Analysis of measurements of absorbed radiation and leaf area indices of wheat and barley crops showed that throughout most of growth the fraction of absorbed solar radiation could be described by a simple exponential equation.

For several of these crops grown under a wide range of weather and husbandry at Sutton Bonington and Rothamsted, 2-weekly values of crop growth rate (C) were closely related to radiation absorbed until ear emergence and about 3·0 g of dry matter (D.M.) were produced by each MJ of photosynthetically active radiation (PAR) absorbed. Final crop weight was closelyrelated to total PAR absorbed during growth (SA); on average about 2·2 g D.M. were produced per MJ absorbed, equivalent to a growth efficiency (Eg) of approximately 3·9%. Unfertilized and drought-stressed crops had a smaller Eg.

The fraction of total crop D.M. harvested as grain (harvest index) varied more for wheat than for barley. Calculations of a maximum realizable grain yield made using the largest values of Eg and SA for the crops measured and assuming a harvestindex of 0.53 (achieved in an experimental crop) showed a grain D.M. yield of 10·3 t D.M./ha to be possible. To achieve such a yield would require full crop cover from the beginning of April until the end of July in a typical English growing season.

A standard method is proposed for establishing the seasonal pattern of production for grasses. The procedure consists in recording the yield from grass swards cut every 4 weeks and from which limitations to growth from the supply of water or nutrients have been removed. Four series of plots are harvested in rotation, spaced a week apart so that there is a routine of harvesting a constant number of plots on the same day each week. A statistical analysis is also described enabling comparisons to be made between the grasses under test. An example is given to illustrate the method and the results obtained.

Two rain shelters, each covering an area of 210 m2, have been built at Rothamsted for use in tillage experiments and drought experiments. Each shelter automatically moves over the experimental area when rain starts, and moves away when rain stops; thus all rain is kept off, but other aspects of the microclimate are little affected. Small experimental plots were used, and, except in the 0·5 m strips at the plot edges, the height and yield of a barley crop were uniform. Irrigation water to some plots was labelled with tritium; when applied to very dry plots, a measurable proportion of this water moved laterally by more than 1·0 m. However, the total quantity of water transferring between adjacent plots was not large enough to inconvenience the tillage or drought experiments.

Previous work has shown a strong relationship between the mean soil temperature during the first 5 weeks of growth of a maize crop, and the final grain yield, warmer soils leading to greater yields. Trials were laid down in 1975 and 1976 to establish how early in the development of a maize crop higher soil temperatures would lead to increased yields. Soil temperatures were raised by polythene mulching applied at planting with six times of mulch removal: at crop emergence, 1, 2, 3, 4 and 5 weeks after emergence. Raised soil temperature led to a greater rate of development and leaf area production during early growth. Greater leaf area was due to greater leaf emergence rate rather than increase in leaf size, since increase in soil temperature was associated with a decrease in individual leaf size. This trend was reversed from leaf number 15 onwards resulting in no differences in leaf area, leaf weight or total dry matter at tasselling. In spite of this, yield differences were observed. Increase in soil temperature during germination alone had a beneficial effect on final grain yield, and this effect increased with duration. Increasing soil temperature for longer than 3–4 weeks from emergence caused no further yield increase. Yields increased from 133 and 172 g/ plant to 220 and 238 g/plant in 1975 and 1976 respectively. Yield increases were associated with more grains per plant rather than greater grain size. The period during which increased soil temperature led to increased yields coincided with the period when the apical meristem was below ground level. The mechanism involved is not yet clear.

A barley-based diet, containing 16% protein, was given at average daily rates of 1·2–2·5 kg (16–32 MJ, metabolizable energy (ME)) to 32 female and 32 castrated male pigs during their growth from 25 to 90 kg. At high intakes there was no difference in growth rate between the sexes, but with progressive feed restriction the growth of males was more severely retarded than that of the females. Both sexes achieved their minimum feed conversion ratios at approximately 25 MJ. The reductions of fat thickness with progressive feed restriction were greater by approximately 20% in the females than in the males. The two sexes had the same mean back fat thickness when the gilts had 4·7 MJ more ME per day than the castrates. It was inferred that the energy requirement for maintenance was 15% greater in the males than in the females.

