1. The degree of dispersion on shaking of the heavy clay Gezira soil has been studied in relation to its initial moisture content when it is added to the water. A minimum dispersibility was found at about 7% initial moisture content. Such behaviour is different from that found with certain English soils by Puri & Keen.

2. Spontaneous dispersion was studied using the same soil, and by this method it was found that the dispersion decreases with increasing moisture content over a range of zero to 9% moisture.

3. This relation between dispersion and water content is discussed in relation to possible effects in the field of practice. Attention is drawn to possible seasonal and daily differences in the effect of rainfall.

Experiments on spring barley at Rothamsted over the years 1974–81 were used to study how sources of powdery mildew inoculum affected responses to fungicide sprays applied at different times. Reinfection of early-sprayed plots was generally faster where they were close to a potent source of inoculum than where they were not. Conversely, effects of sources on yield, although not always significant, occurred mainly in the later-sprayed plots. Sources thus had their most important effects before these later sprays were applied, and probably during the very early stages of the epidemic. This implies that if experiments are to approximate to fields, they should, initially, be part of a large, uniformly-susceptible area of crop.

Regression analyses showed that delaying the application of fungicide sprays after the optimum date caused smaller yield losses in plots near minimal sources of inoculum than in plots near more potent sources. There was no conclusive evidence for effects of inoculum sources on the optimum date to apply a fungicide spray but the tendency was for the optimum to become later as inoculum pressure increased.

Separating fungicide-treated plots with mildew-resistant barley resulted in larger treatment effects and smaller residual mean squares than where there was no separation. Judged by residual mean squares alone, precision was approximately doubled by separation.

In a series of five irrigated cotton sowings (T2, T7, T9, T11, T14) evapotranspiration (Et) was determined for the period between October 1961 and October 1962 by observing frequently the changes in soil moisture storage, calculating through drainage, and solving for evapotranspiration in the water balance equation. Thus a water balance was obtained for each sowing extending over the entire crop.

The average evapotranspiration in wet season sowings was of the order of 6·5 mm day−1 and in dry season sowings of the order of 4·5 mm day−1. The highest evapotranspiration values ranged between 10 and 12 mm day−1 in T2, T7 and T9 and between 7 and 9·5 mm day−1 in T11 and T14.

1. The Hutchinson-MacLennan method for determining the lime requirements of soils, when practised under suitable standard conditions, gives more reliable indications than are obtainable by the ordinary methods of chemical analysis.

2. The method gives indications which appear to be uniformly in excess of the actual requirement of the soil for lime as judged by economic standards: hence a correcting value seems advisable.

3. The correcting value for the soils of Canterbury Plains is about 0·10%.

4. The greater acidity and higher lime requirement of soils of the Southland Plains appears to be due to a combination of lack of natural under-drainage and high rainfall, which prevents aeration and oxidation of organic matter, so that “sour” humus accumulates in the soil.

It is now generally recognized that the glands of internal secretion play an important part in regulating metabolism and so controlling the nutrition of the animal. Hatui found that castration was followed by a putting on of fat except in those cases in which the pituitary underwent a compensatory hypertrophy, when the animal remained normal in weight.

The digestibility coefficients of old barley straw fed with a basal ration of oats, bran and maize to two adult horses and of the same straw after treatment by Beckmann's method were ascertained. The coefficients of the nitrogen-free extractives and the crude fibre of the untreated straw were 33·23 and 38·24 respectively and of the treated straw 54·14 and 63·71. There was a reduction in the digestibility of the small quantity of protein and fat.

Taking into account the 14·5% of dry matter lost during treatment, the starch equivalent value of the treated material was somewhat higher than that of poor quality meadow hay.

The digestibility coefficients were considerably lower for an immature horse previously maintained entirely on fresh grass.

To evaluate the accuracy of various techniques for determining the sexual state of sows, four multiparous Landrace sows were housed in stalls 2–5 weeks after weaning. Catheters were inserted under anaesthetic into a prominent ear vein on each sow. Four days later blood and urine sampling commenced, along with other measurements to assess the oestrous state of the animals.

Oestrus was detected in all four sows and so were corresponding oestradiol·17β peaks (22–49 pg/ml) in serum of the three sows from which blood was successfully sampled during the complete 25·day collection period. Serum progesterone concentrations were highest between days — 5 and — 12 (day 0 = 1st day of standing heat) (peak values of 33·1–58·2 ng/ml), with values of 3·55 ng/ml or less on day 0. Urinary oestrogen was less well correlated with oestrous state than were serum hormone concentrations, but progesterone derivatives in urine corresponded well to serum progesterone with peaks between days —5 and —9. Vulval redness, vulval size, social interest and the occurrence of flehmen were markedly greater during the oestrous period than at other times in the cycle. Body temperature, vaginal pH, the presence of vaginal mucus and behavioural manifestations of oestrus (with the exception of back pressure test) were less well correlated with sexual state. A combination of vulval colour and size, back pressure test, a more detailed study of behaviour and possibly with urinary progesterone derivatives, should give the best indication of the incidence of oestrus in sows.

