A study was conducted at two different sites in the Egyptian western desert to investigate the activity of carnivorous birds on some invertebrates. At the first site (sand-dunes in the Gharbaniat area, 52 km west of Alexandria), the most interesting bird found was the great grey shrike Lanius excubitor which seizes its prey and impales it upon spines of Lycium europaeum or on barbed-wire fencing. Studies carried out from January to July 1977 indicated that this bird prefers to feed on certain tenebrionid or scarabaeid beetles as well as some orthopterous insects and small lizards of the area. At the other site (inland depression near Omaycd, 80 km west of Alexandria, and 12 km from the sea) a snail-eating bird, (bifaciated lark) Alaemon alaudipes, was found to be the commonest bird where the non-saline soil of the site is suitable for the desert snail, Eremina desertorum, to breed, so much so that the snails constitute one of the prominent features of the site.

The latter bird is more active in the winter than in the summer. From February to the end of June 1979, the estimated snail flesh weight eaten by A. alaudipes birds was about 6·50 kg taken from an area of 2·4 ha. The birds seize a snail, fly upwards to a distance of 6–23 m, select a hard stone, then drop the snail. The snail eventually breaks, and the flesh exposed is readily eaten by the bird. In January 1980, a survey was conducted to investigate the species of birds found in the area that extends between Alexandria and el Alamein. Twenty-six resident, as well as migratory, bird species were observed. The number of species and individual birds in cultivated areas, and sites near the sea shore, were found to be greater than those in natural ecosystems at a distance from the sea.

The variability generated in a diallel cross between seven genotypes for vegetative and phenological characters was studied in the F1 and F2 generations in lowland Papua New Guinea. The mean narrow-sense heritability values of mean leaf size and leaf area index at flowering were 88·0 and 78·5%. The parental values of these characters gave good predictability of the performance of the parents in hybrid combination. For mean number of leaves per plant at flowering, environmental effects were of major importance, and consequently selection between crosses for number of leaves is considered futile. There was a large genotype ˣ environment interaction for time to first flower. The role of various environmental factors in causing the interaction for flowering is discussed.

Five Zn-deficient soils designated A–E (pH 7·3–7·7) and a reference soil F (pH 7·6) were used in a glasshouse study on maize in which five fertilizer treatments: 75 μg P/g alone and together with all combinations of 0 and 5 μg/g of Mg and Zn and with 10 μg Mg + 5 μg Zn/g and a control were applied. The forage yield of soils A–E ranged from 2·5 to 2·9 g when no Zn was applied and from 5·1 to 5·6 g with added Zn, showing that Zn was the major limiting nutrient. Applied Mg significantly increased yield, the main exceptions being soils D and E which had the highest exchangeable Mg.

Addition of Mg to a P but not PZn treatment significantly increased P concentration and uptake. For soils B and E, Zn addition significantly depressed P concentration in maize. The P treatment significantly depressed Zn concentration but increased Mg concentration and uptake by maize. Although Mg application either depressed or had no effect on Mg content of maize, it caused a significant increase in Zn concentration and uptake. The correlation coefficient (r) between Zn and Mg in maize was – 0·61 (P < 0·001). Possibly, Mg was replacing Zn in the clay lattice or in its metallo-protein complex within the root.

The aim of this investigation was to grow barley as a fodder crop under highly saline conditions. Saline irrigation waters with an electrical conductivity (EC) of 2·5, 4·0, 6·0 and 8·0 mmhos/cm respectively were used to irrigate test crops of barley over two growing seasons.

It was concluded that in general more highly saline water leads to a considerable increase in soil salinity even over a short period of growth, and a close control of soil salinity through leaching is required. Saline water with an EC of 4·0 mmhos/cm may be utilized without excessively high yield reductions if the soil salinity is well maintained. The saline waters with an EC of 6·0 mmhos/cm and 8·0 mmhos/cm may lead to yield reduction, and they require careful managmeent to control soil salinity build-up.

