In two experiments using cattle implanted with 0 or 300 mg trenbolone acetate and fed restricted diets of low-protein roughage, urea synthesis was measured by plasma dilution of a single intravenous injection of [14C]urea. Urea flow to the gut was calculated as the difference between synthesis and urinary urea output. Because rumen ammonia concentrations were only c. 1 mg/1, it was assumed that urea transfer from the gut to blood was negligible.

In the first experiment, fistulated heifers treated with trenbolone acetate synthesized significantly (P < 0·05) less urea (0·8 v. 1·2 g/h) and had a tendency to excrete less (P = 0·08) urea in urine (0·04 v. 0·14 g/h) and to have a lower (P = 0·07) flow of urea into the gut (0·8 v. 1·1 g/h) than untreated animals. They also had significantly (P < 0·01) lower rumen digestion rates, determined from disappearance of feed dry matter from nylon bags suspended in the rumen for 48 h.

In the second experiment, steers treated with trenbolone acetate synthesized significantly (P < 0·05) less urea (1·0 v. 1·9 g/h) and had a significantly (P < 0·05) lower flow of urea into the gut (0·9 v. 1·8 g/h) than untreated steers.

The results were consistent with an hypothesized sequence of events resulting from treatment with trenbolone acetate. The sequence proposed was a decrease in the rate of tissue protein breakdown, a decrease in the rate of urea synthesis from de-amination of amino acids, a decrease in the amount of urea recycled to the rumen, a decreased rumen digestion rate and thus a decrease in feed intake.

Merino sheep were given abomasal infusions of various amino acids or mixtures of amino acids. Effects on wool growth were measured using autoradiography or a clipping procedure and changes in the concentration of amino acids in plasma were measured in some experiments.

Mixtures of five (28 g/day) or ten (45 g/day) essential amino acids (both mixtures containing 3 g methionine) stimulated wool growth of sheep receiving a maintenance ration; on average, the volume of wool grown increased 48% and 86%, respectively. When cysteine completely replaced methionine in these mixtures, wool growth was markedly reduced, but two-thirds of the methionine could be replaced by cysteine without affecting wool growth. Homocysteine was partially effective in replacing methionine and, when supplemented with betaine, folic acid and vitamin B12, the mixture was still significantly inferior to that containing methionine. In contrast, abomasal supplements of methionine or homocysteine alone were equivalent as supplements for wool growth. The results indicated a specific role for methionine in the control of wool growth, other than the provision of cysteine. This role was postulated to be related to some function of S-adenosylmethionine.

Infusion often essential amino acids caused appreciable increases in the concentrations of cystine, methionine, cystathionine and taurine in plasma; total essential amino acids increased threefold whereas nonessential amino acids decreased in concentration. The replacement of methionine in the infusion by cysteine or homocysteine significantly altered the concentration of cystine, methionine and cystathionine in plasma.

Evidence was obtained that the adverse effects on wool growth of high abomasal doses of methionine (10g/day) could not be reduced or prevented by provision of additional glycine and were not related to the supposed toxic effects of 3-methylthiopropionic acid, a metabolite of the transamination pathway.

The nitrate nitrogen content of the soil (0–90 cm) was measured immediately after the harvest of winter wheat at eight sites in central and eastern England in 1987 and 1988. On average, 50% of the total nitrate detected was in the 0–30 cm, 30% in the 30–60 cm and 20% in the 60–90 cm soil horizon. Although soil nitrate N increased with the amount of N fertilizer applied, it was not a linear relationship. There were small nonsignificant increases in soil nitrate up to the optimum fertilizer rate for yield but, once the optimum was reached, further addition of fertilizer increased nitrate contents significantly.

Therefore, applying the correct quantity of N for high grain yield did not significantly increase soil nitrate residues after harvest compared with the no-fertilizer treatment. This emphasizes the importance of applying the appropriate rate of N for each crop, because applying too much is not only uneconomic but also significantly increases the amount of mineral N which could be subsequently leached over the winter.

