In general, the form and function of living plants reflect a requirement to maximize their interaction with the environment in order to harvest more effectively the energy and materials they require (Corner 1964). Thus, fluctuations in the aerial environment exert a considerable effect upon the physiology of the plant and lead to initiation of a range of responses. Changes in temperature are known to exert a pronounced effect on the growth of plants, and hence upon their productivity (Ong & Baker 1985). Most temperate species spend the majority of their life at mean temperatures below the optimum for their growth, and there are marked genetic differences between plant species in their ability to tolerate nonoptimal temperatures (Pollock & Eagles 1988). This review summarizes some of the ways in which plants are known to sense and respond to temperature change and discusses the potential for improving growth and performance at nonoptimal temperatures. Discussion concentrates upon temperate grasses and cereals because of their suitability as experimental material and because of their economic importance. Consequently, this review is largely concerned with responses to low temperatures, but some responses of tropical cereals to high temperatures are also described.

The descriptive aspects of hepatic fatty acid metabolism, and of ketogenesis in particular, have been extensively described for ruminants. There is, however, a distinct lack of information on the more mechanistic aspects of the subject. The biochemical profile of the livers of ruminant species shows both similarities to, and striking differences from, that of simple-stomached animals. Consequently, it may not always be valid to extrapolate from the situation in, say, rat liver to that in ruminant liver in order to interpret experimental observations in ruminants. Of perhaps greater interest is the recognition that the adaptations in the ruminant system are important not only in enabling us to rationalize the physiological changes observed in ruminants, but are in themselves of interest in the analysis of metabolic regulatory strategies. Consequently, this review deals with the peculiarities of the regulation of hepatic ketogenesis in ruminants, and the biochemical mechanisms that may explain their existence.

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.

Experiments were conducted in wheat planted in microplots at Hisar and Sirsa in Haryana state, India, to observe and simulate the depth distribution of moisture content, electrical conductivity in 1:2 soil-water extract (EC 1:2), and exchangeable sodium percentage (ESP) of soils after irrigation with water of high electrical conductivity (12–19 dS/m) and sodium adsorption ratio (20–80 (mmol/1)0·5). The three simulation models used differed in the procedure of estimation of evapotranspiration (models I and II, Reddy 1983; model III, Arora et al. 1987). In general, the means of the experimental moisture content profiles decreased and those of EC 1:2 and ESP increased with irrigation at both locations. Statistical analysis showed an overall good agreement between the experimental and simulated values of moisture content, EC 1:2 and ESP; the accuracy of simulation of the models followed the order model II = model III > model I, for moisture content and EC 1:2, but was identical for ESP.

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.

The effect of soil water supply on efficiency of N use in wheat and NO3-N accumulation in the soil profile was studied in a field experiment on loamy sand soil at Boothgarh in Hoshiarpur, Punjab, India in 1980/81. As the water supply increased from 509 to 548 mm, the response to N application increased by 11·5 kg grain/kg N and apparent N recovery by 11% at optimum N application rates. The increase in N recovery with additional water supply was related to the NO3-N use from the profile. The accumulation of NO3-N in the profile was related linearly to rate of N application but inversely to water supply up to an optimum value of 580 mm. Further increase in water supply did not increase fertilizer N use. If both the amount of moisture stored in the profile at sowing and the probable rainfall during the crop season are known, the efficiency of fertilizer N use can be predicted.

The effects of single and repeated early applications of chlormequat (at up to and including Zadoks growth stage (GS) 32) on the growth and development of the winter oat cultivar Bulwark were investigated in two seasons of field experiments at Tenby, UK. Early dry matter production, shoot initiation and subsequent shoot survival were unaffected by all treatments. At maturity, reductions in stem length and lodging were best achieved by chlormequat applied at GS 32; this treatment shortened stems by an average of 24% in 1985/86 and 31% in 1986/87. Earlier applications were significantly less effective.

Grain yields were unaffected by single and repeated early applications of chlormequat. However, in both seasons, yields were significantly reduced by repeated treatments with chlormequat, including application at GS 32. Individual grain weight was the yield component principally affected.

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.