A number of early generation inbred families and lines, as far as the S5, have been produced by self-pollination in Lolium perenne L. variety S. 23. The pedigree structure is given for 13 parent plants used in the breeding programme to show the patterns of segregation for self-fertility genes and to give the ancestry of eleven S5 inbred lines. Data on numbers of seed set, flowering time and inflorescence production reveal a wide range of variation due to both environmental and genetic components.

Two years with contrasting weather, 1976 and 1977, were used to investigate the effects of nitrogen fertilizer on the uptake of nitrogen by crops of winter wheat and on the rate of photosynthesis of flag leaves. The studies involved a number of crops which received various amounts of nitrogen fertilizer at various stages of growth. Weekly measurements were made of the amount of nitrogen in the crops and its distribution within the plant, while a mobile gas exchange system measured the photosynthesis of individual flag leaves.

While the treatments imposed in 1976 resulted in different concentrations of nitrogen in the flag leaves, the maximum rate of photosynthesis and its efficiency in dull light were both unaffected when leaves of the same age were compared. The 2 years gave contrasting results in terms of the amounts of nitrogen taken up during grain growth: in the very dry summer of 1976 it could account for only 25% of the nitrogen in the ear at harvest while in 1977 it could account for almost 50%. These different amounts of translocation to the grain were accompanied by different photosynthetic behaviours of the flag leaves and our analysis shows that, in all treatments, the maximum rate of photosynthesis after anthesis was related to the fractional loss of nitrogen from the leaves.

The implications of these results for farming practice and for techniques used to investigate the effects of nitrogen on photosynthesis are discussed.

Five investigations were carried out to determine the magnitude of root-size variation within crops of cv. Chantenay Supreme grown under competitive and non-competitive conditions, and to study possible sources of inter-plant variation.

In the first experiment root-size variation from crops grown at a high population density (245 plants/m2) and at a low density (25 plants/m2) were compared over a 21-week period from sowing. The c.v.s of root weight were always higher from the high density than from the low density over the harvesting period from 11 to 21 weeks after sowing, and ranged from 74 to 94% and from 50 to 63%, respectively. A second study showed that even with a very low population density (3 plants/m2) the c.v. of root weight at harvest was 58%. The third study showed that 40% of the root weight variation was accounted for by the time of seedling emergence. The results of a pot experiment indicated that when the size of seed, sowing depth, rooting medium and time of seedling emergence were made as uniform as possible, a very uniform population of roots was produced with a c.v. of root weight of 32%. In the final field experiment when time of seedling emergence, seed size and spatial distribution of the plants were the experimental variables, the results confirmed the importance of variability in time of seedling emergence and seedling size in creating variation at an early stage of growth.

The results of these studies indicate that competition per se was not a prime source of variation in root size but magnified any initial variation within the crop at the time of seedling establishment. The importance of this early establishment phase in determining the spread of root-size distribution within a crop is discussed together with the factors which influence the time of seedling emergence and seedling size.

Mineral analyses for calcium and phosphorus were carried out on lambs which had been fed diets contrasting in protein or energy or calcium concentration and had been slaughtered at defined live weights. Despite considerable variation in rates of growth arising from the widely different nutritional programmes, the mineral content of these lambs at a given weight remained remarkably stable on practical diets.

The reciprocal relationship commonly used in the analysis of plant yield-density relationships in monoculture is extended to allow a similar treatment of binary mixtures, using the model:

w–1a = Aa × Baapa × Babpb

where wa is the plant weight of component a in mixture with component b, and pa and pb are the plant densities of a and b respectively. The model gives a good fit to fresh weights taken from a glasshouse experiment involving monocultures and mixtures of red clover (T. pratense L.) and Italian ryegrass (L. multiflorum L.) in different proportions, all grown at a range of plant densities. The interpretive and predictive uses of the model are discussed.

In one experiment during 1972 and 1973 five irrigation regimes of every 4, 6, 8 and 10 days and according to stomatal opening, as estimated by the infiltration method, were compared, using an early-maturing variety Zankawa and a late-maturing variety G51. In both experiments early crop growth was checked by the shortest and the longest irrigation intervals.

