Chromic oxide was used to assess the herbage intake of three tropical pastures mixtures namely: Cynodon plectostachyum and Centrosema pubescens (E); E plus Stylosanthes gracilis; Digitaria decumbens plus Centrosema pubescens and Stylosanthes gracilis, by-White Fulani (Zebu) steers and the use of faecal nitrogen to estimate digestibility of grazed herbage.

Chromic oxide recoveries in faecal organic matter ranged from 94·60% in treatment F to ca. 97·2 and 97·5% in treatments E and G respectively.

Positive relationships were found to exist between faecal organic matter nitrogen and herbage organic matter digestibility. Correlation coefficients of the ‘local’ regression equations obtained were positive but of low magnitude in some instances. Estimated mean organic matter intake was comparable to, but slightly lower than, the figures for animals of corresponding live weights in temperate countries while digestible organic matter intake was much lower.

The mean organic matter digestibility values were ca. 70·2 and 66·7% respectively for the two grazing seasons studied.

Two 1-year experiments are described in which a single dressing of 120 lb N/acre (134 kg/ha) was applied to a grass sward as anhydrous ammonia (82% N), ammonium nitrate (34·5% N) or sulphate of ammonia (21% N) at various dates from December to April. The pattern of primary growth from each of the treatments was recorded from early April until mid-June by frequent sampling of the herbage to determine the dry matter and crude protein yields. At every date of fertilizer application from late January to mid-April the growth rate of the herbage was markedly lower with anhydrous ammonia than with ammonium nitrate. With the December applications the spring growth rate of herbage from the anhydrous ammonia treatment was similar to that from the ammonium nitrate treatment. Applications of sulphate of ammonia gave results almost identical with those obtained from ammonium nitrate. The calculation of the dates on which a yield of 2000 lb dry matter/acre (2242 kg/ha) would have been available for dairy cow grazing showed clearly a delay of 12–15 days where anhydrous ammonia rather than ammonium nitrate was applied. The response to anhydrous ammonia was improved by applying it early in the year but solid nitrogen fertilizers, applied either early in the season or when growth was starting, gave higher yields of herbage than anhydrous ammonia.

Ewes of three breeds, Devon Longwool, Kerry Hill and Welsh Mountain were injected with different levels of Pregnant Mare Serum Gonadotrophin (PMSG) for 3 consecutive years. Within the levels of PMSG examined (0–1500 i.u.) the highest mean litter size was obtained at 1000 i.u. for the Devon Longwool (2·10) and the Welsh Mountain (2·33), and at 1500 i.u. for the Kerry Hill (2·41). This represented a response of 0·66, 1·28 and 0·56 extra lambs born for the Devon Longwool, Welsh Mountain and Kerry Hill breeds, as untreated ewes of these breeds produced 1·44, 1·05 and 1·85 lambs/litter. The lambing percentage attained was, however, lower than the response in litter size indicated, due to the incidence of barren ewes and of lamb mortality.

Though the Devon ewes were heavier than the Kerry's, twin lambs out of the latter were bigger than twins from the Devon's. The relationships of body weight and of natural fertility to optimum dosage of PMSG are considered. There is discussion of the maximum litter size and minimum birth weight compatible with the production of viable lambs.

Sixty-six Awassi ewes were divided into two equal groups. The sheep were milked twice daily from lambing for 22 weeks. In one group (weaned) the lambs were separated from their dams within 6 h of parturition. In the second group (suckling) the lambs sucked the residual milk after milking for 15 weeks, after which they were weaned. Milking yields, fat tests, lactational persistency and udder health were not affected by the early weaning. The suckling ewes had greater amounts of residual milk and consumed more concentrates. Further data are presented that suggest that there may be a critical period of attachment of at least 10 days following lambing, during which weaning may effect subsequent milk production. The practical implications of these results are discussed in terms of flock management and the intensification of breeding programmes.

Five experiments (1967–9) on soils formed from calcareous drift examined the effects of soil compaction on seedling emergence and yield of sugar beet, also the interaction between compaction and response to nitrogen fertilizer (N) and phosphate fertilizer (P2O5). Some seedbeds were compacted in winter, others in spring and others prepared with the minimum of compaction; each was tested with 0·6, 1·2 and 1·8 cwt/acre N plus 0·8 cwt/acre additional P2O5. All plots were given a basal dressing of 0–8 cwt/acre P2O6 and enough of other major nutrients.