Experiments were designed to assess the effects of cover crops, compared with bare stubble, on the establishment and yield of a following crop of vining peas sown in March. The cover crops of winter wheat (to simulate self-sown wheat) or winter rye, and bare stubble, were ploughed in on different dates: 1 December, 1 February or 1 March. Cover crops were destroyed with or without the use of herbicide. The three experiments in 1990/91, 1991/92 and 1992/93 were sited on a free-draining, sandy loam soil at Thornhaugh, Cambridgeshire.

The cover crops, sown as soon as possible in September following a winter wheat crop, had low dry matter (DM) production and nitrogen uptake in the dry autumns of 1990 and 1991, but in the third experiment (1992/93), autumn rainfall was higher than the long-term average and DM production and N uptake were greater. Cover crops reduced the overwinter soil mineral nitrogen (SMN) content in all 3 years compared with bare stubble. However, in spring, SMN increased where cover crops had been incorporated, due to the mineralization of the cover crop residues. Rye captured more nitrogen than wheat.

Vining pea vigour and maturity at quick-freezing harvest stage were not affected by cover crop, destruction date or method in any of the three seasons.

On the light soil, satisfactory seedbeds were achieved after ploughing at all three timings for experiments in 1990/91 and 1992/93 and vining pea yields were not reduced by cover crops or by destruction date or method. However, delayed ploughing in February and March in the 1991/92 experiment resulted in lower vining pea yields compared with ploughing in December. This was due to poor seedbeds after late ploughing rather than cover crop, stubble treatment or method of destruction.

Copper has been detected in a large number of plants, and is probably present in very minute amounts in all vegetation. Estimations of copper content of a number of plants have been made, notably by Fleurent and Levi(1), Maquenne and Demoussy(2) and McHargue(3).

Experiments were carried out to determine methane (CH4) consumption in different soil (vertisol) aggregates under elevated carbon dioxide (eCO2) and temperature. Soil aggregates of <0·25 mm diameter (microaggregates), 0·25–1 mm diameter (mesoaggregates) and 1–2 mm diameter (macroaggregates) were incubated under different CO2 (400, 800 and 1200 µm/m or ppm CO2) and temperature (25, 35 and 45 °C) conditions. Methane consumption was high in mesoaggregates and low in microaggregates under ambient CO2 and temperature (25 °C). However, eCO2 and temperature significantly inhibited CH4 consumption and decreased culturable microbial numbers. Methane consumption in mesoaggregates was inhibited by 21–66% at 800–1200 ppm of CO2. Principal component analysis designated soil aggregate size as the most important component of variation, followed by temperature and CO2. Ordination biplot indicated eCO2 and temperature impacted negatively on CH4 consumption and culturable methanotrophs. Results highlighted that mesoaggregates of 0·25–1·00 mm are hotspots for CH4 consumption and that rising atmospheric CO2 and temperature may inhibit CH4 consumption significantly in a tropical vertisol.

Growth and visceral organ weights of male guinea fowl (Numida meleagris) given different levels of oxytetracycline have been studied in two experiments. In the first experiment 0, 5·0, 10·0, 15·0 and 20·0 mg oxytetracycline per kg diet were given to male guinea fowl from day 1 to 12 weeks. Body weight showed significant (P < 0·05) increases with incremental levels of the antibiotic up to 10 mg/kg diet. No further increases in growth were recorded with supplementation above this level. There were no treatment effects on the gizzard, lungs and male reproductive organs. Only the heart, liver and intestine weights were significantly (P < 0·05) affected by the treatment, and then only at the highest (20 mg/kg) of the inclusion rates examined. A second experiment was conducted to find out if the growth response obtained with 10 mg/kg oxytetracycline could be produced with a smaller dose. This was achieved at 6·6 mg/kg.

Oestrone sulphate, progesterone, total protein, Na and K concentrations in mammary secretions of Friesland sheep have been determined from 11 days before until 8 days after parturition. Mammary secretions were obtained on most days for at least 1 week before parturition in 9 of 14 ewes, and in all animals after lambing. Oestrone sulphate concentration had doubled on the morning of parturition compared with the value 24 h earlier, and this sharp rise was a useful indicator that delivery was imminent. Values continued to rise during the day of delivery, remained high for a further 24 h and then declined over the next 2 days. Progesterone, in contrast, decreased linearly between day –2 and day +2 when it reached baseline values.

Total protein concentration in pre-colostral and colostral mammary secretion (10–15 g/100 ml) was higher than that in goats, and decreased to a mean value of about 6 g/100 ml by day +8 after delivery. Na declined from about 55 mM on day –10 to 36 mM on day 0, whereas K increased from 20 to 29 mM. There was a sharp rise in K/Na, but this occurred after rather than before parturition and was not a useful predictor of parturition.

The onset of copious milk secretion occurred when oestrone sulphate in mammary secretions was high and progesterone was low, which is consistent with the hypothesis that the cessation of progesterone secretion is an important regulator of the onset of lactogenesis in sheep. Efficiency of milk secretion in the first 14 days of lactation was correlated, however, with the maximum oestrone sulphate concentration in colostrum on the day of parturition.

