The digestibilities of grass cell wall constituents determined in a digestion trial were compared with those obtained by suspending various isolated cell wall preparations in nylon bags in the rumen of a sheep. Particular attention was paid to acetyl groups and to individual sugars, which were determined in both cases by gas liquid chromatography.

For dried grass and hay in the digestion trial the cell wall constituents showed digestibilities decreasing in the following order: arabinose, galactose, glucose, xylose, acetyl, lignin.

For a leaf cell wall preparation derived from all cell types except mesophyll, the nylon bag technique allowed the same order of digestibilities; rhamnose and uronic acids were also measured and found to be rapidly digested. Mesophyll cell walls placed in nylon bags were more readily digested than non-mesophyll. All the sugars, and also acetyl groups, were digested to the same extent.

In a grass cell wall preparation isolated from sheep faeces, tested similarly, xylose and glucose were digested to the same extent, but acetyl groups were less digested.

Removal of acetyl groups, using sodium ethoxide, which left the sugar composition and lignin content unchanged, increased the digestibility particularly of the cell walls from faeces.

The results are discussed with reference to the relationship between cell wall composition and digestibility.

The Woburn Market-Garden experiment was started in 1942 to investigate the development of a market-garden type soil from an ordinary agricultural soil on light land by applying organic manures regularly. The ‘organics’ used were farmyard manure, sewage sludge, and composts of these with straw and farm waste. The use of sewage sludge was discontinued in 1961 and the yields of the crops up till then were published by Mann & Patterson (1963).

1. In an experiment with ninety-nine lambs the effects on the body composition of male and female lambs were examined when five diets containing different concentrations of crude protein (in the range 10–20%) were given at three levels of feeding and lambs were slaughtered at two live weights (27·5 and 40 kg).

2. With lambs slaughtered at 27·5 kg there were significant increases in the rate of both nitrogen and fat retention with increases in levels of feeding. There were also linear increases in the rate of protein deposition and decreases in fat deposition with increases in the concentration of crude protein. This effect was particularly marked at the high level of feeding.

3. With lambs slaughtered at 40 kg live weight there were also linear increases in fat and in nitrogen deposition with increasing feeding level but the effect of increasing the protein concentration on increases in nitrogen retention departed from linearity.

4. While at 27·5 kg there were no significant effects of feeding level on nitrogen and ether-extract content of the bodies at slaughter, with animals slaughtered at 40 kg there was a significant linear decrease in ether-extract content with increasing feeding level and a corresponding linear increase in nitrogen content with increased level of feeding.

5. Male lambs deposited more nitrogen and less fat than females. This was true of both rate of deposition and of carcass composition at 40 kg live weight.

Plant-specific transcription factors belonging to the dehydration response element binding (DREB)/C-repeat binding factor (CBF) subfamily of the AP2/EREBP family specifically interact with dehydration-responsive elements (DRE)/C-repeat (CRT) and control the expression of many stress-inducible genes in plants. Two major subgroups of DREB proteins are represented by DREB1 and DREB2, which are induced specifically under cold and drought/salt stress, respectively. A DREB2 transcription factor gene from sorghum, SbDREB2 was identified and cloned in binary vectors, such that it was driven either by a constitutive CaMV35S promoter or a stress-inducible rd29A promoter. These gene constructs were transferred into rice through Agrobacterium tumefaciens-mediated transformation. Expression patterns of the native DREB gene (OsDREB2) and the transgene (SbDREB2) were similar. Both genes showed induction at 1 h exposure to drought, after which expression gradually dropped to basal levels by 24 h. Constitutive expression of SbDREB2 led to pleiotropic effects in rice and these transgenics did not set seed. The rd29A: SbDREB2 rice plants set seed and the grains collected from primary transformants were sown to raise T1 plants. The drought-stressed rd29A: SbDREB2 transgenics showed a significantly higher number of panicles as compared to the wild-type rice plants. Other phenological and agronomic traits were not affected in wild-type and rd29A: SbDREB2 transgenic rice.

