Partial closure of the stomata occurred during the middle of the day even when tea plants were growing in a wet soil and there were similar diurnal changes in the xylem water potential (ψx). As the soil dried the daily minimum values of ψx declined, more in some clones than in others, and there were also interesting differences between clones in the sensitivity of their stomata to changes in ψx. Possible ways in which these observations could form the basis of tests for screening clones for drought resistance are discussed.

The reproductive potential of a sheep system is much reduced by the failure of released ova to be fertilized and to survive to parturition. This paper looks at currently available information on fertilization failure and early embryonic deaths. Separate hypotheses are proposed for fertilization and for early embryonic mortality. For fertilization, the hypothesis is that a ewe that mates with a ram will end up with either all or none of her released ova fertilized. For embryonic mortality, the hypothesis is that the survival of a fertilized ovum depends only on how many ova were released with it and is independent of the survival or death of those released with it. A mathematical model is constructed on these hypotheses and its predictions are compared with published experimental results of other workers.

Aberdeen Angus and Friesian cattle were reared from 4 months of age to slaughter weight at 18–24 months on either high-barley or high-hay diets. Samples of subcutaneous fat were taken by biopsy at 3 monthly intervals, and the degree of fatness of each animal was estimated ultrasonically prior to slaughter, and by visual inspection of the carcasses.

The barley-fed animals gained weight more rapidly, and fattened more quickly than the hay-fed animals with the Angus being fatter than the Friesian at the same age. The percentage stearic acid (C18:0) in subcutaneous fat decreased with age and was replaced by octadecenoic acid (C18:l) and hexadecenoic acid (C16:l), these changes being more rapid in barley-fed than in hay-fed animals. At the same degree of fatness the depot fats of the Friesians were more unsaturated than those of the Angus, and in both breeds the fatter the animal the more unsaturated was its depot fat.

In the hay-fed cattle the percentage C16:0 in subcutaneous fat increased during the last half of the experiment and at slaughter the percentage C16:0 was significantly higher, and C18:l significantly lower, in all depot fats compared with those of the barley-fed animals.

It is concluded that the fatty acid composition of bovine depot fats is modulated by the degree of fattening, and can be affected by diet.

The effect of six intervals between harvests and two levels of N application on the proportion and digestibility of cell wall was studied in two perennial ryegrass (Lolium perenne) varieties in the first and second harvest years in a field experiment. In the oase of four of the six intervals between harvests the proportion and digestibility of cellulose, hemicellulose and lignin and the N content of cell wall were determined. Diets derived from three of the harvesting treatments were fed, at maintenance level, to sheep as a partial in vivo check on the in vitro procedures. The effect of six intervals between harvests and two levels of N application on the proportion of lignified tissue in leaf cross-section was determined in two varieties in the first harvest year.

Effects of interval between harvests and time of year on herbage digestibility were due to effects on both proportion and digestibility of cell wall, particularly the latter. Hemicellulose digestibility appeared to be rather more affected by interval between harvests and rather more closely associated with the proportion of lignin than was cellulose digestibihty. The proportion of cell wall was particularly low and its digestibility particularly high in April and early May.

The N in cell wall accounted for about 10% of total N in harvested herbage on all treatments. The ratio of cellulose to hemicellulose averaged 1:0·88 and hemicellulose was rather more digestible than cellulose. Cellulose and cell wall were less digestible in vitro than in vivo.

The application of N tended to reduce the proportion of cell wall and to increase its digestibility in leafy but not in stemmy crops.

Interval between harvests and N application had no effect on the proportion of lignified tissue in leaf cross-section.

