The percentage emergence from monogerm sugar-beet seed in field experiments was reduced by high soil moisture content and soil compaction, but was unaffected by soil temperature. Seed lots were differentially influenced when the soil conditions were very adverse. Pelleted seed emerged a little better in good soil conditions and was not more sensitive to high soil moisture content than raw seed.

The relation between laboratory germination and the number of emerged seedlings was variable and followed no obvious trends, and there was no consistent rank order in the emergence ability of four commercial cultivars.

Twenty-three shorn, adult Merino sheep weighing 22·6–63·1 kg were killed and total skin surface area and eight regional skin surface areas measured after skinning. Bodyfat content (1·9–43·6% of body weight) was estimated from the tritiated-water space and body dimensions were recorded before slaughter.

Body weight was the best single measure for predicting total area and regional areas, and little advantage was gained by using multiple regressions incorporating body weight, fat content and body dimensions. Proportional surface areas of all regions except the neck were significantly related to body weight; positively for the trunk, and negatively for the ear, lower leg, upper leg and head. Equations relating regional surface area (% total area) to body weight are presented.

Results of matings made in the Belmont breeding programme from 1954 to 1968 have been analysed. The analysis has been made within three groups. (1) The foundation cows in the years 1954–9; (2) the F1 generation which were mated within line in the years 1957–62; (3) the F2 and F3 generations which were mated within Africander cross (AX), Brahman cross (BX) and Shorthorn-Hereford (SH) lines in the years 1960–8. Fertility was based on the number of calves born, whether alive or dead, to the number of cows mated.

In the foundation cows, Hereford cows had a fertility 9% higher than the Shorthorns. The difference between the bull breeds was not significant although the mean for the Brahman bulls was 16% below the mean of the other three breeds. There was a large variation in the fertility of the Brahman bulls. The fertility of the Shorthorn cows was depressed (by 8%) in the lactating cows as compared with dry cows, while there was an opposite effect in the Herefords. These latter effects showed year to year variation.

In the F1 generation the differences between the breeds were not significant although both the AX (76·4%) and the BX (81·2%) were more fertile than the SH (70·1%). Estimates of heterosis in the F1 generation were 42% for the AX, 43% for the BX and 12% for the SH. Lactating cows were 7% more fertile than non-lactating cows. There were significant differences between the BX bulls used but not between bulls of the other two breeds. The effect of sires within breed on fertility of daughters was significant only within the SH, and the heritabilities of fortuity were estimated from the variance components for sires within breed to be 9%, 14% and 22% for AX, BX and SH respectively.

In the F2 and F3 data the breeds were significantly different in fertility with averages of 77%, 61% and 67% for AX, BX and SH respectively. Thus by comparison with the fertilities of the F1 cows no loss of heterosis for fertility occurred in the AX, a very marked loss in the BX and only a slight loss in the SH. A significant interaction between age of cow and lactational status showed that in the mature cows, wet cows had a higher fertility than dry, while the converse applied in the 3-year-old cows. The interaction of lactational status with breed consisted of the wet zebu cross cattle having a relatively low fertility while the wet British cattle had a relatively high fertility. There were significant differences between bulls within each of the three breeds. The effect of sires was significant in the BX and SH. Heritabilities estimated from between sires within breeds variance components were – 12%, 22% and 25% for the AX, BX and SH respectively.

Thirty-two milk-fed Murrah buffalo calves of 3 weeks of age were randomly allotted to four dietary groups: milk, concentrate-berseem hay in the ratios 1:1 and 1:3, or berseem hay alone. Milk intake was gradually reduced and completely stopped after the sixth week of age in the groups given dry feeds. Two calves from each group were slaughtered at 6, 9, 12 and 15 weeks of age. In addition, four buffalo calves were slaughtered at 21 days of age for comparison.

Observations on ruminal tissue weight, content weight and the ruminal capacity indicate that the ruminant stomach of buffalo calves weaned on dry food after the sixth week of age becomes structurally developed by 9 weeks of age, whereas the rumen remains underdeveloped in calves fed milk to 15 weeks of age.

An assessment was made of the possible significance of hypocotyl length in the identification of brussels-sprout varieties. The investigation was based on the analysis of 162 samples of varieties currently in commerce, a search for sibs amongst supposed F1 varieties and the comparison of known and unknown varieties. Varieties were found to vary consistently from one another, although environmental and environmental by genotype interaction effects were significant. It was found that sibs could be recognized easily in F1 hybrid samples known to contain them and it was inferred, and later evidence confirmed, that they were present in other F1 hybrids. Up to 8 out of 13 F1 varieties were correctly identified from coded samples and it was concluded that hypocotyl characteristics could be used with other measurements in the description of new introductions.

