The consequences of selection for shorter, stiffer-strawed varieties that are less susceptible to lodging on the degradability of forage and straw obtained from cereal crops were investigated with particular reference to the characteristics of the basal internode where the mechanical stress is likely to be greatest. Quantitative measurements of tissue area, mean cell wall thickness, cell wall density and cellsize were made on two wheat cultivars, Riband (strong) and Norman (weak), and on two barley cultivars, Blenheim (strong) and Tyne (weak). The cultivars were selected for comparison on the basis of their straw strength in field trials.

At growth stage (GS) 59 in wheat (ear emergence complete) the neutral detergent fibre (NDF) content of the basal internode of Riband (74·6%) was lower than Norman (86·0%), and the NDF degradability (NDFD) of Riband (34·7%) was slightly greater than Norman (32·0%). No significant differences in lignin content were found between the wheat cultivars. In barley at the same growth stage, the NDF content of the basal internode of Blenheim (84·8%) was lower than Tyne (89·2%), and the NDFD of Blenheim (30·2%) was greater than Tyne (23·7%) but no significant differences in lignin content were associated with the difference in NDFD. At GS 32–37 (stem elongation) in barley the NDF content of the basal internode of Blenheim (81·5%) was also lower than Tyne (86·3%), but the NDFD of Blenheim (71·7%) was much greater than Tyne (42·8%). No significant differences in lignin content were associated with this large difference in NDFD.

The cultivars of wheat and barley less susceptible to lodging showed lower NDF content and higher in vitro degradability in the basal internode than the more susceptible cultivars. No evidence of differences in the extent of cross-linking by ether-bound ferulic acid was found in wheat, but stems of Blenheim barley showed evidence of a greater degree of cross-linking than in Tyne. The anatomical features of Norman wheat were consistent with stem weakness caused by thinner, smaller cells than the stronger Riband. However, in contrast, the anatomy of Tyne barley indicated that the straw may be too stiff, resulting in failure due to root lodging or brackling while the thinner more cross-linked cell walls of Blenheim may allow the stem to bend under load.

The relationship between the anatomical features, chemical composition and in vitro degradability of the stems was investigated using stepwise multiple regression. Thickness of sclerenchyma, thickness of epidermis and density of epidermis (area fraction of cell wall) were selected by the method of ‘backward elimination’ from an initial regression model to predict NDFD using all the anatomical features measured. Thickness of sclerenchyma was ranked first when the selected anatomical features were incorporated into a regression model with NDF and lignin content using the method of ‘forward selection’. Anatomical differences between varieties had an effect on degradability distinct from that due to the overall chemical composition. The results emphasise the contribution made by anatomical features to the stem degradability and lodging characteristics of cereals.

Measurements were made during 1987/88 on 20 winter wheat crops grown in Essex, four on each of five soil types – sandy loam, sandy silt loam, silt loam, calcareous clay loam and clay loam – where winter wheat, dried peas, winter faba beans or winter oilseed rape was the previous crop in 1986/87. The sites had a wide range of soil mineral N (SNS), 40–198 kg/ha N, as NH4 plus NO3, in the 0–90 cm soil profile. Optimum grain yield and fertilizer N could not be estimated but yields measured in the absence of fertilizer N enabled evaluation of the use of SNS on its own and the response to fertilizer N (187 ± 32 kg/ha). For crops receiving fertilizer N, each tonne of grain was associated with 35kg of total available N in the soil profile (SNS + fertilizer N); a little over 63% of this N was found in the above-ground parts of the crops at harvest. Fertilizer N requirement was predicted as:

Fertilizer N needed (kg/ha) = [35 × predicted grain yield (t/ha)]–SNS (kg/ha)

An arbitrary assumption of 8 t/ha grain for every site (fortuitously the same as the average of 8·07t/ha measured in crops given fertilizer N) showed that differences between added and predicted amounts of N differed by c. 30 kg/ha for only seven of the 20 sites, mostly because of large SNS or yields much less than 8 t/ha. Measuring SNS and using the formula would be justified in the majority of winter wheat crops, provided reliable yield estimates could be made in time.