Concentrations of serum lipids, concentrations and compositions of liver lipids, and ultrastructural composition of hepatocytes were measured in non-lactating cows following a 6-day fast. There was no change in the concentration of serum lipids due to fasting. The content of total lipid in liver (g/kg of liver wet weight) doubled due to an eightfold increase in triglyceride, a twofold increase in cholesterol ester, a fourfold increase in free fatty acid and a 50% increase in cholesterol. The composition of liver lipids (g lipid/100 g of total lipid) changed with an increase in the proportions of triglyceride and free fatty acid, a decrease in the proportion of phospholipid, and no change in the proportion of cholesterol and cholesterol ester. The ultrastructural composition of the hepatocytes changed in fasted cows with an increase in the volume density of cytoplasm occupied by lipid droplets and lysosomes and a decrease in the volume density of glycogen. The number of mitochondria per cell decreased and volume of individual mitochondria increased. The fatty liver induced by fasting non-lactating cows was chemically and morphologically different from the fatty liver induced by fasting lactating cows.

The effects of six intervals between harvests and three levels of N application on the initiation, emergence and longevity of leaves and longevity of tillers of Italian ryegrass and on dimensions and weights of leaves of four ryegrass varieties were studied in the first harvest year in field experiments. Dimensions and weights of leaves and ‘stems’ of the four varieties were recorded on three dates in the second harvest year.

The number of leaf primordia on the shoot apex of young Italian ryegrass tillers was increased by N application and seemed to be increased by increasing the period of uninterrupted growth allowed to the parent tillers. The number of leaves which emerged on marked tillers during a 30-week period was approximately halved by increasing the interval between harvests from 3 to 10 weeks, but was not affected by N application. The number of leaves which died on marked tillers was at least doubled by increasing the interval between harvests from 3 to 5 weeks. The second and third leaves to emerge on a tiller had a longer potential life than the first leaf. Increasing the interval between harvests greatly increased the average age of the green leaves in the canopy at the time of harvest.

Length and width, but not thickness, of fully expanded green leaf blades were increased by both N application and increased interval between harvests. The effect of applied N in increasing leaf size appeared to be an important reason for the positive effect of N on yield, particularly with the longer intervals. The effect of N in increasing the number of tillers and leaves was important with the shorter intervals. Applied N reduced dry weight per unit volume of plant tissue and increased ‘stem’ length and increased weight and volume of herbage per unit volume of canopy. The area of exposed surface of ‘stem’ seemed too large to be ignored when considering the photosynthetic capacity of the canopy, particularly with the longer intervals.

Over 14 h of daylight and high day temperature singly or in combination delayed flowering of the upland cotton J 34, whereas the photosensitive variety MCU 5 did not flower under long days alone or long days plus high temperature. These treatments promoted vegetative growth and made the plants tall and bushy. Though the treatments were discontinued 75 days after germination the subsequent reproductive growth was adversely affected with significant reduction in boll weight.

The upland genotypes when grown at latitudes 29° N, 21° N and 11° N flowered progressively earlier and at lower nodes at more southerly latitudes because of reduction in daylength and temperatures. It is concluded that the upland cottons of northern India differ from classical types because daylength together with temperature appeared to determine flowering.

The (early maturing) maize hybrid, Anjou 210, was sown on 1 May (1975) and 50000 (LD) and 150000 (HD) plants/ha established. Leaf, stem, ear and husk components of the shoots, and whole shoots were separately examined for changes in dry weight, soluble sugars, starch, hemicellulose and cellulose at regular intervals from 104 to 154 days after planting together with whole shoots after ensiling.

Throughout the sampling period whole shoot and ear dry weights increased steadily whereas those of leaf and stem decreased in plants from both treatments.

Total soluble sugar contents for plants grown at LD were at a maximum 104 days after planting compared with 125 days after planting for the HD crop. Immediately prior to ensiling whole shoot soluble sugar content was 74 and 93 g/kg D.M. for LD and HD treatments respectively.

Small amounts of starch (g/kg D.M.) were found in stems (10–25), husks (40–80) and leaves (17–35) of plants grown at both densities. The starch content of the ear increased from 57 to 390 g/kg D.M. and 168 to 376 g/kg D.M. in plants grown at LD and HD respectively.

For plants from both treatments hemicellulose contents of husks, leaves and whole shoots increased with age whereas those of stems decreased. Cellulose contents did not vary greatly over the growing season.

