This research was done in order to explore genetic variation in carbon exchange rate (CER) of spring wheat (Triticum aestivum) leaves in response to variable photosynthetically active radiation (PAR) and to compare old and new Israeli cultivarsin this respect. Leaf gas exchange was measured in detached turgid leaves of 17 cultivars inan open system at 25 °C when PAR was reduced from c. 1200 to 200 μmol/m2 per s. Linear regressions of CER, stomatal conductance, transpirationand leaf internal CO2 concentration (Ci) on log PAR were fitted for each leaf(regression r2 was never <0·79) and the regressions were compared among cultivars by analysis of variance.

Genotypes differed significantly for the slope (b) but not the intercept (a) of the regression of CER on log PAR, indicating that genotypic differences for CER increased with increasing PAR. Photosynthetic capacity, as expressed by the ratio of CER/Ci, differed significantly among cultivars only at high PAR. Stomatal conductanceand transpiration increased in a linear or a nonlinear fashion with log PAR and differences among cultivars for both were greatest at medium to low PAR. Photosynthetic water–use efficiency (WUE) and its variation among cultivars were greatest at the highest PAR. Genotypic variation in CER athigh PAR was confirmed by repeated results for 11 cultivars intwo independent experiments.

The recently developed high-yielding cultivar V652 had a higher maximum CER, higher photosynthetic capacity and greater WUE at high PAR than older and lower-yielding cultivars. The results suggest an upward genetic shift in photosynthetic capacity andin CER at high PAR when selection for yield was performed under the high-irradiation conditions of Israel.

Rice plants (Oryza saliva L., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 μmol CO2/mol air) CO2 concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO2 concentration, thegreatest increase occurring between the 160 and 500 μmol CO2/mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO2 concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasingCO2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO2 treatments. Doubling the CO2 concentration from 330 to 660 μmol CO2/mol air resulted in a 32 % increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO2 concentration of the earth's atmosphere continues to rise.

Cultivars of Phleum pratense, Festuca pratensis, Festuca arundinacea, Dactylis glomerata and Lolium × Festuca hybrids were exposed to 4- and 3-cut harvest systems in Prince Edward Island, Canada, in 1985–87. Lolium perenne × F. pratensis, Lolium multiflorum × F. pratensis and L. multiftorum × F. arundinacea hybrids and D. glomerata had more uniform growth among the harvests than other grasses during the growing season. L. perenne × F. pratensis and L. multiflorum × F. pratensis had lower contents of neutral and acid detergent fibre than other grass cultivars, particularly early in the growing season. P. pratense cv. Farol had the lowest and L. perenne × F. pratensis cv. Prior the highest tiller population density. The stem apex of all cultivars was above the cutting height of 5 cm in c. 50% of tillers of primary growth. Leaf area per tiller was largest for P. pratense cv. Farol in the primary growth stage but differences were small in subsequent cuts.

Flower, pod and seed development were studied in the cultivars Cita-1 and Cita-2 in two field trials in 1985–86, in Ibadan, Nigeria. Flowering within any inflorescence was acropetal. On each plant the terminal inflorescence was the first to flower and, generally, inflorescences developed basipetally. A total of 569 flowers (mean of five plants) opened on Cita-1; of these, 20 were on the terminal inflorescence, 130 on axillary inflorescences and 419 on inflorescences on primary branches. For the 605 flowers (mean of five plants) which opened on Cita-2, the distribution was 19, 161 and 425, respectively.On Cita-1, 158 pods formed on average, of which 7 were on the terminal inflorescence, 33 on axillary inflorescences and 118 on inflorescences on primary branches lower down the plant. On Cita-2, for the 185 pods counted at maturity, the distribution was 8, 43 and 134, respectively. Some 72 and 69% of the total number of flowers which opened on Cita-1 and Cita-2, respectively, were aborted. In both cultivars, 99% of the mature pods were formed from flowers which opened within 24 days of the start of anthesis; the number of pods retained largely determined seed yield. The inflorescences which developed on the primary branches contributed 70% (Cita-1) and 66% (Cita-2) of the total seed yield. Early-formed pods were heavier than those formed later. Individual pods attained physiological maturity 35–42 days after successful pollination of the flower. At physiological maturity of the pod, the seed contained 3·72 % N, 0·45% P and 2·76% K, and the husk contained 1·98% N, 0·16% P and 1·96% K. The majority of open flowers which aborted were produced on primary branches, indicating that the primary branches have the greatest potential for increasing seed yield. A shorter flowering period might ensure greater retention of open flowers.

