In this investigation the largest amount of nitrogen used, 44 kg per hectare, increased leaf size, yield and amount of nicotine in the leaf. The three carriers of N had similar effects on growth and yield at each amount applied but calcium ammonium nitrate produced tobacco inferior in quality to that with ammonium sulphate and urea. Increasing topping height from 8 to 10 and to 12 leaves increased the total leaf area per plant and yields, delayed maturity and lowered the quality of the tobacco. The greatest yield was produced by using 44 kg of N and topping at 12 leaves, but the best quality resulted from using 44 kg of N and topping at 8 leaves.

The copper, molybdenum, and total sulphur contents were estimated in 124 samples of oats and 67 samples of barley obtained from various parts of Northern Ireland. Copper contents were in the low-normal range, the average of all oat samples being 3–9 ppm and of barley samples 4–9 ppm, and the range 1–5 to 8–4 ppm covering all samples analysed. The corresponding averages for molybdenum were 0–25 ppm and 0–30 ppm, about 10% of the samples in each case containing less than 0–02 ppm. Sulphur contents (expressed as sulphate) ranged from 0–23 to 0–46 %. The low molybdenum contents are considered to be of significance in the copper metabolism of housed sheep.

Twenty-five soils, including some subsoils, with widely differing properties were cropped with perennial ryegrass in the glasshouse, and measures of Mg availability in the soils were related to the Mg concentration in the plants.

No single measure satisfactorily characterized Mg availability. The ion activity ratio, √aMg/√aca+Mg when the soil neither gained nor lost Mg on equilibration with 0–02 N-CaC12, was more highly correlated (r = 0·;75***) with Mg concentration in the ryegrass than was the best of the capacity measures tested (CaCl2-extractable Mg, r = 0·68***), particularly if the potential buffering capacity (PBCMg) of the soils was also taken into account, in which case r = 0·83***.

Exchangeable Mg (r = 0·67***) was a poorer index of Mg availability than percentage Mg saturation (r = 0·73***) or exchangeable Mg expressed as a percentage of the total exchangeable bases (K, Na, Ca and Mg) in the soil (r = 0·81***). This latter quantity was better than the activity ratio as a predictor of Mg availability (r = 0·81*** compared with r = 0·75***).

A significant proportion of the variation in Mg concentration in the ryegrass could be attributed to the K content of the soils, and closer correlations were obtained when K was included in the composite activity ratio, √aMg/(√aca+Mg + B. aK) (r = 0·88***) or when a term for exchangeable K was included in regression analysis with √aMg/√aca+Mg and PBCMg (r = 0·93***).

The concentration of Mg in equilibrium soil solutions was generally a less satisfactory indicator of Mg availability than were the activity ratios. Soils derived from basaltic parent material had much higher contents of readily exchangeable Mg than the remainder: parent materials other than basalt had little influence on the availability of Mg in the soils. Exchangeable Mg and per cent Mg saturation were higher in gleyed soils than in freely drained soils derived from similar parent material.

Populations of Lolium perenneL. derived from fields where the management was paddock grazing were compared with plants from breeder's seed of the cultivars originally sown at the collection sites. In the first trial the ‘survivor’ population derived from an S. 24 ley was better adapted to withstand intensive sheep grazing and high nitrogen application (672 kg/ha/ annum) than either S. 24 or Stormont Zephyr. Extra treading by sheep in addition to that involved in the high stock density (1186sheep/ha) used at the time of grazing produced only a small reduction in yield of dry matter. In the second trial, the ‘survivor’ population derived from an S. 23 ley had a higher yield of dry matter than S. 23 at the high level of N application (672 kg/ha/annum). There was no difference in the yields when 168 kg N/ha/annum was applied. In both field trials yield in the year of sowing was high for all swards, although the survivor populations were slower to establish than the original cultivars. The evaluation of the ryegrass populations in terms of dry-matter yield was affected by the small quantity of Poa trivialispresent when this grass was sown with the ryegrasses. In the second trial this conclusion also applied to yield of nitrogen in the herbage.