The ability to adapt to a range of edaphic conditions favours the widespread use of marandu palisade grass in high as well as low input systems of animal production in Brazil. However, little information exists regarding the influence of grazing management practices on sward structure and the carry-over effects on animal responses. The present experiment was planned to evaluate animal behaviour, herbage intake (HI) and nutritive value, herbage accumulation and body weight gain (BWG) of beef cattle heifers grazing marandu palisade grass subjected to intensities of continuous stocking management. Treatments corresponded to four sward surface heights (SSH: 100, 200, 300 and 400 mm) and were allocated to experimental units (1200 m2 paddocks) according to a randomized complete block design with four replications. Herbage accumulation rate (HAR) varied with season of the year and SSH, with highest and lowest values recorded during summer and winter, respectively. During the summer, herbage accumulation was larger on swards managed at 200, 300 and 400 mm, with the opposite occurring during winter/early spring. Stocking rate (SR) and number of grazing days (GD) followed a similar seasonal pattern of variation, with values decreasing as SSH increased. Crude protein (CP) and in vitro organic matter digestibility (IVOMD) of hand-plucked herbage decreased as SSH increased from 100 to 400 mm, while the inverse happened with BWG (from 0·190 to 0·930 kg/day, respectively). Bite mass (BM) increased and rate of biting and grazing time (GT) decreased as SSH increased, with daily HI being larger on tall (300 and 400 mm) relative to short (100 and 200 mm) swards. Grazing management affected the nutritive value and the amount of herbage consumed, particularly through changes in BM. However, variations in intake were relatively more important than variations in nutritive value in influencing animal performance, highlighting the importance of providing favourable harvest conditions for grazing animals by establishing adequate sward targets for management.

Grass is a complex crop and its value for agriculture must be assessed in terms of the quantity and quality of downstream livestock products (milk, meat and wool). In addition to being a natural low-cost feed for ruminants, grassland protects soil and water resources and enhances the landscape. Temperate grasslands support a major share of the world's milk and beef production but now there is increasing emphasis on sustainability in livestock farming systems rather than maximizing outputs. The economic sustainability of livestock producers in many developed temperate regions is increasingly linked to production from fewer animals giving a higher quality product. A key element in the efficiency of all grassland systems is to optimize the protein/energy balance of forage and value it in a similar way to other livestock feeds. Grasses are rich in energy comprising structural and non-structural carbohydrates while forage legumes are rich in protein. The main forage legumes used in Europe are white and red clover, and lucerne, which form an essential part of sustainable farming systems because of their high nutritive value and ability to fix nitrogen. The productivity of grasslands containing legumes generally reflects the amount of N fixation, which is 65–280 kg/ha/year in W. Europe. Animal production from white clover-based pastures in Europe can be 0·8 that obtained from grass pastures fertilized with 400 kg N/ha/year, and that from lucerne and red clover can be equivalent to animal production from such pastures.

It is unlikely that as a formulated problem any consideration of settled crop-husbandry is of greater antiquity than the cereal yield problem. In its broad form it embraces all the possible means of increasing the output of grain per unit area. The earliest civilizations of Mesopotamia and Egypt must have been compelled to explore these means as soon as they began to encounter the limitations to cultivable area which dwelling in fixed communities imposed. Wheat and barley were their principal food stuffs so that the cereal yield problem, the most comprehensive concern of present-day agriculture, goes back to the remotest antiquity. It must have evoked incessant effort along divers lines and the cumulative result is appreciable from a comparison of the best cereal races of to-day and the forms which like Hordeum spontaneum and Triticum dicoccum dicoccoides have been regarded as the progenitor types. Unfortunately it is not possible to trace back very far the sequence of the solution of the problem as constituted by improvements in husbandry and the utilization of better cereal forms. Fragments of information may be culled from the writings of various periods but they are of doubtful value. The author's reliability is often in question, the unit of measure uncertain, and even the identity of the crop a matter of doubt. Herodotus' well-known story, passed on from another, of increases of 200 and even 300 fold yielded by barley in Mesopotamia in 500 B.c. is possibly the oldest fragment. It is difficult to interpret but it gains colour from the further statement that the leaves of the plant were of the width of four fingers. Concerning progress in England, while reasonably precise information goes back no further than forty years, there are widely separated records of sufficient worth to indicate the historical trend. It has been deduced from the Manorial Records that at the time when that system had become established there was a flat rate of about ten bushels per acre for wheat. Much later, when Sir Charles Davenant compiled An Essay upon the Probable Methods of making a People Gainers in the Ballance of Trade (published 1699), he computed the “neat produce” of eight million acres of arable land to be 79 million bushels of grain.

