The potential digestibility of cellulose is defined as the maximum digestibility obtainable when the conditions and duration of digestion are not limiting factors. Techniques for measuring potential cellulose digestibility were examined and the relationship between potential cellulose digestibility and in vivo cellulose digestibility was explored for a range of grasses.

Cellulose digestibility was found to reach a maximum value after 5 days incubation in vitro. No further cellulose was digested when the residues from an initial incubation for 6 days were incubated with a second rumen liquor inoculum. The values measured after a single incubation of 6 days duration were similar to cellulose digestibility coefficients measured by the suspension of ground forage samples in nylon bags in the rumen for 6 days. Plant factors appear to limit further digestion and the residue from prolonged digestion in vitro consisted only of lignified and cutinized tissue. Potential cellulose digestibility measured by either of the above techniques was higher than cellulose digestibility in vivo. The difference varied between forages and when the difference was large, the digestibility of cellulose in faeces was high.

It is suggested that measurements of the potential digestibility of cellulose in feed and faeces may be of use in estimating the digestibility of grazed herbage.

Sixteen field experiments made between 1963 and 1967 on direct-drilled sugar-beet seed crops compared the effects of cultural practices on the yield and quality of seed. Sowing in July gave earlier flowering and ripening than sowing in August and usually increased yields, cluster size and percentage germination. Downy mildew was sometimes more prevalent in late sowings.

Seed yields increased as the crop changed colour from green to yellow and percentage germination increased greatly as more clusters contained ‘mealy’ rather than ‘milky’ perisperm. Because of natural shedding and bird damage, seed yields then decreased and losses of 0·6 cwt/acre/day were recorded for early ripening treatments. Cluster size and percentage germination continued to increase while yield was decreasing. Crops ripened a month earlier in 1967, the ‘earliest’ year, than in 1965, the latest year.

Crops grown in rows 10 in apart lodged less than those sown 20 in apart, ripened earlier and produced, on average, 3 cwt/acre more seed, which was slightly smaller. In one experiment rows 5 in apart gave similar yields but smaller clusters than rows 10 in apart. Row width had little effect on percentage germination. Increasing the distance between plants in the row gave smaller yields with wider spaced rows, but with narrow rows plants 6 in and 12 in apart yielded more than those 2 in apart. Yields from a plant population of 52,200 plants/acre were 4 cwt/acre greater when plants were 12 in apart in narrow (10 in) rows rather than 6 in apart in wide (20 in) rows. Spacing further apart in narrow rows increased seed size. In wide rows many plants 12 in apart lodged, made secondary growth and produced small, late maturing clusters, of which few germinated.

Response to fertilizer nitrogen applied in spring was less, and less was needed for maximum yield on the thin Cotswold soils than on the silty clay loam in Lincolnshire, where it doubled yield in 1966. Phosphate and potash applied in spring had little effect on yield. Usually fertilizers had no effect on cluster size or germination percentages, but 1·6 cwt/acre N given to a late-ripening crop in 1965 decreased seed size and germination.

Ramularia leaf spot, which defoliated crops in the Cotswolds, was worst on early sown and closely spaced plants, and was unaffected by fertilizer.

Internal and external follicle diameters of both primary and secondary follicles of Texel x Ossimi and Merino x Barki ewes were greater, at birth, than those in either respective parent breed; the density of primary follicles at birth was less in the cross-breds than in the parental breeds, for both crosses. There was a greater increase of follicle diameter with age in the Egyptian breeds, and mean follicle diameters of the crossbreds were intermediate between those of parent breeds at ages of 3–6 months and above.

Grading up Ossimi sheep with the Caucasian Merino resulted in progressive decrease of mean internal follicle diameter. The F2, with more merino blood, had a greater frequency of the smallest diameter follicles than had the F1.

Variety, sowing date, irrigation water and plant spacing were the variables in five experiments over three seasons in southern Arabia. The results are used to develop the idea that morphological change and increase in dry weight—two aspects of the growth of cotton which are often studied separately—must be linked to explain or predict crop performance.