The effects of low protein and low Ca intakes during pregnancy on the chemical composition and histological appearance of selected bones of ewes and lambs is reported. Twenty-eight 6½-year-old Blackface ewes were used in a 2 x 2 experiment in which semi-purified diets containing 11·8 and 6·0% crude protein and 1·2 and 0·11% Ca in the dry matter were offered in amounts designed to induce a level of undernutrition typical of that experienced by hill sheep in winter. In addition, six sheep were killed in early pregnancy as controls, and a further six were offered, during pregnancy, a conventional diet containing 16% crude protein and 1·9% Ca in the dry matter at levels which prevented energy undernutrition. Ewes and lambs were killed at parturition and the tibias, 3rd ribs and 3rd and 4th lumbar vertebrae removed for chemical and histological examination.

The degree of mineralization of the organic matrix (ash:organic-matter ratio) of the bones at the beginning of pregnancy was poor and it increased in all groups during pregnancy largely irrespective of protein or Ca intake, but especially in the wellnourished sheep. The density of ash in the whole bone (ash:volume ratio) increased in the well-nourished and high-protein groups but did not change in the low-protein groups. These differences were attributable to the effect of protein nutrition on the density of the bone organic matrix (organic matter:volume ratio). Matrix density of the bones of the well-nourished groups increased while that of the low-protein groups decreased.

The histological data essentially confirmed this picture and showed that trabecular or cancellous bone from the tibial head and vertebrae of the low-protein and to a lesser extent the high-protein sheep was porotic, but microscopic assessment conflicted with the chemical findings in that histologically Ca intake appeared to affect bone quality in the vertebrae.

There was considerable variation in the histology of individual lamb bones which was independent of maternal nutritional experiences, but the overall size of the bones was determined by maternal protein nutrition.

The development of precipitins to Micropolyspora faeni in cattle fed hay treated with a bacterial and mould inhibitor is compared to that in herds fed untreated hay. The results indicate that, even when fed only treated hay, exposure to M. faeni was such that a considerable proportion of precipitin-free cattle did develop precipitins.

A total of 72 pigs comprising 36 boars and 36 castrates of 22 kg live weight were allocated to one of three protein levels in the diet. The crude protein concentrations were 16·0, 18·0 and 20·0%. The diets were fed to appetite for three half-hour periods per day from 22 to 90 kg live weight.

Up to 55 kg live weight both boars and castrates showed an initial positive response to the increased protein concentration. This was followed by a negative response during the 55–90 kg period for both food conversion and daily live-weight gain. For the overall period the differences in performance were not significant. From 22 to 55 kg, and from 55 to 90 kg the average daily feed intake of boars was significantly less than that of the castrates.

Boars had a significantly better overall food conversion, larger eye muscle area and decreased back fat.

This experiment indicated that there was no advantage in feeding boars a protein concentration higher than that generally used for gilts or castrates while on a semiad libitum feeding system.

Growing wether sheep in metabolism cages were fed a low phosphorus diet (0·75g P/day) supplemented with 1·75 g P/day as either a magnesium phosphate (20·0% Mg, 18·5% P) or a calcium magnesium phosphate (16·1% Ca, 6·0% Mg, 18·5% P). In addition, the magnesium phosphate provided 1·87 g Mg/day and the calcium magnesium phosphate 0·57 g Mg/day. In each case comparisons were made with equivalent amounts of phosphorus and magnesium supplied as dicalcium phosphate (26·5% Ca, 16·0% P) and magnesium oxide (60·0% Mg).

All the supplements resulted in similar positive phosphorus retentions of between 0·77and 0·92 g P/day compared with a daily loss of 0·17 g P/day for the low phosphorus diet. Calcium retentions were higher (1·40 and 1·70 g Ca/day) whendicalcium phosphate rather than the magnesium phosphates (1·16 g Ca/day) were given. Magnesium retentions were increased from 0·1 g Mg/day (unsupplemented) to 0·3–0·4 gMg/day and were similar for both magnesium oxide and the magnesium phosphates.

Blood phosphorus and magnesium concentrations were increased to a similar degree by all forms of supplementation.

