Pollination of red clover by honey bees would be expected to increase if varieties could be produced in which the nectar is within 7 mm of the mouth of the corolla tube and so within the bee's reach.

Pollination by honey bees in a small glasshouse increased the height of nectar in the resulting stock of red clover but when this was again pollinated by honey bees there was no further increase.

Selection of plants with above average nectar height ultimately produced a stock in which the nectar height was 0·76 mm higher than in the original; a difference which was significant. There was also a considerable and significant increase in the proportion of florets with nectar within 7 mm of the mouth of the corolla tube.

It was concluded that the height of nectar can be increased by selection; this would be of particular value for the pollination of red clover varieties with long corolla tubes grown for seed where there are insufficient numbers of bumble bees.

1. Fifty lambs weaned at about 5 weeks of age were fed ad libitum on mixtures of barley and fish meal containing either 11·0, 15·7 or 19·4% crude protein in dry matter. Male and female lambs on each diet were killed at intervals, starting after they had been on the diets for 3 weeks. The last to be killed had attained a live weight of about 55 kg.

2. The mean rate of voluntary feed consumption was less at all live weights for the lambs on the diet containing 11·0% crude protein than for those on the other diets and the difference was statistically significant at live weights of 30 and 35 kg. Mean rates of live-weight gain on the low, medium and high protein diets were respectively 191, 270 and 330 g per day for the male lambs and 177, 225 and 301 g per day for the females, the increase with protein concentration being highly significant. Feed conversion rate (kg feed/kg gain) over the whole experiment increased with increasing weight at slaughter. After adjustment for this effect the mean values showed significant dietary effects, and were least on the highest protein concentration.

3. The percentages (y) of nitrogen or of ether extract in the dry matter of the carcass or of the whole empty body were found to be related non-linearly to the empty-body weight (x) at time of slaughter. The relationships were satisfactorily described by equations of the form y = A + Be-Cx, where A, B and C were fitted constants. The relationships for males and females had to be fitted separately, but a common value of A could be used with each of the three groups of male lambs and similarly for the three female groups.

4. These relationships were used to obtain estimates of the nitrogen, ether extract and energy content of empty-body gain per unit live-weight gain. The estimated percentages of energy retained as fat were of the order of 76–83%, in agreement with ARC estimates (1965), except for male lambs between 14 and 20 kg live weight on medium or high-protein diets, for which the estimates were only 62 and 63%.

5. The implications of these relationships are discussed with particular reference to the finding of dietary effects on body composition during the growth period of the lambs and to the tendency for these differences in body composition to diminish as mature live weight was approached. The differences in body composition between male and female lambs showed no such tendency to diminish.

Nineteen male cross-bred lambs, aged between 2 and 5 days, were allotted to each of three dietary treatments for an experimental period of 3 weeks. The protein contents of the diets (on a dry-matter basis) were 12·0% (diet A), 28·5% (diet B) and 45·5% (diet C). The diets were fed as artificial milks that contained 15% total solids, and the energy intakes of groups of lambs within each dietary treatment varied from below maintenance to ad lib.

Metabolizable energy (ME) as a percentage of the gross energy was constant for all diets, at all levels of energy intake, at 94·3 ± 0·3%. ME intake was linearly related to energy retention above maintenance with all diets. There was a significant linear decrease in the net efficiency of ME utilization as the protein content of the diet increased. However, the individual regressions did not differ significantly from the common regression coefficient of 0·686 ± 0·018, i.e. a net efficiency of 68·6 ± 1·8%. The individual coefficients were 0·740, 0·679 and 0·634 for diets A, B and C respectively.

The ME requirement for energy equilibrium (maintenance) of lambs given diet B (100·4± 11·7 kcal/kg0·73 day) was significantly lower than that of lambs given diet A (126·4 ± 14·3) or diet C (119·2 ± 15·6). The energy costs of fat and protein deposition, calculated by multiple regression analysis of the pooled data, were 11·1 kcal ME per g fat and 8·5 kcal ME per g protein respectively.

1. The Awassi ewes reached an average live weight of 45 kg at two years of age and a mature weight of 57 kg at four years of age.