Blood samples were taken from 172 Friesian bulls during 1973–5 on three or four occasions. The bulls were in Milk Marketing Board cattle breeding centres in England and Wales and were from 1 to 14 years of age.

The blood samples were analysed for packed cell volume, haemoglobin, erythrocytes, mean corpuscular volume and glucose, and samples of serum for the concentrations of albumin, total protein, urea-nitrogen, inorganic phosphate, Ca, Mg, K, Na and Cu.

Packed cell volumes and haemoglobin and K concentrations were higher in bulls than those previously recorded in dairy cows. There were significant age relationships for packed cell volume, haemoglobin, albumin and globulin (P < 0·001), inorganic phosphate and erythrocytes (P < 0·01) and Ca and Mg (P < 0·05).

Repeatability estimates were calculated and compared with estimates previously obtained for dairy cows.

On the basis of improved contemporary comparisons of the bulls, there was a significant relationship between the average milk yield of a bulls daughters and the concentrations of urea, inorganic phosphate and K (P < 0·05) in the blood serum of the bull.

The management of an experimental flock of dairy sheep was changed from a onceyearly to a frequent-lambing regime. Results are reported on the performance of the flock under the new regime in the course of 3 years. There were 53 and 160, 46 and 242, and 70 and 237 Awassi and Assaf (East-Friesian x Awassi) ewes, respectively, in the flock at the beginning of the 3 consecutive years. A breeding calendar was adopted to produce four mating seasons each year, namely June–July; September–October; December–January; March–April.

Average annual production was 1·16 ± 0·24 lambs and 209±9 kg milk for Awassi ewes, and 2·07 ± 0·20 lambs and 287 ± 19 kg milk for Assaf ewes. Hoggets of the same breeds produced 0·61 ± 0·14 and 1·23 ± 0·10 lambs and 99 ± 37 and 220 ± 21 kg of milk, respectively.

Following the February-March lambing, conception rates of hormone-treated ewes weaned 2 or 70 days post-partum were 57·1 and 48·8% respectively (P < 0·10). There were no differences in the length of the post-partum interval to conception between low and high milk-yielding ewes. Fertility was highest in the September–October and December–January mating periods, intermediate in June–July and lowest in March–April.

Twenty-seven per cent of the original 126 mature Assaf ewes and 15% of the original 46 mature Awassis remained in the flock at the end of 3 years for further breeding. Thirty-one per cent of the mature Assaf population (mixed ages) and 21% of the hoggets were culled in the course of 3 years due to failure to conceive within 6 months post-partum. With Awassi ewes the rate of failure was much higher.

Ewes which had lambed twice and completed, on average, 1·5 lactations in a year, produced 30% more milk per year than those which lambed only once during the same period. The more frequent lambing resulted in shorter lactations (156 days) and lower average daily milk yields (1·27 kg) compared with the 182 days and 1·41 kg in the less frequently lambing groups. Pregnancy during early stages of lactation had a small but significant (P < 0·05) effect on the concurrent lactation. Shortening the breeding interval had a much more marked effect on the subsequent lactation. Ewes that conceived, on average, 120 days post-partum, in the subsequent lactations produced 17% more milk than those conceiving 60 days post-partum (P <0·02).

Ewes gaining weight at a rate of 5–7 kg during the first 2 months of pregnancy produced, on average, 0·27 kg less milk per day than those which either lost or maintained their weight in that period (P < 0·01).

The pollination requirements of eight cultivars of swede rape (Brassica napus) and two of turnip rape (Brassica campestris) grown in a glasshouse, were compared. Cultivars differed in the number of pods, and of seeds per pod set by auto-pollination. Cultivars of turnip rape yielded more when cross-pollinated than when self-pollinated by hand but those of swede rape did not, although additional pollination of swede rape increased the set of early flowers. Inadequate pollination probably limits yield in self-fertile cultivars of swede rape that auto-pollinate poorly and in turnip rape cultivars that are nearly self-sterile.

