Growth and nutrient uptake by an upland rice variety, Agbede and a swamp rice variety, BG 79, were studied under four different soil moisture regimes (60, 80, 100% soil moisture saturation and flooding).

BG 79 (Swamp rice) ultimately attained greater mean total dry weight than Agbede (Upland rice), except in the flooding treatment, where the reverse applied. For both, 100% soil moisture saturation gave the greatest total dry weight increase, whereas the driest soil depressed dry-matter production: plants grown on soil maintained at 80% moisture saturation ultimately attained greater mean total dry weight than those grown on flooded soil. Flooded plants of the swamp rice outyielded plants grown on soil maintained at 80% moisture saturation, but the reverse applied to the upland rice.

Total leaf numbers were usually greater in BG 79 than in Agbede during the tillering and mid-vegetative stages. Increase in the soil moisture up to complete saturation increased the total leaf number in both varieties.

Mean leaf area was greater in Agbede than in BG 79 during the tillering and midvegetative stages. During these two periods of growth the 100% saturation treatment produced plants with the greatest leaf area, whereas 60% soil moisture saturation produced plants with the smallest leaf area in both varieties.

BG 79 had more shoots than Agbede. During tillering saturated and flooded soil encouraged the production of shoots in both varieties, but the driest soil prolonged the tillering period, especially in BG 79. Final shoot number tended to decrease with decreasing soil moisture. The percentage shoot mortality in Agbede was not significantly affected by soil moisture regimes, but BG 79 plants grown on the driest and saturated soil had significantly greater percentages of shoot mortality than flooded plants. In both varieties, plants grown on the driest soil had significantly greater percentage shoot mortality than those grown on soil maintained at 80% moisture saturation.

Mean Relative Leaf Growth Rate and Net Assimilation Rate were significantly faster in BG 79 than in Agbede variety, but the reverse applied with regard to Leaf Weight Ratio.

In both varieties flooded plants had the lowest concentration of manganese, especially during tillering. The small adsorption of Mn with flooding is attributed to a probable antagonism between iron and manganese.

Upland rice (Agbede) and swamp rice (BG 79) varieties grown on flooded soil, and on soil maintained at 80 and 100% moisture saturation were sprayed with solutions containing 0 ppm (MO), 10 ppm (Ml), and 20 ppm (M2) of manganese.

The M 2 treatment depressed total dry weight and dry weights of leaf laminae, stems, leaf sheaths and root of both varieties grown on soil maintained at either 80 or 100% moisture saturation. The M 1 treatment increased the ear weight of Agbede grown on soil maintained at either 80 or 100% moisture saturation, while the M 2 treatment increased the ear weight of plant grown on saturated soil. In flooded soil both the M 1 and M 2 treatments significantly increased dry weight of Agbede plants, but only the M 2 treatment increased ear dry weight of BG 79. The ear weight of Agbede plants receiving M 0 and M 1 treatment decreased with increasing soil moisture while that of BG 79 increased.

It is considered that manganese supply limits yield of Agbede grain grown on flooded soil.

Variations in the host–parasite relationship of bacterial blight of cotton, caused by Xanthomonas malvacearum, E. F. Smith (Dowson), axe elucidated in terms of the three main components of variation, namely, genetic variation in the host, genetic variation in the parasite and variations in environment.

Although the relative resistance shown by host varieties differed both with the culture of the pathogen used for inoculation and with the environmental conditions, over-riding patterns of host resistance could be detected, showing that certain varieties maintained their resistance over a wide range of conditions.

It was found that phage type in X. malvacearum was not related to virulence. Moreover, none of the cultures of the pathogen which had been isolated from different sources, could be shown to be identical when inoculated into a range of host varieties under a range of environmental conditions. It was concluded that the pathogen showed continuous variation in virulence and that it would be difficult and of little value to attempt to define races.

Some success was achieved in relating observed variations in the host–parasite relationship to easily measured components of the environment, by using multiple regression analyses. It is suggested that this might provide a means of characterizing the complex variations observed and that the host–parasite relationship could be regarded as a dynamic system, in which disease expression is a function of the interactions of environmental factors and two polygenic systems, that of the host and that of the parasite.

Intrapopulation variances were also studied in the host varieties. A population which showed little variation for resistance under one set of conditions might show considerable variation in a different environment or when inoculated with a different culture. It is suggested that selection for resistance under conditions which favour the expression of variation can lead, by repeated selection and inbreeding, to the production of resistant populations which retain their resistance under conditions in which the parental stocks showed no worthwhile resistance. These conclusions are discussed in relation to problems in resistance breeding and genetics.