Eight genotypes of groundnut and two of pigeon pea were evaluated in intercropping at the Indian Institute of Technology, Kharagpur, during the monsoon and winter seasons in 1985 and 1986, to identify plant characters associated with high yield in intercropping. The pod yield of groundnut decreased when intercropped with pigeon pea, the extent of the decline differing with groundnut and pigeon pea genotypes. The reduction in groundnut pod yield and the degree and duration of shading was less when grown with pigeon pea type ICPL87 than with LRG30. During the monsoon, pod yield among intercropped groundnut genotypes ranged between 47% and 88% of their yields under monocropping because of differences in growth pattern and duration (90–125 days). The groundnut type most suitable for intercropping had early vigour, early maturity and high partitioning and pod growth rate. However, variation in pod yield among groundnut genotypes was not observed during the winter season because they showed less variation in duration and growth and there was less shading by the associated pigeon pea.

Powders made from 15 plant species were tested in the laboratory against C. maculatus on stored cowpea seeds. Fewest eggs were laid on seeds mixed with Nicotiana tabacum powder. Few eggs were also laid on seeds mixed with powders obtained from Erythrophleum suaveolens and Ocimum gratissimum. N. tabacum powder, followed by E. suaveolens powder, was the most effective in reducing egg hatch.

The phenology of anthesis, anther dehiscence, fertilization and petal fall in the linseed cultivar Antares and its response to supplementary pollination when grown in a glasshouse were investigated. Anthesis commenced 15–30 min after the onset of the photophase and was complete within 2 h. Anthers dehisced when buds were in the tube stage of opening and produced a mean of c. 4·5 × 103 pollen grains per flower. Most ovules were fertilized within 6 h of the onset of the photophase. Flowers self pollinated naturally and, although supplementary pollination increased the percentage of flowers that produced capsules and the number of seeds per capsule, it decreased flower production and individual seed weight and conferred no increase in seed yield. Flowers retained their petals for at least 2 h after the onset of the photophase but, by 10 h, 97% of hand-pollinated flowers had shed their petals; those naturally self pollinated or shaken retained their petals for longer.

In studies of 36 genotypes of Boehmeria nivea, height of plants grown from rhizomes at 70, 90 and 110 days after planting showed positive and significant phenotypic and genotypic correlations with establishment percentage from stem cuttings, indicating that genotypes producing tall plants from rhizomes could establish more easily from stem cuttings than genotypes producing shorter plants. A higher genotypic than phenotypic correlation coefficient and a higher coheritability percentage indicated that plant height and establishment percentage were genetically linked and influenced little by environment. It was concluded that vigour of plants grown from rhizomes may be used as a criterion in selection of genotypes for ease of establishment of stem cuttings.

The relationships between the amounts of nitrogen fertilizer applied and taken up by sugarbeet crops and the concentrations of sugar and α-amino-N in the storage root were examined using data obtained from fertilizer-response trials on different soils in the UK and Belgium between 1974 and 1985. On unmanured mineral soils, crop uptakes of N without fertilizer ranged from 65 to 190 kg/ha and increased linearly with the amount of fertilizer N applied. On organic soils or mineral soils that had received large applications of organic manure, crop uptakes of N were very large (295–383 kg/ha) and were not increased by applications of fertilizer N.

The amino-N contents of harvested beet increased with crop N uptake. The distributions of crop N to the storage root and of storage-root N to amino-N differed, especially in manured, diseased and drought-affected crops. Greater proportions of crop N were present in the storage roots of manured crops than in conventionally fertilized crops, and more of the storage-root N was present as amino-N in crops affected by virus yellows or drought than in healthy, unstressed crops.

The fresh weight concentrations of sugar in the storage root also differed between sites and years but were not consistently reduced by applications of fertilizer N at individual sites. However, when compared across sites, concentrations were negatively correlated with crop N uptakes and the amounts of N in storage roots. This was because particular crops grown on mineral soils with large applications of manure or on organic soils had large N uptakes and exceptionally low concentrations of sugar.

The physiological implications of these relationships between N uptake and amino-N and sugar accumulation are discussed.