Serial sowings of three cultivars of oilseed rape were made from autumn (May) to spring (October) at two sites, one in the north and one in the south of Tasmania, in 1981. The highest seed yields at both sites exceeded 5 t/ha from early sowing, ranging down to c. 2 t/ha from late sowing at a site where irrigation was adequate and to < 1 t/ha where late-sown crops suffered from water stress. The midseason cultivar Marnoo gave the highest yields at both sites, resulting from a combination of substantial (800 g/m2) top growth before flowering, excellent seed survival, a long period for grain filling and high oil content. The early-flowering line RU1 made much less growth before flowering; while this was partly made up for in later growth, nearly as many seeds per pod being retained as in Marnoo, oil content was low. The later-flowering cultivar Wesbell made more growth before flowering than the other cultivars, but when sown early it tended to grow tall, lodge and lose many pods in the dense, tangled canopy. This, combined with generally fewer seeds per pod, resulted in a much less efficient crop in allocation of dry matter to seeds and oil. Wesbell failed to flower uniformly from the late sowings, indicating segregation for vernalization response. The many immature seeds at harvest gave a low overall oil content. All three cultivars responded to vernalization and longer photoperiod in a pot experiment. While photoperiod appeared to be the main factor controlling the development rate to flowering in the field, there were interactions with vernalization response andtemperature.

Inadequate soil moisture is one of the main constraints on the productivity of chickpea in the rainfed farming systems of the dry areas in West Asia and North Africa. The response to irrigation at flowering and pod filling of winter- and spring-sown kabuli chickpea was studied in 1983–86 at ICARDA's main research station at Tel Hadya in northern Syria. In 1983/84 when the cultivar ILC3279 was sown in winter, irrigation increased yield by 105% over a crop receiving 229 mm of precipitation. In 1984/85, ILC3279 was sown in winter and spring. Advancing the date of sowing to winter increased yield by 65% and irrigation increased seed yield by 73% in winter and 143% in spring sowings compared with crops grown receiving 373 mm rainfall.

In 1985/86, six cultivars (ILC482, ILC3279, FLIP81–57W, FLIP81–293C, FLIP84–19C and FLIP84–80C) were compared, but differences in their response to irrigation were negligible. Advancing sowing from spring to winter increased seed yield by an average of 66%. Irrigation increased seed yield in winter and spring sowings by 56% and 72%, respectively, over those receiving 316 mm annual precipitation. Irrigation is, therefore, a way of increasing the productivity and yield stability of chickpea in northern Syria but the improvement in yield depends on the total rainfall and its distribution over the growing season.

Three double-marker systems were used in cannulated steers offered straw-based diets supplemented with barley, fishmeal or a combination of both, in an attempt to reduce the risks of misinterpreting biological results based on calculations of digesta flows using markers. Ruthenium phenanthroline (Ru-phe), ytterbium acetate (Yb-ac) and the indigestible acid detergent fibre fraction (IADF) were used as markers of the particulate phase of digesta in conjunction with Cr-EDTA as a liquid-phase marker to estimate duodenal and ileal digesta flows. The present paper presents the difficulties met in the application of marker techniques.

The particulate marker used in a double-marker system for calculation of nutrient flow modified the degree of statistical significance observed for dietary treatment effects on digesta flow parameters.

The data suggest that the type of diet used affects the behaviour of individual markers in different ways and could incur some bias in the results. It is hypothesized that the physical and chemical characteristics of digesta, in different dietary conditions, can be responsible for differential attachment of markers to particles of the solid phase. In such cases, the distinction made in the double-marker technique between particulate and liquid phases may not be sufficient to correct for lack of representativeness of digesta contents sampled from T-shaped cannulae.

For the diets studied it was concluded that the interpretation of digestion parameters should be based on both Ru-phe and Yb-ac results.

Four adult swamp buffaloes (Bubalus bubalis) and four adult Brahman cattle (Bos indicus), maintained in climate rooms, were provided ad libitum with a pelleted NaOH-treated barley straw ration (10·7 g N/kg dry matter) supplemented with sulphur, minerals and vitamins and 0, 14·5 or 22 g urea/kg. The animals were given each diet when housed at 32 °C and, in addition, were given the urea unsupplemented diet at 22 °C. All animals received all treatments for periods of 21 days, measurements being made during the last 8 days, after the animals had been given single doses of two nonabsorbable markers (Cr-fibre and Co-EDTA). Intake, digestibility and gastro-intestinal passage rate were low on the unsupplemented N-deficient (10·7 g N/kg dry matter) diet at both temperatures. Urea supplementation to provide diets of 17·3 and 20·7 g N/kg dry matter was associated with increased intake and digestibility of the feed and increased rate of passage of digesta through the gut.

