The edge effect (calculated as the mean of the two outer rows as a percentage of the mean of the four central rows of 6-row plots) was measured in ten comparative trials conducted in Cyprus during 1987–90, with two cultivars each of rapeseed, safflower and sunflower, and one cultivar each of barley and durum wheat. Grain, straw and total biological yields obtained from the outer rows were usually higher than those obtained from the central rows by 1–384%. In one trial with sunflower, the grain yield of the outer rows was only 64% of that of the central rows, which could not be explained, considering all the other data. Differences in edge effects between species and trials were significant. Grain yield estimated from the central rows was on average 53% of that estimated from whole plots, and this varied with species and season. Therefore, in comparative trials, the outer rows should be removed before harvesting. There was no significant edge effect on the oil content of the oilseed crops. Edge effects on harvest index, volume weight, 1000-grain weight and nitrogen content were generally smaller than those on yield, and on average ranged from 100 to 113, thus the values computed from the outer rows were only 0–13% higher than from the central rows.

Wheat, barley and two morphologically contrasting cultivars of peas (leafy and semi-leafless) were grown in pure stands, at standard agricultural densities, and in additive mixtures of cereals with peas. The stands were grown in boxes in the field, and partitions were used to separate the effects of root and shoot interactions. The cereals and peas were either planted at the same time, or one species was planted 10 days before the other. The origin of the N present in each species was determined by applying N fertilizer labelled with 15N.

Both cultivars of peas had greater shoot and root competitive abilities than wheat or barley, probably because of their larger seed size; leafy peas had greater shoot and root competitive abilities than semi-leafless peas. Sowing peas after cereals reduced their competitive ability.

The relative yield total (RYT) of cereal-pea mixtures, based on total biomass, averaged 1·6 when only the root systems interacted, and 1·4 when only the shoot systems interacted, but did not differ significantly from 10 when both root and shoot systems interacted. RYT values were greater when peas were grown with wheat, rather than with barley, and when peas were sown at the same time as the cereals.

Shoot competition from peas increased the N% of cereals, but substantially reduced their total N content, because biomass yield was reduced. Shoot competition from cereals had no effect on the N% of peas, and only slightly reduced their total N content. Shoot competition between cereals and peas had no significant effect upon the proportion of N derived from various sources by either cereals or peas.

Root competition from peas significantly reduced both the N% and total N content of cereals. Root competition from cereals had little effect on the N% of peas, but significantly reduced their total N content and increased the proportion of N derived from rhizobial fixation from 76 to 94%. Since cereals and peas largely used different sources of N, resource complementarity for N was probably an important component of intercropping advantage, when the roots of cereals and peas shared soil resources.

A study, conducted in the Peace region of Canada, determined the effects of the stand and management treatments of four herbage experiments (1986–88) on the yield and quality of subsequent crops of barley (Hordeum vulgare L.) harvested in 1989 and 1990. Quantitative relationships indicated that the crop management treatments most conducive to good yield and quality of herbage were also the most beneficial for subsequent high yield and quality of the barley grain. Unless designs orthogonal to those previously used can be found, covariance adjustment procedures are recommended to minimize the residual effects of previous experiments.

A 3-year field study (1986–88) was conducted in central Alberta to discover how diverse soil-plant systems function under cryoboreal subhumid conditions. Barley, fescue, faba (field) bean and a barley/field pea intercrop were grown continuously on different soils at Ellerslie and Breton using two distinct tillage methods. The agronomic performance, weed-crop interactions and below-ground productivity of these cropping systems were examined. The main findings were as follows: different soil properties did not affect yields of barley, barley/field pea and fescue fertilized with N and P; silage yield of faba bean at Breton was greater than at Ellerslie; barley/field pea and faba bean could be grown without tillage at Ellerslie; barley/field pea plots had the lowest weed counts; fescue root biomass was greatest at all depths followed by faba bean and barley; and soil properties appeared not to induce differences in root production of a cereal, an annual forage legume and a perennial grass. Increasing the use of annual legumes into rotations, either as sole crops or as intercrops with cereals, may be a viable alternative to continuous cereal cropping because annual legumes contribute N through biological N fixation, reduce weed competition and increase the input of root mass in soil.

Fifteen grassland species were grown in a heated glasshouse in February-April 1985. The harvested herbage was separated into leaf and ‘stem’ and analysed for neutral detergent fibre, digestibility, physical breakdown when macerated, fibrosity, water soluble carbohydrate and N, P, K, Ca, Mg and Na.