A straight line related the number of flower buds counted at any time to the number of mainstem nodes on a plant. The mainstem was therefore a simple parameter for the effect of age, temperature and water on the development of plant structure. The relationship was explained by a model in which fruiting branches compete with one another. The structure of the crop plants, as measured by the types and number of nodes, developed along a course in time determined by variety and spacing at a rate dependent on temperature. The rate decreased with age, but was independent of the quantity of water available, until a critical amount had been used, when development stopped abruptly.

Accumulated day degrees accounted for the differences between dates of sowing in the subsequent production of nodes. This relationship was consistent with work on temperature elsewhere. Date of sowing effected the position of the first fruiting branch in the variety Bar XL 1 but not in Wild's Early. The position of the first fruiting branch and spacing affected the number of vegetative branches. Wider spaced plants produced flower buds faster only because they had more fruiting branches, a result in turn of more vegetative branches. The ratio between the mean rates of production of nodes on vegetative branches, and on fruiting branches were varietal constants and agreed with results elsewhere in contrasting conditions.

Variety, water and spacing were treatments in two experiments with cotton in 1963 and 1964 in which fruiting points, flowers and bolls were counted and the dry weights and leaf areas of plants were measured at intervals during the season.

Until leaf-area index, L, started to decrease, the equation described how dry weight, W, changed. The equation gave smoothed estimates of crop growth rate, C, which were consistent with estimates of photosynthesis made with de Wit's (1965) model. The relationship between G and L conformed to , derived from Beer's Law, rather than C = aL — bL2 derived from the linear regression of E on L. When L > 3 the crop appeared to use most of the available light, so that C approached a maximum. Treatments initially affected dry-matter production through the numbers and types of branches and nodes, which in turn affected the sinks available and thus the proportion of dry matter reinvested in new leaf. This initial period, when growth was simple to describe in conventional terms, was denned as the vegetative phase of growth.

The start of the reproductive phase of growth overlapped the vegetative phase. The change from one to the other was completed when the rate of dry weight increase of the bolls, CB, equalled C. This indicated that the sink formed by the bolls had increased sufficiently in size to use all the assimilates available for growth. Sink size increased as the crop flowered and was estimated from the product of the number of bolls and the growth rate of a single boll.

When CB equalled C, bolls were shed which prevented the size of the sink to increase beyond the ability of the plant to supply it with assimilates. This agrees with Mason's nutritional theory of boll shedding. Because of the crop's morphology and because age decreased the photosynthesis of the crop, the size of the sink inevitably increased out of phase with the supply of assimilates. The extent to which this was so determined when CB equalled C. It is postulated that environment, genotype and agronomic practice affect yield according to whether they increase or decrease the extent to which the sink size and the supply of assimilates are out of phase.

A series of three large-scale field trials, involving 3500 ewes over a 3-year-period, was conducted to study the effect of restricted nutrition of breeding ewes in early pregnancy. Control or non-restricted ewes were fed at approximately maintenance level and restricted ewes at approximately half-maintenance. The majority of ewes fell into two categories—those 2–3 weeks pregnant at the time restriction was commenced and those 5–7 weeks pregnant. Restriction was applied for from 5 to 8 weeks, live-weight differences of approximately 10 1b were achieved.

Differences in performance in individual trials were invariably very small, and nonsignificant. The main effect of restricted nutrition over all trials was to decrease twinning by 0·5% and decrease the number of barren ewes by 0·8%. These differences are considered to be negligible. Only one statistically significant effect was observed within one of the trials—this was a depression in twinning in ewes 18–24 days pregnant at the time of applying the treatment, but this effect could not be confirmed in the other two trials. However, the fleece grown was affected by treatment—the fleece weight being depressed by approximately ½ lb, and grade reduced slightly.

It is concluded that restricted nutrition at the level and time applied has no effect on reproductive performances of ewes and therefore the practice of restriction in early pregnancy to conserve feed for late pregnancy is a sound policy.

Statistical analyses were carried out on the data obtained under very strict conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2–6 months earlier and whose daily milk production ranged from 11 to 20 kg.

The correlations between faecal and urinary phosphorus losses, phosphorus in milk, digestible phosphorus and phosphorus balance and the other nutritive factors of the 55 above-mentioned experimental diets have been calculated.