The largest yields of wheat and potatoes came from the combination of longer ley plus optimum fertilizer N but yields of winter beans were decreased where N had been given to the previous crops. Without fertilizer N, two year old leys significantly increased yields compared to one year leys and the effect of longer leys was small except for the first wheat, when grain yields were large and plateaued after the three year ley.

Exponential response curves were fitted to the wheat yields and an exponential plus linear trend to the potato yields after each of the leys. Maximum yields and maximum economic yields and their associated N dressings were then estimated. Maximum economic yields of wheat in 1987 ranged from 811 to 914 t/ha grain and the fertilizer N needed declined from 174 kg/ha after the one year ley to 48 kg/ha after the six year ley. For potatoes in 1988, yields ranged from 63 to 71 t/ha tubers but the N required (137–150 kg/ha) varied little with ley age. For winter wheat, in 1989 yields ranged from only 5·51 to 6·99 t/ha grain, because of drought but, as with the potatoes, the N required (203–218 kg/ha) varied little. For each crop the six individual N response curves could be shifted to bring them into coincidence, and the benefits of the ley estimated in terms of a quantity of fertilizer N applied in spring (horizontal shift) and effects other than spring N (vertical shift). The spring N effects relative to the one year ley varied with ley age; for the first wheat the range was from 6 to 126 kg N/ha for the two to six year leys respectively. Spring N effects were negligible, however, for potatoes (average 6 kg/ha) and also for wheat in the third year (6 kg/ha). Benefits other than those which could be ascribed to spring N increased yield of the first wheat, on average, by 0·94 t/ha grain for the two to five year leys; for potatoes they ranged from 3·5 to 8·1 t/ha tubers for the three to six year leys; for the third crop wheat they ranged from 0·86 to 1·49 t/ha grain for the three to six year leys.

On average, the first wheat recovered only 34% of the applied fertilizer N whilst potatoes and the following wheat recovered 55 and 56% respectively. There was a benefit from the longer leys which affected the efficiency with which fertilizer N was used.

Increasing ley age up to five years increased total soil carbon by a maximum of 0·17%C; 18% of the carbon content of the soil in the one year ley plots. This small increase in soil organic matter provided up to 230 kg/ha mineral N in the first autumn after ploughing. Between 17 October 1986 and 27 April 1987 the average loss of NO3-N from soils following three to six year leys was equivalent to 202 kg N/ha, whilst the average uptake of N by 11 May in the above-ground wheat was only 88 kg/ha; the net loss was 114 kg N/ha. A computer simulation, which included mineralization of organic N during this period together with N uptake and nitrate leaching losses, computed a loss of 250 kg N/ha following the six year ley, and this would have given 400 mg NO3/1 in the 275 mm through drainage that winter.

1. Using blood plasma FFA and ketone values to assess the nutritional state of individual ewes, high (H), medium (M) and low (L) planes of nutrition were imposed on 3 groups of Blackface ewes during pregnancy. By this method, ewes bearing single or twin foetuses were equally well or severely undernourished within treatment groups. The effects of these planes of nutrition during pregnancy have been assessed in terms of milk production, lamb growth, and live-weight changes by the ewes duriug their subsequent lactation. Immediately after parturition all ewes were individually fed a pelleted food ad lib. and their voluntary food intakes recorded. From 5 weeks of age individual voluntary intakes of solid food by the lambs were also recorded. Because of insufficient pen accommodation group-M ewes and lambs were discarded after 5 weeks of lactation.

Some applications of near infra-red reflectance (NIR) analysis in plant breeding have been tested. Prediction of the nitrogen content of cereals, kale and beans, and nitrogen and oil in rapeseed was sufficiently accurate for screening purposes although wheat straw gave a less accurate result. The prediction of nitrogen content of wheat grain could be supplemented by the simultaneous estimation of grinding resistance and bran cleanliness, characters of importance for bread-making quality. Hagberg falling number, sodium dodecyl sulphate (SDS) sedimentation volume and loaf volume could not be accurately predicted by NIR. Encouraging results were obtained for predicting malting quality of barley and the digestibility of kale samples.

An experiment is described in which the possible yield benefits of mixing dwarf sorghum and beans were examined under intensive farming conditions. A ‘replacement series’ of pure sorghum, two-thirds sorghum/one-third beans, one-third sorghum/twothirds beans and pure beans was used at four plant populations. A high level of nitrogen was applied to the sorghum to eliminate the effects of nitrogen transfer from the beans.