2. The average yearly production of grease wool has been 2·2 kg.

3. When rams were kept with the flock throughout the year approximately 60% of the lambings occurred during January–February. It declined rapidly during the following months and no lambs were born in July–August.

4. Single lambs had an average birth weight of 4·6 kg for males and 4·3 for females. Twin lambs were about 20% lighter than singles. The corresponding weaning weight at two months of age was 17·9 and 16·8 for singles and 13·4 and 12·4 for twins.

5. The twinning rate increased from 5% at first lambing to 30–35% at 6th lambing, when the ewes were about seven years old.

By alternately joining the rams with the ewes for two months and separating them for the following two months' period 63% of the lambings took place at eight-month intervals.

The conception rate was 85% for October–November breedings, 58 for February–March and 43 for June–July. The twinning rates for corresponding periods were 38, 8 and 7. The length of the post-partum interval had no significant influence on the conception rate.

For October–November breeding 63% of the lambings occurred between 150 and 169 days after the introduction of the rams, whereas the corresponding figures for February–March and June–July were 47 and 14, respectively.

The yearly lambing percentage was 119 as compared to 86 for a previous period from 1955 to 1963, when the rams were kept with the flock throughout the year.

A method of collecting data in a form suitable for computer analysis is described. Cards are marked in the field or laboratory with a pencil and are read by an optical mark reader which enables the data to be processed by a computer. Accuracy is achieved by verifying a printed list of data as stored by the computer against written figures at the top of the marked cards. Apart from this, no other intermediate step is required and this has enabled a summary of experimental data to be available to the experimenter within one week of collection. Provided an optical mark reader is available locally, the method is inexpensive, involving only computer time and the small cost of cards.

A population of 12 ryegrass genotypes was grown at densities of 0·25, 16 and 8 ryegrass + 8 white clover plants per sq ft and was periodically cut to stubble heights of O5 in. or 3 in. For individual plants, yields, tiller numbers, tiller lengths and emerged inflorescence numbers were recorded. Density was the main determinant of plant size, but cutting-height effects were shown, most markedly for the number of inflorescences.

Initially the frequency distribution of plant weight was positively skewed under all treatments, but became less skewed for the population at 0–25 plants per sq ft and more skewed for the population at higher densities. Development of the skew was delayed where white clover was grown. Generally, increasing skew was associated with increasing positive kurtosis.

Frequency distributions of tiller numbers were less skewed than those of yields. Frequency distributions of tiller length were less skewed than the corresponding higher density distributions of yield and tiller number.

Treatment effects on population means demonstrate the different responses which may be obtained with widely spaced plants or those grown in swards. Changes of the frequency distribution of the population are interpreted using the model of Koyama & Kira (1956) and are related to procedures assessing the performance of plants under selection for growth in swards.

Soluble ammonium nitrate (AN) and urea were compared with slow-release oxamide and sulphur-coated urea (SCU) as N sources for clipped annual ryegrass (Lolium multiflorum) or common bermuda grass (Cynodon dactylon) in four greenhouse experiments. Mixed and surface applications of a wide range of N rates were evaluated for 9 to 14 cuttings of grass forage. Both granular oxamide and SCU exhibited slow-release N properties, especially when surface-applied. Uptake distribution of N with high application rates of AN and urea tended to resemble that with the slow-release sources. Slow-release properties of oxamide and SCU were accentuated at high application rates. Lower N recovery from surface-applied urea than from AN indicated volatilization loss of urea N. Volatilization loss also occurred with oxamide, but low N recovery from oxamide and SCU resulted largely from incomplete dissolution of the granules during the 18- to 34-week experimental periods. Very low N recovery was obtained from urea formaldehyde having an activity index of 42.

The efficiency of utilization of the energy of food in White Leghorn laying hens for egg production was measured. A ration with a gross energy of 4469 kcal/kg dry matter and 19·4% crude protein had a metabolizable energy of 80·1±1·7% of the gross energy, and 78·5±5·3% of the metabolizable energy was present as net energy.

The maintenance requirement of metabolizable energy of White Leghorn hens weighing 1·723±48·5 kg and a production of 19·3±0–49 eggs per month was 125·8 kcal/kg0·75/24 hr.