On ensiling plants from both densities, total soluble sugars had virtually disappeared after only 3 days. Apparent losses (approximately 0·3 g/g), over a longer period of time, were observed in hemicellulose sugars and starch. Apparent increases were observed in cellulose contents of approximately 0·15 g/g.

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.

Soils were analysed from two long-term liming experiments on a sandy-clay loam at Rothamsted and a loamy sand at Woburn. Plots given four levels of limestone factorially combined with phosphate and potassium fertilizers (with magnesium subplots in 1974) were cropped with beans, barley, potatoes and oats from 1963 to 1974.

The smallest limestone applications (5 t CaCO3/ha) increased soil pH the following year to values predicted by lime-requirement determinations using a standard advisory method. The larger limestone applications (10 and 20 t/ha) increased pH proportionally less. Soil pH decreased after the first year with 5 t/ha in both experiments but increased at the 20 t/ha rate for 6 years in the sandy-clay loam and for 3 years in the loamy sand before starting to decline.

Exchangeable calcium (soluble in N ammonium acetate) decreased at approximately linear rates in all plots of both experiments from the first year. Slopes of the regressions were smaller at low than at higher rates of liming, depending primarily on the average pH. Rates of CaCO3 losses from the surface 23 cm of soil ranged from 225 to 823 kg/ha per year at Rothamsted and from 307 to 852 kg/ha per year at Woburn.

Observed rates of Ca loss were compared with an empirical relationship suggested by Gasser (1973) between annual Ca losses and soil pH under average rainfall conditions and estimates based on a model system.

In two long-term liming experiments on a sandy-clay loam at Rothamsted and a loamy sand at Woburn the responses of potatoes in 1974 and oats in 1975 to cumulative dressings of superphosphate and potassium chloride applied since 1962 and magnesium sulphate applied in 1974 were measured at four pH levels within the range pH 4–pH 7.

Yields of both crops were similar over the whole pH range when standard rates of NPKMg fertilizers were given. Without added P and Mg, yields of potatoes were much smaller on the more acid soils, but without K, yields were larger. A similar pattern of yield responses to P and Mg fertilizers occurred with oats but there were no differences between the small responses to K additions over the whole pH range.

Analyses of potato leaves sampled at the 10% flowering stage showed differences related to the yield effects for K and Mg but not for P. Yield responses were associated with concentrations less than 4% K and 0·18% Mg in the dry matter of topmost fully mature leaves.

The differences in yield response caused by liming were not associated with differences in ‘available’ nutrients in the soils (determined using standard methods).

A replicated trial of 18 families of Navy-bean breeding lines in the F4 generation was grown at Cambridge. The selection-index technique was used to investigate means of improving the efficiency of simultaneous selection for four criteria, namely yield, seed shape (numerical scores from ‘good’ to ‘poor’), early maturity and increased height of pod tips. Relative economic weights were chosen. The yield components and a range of characters describing plant type were measured making 15 characters in all, and combinations of these were included in 32 indices.

It was predicted that simultaneous selection would be limited by adverse correlations between some of the four selection criteria, especially early maturity and height. The estimated efficiency of selection would hardly be improved by including information on the yield components. Combinations of the plant type characters, on the other hand, were predicted to provide considerable additional advance amounting to a 10% improvement when information on total number of nodes and inflorescences and hypocotyl diameter was included.

It was concluded that the time involved in collecting yield component data would be better spent collecting information on a limited number of plant type characteristics in future trials, and that an ideal plant was one with reduced branching and a few heavily podded inflorescences borne on a tall plant with a strong base.

Feeding and balance trials with 32P were carried out to measure the true absorption of P in battery and broiler waste and to assess the risk of urolithiasis in sheep.

Groups of six, 8-week-old Scottish Blackface lambs were given one of eight experimental diets containing barley and either 15, 30, 45 or 60% of dried broiler or battery waste. After about 12 weeks on the diet, balance trials with 32P were conducted on a sample of the female lambs from each dietary group. The phosphorus intakes ranged from 4·6 to 15·9g/day.

