Yields of arable crops are commonly lower on the crop margins or headlands, but the nature of the relationship between yield and distance from the crop edge has not been clearly defined, nor have the reasons for lower marginal yields. Surveys of 40 winter wheat headlands were carried out in 2 years to determine how yield changed with distance, and what factors might influence this relationship. Two field experiments were also conducted over 3 years in winter cereal headlands, in which the effect of distance was measured under conservation headland and conventional (fully sprayed) management.

Yields in the headland surveys varied from 0·8 to 10·2 t/ha. An inverse polynomial regression model was fitted to yield and weed data. Best fits were obtained by using separate parameters for each site. Adjusting yields to take account of weed dry matter improved the non-linear fit between yield and distance from crop edge. Field experiments provided similar results but the non-linear relationship was not as apparent.

There was a negative relationship between soil compaction, as measured by a cone penetrometer, and yield in one field experiment, where soil density values were relatively constant. No relationship was found between pattern of nitrogen fertilizer application and yield. Conservation headland management resulted in lower yield at one experimental site, especially in the third year, but not at the other site. Where yields were affected, weed dry matter was higher in conservation headland plots than in fully sprayed plots.

Although greater weed competition appears to account for at least part of the observed yield reductions on headlands, the role of other factors, particularly soil compaction, needs further study. Increased weed infestation may be an indirect result of reduced crop competition caused by other adverse conditions.

The genetic control of pod dehiscence was studied through the production, field trial and subsequent analysis of a full diallel involving seven parents selected for high and low resistance to pod shattering. Additive gene effects were most significant among the measures of pod shattering resistance with only minor contributions from non-additive gene effects. Genetic variation in measures of the stiffness of the pod wall were, however, determined by dominant gene effects. Genes for increased pod shattering resistance acted recessively. All characters showed high levels of heritability. Correlations among pod shatter resistance characters and other pod, raceme and plant characters were low suggesting that resistance is likely to be independent of other important agronomic traits.

A comparison of the fibre and seed development in fibre flax and linseed types of Linum usitatissimum (L.) was carried out in replicated field plot experiments in 1993, 1994 and 1996 in Northern Ireland. Flax cultivar Ariane, and linseed cultivars Barbara (1993 and 1996) and Flanders (1994) were each grown at seed rates of 500, 1000 and 1500 seeds/m2 and sampled at 7-day intervals from the start of flowering until harvest. The number of buds, flowers and capsules per plant were counted and straw height and total, seed, straw, total fibre, long fibre and short fibre dry matter ( DM) yields determined for each sample date. Fibre yields were determined after water retting the straw for 7 days at 20°C and extracting the fibre by scutching and hackling.

The emergence dates were similar in all years, but site and season interactions resulted in later flower and capsule development in 1993. Although the total biomass of flax and linseed were similar at the start of flowering, flax maintained a more rapid straw growth rate and linseed a more rapid seed growth rate giving final fibre yields that were 1300 kg/ha higher in flax than linseed and seed yields that were 800 kg/ha greater in linseed than flax. The proportion of fibre in the straw was higher in flax than linseed and the proportion of long fibre within the total fibre fraction was also greater. Final seed yields were highest in 1993, and fibre yields from flax were higher in 1994 than in the other years. Seed rate had no effect on seed yield in either flax or linseed but at the lowest seed rate, which gave plant counts of about 400 plants/m2 , the total fibre yield was significantly reduced compared with the higher seed rates with plant counts of about 1200 plants/m2 . It is concluded that decreasing fibre flax seed rates from 1500 to 500 seeds/m2 will reduce potential fibre yields by 25% but have little effect on seed yield, whilst increasing linseed seed rates from 500 to 1500 seeds/m2 would only result in marginal increases in the potential yield of fibre.