Late growth, on the other hand, was promoted by the shortest intervals in both seasons. Thus the highest yield in 1972 was obtained from the 4–day regime, followed by the infiltration method, then progressively greater yields with shorter intervals. In 1973, however, the shortest interval resulted in the lowest yield, which was significantly less than the other treatments, which showed a similar trend to those of 1972.

In a second experiment during 1974 and 1975 a medium-maturing variety 22/9/1 and a late–maturing variety 44/E were added to those of the previous experiment. Watering every 4 and 6 days were eliminated and watering every 12 days added, during the early growth period. Each of these regimes was given irrigation every 6, 8, 10 and 12 days during the late growth period. The early-maturing varieties yielded best when irrigated every 12 days in the early stages, and every 10 days in the late stages, whereas the late-maturing varieties yielded best when irrigated every 10–2 and 8 days in the early and late stages of growth, respectively.

Nuclear staining with acridine orange was used to study death of the root cortex of winter wheat grown after grass and non-graminaceous break crops in a field trial site in 1978. The top 5·4 cm of first seminal root axes had several anucleate cortical cell layers by late-February, and nearly five dead cell layers (of a maximum six) by mid-April. One of the next pair of roots to emerge (designated ‘2’) showed similar cortical death, but one of the subsequent pair (designated ‘4“)showed substantially less death at these times.

Significantly more root cortex death was seen in first to third wheat crops after 1 or 2 years of grass than after swedes-potatoes, and in one replicate block compared with the other in the trial. But there was no significant difference in cortical death between first, second, third and 16th successive wheat crops.

Root cortex death could not be attributed to infection by Gaeumannomyces graminis, Phialophora radicicola var. graminicola or the nematode Rotylenchus robustus. But its implications for root–infecting parasites are considered and, in particular, the enhanced cortical death in some crops compared with others may help to explain the reported differences in infection of wheat by P. radicicola var. graminicola, a biological control agent of take-all.

Four lactating Friesian cows with cannulae in the rumen and in the proximal duodenum were subjected to each of four different dietary treatments. Treatments differed with respect to concentration of crude protein, supply of urea nitrogen and frequency of feeding. The rations used consisted of hay, maize silage and concentrates and were offered to the animals according to milk yield.

During the last 5 days of each experimental period (5 weeks), ingesta flow at the proximal duodenum was estimated by Cr-EDTA. Samples were taken from the duodenum at 2 h intervals and were analysed for thiamin, total nitrogen and microbial nitrogen. Labelling of microbial N was achieved by continuous infusion of 16N-urea into the rumen.

With treatment 2 (26% less N than with treatment 1) thiamin net synthesis in the forestomachs and total thiamin entering the duodenum were significantly reduced whereas treatment 3 (substitution of 26% plant N by urea-N) and treatment 4 (six times instead of twice feeding daily) had no effect on synthesis and flow of thiamin to the small intestines. There were significant linear regressions between flow of microbial N and flow of thiamin to the duodenum and between organic matter digested and flow of thiamin.

A blood sample was taken at each hourly interval between 07.00 and 16.00 h on five consecutive days from each of two groups of five lactating and two groups of five nonlactating cows. The sampling was organized so that each cow was sampled twice daily and once at each time of day. Samples were analysed for blood glucose and haemoglobin, serum urea, inorganic phosphate, Ca, Mg, Na, K, total protein, albumin, Fe and Cu and plasma β-hydroxybutyrate. The sources of variation in the concentration of each constituent were determined.

Definite patterns of changes in concentrations with time of day were observed for β-hydroxybutyrate, urea, Ca, Na, Mg and Cu. In lactating cows there was a 2½-fold increase in the concentration of β-hydroxybutyrate from the lowest at 07.00 to the highest at 11.00 h. Variation in the concentrations of the other constituents with time of day was a relatively small proportion of the total variance.