Coles (1957) has reported the results of a hatchability trial in which four pens of hens each received 10% of a different sample offish meal (A–D) in their diet as the only experimental variable. There was a high level of egg production in each pen, but differences in hatchability as indicated in Table 1. The pen with lowest hatchability received fish meal D, which was darker in colour than the others. It was suggested that this might indicate a scorching of the meal with heat damage, and that in turn this might be responsible for the lower hatchability. The meals have now been analysed to investigate this point.

Part I described the growth of Angoni cattle as shown by changes in live weight. This Part deals with proportional growth as shown by linear growth and carcass characters.

LINEAR GROWTH

A virtually complete summary of the basic work on linear growth has been given by Brody (1945) and specific references will therefore be quoted only as required for discussion.

In a previous communication we have summarised the results obtained by us in a study of the nature and extent of atmospheric pollution in different parts of the city of Leeds and in further studies of some of the effects of smoke upon plant growth.

The active germplasm Bank of the Integrated Unit (Facultad de Ciencias Agrarias, Unversidad Nacional de Mar del Plata and the Experimental Station of INTA) at Balcarce, keeps both in vivo (live herd) and in vitro Criollo Cattle (samples of semen and embryos cryogenically), with the aim of preserving genetic variability for potential future use. Parameters based on probable origin of genes, on population size and on the estimation of components of (co)variances for birth and weaning weights were estimated to evaluate the genetic variability of the material contained in the Bank. The information available came from 667 individuals, of which 84 had unknown parents, and 142 half-founders (only one parent known), having a mean number of births per year of 24 calves from four different sires. AI was performed during the mating season almost every year. The evolution of effective number of founders (fe), effective number of ancestors (fa), effective number of founder genomes (Ng) and the ratio fe/fa over different periods from the creation of the Bank, were analysed. Annual increase of inbreeding coefficient (F) was 0·2% and the effective population size (Ne) was estimated as 23, 14 and 25 individuals for the periods defined by years 1978–82, 1983–87 and 1993–97, respectively. The ratio fe/fa was higher in the years where the ratio number of sires/number of dams was lower, indicating that the impact of the effective number of sires is more important than the effective number of females in generating genetic bottlenecks. When the reference population was taken for the period 1989–97, 16·45 out of the 85·63 founders of the population made contributions not explained by other ancestors, but if possible losses of genomes due to genetic drift are considered, the number of genomes still present was reduced to 9·09 indicating a possible narrow genetic bottleneck in the last period. The Ng/fe ratio was 0·11, 0·10 and 0·11 for the reference populations defined by years 1989–92, 1993–97 and 1989–97, respectively. The main objective in germplasm conservation programmes should be the maintenance of genetic variability. Thus, matings in the population under conservation should be designed in order to mate those animals that maximize the effective number of genome founders (Ng) to avoid losses due to genetic drift.

Of the two available methods for the determination of hydrogen-ion concentration, the electrometric is the more fundamental and satisfactory but it requires somewhat elaborate and expensive apparatus. The colorimetric method, on the other hand, though not lacking in difficulties if accurate results are wanted, requires no special apparatus and the actual procedure is simple. It is based on the electrometric method, and involves the use of buffer solutions of known hydrogen-ion concentration determined originally electrometrically.

A low phosphorus diet given to growing sheep in metabolism cages was supplemented with different sized fractions of either defluorinated phosphate or dicalcium phosphate. For material of particle size between 0·50 and 0·25 mm diameter, significantly less fluorine was present in the urine and more in the faeces of sheep given defluorinated phosphate than for those given dicalcium phosphate. The fluorine present in coarser defluorinated phosphate was of similar availability to that smaller than 0·50 mm. Finer grade defluorinated or dicalcium phosphates smaller than 0·25 mm diameter were not more biologically available in respect of either fluorine or phosphorus than those of particle size 0·50 to 0·25 mm. The availability of the phosphorus in defluorinated phosphate was reduced when material coarser than 0·50 mm was given to the sheep.

In the application of the Scholander pressure chamber technique to cassava water relations studies, the leaf water potential measured on central lobules was initially compared with that measured on entire leaves (including petiole). Measurements made using both a Campbell-Brewster hydraulic press and a pressure chamber of the leaf water potential in six different cassava clones were also compared. Although the central lobules showed a greater sensitivity to moisture loss after sampling than entire leaves, their leaf water potential was in close agreement with those measured on the entire leaves (r3 = 0·96). Therefore, for routine and field estimates in cassava, measurements made on the central lobules may be used to avoid the large reduction in total leaf area. The Campbell-Brewster hydraulic press satisfactorily estimated leaf water potential in M.Col. 1684 clone, which had the longest and narrowest lobules, but in other clones the leaf water potential was overestimated at high leaf potential (> -12·5) and underestimated at low water potentials (< -12·5). Over a wide range of leaf water potentials, a poor relationship between leaf water potentials estimated with hydraulic press and with the pressure chamber was observed for cassava because press estimates are influenced by lobule length and lobule width.