An experiment comparing most combinations of six seed sizes and four spacings between seeds to give a range of common seed rates, was repeated for 3 years with the eultivar Ulster Prince. For the earliest harvest, total yield was reasonably related to seed rate, but for subsequent harvests the yield response was more closely related to number of stems; this pattern was more pronounced in yields of the canning grade.

Twenty experiments between 1970 and 1974 tested the effect of spring applications of all combinations of five amounts of potassium (0–333 kg K/ha) and two amounts of sodium (0, 150 kg Na/ha) on sugar-beet yield, profitability and the amount of K and Na in the crop in mid-summer. The experiments were in commercial sugar-beet crops where soils contained little exchangeable potassium, most having less than 100 mg K/l in top soil. On average, sugar yield was greatest when 150 kg Na/ha plus 167 kg K was used, the fertilizer increasing yield by 0·71 t/ha. Response to this combination of K and Na fertilizers was 1·45, 0·57 and 0·22 t sugar/ha when the soil contained less than 60, 61–120 and more than 120 mg K/l respectively.

From results of earlier experiments, it was thought that response to even a large amount of K without Na would be less than to Na without K because usually there is insufficient rainfall in the spring for maximum response to K. In fact, 333 kg K/ha increased yield by about the same amount as Na, probably because a large proportion of these experiments were made in wetter-than-average springs.

The concentration of K in dried tops and roots in mid-summer increased linearly with soils containing from 40 to 120 mg K/l but when there was more K in the soil the concentration of K in the plants did not increase further. By contrast, the concentration of Na in plants did not reach a similar plateau. Whole plants in mid-summer contained between 128 and 251 kg K/ha and 42–102 kg Na/ha, depending on the fertilizer treatment. Recovery of applied K varied from 90% when small amounts were used on fields containing least K to about 20% when large amounts were given on fields containing moderate amounts. Recovery of Na varied from about 50 to 23%.

The comparison of the financial return from using K alone or K plus Na showed that Na was essential for maximum profit. On average, the most profitable dressing of K gave a return of £14/ha whereas K plus Na gave up to £46/ha. On fields with least K, the corresponding results were £50 and £115/ha respectively. In relation to soil K, the most profitable application was 150 kg Na/ha plus about 150 kg K/ha on soils with 60 mg K/l or less, and 150 kg Na/ha plus about 75 kg K/ha on most other soils.

Experiments with wheat describing the effects of crop thinning on grain yield and its components are presented. These were carried out over 5 years in northwest Mexico, using a high-yielding dwarf spring-wheat variety (Triticum aestivum cv. ‘Yecora 70’) grown under irrigation and high fertility. It was shown that thinning largely relieved competition for light, thus increasing photosynthate levels in the plants remaining after thinning. The objective was to evaluate this simple technique as a guide to understanding when grain yield and its components were determined and, in particular, the extent to which post-anthesis photosynthate supply limited yield.

There were major responses in grain yield with thinning between about 50 and 100 days after seeding, and in number of spikes and of grains with thinning between 50 and 90 days (50% anthesis was reached at 87 days). Number of spikelets per spike showed small responses to early thinning (before 50 days). Number of grains/spikelet and kernel weight snowed positive responses to thinning between 65 and 90 days, and 90 and 115 days, respectively. These results agreed with adjacent shading and CO2 fertilization studies but, because of certain difficulties in interpretation of responses, pre-anthesis thinning was not considered a very useful technique.

Anthesis thinning was carried out on 21 separate crops: the kernel weight increase relative to the unthinned control ranged from 6 to 41%, averaging 20%. Anthesis thinning led to increases in stem weight during the first half of the grain filling period, followed by increases in grain growth rate in the latter half. The increase in final kernel weight was greater with higher temperature and lower radiation during grain filling; these variables explained 64% of the variation in kernel weight response. It is suggested that the kernel weight response does indicate the degree of photosynthate limitation during grain filling, showing reasonable agreement with adjacent shading and CO2 fertilization studies. It was concluded that anthesis thinning, because of its relative simplicity, is a useful technique. Implications for yield improvement in Yecora of the results provided by this technique are discussed.

Mature green plantains (Bini variety) dipped in fungicide and stored with Purafil in polyethylene bags, remained green and hard for 3–4 weeks before ripening started. Fruits stored with Purafil or potassium permanganate kept longer (by 2 weeks) than those stored with potassium iodate or potassium dichromate. Severe chemical and fungal damage occurred in fruits stored with calcium hypochlorite, indicating that plantain fruits may be sensitive to chlorine. No significant difference in storage life was observed between fruits stored in polyethylene bags alone and those stored in potassium iodate or potassium dichromate. There was much lower incidence of fungal infection in fruits dipped in thiabendazole (1 g/l) than those dipped in Diathane M45 (3 g/1). Fruits dipped in thiabendazole before storage remained virtually free of fungal attack even after they had completely ripened.