In three experiments with mixtures of barley and oats, a combination of Midas barley and Karin oats gave consistently higher yields than the mean of the components and slightly higher yields than the better component. The performance of this mixture was maintained over different sowing patterns and seed rates, but where sowing was arranged to give an advantage to one component of the mixture at the expense of the other, mixture yields were less than where both components were closely mixed.

The increased yield of the mixture was attributed to the greater tillering of barley in mixture than in pure stand, brought about by less competition before heading, and to a higher weight per grain of Karin in mixture than in pure stand, a result of its greater height after heading and the favourable disposition of its panicles and upper leaves in the canopy.

The herbage production and response to nitrogen fertilizer by kikuyu grass were measured in a field experiment conducted over a 12-month period. The experiment was designed to measure the growth of kikuyu grass at different rates of application of nitrogen fertilizer but without limitation due to mineral nutrient supply other than nitrogen, soil pH effects of nitrogen fertilizer, defoliation and pests and diseases.

Growth rate and response to nitrogen were closely related to mean temperature and moisture supply. Relations were established between growth rate, nitrogen response and apparent nitrogen recovery and the climatic variables, mean temperature and mean available soil moisture in 14-day periods. With nitrogen applications of 224 kg N/ha the predicted growth rate at 13 and 23 °C mean temperature were 38 and 196 kg D.M./ha/day, respectively; with 112 kg N/ha growth rate at the higher temperature was 106 kg D.M./ha/day. Growth and response to nitrogen ceased at mean temperatures around 10 °C.

Apparent recovery of nitrogen in harvested herbage over a 16-week growth period after nitrogen application was 51%; recovery in the first 4 weeks of growth varied from 1 to 56 % depending on temperature and moisture supply.

Relations between growth rate and mean temperature were used to predict the seasonal growth pattern for a range of environments in which yield data for the species are available. The results indicate the potential for high annual dry-matter production from kikuyu grass when adequately supplied with nitrogen and moisture is nonlimiting. The grass is also adapted for growth and survival in areas ranging from moist sub-tropical to cool-temperate.

The rectal temperatures of ten cows were measured each morning and their milk temperatures measured at each morning and afternoon milking for 40 days in order to study the value of these temperature measurements in determining the best time to inseminate, whether or not standing oestrus is exhibited. The best determination was based on the observation that a cow in oestrus had a milk temperature, taken at morning or afternoon milking, at least 0·1 °C higher than the corresponding temperature on any one of the previous 15 days. This method successfully detected 12 of 14 oestrous periods in the 10 cows (86%) and gave a false positive diagnosis on 6 days out of a total of 236 non-oestrous days (2·6 %).

When etiolated seedlings of maize and cowpea were subjected to a heat stress of 45 °C for 8 h and subsequently illuminated, there was a retardation in the rates of leaf elongation and chloroplast formation, but the rate of increase in dry weight was not affected. However, a heat stress of 45 °C for 16 h decreased all the three rates measured, the effects being more pronounced with the longer duration of stress in the case of leaf elongation and chloroplast formation. The cowpea seedlings were more sensitive to heat than the maize seedlings. The decreased yield (dry weight) in the 16 h treatment was due, at least partly, to the heat-induced retardation of the growth of the photosynthetic apparatus.

The production of root axes and the growth of the root system are reported for a commercially grown crop of Maris Huntsman winter wheat. Soil cores were extracted on 17 occasions during the growing season permitting a detailed study of root length and root dry weight with depth and time.

Production of seminal root axes was complete by the beginning of March when all plants possessed six (occasionally seven) axes which persisted throughout the life of the crop. Nodal axes were produced continuously from mid-February until late May and finally numbered approximately 20 stem nodal axes per main stem. Total root dry weight increased exponentially until the beginning of April and then almost linearly to reach a maximum of 105 g root/m2 field in mid-June (anthesis). After anthesis, total root dry weight decreased but root growth continued below 80 cm. From April onwards, approximately 65% of the total root dry weight was in the 0–30 cm layer.