Groundnut is an important crop of the semi-arid tropics where potential yields are frequently reduced by heat and water stress. Eight groundnut genotypes varying in heat tolerance were grown in controlled environments and exposed to either high (40/28°C) or near-optimum (30/24°C) temperature from 32 days after sowing (DAS) to maturity. There was significant variation among genotypes in mainstem leaf number and total flower number at 30/24 and 40/28°C and rates of appearance were faster at 40/28°C than at 30/24°C. Days from sowing to first flowering varied among genotypes from 28 to 41 days and therefore the time plants were exposed to high temperature relative to first flowering ranged from −4 to 9 days. Fruit number for seven out of eight genotypes at 40/28°C was linearly and negatively related to the time of first flowering relative to the onset of high temperature (r2 = 0·93; n = l7; P < 0·001), indicating that ‘escape’ was an important component of heat tolerance in this experiment. Further analysis showed that fruit number in all genotypes at 40/28 °C was closely associated with the cumulative number of flowers that had opened between first flowering and 3 days after the onset of the high temperature regime (r2 = 0·95; n = 8; P < 0·001). Variation in fruit number was therefore due both to the timing of flowering and the initial rate of flower production. These data also suggest that the most sensitive stage of development to high temperature in groundnut occurred around 3 days before flowers opened. Therefore, it was the timing of flowering, rather than heat tolerance or susceptibility, that was the dominant attribute determining fruit number.

The possible impact of global rises in atmospheric CO2 concentration and temperature on the growth and development of French beans (Phaseolus vulgaris) was examined using growth cabinets. Five CO2 concentrations of 350, 450, 550, 650 and 750 vpm and five temperatures of 14·5, 15·5, 16·5, 17·5 and 18·5°C were tested using a fractional factorial design comprising nine treatment combinations of the two factors. Plants were grown under constant irradiance, common atmospheric humidities (vpd 0·5 kPa) and non-limiting supplies of water and mineral nutrients. The plant growth response was modelled by fitting polynomial response function curves to the times to first flower opening, first bean set, 50% maturity and the number and yield of beans. The effects of temperature were large and positive for most of the measured variables, whereas the effects of CO2 were small and negative or non-existent. Increased temperature substantially reduced the time to flowering and the time from bean set to 50% maturity and increased the number and yield of mature beans whereas increased CO2 concentration had little effect on plant growth except that bean yield was very slightly reduced. There was no significant evidence of interaction between the CO2 concentration effects and the temperature effects.

The time to maturity and yield of mature beans was simulated for the 2020s (2010 to 2039) and the 2050s (2040 to 2069) using the fitted polynomial models and four climate change scenarios suggested by the UK Climate Impacts Programme. These simulations showed that, depending upon the assumed scenario, the 2020s yields could rise by 39–84% and time to maturity reduce by between 6 and 15 days whereas the 2050s yields could rise by 51–118% and time to maturity reduce by between 9 and 25 days.

Pods of white lupin are characterized by a high proportion of pod walls in the pod mass at maturity. Genotypic variation in pod wall thickness at maturity and in proportion of pod walls has been described in this species. The objective of this study was to describe the pod and seed development in two ecotypes and one cultivar of spring-sown white lupin differing in proportion of pod walls, and to estimate the precise stage of development when the differences in pod wall dry matter among genotypes are first observed. The nitrogen content was also determined during the pod development of three genotypes. LA356, E084 and Lublanc were grown in the field in the UK and France in 1998 and 1999. The duration of pod and seed development was similar among genotypes and environmental conditions. Proportion of pod walls by dry weight at maturity were 0·21–0·23 for LA356, 0·27–0·28 for E084 and 0·30 for Lublanc. The ecotype with the lowest proportion of pod walls accumulated less dry matter in the pod walls than those with the highest proportion.

Variation in pod wall dry matter per seed between genotypes was observed early during the pod development (300°C days from flowering) and it was maintained during all pod development. No significant differences were observed for the total nitrogen content at maturity among genotypes with high and low proportion of pod walls.