Despite differences in respiration rate and plasma thyroxine (T4) and triiodothyronine (T3) concentrations at the two temperatures, no effects of temperature on intakes and digestion of the unsupplemented diet were seen. Differences between species were seen in respiration rate at 32 °C and plasma T4, which were higher, and mean retention time of Cr in the gut at 22 °C and water intakes, which were lower, in Brahman cattle than in buffaloes. There were no significant species differences in response to dietary urea supplementation.

Field experiments were conducted in two wet and two dry seasons in 1984–86 to evaluate efficiencies of different urea-based fertilizers, and methods of application, for irrigated rice. Response to applied N was significant in all seasons. In the wet season, use of dhaincha (Sesbania aculeata) green manure and urea (Dh + U), reduced zone placement of urea supergranules (USG), surface application of laccoated urea (LCU) and prilled urea in three split doses (PU-split) gave similar results, and all were better than basal broadcast application of urea coated with neem (Azadirachta indica) cake (NCU) or prilled urea (PU-basal). In the dry season, USG was significantly superior to PU-basal, NCU and (Dh + U). Nitrogen uptake by rice was greatest 15–30 days after transplanting (DAT), followed by a second peak during the reproductive phase of the crop. Ammonium-N in the soil decreased sharply up to 30 DAT, more slowly up to 60 DAT and then increased slightly. Ammonium-N in the soil was higher with USG, (Dh + U) and PU split than with other treatments, especially in uncropped conditions.

No-tillage and dry ploughing were compared with puddling under identical cultivation conditions for their effect on growth and yield of wet-season rice. The experiment was conducted on an alluvial sandy clay–loam soil over 5 years (1978–82) at Cuttack, India. In the preceding dry season, each plot was split into two halves for growing dry-season crops, with and without tillage. Growth of rice seedlings without applying N to the seed bed was faster and more vigorous after puddling, as shown by greater shoot and root weight per hill and a higher shoot:root ratio, and remained so until maturity. This was reflected in earlier flowering and maturity, followed by greater grain and straw yields. These results are attributed to the ability of the roots to obtain more N from the puddled soil.

Under high water table conditions, extractable and soluble N in the root zone were not much influenced by tillage treatments. Grain and straw yields after no-tillage were similar to those produced by dry ploughing but smaller than those produced by puddling, although the differences were not significant in some years.

Soil strength measured at the end of the rice-growing season in 1980 and 1981 was significantly greater after continuous no-tillage. The decreasing trend in grain and straw yield and number of panicle-bearing tillers/m2 from 1980 onwards after continuous no-tillage, was associated with increasing soil strength. The results suggest that, where percolation losses of water and nutrients are small, puddling, which is capital intensive and detrimental to soil structure, could be replaced by notillage accompanied by suitable N and weed management. However, continuous no-tillage is not recommended for a soil with a lower clay content because the soil will gradually harden with time.

Measurements were made of the recovery and germination rates of seed of eight species of annual medic (Medicago spp.) and three of clover (Trifolium spp.) after ingestion by sheep. Recovery of medic seed was measured as the number of seeds collected from faeces after feeding, in addition to a basal diet, either (i) 200 g of pods at a single meal, or (ii) a quantity of pods estimated to contain 30000 seeds at a single meal or (iii) 200 g of pods daily for 21 days. Only the first method was applied to the clovers.

There were large differences (P < 0·001) in seed recovery between species, from < 2% to nearly 20% in medics, and up to 59% in T. campestre, which has low single-seed mass. Although there was a curvilinear decrease in seed recovery as single-seed mass increased (r2 = 0·80), the high recovery of M. rotata, a fairly large-seeded species, suggests that there are important differences between species, irrespective of seed size.

When 200 g of medic pods was offered to sheep at a single meal, mean seed recovery was slightly lower than when 200 g of medic pods was offered daily for 21 days. Seed recovery of medics was much higher (P < 0·001) when 30000 seeds were offered at one meal.

Germination rate before ingestion was 1·9–6·5% (P < 0·001) for hard-seeded medics and 2·7–9·7% (P < 0·001) for clovers with low single-seed mass; passage through the digestive tract increased (P < 0·001) germination rate in both medics and clovers.