It was concluded that diurnal variation in blood composition was unlikely to be a major source of error in interpretation for the usual constituents of a metabolic profile test. However, if β-hydroxybutyrate were to be included great care would be required in selecting a time for sampling.

In an initial experiment four mature sheep were injected with saline or 25, 75 or 150 m units bovine thyroid stimulating hormone (TSH)/kg live weight. All doses of TSH stimulated a similar release of thyroxine.

In a second experiment ten lambs were fed chopped dried grass from weaning until 108 days old (period 1). Five of the lambs (group 1) were then fed 30% barley: 70% grass until 178 days of age; the remaining lambs (group 2) continued to receive grass (period 2). After 178 days group 1 was fed 70% barley: 30% grass and group 2 30% barley: 70% grass (period 3). All lambs were injected with 25 m units TSH/kg live weight at 105–108 days of age, 174–178 days and 220–227 days. The thyroxine response to TSH was greatest in lambs fed 30% barley: 70% grass in periods 2 and 3. Plasma insulin and glucose concentrations tended to decrease after TSH.

Automatic plot covers were used in a study of the effects of drought on the yield and water use of two spring wheat genotypes. The experiment tested the effects of drought at different stages of growth on yield and yield components. There was complete control over the water supplied to the plots, and a fully irrigated control treatment was included.

The yields of the two genotypes were similar under fully irrigated conditions, but the yield components differed: Highbury had more grains per ear and TW 269/9/3/4 more ears per unit ground area and a higher mean grain mass. An early drought, which began 4 weeks before anthesis, caused a reduction in number of grains per ear in Highbury, which was outyielded by TW 269. Late drought also reduced yields differentially, reducing mean grain mass, and hence grain yield, more in TW 269 than in Highbury. Total shoot dry matter and grain yield were found generally to increase as water use increased. The average water use efficiency was found to depend upon the genotype and treatment.

Six compounds which show juvenile-hormone-like (JH) activity (TH6040, JH-25, Altosid, Altozar, ZR-777 and ZR-619) were tested on larvae of Culex pipiens. The reproduction potential of the females obtained during two successive generations was not affected greatly, but there was a decline in pupation rate with some compounds. There seemed to be a direct relationship between the size of females of this species and treatment with JH compounds tested in the present investigation, since treatment with concentrations to inhibit the emergence of 10% or 50% of adults caused significant changes in the width of head, wing dimensions or length of hind legs.

The effects of various lengths of water deprivation were studied with Yankasa sheep fed either a high roughage or a high concentrate diet in two experiments. Water was given once in 24, 48, 72 and 96 h. Free water intake decreased linearly (P < 0·01) as the period of water deprivation increased but feed intake was not similarly affected. There was a marked decrease in live-weight gain and consequently a decline in feed efficiency (kg gain/kg feed). In the metabolism study, there was a tendency towards reduced mean faecal and urinary nitrogen excretion, faecal moisture content and increased mean nitrogen retention and nitrogen and dry-matter digestibilities as the period of deprivation increased. Rams given water once in 72 and 96 h were very inactive and dull and one and three rams respectively, died of severe dehydration from those treatments in Expt 2.

Thirty-eight spring wheat genotypes of north temperate or low latitude origin, all reasonably well adapted to the English environment, were grown in controlled environments providing the four combinations of 10 and 14 h photoperiods and temperatures of 8 and 16 °C for 6 weeks. They were then transferred to a glasshouse to assess their responses to these treatments. In separate experiments the responses of the genotypes to vernalization for 2 and 4 weeks at 2 and 8 °C were compared with unvernalized controls. The genotypes were also compared in field experiments from early, intermediate or late sowing over 3 years.

Both high temperatures and long days hastened ear emergence. At the higher temperature more leaves and spikelets were produced on the main stem while in long days the plants had fewer leaves and spikelets.