Winter wheat (Triticum aestivum L., cv. Hereward) was grown in the field within four double-walled polyethylene-covered tunnels along which near-linear temperature gradients were imposed at normal atmospheric or at an elevated CO2 concentration (c. 700 μmol mol−1 CO2) in 1991/92 and in a further experiment in 1992/93. Development was more rapid the warmer the temperature. In 1991/92 an increase in mean seasonal temperature of 3·5 °C reduced the duration from sowing to harvest maturity (the stage when grain moisture content reduced naturally to 15–18%) by c. 38 days, and reduced the duration from the double ridge stage to harvest maturity by c. 34 days. A similar difference resulted from only 1·6 °C warming in 1992/93. Although the range of mean seasonal temperatures differed between years, the relation between temperature and rate of development from sowing to harvest maturity was common to both years (base temperature, −0.8 °C; thermal time 2410 °C d). Carbon dioxide concentration had no effect on this relation or on that between temperature and the rate of development from sowing to the double ridge stage and from the double ridge stage to harvest maturity. Carbon dioxide enrichment increased tillering substantially in 1991/92; there were 200 more shoots m−2 at terminal spikelet formation in crops grown at elevated compared to normal CO2 (additional shoots were principally coleoptile tillers and those developing after tiller 2) and this difference was reduced to 100 shoots m−2 approaching harvest maturity (additional shoots remaining were those developing after tiller 2). In contrast, no effect of CO2 enrichment on tillering was detected at any stage of development in 1992/93. The number of tillers per plant at terminal spikelet formation was a linear function of main stem dry weight at this developmental stage; this relationship was not affected by year or CO2. As CO2 enrichment increased main stem dry weight in the first year only, when main stem dry weights at normal CO2 were only one half of those values determined in the following year, it is concluded that any benefit of increase in CO2 concentration to tillering in winter wheat may be greatest in those crop production environments where main stem dry weights at terminal spikelet are least and vice versa.

Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown within temperature gradient tunnels at a range of temperatures at either c. 350 or 700 μmol mol−1 CO2 in 1991/92 and 1992/93 at Reading, UK. At terminal spikelet stage, leaf area was 45% greater at elevated CO2 in the first year due to more tillers, and was 30% greater in the second year due to larger leaf areas on the primary tillers. At harvest maturity, total crop biomass was negatively related to mean seasonal temperature within each year and CO2 treatment, due principally to shorter crop durations at the warmer temperatures. Biomass was 6–31% greater at elevated compared with normal CO2 and was also affected by a positive interaction between temperature and CO2 in the first year only. Seed yield per unit area was greater at cooler temperatures and at elevated CO2 concentrations. A 7–44% greater seed dry weight at elevated CO2 in the first year was due to more ears per unit area and heavier grains. In the following year, mean seed dry weight was increased by > 72% at elevated CO2, because grain numbers per ear did not decline with an increase in temperature at elevated CO2. Grain numbers were reduced by temperatures > 31 °C immediately before anthesis at normal atmospheric CO2 in 1992/93, and at both CO2 concentrations in 1991/92. To quantify the impact of future climates of elevated CO2 concentrations and warmer temperatures on wheat yields, consideration of both interactions between CO2 and mean seasonal temperature, and possible effects of instantaneous temperatures on yield components at different CO2 concentrations are required. Nevertheless, the results obtained suggest that the benefits to winter wheat grain yield from CO2 doubling are offset by an increase in mean seasonal temperature of only 1·0 °C to 1·8 °C in the UK.

Four field experiments were conducted over the 1992 and 1993 seasons (southwest monsoon seasons, June–October) in the warm subhumid tropical region on the west coast of the Maharashtra State, India. The objective was to investigate the effect of recycling limited amounts of rice straw (RS) (as a source of K and Si) integrated with the use of prilled urea (PU) and urea briquettes (UB) at 60 kg N/ha on the growth and yield of rainfed transplanted rice (Oryza sativa L.). The management practice, consisting of basal incorporation of RS (2 t/ha) integrated with deep placement of UB (one 2·1-g UB/4 hills) immediately after transplanting using a modified 20 × 20 cm spacing, produced a significantly higher grain yield (average increase of 1·3 t/ha) and straw yield (average increase of 1·1 t/ha) than did the RS practice integrated with two equal split applications of PU at the same N rate and hill spacing. The additional yields were attributed to the increase of total and productive tillers/m2 and panicle weight. The results indicate the potential of the integrated RS–UB management for increasing yields of rainfed transplanted rice in the warm subhumid tropical zone.