Automatic mobile shelters were used to keep rain off a barley crop in a drought experiment. The treatments ranged from no water during the growing season to regular weekly irrigation. This paper reports the effect of drought on the harvest yield and its components, on water use and nutrient uptake.

Drought caused large decreases in yield, and affected each component of the grain yield. The magnitude of each component varied by up to 25% between treatments, and much of the variation could be accounted for by linear regression against the mean soil water deficit in one of three periods. For the number of grains per ear, the relevant period included tillering and ear formation; for the number of ears per unit ground area, the period included stem extension and tiller death; for grain mass, the period included grain filling.

The harvest yields were linearly related to water use, with no indication of a critical period of drought sensitivity. The relation of grain yield to the maximum potential soil water deficit did show that a prolonged early drought had an exceptionally large effect on both yield and water use.

Two unsheltered irrigation experiments, also on barley, were made in the same year on a nearby site. The effects of drought on yield in these experiments were in good agreement with the effects observed on the mobile shelter site.

When fully irrigated, the small plots under the mobile shelters used water 11% faster than larger areas of crop, because of advection. The maximum depth from which water was extracted was unaffected by the drought treatment. When 50% of the available soil water had been used the uptake rate decreased, but the maximum depth of uptake continued to increase.

Measurements of crop nutrients at harvest showed that nitrogen uptake was large, because of site history, and that phosphate uptake was decreased by drought to such an extent that phosphate shortage may have limited yield.

An investigation was carried out to detect and evaluate the oestrogenic activity of three successive cuts of Egyptian clover berseem (Tifolium alexandrinum). Changes in oestrogenic activity due to wilting, drying and fermentation were also studied.

Oestrogenic activity was higher (P < 0·01) in first-cut berseem (49–6 ug diethylstilbestrol equivalency (DES)/kg D.M.) than in the second (38·2 ug) and the third cuts (36·1 ug), and was decreased in the three successive cuts by wilting and dehydrating to 88% D.M. It was greater (P < 0·01) in the wilted berseem than the dried material of the second cut. Oestrogenic activity was increased (P < 0·05) in all cuts by fermentation, but it was higher (P < 0·01) in the fermented second cut than the other cuts.

An intake of 10 kg D.M. of silage would be equivalent to 0·98 mg DES, which have no adverse effects on production and reproduction.

Volumetric soil water content and soil water potential were measured beneath a winter wheat crop during the 1975 growing season. Almost no rain fell between mid-May and mid-July and the soil dried continuously until the potential was less than – 20 bars to a depth of 80 cm. Evaporation was separated from drainage by denning an ‘effective rooting depth’ at which the hydraulic gradient was zero.

Rates of water uptake per unit length of root (inflow) were calculated for the whole soil profile and for individual soil layers. Generally, inflow decreased throughout the period of measurement from a maximum of 2·5 × 10–3 to a minimum of 0·66 × 10–3 ml water/cm root/day. Values in individual layers were frequently higher than the mean inflow and the importance of a few deep roots in taking up water during a dry season is emphasized. A similar correlation between inflow and soil water potential was found to apply for the 0–30 cm and 30–60 cm layers during the period of continual soil drying. This relationship represents the maximum inflow measured at a given soil water potential; actual inflow at any particular time depends upon the interrelationship of atmospheric demand, soil water potential and the distribution of root length in the soil.

The regrowth of Aberystwyth S. 22 Italian ryegrass, S. 24 perennial ryegrass and S. 37 cocksfoot was studied in field swards with and without applied nitrogen during the 21 days following a cut or grazing, there being a total of five periods of study at different times of year and in different years.