An earlier report of leaf scorch and diminished yield when using large amounts of urea on winter oilseed rape (Brassica napus) was investigated by applying 200 kg N/ha as calcium ammonium nitrate (‘Nitro-chalk’) or urea as a single dressing or divided in six ways. The ‘single-low’ variety Mikado (low in erucic acid) was grown in 1986 and was compared with the ‘double-low’ variety Ariana (low in erucic acid and glucosinolates) in 1987 and 1988. No scorch was seen in these experiments. Yield from rape fertilized with prilled urea was, on average, 98% of that from rape fertilized with ammonium nitrate. The timing and distribution of the fertilizer also had little effect on yield, though yield slightly decreased when part of the dressing was withheld during March. The earlier-maturing variety Mikado always outyielded Ariana except when harvest was delayed by bad weather.

When plots were fertilized with urea, the oil content of the seed was a little larger than when fertilized with Nitro-chalk, which compensated for the smaller seed yield, resulting in almost equal oil yield from both forms of N fertilizer. Crude protein content was lower after a large single dose of urea fertilizer but parity with ammonium nitrate was restored by smaller amounts applied on a number of occasions. Neither form nor timing of N fertilizer had any consistent effect on the total glucosinolate content.

The incidence of disease was significantly greater in rape given either form of N fertilizer than where none was given, but when downy mildew (Peronospora parasitica) was prevalent on pods there was significantly less infection in plots fertilized with urea than with ammonium nitrate.

Crop patterns of natural origin and man-created crop marks are frequently recorded on aerialphotographs taken over England and Wales. They usually indicate subsil variation over short distances, but differences in crop growth may also be evident in relation to topsoil variability. Different kinds of crop patterns and the soils on which crop patterns and marks develop are briefly described. Soil associations in which crop patterns and marks are frequently and extensively recorded cover 25% (37664 km2) of England and Wales; in dry years, patterns and marks are extensively recorded over a further 6·5% (9884 km2). Crop patterns and marks indicate that over much of England and Wales crop growth may be impeded by properties intrinsic to the soil, which are not easily ameliorated by farmers. When siting crop experiments, care should be taken to avoid these areas of complex soil patterns.

The responses to Zn fertilizer of wheat, barley, oats, lentil, chickpea, pea, mustard and linseed were studied on a Typic Ustochrept soil in Pura, India in winter 1982/83 and 1983/84. Application of Zn significantly increased the grain or seed and total biomass yield of all the crops and enhanced Zn concentration and uptake. The response was greatest in lentil, followed by chickpea, pea, wheat, linseed, mustard, barley and oats. Cereals accumulated the most Zn, followed by the pulses and oilseeds. The pulses were more sensitive to Zn deficiency than the other crops.

Contents of the caecum and the colon of four steers and four cows fed concentrate-plus-roughage diets were obtained at an abattoir, transferred to the laboratory and incubated anaerobically with maize starch in the presence (10mg/l) or absence of monensin. Samples taken at the end of incubation were assayed for fermentation acids and methane production.

Monensin significantly increased the molar percentage of propionate and decreased that of butyrate. Acetate percentage was not significantly influence by the addition of monensin. There was no consistent effect of monensin on total volatile fatty acid concentrations. Monensin decreased methanogenesis in all incubations. The production of methane was small, only 1 mmol/13–50 mmol of volatile fatty acid.

Between weeks 3 and 18 of lactation, 141 British Friesians all received concentrate (metabolizable energy (ME) 12·9 MJ/kg dry matter (DM), 202 g crude protein (CP)/kg DM) at 8·0 kg fresh weight/day. In addition, cows received ad libitum either grass silage (ME 11·7 MJ/kg toluene DM; 219 gCP/kg DM) or a mixture containing grass silage and 15, 25 or 40% (DM basis) of winter barley straw (cv. Igri) either untreated (UTS) or treated (TS) with 4% NaOH. Forage treatments were imposed at either week 3 or week 9 of lactation.