Four grass species, three hybrids and three mixtures were grown in field swards near Aberystwyth. All swards were amply supplied with nutrients and were cut at 5-week intervals during the year of sowing (1989) and during the following 4 years. The order of the grasses in rate of establishment was: Westerwolds ryegrass > Italian ryegrass (Lolium multiflorum) > Italian ryegrass × perennial ryegrass, Italian ryegrass × meadow fescue, perennial ryegrass (Lolium perenne) > perennial ryegrass × meadow fescue, meadow fescue (Festuca pratensis) > tall fescue (Festuca arundinacea). During the sowing year as a whole, Italian ryegrass was the highest yielding grass, followed by Westerwolds ryegrass. During the remaining period (1990–93), as a whole, the highest yields were obtained from perennial ryegrass sown alone or in a mixture with tall fescue. Tall fescue sown alone was one of the lowest yielding grasses in the year of sowing, but developed to be the highest yielding in 1992 and 1993. Westerwolds ryegrass persisted least well, although some plants did survive until 1992. Italian ryegrass persisted better than Westerwolds and Italian ryegrass × meadow fescue persisted better than Italian ryegrass. Hybrid ryegrass and perennial ryegrass × meadow fescue persisted satisfactorily but with fewer tillers/m2 than perennial ryegrass or tall fescue. The yield of tall fescue in March was as high as that of Italian ryegrass in 1990 and 1991 and higher than that of any of the other grasses in 1992 and 1993; the tiller density of tall fescue was particularly high in March. The yield of mixtures (Italian ryegrass with perennial ryegrass, Italian ryegrass with tall fescue and perennial ryegrass with tall fescue) was, on average, 2·5% more than the mean of the component species when sown alone. When grown with ryegrass, tall fescue was not prominent initially but its proportion in the sward gradually increased.

Potato production in the lowland tropics is constrained by lack of affordable supplies of planting material. Therefore, the potential to produce in situ tuber seed from true potato seed (TPS) seedlings and rooted stem cuttings under nursery conditions in the warm tropics was studied, and their yields were compared with those of the same materials obtained under cool conditions. Subsequently, their field performance in the warm tropics was evaluated.

Tuber yield from TPS seedlings and rooted cuttings transplanted in nursery beds under warm conditions ranged from 50% to < 20% of that obtained in cool conditions, but reductions in tuber numbers were less marked under warm conditions. Survival of seedlings was less than that of stem cuttings, but tuber numbers of seedlings exceeded those of rooted cuttings by a factor of two or more (e.g. 700 m−2 for seedlings v. 224 m−2 for rooted cuttings). Low tuber number is physiologically inherent in cuttings, as is high tuber number in seedlings. Total tuber yields varied significantly amongst clones grown in the warm climate from rooted cuttings, not always in proportion to the number of tubers produced. Differences in tuber yield and tuber number were less marked between the two TPS progenies studied.

The field comparisons highlighted the 30–40% lower yield potential for warm-climate-produced nursery seed materials. Slower emergence and fewer stems apparently were in part responsible for this effect; however, neither tuber number harvested nor the proportion of marketable tubers was affected by site of production of seed materials. Cutting medium-sized warm-produced tubers (mean 23 g), the use of larger sized whole tubers (10–20 g v. 5–10 g) or increasing the planting density of 5 g tubers from 8·8 to 15·5 plants m-2 significantly increased yields by 4·9, 2·25 and 3·5 t ha-1, respectively, but yields were not increased further by 20–40 g tubers nor by 22·2 plants m-2. Small seedling tubers (≤ 5 g) can potentially lead to high stem numbers per unit weight of tubers, but their success in plant establishment was hampered in warm climates, especially in the presence of soil pathogens. Cool-climate-produced seedling tubers and tubers from cuttings can compete physiologically with field-produced seed tubers when used as planting materials in the warm tropics. However, with few exceptions, no crop from tubers produced under warm conditions could match the performance of crops from similar cool-produced tubers when planted out in the warm tropics.