The dry-matter content of the harvested herbage deoreased by 4–8 percentage units on average from day 6 to day 18 of regrowth, supporting the evidence of earlier experiments with ryegrass and suggesting that a decrease at about this stage is typical. In the present experiments the same trend was evident after removal of surface moisture. Dry-matter content before removal of surface moisture was sometimes as low as 10%, which could adversely affect animal production. The water potential of fully expanded leaf blades was typically more negative on days 2 and 5 of regrowth than subsequently, so that the moderately high dry-matter content during the first week of regrowth seems to indicate some degree of moisture stress. Emerging leaves were less stressed than fully expanded ones during the very early stages of regrowth. Leaf water potential tended to be rather less negative in the cooksfoot than in the ryegrasses. The application of N reduced dry-matter content, but did not affect leaf water potential.

The digestibility of the harvested herbage was little affected by the stage of regrowth. The cocksfoot was less digestible than the ryegrasses. The application of N generally increased digestibility, particularly in cocksfoot.

When two species are interplanted the interpretation of experimental data presents statistical difficulties because the yields of the two crops will not in general be independent. It is therefore desirable to have a method that will both allow significance levels to be determined and give full importance to the treatment means of the two crops. It is shown that a bivariate analysis of variance can be carried out with little difficulty and precise tests can be based upon it. If it would be helpful to combine the two crops in any way, e.g. on the basis of calorific value or price, the task is readily accomplished.

Features of the gross morphology of primary growth of Dactylis glomerata and Lolium perenne, and associated changes in digestibility are described.

Species differences were noted with regard to the relationships between head emergence and the time when stem apices were raised to defoliation height, vegetative/ reproductive tiller ratios, and tiller size.

Also there were differences in the sequence of extension growth of leaf sheaths, internodes and inflorescence leading to emergence of the head. Associated changes in the vertical distribution of leaf blades were examined.

In perennial ryegrass extension growth of the inflorescence continued after emergence had begun, but not in cocksfoot. Weight increments in the inflorescence, from emergence onward, followed the same pattern in the two species, however.

Differences in the developmental patterns of the two grasses did not appear to influence their relative digestibility.

Upper internodes of reproductive tillers of S. 24 ryegrass declined rapidly in digestibility Species differences, and the pattern of changes in the digestibility of lower and upper parts of reproductive tillers are discussed in relation to mechanical aspects of sward development and micro-environmental effects.

The regrowth of Aberystwyth S. 22 Italian ryegrass, S. 24 perennial ryegrass and S. 37 cocksfoot was studied in field swards with and without applied nitrogen during the 21 days following a cut or grazing, there being a total of five periods of study at different tunes of year and in different years.

The proportion of cell content in the harvested herbage, as measured by neutral detergent, increased by nearly 9 percentage units from day 3 to day 18 of regrowth. The proportion of cell content as measured by acid pepsin also increased during regrowth, but to a lesser extent. The proportion of cell content in leaf blades of two age categories, as measured by neutral detergent, also increased during regrowth. The above increases in proportion of cell content were found in all three grasses. The increases were associated with increases in the proportion of crude protein in dry matter, which were only partially offset by reductions in the proportion of water-soluble carbohydrate. The broad pattern of change in N and nitrate-N content of Italian ryegrass herbage during regrowth in spring with different amounts of N applied, noted in earlier experiments, was confirmed and found to apply to perennial ryegrass and cocksfoot also. During a September-October period of study there was little sign of decline in nitrate-N content within the 21 days where N had been applied. Younger leaf blades had a rather lower nitrate-N content and a slightly higher total N content, on average, than, older blades. The application of N increased the proportion of crude protein more than it reduced the proportion of water-soluble carbohydrate and it increased the proportion of cell content. The increase in proportion of cell content was sufficient to explain the positive effect of N application on digestibility. The average proportion of total herbage N which was found in the cell wall fraction was about 12%.

There appeared to be a relationship between chemical composition and dry-matter content. The chlorophyll content of leaf blades increased during regrowth and was increased by N application. The experimental results on balance, particularly those for proportion of cell content, suggest an improvement in nutritive value of grass during regrowth up to about 3 weeks in contrast to the well-recognized decline in nutritive value where regrowth proceeds beyond about 3 weeks.