In dry and lactating cows, with very variable intakes of phosphorus, phosphorus faecal and urinary losses show very wide variations and may be important. They are not influenced by phosphorus intake, and are related, among the many other nutritional factors we analysed only to ingested water and to a lesser extent to the nitrogen of the diet.

The phosphorus balance is thus also very much variable and not really related to the composition of the ration.

This low influence of the diet on the apparent fate of phosphorus can be explained by the interference of unpredictable but certainly quite variable endogenous phosphorus excretion, which is also probably responsible for the effect we found of individual factors and of the previous nutritional status.

In the lactating cows, the phosphorus requirements for milk production influence the utilization of phosphorus since a significant correlation exists between phosphorus secreted in the milk and urinary phosphorus.

In our experimental conditions, the Ca: P ratio does not seem to influence the fate of dietary calcium and phosphorus.

The biological and economic performance of a cotton crop are examined. The effects of variety, water, sowing date and spacing on crop performance are considered in relation to their effects on crop growth, which had been studied previously, or noted in the literature. Suitable varieties and agronomic practices are discussed. An empirical relationship between available water, dry matter production and yield of seed cotton is evaluated physically and biologically on the basis of Penman's and de Wit's work, and practically in the light of commercial yields and rates of watering.

Statistical analyses were carried out on the data obtained under very strict conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows, and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2–6 months earlier and whose daily milk production ranged from 11 to 20 kg.

The authors have calculated and studied the correlations between faecal and urinary losses of chloride, chloride excretion with the milk, digestible chloride and chloride balance and many other nutritive factors which were analysed for each of the 55 above mentioned experimental diets.

The results show that the digestion and utilization of chloride is not influenced by the amount of ingested chloride at the time of the trial. The digestion is generally very high, negatively correlated with dry matter, energy, and pentosans intakes, and positively with nitrogen and potassium intakes. But the most important factor in the fate of dietary chloride seems to be the necessity for the cow to eliminate most of the time high amounts of potassium in the urines.

A total of 512 pigs were given from 50 lb live weight one of 16 diets (four lysine levels at each of 12, 14, 16 and 18% protein), at one of four levels of intake. They were killed at 100, 150, 200 or 250 lb live weight and the carcasses jointed in a standard manner and right sides dissected into lean meat, fat, skin and bone.

Mean percentage proportion of shoulder, middle and ham joints in the dressed sides at the four weights was 36·3, 36·4 and 27·3; 35·4, 37·9 and 26·7; 34·5, 39·6 and 25·9; and 33·8, 40·7 and 25·5, respectively. Mean percentage lean meat at the four live weights was 61·5, 59·9, 56·7 and 54·2 and the mean percentage fat was 20·7, 24·4, 29·4 and 32·8.

Carcass quality was influenced significantly by dietary treatment and sex. Increasing the level of protein in the diet up to 16, 16, 14–16 and 14%, respectively, for the four live weight groups gave a significant increase in carcass leanness. Increasing the level of lysine in the diet did not have a very marked effect on carcass composition, while increasing feed intake to the highest level produced fatter carcasses at all weights. Carcasses of males were fatter and with a lower proportion of ham than those of females. Interactions involving dietary treatments and sex were described.

Chemical composition of the m. longissimus dorsi was not altered markedly by dietary treatment or sex but dry matter and intramuscular fat content rose with increasing weight. Protein content of the dry matter remained fairly constant at all weights, while colour and shear value rose with increasing weight but were not significantly influenced by dietary treatment or sex.

The pH values of the m. multifidus dorsi just after slaughter or on the day following were not markedly affected by dietary treatment, sex or weight.

A simple and rapid technique for estimating changes in fibre brush-end formation rate is described. The technique was used to give a quantitative estimate of the extent of brush-end formation induced by exogenous hormonal treatment of normal sheep and to establish the time relationship between treatment, fibre brush-end formation and the subsequent casting of the fleece.