Chalk in the 0–9 in topsoil of Broadbalk has declined from nearly 5% in 1865 to less than 1 % in some plots in 1966, and fastest in plots given ammonium sulphate. Losses were equivalent to 5–8 cwt limestone/acre annually. The paper relates these rates to estimated anion losses, especially bicarbonate, from the plots. Af-ammonium acetate dissolved Ca and Mg from chalk particles in the soils. After correcting for this, exchangeable magnesium had increased during the first 50 years but decreased since 1914 in the F.Y.M. plot. In plots given none or 10 lb/acre of magnesium in fertilizer annually, exchangeable magnesium had changed little since 1865. Thissuggests that equilibrium was soon established between additions and losses of Mg in all except the F.Y.M. plots. Estimates of annual additions and losses of Mg from each plot show that an equilibrium is feasible without large gains from non-exchangeable soil resources. A method of calculating losses of Mg in the drainage using activity ratios and annual calcium losses was developed.

Results are reported of ripening studies with maize (var. Inra 200) at Oxford, 1967–9. Sowings were made in late April or early in May, and crops grown at a standard density of 7–2 plants/m2. Areas were provided with cloche protection, for a 4- to 5-week period from time of sowing, to produce material for studies of the effects of flowering time on ripening patterns. From plants of known flowering date collections of 30–40 ears were taken at intervals from 30 until 100+ days after silking.

Information is presented on water content, grain dry weight and number of grains/ear at the various times of harvest. Asymptotic, polynomial and inverse-polynomial regression models have been fitted to the data to elucidate the interrelationships between time (measured from date of silking), grain water content and grain dry weight.

In plants flowering in mid-July grain continued to increase in dry weight until water content was reduced to 35 %, whereas in plants flowering early in August maximum dry weight was attained at a water content of around 40 %.Maximum dry weight of grain was approximately 10% higher in the earlier flowering plants; the corollary is that in the marginal areas of maize grain production in England maturity in such varieties as Inra 200 is often imposed by the environment with a consequent loss in potential yield.

In the early flowering plants, the time taken from silking to reach the harvestable stage of 40 % grain water content was 69 d in 1967, 79 d in 1968 and 64 d in 1969. Rate of water loss from the grain during ripening was closely related to prevailing air temperatures. In the later flowering plants, differing by an average of 11 d in time of silking, 8 days longer was required for grain to be reduced to 40% water content, giving an average difference of 19 days in permissible dates of harvest.

The results suggest that, in varieties of similar ripening pattern to Inra 200, an advance of about 7 days in flowering time is required to establish the maize grain crop beyond its present confines in south-east England.

Changes occurring during ripening in dry weight and percentage dry-matter content of grain and rachis (cob) have been studied in Inra 200, and comparable data obtained for a U.S.A. dent hybrid, Minnesota 803, a Canadian flint × dent hybrid, OX 302, and a range of European flint × dent hybrids (Prior, Kelvedon 59A, De Kalb 202, Maris Carmine, Pioneer 131 and Anjou 210).

In Minnesota 803, OX 302 and, to a lesser extent, Prior, loss of water from the grain was more rapid than in Inra 200 during later stages of ripening. OX 302 reached a harvestable stage (40% grain water content) 10–12 weeks after silking, about 7 days earlier than Inra 200 in favourable seasons, and nearly 14 days earlier when conditions for ripening were less satisfactory. The patterns of changes occurring in the cob were quite different from those in ripening grain. Maximum dry weight of cob was reached when the grain was in the milk stage, and then declined throughout the period of rapid grain development; in the ripe ear, cob dry weight was 15–20% below its earlier maximum. At comparable grain water contents, the cob in Inra 200 was wetter than in Prior, Minnesota 803 and, even more markedly, OX 302. In contrast, water content in the cob of Maris Carmine and Anjou 210 was slightly higher than in Inra 200. The possible relationship between the differing varietal trends in ripening grain (and cob) and resistance to stalk rot is discussed.

The dry weight of the cob in ripe ears of Inra 200 was barely half that found in OX 302 and Minnesota 803, and lower than in other European flint × dent hybrids. Shelling percentage in ripe ears of Inra 200 was 88–90; it was 84–86 in other European flint × dent hybrids, about 80 in Minnesota 803 and 75 in OX 302. Mention is made of the relevance of this information to choice of variety for production of ground ear maize.