Despite numerous reports on the positive effects of vesicular arbuscular mycorrhizae (VAM) on plant growth in temperate soils, surprisingly little data exist on the importance of VAM for crop growth on acid sandy soils of West Africa. A pot experiment conducted with local genotypes of pearl millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor L. Moench) and cowpea (Vigna unguiculata) with and without phosphorus (P) application in a sterilized sandy soil from a farmer's field in Niger showed large growth-enhancing effects of VAM. Phosphorus application led to 18- and 24-fold increases in pearl millet root and shoot dry matter independently of VAM, whereas the shoot and root dry matter of sorghum and cowpea depended largely on the interaction between P application and VAM. With P, VAM increased total uptake of P, K, Ca, Mg and Zn by 2·5- to 6-fold in sorghum and cowpea. On severely P deficient West African soils P application can lead to large increases in early root growth, a prerequisite for early mycorrhizal infection and a subsequent significant contribution of VAM to enhanced plant growth and nutrient uptake.

Near infrared spectroscopy (NIRS) is widely used in the flour milling industry for rapid determination of moisture and protein in wheat. However, these measurements give little indication of the nutritive value of wheat when fed to poultry or pigs. Accurate estimates of nutritive value require specialist facilities and are time-consuming and costly. Accordingly, prediction from chemical or NIRS measurements would be of some considerable benefit. In the current study 160 samples of wheat, representing 24 different varieties, were used to generate NIRS calibration equations for chemical, nutritive and agronomic characteristics. Predictions of chemical constituents in wheat were very accurate. Coefficients of determination (r2) were 0·94 for dry matter, 0·90 for crude protein, 0·97 for ash, 0·78 for starch and 0·98 for oil. True metabolizable energy in broiler chickens was predicted more accurately (r2 = 0·52 for adult birds, 0·74 for young birds) than apparent metabolizable energy (r2 = 0·45). Digestible energy (r2 = 0·17) and nitrogen digestibility (r = 0·22) in pigs were not predicted very accurately on a smaller subset (n = 33). Agronomic characteristics were predicted very accurately (r2 = 0·98 hardness, 0·80 bushel weight, 0·99 thousand-grain weight). Predictions of nutritive value of wheat from chemical or agronomic characteristics are very inaccurate, since coefficients of determination vary from zero to 0·25. It is concluded that NIRS can accurately estimate the chemical composition of wheat, but accurate prediction of nutritive value is reduced by animal variation. Nevertheless, NIRS is potentially more reliable for assessing nutritive value than chemical composition or agronomic characteristics.

The study examined the extent to which n-3 PUFA from different sources were biohydrogenated in the rumen and their effects on rumen microbial efficiency and whole tract nutrient digestibility. Four ruminally and duodenally cannulated wether lambs were used in a 4×4 Latin square design. Four iso-energetic and iso-nitrogenous diets based on dried grass were formulated to provide similar fat levels (60g/kg DM) from different sources; Megalac (palmitic acid: C16:0; Control), whole linseed (α-linolenic acid, C18:3n-3 ; Linseed) fish oil (eicosapentaenoic acid, C20:5n-3, EPA and docosahexaenoic acids C22:6n-3, DHA; Fish oil) and whole linseed plus fish oil providing equal amounts of oil (LinFish). Diets were offered at a rate of 1·2kg/day in 12 equal portions.

Total fatty acid intake was similar on all diets whilst duodenal fatty acid flow varied between 101, 94, 87 and 90% of dietary intake for animals fed the Control, Linseed, Fish oil and Linfish diets respectively. Duodenal flow of C18:3 n-3 in animals fed the Linseed diet was twice that of animals fed the Control diet (P < 0·01) whilst animals fed the Fish oil diet had a significantly greater flow of EPA and DHA than those fed any of the other dietary treatments. Duodenal flow of trans C18:1 in animals fed the Linfish diet was significantly greater than that in animals fed either Linseed, Fish oil or Control diets (P < 0·001). Biohydrogenation of C18:3n-3 was 80 to 93% in all diets whilst that of C20:5n-3 and C22:6n-3 was 72 to 79% in diets that contained fish oil or linseed and fish oil. Apparent fatty acid digestibility (duodenum to rectum) tended to be greater for unsaturated than saturated fatty acids whilst whole tract fatty acid digestibility (mouth to rectum) was significantly greater in animals fed diets containing fish oil (P0·05). All dietary n-3 PUFA sources decreased microbial protein synthesis and efficiency when expressed as either gN/kg organic matter (OM) apparently or truly degraded in the rumen. Additionally, the inclusion of fish oil increased the proportion of propionate in the rumen whilst depressing the rumen digestibility of OM and fibre (P < 0·01), but had no significant effect on whole tract OM or fibre digestibility.