Four field experiments (1968–71) investigated the effect of changing the length of the growing period on the nitrogen fertilizer requirement of sugar beet. The crop was sown on three occasions (March–May), harvested on three occasions (September–December) and given four amounts of fertilizer (0–225 kg N/ha). Plant samples were analysed at several stages of growth (1969–71) in an attempt to predict the amount of nitrogen fertilizer needed for maximum sugar yield and also at the end of the season to determine the nitrogen uptake. Increasing the length of the growing period increased sugar yield greatly but the amount of nitrogen fertilizer needed for maximum sugar yield was unchanged. The crop given the largest dressing of nitrogen and with the longest growing period contained most total nitrogen, but in every experiment, giving more than 75 kg N/ha neither increased nor decreased the sugar yield significantly. As a result of the small variations in nitrogen requirement, the plant analyses during the growing season were of little value in predicting the needs of the crop.

Estimates of genotypic and phenotypic variances and covariances were determined for yield and yield components in ten field beans varieties grown at two locations over three seasons.

Substantial amounts of genotypic variance were obtained for yield/plot, 1000-seed weight and number of pods/plant. Variability in number of seeds/pod and much of the variation in yield/plant was attributable to environmental effects and their interaction with the varieties. Seed yield/plot was closely and positively correlated with number of pods/plant and yield/plant, while it was closely and negatively correlated with 1000-seed weight.

The implications of these correlations for selection are discussed.

Experiments made between 1967 and 1970 tested the effects of sowing oilseed rape on different dates in autumn and spring. Much greater oil yields were obtained from autumn sowings, due to higher seed yields and oil content, but the effect varied considerably between experiments, varieties and seasons. Autumn-sown crops flowered in late April or early May, and by the time pods were developing rapidly in June the leaves had senesced almost completely. Spring-sown varieties followed a similar pattern but about a month later, and did not reach the same peak in pod growth.

There was a major effect of sowing date, late-autumn sowings (after mid-September) giving lower yields than early-spring sowings. The best autumn sowings (early September) gave about 3 t/ha of seed, but late sowings less than half this; oil content also decreased with delay in sowing – from 45% to as low as 38%. Delayed sowing restricted growth, leaf area and pod production, and also had a slight effect on seed weight. Frost damage on flower buds appeared to be the cause of reduced yield from early sowing (August) in one experiment. In spring, the earliest sowing (late March) gave the best yields. Vigorous but late vegetative growth from the latest sowing (end of April) did not lead to high yields, possibly due to pest and disease effects.

A study of correlations among certain morphological traits of progenies from a 6 x 6 diallel cross was made. In general, genotypic correlations were similar in sign to the phenotypic correlations in all but two of the 21 cases, but there were differences in magnitude (nine differed by 0·40 and four of these by more than 0·70). Some estimates of the environmental correlations were large (1·57, 1·52, 0·78, 0·75, 0·73 and 0·54). Positive and significant correlations indicated that improvement in some characters related to forage and seed yield should be possible by selection among the diallel progenies.

Path analysis was used as a means of analysing phenotypic correlation coefficients among seven contemporary variables. The method was employed to analyse the system of all possible correlations among certain plant measurements. By this technique one may find the maximum effect, compatible with the data, which can be assigned to a general size factor (common to all variables) and determine the nature and degree of influence of residual, group, and special factors. In most of these the influence of the general size factor predominated (minor in the case of leaf width, pCX = –0·31; and florets per spikelet, pGX = –0·09). Only two of the 21 correlations required factors in addition to the general size (florets per spikelet and spikelets per panicle, excess correlation –0·46; and leaf width and culm diameter, excess correlation +0·53). Special factors acting on each part separately from the other were present in all cases. The study indicated that the genetic differences in this study were largely in general size and to a small extent in group and special factors.

A diallel arrangement, which incorporated the essential features of the de Wit density replacement series, was employed to study the effects of competition amongst five genotypes of perennial ryegrass (Lolium perenne). Of the five genotypes concerned two were derived from S·24, two were collected from natural populations in South Wales, while the remaining genotype originated from S· 23. These five genotypes were grown as monocultures and in all ten binary combinations. Within each combination there were three mixture proportions, namely 75:25, 50:50 and 25:75. All mixtures and monocultures were represented by two boxes, one of which was cut at 3-week intervals (frequent cutting) the other being cut at 6-week intervals (infrequent cutting). At each cut all plants within the appropriate mixtures and monocultures were harvested individually and their dry weight recorded.