The expected merits of the semi-hybrid variety, produced by bulk interpollination of two populations (Foster, 1971a, 6, c), are examined in relation to those of the synthetic variety. With diploid inheritance, the mean expression of both types of variety is seen to be the same. Any postulated difference in productivity must depend not only on the preferential establishment and survival of a small fraction of the total population, but on the existence of a correlation between characters determining productivity and establishment. For two populations producing a heterotic hybrid, a correlation due to loose linkage or gene association without linkage may result in the superiority of the semi-hybrid, but tight linkage or pleiotropy are more likely to favour the synthetic variety. It is concluded that superiority of the semi-hybrid mode of varietal production can only be established by means of a direct comparison with its synthetic counterpart, and not solely by the demonstration of upper-parent heterosis for productivity.

A mathematical model has been constructed to simulate pasture contamination by the faeces of grazing cattle and the effects on herbage intake. The model describes the rate of deposition of faeces in relation to herbage intake, the effects of contamination on intake as modified by grazing pressure, and the rate at which the influence of faeces on grazing behaviour declines after deposition.

The information available on these processes is incomplete and imprecise in a number of respects. It appears from the modelling exercise that further data are most urgently needed on the rate at which the inhibitory influence of faeces declines, and on the precise effect of grazing pressure on the amount of herbage rejected.

A secondary effect of contamination is recognized, in which the utilization of herbage initially rejected because of the presence of faeces is modified subsequently because the temporary protection from grazing allows it to become too mature. This effect may be quantitatively larger than the primary contamination effect on untrimmed pastures, but its accurate prediction depends on the establishment of comprehensive relationships between the amount and composition of herbage on offer and intake by the grazing animal. The latter studies deserve at least an equal research priority, in relation to the contamination problem in toto, as the elucidation of the details of the primary effect.

The biological and useful yield of Phaseolus vulgariscv. ‘Banja’ and cv. ‘Diacol Nima’ were compared when sown at populations, in row spacings, equivalent to 5–4–32–3 plants m~2, at four levels of fertility achieved by the use of zero, five, ten and 20 cwt ae-1 respectively of a fertilizer mixture containing by weight 2:2:1 calcium ammonium nitrate, single superphosphate and muriate of potash. Yield and its components were determined at final harvest. The two cultivars behaved generally similarly. Crop Index, while highest in the plants with no fertilizer, was more or less constant for each cultivar over a wide range of biological yields in those plants receiving fertilizer. Yield is determined to the extent of 85–7% and 86–1% respectively for 'Diacol Nima’ and ‘Banja’ by the product of pods/plant and plants surviving to harvest. High densities, although giving the highest grain yields, are wasteful of seed in that the percentage of plants surviving to contribute to yield is much reduced.

Fifty Clun Forest ewe lambs with uniform birth dates were randomly stratified into two groups (A and B) of 25 each according to date of birth and body weight at 23 August 1971. On 26 August Group A (control) was joined with rams whilst Group B remained completely isolated from any contact with rams until 18 October.

The sudden introduction of rams to ewe lambs in the transition from non-breeding to breeding activity resulted in a high degree of synchronization of first matings in Group B. However, it did not affect the mean date of onset of oestrous activity.

Nine different capacitance probe methods were used to estimate the herbage yields of 32 small pasture plots; ten meter readings were used in conjunction with the yield data from a variable number (n) of quadrats in each plot. Expected yields were determined by cutting ten quadrats per plot. Estimated yields were compared with expected yields for both the differing methods and the differing values of n. At each level of n the yield estimates from the different probe methods were compared with those obtained simply by cutting n quadrats.

Using calibration data from only one quadrat per plot (n = 1), all probe methods except one gave greater accuracy than that obtained from the single quadrat yields only. For n = 2, the advantage of the probe methods was less pronounced and where n = 3 only one probe method (one which involved no regression computations) gave superior accuracy to that obtained merely by using the yield data from the three cut quadrats. At n > 3, only the one probe method gave increased precision; all other probe methods were markedly less accurate than the equivalent raw quadrat results.