This study was carried out from September 1998 to August 1999, by conducting three experiments, one each in the monsoon, winter and summer seasons. The forage availability and botanical composition of native range were obtained. Five 3–4-year-old Kutchi males, weighing 50–55 kg, were used to determine total faecal output, and were observed to allow the diet selected to be sampled by the hand plucking method. Dry matter (DM) yield of range was highest during winter and lowest during monsoon, annual mean being 1611 kg DM/ha. Contribution of shrub foliage to total forage yield in monsoon, winter and summer was 3·81, 1·64 and 9·98%, respectively. Crude protein (CP) content (g/kg DM) of ground vegetation declined from 99 in monsoon to 72 in winter and 66 in summer, while that of top foliage remained similar in all the seasons (mean CP 142 g/kg). Goats consumed a diet of almost the same CP content (mean CP 137 g/kg) in all the seasons. Goats consumed 64·0, 54·0 and 55·9 g DM/kg W0·75/day, in monsoon, winter and summer (annual mean 58·0 g DM/kg W0·75 /day). DM and CP digestibility coefficients were higher in monsoon and summer (mean DM 0·595; CP 0·533) and decreased (P < 0·05) in winter (DM 0·485, CP 0·424). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) digestibility coefficients were highest in monsoon (NDF 0·542; ADF 0·446), and declined (P < 0·05) to 0·340 and 0·266 in winter and 0·415 and 0·326 in summer. Digestible crude protein (DCP) intake was almost similar in monsoon and summer (mean 4·6 g/kg W0·75 /day) and declined (P < 0·05) in winter (3·1 g/kg W0·75 /day), while metabolizable energy (ME) intake was higher in monsoon (0·90 MJ/kg W0·75 /day) and declined (P < 0·05) to 0·78 and 0·80 MJ/kg W0·75 /day, in winter and summer, respectively. Average body weight of goats in monsoon, winter and summer was 54·0, 54·6 and 56·5 kg, respectively (annual mean 55·0 kg). It is concluded that goats grazing on a semi-arid rangeland meet their DCP and ME requirement throughout the year.

Caecal contents of 3-month-old rabbits were analysed and used as inoculi of cultures supplied with plant proteins (gluten, gliadin, zein), mucin, casein, ribonucleic acid (RNA) and glucose. The caecal digesta contained dry matter, total N, protein, trichloroacetic acid (TCA)-soluble N and NH3-N at 234, 10·2, 42·6, 3·2 and 0·27 mg/g (on average), respectively. One g of the caecal digesta contained 180 μmol of glycine equivalents of amino acids in TCA-soluble fraction. Because ninhydrin reaction was almost three times greater after HCl hydrolysis, peptides rather than amino acids were the primary component in this fraction. Urea concentration was only 2·3 μg N/g.

Net production of volatile fatty acids (VFA) in cultures with casein and mucin was higher than in cultures with gluten, gliadin, zein and RNA. Zein was the least fermentable substrate tested. Acetate was the principal fermentation end-product, followed mostly by butyrate and propionate. Branched-chain VFA proportions in VFA produced in cultures with casein, gluten, gliadin and zein were higher than in those supplied with glucose, mucin and RNA. In the former cultures, branched-chain VFA accounted for 10·2–17·7 molar % in the total VFA. In cultures supplied with proteins, there was a significant correlation between methane and VFA production, and between VFA and ammonia. The highest concentration of ammonia was found in cultures with casein. Production of methane was increased on glucose and nitrogenous substrates containing a carbohydrate moiety (mucin, RNA). It can be concluded that the caecal contents of rabbits are rich in nitrogenous compounds. The caecal fermentation of nitrogenous substrates supplies nutrients both for caecal microorganisms (branched-chain VFA, NH3) and for the host (VFA).