Poultry waste was a good source of P. The proportion of dietary P absorbed by the lambs (A) ranged from 0·49 to 0·90 and was inversely related to the dietary intake of P (I). The relationship was A = 0·893 – 0·0219I. All lambs were in positive P balance (0·24–2·81 g/day), but only the bones from the lambs consuming the diets containing 45 and 60% broiler waste were not osteoporotic.

All lambs absorbed more P than they retained and the partition of the excess between urine and faeces were very variable.

No clinical cases of urolithiasis were seen, but uroliths were found at post-mortem. The incidence was highest in lambs consuming broiler waste and in lambs consuming the diets containing 15% poultry waste.

Studies were made on the effect of 50% reduction in daily water intake during summer on food intake, digestibility coefficients of the cell-wall constituents (CWC), nitrogen retention and water excretion in urine and faeces in the Marwari breed of sheep of the Rajasthan desert, India. The water-restricted animals consumed 54 and 42% less dry matter and digestible energy respectively than normally-watered animals. The digestibility coefficients of different CWC were apparently, though not significantly, higher in water-restricted animals. Throughout the study period, animals of both the groups, particularly the water-restricted group, remained in negative nitrogen balance. Moisture loss through the faeces was about 22% less in the water-restricted group than in the control animals. The water-restricted animals lost 21·1% of body weight in 23 days and these animals, when allowed water ad libitum, were able to recover 71·5 % of the lost body weight within 3 days.

The effects of the physical environment in Manitoba on the growth of Vicia faba minor cv. Diana were monitored during 1974–5. Seed yields and dry-matter production were considerably lower than have recently been achieved with similar varieties in Britain. Factors integral to the prairie environment are suggested to be the cause of this productivity differential. In particular, high soil moisture stress appears to be capable of severely reducing yields especially when experienced during the early phases of reproductive development. Satisfactory dry-mayEer production is not likely to be achieved if the seasonal soil heat accumulation (above 5 °C) is less than 1000 degree days. Low soil temperatures in the initial vegetative growth stage may also be responsible for the failure to achieve potential crop growth. Similarly high ambient temperatures (above 20°C) appear to be deleterious to crop growth.

Field-bean heat units were defined to facilitate the examination of potentially useful atmospheric heat on crop growth.

Seeds of the plant Crotalaria retusa L., containing 4·4% of the pyrrolizidine alkaloid monocrotaline, were fed in a finely ground form to broiler chickens at 0·005, 0·01, 0·05, 0·10 and 0·50% by weight of the diet continuously for 8 weeks.

Feeding 0·005% and 0·01% had no effect on the growth performance of the birds. A non-significant reduction in live-weight gain, one death and chronic disease resulted from feeding 0·05%. At 0·10% and 0·50% there was high mortality and reduced voluntary feed intake, live-weight gain and feed conversion efficiency, the severity of the response being greater at 0·50%.

Feather development was inhibited in birds fed 0·10% and 0·50% C. retusa seed.

Until further research is done to determine the effect of feeding between 0·01% and 0·05% ground C. retusa seed in the diet of broiler chickens, it is suggested that the maximum should be 0·01%.

Nine field experiments (1970–5) investigated the effects of single or split applications of nitrogen fertilizer in February, March, April and May to in situ sugar-beet seed plants in their second year's growth. All experiments were within commercial crops of existing multigerm and monogerm varieties grown on fertile, deep soils in south Lincolnshire, north Cambridgeshire and Northamptonshire and on shallow limestone soils in the Cotswolds.