The mean forage DM intake of cows receiving grass silage only was 8·60 kg/day. When 15, 25 and 40% UTS was introduced into the rations at week 3 or 9 of lactation, forage DM intakes were 884, 8·43, 7·62 and 8·63, 8·83, 819 kg/day, respectively; the corresponding values for TS were 8·88, 855, 8·99 and 8·97, 8·98, 9·35 kg7sol;day. The milk yield of cows receiving grass silage only was 22·1 kg/day. When 15, 25 and 40% UTS was introduced into the rations at week 3 or 9 of lactation, milk yields were 21·1 kg/3, 20·1 kg/1, 20·1 kg/5 and 20·1 kg/1, 21·4, 20·5 kg/day, respectively; the corresponding values for TS were 21·8, 22·1, 21·3 and 22·5, 21·4, 22·6 kg/day. When averaged across the three inclusion rates, TS significantly increased forage intake (P < 0·05) and milk yield (P < 0·01) compared with UTS. Intermediate values were recorded for the diet with grass silage alone. The inclusion of TS in the ration did not affect milk yield compared with grass silage alone. No major changes in milk composition were recorded by the inclusion of either TS or UTS. However, the yields of milk fat, protein and lactose for the TS treatments were higher than for UTS and were significant for protein (P < 0·01) and lactose (P < 0·001). Cows with UTS in their ration tended to have lower live weight gains than either the control group or treatments with TS.

When compared with grass silage only, the inclusion of TS or UTS decreased digestibility coefficients and ME contents, determined in vivo using wether sheep fed at maintenance. However, the treatment of straw with NaOH (4%) increased its digestibility coefficients of dry matter from 0·-393 to 0·668, of organic matter from 0·445 to 0·686, of acid detergent fibre from 0·442 to 0·713, gross energy from 0·438 to 0·640 and ME content from 7·0 to 9·4 MJ/kg DM.

Direct-cut silage was made in mid-October 1985 from established swards of predominantly hybrid ryegrass (Lolium perenne x Lolium multiflorum). The crop contained 161 g dry matter/kg and 94 g soluble carbohydrate/kg and was ensiled in bunker silos with (i) no additive (control), (ii), formic acid (5 litres/t) or (iii) addition of 45 kg rolled barley per tonne of grass in silo.

The inclusion of barley reduced effluent production to 27 litres/t of ensiled grass compared with 51 litres for the control and 60 litres for the formic acid treatment. Losses of DM in effluent were small but total in-silo DM loss was reduced from 25 % for the control to 11% by formic acid and to 13% by inclusion of barley.

DM content of the silage containing barley was 30 g/kg higher than that of the other silages. Silage treated with formic acid contained least ammonia-N, 6% of the total N, compared with 9% in the barley-added silage and 11% in the control. In vivo assessment in sheep gave metabolizable energy values of 98, 10·9 and 11middot;2 MJ/kg for the control, formic and barley silages, respectively; N retention was higher in the formic acid and barley-added silages.

The silages were fed ad libitum to beef cattle for 8 weeks, with a daily feed supplement to the control and formic acid groups to equate barley intakes. Silage DM intake was higher for the barley silage, daily live weight gain per animal was similar for the barley-added and formic acid silages (c. 1 kg), both being higher than the control (0·8 kg).

It was concluded that barley inclusion achieved similar improvements in silage quality, in-silo losses and cattle performance to formic acid treatment but with the additional benefit of markedly reducing effluent production.

The study was carried out in northern Kenya in 1984–87. Forestomach volumes and digesta retention times were measured using Cr-EDTA or Co-EDTA as fluid markers and Ce-labelled particles or Cr-mordanted particles as paniculate phase markers.

Mean retention times of fluid and of particles were longer in the dry season than in the green season in all four animal species. The increase of particle mean retention time, as a percentage of the values in the green season, was highest in sheep (46%), followed by cattle (27%), goats (22%) and camels(18%). Forestomach volumes were also greater in the dry than in the green season; the increase was again highest in sheep (55%), followed by cattle (31%), goats (29%) and camels (28%). Outflow rates of fluid from the forestomach and the selectivity factor, by which small particles were retained longer in the forestomach than fluid, did not differ significantly between the seasons.

It is suggested that the increase of forestomach volumes is an effective adaptation to dry-season pasture conditions. It enables the animals to retain feed particles longer in the forestomach and so improve fibre digestion when feed quality is low. Cattle and sheep, which depend on a poor quality diet, improve fibre digestion in this way in the dry season more effectively than camels and goats. Camels and goats, on the other hand, were able to select a diet of such quality, even in the dry season, that their need to augment fibre digestion was reduced.