A total of 1659 ejaculates was collected from four Friesian bulls imported from Europe and ten of their offspring born in Iraq while in regular artificial service at the Abu-Ghraib Experiment Station. The work covered a period from 1 January 1965 to 30 June 1967.

The five semen characteristics, volume, density, mass activity, individual motility and pH were studied and the influence of age of bull and season on these characters was investigated. The relationships between the characters were also investigated.

Deterioration was observed in volume of ejaculate, density, mass activity and individual motility in the Iraqi Friesians. Influence of season on all semen characters lacked significance with the exception of mass motility in the European Friesian bulls (P < 0·05). Highly significant positive correlations were found between most of the characters studied.

The micro-Kjeldahl technique and paper electrophoresis were used to measure the total protein and γ-globulin concentrations in the sera of 423 2-day-old Finnish Landrace, Scottish Blackface, Merino and Merino × Cheviot lambs, and the total protein concentrations in the sera and colostra of their mothers. The concentrations were higher in Finnish lambs than in lambs of other breeds. The interbreed variations between single lambs were not significant, but the variations between lambs from larger litters were highly significant, because the concentrations in Finnish twins and triplets were as high as in single lambs, whereas the concentrations in Blackface and Merino × Cheviot lambs were negatively correlated with litter size. The differences between the breeds were attributable to the particularly high protein concentrations in the colostra from the Finnish ewes, to the small size of their lambs, and, probably, to a higher rate of production of colostrum by Finnish than by other ewes. There was some evidence of a positive correlation between the lengths of the gestation periods and the γ-globulin concentrations of the lambs.

Four varieties of barley, selected for characteristics which could have value in a barley variety intended primarily for animal food, were compared with the variety Proctor under two levels of irrigation and two levels of nitrogen fertilizer. The exotic varieties yielded less grain and total dry matter than the adapted varieties, but differed in their response to irrigation. This difference was due chiefly to the ability to form extra ears when irrigated and the other yield components were less affected. Nitrogen fertilizer did not affect yield, although more ears were formed in the highlevel than the low-level treatment. The yield of nitrogen in the whole plant and in the yield of grain nitrogen were increased by high-nitrogen fertilizer and one of the exotic varieties was found to be capable of high yields of both grain nitrogen and total nitrogen, but there were no varietal differences in the response to nitrogen fertilizer.

The varietal differences in response to irrigation are briefly discussed and related to development and possible drought resistance. The nitrogen yield of the grain is analysed in terms of total nitrogen uptake and distribution within the plant and the possibility of using the variation in these characteristics in a breeding programme is raised.

Samples of hays (132) and silages (146) were analysed for calcium, phosphorus, magnesium, copper and manganese. Assessments were made of their ability to supply minerals to cattle in accordance with the A.R.C. (1965) minimal requirements.

The concentrations of all these minerals were greater in silage than in hay. The proportions of the hay samples which in 20 lb of dry matter, provided inadequate amounts of minerals to maintain cattle of 1100 lb live weight were 4% (Ca), 98% (P),21% (Mg), 90% (Cu) and 39% (Mn). In a similar manner 15 lb of silage dry matter proved inadequate to a comparable degree. For the samples examined 4% (Ca), 99% (P), 19% (Mg), 62% (Cu) and 15% (Mn) did not meet the proposed standards.

Data are presented to indicate the amounts by which a variety of cattle diets based on hay and silage fail to meet the A.R.C. (1965) minimal requirements in respect of calcium and phosphorus intakes for milk yields up to 4 gal.

Skin temperatures, deep body temperatures and respiratory rates have been measured in Southdown and Merino sheep following feeding, and during infra-red irradiation, rumen infusions of hot and cold water, and cold exposure induced by shearing. The increases in respiratory rate and skin temperatures induced by infra-red heating and the heat increment of feeding were reversed by addition of iced water to the rumen and were suppressed by shearing. These responses could not be systematically related to particular body temperatures in the sheep and appeared to be continuously variable rather than ‘all-or-none’ phenomena. Considerable overlap was observed between respiratory and vasomotor mechanisms of thermoregulation. Measurements of the surface area and weight of ears and legs showed that these regions contribute approximately 23% of the surface area and 8% of the body weight in Merino sheep. Calculations suggested that up to 70% of the additional heat produced in the 2 h after feeding in sheep may be stored in the tissues through increase in mean body temperature. Sheep kept in short wool throughout the winter appeared to establish a new thermoregulatory ‘set-point’ associated with lower rectal temperatures than those in sheep with a full fleece.