Lolium perenne was digestible, but rather high in neutral detergent fibre and not readily broken down by maceration. The other grasses tested, Holcus lanatus, Poa annua and Glyceria fluitans, tended to be less digestible and higher in neutral detergent fibre than L. perenne.

The leaves of all 11 dicotyledonous species were much lower in neutral detergent fibre than the leaves of the grasses, and most broke down readily when macerated. The stems of Medicago saliva and of two shrub species (Lonicera periclymenum and Prunus spinosa) were the highest in neutral detergent fibre.

Rumex obtusifolius, Spergula arvensis and Stellaria media were high in Mg; Plantago lanceolata, S. arvensis and S. media were high in Na; and S. arvensis was high in P.

Three perennial and two annual herbaceous, dicotyledonous non-legumes were selected as being of sufficient promise and interest to be compared with Lolium perenne in feeding experiments: Plantago lanceolata, Taraxacum officinale, Rumex obtusifolius, Spergula arvensis and Stellaria media.

Six plant species were compared as food for sheep: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). In two experiments at Aberystwyth in 1985 and 1986, the species were fed to lambs as the total diet, after artificial drying. In another experiment in 1987, they were fed fresh, in 1·5 minute meals, to yearling sheep.

The dicotyledonous species had a lower proportion of cell wall (neutral detergent fibre) in dry matter than perennial ryegrass. The true dry matter digestibility of chickweed, dandelion, dock and leafy ribwort was as high as that of ryegrass, but the in vivo digestibility of all five dicotyledonous species was lower than that of ryegrass. The voluntary intake of the dicotyledonous species was higher than might have been predicted from their digestibility. The voluntary intake of spurrey was > 20% higher than that of ryegrass.

When the species were fed fresh, spurrey had the highest rate of intake as a consequence of a high chewing rate and a low requirement for number of chews/g of dry matter consumed. Chewing rate was higher on all the dicotyledonous diets than on ryegrass. The rate of intake of dandelion was above average, but that of dock was low and variable, particularly when the plants had been chopped.

Thirteen experiments conducted near Tenby, Dyfed, between 1973 and 1980, examined the effects of seed-tuber weight and within-row spacing on tuber yields of seven potato varieties grown for early production. These data have been used in an attempt to develop an approach to the determination of optimum tuber planting densities in early crops which will provide agronomists with logically applicable principles. Tuber planting densities, which maximized the net crop return (ware value minus seed cost), were estimated for eight ratios of seed cost to ware value ranging from 0·25 to 8·0. Optimum tuber planting densities decreased with the use of higher ratios of seed cost: ware value and heavier seed, except for ratios of 0·25 and 0·50 applied to yields of tubers > 25 mm harvested in June. In general, later harvesting together with the use of larger riddle sizes give a lower optimum density with ratios < 2·2·0. Optimum densities for Red Craigs Royal, Ulster Sceptre and Vanessa were higher than for the other varieties.

The results provide an illustration of how to approach the problem of selecting tuber planting densities in order to maximize net crop returns in early potato varieties.

The flowering response of a late-flowering mutant of Sesbania rostrata was compared with that of the parent plants by sowing it on ten different dates, from December 1990 to September 1991, in India. Flowering response was also studied following exposure to an 8-h photoperiod at four different stages of growth. The parent flowered at different times of the year depending on the time of sowing, while the mutant flowered only during October–November irrespective of sowing date. The parent was sensitive to a short-day photoperiod as early as 15 days after sowing, but the mutant became sensitive to the critical photoperiod only after 60 days of vegetative growth. The mutant, by virtue of its longer vegetative phase, had the potential to produce adequate phytomass irrespective of the time of sowing.

Bambara groundnut (Vigna subterranea (L.) Verde.) is grown throughout southern and western Africa, primarily as a subsistence crop, but agronomic information is scarce. The rates of emergence, flowering and pod production were assessed for 20 weekly sowings between 16 October 1990 and 26 February 1991 at Sebele, Gaborone, Botswana. Daylength during this period changed from 12·7 h to 13·7 h and back to 12·6 h. Mean time to 50% emergence was 111 days while mean time to 50% flowering was 47·5 days. The thermal time to first pod production varied with daylength, decreasing as daylength decreased, to an approximately constant value when daylength after flowering was less than about 12 h. Consequently, the plant size at which pods were produced also varied. The practical implications for date of sowing and plant spacing are discussed.