The results obtained over the first 18 weeks of the experiment (i. e. the first three complete growing periods) establish that competition is occurring in nine of the ten binary combinations. Within these nine combinations competition may be classified into one of three groups: first, it may be compensatory, in which the gains and losses incurred by the two components counterbalance; secondly, it may be positive complete complementation, where the advantage gained by the stronger component is such that the mixture performance matches that of the better monoculture, and thirdly, it may be positive over-complementation, where the yield of the better monoculture is surpassed by the mixture. Further tests disclose that a long-leaved S· 24 genotype is the strongest competitor, while a short-leaved, prostrate, indigenous genotype proves to be by far the weakest competitor.

Estimates of the equilibrium proportions for each genotype combination suggest that most combinations are expected to become monocultures of the strongest component, with only the combination between the long-leaved indigenous and longleaved S· 23 genotypes remaining a mixture at equilibrium. None of these equilibria coincides with the proportions required to achieve maximum productivity from a particular combination. The results are considered in relation to the known characteristics of these five perennial ryegrass genotypes, while the wider agronomic implications are also discussed.

In experiments at Sutton Bonington between 1967 and 1970, which tested 0–300 kg N/ha applied in spring, maximum oil yields of both autumn- and spring-sown oilseed rape were obtained by applying 200 kg N/ha. The seed-oil content was reduced by nitrogen application but only seriously when 300 kg/a was applied. Responses to high levels of potassium (180 rather than 60 kg K20/ha) were only obtained at 200 kg N/a. Successive increments of nitrogen from nil to 300 kg/ha improved plant growth, increasing leaf area and the dry weight of leaves and stems. The last increment from 200 to 300 kg N/ha was less effective and either reduced or did not affect pod production.

In one experiment 300 kg N/ha stimulated husk growth, apparently at the expense of seed growth, with 200 kg/ha giving the highest proportion of pod dry matter as seed. More nitrogen always raised number of seeds per pod, but only increased seed weight in one autumn-sown experiment.

Serial harvests of one experiment indicated that the maximum seed and oil yield was obtained by cutting plants before they were fully ripe, thus avoiding seed loss through pod shatter. The oil content of the bulk samples reached a peak about a week before maximum oil yield, probably because later-ripening seed did not reach full maturity. All nitrogen levels delayed flowering, but only the highest delayed maturity in the autumn-sown crop.

In each of the crops studied, weeding increased grain yield, weeding 2 weeks after sowing being better than weeding either four or eight weeks after sowing and weeding two and four weeks after sowing being better than weeding either two and eight weeks or four and eight weeks aftersowing. Weeding thrice (two, four and eight weeks after sowing) was significantly superior to all the other weeding treatments. Weeding increased leaf area index, dry weight of side and mainstem and number of mature pods at harvest in green gram and cowpeas. In sorghum, apart from increasing leaf area index, it also increased the length of ears and grain weight per unit lengthof ear. The weeding treatments affected grain yield in cowpeas and green gram due totheir influence on leaf area development, development of the main and side stems and on the number of mature pods produced at harvest. The effect of the weeding treatments on grain yield of sorghum was due to their influence on leaf area development, length of ear and grain weight perunit length of ear.

An examination of the role played by associate plants in conditioning the behaviour of a competitor was carried out on a diallel arrangement of five perennial ryegrasa genotypes using regression techniques similar to those devised for the analysis of genotype-environment interactions. By far the largest proportion of the significant genotype x associate interaction could be ascribed to differences between the slopes of the fitted regression lines, with the three long-leaved genotypes (A, C and E)having the highest slopes and hence being the most sensitive to changes in the associate environment. Significant departures from the fitted regression lines occurred, however, but these could be traced solely to genotype C.

Theoretical models capable of identifying those conditions under which 50:50 mixtures may be expected, first, to exceed the average of their component monocultures, and secondly, to surpass the better monoculture, were developed. Applying these models to the present experiment confirms that the performance of the 50:50 mixtures generally exceeds the monoculture average, but rarely surpasses the better monoculture.

The scope of the regression technique was broadened to incorporate the 75:25 and 25: 75 mixtures, thereby revealing that the response of the two strongest competitors (C and E) is frequency dependent. Density dependent effects were also uncovered in this material, with genotype C the strongest competitor, being particularly noteworthy in this respect. The role of this regression technique in the development of new and highly productive mixtures is briefly discussed.

Results from 10 field experiments are reported. Inra 200, the standard variety in official maize grain trials in Britain, was grown in six of the trials; comparative information was obtained on a range of competitive commercial hybrids and an experimental, early flowering, hybrid. The final plant densities most commonly involved ranged from 5 to 20 plants/m2, with extremes of 2 and 30 plants/m2. The effects of spatial arrangement were also considered in multifactorial or systematic designs; in general, yields increased slightly with more even spacing but no evidence was adduced that spacing, within the limits likely to be encountered in commercial practice, would significantly modify interpretations of density effects.