Yields of the mixtures were up to 55% higher than could be achieved by growing the crops separately. As with some earlier maize/beans experiments (Willey & Osiru, 1972), it is concluded that these yield increases must have been due to a greater utilization of environmental resources. It is suggested that the main factors which made this possible were probably the different rooting depths of the two crops and their different growth cycles.

In agreement with the earlier experiments, mixtures which consisted of two-thirds sorghum/one -third beans gave greatest yield increases at high populations and also had a higher optimum population than the pure stands. However, no such trends were apparent in the mixtures which consisted of one-third sorghum/two-thirds beans.

For both species intra-specific competition was greater than inter-specific competition. In contrast to the earlier maize/beans experiments, the relative interspecific competitive abilities of the species changed with change in the initial proportions of species in the mixtures. In the two-thirds sorghum/one-third beans mixtures the sorghum was the more competitive species, whilst in the one-third sorghum/two-thirds beans mixtures the bean was the more competitive species. Also in contrast to the maize/beans experiments, these relative competitive abilities were not affected by change in theoverall plant population pressure.

Tritiated water (TOH) space was determined in sixty-one sheep of known age (3 days to 18 months). Representative samples of the minced carcass were subsequently analysed to determine body composition (water, fat, protein, ash and energy). The regressions of the weight of the various body components on TOH space and body weight reported here gave equations suitable for prediction. These were similar to equations derived from published results for adults. Combining data on young sheep and adults gave broadly based equations that could be used to predict the body composition of healthy sheep of all ages from 3 days to adults.

Some aspects of intervarietal crossing in Lolium perenne have been studied.

Using a number of experimental designs with non-red plants as the tester variety, results have been obtained as to the effects of isolation distance on intervarietal crossing.

In all cases contamination decreases rapidly, at first with increasing distance, but there is a progressive reduction in the rate of decrease produced by repeated increases in isolation distance. The actual rate of decrease varies with the number and arrangement of plots.

The effect of intravarietal pollen in reducing intervarietal crossing appears similar to that of distance in its mode of action. Within short distances from the contaminant, additional rows of intervening plants are highly effective in reducing contamination. This suggests that pollination within a population of plants occurs chiefly between neighbouring plants.

The flowering periods of the different strains of Lolium perenne and L. italicum overlap to varying degrees. Several early strains flower at the same time, e.g. British commercial, New Zealand Certified Mother Seed and Station-bred S24 perennial rye-grass; others, such as Kentish indigenous perennial ryegrass and strains of L. italicum, which are intermediate in date of flowering, overlap with both the early- and late-flowering strains.

Intervarietal crossing is considerably reduced when varieties which differ widely in date- of flowering are grown in close proximity to one another, but even in the case of extreme early and late strains some spatial isolation, or discarding of border rows, is necessary for maintaining varietal purity.

In certain instances when seed crops of early-flowering strains are endangered by late-flowering plants growing in adjoining leys, satisfactory isolation may be achieved through cutting back the contaminant crop just before flowering. When seed crops of late-flowering strains are grown alongside leys containing early-contaminant varieties, cutting back should be delayed until a few days prior to commencement of flowering in the seed crop.

The practical application of the results to grass seed production has been discussed. Existent isolation requirements appear not too great for grass seed crops intended for further seed multiplication, but for commercial seed crops the spatial isolation distance generally recommended may be reduced to 100, or even 50 yd., in the case of large fields.

Calorimetric experiments were made with a complete extruded diet for ruminants, ‘Ruminant Diet A’ prepared by Messrs U.K. Compound Feeds Ltd. Twelve determinations of energy and nitrogen retention were made using sheep and it was found that the diet had a metabolizable energy value of 2–32 kcal/g organic matter, and the net availabilities of its metabolizable energy were 42–7 % for fattening and 68–0 % for maintenance. These values agreed well with those predicted from equations published by the Agricultural Research Council. On a dry basis the starch equivalent was 38–3 %.

1. In the course of a 2-year field trial (1959–60) conducted in mid-Wales, 525 cattle were entered by 317 co-operating farmers for treatment with p.m.s. in the induction of multiple-pregnancy. Most animals were commercial, non-pedigree cattle maintained in accord with local custom. The cattle were of mixed ages and included some milking cows as well as animals used in calf rearing.