Dry-matter intake (D.M.I.) from Panicum maximum(guinea grass) was studied in digestibility trials with Holstein and water buffalo bulls and in a feeding trial with lactating cows.

Differences in voluntary D.M.I. per unit body weight0·73 between the Holsteins and water buffaloes were not significant. Average D.M.I. for all bulls in all main trials was 2·16 kg per 100 kg B.W. Average D.M.I. by the lactating cows was 2·08 kg per 100 kg B.W., for all practical purposes the same as for the bulls.

D.M.I. was not related to stage of maturity or season of harvest of the guinea grass. Intakes of digestible protein, T.D.N., and digestible energy in different seasons and at different growth stages were related to the percentage of those nutrients in the grass.

Correlation coefficients were 0·68 between D.M.I. and B.W.0·73, 0·59 between D.M.I. and T.D.N. content, and 0·58 between D.M.I. and crude protein content, D.M.I. was not closely related to dry-matter content (r = 0·30) or crude fibre content (r= 0–01) of the guinea grass.

The results of progeny tests of families of F1 and F2 selections derived from S 100 white clover are reported. The selection criterion was a high total nodule mass per plant coupled with an effective symbiosis with a known effective strain of Rhizobium trifolii. Selection for increased nodule volume produced a correlated increase in nodule number. F1 and F2 had significantly higher means than S 100 but F2 was not significantly higher than F1.

Scores for nodule mass showed a significant increase in F1 and a smaller but insignificant increase in F2. An estimate of the efficiency of nitrogen fixation on a unit-nodule basis indicated that as nodule size increased efficiency decreased.

The growth of 120 Friesian heifers born into one herd over a period of 12 years was studied for the period from 6 months of age to calving at about 30–35 months of age. Live weights were recorded weekly and rates of live-weight gain were calculated for each 3-month period for each animal. Δt 6, 12, 18, and 24 months of age the heifers weighed 360, 590, 800 and 950 lb. The coefficients of variation of live weight did not vary with age and averaged ±10·0%. Coefficients of variation of live-weight gain increased from ± 20% at 6–9 months of age to ±60% at 24–27 months of age. Growth rate declined by 0·02 lb/day from 12 months to 30 months of age for animals under constant managerial conditions. Heifers wintered indoors grew faster than those wintered outdoors. The growth of younger animals was decreased more by outdoor wintering (a reduction of 0·6 lb/day at 15 months) than was the growth rate of older animals (a reduction of 0·3 lb/day at 21 months of age). When live-weight gain was low in winter there was marked compensatory growth at grass the following summer. Pregnant heifers grew 0·1 lb/day faster in early pregnancy and 0·6 lb/day faster in the last 4 months of pregnancy than did barren heifers.

There was no appreciable difference between the live-weight gain of spring- and autumn-born heifers. With an autumn calving policy spring-born heifers were served and conceived 135 days earlier and weighed 106 lb less at calving than did autumn-born heifers. There was little difference in the milk yield of the two groups in 305 days of the first lactation.

The regression equation of live weight (lb) on age (months) to 3rd calving was W = 1449 – 2027 e-0·042t. It was concluded that in the interests of economic rearing the dairy farmer could with advantage exercise greater control of the relationship between nutrition and growth during high cost winter periods and low cost summer periods.

In spite of the entomophilic structure of the rape flower, which is very attractive to nectar- and pollen-gathering bees, the crop gives good yields without insect pollination.

Thirty-four soils from the Rothamsted Experiments were exhaustively cropped with ryegrass in the glasshouse. The concentration and yield of potassium in ryegrass tops and the potassium intensity in the soil were measured every 4 weeks, after harvesting the grass.

The change in K-intensity of soils, rich in potassium, with exhaustion differed from that of ‘poor’ soils. This change was related to the rate of change of the cumulative K-yield. The rate of change of soil K-intensity demarcated periods of intense and limited exhaustion and partial recovery of the soil during cropping.

The cumulative K-yield of ryegrass was very significantly related to the K-intensity of the uncropped soil; the ‘16-week’ yield was slightly better related than the ‘60-week’ yield. For Park Grass soils, the relationship was improved by allowing for variations in soil pH.