The energy cost per g of protein and fat synthesized by laying White Leghorn hens was estimated to be 7·20 and 12·13 kcal metabolizable energy respectively.

A sheep-feeding experiment was carried out to compare the influence of starch supplementation on the utilization of protein contained in a roughage (lucerne hay) and in a concentrated feed (soya-bean meal). Twelve young rams were divided into four groups, all of which received 150% of the theoretical protein requirement for maintenance. Two groups received soya-bean meal, and the two other groups were given alfalfa hay as protein source. One soya-bean group and one lucerne hay group served as control groups and received the theoretical requirement of energy, whereas the energy content of both experimental groups was raised by addition of grain to 150% of the theoretical energy requirement.

A N-balance experiment carried out with both control groups did not indicate the superiority of lucerne hay over soya-bean meal as had been found in previous experiments in which the sheep were fed diets just supplying the theoretical protein requirement. The advantage of roughage protein disappeared as a result of changes of dietary regime, such as the ingestion of protein surpluses and the reduction in the amount of cottonseed hulls.

The N retention from the lucerne-hay ration was enhanced much more than the soya-bean meal ration by the addition of maize. Biochemical analyses of the rumen oontent showed that a much higher metabolic activity of the micro-organisms was induced by feeding a lucerne-hay diet supplying 150% of the theoretical protein requirement than that induced by ingestion of a corresponding amount of soya-bean meal. It was concluded that the increased biochemical potential of the lucerne-hay diet could be used advantageously only in presence of ample amounts of soluble carbohydrates. The digestibility of the carbohydrates contained in all four diets was examined by in vivo and in vitro methods. The digestibility of crude fibre in the lucerne-hay ration was somewhat raised by the addition of maize whereas the digestibility of crude fibre in the soya-bean meal ration was considerably depressed by the addition of maize.

The digestibility of the carbohydrates contained in all four diets was examined by in vivo and in vitro methods. The digestibility of crude fibre in the lucerne-hay ration was somewhat raised by the addition of maize whereas the digestibility of crude fibre in the soya-bean meal ration was considerably depressed by the addition of maize.

The contribution of the legume Stylosanthes gracilis to the nitrogen economy of mixed swards was assessed under both cutting and grazing conditions. In a cutting experiment, carried out during two wet seasons, a S. gracilis/Chloris gayana sward gave the same yields of dry matter and crude protein as a C gayana sward receiving 75 lb N and 167 lb N/acre (84 kg, 187 kg/ha) respectively. Lower yields were obtained from mixed swards containing Centrosema pubescens and Desmodium scorpiurus.

In a grazing experiment the mean live-weight production from a S. gracilis/Digitariasmutsii sward was equivalent to that produced from a pure grass sward receiving only 13 lb N per acre (5·9 kg/ha), although greater beneficial effects of the legume were apparent under high stocking conditions. In both experiments the legume tended to become dominant after 2 years.

Herbage yields from a S. gracilis/C. gayana pasture were significantly increased by phosphorus and sulphur; S. gracilis was particularly responsive to these elements. Under lenient defoliation, nitrogen reduced the proportion of the legume in the mixed sward, although frequent defoliation reduced the harmful effect of the nitrogen.

The results are compared with other published data and are discussed in terms of ways in which the grass/legume balance can be altered by different management practices.

In an 80 acres (32·4 ha) grazing trial carried out over a 2-year period significant increases in cattle live-weight gains were achieved following the oversowing of savanna grassland by 4 lb/acre (1·8 kg/ha) of Stylosanthes gracilis (stylo) seed. The beneficial effects of the stylo was particularly apparent during the early part of the dry season. The early growth and subsequent survival of the stylo was not outstanding.

Better results were achieved in a second experiment where stylo was grown as a pure crop and ration-grazed in the dry season in association with unimproved savanna. The live-weight gain of cattle grazing the stylo only during the 12 h night period was the same as cattle receiving 1·8 lb (0·82 kg) whole cotton seed per day. In general, cattle live-weight gains were directly proportional to the time spent on the stylo.