2. The method of hormone treatment tested consists of a single subcutaneous injection of a freeze-dried preparation of p.m.s. administered in the follicular phase of the oestrous cycle. Most cows were injected 16 or 17 days after a previous oestrus and bred by a.i. at the heat period following injection.

3. Of the 525 cattle injected 416 provide comprehensive data on factors affecting ovulatory response; seventy cattle, which had a ‘silent heat’ after injection, provide additional but partial information. In thirty-nine cattle, it was not possible to obtain reliable evidence of response. Data on ovulation and pregnancy were obtained by examinations per rectum conducted during the early weeks of pregnancy.

4. Ovulation data relate to 416 cows which were injected, came in oestrus shortly afterwards and inseminated, then examined for evidence of fresh corporea lutea at the following mid-cycle stage. Five dosage levels of p.m.s. were employed (800, 1000, 1200, 1600 and 2000 i.u.). The normal process of ovulation did not appear adversely affected by any of the doses employed. 173 of the 416 cows (41·6%) produced more than one egg.

5. There is clear evidence of a dose-response relationship over the dosage range employed. The mean number of ovulations varies from 1·43 at 800 i.u. to 3·97 at 2000 i.u. The percentage of cattle shedding additional eggs rises from 33 at 800 i.u. to 56–6 at 2,000 i.u., but increasing dosage level leads to considerable variability in ovulatory response: range of ovulations at 800 i.u. is 1–5, and at 2000 i.u. is 1–25.

6. Little affect was observed in ovulatory response according to the stage of p.m.s. administration. At low dosage levels, an interval of at least 2 days between injection and oestrus was necessary to allow response to occur. Among factors affecting response to a standard dose of p.m.s., lactation and state of normal ovarian activity appeared to have some importance. There was no evidence of an effect on cycle length. Treatment did not give rise to abnormal mating behaviour and the incidence of adverse side-effects following p.m.s. injection was negligible. The occurrence of large unovulated follicles occurred more frequently following treatment with 2000 i.u. than with lesser dosage levels. 59·1% of all ovulations occurred in the right ovary and 40·9% in the left. In examinations made prior to injection, the incidence of spontaneous double ovulations was 4·1%.

7. With the p.m.s. approach, it is found that one problem in cattle is that of silent heat, the condition where ovulation is not accompanied by the usual symptoms of oestrus. In 486 animals for which information was obtained, silent heat occurred in 70 (14·4%). There is some tendency for the condition to occur more frequently where low dosage levels are used or where p.m.s. is administered very late in the oestrous cycle. Lactation appears to affect the incidence of the defect. The lowest incidence (4·8%) occurs in ‘dry’ cows and the highest (22·7%) in cattle rearing three to four calves. Superovulation occurred less frequently at silent heat than at normal oestrus. There is no evidence that p.m.s. injection is the direct cause of the condition. It appears that time of ovulation in animals showing silent heat is comparable with that for cattle showing the normal symptoms.

8. Of the 416 cattle put to a.i. shortly after p.m.s. administration, 317 (76·2%) were pregnant when examined some 6 weeks after first insemination. This compares closely with the normal 30–60 day non-return figure for the mid-Wales area (78·5%). Cattle conceived as readily after injection with 2000 i.u. as after treatment with 800 i.u. Even where animals shed many eggs (e.g. more than six) the conception percentage (84·0) was high. It is clear that this form of therapy does not adversely affect the processes of ovulation, fertilization and implantation. There is some suggestion that p.m.s. aided conception in repeat-breeder cattle. Examinations in the mid-cycle stage following a.i. did not adversely affect conception.

9. Data on the number of eggs surviving (as foetuses) in the 6th week after mating, in relation to the initial number of ovulations, clearly show a heavy loss in eggs in early pregnancy. 41·6% of cattle shed additional eggs but only 23·1% possessed multiples in early pregnancy.

10. Reduction to a single foetus seemed particularly liable to occur in cattle producing two eggs-only. Of sixty-seven double-ovulating animals that conceived, thirty-two possessed twins at the 6th week (47·7%). The survival of both eggs in such cows was better when one egg was shed by each ovary (61·5%) than where both ovulations occurred in the one ovary (28·6%). Analysis of data on egg survival according to factors such as age, breed, time of treatment did not reveal differences.

11. Trans-uterine migration of eggs was rarely (1 case in 197 examinations) noted. The ability of a single uterine horn to sustain more than two foetuses was limited. In cattle where three to six eggs were shed by an ovary, the survival of twins in the associated uterine horn was observed in a majority (57%) of cases. Where many eggs (ten to fifteen) were shed by an ovary, twins were rarely sustained by the associated uterine horn.