In 12-year (1975–87) fertilizer trial on a pearl millet-wheat rotation, there were no responses to applied K and exchangeable K decreased from 620 to 200 kg/ha. In spite of progressively diminishing exchangeable K, removal of K by crops was independent of soil K status, indicating that exchangeable K had no relation to K uptake in this soil. Thus, nonexchangeable K made a major contribution to plant K, up to 90% in untreated plots and > 70% in K-treated plots. A significant (r = -·708) relationship between nonexchangeable K and K fixation capacity was found. Nonexchangeable K was also significantly but negatively correlated (r = -0·583) with free energy exchange (ΔGr). Potassium supply values, expressed by pK-½p (Ca + Mg), were positively and significantly correlated with K removal by crops in 1987 and with the K saturation values of the exchange phase, so that both these measures can be successfully used to test soil K availability. The results of this study suggested that on this soil, under a pearl millet-wheat crop system, inclusion of K in the fertilizer programme may soon be needed.

The response of an old, unimproved mixed-species pasture to fertilizer nitrogen was examined under 4-weekly cutting or continuous grazing with young beef cattle. Five N fertilizer rates were applied: zero, 100, 200, 400 or 800 kg/ha per year. The investigation was carried out in Devon, on a heavy clay soil in a region of high winter rainfall in 1984, 1985 and 1986.

Annual total herbage dry-matter (DM) production, live weight gain (LWG) and utilized metabolizable energy (UME) output all increased with successive increments of fertilizer N up to 400 kg N/ha per year. Under 4-weekly cutting, the response per kg applied N fell below 10 kg DM at an application rate of 268 kg N/ha per year, giving a yield of 10·6 t/ha per year. Under grazing, the overall response during the grazing season per kg applied N fell below 300 kg live weight carried per ha at a fertilizer rate of 248 kg/ha per year, giving a UME output of 78 GJ/ha over the grazing season. High available soil N contributed to the high productivity from these swards. Animal output at moderate (200 kg N/ha per year) N application rates did not appear to be constrained by the initial botanical composition of this unimproved sward. Repeated high N applications in the 400 kg N/ha per year treatment reduced output in 1986 under grazing and cutting, compared with treatments which had received the lower N applications.

The DM yield from the 4-weekly cutting study gave a satisfactory prediction of UME output from this pasture. Climatic conditions, particularly high rainfall, appeared to be an important constraint on animal performance at pasture.

The high UME output achieved from this pasture at 200 kg applied N/ha was well above the average UME for commercial farms.

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.

Two rotation field experiments of a single forage–cereal cycle each were conducted on a clay loam soil (Vertic Cambisols) in Cyprus in 1982–85. The forages in the first cycle (1982–84) were pure stands of vetch (Vicia saliva L.), peas (Pisum sativum L.) and oats (Avena sativa L.) and mixtures of each of the two legumes with oats at sowing ratios of 90:10, 75:25, 50:50 and 25:75 grown with 15, 30, 60, and 90 kg fertilizer N/ha. For the second cycle (1983–85) the same crops were used but with only two mixture ratios (legume:oats 90:10 and 75:25), and with 0, 15, 45 and 90 kg N/ha. Barley (Hordeum vulgare L.) was the test crop after the forages in both cycles. Legumes did not respond to N fertilization, whereas the yields of the pure stand of oats and the mixtures increased. The legumes yielded more N but less dry matter than the cereals. The grain and N yields of barley were higher after legumes than after oats, with intermediate yields after the mixtures. Barley responded to residual N fertilizer, irrespective of whether it was applied on legumes, oats or mixtures in the previous year. When choosing the forage to be grown, farmers should consider (a) the need for roughage and protein, (b) the costs of N fertilizer for crops and of protein for animal feed stuff and (c) the rotational role of the crop.

Plots at Hurley, UK, sown to perennial ryegrass (Lolium perenne) in 1968 were given 188, 376 or 752 kg N fertilizer/ha per year. Half of each plot at the lowest and highest rate of N fertilizer was given a severe pesticide (phorate) treatment at frequent intervals. Plots were cut and their herbage yield was assessed on five occasions during each of the following 20 years. There was no indication of a long-term decline in total annual herbage yield at any rate of N fertilizer use. The severe pesticide regime enhanced yield by an average of 14·6%/year during the first 11 years, but tended to have little effect or to reduce yields subseque7tly. Initially (1969) all treatment plots comprised at least 85% perennial ryegrass, but this proportion declined to between 67% (medium N) and 40% (high N) by 1989. Apart from ryegrass, the main sward components were species of the grasses Agrostis, Poa, and Elymus and traces of the broad-leaved species Stellaria media and Taraxacum officinale.

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.