Compaction decreased seedling populations in four experiments but increased it in one year, when the weather was dry while the seeds were germinating. However, in every experiment compaction significantly decreased yield of roots and sugar. It also interacted with the fertilizer treatments, significantly on average, increasing nitrogen requirement and decreasing phosphate requirement. On average, 0·6 cwt/acre N and 1·6 cwt/acre P2O5 gave the greatest yield without compaction and 1·2 cwt/acre N and 0·8 cwt/acre P2O6 with compaction.

The amount of dry matter produced and N taken up by seven grass species and varieties grown in a glasshouse were compared with perennial ryegrass (S. 23) and Italian ryegrass (S. 22) at different day-lengths and light intensities.

The ryegrasses Westerwolds, Italian (S. 22) and Perennial (S. 321) yielded more than S. 23. At the smallest light intensities, Westerwolds, Italian (S. 22) and Perennial (S. 24) (S. 321) ryegrasses and Meadow fescue (S. 215) took up more N than S. 23. Westerwolds and Perennial (S. 24) (S. 321) ryegrasses should be useful alternatives to the S. 23 or S. 22 strains as test crops in nutrient experiments in the glasshouse, especially when grown in the dim light during winter.

Two methods have been used previously to resolve the ‘mineral’ and ‘organic’ fractions of the cation exchange capacities of soils. Williams (1932) and Hallsworth & Wilkinson (1958) used multiple regression analysis to relate cation exchange capacity (CEC) in several soils to percentage organic matter (OM) and percentage clay, and thence to calculate the average values of the CECs of OM and clay. For individual soils, Davies & Davies (1965) and Clark & Nichol (1968) measured the CEC before and after oxidizing the OM with hydrogen peroxide.

The response of irrigated, perennial ryegrass to fertilizer nitrogen was studied in four consecutive periods of the growing season by applying 0–350 kg N/ha to a fresh sward at the start of each period, and measuring both herbage dry matter and its content of nitrogen.

Responses in yield were highest in the first period, which ended at inflorescence emergence; in this period, both the percentage recovery of nitrogen and the extent of its utilization in producing dry matter were greater than in the later periods. Some damage to the sward was seen following the harvest of grass grown with the high levels of nitrogen in the first period. When the yields were 90% of the predicted maximum the nitrate-N content of the herbage ranged from 1000 to 2000 ppm, except in the first period when it was 200 ppm.

The response curves were used to calculate the nitrogen requirements of the grass which would maintain given incremental yield responses. To produce near-maximum yields, irrigated grass swards may require fertilizer nitrogen equivalent to 2 kg N/ha/day prior to inflorescence emergence, and up to 5 kg N/ha/day for the remainder of the growing season.

The apparent efficiency of conversion of the radiant energy, usable for photosynthesis, into plant energy averaged 3·2%; it did not vary greatly among the four periods.

The experimental results indicate the seasonal requirements of grass for fertilizer nitrogen and some of the implications for animal husbandry are discussed.

A greenhouse pot experiment was conducted with paddy rice (Oryza sativa L. var. ‘Nato’) grown on Mountview silt loam at its initial low P level and on this soil receiving preplant unlabelled P applications (medium and high soil P levels). Labelled granular CSP (concentrated superphosphate) alone, a 2/1 mixture of CSP and DCP (dicalcium phosphate) and a 1/2 CSP-DCP mixture were evaluated.

Dry-matter yields and tillering increased markedly with amount of applied P on the low P soil, and slightly on the medium P soil; there was no response on the high P soil. Response decreased with decrease in water solubility of the applied P at the low and medium soil P levels. Total uptake of P by rice showed similar trends, except that uptake increased significantly with amount of P applied at the medium soil P level.

Percentages of plant P from the labelled fertilizer and uptake of fertilizer P increased in all situations with amount of applied P, decreased with decrease in water solubility of the applied P, and decreased with increase in soil P level. Uptake of soil P increased markedly with increase in soil P level. Soil labelling was much less satisfactory than fertilizer labelling for evaluating the effectiveness of P in different fertilizers.