Muscle metabolism was studied in pregnant sheep over the final 4 weeks of pregnancy, between January and March 1985 and between December and March 1986, to investigate the effect of (i) chronic cold exposure, induced by shearing pregnant ewes 8 weeks before lambing and (ii) undernutrition in shorn and unshorn ewes. This was achieved by measuring hind-limb tissue metabolism using a combination of isotopic and arterio–venous difference techniques.

The rates of blood flow, oxygen uptake, carbon dioxide production and calculated heat production were all significantly higher across the hind-limb tissues in shorn than in unshorn ewes. The increase in hind-limb energy metabolism in the shorn group was such that 65% of the difference in wholebody heat production between shorn and unshorn groups could be attributed to muscle tissue. Following underfeeding, all of the difference in whole-body heat production between the two groups was completely attributable to muscle tissue.

Nonesterified fatty acid (NEFA) oxidation by muscle accounted for 46% of the difference in whole-body NEFA oxidation rate between fed shorn and unshorn groups. Underfeeding significantly increased the mean arterial plasma concentration of NEFA in shorn and unshorn ewes and the rate of NEFA oxidation across the hind-limb tissues in shorn ewes. The difference in whole-body NEFA oxidation between shorn and unshorn groups could, therefore, be completely accounted for by muscle. No significant differences in the arterial plasma concentrations of glucose, lactate or 3-hydroxybutyrate were recorded between shorn and unshorn ewes, although the rate of glucose uptake across the hind-limb tissued was significantly higher in the shorn group. Calculation of the maximum potential contribution of these substrates to hind-limb metabolism demonstrated that NEFA were the predominant energy source in all experimental conditions studied in all ewes. When data from fed and underfed shorn ewes were pooled, regression analysis revealed a significant negative correlation between the arterial plasma concentrations of glucose and 3-hydroxybutyrate, and significant positive relationships between the arterial concentrations of both glucose and 3-hydroxybutyrate and their rate of uptake across the hind-limb tissues. These relationsips were not observed in unshorn ewes.

It is concluded that the muscle mass plays a major role in the nonshivering thermogenic adaptation to chronic cold exposure in shorn pregnant sheep and that NEFA are the major substrate utilized for oxidative metabolism in this tissue.

The in vivo digestibility of soyabean integuments, rape integuments and dehydrated beet pulp was determined in sheep in the Centre de Recherches de Clermont-Ferrand-Theix, in 1985. Organic matter digestibility was 83·5, 59·6 and 85·0%, respectively, for the three feeds. The nylon bag method was used to determine the disappearance of dry matter (DM) in the rumen. After 72 h, 89 and 96% DM had disappeared for soyabean integuments and beet pulp, respectively, but only 61% for rape integuments. The DM disappearance rate was slowest (P < 0·05) for soyabean integuments. Microscopic examination showed that the different layers of the soyabean integument could be ranked in increasing order of resistance to microbial degradation as follows: parenchyma, aleurone layer, column cell layer, palisade layer and epidermis. The hilum area was the most resistant and the only one lignified. The cell layers of the rape integument could be ranked in increasing order of resistance as follows: epidermis, aleurone layer and palisade layer. The last was highly lignified and not degradable. Degradation of beet pulp was fast, occurring first in the parenchyma. The vessels resisted degradation but were only a small part of the feed. This study shows why beet pulp has a low fill value and allows high intake. The soyabean integument is very digestible and is degraded slowly, whereas almost half of the rape integument is made up of a cell layer that is not degradable.

Male and female New Zealand White rabbits were exposed for 3h to 34 °C and 36 °C (both at 40% r.h.) when hydrated and dehydrated. Females had lower rectal and skin temperatures and respiratory rates than males (P < 0·001). Differences between the sexes in rectal temperature were greater at 36 °C than at 34 °C. Withholding water for 24h significantly increased the responses in rectal temperature; the differentials between hydrated and dehydrated males and females being 0·3 °C and 0·2 °C, respectively. In contrast, respiratory rates were lower in dehydrated than in hydrated rabbits, suggesting that the former were attempting water homeostatis at the expense of thermoregulation.

The results suggest that the performance of rabbits in the tropics is likely to be maximized when drinking water is available at all times, and that of males, particularly breeding bucks, might be improved simply by housing them in the coolest available location. Significant individual differences in observed responses point to the need for genetic studies of heat tolerance and the possibility of developing better adapted genotypes.