The in vitro resistance of five white and four coloured-flowered lines and cultivars of Vicia faba to seed and root inoculation with spore suspensions of the pathogenic soil-borne fungi, Fusarium culmorum and Pythium debaryanum, was investigated under aseptic conditions in the UK. The presence of foliar diseases was also assessed in the field in 1989/90. White-flowered lines were more susceptible than coloured genotypes to fungal infection during germination but equally resistant during seedling growth. High-tannin containing seed coats had chemical and physical properties which protected seeds against fungal infection during germination. Frequent cracking of the seed coat in a zero-tannin line was associated with a greater fungal contamination of seeds. Resistance to the foliar diseases Uromyces viciae-fabae and Botrytis fabae was not related to flower colour. The results are discussed in relation to emergence in white-flowered types.

An erect, 60-day cultivar of cowpea, IT84S–2246, was grown with adequate soil moisture at two locations in Nigeria in 1990/91, Ibadan (7° N) and Kano (12° N), contrasting in total incident radiation (Q) and at plant population densities of 1·9–7·7 and 5·4–16·3 plants/m2, respectively. Leaf area, radiation interception and dry matter (DM) accumulation and partitioning were measured. Total shoot and seed dry weights were greater at Kano (mean 4·10 and 1·61 t/ha, respectively) than at Ibadan (mean 1·89 and 0·68 t/ha, respectively), and greater athigher plant densities. Relationships between the reciprocal of total shoot (Wt) and seed dry weight (Ws) per plant and plant population density (Np) determined at Kano and Ibadan were linear and parallel; intercepts, however, were significantly different (P < 0·005). The theoretical maximum potential Wt and Ws per unit area (i.e. 1/b) was therefore the same at Kano and at Ibadan, 448 and 170 g/m2, respectively. However, the optimum Np at Kano and Ibadan was markedly different, c. 10 and 40 plants/m2, respectively. These differences in the relations between DM yields and Np at Kano and Ibadan are examined in terms of leaf area, radiation interception and the partitioning coefficient, and the implications for the design of other agronomic investigations in cowpea are discussed.

Biogenic amine formation was studied in silages made from perennial ryegrass. In 1991 two batches of grass from the same sward of the ID–DLO permanent pasture were wilted to either 250 or 450 g dry matter (DM)/kg, and ensiled in eight 1-litre laboratory silos for eachtreatment (Expt A). To induce differences in fermentation pattern, the grass was ensiled without additive (CON) or treated with formic acid (5 ml/kg; FA), cell wall degrading enzymes (2·1 ml/kg; ENZ), molasses (50 g/kg; MOL), or inoculated with Lactobacillus plantarum (107 colony forming units (CFU)/g; LP), a combination of Lactobacillus plantarum and Streptococcus faecium (105 CFU/g; LPSF), or Enterobacter sakazakii (6×lO6 CFU/g; EB). One silo for each treatment was opened after 1, 2, 4 and 7 days for pH determination and duplicate silos were opened after 10 and 90 days for pH determination and analysis of fermentation products. Two similar experiments (B and C) were performed using the CON, FA and LP treatments.

Total amine content of the grass was low (0·1–0·2 g/kg DM). The well preserved silages in each experiment contained considerable amounts of amines, ranging from 0·1 g/kg DM in the wilted LP and FA silages to 7·4 g/kg DM in a low DM CONsilage. Tyramine, cadaverine, putrescine and histamine were, in descending order, the principalbiogenic amines formed, representing together 90 (S.E. 9)% of the total biogenic amine contentof the silages. Formation of amines occurred mainly during the first 10 days of fermentation, and was highest in silages with a slow acidification rate. Ensiling at high DM content, with formic acid or inoculation with large numbers of lactic acid bacteria significantly (P < 0·01) reduced the amount of amines in the silage. Total and individual amine contents of the silages were significantly correlated with concentrations of ammonia and acetic acid. It was concluded that the formation of biogenic amines in grass silage is related to protein degradation, and that amine formation can be reduced by restriction of fermentation in the silage, or by achieving rapid acidification during the first phase of ensiling.