Only one probe technique (which combined data from markedly dissimilar swards) gave yield estimates which were noticeably biased.

Results from an earlier study are presented to demonstrate the influence of season, species and irrigation on probe calibration.

Recommendations are made on the various probe methods which may prove effective in some experimental situations.

In two experiments with potatoes the effects of plant population (from 13 to 59 stems/m2 in 1969 and 18–111 stems/m2 in 1970) and harvest date (from mid-June till late August/early September) on the yields of tubers and particularly those of canningsize (2–4 cm) were studied in the cv. Maris Peer.

Yields of canning-sized tubers increased linearly with increases in the number of mainstems over the range 13–64 stems/m2. The response was similar for harvests made at different stages of growth except for the period of 2–3 weeks after tuber initiation when the effect of plant population on yields was small. For crops grown at low plant populations yields of canning-sized tubers rose to a maximum early in the season and then declined with further growth of the crop. Progressive increases in plant population resulted in maximum yields at progressively later stages in the growth of the crop. The period over which it would have been possible to harvest crops having an acceptable quality and each giving their maximum yield was 4–6 weeks in 1969 and 3–4 weeks in 1970.

There was no effect of seed tuber size per se on total tuber yields or yields of tubers in size grades. In both years at least twice the weight of large (over 66 g) as opposed to small seed (22 and 27 g) was required to establish the same stem population/m2. The production and use of small seed suitable for canning potato production is discussed.

The yield results are reported for the final 3 years of a 6-year experiment in which twenty-one rates of nitrogen fertilizer ranging from 0 to 800 lb/acre (897 kg/ha) were applied annually on S. 23 perennial ryegrass swards with and without S. 100 white clover. The long-term effects of the treatments on herbage yields are discussed using the results from all 6 years. Four-parameter exponential curves fitted to the herbage yield data from each year show that the response pattern for the pure-grass sward remained relatively constant over the years although the mean annual yields varied slightly. The response of dry-metter yield to nitrogen rate on this sward was almost linear between the 0 and 300 lb nitrogen/acre (336 kg/ha) rates, then it decreased progressively, becoming non-significant about the 500 lb/a ere (560 kg/ha) ra te. Crude-protein yield responded almost linearly up to the 600 lb/acre (673 kg/ha) rate. The average yield responses over the 6 years for the pure-grass sward with nitrogen rates between 0 and 300 lb/acre was 27–8 lb dry matter (range 25·8–29·8 lb) and 4·2 lb crude protein (range 3·8–4·8 lb) per lb of nitrogen applied. At high nitrogen rates the yield curves for the grass and clover sward were similar to those for the pure-grass sward but at low rates the grass and clover sward gave a lower response to nitrogen and a greater yield at each nitrogen rate. The yield response to nitrogen rates between 0 and 300 lb/acre applied on this sward increased from 13·1 lb dry matter/lb of nitrogen in the first year to 20·2 lb in the sixth year. The difference in yield between the grass and clover and the pure-grass swards given no nitrogen fertilizer decreased from 4850 lb dry matter/acre (5440 kg/ha) to 2370 lb/acre (2660 kg/ha) over the same period. Within each year the yield difference between the two swards decreased with increasing nitrogen rate reaching an insignificant value at a rate of about 350 lb/acre (392 kg/ha) in the first year declining to 150 lb/acre (168 kg/ha) in the sixth year. On average the weight of nitrogen required annually on the pure-grass sward to give the same herbage yield as the grass and clover sward receiving no nitrogen was 125 lb/acre (140 kg/ha) on a drymatter basis and 195 lb/acre (219 kg/ha) on a crude protein basis.

