feeding given 300 i.u. PMS but the difference was not significant. A minority of lambs showed broken oestrous periods.

Soils from long-term experiments at Rothamsted and Woburn were cropped for very long periods (up to 5½ years) with ryegrass in pots. Measurements of the potassium taken up by the ryegrass that was not exchangeable to ammonium acetate and the kinetics of its release both suggested two categories of non-exchangeable K. Of these, the first to be released was closely related to the initial exchangeable K, whilst the second, though partly related to the initial exchangeable K was also influenced by the clay percentage. Release of both categories may have been controlled by diffusion, because both showed good relationships between the quantity released and time. It is suggested that the first category may be K ‘trapped’ when K fertilizer added in the field decreased the interlamellar spaces of vermiculite layers in clay particles, whilst the second may simply be the ‘native’ K (described by others) present in clay and other minerals in the soil.

Resowing the soils (without drying them) during the later stages of K. uptake suggested that the ability of the old ryegrass to absorb K was not a factor limiting K uptake even after long growth.

When the ryegrass ceased to grow, the mean K potentials in the exhausted soils were close to the ‘uptake potential’ for ryegrass derived earlier by considering K uptakes from soils in relation to the quantity/potential relationships of the soils. Drying and rewetting the exhausted soils released K; the amount was influenced in one group of soils by the exchangeable K in the moist exhausted soil and in another group by the clay percentage.

Seeds of Amaranthus, melon, cowpea and tomato were planted in moist soil at 1, 4 or 7·5 cm depth and subjected to a heat stress of 45 °C for 10 h on the day of sowing (day 0), 1 day after sowing or 2 days after sowing. Seedling emergence was retarded by heat stress, the most drastic retardation being due to heat stress on day 1 for cowpea and tomato, day 2 for melon, and day 0 for Amaranthus. Emergence also decreased with increasing depth of sowing. The interaction of depth and heat stress was also significant in all cases, such that the delay in emergence due to heat stress tended to be greater with increasing depth of sowing. The agronomic significance of the results is discussed.

Experiments made at Shika, Nigeria, over a period of 3 years showed that the drymatter response of Andropogon gayanus to applied N was curvilinear over the range 0–896 kg N/ha, with maximum yields being obtained at an application rate of about 500 kg N/ha. However, the highest return of dry matter per unit of fertilizer applied (14·4 kg D.M./kg N) occurred at 28 kg N/ha and there was only a modest increase in crude-protein content as N was increased, reaching a maximum of 10·5% at the highest level of N. Also, at both high and intermediate levels of N, A. gayanus was replaced by less desirable grasses.

May, the beginning of the rainy season, was found to be the most efficient time to apply N, although reasonable dry-matter responses were obtained by applying N in the dry season. ‘Nitro-chalk’ and calcium nitrate were more efficient sources of N than urea, sodium nitrate and, in the long term, ammonium sulphate.

Bean plants (Phaseolus vulgaris L.) were grown in field plots with the objective of comparing the effect of some soil amendments on sodium uptake and translocation at three levels of salinity in the soil.

Gypsum and wheat straw mulch treatments reduced the translocation of sodium from the roots to the stems and leaves at the higher external sodium level. Incorporation of animal manure with the soil had little effect on translocation at the higher level but may have promoted sodium translocation to the stems at the lower level.

Plant growth and survival were negatively correlated with the sodium content in the plant, particularly with that of the stems.

Tetraploid lines were produced from colchicine treatments of European multigerm diploid material, and seeded in polycross plots. The same lines were crossed with European multigerm diploids to give anisoploid varieties, and also used as pollinators of American male-sterile diploids to yield monogerm and multigerm triploid varieties. Bigerm triploids were obtained from male-sterile hybrids heterozygous for the monogerm character, using European multigerm O-types in the grandparental generation. Double-cross monogerm triploids were obtained by crossing male-sterile diploids with non-equivalent O-types to provide male-sterile hybrids, and pollinating these with outbred tetraploids.

Results from 35 root-yield trials showed that the sugar yields of the anisoploids and triploids were similar to those of contemporary commercial varieties, but that outbred tetraploids were slightly, and inbred tetraploids considerably, less productive. Changes induced in characters other than root weight by chromosome-doubling of diploid material were sometimes important, but not consistent in magnitude or direction. It is suggested that these changes result from selection and random drift rather than the ploidy change.

A seed-yield trial demonstrated advantages of using hybrid seed-parents for triploid seed production. Problems of seed quality are discussed with particular reference to triploid varieties.

It is concluded that the main importance of multigerm anisoploid varieties was in their combination of good sugar yield with near-monogerm fruit clusters at a time when commercial monogerm varieties were deficient in yield; the chief value of triploidy lay in its application to the short-term improvement of genetic monogerm varieties. The development of monogerm anisoploids is considered unlikely; but some advantages of deriving monogerm triploid varieties from tetraploid seed-parents are indicated, and it is suggested that these may become increasingly important in the future.