Most genotypes of north temperate and low latitude origin were responsive to photoperiod but not to the vernalization treatments. As a group, the low latitude ones were as responsive as the north temperate group. Five genotypes of north temperate origin were responsive to vernalization but not to photoperiod and were designated as ‘winter’ ones. Pitic 62 and Hork, from low latitudes, were responsive to vernalization and Hork was unique in also being responsive to photoperiod. The main difference between the north temperate and low latitude genotypes was in time to ear emergence and it is suggested that these differences were due to the effects of earliness genes as distinct from those determining photoperiodic response.

Taking all genotypes individually there were no correlations between yield or its sensitivity to sowing date and any of the attributes measured in controlled environments. However, considering class means, the winter genotypes were the latest to reach ear emergence in the field, and their yields, while greatest from the earliest sowings, were proportionally more depressed by late sowing than the others of the north temperate origin. Thus, it may be unwise for plant breeders to incorporate a vernalization response in spring wheat varieties unless genes for ‘earliness’ are also included. The low latitude class gave only slightly lower yields than the north temperate class.

It is concluded that genes other than those controlling responses to photoperiod, temperature and vernalization were more important determinants of the differences in yield among this set of genotypes.

Ten Scottish soils were cropped in a glasshouse with three sowings of perennial ryegrass (Lolium perenne, cv. Dutch Barenza) without added magnesium. After 25 cuts (185 weeks) growth was poor in some soils, but soil Mg was not limiting growth in others.

Uptake of Mg and the Mg concentration in the ryegrass correlated well over the entire cropping period with the equilibrium Mg-concentration ratio Mg/(Ca, Mg) = CR0, determined from the Mg quantity/intensity isotherms measured before cropping in 0·01 m chloride solutions. A CR0 value of 0·16 was required in the early stages of cropping to give 0·2 % Mg in grass dry matter.

Seven soils released 12–37 mg non-exchangeable Mg/kg, between one-fifth and one-third of the total Mg uptake. These reserves probably came from vermiculite minerals, but the release was too slow to maintain Mg concentrations of 0·2 % in the ryegrass.

Adult goats provided with permanent jugular and portal vein catheters were used to study the effect of feeding hay and concentrates on blood composition in order to determine which blood constituents might act as signals in the control of feed intake. Animals were fed limited amounts of feed, or were allowed to eat unlimited amounts for restricted periods, once or twice daily. Blood samples were collected at hourly intervals up to 9 h after feeding and often more frequently in the initial hour, and were analysed for volatile fatty acids (VFA), lactate, glucose, insulin and glucagon.

Feed consumption resulted in rapid and large increments of jugular blood acetate, propionate, n-butyrate and 3-methylbutyrate concentrations whereas isobutyrate and 2-methylbutyrate increased only slightly. Jugular propionate, n–butyrate and 3–methyl–butyrate increased within 10 min and acetate within 20 min after feed was offered, both when hay and when concentrates were eaten. Fasting decreased circulating VFA to very low values. As a rule changes of portal VFA paralleled those in the general circulation although both the concentrations and the changes were much greater. Plasma lactate increased within 30 min on a concentrate diet but not at all on a hay diet.

Blood glucose declined in the initial hour after feeding and subsequently increased, resulting in a more or less elevated plateau. In some but not all experiments glucose declined before feed consumption, probably owing to ‘anticipation’. Circulating plasma insulin and glucagon appeared to increase slightly, if at all, after feeding. Increased feed intake was reflected in higher base line glucose and insulin concentrations in the jugular vein but the jugular glucose and insulin response to feed consumption was unaffected. Jugular glucagon was not influenced by the amount of feed. Jugular insulin and glucagon sometimes showed a brief peak during eating. Portal glucose, insulin and glucagon gave essentially the same pattern as seen in the jugular vein.

In conclusion, it appears that, of the substances studied, acetate, propionate, nbutyrate and 3-methylbutyrate are most suited for the function of feedback signals in the physiological control of feed intake in goats under the conditions of the present experiment. It seems less probable that glucose, insulin and glucagon can play such a role.