Two barley experiments are described in which a range of plant populations were shaded during different periods of development. Shading during the ear development period caused considerable reductions in grain yield, largely by reducing the number of grains per ear. Shading during the grain-filling period caused no reduction in grain yield. It is suggested that under conditions of these experiments there was probably a potential surplus of carbohydrate available for grain filling and that grain yield was largely determined by the storage capacity of the ears. The importance of the number of grains per ear as an indicator of individual ear capacity is emphasized.

The effects of plant population on grain yield and its components are also examined. It is concluded that the number of grains per ear is the component having greatest influence on the decrease in grain yield at above-optimum populations and attention is again drawn to the possible importance of ear capacity. It is argued that on an area basis the number of grains per unit area may give a good indication of ear capacity. Examination of this parameter shows a close relationship with grain yield per unit area for both the shading and population treatments. It is particularly evident that a decrease in grain yield at high populations was associated with a comparable decrease in the number of grains per unit area. It is suggested that this decrease in grain number may be due to a lower production of total dry matter during ear development rather than an unfavourable partitioning of this dry matter between the ear and the rest of the plant. This lower production of total dry matter is attributed to the crop growth rates of the higher populations having reached their peak and then having declined before the end of the ear development period. This crop growth rate pattern, through its effect on grain number per unit area, is put forward as the basic reason why, in the final crop, grain yield per unit area decreases at above-optimum populations.

Three wheat experiments are described in which a range of plant populations were shaded during different periods of development; in two of the experiments plant thinning was also carried out at a number of growth stages. Shading during the period of ear development caused an appreciable decrease in grain yield by decreasing the number of grains per ear. Shading during the grain filling period also reduced grain yield, this being brought about by decreased grain size. Thus in contrast to the barley experiments reported earlier (Willey & Holhday, 1971), these particular results gave no indication of a potential surplus of carbohydrate for grain filling and an associated limited ear capacity. However, when plant thinning was carried out at anthesis to make more carbohydrate available for grain filling in the remaining ears, grain yield per ear did not increase. It is argued, therefore, that grain yield probably was determined at least partly by a limited ear capacity. Plant thinning at earlier stages showed how the development of competition during the ear development period progressively reduced the potential capacity of the ear; the greater competition of higher plant populations accelerated this reduction in ear potential.

From an examination of the effects of plant population, it is suggested that the number of grains per ear is the component having greatest influence on the decline in grain yield at above-optimum populations. The possible importance of the number of grains per unit area as an indicator of ear capacity on an area basis, and as a determinant of grain yield per unit area, is emphasized. A close relationship between grain yield per unit area and number of grains per unit area is illustrated for a number of plant-population response curves, and it is suggested that the decrease in grain yield at high populations is probably determined by a decrease in the number of grains per unit area. Evidence is presented to substantiate the idea put forward in the barley paper that this decrease in the number of grains per unit area may be attributable more to a lower production of total dry matter by the high populations during the later stages of ear development, than to an unfavourable partitioning of such dry matter between the ear and the rest of the plant.

Merino lambs had higher serum protein concentrations at birth than Blackface lambs. In both breeds single lambs had higher concentrations than twins. The maximum mean immunoglobulin concentrations in Merino singles, Blackface singles and Blackface twins were 2·50±0·12, 2·50±0·19 and l·96±0·15 g/100 ml serum respectively, and were recorded 18 or 21 h after birth.

A feeding and balance trial was conducted for 15 weeks on 25 lambs (aged 3–5 months) divided into five groups of 5 animals each on a basal ration consisting of oats, groundnut cake, barley, common salt, green grass and wheat straw. The five groups were fed a mineral supplement as follows:

Group I. Basal ration plus ‘Supermindiff’ mineral mixture (control group).

Group II. Basal ration plus calcined superphosphate.

Group III. Basal ration plus superphosphate.

Group IV. Basal ration plus superphosphate plus oral cobalt chloride (3 mg Co/10 kg body weight).

Group V. Basal ration plus superphosphate plus parenteral vitamin B12 (50 μg/week/ animal).