Twenty-two Finnish Landrace × Blackface ewes suckling either single, twin, triplet or quadruplet lambs were maintained indoors during a 12-week lactation period. Milk production was estimated at weekly intervals by hand milking following oxytocin administration. Milk was collected from each ewe in four similar volumetric portions which were retained in order of withdrawal and analysed for maj or constituents. Weighted volumes of milk from each of the four portions were bulked to give a single sample for analysis. Estimated mean total milk production over a 12-week period from parturition was 134, 205, 212 and 218kg for single-, twin-, triplet- and quadruplet-suckled ewes respectively. Most of the difference in total yield between multiple-suckled groups of ewes occurred during the first 3 weeks of lactation, and the data indicate that the number of lambs born, or the total weight of concepta, influences the initial quantity of milk available to the lambs. Regression analysis showed significant evidence for difference between the linear components of the regression of milk yield, fat, protein, lactose and Gross Energy on the stage of lactation for all suckling groups. The concentration of all constituents other than lactose and ash was higher in colostral milk, but was significantly higher only in respect of fat, protein and Gross Energy. Substantial differences found between suckling groups in respect of fat and protein, content of the milks indicate an influence on these constituents due to the number of lambs suckled. The mean growth rates of the triplet- and quadruplet-suckled groups of lambs were each significantly lower than each of the single- and twin-suckled groups. The food intake of the ewes in relation to shape of lactation curves and consequent lamb growth is discussed.

Two experiments axe described which investigated the effect of two row widths, 68·6 cm and 137·2 cm, on the total and graded yields of three potato varieties, Majestic, Up-to-Date and King Edward, grown at a wide range of seed rates.

Numbers and yield of small (< 3·81 cm) tubers were reduced by wide rows but effects were less on larger tubers and yields of large tubers (> 5·08 cm) were even increased by wide rows at high seed rates. Row width had least effect on King Edward, which produced the most tubers.

The results suggest that much wider rows than have hitherto been used for potatoes may be justified and lead to only small reductions in ware yields.

The dietary and individual factors influencing the utilization of digestible nitrogen in the dry cow were studied with numerous rations fed to Friesian cows kept in metabolism stalls.

Urinary nitrogen excretion and nitrogen balance were above all influenced by the level of digestible nitrogen intake. They are also correlated to metabolizable energy and digestible potassium intakes.

Endogenous urinary nitrogen, estimated by extrapolation, was 30·6 mg N/kg body weight/d or 0·169 W0·73 g/d with the rations meeting approximately the energy maintenance requirements of the cow.

The changes in diet accounted for 80% of the variability of nitrogen balance.

A method was worked out for calculating the body condition of the cow from the live-weight variations.

The changes in body condition accounted for 11% of the variability of nitrogen balance.

Intact barley coleoptiles subjected to high temperature stress of 46°C for up to 4 h showed a significant decrease in their growth rate, and in the final length attained by the coleoptiles before exsertion of the true leaves within. These effects of high temperature were progressively more pronounced with increase in duration of stress. Excised wheat coleoptile sections also experienced a similar growth retardation due to heat stress. This heat-induced growth retardation could not be prevented by exogenous applications of 0·5–100 ppm indole-3-acetic acid or 0·5–5 ppm gibberellic acid; nor by dilute aqueous solutions of calcium chloride, cobalt nitrate or zinc sulphate. The agronomic significance of heat-induced coleoptile stunting is briefly discussed.

Six mature rams were used in a 6 × 6 latin square experiment. They were put on a high concentrate ad lib. diet. Voluntary food intake was measured on the rams which received the following treatments: control, thiouracil, sodium acetate, thyroxine, sodium acetate plus thiouracil and sodium acetate plus thyroxine. Acetate was infused intraruminally at the level of 6·2 g/kg W0·75 per day for 4 successive days. Thyroxine was injected subcutaneously at the level of 0·3, 0·6, 0·9 and 0·9 mg/kg W0·75/day successively. Thiouracil was given orally as the propionyl derivative at a level of 0·03, 0·06, 0·06 and 0·06 g/kg W0·75/day successively.

Respiration rate, pulse rate and rectal temperature were measured before and 1 h after dosing. A period of at least 25 days was allowed between the trials. All the results were calculated as feed intake (g dry matter)/kg W0·75.

Injection of thyroxine, sodium acetate and both together inhibited food intake significantly. Thiouracil showed no significant effect on feed intake but it relieved part of the depression caused by acetate. Pulse rate showed significant differences between treatments but rectal temperature and respiration rate did not change significantly. The results are discussed in the text.