The changes in the buffer components and pH in the surface layer of a pig and a cattle slurry were studied in the laboratory of the Department of Soil Science, Lincoln University in 1994. The slurries were spread to a depth of 7 mm in Petri dishes open to the atmosphere. Slurry pH, total inorganic carbon (TIC = CO2 + HCO- + H2CO3), total ammoniacal nitrogen (TAN = NH3 + NH4+) and volatile fatty acids (VFA = C2-C5 acids) were determined at 8–10 intervals after 1–96 h of incubation at 10, 16 and 22 °C. A great increase in pH over the first 8 h was due to the release of CO2. If the initial TIC > TAN, pH then increased steadily but slowly from 8 to 96 h. When the initial TIC < TAN, the pH declined or did not change after 20 h incubation. The initial pH elevation rate increased with temperature and initial concentration of TIC. Calculation indicated that the NH3 partial pressure (PNH3) in equilibrium with the slurry increased and pH decreased at increasing temperature if gases could not exchange between the slurry and the atmosphere. From the open slurry system PNH3 increased with temperature during the first 1–20 h. At 16 and 22 °C the PNH3 declined to low values after 20 h, whereas at 10 °C the PNH3 remained appreciable after 20 h. This explains why high accumulated NH3 losses may occur when slurry is applied to the field at low temperatures.

As part of a long-term breeding programme aimed at improving the performance of Omani goats and sheep, a 3-year performance trial was carried out between 1991 and 1993 to evaluate the reproductive and productive performance of three breeds of goat: Batinah (BT), Dhofari (DH) and Jabal Akhdar (JA), and one breed of local Omani sheep. In each year, flushing started on 1 September, mating started on 1 October and terminated on 15 November, and the kidding/lambing season started on average on 1 March. Kids and lambs were weaned at c. 3 months of age, then put on a 3-month performance test, fed on concentrates ad libitum and Rhodes grass hay. Some 3706 dam and 3011 progeny performance records were available over a 3-year period from 1991 to 1993. Ewes were lighter in body weight and lower in litter size weaned but higher in fertility than the does. Although the lambs had lighter birth weights, they were heavier at weaning and at 6 months of age. Among the goats, the DH does had lighter body weight but higher litter size weaned than both the BT and the JA goats. DH kids were somewhat lighter at birth, weaning and 6-month body weights than the other two breeds but had higher survival.

The sheep had higher output per ewe exposed (3·28 kg, 33%) and per ewe lambed (3·27 kg, 26%) and were 35% more efficient in production than the goats. Although the DH goats had a lower output per doe exposed than the BT and JA goats (0·9 kg, 9 % and 0·76 kg, 7% respectively) and per doe kidded (1·11 kg, 9% and 1·29 kg, 10%), they had higher efficiency of production than both BT (0·05 units, 6%) and JA (0·11 units, 14%).

In view of these results, attention should be paid to the sheep industry through the introduction of promotion schemes. The DH goats would be even more useful if involved in a crossbreeding scheme and the JA goats would benefit from selection for maternal care.

The starchy seeds of jackfruit (Artocarpus heterophyllus Lam.) contain 124 g crude protein and 740 g total carbohydrates per kg. The possible replacement value of jackseed meal (JSM) for maize in chick diets was evaluated in Peradeniya, Sri Lanka between 1986 and 1989. In Expt 1, the inclusion of 125 and 250 g raw JSM/kg diet severely depressed growth performance and increased mortality in chicks. Organ weights, relative to body weight, were also affected in chicks fed on diets containing 250 g raw JSM/kg diet. Subsequent analyses revealed lectins and trypsin inhibitors to be responsible for the toxic effects of raw JSM. Processing of JSM by moist-heat treatment completely destroyed these antinutritional factors. This was demonstrated by the results of Expt 2, where the feeding value of processed JSM was found to be comparable to that of maize up to 250 g/kg diet. Moist-heat treatment also improved the in vitro protein digestibility (56·7 v. 84·2%) and apparent metabolizable energy (8·97 v. 13·72 MJ/kg) values of JSM. In Expt 3, the inclusion of 500 g processed JSM/kg diet resulted in reduced broiler performance and lowered the apparent dry matter digestibility and apparent energy utilization of the diets. The non-starch polysaccharide component of the JSM may have been responsible for these negative effects.

This group, which is concerned with the applications of mathematics to agricultural science, is sponsored by the Biotechnology and Biological Sciences Research Council. It was formed in 1970, and has since met at approximately yearly intervals in London for one-day meetings. The twenty-eighth meeting of the group, chaired by Dr. D. A. Rose of the Department of Agricultural & Environmental Science, University of Newcastle, was held in the Wellcome Meeting Room at the Royal Society, 6 Carlton House Terrace, London on Friday, 29 March 1996, when the following papers were read.