Calcination of fertilizer-grade superphosphate at 600°C for 2 h reduced the fluorine content from 23350ppm to 1600 ppm. The results show that high fluorine or superphosphate significantly reduced growth rate and retention of calcium and phosphorus and significantly increased blood inorganic phosphorus. Calcination of superphosphate in Group II gave comparable results to the control group (Group I). The oral Co or parenteral vitamin B12 supplementation (Groups IV and V) did not ameliorate the adverse effects of high fluorine in superphosphate.

It is concluded that calcination of superphosphate at 600°C for 2 h yields a suitable defluorinated product which can be used as a phosphorus supplement in the feeding of animals. Fertilizer-grade superphosphate is unsuitable due to its high fluorine content, the adverse effects of which are not mitigated by oral Co or parenteral vitamin B12 supplementation.

Treatment effects on levels of soil carbon and nitrogen in four long-term experiments at Samaru are reviewed in relation to an expected change in the future away from a bush-fallowing agricultural system towards an intensive mechanized system of permanent agriculture.

Where different rates of farmyard manure were applied to the soil annually for nearly 20 years marked differences in soil organic matter contents developed. The mean soil carbon (0·82 per cent) of plots that received 12·5 tonnes ha-1 annum-1 is now almost four times as great as the mean content (0·22 per cent) of control-plot soils. Phosphate applications tended to encourage higher levels of soil organic matter, but where mineral fertilizers (N, P and K) were applied with farmyard manure lower soil organic matter levels and C:N ratios than those of manure-only plots resulted. Apparent retention in the soil of carbon and nitrogen applied as farmyard manure was of the order of 12–15 and 30% respectively. A groundnut shell mulch, applied for 9 years, produced significantly higher levels of soil organic matter than control plots.

In a rotation experiment in which three years of cropping alternated with either 2, 3 or 6 years of planted Gamba grass (Andropogon gayanus) fallow, large differences in soil organic-matter status and rate of turnover existed between the three rotations. In particular the 3-year fallow showed an annual rate of soil organic-matter increase over twice that of the 2-year fallow. Soil nitrogen build-up exceeded 50 kg ha-1annum-1 in the 3-year fallow.

Shortage of farmyard manure and the relatively poor return from systems that include unproductive fallows suggest that in future soil organic matter must be maintained by the return to the soil of all crop residues.

Experiments were carried out to assess the effect of the following diets: unwilted and wilted silage, barn-dried hay and wilted silage and ensiled mixtures of grass and barley on the ruminal VFA patterns in sheep.

There was a tendency for the unwilted silage to result in a slightly higher level of rumen acetate and a lower level of propionate than grass, wilted silage or barn-dried hay. In two of the experiments (Exps. 2 and 4) significant direct relationships were found between rumen acetate and the crude-fibre content of the diets and significant inverse relationships were found between the rumen propionate and the crude-fibre content of the diets.

Significant relationships were also found between the rumen acids and the metabolizable energy content of the diets and in Exp. 2 there was a significant relationship between the rumen acetate and the water-soluble carbohydrate content of the diet.

The addition of barley meal to grass produced different ruminal VFA patterns in sheep fed the ensiled material and the resulting silage.

The graphical and statistical analyses of competition diallels devised by Durrant were applied to an experiment investigating competition between four spring-wheat varieties. The results indicated that at low seed rates mixtures between varieties having a wide phenotypic difference between them in competitive characters, such as height and early maturity, could significantly outyield pure-stands of the component varieties. However, the results of a second experiment, in which these mixtures were grown at a range of seed rates, indicated that the yield advantage of mixtures over pure-stands was unlikely to occur at normal seed rates.

It is suggested that, at the low seed rates likely to be used in growing F1 hybrid wheat crops, mixtures of F1 hybrids and male parental lines might achieve very nearly the same yield as the pure F1 hybrid variety with a seed bulk that was cheaper to produce.

The growth and development of the spring wheat varieties Kolibri, Sirius and TB 435 ranging in height from relatively tall to semi-dwarf were compared when sown at 50, 200 and 800 plants m−2, with and without a spray application of CCC at the six-leaf stage. Growth analysis measurements were made throughout the season. Yield and yield components were determined at final harvest.

A number of varieties x density and variety x CCC interactions were found which support the hypothesis that genotypic variation and environmentally induced differences in GA metabolism affect the agronomic performance of the crop.