1. Three methods, based on treatment with neutral detergent or acid detergent, or involving ultrasonic disintegration, are described and compared for the direct estimation of undigested dietary nitrogen in individual samples of sheep faeces. Estimates of the true digestibility of the nitrogen in several sheep diets derived from analyses performed with these methods agreed well with each other, and were in accord with published estimates, derived by extrapolation techniques. Two other methods, based on treatment with phenol–acetic acid–water, and lysozyme–trypsin, respectively, were found to be unsuitable for such estimates.

2. The quantitative distribution of nitrogen between undigested dietary residues, bacterial residues, endogenous debris residues and the water soluble fraction was determined chemically. It was concluded that 57–81% of the non-dietary faecal nitrogen was associated with bacterial material.

3. Indirect evidence suggested that most of the bacterial nitrogen in faeces originated in the rumen.

Two greenhouse pot experiments were conducted to evaluate labelled concentrated superphosphate (CSP) and labelled dicalcium phosphate (DCP) alone and in mixtures for maize grown on soils low, high and very high in available P. On the low P soil yield of dry forage, total uptake of P and uptake of fertilizer P increased linearly with 0, 20, 40 and 80 ppm of P applied as the various fine and granular sources varying widely in P water solubility. Hence, all of these criteria were highly correlated and suitable for evaluating effectiveness of the P on the low P soil. On the soil high and very high in P, only uptake of fertilizer P, which also increased linearly with rate of application, was suitable for evaluating the sources. Total uptake of fertilizer P decreased with increase in soil P level, but relative differences among granular sources were similar at the three soil P levels. Effectiveness of the P fertilizers decreased markedly with decreasing water solubility of the granular sources on all soils; the same trend was true for the fine sources at high soil P levels.

Actual uptake of fertilizer P or percentage recovery of labelled P applied was a better basis for source evaluation at high soil P levels than were calculated A values. There was little advantage in this study of labelling with 32P for P source evaluation at the low soil P level over use of multiple rates of the unlabelled fertilizers. However, labelling was essential at the higher soil P levels.

The results of three cotton irrigation experiments in the western Negev region indicate that by increasing the intervals between irrigations and by applying the first irrigation at the beginning of flowering, maximum yields of 1700–2100 kg/ha can be obtained with three irrigations. In all treatments except the one with four irrigations, about 0·31 kg of lint was produced for each 1 m3 of irrigation water. In the three driest treatments, where cotton suffered from moisture stress during various periods of growth, no differences in lint quality could be detected in comparison with wetter treatments. As long as there were clear drought symptoms, such as in the three driest treatments, additional irrigation increased the number of bolls/plant, while the average boll weight remained unaffected. Additional irrigation in treatments where there were no clear water stress symptoms did not increase the number of bolls/plant, but increased the average boll weight.

Increases in nitrite in ten gamma-irradiated soils have been investigated under aerobic conditions up to 7 days after treatment over the range 0·25–2·5 Mrad. The formation of nitrite showed significant correlations with the percentage of soil inorganic carbon and incubation time, and over 100 ppm nitrite-N accumulated within 3 days in Broadmoor series, which contained the most inorganic carbon. Only the very acid series failed to produce nitrite, but formation and persistence was poor in all soils below pH 7.

Leaching with ammonium or nitrate ions after irradiation suggested that microbial reduction of nitrate was the mechanism responsible for nitrite accumulation, rather than inhibition of nitrite oxidation.

The growth of ½ ⅝, and ¾ bred Dorset Horn lambs was examined in Western Uganda. These were produced by mating Dorset Horn rams with East African Blackheaded, ¼ bred Dorset and 1/2 bred Dorset females respectively.

The influence of type of birth (single or twin) was maximum at the end of the main 2-month suckling period and progressively decreased to 11 months of age. The influence of maternal age did not decline as lambs grew older. Dorset ewes, ¼ and ½-bred, had superior milking capabilities, as measured by lamb growth at 2 months of age, to indigenous ewes. Lambs, ⅝ and ¾-bred, were 26 % heavier than ½-bred lambs at 2 months of age, and as all three types grew at the same rate from 2 to 11 months, ⅝- and ¾-bred lambs retained this initial advantage.