Herbage yield obtained from grass swards is influenced by the presence of grazing animals (Brockman, Rope & Stevens, 1971a, b; Holmes, 1968; Shaw, Brockman & Wolton, 1966). The net effect of grazing in a particular situation depends on the balance between the effects of excretal-N return, which tends to increase yields (Brockman & Wolton, 1963) and those of treading and other sward damage, which tend to reduce yields (Edmond, 1970). This net grazing effect on yield can be measured by comparing yields of cut and grazed swards under management that is in all other respects identical (Shaw et al. 1966). Available data have been examined to obtain quantitative estimates of the net effect of grazing and of the changes in these effects that occur with changes in sward N supply.

A mathematical model of whole plant growth in soil is presented. Particular emphasis is given to those factors which relate to the absorption of nutrients and water by the root system. There are two basic premises; that a plant is made up of two pools, structural material and precursors to structural material, and that structural material is produced by a reaction between a given ratio of precursors. The precursors are soluble carbohydrate and unbound nitrogen, probably nitrate. Increase in leaf area and root length is a consequence of absorbed nitrogen combining with photosynthate.

The absorbing power and the distribution throughout the soil of the roots is controlled, through feedback mechanisms, by the ratio of the precursors, within the plant. The description of plant growth is interfaced with a model of one-dimensional flow of water and solutes in soil, and gives a model for investigating plant growth, or competition between root systems of more than one plant. The results of a number of simulations are presented. A sensitivity coefficient is defined to compare the effect of various properties on overall growth. Its value is calculated for 11 plant properties. It is some measure of the competitive advantage conferred on the plant by a change in the value of each property. The results of the competition experiments are given as replacement diagrams.

The model has weaknesses. Because it is explicit, it defines in precise detail the experiments which would support the hypotheses, or suggest modifications to them. As a holistic analysis, it brings together ideas from different disciplines into one comprehensible framework.

Information is given on dates of sowing and mid-silk for Inra 200 in 40 experiments (two each year at Oxford, 1962–75, and at Cambridge, 1970–5), together with cumulative temperatures between these dates. Two methods of defining effective temperature for maize development have been considered, namely the method advocated by U.K. Meteorological Office with 10 °C as the base temperature (the Ag. Met. method) and that defined in Ontario units. The regression relation between accumulated temperature and dry-matter content of the grain during ripening has also been calculated, from data obtained in the years 1966–74, and assessments made of cumulative totals in Ag. Met. day °C and in Ontario units from the date of silking until the grain D.M. content is 40%, when the crop is considered suitable for ensiling, and from silking until grain D.M. content is 60%, when the crop may be considered ripe.

Cumulative temperature totals were significantly more stable over experiments than time expressed in calendar days. Totals of Ontario units were less variable than totals of Ag. Met. day °C. Estimated requirements for Inra 200 were 405 day °C or 1380 Ontario units from sowing to mid-silk, 255 day °C or 800 Ontario units from silking to 40% D.M. in the grain (for silage crops), and 380 day °C or 1235 Ontario units from silking to 60% D.M. in the grain.

Four annual experiments were carried out on the control of couch grass by undersowing barley and field beans with Italian ryegrass and broad red clover. Pieces of couch grass rhizome 15 cm long were planted in the plots in spring and lifted in late autumn. Couch grass grew more under beans than under barley. Undersowing lessened the growth by a factor of two under barley and by a larger factor under beans, although the total amount of couch lifted from under beans was greater than under barley. Undersowing spring cereals can appreciably retard the spread of couch grass and prevent its rapid spread after harvest if cultivation or spraying is delayed.

The uptake efficiency of roots for sulphate and potassium was evaluated in wheat, sugar beet, and tomato, at different ploidy levels. At increasing ploidy, wheat and sugar beet showed higher, tomato lower efficiency, the polyploid absorption system being characterized in sugar beet by higher Vmax and Km, in wheat by higher Vmax and unchanged Km, in tomato by lower Vmax and Km. Uptake efficiency of roots appears tightly bound to the evolutionary progress, that is to the level of environment adaptation of plants, and should be susceptible of further improvement by breeding practices.

Administration of ACTH to Finnish Landrace × Dorset Horn ewes during days 13–16 of the pre-mating oestrous cycle resulted in a significant delay in the onset of oestrus (mean cycle length of 17·5 ± 0·39 days as compared with 16·4 ± 0·61 in a control group). Subsequent ovulation rate was significantly higher than in the control group (3·12 and 2·44 ova/ewe respectively).

In a second experiment with Scottish Blackface ewes the effects on time of onset of oestrus and on ovulation rate of environmental stress, ACTH, cortisone acetate or metyrapone were studied. Environmental stress and administration of ACTH through the oestrous period significantly reduced ovulation rate (1·54 and 1·39 ova/ewe respectively) compared with the control (1·96). ACTH administered during days 13–16, as in the first experiment, and cortisone acetate administered through oestrus had no effect on ovulation rate (1·88 and 1·86 respectively). Administration of metyrapone reduced ovulation rate to 1·70 but this was not significantly different from the control. Both forms of ACTH treatment resulted in a delay in onset of oestrus but environmental stress had no effect on this character.