Yield of seed averaged over years and sites ranged from 4·3 to 4·6 t/ha and so was not affected by nitrogen treatments, which also did not noticeably delay harvest. The usable proportion of seed from multigerm crops was 350–650 g/kg, and from monogerm ones 90–200 g/kg but neither was affected by nitrogen treatment. Application of nitrogen in May reduced laboratory germination by about 3% and seedling emergence in the field by about 5 seedlings per 100 fruits sown. The proportion of single seedlings fmonogermity') was not affected by nitrogen treatments, although it was affected by the monogerm or multigerm nature of the crop. An attempt to assess seed vigour was made by determining average seedling weight when grown in the field in the year following harvest, but results were inconsistent. Leaf petiole nitrate concentrations declined progressively throughout the season, but were increased by about a quarterin the month following nitrogen application. At all times they were large and probably not limiting growth. The test had no value for predicting nitrogen application rates or times.

In practice it appears that the spring top dressing of nitrogen fertilizer should be made as a single application at the end of February or as soon as possible thereafter.

In the Highlands of Kenya every 1-week delay in planting maize after the onset of the rains reduces the grain yield by approximately 0·6 t/ha. No satisfactory explanation has been found for this phenomenon. A physiological growth study was made on four dates of planting per year over 4 years. Early growth rates and maximum crop growth rates showed a progressive decline with delay in planting which resulted in smaller plants at 5 weeks post-emergence and at 50 % tassel emergence in maize planted later. There was a strong relationship between the size of plant at tasselling and the final grain yield and a highly significant relationship (r = 0·94) between the size of plant at 5 weeks post emergence and the final grain yield. Other environmental studies showed that soil temperature at 7·5 cm, coupled with a soil moisture stress factor, largely controlled the dry-matter production rate during early growth, and consideration of the mean value of these two variables over the first 5 weeks of growth accounted for 70% of the variation of dry matter at 5 weeks post-emergence. It was further shown that 82% of the variation in final grain yield caused by date of planting could be accounted for by consideration of the mean value of these two variables during the first 5 weeks of growth.

Seeds of the plant Crotalaria retusa L., containing 4·4% of the pyrrolizidine alkaloid monocrotaline, were fed in a finely ground form to groups of four pigs from 6 weeks of age. Six levels, 0·004, 0·01, 0·02, 0·05, 0·10 and 0·50% by weight of seed in the diet, were fed continuously for up to 19 weeks. In addition a separate regime, designed to mirror an outbreak of poisoning at a local piggery, consisted of feeding 0·10% for 3 weeks followed by 0·05% for 1 week.

Exposure to more than 0·01%, whether fed continuously or not, resulted in reduced voluntary feed intake and live-weight gain, and high mortality. At 0·50% a reduction in feed conversion efficiency was also obvious. Levels of 0·004% and 0·01% had no significant effect on the production performance of the pigs.

The results of this trial suggest that no more than 0·01% ground C. retusa seed should be included in the diets of pigs. When 0·004%–0·01% is included care should be taken as the long-term effect of the subclinical disease produced is not known.

Balance trials were carried out in which different amounts of Mg (0·44–2·9 g/day) were infused alternatively into the rumen and into the omasum, abomasum or duodenum of sheep consuming a low Mg diet (0·2 g Mg/kg D.M.). Absorption from the region between the infusion sites was measured from the change in urinary excretion and apparent absorption caused by changing the site of infusion.

Absorption was greater from a ruminal than from a comparable duodenal infusion. There was evidence, however, that the absorption mechanism within the stomach area was becoming saturated at the higher infusion rates in that the relationship between the amount absorbed and infused was curvilinear. The proportion of infused Mg which was absorbed from the stomach area fell from 0·61 to 0·14 as the infusion rate increased from 0·44 to 2·80 g/day.

The main site of absorption within the stomach area was the rumen; a small amount was absorbed from the omasum, but none from the abomasum. Positive differences between omasal and duodenal infusions were seen in plasma concentration at the two lowest and in urinary excretion at all infusion rates.

Increasing the amount of Mg infused into the duodenum caused an increase in plasma concentration and a linear increase in absorption.

When the ruminal and duodenal infusions were repeated with the sheep consuming hay, the results were similar but the proportion of infused Mg absorbed was reduced.