Field studies conducted in 1983/84–1985/86 at Ludhiana showed that the response of physiological and yield characters of Brassica juncea to foliar sprays of chlorocholine chloride as cycocel (CCC) at 250 and 500 p.p.m. and ethrel at 500, 1000 and 1500 p.p.m. differed at different doses of N (O, 50 and 100 kg/ha). The crop did not respond to CCC or ethrel in the absence of N, whereas a significant response was obtained with 250 p.p.m. CCC or 500 p.p.m. ethrel at 50 kg N/ha and 500 p.p.m. CCC or 1000 p.p.m. ethrel at 100 kg N/ha. Response to increasing doses of N increased in the presence of CCC or ethrel spray. The highest concentration of ethrel (1500 p.p.m.) proved detrimental at 0 and N/ha. CCC and ethrel reduced the crop canopy, enhanced the chlorophyll content of leaves, interception of photosynthetically active radiation and sink capacity (number of pods per plant and 1000-seed weight) at 50 and 100 kg N/ha. A higher leaf area index was obtained during the pod development phase with CCC and ethrel sprays. The oil content and germination potential of seeds from crops treated with CCC (250 and 500 p.p.m.) and ethrel (500 and 1000 p.p.m.) were as high as in the untreated crop, irrespective of N dose. However, 1500 p.p.m. of ethrel sprayed on a crop raised without N suppressed germination capacity.

In order to determine the accuracy of controlling the time of maturity of a cauliflower crop by regulating the planting date, a series of transplantings of the variety White Fox was grown on a range of sites over 3 years and sampled throughout growth.

The time from transplanting to maturity and the time from curd initiation to maturity were both quadratically related to the time of transplanting but there were marked differences in the relationships between years. Differences between years in the time taken to reach maturity tended to increase with later transplanting; for example, cauliflower crops transplanted in May took between 77 and 94 days to mature, while those transplanted in July matured in as few as 67 or as many as 106 days. These differences resulted from a combined effect of the time taken to satisfy the vernalization requirement and the duration of curd growth, both of which are temperature-mediated and therefore subject to seasonal and annual variation. Differences in the vernalization requirements of different cauliflower crops are illustrated by the number of leaves formed before curd initiation, which varied from 22·5 to 37·3.

Variation in the time to maturity between crops transplanted at similar times of the year, in the same and different years, resulted in large deviations from planned production programmes and it is suggested that a complementary technique to aid crop marketing would be prediction of the time of crop maturity. However, the data collected in this study show that predictions based on the duration of crop growth from transplanting or curd initiation are unlikely to be sufficiently accurate and it is argued that predictions should be based on changes in curd dimensions with time.

Effects of hedgerow species on surface soil physical properties were studied in an on-going trial established since 1981 on an Oxic Paleustalf in southwestern Nigeria. The experimental treatments were Leucaena leucocephala, Gliricidia sepium, Alchornea cordifolia and Acioa barterii hedgerows planted at 4 m interhedgerow spacings and a control (no hedgerows). Plots were sequentia-ly cropped with maize (Zea mays) and cowpea (Vigna unguiculata). Soil physical properties, i.e. particle size distribution, bulk density, apparent pore size distribution and water infiltration, were monitored during the dry season in January and the main growing season in June 1989. Soil temperature was monitored at approximately monthly intervals from February to June 1989. Soil properties of alleycropped plots were superior to those of the control. Soil compaction was highest in the control and lowest with L. leucocephala. Between the hedgerow species, within-season increases in soil compaction were largest with A. cordifolia. Lowest soil temperatures were observed with L. leucocephala and A. barterii. Frequency, quantity and quality of prunings produced by the hedgerow species appeared to have a major beneficial effect on soil physical properties.