The K-intensity of all soils, with or without manuring, decreased to nearly 10-3 (M)½ in (AR)0 units after 16 weeks cropping, although large differences in K-yield persisted until much later.

K-buffer capacity per unit clay content of the soil, measured by a laboratory method, was inversely related to the K-intensity of the uncropped soil. The K-buffer capacities of soils rich in potassium, measured in laboratory and glasshouse experiments, were significantly related, but were unrelated for ‘poor’ soils. The K-buffer capacity (laboratory method) of Rothamsted soils with different manurial treatments was only very approximately related to the cumulative K-yield.

Less K was taken up from all Rothamsted soils given nitrogen fertilizer in the field and their K intensities were also smaller than the corresponding soils without ‘N’. Field liming of acid soils decreased their K-intensity and increased their K-buffer capacity, presumably because more potassium was removed by the field crop.

A rapid method is suggested for measuring potassium intensities of soils.

An artificial rumen technique which simulated in vivo conditions was applied to the study of the effects of non-protein nitrogen on fermentation and nitrogen distribution in the rumen. Using this technique it was possible to reproduce in vitro a series of biochemical and other effects on fermentation that had been produced in vivo by the addition of various sources and levels of non-protein nitrogen to the rumen. It was shown that with a basal diet of cellulose, protein was synthesized from urea both in the presence and absence of starch over a period of 24 h and a typical rumen fermentation pattern was maintained.

Crosses between eelworm-resistant tetraploid red clover plants varied significantly in corolla tube length and in the distance between the top of the nectar and mouth of the corolla tube. Variability between plants in height of nectar above the base of the corolla was positively correlated with corolla tube length but a significant residual variance in nectar height was independent of corolla tube length.

Tetraploids had higher nectar but longer corolla tubes and greater distances for bees to reach than those in related diploids which were previously reported.

The implications of the findings are discussed in relation to the improvement by breeding of the attractiveness of tetraploid red clover to honey-bees.

Results are reported of twelve experiments—over a period of 11 years—on the effects of date of sowing on development and yield of maize at the Oxford University Field Station, Wytham. Information was obtained on 14 varieties, representative of the range of types likely to be considered for commercial cultivation in England, and sowing dates ranged from mid-March until the end of June.

All varieties gave excellent emergence from May and June sowings but, from sowings made in March or early in April, some American varieties (e.g. White Horsetooth, Wisconsin 255) were slower and poorer in emergence than varieties of northern European origin. For northern European varieties emergence exceeded 70% from March sowings and approached 90% from mid-April sowings. Sowing date markedly affected speed of emergence. More than 40 days elapsed from March sowings until mean date of emergence; about 25 days from mid-April sowings; 18 days from late April sowings and 8–9 days from late May or June sowings.

Plants from sowings made in March or early in April were not significantly earlier or more productive than plants from sowings made in late April. For grain production, however, any further delay in sowing time usually led to lower yields, even with the earliest varieties tested. In contrast, final production of dry material from the shoot was higher, on average, from mid-May sowings.

Provided growth was not arrested by autumn frosts before flowering was completed, plants from later sowings were taller and had more leaves than plants from earlier sowings. The causes of these changes in plant development following variations in sowing date are discussed in the light of published information on the effects of temperature and of length of day on growth of maize.

The practical conclusion drawn from the experiments is that the end of April is an appropriate time to sow maize in central and southern England. No further delay is warranted for grain production. The effect of sowing date on the value of fodder or silage maize requires further information.

The production of herbage dry matter harvested from a mixture of S. 24 perennial ryegrass, S. 37 cocksfoot and S. 48 timothy is compared with the yields of the same species sown alone. Various levels of fertilizer nitrogen were applied to the grasses which were harvested by cutting fourteen times over a 3-year period.

The possibility that the mixture produced a greater yield than swards of pure species (after taking into account that the three species are not present in equal proportions in herbage harvested from the mixture) was examined using the concept of ‘the sum of the relative yields’. There was no evidence of a beneficial or antagonistic effect of one species on another; rather, the species seemed to be ‘mutually exclusive’ (de Wit & van den Bergh, 1965).

The botanical composition of the mixture changed through the course of the experiment, e.g. cocksfoot became increasingly dominant, particularly at the highest level of nitrogen. Changes in composition accounted for any tendency for the yield of the mixture to deviate from the mean of the pure-sown swards.

Some of the advantages and disadvantages of using mixtures are discussed and it is concluded that a rational approach to grassland husbandry should be based on swards sown to a single grass variety.