The duration of flowering was investigated in 14 accessions of indeterminate faba (field) beans (Vicia faba L.) planted near Adelaide, South Australia in 1986 and 1987. All flowers and young pods were removed from plants at 4–7 day intervals. Plants of ‘Mediterranean’ origin produced 20–30 flowering nodes while those of European ‘spring bean’ type produced up to 50. Terminal inflorescences were eventually produced in all accessions. In control plants, the number of days between anthesis at successive nodes was partly dependent on nocturnal minimum temperature and varied very little between genotypes. It should be possible to make best use of the growing season by optimizing the potential production of nodes, but there is little opportunity for manipulating the rate of their appearance.

The mineralization and nitrification processes in pig slurry were investigated in Spain in 1990 in three calcareous soils, differing mainly in content and type of clay, two classified as Typic Calciorthids and one as a Xerollic Calciorthid. Two different amounts of slurry were mixed with the soils, one equivalent to 273 mg N/kg soil and the other equivalent to 546 mg N/kg soil. The mixtures of soil and slurry were aerobically incubated for 16 weeks at 28 °C. A mean initial immobilization of 22·19% of the total-N added was detected in soils treated with the lower rate of slurry. The amount of mineralized N after 112 days of incubation was between 36 and 47% of the total-N added with the lower slurry application to the three soils. The net amount of N mineralized throughout the experiment was therefore within the range 14–23% of the total-N added. The nitrification of the NH4-N added to the soil began after 7 days of incubation, and followed a first-order kinetic model. The mean values of potential nitrate formation were 61 and 51% of the total-N added in soils amended with 273 and 546 mg N as pig slurry per kg soil respectively. The rate constants were higher in the treatments with the lower slurry application (0·043–0·083 per day). Therefore, in these treatments, the nitrification process was faster and total nitrate levels were higher than in soils receiving double that amount of slurry. The NO3-N evolution was parallel to the total-N evolution from the 14th day of incubation onwards. The N-mineralization process was limited by the transformation of the organic-N into ammonium (ammonification).

Voluntary intakes of a medium-quality grass hay were measured in winter (early January) and in spring (late April) near Edinburgh for two separate groups of six red deer, together with digestibility and mean retention times of the particulate-phase marker, 103Ru-phenanthroline. The deer were then slaughtered and the weights of digesta and the dimensions of the alimentary tract were measured. Voluntary intakes of dry matter were significantly higher in spring than in winter, but there was no difference in digestibility or mean retention time of 103Ru-phenanthroline. There were no significant differences in any of the organ weights or the dimensions of the intestines between the groups slaughtered in winter and spring. Dry matter proportions of digesta in the rumen, abomasum, small intestine and caecum, the wet and dry weights of rumen digesta and the water-filled capacity of the rumen were significantly greater in spring.

The luteolytic effect of prostaglandin F2α (PGF2α) during the confirmed luteal phase of the oestrous cycle was evaluated in ten Boran and ten Boran × Friesian cross-bred heifers. Following injection with 25 mg Lutalyse, animals were bled every 6 h for 96 h and plasma progesterone (P4) determined by the ELISA technique. Borans had significantly (P < 0·05) smaller corpora lutea (12·01±0·72 ν. 17·03±2·10 mm) and responded faster to PGF2α injection (65·57±1·40 ν. 78·27±2·18 h) than the cross-bred heifers. However, there was no significant difference in either the initial P4 values (6.24±0·98 ν. 8·00±1·71 ng/ml) or the rate of its decline following PGF2α injection between the two breeds. Values declined sharply to basal levels (11% of the initial pretreatment values) within 48 h in both breeds. All ten cross-breds and eight Borans showed standing oestrus within a week of treatment. However, oestrus was better synchronized (P < 0·05) in Borans than cross-breds. It was concluded that PGF2α is effective for oestrus synchronization in both breeds, but oestrus occurred earlier and was more precise in Borans than in cross-breds.