12. A steady increase in the percentage of cows carrying multiples (at 6 weeks) was noted over the dosage range employed. 20·8% of cows injected with 800 i.u. carried multiples, the figures for doses of 1000, 1200 1600, and 2000 i.u. being 25·2, 31·3, 41·7 and 42·7, respectively. Multiples in the form of triplets and quadruplets occurred more frequently at the higher dosage levels than at 800–1000 i.u. of all cows with multiples considered, 36·5% possessed more than two foetuses at examination in the 6th week.

13. Pregnancy diagnosis examinations were conducted over a period ranging from 35 to 101 days after mating, with most falling in the period 41–44 days. It appeared that the most appropriate time for diagnosing multiples was at the end of the 6th week of pregnancy. The need to conduct diagnosis at a specific time after mating, and the fact that the examination may lead to total litter loss in many animals, makes the procedure unsuitable for any widespread practice. Partial litter loss (loss of one foetus) was observed in 12·5% of cows carrying twins at 6 weeks and in 20·0% of those with triplets.

14. In nineteen cows, each possessing either three or four foetuses, an attempt was made in the 6th week of pregnancy to control litter size to two. This was by rupture of excess amniotic vesicles by manipulation per rectum. Two of those so treated eventually produced calves, the others either aborting or returning in oestrus soon after the control procedure. The method is unsuitable for farm application for reason of the delay in returning to normal breeding after such cases of failure of pregnancy.

15. A substantial proportion (32·5%) of those cows which were subjected to pregnancy diagnosis lost the conceptus a short time afterwards. Foetal loss in cows with twins was greater (43–46%) where foetuses were both in the one horn than where distributed between both horns (31%). The various factors which were possibly involved in foetal loss are discussed. Evidence was obtained that total foetal loss occurred more frequently in animals shedding many eggs than in those shedding few.

16. Information is recorded for 147 injected cattle which produced single calves following conception at the oestrus immediately following hormone treatment. Additional data on single calvings are provided by 200 untreated cattle which were studied in the area of the trial. These data show birth weight of single calves to be 78·6 lb., and the incidence of calf mortality, retention of foetal membranes and difficult calvings to be 4·9, and 6·0%, respectively. The mean duration of the gestation period was 283·4 days.

17. The outcome of multiple calving was observed in forty-four cattle (thirty-five sets of twins, eight sets of triplets and one set of quintuplets). As a result of earlier examinations, farmers were usually alert to the fact that cows were carrying twins. Herd owners were encouraged to provide such cows with an additional 2 cwt. of a suitable concentrate feed during the final 2 months of pregnancy. Although a number of herd owners followed the recommended feeding programme, in a number of instances the most appropriate pre-calving preparation was not given. The outcome of calvings in relation to the level of additional feeding is considered under three headings, high, moderate and low plane.

18. Given good feeding (high plane) the outcome of twin calvings was satisfactory. Results suggest that the problems often associated with twins (low-weight calves, high rate of mortality, retained foetal membranes, loss of conditon and poor subsequent breeding of the dam) may largely be overcome by an adequate ‘steaming-up’ policy. In cows adequately prepared, birth weight ranging from 59 to 89 lb. were recorded (mean 73·9 lb.) Mean gestation was a little less (280·6 days) than for singles. The incidence of retained foetal membranes (18·2%) was greater than that for single-bearing cows, but did not constitute a serious problem in any animal.

19. Less satisfactory results were noted in cows not given adequate preparation for twins. Where triplets were carried, the outcome for cow and calves, regardless of the feeding attention given, was unsatisfactory. Triplet-bearing cows calved earlier, and the incidence of retained foetal membranes, difficult calvings and calf deaths was much above that noted for the twin-bearing animals. The single set of quintuplets was born prematurely, all calves being dead.

20. Problems in the field application of the p.m.s. technique are considered in the light of the results obtained in the trial and from discussion with farmers in the area of work.

21. Information was obtained on the incidence of natural twins in 3826 calvings in the mid-Wales area. The figure of 2·82% compares closely with that noted in other surveys in the United Kingdom. Literature on the incidence is reviewed.