Source–sink balance was studied by imposing different canopy defoliation treatments on wheat crops grown in Los Banos (Philippines) in 1985/86 and 1986/87, Sonora (Mexico) in 1972/73 and 1974/75 and New Delhi (India) in 1987/88. The crops were grown in replicated trials with optimum cultural management. Six defoliation treatments were imposed at anthesis on all shoots in the canopy in an area ranging between 1·65 and 3·0 m2. Defoliation reduced dry weight in proportion to the reduction in percentage light interception. The number of grains per unit land area was reduced slightly, and in most cases not significantly, except when all leaves were removed. Despite reduction of leaf lamina area index to as low as 0·5, the decrease in grain yield was small. In particular, flag leaf removal led to a remarkably small reduction in grain yield. Grain nitrogen content in defoliated crops decreased much less than expected from the amount of N removed by defoliation. The slope of the relation between reduction in grain yield with defoliation and reduction in post-anthesis dry matter accumulation was 0·56, indicating moderate source limitation for grain filling. The crops at the hottest site, in the Philippines, were less limited by source than the other crops. It is suggested that selection for smaller flag leaves may be worthwhile for high-input wheat crops.

Lentils (Lens culinaris Medik.) were sown on eight sowing dates from April to November in two seasons in Canterbury, New Zealand. In 1984/85, six sowing dates were combined with two lentil cultivars (Olympic and Titore) and two irrigation treatments. In 1985/86, Titore was sown on two dates, with four irrigation treatments. An additional experiment grown under rain shelters examined the response of Titore to four irrigation regimes. The 1984/85 season was dry and rainfall was only 70% of the long-term mean. In this season, seed yield was high, 3·3 t/ha from the May sowing. The 1985/86 season was wetter than average and seed yields were lower, ranging from 0·6 to 1·5 t/ha. Under rain shelters, seed yield ranged from the equivalent of 0·32 to 2·5 t/ha.

Sowing date had the most marked effect on seed yield. In the 1984/85 season, all autumn and winter sowings yielded 2·4–3·3 t/ha, whereas the spring sowings yielded 0·5–1·5 t/ha. In 1985/86, unirrigated plots from the May sowing yielded 1·5 t/ha, whereas all other plots yielded c. 0·8 t/ha.

Generally, the small-seeded cultivar Titore outyielded Olympic. Dry matter (DM) accumulation followed similar trends to seed yield. Seasonal DM accumulation followed a sigmoidal curve. Functional growth analysis indicated that plants from autumn/winter sowings had a weighted mean absolute growth rate of 110–171 kg/ha per day, whereas spring-sown plants grew at 96–137 kg/ha per day. The maximum crop growth rate was 230 kg/ha per day in the July 1984 sowing.

There was little positive response to irrigation in both seasons. Under rain shelters, there was a linear increase in both dry matter and seed production with increased total water. Fully irrigated plants produced 1·27 g DM and 0·72 g seed/m2 per mm of water received.

In the field experiments there was no relationship between maximum potential soil moisture deficit (D) and yield. Under rain shelters, however, there was a linear relationship which indicated a limiting deficit of c. 130 mm. The relationship showed that, for each millimetre increase in D above D1, 0·39% of the maximum yield was lost.

Under the rain shelters, there was a strong relationship between yield and actual evapotranspiration (ET). Water-use efficiency (WUE) ranged from 2·81 g DM/m2 per mm ET in unirrigated plots to 0·69 g seed/m2 per mm ET.

The results showed that lentil growers in Canterbury, and presumably in similar environments, are unlikely to benefit from irrigating their crops. In such environments, lentils appear to be an ideal dryland crop.

The effects of winter shearing, 8 weeks before lambing, on ewe and lamb live weight changes over the first 30 days of lactation were studied in Reading between February and March 1984. Differences in ewe body condition score (BCS) and plasma concentrations of glucose, nonesterified fatty acids (NEFA), 3-hydroxybutyrate, growth hormone (GH), insulin, cortisol and thyroxine between shorn and unshorn groups of ewes were measured over the same period.

Lambs from shorn ewes grew, on average, 20% faster than those from unshorn controls even though both groups of lambs were of similar mean birth weight. There was no difference in maternal feed intake between shorn and unshorn groups, and ewe live weight and BCS decreased between the day of lambing and day 30 of lactation in all ewes. Plasma samples taken at hourly intervals for 24 h on days 12 and 27 of lactation demonstrated that shorn ewes had significantly lower plasma concentrations of insulin than unshorn controls; on day 27 of lactation, higher circulating concentrations of GH were recorded in the shorn group. There were no differences in the plasma concentrations of glucose, NEFA, cortisol or thyroxine between the two groups of ewes. It is concluded that metabolic adaptation by shorn ewes to the cold environment of a British winter during early lactation results in endocrine changes in ewes which are likely to increase the partition of nutrients towards milk production. This results in a higher lamb growth rate than in lambs reared by unshorn controls.