Nitrogen balance and flow of nitrogen along the gastrointestinal tract were determined in growing wether sheep fed a dried grass pellet diet with or without intraruminal propionic acid infusion. Plasma free amino acid and glucose concentrations tended to be higher in peripheral blood of animals receiving propionate (P < 0·10). Overall total nitrogen and amino acid digestibilities and apparent digestibilities of each fraction along the digestive tract were not affected by infusion of propionic acid. The contribution of microbial amino acids to total amino acid flow in the duodenum measured using purine bases as the microbial marker averaged 0·49 and was not affected by propionic acid infusion. It is suggested that changes in circulating amino acid levels arise from reduced utilization of luminal amino acids by gastrointestinal tissues due to the increased availability of alternative energy-yielding substrates.

Oestrus and ovulation data from 104 adult Corriedale ewes, recorded daily from February 1988 to May 1990 in Argentina, were analysed to estimate repeatabilities of and phenotypic correlations between onset and cessation of the breeding season, duration of the anoestrus and ovulation rate.

The repeatability of dates of onset and cessation of the breeding season and duration of the anoestrus was 0·48±0·080, 0·49±0·075 and 0·50±0·081, respectively.

The duration of the anoestrus was significantly correlated both with onset (r = 0·24; P < 0·05) and with cessation (r = –0·47; P < 0·01) of the previous and subsequent breeding seasons, respectively.

There was no correlation between dates of onset and cessation of the breeding or non-breeding seasons.

Repeatability estimates of ovulation rate were 0·27 ± 0·034, 0·34 ± 0·081 and 0·43 ± 0·094 using the normal, logit and probit scales, respectively. Phenotypic correlations between ovulation rate and the components of the breeding and non-breeding seasons were all non-significant.

Five Suffolk crossbred ram lambs were administered ritodrine, a β2-agonist drug, by continuous intravenous infusion at 0·5 μg/kg per min for 9 days to determine effects of prolonged β-agonist infusion on metabolism and on the responsiveness of the animals to short-term infusions of adrenaline. Consistent with other investigations, this study showed that initially the drug caused rapid increases in heart rate and plasma concentrations of free fatty acids (FFA), lactate and insulin, but decreased plasma growth hormone. There was no effect on plasma glucose or pancreatic glucagon concentrations. After 24 h of ritodrine infusion, these effects were attenuated as tachyphylaxis to the drug developed. On days 2–9 of the infusion, heart rate remained significantly higher than preinfusion values, but plasma glucose concentration was significantly lower than before infusion. Despite the rapid disappearance of these ‘side-effects’ of the drug and the apparent normality of most metabolic parameters, short-term infusion of adrenaline (50 ng/kg per min for 60 min then 500 ng/kg per min for a further 60 min) after 9 days of ritodrine infusion showed that the responses of lactate, FFA and heart rate to adrenaline were significantly attenuated in comparison with the responses determined before β-agonist infusion. This result, together with similar earlier observations on fetal lambs, implies that selective attenuation of β-receptor mediated cardiovascular, metabolic and endocrine responses to the endogenous catecholamines could play an important role in determining how β-agonist drugs act to modify carcass development.

Rumen fluid was removed from four sheep 6 h after feeding, and the fluid was centrifuged to remove the micro-organisms. Perchloric acid (PCA) was added to the supernatant fluid to precipitate soluble proteins, which were again removed by centrifugation. The PCA extract was neutralized with KOH and the precipitate was removed by centrifugation. The supernatant fluid was hydrolysed with 6 MHC1 at 110 °C for 24 h, then dried by rotary evaporation, and the amino acid composition of each extract was analysed by ion-exchange chromatography. The recovery of amino acids was 98%, except for methionine, cysteine and tryptophan, which were destroyed. The recovery of amino acids from added Trypticase was 92% of the peptide mixture as amino acids. The free amino acid composition of extracellular rumen fluid was low and variable in both amount and composition (0·36, S.D. 0·49, μmol/ml). The concentration of amino acids released by acid hydrolysis of the PCA extract, presumed to be derived from peptides, was larger and its composition was less variable (1 ·02, S.D. 0·30, μmol/ml). Aspartic acid and histidine were enriched in peptides in comparison with the amino acids present in the feed or in rumen particulate material. Glycine and proline contents were higher in peptides that in particulate material. In contrast, the contents of isoleucine, leucine, tyrosine and phenylalanine tended to be lower in peptides than in the other materials. It was concluded that extracellular degradation-resistant peptides had a composition that was different to microbial protein and to the feed. The peptides appeared to be enriched for amino acids which previous studies with pure peptides had shown tend to make peptides more resistant to degradation.