The experiment described here is the second of a series of experiments investigating the effect of the time of application of certain plant nutrients on the growth of the potato crop. In this experiment all combinations of three rates of nitrogen (0, 0·75 and 1·50 cwts nitrogen per acre), two times of application (at planting and at the time of tuber initiation) and two rates of application of CCC (0 and 4 lb/acre applied twice, shortly after emergence) were tested and studied by the technique of growth analysis.

There was a linear relationship between leaf area duration (D)and tuber dry matter yield, D accounting for 95 % of the variation in the latter. The maximum amount of nitrogen accumulated in the leaves (Nmax) was linearly related to D, and accounted for 86 % of the variation in D. This relationship was improved if separate regressions were calculated according to whether CCC had been applied or not. Calculated in this way, the regressions indicated that more nitrogen was required for a given value of D when plants were treated with CCC.

Delaying the application of nitrogen resulted in a considerable improvement in the recovery of fertilizer nitrogen (ammonium nitrate). A heavy dressing of nitrogen at the time of planting did not enable the crop to take up sufficient nitrogen for maximum yield. Because of these factors, delaying the application of nitrogen significantly increased tuber yield at both rates of nitrogen tested.

Increasing the rate of nitrogen and delaying its application tended to increase the proportion of stem in the total dry matter; CCC had the opposite tendency. CCC, however, reduced leaf area and the mean effect of CCC was to reduce tuber yields. While there wore no significant interactions between CCC and nitrogen treatments on final tuber yield, it was observed that CCC slightly increased yield when the highest rate of nitrogen was applied late. Ways are suggested in which CCC may be more effectively used.

Eleven forages of known digestible energy/kg dry matter (Naga & el-Shazly, 1963) were used in in vitro fermentation experiments. Direct determinations of digestible energy (D.E./kg D.M.) using the bomb calorimeter were also included, and the values were corrected for gas losses.

In vitro fermentations were interrupted every 12, 8 and 6 h, the medium was renewed and volatile fatty acid (VFA) production and cellulose digestion were estimated. Volatile fatty acid production from legumes was high early in the fermentation periods and became lower in later periods. Non-legumes behaved in an opposite manner.

Significant negative correlation coefficients between VFA production and D.E./kg D.M. were found for legumes at later intervals of fermentation, while correlation coefficients for non-legumes lost their significance at later periods of fermentation.

Digestible energy/kg dry matter could best be predicted for legumes from the volatile fatty acids produced in the second 12 h fermentation period or from the sum of the VFA produced in second, third and fourth 6 h periods of fermentation.

Thirty-eight experiments were made on commercial farms to determine the fertilizer requirement of sugar beet grown with farmyard manure (F.Y.M.). They were in two groups; the first (1961–3), with uniformly applied F.Y.M., tested the value of additional fertilizer—nitrogen, phosphate and potash, with and without agricultural salt (crude sodium chloride). The second (1964–7) tested the value of fertilizer N and agricultural salt with and without F.Y.M.

The average economic optimum dressings of fertilizers with F.Y.M. were 0·6 cwt/acre N, 0·3 cwt/acre P2O5, 0·5 cwt/acre K2O, with agricultural salt which largely replaced the need for potash. Chemical analyses of samples of F.Y.M. used in the second group of experiments gave no reliable guide to the requirement of additional nitrogen or sodium. With adequate P2O5 and K2O, the F.Y.M. increased sugar yield at all except one site, on average equivalent to the increase from 0·3 cwt/acre N. Agricultural salt increased yield economically at most sites except on the silts round the Humber and the Wash. No clear relationship was found between soil analysis for sodium and sugar yield response to agricultural salt, but where the exchangeable soil sodium was less than 25 ppm Na, a response was likely.

A comparison was made of six different methods of inoculation with Cercosporella herpotrichoidesFron on field plots of the spring barley variety Impala. All inoculation treatments produced significant differences in terms of disease incidence and grain yield compared with the uninoculated controls. Significant differences were found between treatments in terms of disease incidence, disease severity, mean yield/head and 1000 grain weights. The time of inoculation was also found to be significant. The earlier inoculation caused a reduction in yield of approximately 66 % compared with 50 % at the later inoculation. The application of these methods is discussed.