22. It is clear, from the results obtained in this trial, that the technical problems facing commercial usage of p.m.s. are too numerous to allow any practical recommendation to be made. While none seems to be of such a nature as to make the eventual development of a twinning technique unlikely, there is little hope of immediate solution to many of them. The lines of work which may lead to more satisfactory results are discussed in the final section of the paper.

Liming is often recommended to minimize the plant uptake of potentially toxic elements from sludgeamended soils. In outdoor experiments conducted during 1989–91 in a rural location, near Brentwood (UK), wheat, carrots and spinach were grown on soils from a wide range of sites previously amended with heavy applications of sewage sludge. The objective of these studies was to examine the effect of liming on the accumulation of sludge-borne metals in the crop plants. The results showed that liming the soils to pH 7 prior to sowing significantly reduced metal concentrations in carrots and spinach, although the reduction appeared to be greater for Cd, Ni and Zn than for Cu and Pb. The wheat crop was grown on soils which had been limed 2 years previously, and the average pH of these soils was 6·5 compared to a pH value of 5·95 in the unlimed soils. This comparatively small pH difference between limed and unlimed soils (6·50–5·95) generally had little influence on metal contents in wheat.

These results suggested that maintaining the soil at pH 7 is better than pH 6·5 for minimizing the accumulation of potentially toxic elements from soils which have received relatively high levels of sludge application over many years. The data for winter wheat suggested either that metal uptake into the grain was not sensitive to differences in soil pH or that a relatively small residual effect of past liming was not high enough to reduce metal uptake.

It has been shown that structural failure in small grain cereals occurs by buckling rather than by loss of anchorage. A theoretical study established the relationship between a lateral force applied to the head, and failure of the straw. Resistance to bending is determined by two factors, Young's modulus and outer diameter of the straw. These were determined in laboratory tests. The value of Young's modulus was affected by stage of maturity of the straw. Wind-tunnel experiments established a relationship between air velocity and deflexion of the head. An attempt was made to calculate the wind speed necessary to cause straw breakage in the field. The kinetic effect of raindrops was not a significant factor in lodging. Attention has been drawn to the possible importance of taper in the straw.

The viability of commercial potato production is influenced by spatial and temporal variability in soils and agroclimate, and the availability of water resources where supplementary irrigation is required. Soil characteristics and agroclimatic conditions greatly influence the cultivar choice, agronomic husbandry practices and the economics of production. Using the latest (UKCP09) scenarios of climate change for the UK, the present paper describes a methodology using pedo-climatic functions and a geographical information system (GIS) to model and map current and future land suitability for potato production in England and Wales. The outputs identify regions where rainfed production is likely to become limiting and where future irrigated production would be constrained due to shortages in water availability. The results suggest that by the 2050s, the area of land that is currently well or moderately suited for rainfed production would decline by 88 and 74%, respectively, under the ‘most likely’ climate projections for the low emissions scenario and by 95 and 86%, respectively, for the high emissions scenario, owing to increased likelihood of dry conditions. In many areas, rainfed production would become increasingly risky. However, with supplementary irrigation, c. 0·85 of the total arable land in central and eastern England would remain suitable for production, although most of this is in catchments where water resources are already over-licensed and/or over-abstracted; the expansion of irrigated cropping is thus likely to be constrained by water availability. The increase in the volume of water required due to the switch from rainfed- to irrigated-potato cropping is likely to be much greater than the incremental increase in water demand solely on irrigated potatoes. The implications of climate change on the potato industry, the adaptation options and responses available, and the uncertainty associated with the land suitability projections, are discussed.

The Japanese rice cultivar, Akenohoshi, has numerous spikelets in a panicle (extra-heavy panicle type) and achieves a large yield sink capacity. However, this cultivar, as well as other extra-heavy panicle types, does not always produce higher yields because of poor grain filling of the spikelets on the secondary branches in a panicle. To determine whether the poor grain filling found in Akenohoshi was due to source-limited or sink-limited conditions, the present study examined the responses of grain-filling characteristics to several spikelet-removal treatments immediately after heading. Only when the spikelets on secondary branches remained was a significant increase in filled grain percentage in this spikelet position observed. This increase seemed to be associated with the increases in rate and duration of the grain-filling process and in single grain weight in this spikelet position. These results clearly indicate that the poor grain filling in the spikelet on secondary branches of Akenohoshi could mainly be attributed not to sink-limited conditions, but to source-limited conditions probably at specific stages of grain filling.