Irrigation experiments are described in which three cultivars were subjected to varying degrees of drought in the cool and hot seasons in Lima, Peru. The most severely draughted plots received, on average, 20% and 35% less water than the well-watered control plots, resulting in 20% and 52% yield reduction in the cool and hot seasons, respectively. Average fresh tuber yields ranged, according to cultivar, from 1370 to 2450 g/m2 in the summer and from 2800 to 4450 g/m2 in the winter, with tuber dry-matter percentages of c. 17% and 20%, respectively. The production of total dry matter per unit intercepted solar radiation (the conversion coefficient, estimated from the slope of the regression, in g/MJ) was markedly less during the hot season but, regressed on a photo thermal quotient ∑((MJ/m2)/(°C > 4·5°C)), a common relationship across seasons was achieved. The conversion coefficient was less in draughted than in well-watered plots, more so in the hot season.

Crop transpirational and evapotranspirational water use efficiencies (WUE) were less in the hot season largely because of the greater saturation vapour-pressure deficit. However, because of greater harvest index (HI) and more-efficient interception of solar radiation per unit of applied water by draughted than by well-watered plots in the summer, and despite a lower conversion coefficient, draughted plots showed greater WUE. Based on total water applied and final fresh tuber yields, WUE was, on average, 3·9 and 12·4 kg/m3 in the hot and cool seasons, respectively, values close to the extremes of the range of published values. Low HI in the summer was, to some extent, responsible for this seasonal difference.

Tissues of maize grown under different temperature regimes showed remarkable differences in anatomical and chemical properties and in vitro digestibility. A high temperature regime (12 h at 30 °C and 12 h at 24 °C) resulted in decreased cell wall thickness, cell diameter and cell wall yield, doubled lignin content and decreased in vitro digestibility, compared with plants grown under a low temperature regime (12 h at 18 °C and 12 h at 12 °C). A reduction in intensity of staining for lignin was observed in plants grown at 30/24 °C. Cell wall digestibility was thought to be limited by an indigestible cell wall layer between the secondary walls of adjacent cells. The use of lignin staining was of limited value for predicting cell wall digestibility. High temperatures probably affect physiological processes leading to lignin formation and deposition.

Samples of rumen fluid were removed from pairs of sheep on four grass-hay-based diets 7 h after feeding. Micro-organisms were sedimented by centrifugation and the cell-free supernatant was treated with perchloric acid (PCA) to precipitate protein. The remaining fluid was analysed for peptides by several methods to determine how much peptide escaped degradation. Ammonia interfered with analysis by amino group reagents, especially ninhydrin. In this respect, o-phthalaldehyde and trinitrobenzene sulphonic acid were more specific and more useful than ninhydrin. Use of all these reagents showed that significant quantities of amino groups (equivalent to up to 153 mg amino acid N/1 of rumen fluid) were released by hydrolysis of the PCA extract with 6 M-HCI for 24 h. However, fluorescamine analysis indicated that the peptide content of the unhydrolysed PCA extract was < 3 mg N/1. The true amino acid content of different extracts was resolved by chromatographic amino acid analysis: the sum of individual amino acid concentrations in acid-hydrolysed PCA extracts of extracellular rumen fluid ranged from 7·8 to 14·5 mg N/1. Thus most of the free amino N released by hydrolysis of the PCA extract was not from amino acids, and most of the amino acids that were released were originally present in a form that did not react with fluorescamine. Although none of the methods gave a reliable estimate of peptide concentrations, amino acid analysis provided an upper limit. It was therefore concluded that peptide concentrations in extracellular rumen fluid are much lower than indicated by previous ninhydrin estimations, and that little dietary peptide escapes degradation for a prolonged period in the rumen.

A technique has been developed for the measurement of pituitary hormone secretion rates in conscious sheep. The technique involves the continuous and simultaneous sampling of blood from the carotid artery and jugular vein and the measurement of cephalic blood flow by an indicator dilution technique. Veno-arterial differences in hormone concentrations multiplied by cephalic blood flow gave average secretion rates which were measured after single or repeated large doses of luteinizing hormone releasing hormone (LHRH) and thyrotrophin-releasing hormone (TRH) at various times in the reproductive cycle.