In all varieties tested, a satisfactory model for the response in yield of grain to changes in plant density was 1/y = a + bx + cx2, where y = grain yield/plant and x = density. Estimated parameter values, however, were not the same for all varieties and significant genotype × density interactions were obtained.

Grain yield/unit area in Inra 200 was maximal at densities of 8–10 plants/m2, but the response curve did not have a pronounced peak; differences in average yieldat densities ranging from 6 to 14 plants/m2 were less than 6%, and yield at 20 plants/m2 was about 80% of the maximum. Other flint × dent hybrids grown commercially for grain in northern areas (Anjou 210, L.G. 11, Warwick SL 209) reached maximum grain yield/unit area at lower densities (6–8 plants/m2), and the decline in yield with increasing density was much more marked than in Inra 200. In contrast, an earlier flowering, shorter growing, experimental hybrid (ARC 51 A) did not reach maximum yield until density was raised to 14 plants/m2, and was even more tolerant of high plant densities than Inra 200. With increasing plant density the number of ears/plant declined, falling below 1–0 in Inra 200 at densities in excess of 10 plants/m2, and averaging about 0–8 at plants/m2. Over the range 6–20 plants/m2 shelling percentage was reduced by no more than 4%, but water content of the ear (grain plus rachis) increased significantly with density. In the very early hybrid, ARC 51A, the difference in water content of the ear at 6 and 20 plants/m2 was less than 3%, but in Inra 200 it averaged about 8% and in varieties less tolerant of high densities it was often ofthe order of 15%. These results could be related to the delaying effects of increasing density on time of silk emergence. Relatively, time of pollen shed was little affected by density changes. In Inra 200 the difference in time between mid-anthesis and mid-silk was about 7 days more at 20 plants/m2 than at 6 plants/m2 while in Anjou 210 and Kelvedon 59A the comparable increase was 14 days.

The practical significance of the findings is discussed in relation to current grain and silage maize production practices, and to future breeding and testing programmes in Northern Europe.

The efficiency of utilization of the energy of food by weaned pigs of the Large White breed was measured. Three diets based on maize (40–60%) had a metabolizable energy of 75·8±1·2% of the gross energy, and 78·2 ±3·4% of the metabolizable energy was present as net energy.

The maintenance requirement of metabolizable energy of pigs weighing 14·3 ± 2·1 kg was 143·6 kcal/kg°0·75/24 h (601 kJ/kg0·75/24 h).

The energy cost per g protein and fat synthesized by piglets was estimated to be 7·43 and 12·05 kcal (31·1 and 50·4 kJ) metabolizable energy, respectively.

Equations for calculation of metabolizable energy (Yl, kcal) and of the net energy (Y2, kcal), based on digested nutrients, were:

Y1 = 4·64×1 + 9·12×2 + 4·25×3'CV = ± 1·2%,

Y2 = 3·84×1 + 7·09×2 + 3·28×3'CV = ± 1·4%,

where X1 = g protein digested, X2 = g fat digested, X3= g carbohydrate digested (crude fibre × N-free extracts).

Ryegrass populations collected from intensively used swards, both leys and permanent pastures, were compared under spaced plant and sward conditions.

On average, the bred ryegrasses were higher yielding, more resistant to crown rust, and more persistent under intensive conditions than the permanent pasture populations, but there was no significant difference in cold-resistance between these two groups.

The potential yield of dry matter of the best of the permanent pasture populations was similar to that of the highest-yielding leys. Several of even the most intensively used pastures were, however, dominated by ryegrass that was not nearly as high yielding as the best of the bred varieties. In addition to differences in yield of dry matter, there was a wide range in persistency, resistance to low temperature and crown rust (Puccinia coronata), as well as in mean date and variance of inflorescence emergence and in yield of digestible organic matter in dry matter (DOMD). Thus, no one type of ryegrass could be associated with permanent pastures, even when the sample was restricted to a narrow range of managements associated with intensive use.

Some of the highest-yielding swards were based on complex mixtures of ryegrass cultivars; this might give rise to difficulty in relating management to stage of maturity and in predicting the composition of the sward established.

A comparison of survivor material derived from S·23 leys revealed no difference in yield of dry matter or DOMD under sward conditions. Other data, however, showed that the populations differed in yield as spaced plants, rust resistance, cold-hardiness, persistency and date and variance of inflorescence emergence.

There was no indication of ryegrass yield decreasing with the age of the ley from which the plants were derived.