A solution of labelled CSP was applied in a second experiment at time of transplanting and 3 or 6 weeks later. On the low P soil, yields, P uptake and tillering increased with rate of applied P but decreased with later date of application. On the medium P soil, yields, tillering and uptake of P by the grain were rather similar among treatments. Uptake of P in the foliage and mature straw, however, increased with later date of application. These results indicate that late-applied P is readily absorbed by rice but is not effective for increasing yields.

Experiments to study the effect of date of sowing at two centres in each of 3 years, 1967–9, are described and the results discussed. The earliest sowing date (early March) gave the highest yield of spring barley at both centres and of spring wheat at Sutton Bonington, but at Boxworth in 1967 and 1969 later sowing (early or late April) gave higher yields of grain, which were attributable mainly to increased grain numbers per ear. It is argued that in 1968 poor weather conditions in July and August resulted in very low 1000 grain weights, and although grain numbers were again higher from late sowing at Boxworth this treatment gave the lowest yields because of poorly filled grain. The date of sowing also affected yields of total dry matter, ratios of grain to straw, leaf-area indices, numbers of grains per ear and 1000 grain weights.

A ryegrass silage with pH of 3·8 was prepared and part was neutralized to pH of 5·4 with sodium bicarbonate. Sheep were fed ad lib. in four treatments in which the two silage feeds were fed with either all the feed being consumed per os or with the introduction of silage (15 g D.M./kg LW0·75 per day) directly into the rumen through a fistula. Intake per os was significantly higher (P < 0·001) for the modified silage than for the original silage and was significantly lower (P < 0·001) for the treatments which included feeding per rumen rather than all the food being consumed per os. Feeding per rumen resulted in a small but significant (P < 0·05) increase in the total (per os + per rumen) intake of both types of silage. This increase in intake through feed being introduced directly into the rumen suggests that factors sensed in the oro-pharyngeal region which were by-passed with this treatment may have some limiting effect on the intake of both these silages. The effect of the introduction of feed directly into the rumen on intake per os was similar for the two silage feeds, despite much higher levels of consumption of the modified silage for both feeding methods. This suggests that the increase in intake brought about by partial neutralization was not mediated through this treatment affecting any oro-pharyngeal limitation on the intake of silage.

Volatile fatty acid concentrations in the rumen were higher for the modified silage treatments, but differences between silage treatments for molar proportions of volatile fatty acids, rumen pH and rates of cellulose digestion were non-significant. The initial digestion of cellulose was slower, the molar proportions of acetic acid were lower and of propionic acid higher for treatments which involved feeding per rumen rather than all the food being consumed per os. These observations are discussed in relation to the use of the intra-ruminal feeding techniques and to possible factors limiting the intake of highly acid silages.

An isotope dilution technique has been used to measure the rate of entry of glucose into the metabolic glucose pool and its rate of oxidation in three sheep given diets of barley (85% barley, 15% protein-mineral-vitamin supplement), dried grass or hay. A latin-square design was used and the sheep were fed continuously from an automatic feeding device.

Despite large differences in the amounts of α-linked glucose polymer and of crude protein supplied by the diets there were no significant differences between treatments in glucose entry rate, in plasma glucose concentration or in the size of the total body pool of glucose.

Calculations based on the specific radioactivity of expired CO2 after 3 h infusions indicated no significant differences between treatments in the percentage of glucose oxidised to CO2 or in the percentage of expired CO2 derived from glucose. The absence of a final ‘plateau’ position in the CO2 activity-time curve, even after 6 h infusions, casts doubt on the validity of these calculations.

Ryegrass was used to remove potassium from two acid soils limed to different pH values. Most non-exchangeable potassium was removed from the unlimed soils (pH 4·5) but differences in removal between pH 5·5 and 7·0 were small. Air-drying the soils after cropping released further potassium into the exchangeable form in amounts independent of soil pH.

Equilibrium potassium activity ratios (ARK) after each out declined to small constant values characteristic of the soils. A sandy soil (Woburn) initially contained less exchangeable potassium than a soil with more clay (Sawyers), but after a few crops, ARK, % K in the grass and K uptakes per cut were larger from Woburn soil, showing that non-exchangeable potassium was being released faster than in the other soil.