In a field trial at Rukuhia, New Zealand, ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) seed was direct drilled into pasture (i) without herbicide suppression of the resident sward, (ii) with banded application of glyphosate or paraquat herbicide at drilling to remove 50% of the resident sward and (iii) after complete removal of the grass and weed components of the old sward with glyphosate or paraquat before drilling. These treatments were compared with the untreated old swards. Where the old sward was removed by herbicide before drilling, pests moved onto the drilled seedling rows, but, where herbicide was sprayed in bands over the drill rows, the pests remained in or moved into the residual bands of the old sward. Significant beneficial interactions between herbicide use and in-furrow applications of molluscicides and insecticides resulted in reductions in the numbers of pests on the seedling rows. The influence of vegetation control on the pest burden is discussed in the context of current pasture renovation practices.

In field and wind tunnel experiments in 1988 at the Scottish Centre of Agricultural Engineering, moisture loss in the 24 h after cutting increased when grass swaths were mixed, spread or turned and was positively related to the number of mixings. In the field trials, dry matter loss from conditioned swaths increased when the swaths were mechanically mixed or spreadafter cutting.

Crop yields and soil properties of grazed grass–clover pasture and arable plots at the Grasslands Research Institute, Hurley, UK. were measured over 30 years (1955–84). Yields of herbage declined from 9·6 t DM/ha in the first harvest year to 4–6 t in years 5 to 8 but subseque8tly increased (after liming) to give a mean yield of 8·2 t for 1963–84. Yields of barley in plots receiving a seed-bed application of 45 kg N/ha averaged (1962–80) 3·1 t/ha and, in plots top dressed with an additional 100 kg N/ha, 4·1 t/ha but after 1969, response to additional N and yield under both N treatments showed a marked decline.

Soil carbon increased during the first 10 years under pasture from 1·2 to 1·8% and soil N from 0·13 to 0·17%. These increases, equivalent to 1 t C and 75 kg N/ha per year, occurred at the same time as the initial decline in herbage yield noted above. During the subsequent 20 years, C and N remained relatively constant and herbage yields increased. Soil C and N decreased under 30 years' arable management to 0·8% C and 0·1% N, equivalent to a loss of 290 kg C and 25 kg N/ha per year.

Major factors that appear to have influenced herbage yields were (i) soil moisture, (ii) accumulation of N in the soil organic matter during the first 8 years and the subsequent increase in the rate of mineralization, and (iii) the action of the earthworm population in creating a stone-free, fertile layer of top soil. As for barley, it was concluded that yields could not be maintained indefinitely on this soil series, as a result of the loss of soil structure and the development of a compact layer of soil at plough depth.

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.

The effects on a winter wheat test crop of a preliminary year of winter or spring field beans (Vicia faba), winter oats, winter oilseed rape, winter or spring peas (Pisum sativum), winter wheat, spring lupins (Lupinus albus), spring sunflowers (Helianthus annuus) or a cultivated fallow were compared in three 2-year experiments on clay-with-flints soil at Rothamsted from 1986 to 1989. In one experiment, autumn-sown ryegrass (Lolium perenne) and an uncultivated fallow, given weedkiller, were also included in the first year. Plots of test-crop wheat were divided to compare no N fertilizer with an optimal amount estimated from a predictive model.

Amounts of take-all (Gaeumannomyces graminis) in the test crop of wheat following wheat were very slight in the first experiment, but large in the second and third. All the break crops reduced takeall to none or very slight amounts.

Amounts of NO3-N in the soil in autumn after the first-year crops ranged from 7 to 95 kg N/ha. On average, they were least after oats, and most after cultivated fallow. In autumn 1988they were least after autumn-sown ryegrass. In early spring, amounts of NO3-N were generally less, ranging from 7 to 55 kg N/ha, depending on preceding crops, sowing date of the wheat and the weather. Amounts of NH4-N in soil were little affected by preceding crops or weather and were generally smaller in spring.

The estimated average N fertilizer requirement of test-crop wheat following winter wheat was 230kg N/ha. This was increased by 10 kg N/ha following winter oats, decreased by 40 kg N/ha after spring peas and by 30 kg N/ha after winter rape, winter peas, spring beans and cultivated fallow. Other preliminary crops not represented every year had effects within this range.

Grain yields of test-crop wheat given optimal N averaged 7·2 t/ha after winter wheat, c.1·5 t/ha less than the average after most of the break crops. The yield after oats was limited by self-sown ‘volunteers’ and that after ryegrass by limited soil N after ploughing.

Of the break crops tested, winter and spring beans, winter oats, winter rape and spring peas all gave satisfactory yields. A farmer should choose between these on the basis of local farm circumstances and current economics of the break crops. Differences between effects on take-all and savings on fertilizer N were too small to influence this decision.