Levels of plasma luteinizing hormone (LH) were estimated on representative animals. These showed that ACTH and environmental stress influenced the pattern of the ovulatory surge of LH in respect of time of onset of the surge relative to onset of oestrus, duration of surge and peak levels.

The pre-weaning and post-weaning gain, oaroass production and stomach development of oalves fed four levels of whole milk (8%, 10%, 12% and 14% of live weight daily) was studied in two experiments. Calves had access to pasture at all times and were weaned at 12 weeks. Pre-weaning gain, weaning live weight, and carcass weight at weaning all increased as the quantity of milk increased. At the 14% level, male calves reached heavier weaning live weights and produced heavier carcasses than females. Reticulo-rumen weight, when expressed as a percentage of total stomach weight, was significantly reduced with increased milk feeding. Calves reared on the higher quantities of milk gained more slowly after weaning, this being attributed to their poorer reticulo-rumen development at weaning.

In two separate experiments, ewes of the Scottish Blackface breed were subjected to management stresses in the first or second 10-day period after mating or were treated with daily injections of 60 i.u. ACTH for the whole 20-day period. Embryonic loss is defined as the number of corpora lutea not represented by viable embryos at slaughter. Examinations were carried out between 26 and 32 days post-mating. In the two experiments combined, losses were 29·9, 29·0, 37·7 and 17·2%, respectively, for ewes subjected to environmental stress during days 1–10, during days 11–20, treated with ACTH or kept as unstressed control. Expressed as the percentage of ewes in which partial or complete loss of shed ova occurred, the results were 49·0, 46·0, 54·3 and 25·5%, respectively. Losses were significantly higher in all treated groups than in the unstressed control.

A winter barley variety, from the USSR, 13031, lacking vernalization requirement but sensitive to short days and more frost resistant than varieties now commercially grown in Britain, was hybridized with Shimabara, a Japanese variety which requires vernalization but is less sensitive to short days and more susceptible to frost than 13031. The resulting segregating population was then selected under short days and non-vernalizing conditions and in artificial freezing tests, in order to isolate recombinant lines.

Five lines derived in this way, together with the parents and the standard winter barley variety, Maris Otter, were included in a detailed developmental study made in a glasshouse under cool, short days.

Four of the lines had very similar developmental characters, namely few leaves and a high rate but short duration of spikelet initiation. Developmentally these selections resembled the parent Shimabara more closely than 13031 but the rate of spikelet initiation was faster than that of either parent and the duration of spikelet initiation was shorter. The fifth selection also resembled Shimabara more closely than 13031 but had more leaves and a lower rate and longer duration of spikelet initiation than the other selections. This selection was found to have a strong vernalization requirement.

One selection closely resembled 13031 in its frost resistance but had low short-day sensitivity and no detectable vernalization requirement. The complementary characters of the two parents were therefore recombined in this line.

Vernalization had little effect on the development of any of the genotypes under cool, short days in a glasshouse.

A thin layer of soil was washed from a smoothed soil profile and the length of the roots visible at the profile wall estimated. A grid net was used to count every visible part of a root which was nearly 5 mm long. Roots which were longer than 5 mm were counted more than once. This improvement of the traditional trench profile method provides an estimate of the root length in a soil volume.

A method is described for the determination of rumen volume using Cr-EDTA colour measurement in a spectrophotometer at 550 nm. The results of several determinations of rumen volume comparing this method with Cr-determination as chromate and polyethylene glycol as markers gave similar values with differences ranging from 1 to 14% with an average of 6%. Direct measurements through evacuating rumen contents gave values 20·68% higher than those estimated by the colour method. The values were similar when corrected for dry matter.

Five levels of frozen grass and heather (Calluna vulgaris, L. Hull) which contained 85% of the current season's shoots, were offered to five castrated male Scottish Blackface sheep per level. The levels of grass were 0, 200, 400, 600 and 800 g D.M./day, and heather was offered ad libitum after the grass had been eaten. Both the grass and heather were harvested in September. Voluntary intakes of heather increased by 0·46 g/g of additional organic matter intake (OMI) of grass between the two lowest levels of grass, but at higher levels of grass there was a highly significant (P < 0·001) linear decrease in OMI of heather of 0·57 g/g additional OMI of grass.

No associative effects of grass (OM digestibility 70%) and heather (OM digestibility 44%) on OM or neutral-detergent fibre digestibility could be demonstrated. Intakes of digestible OM and nitrogen balance increased in a positive and linear manner with the proportion of grass in the diet. To meet the nitrogen and energy requirements for maintenance of the sheep the diet would require to contain 50% of grass. These findings are discussed in relation to the nutrition of sheep grazing heather-dominant moorlands.

During four winter seasons eight spacing and density experiments were made under irrigated high fertility conditions in north-west Mexico (latitude 27° N). Experiments included various Triticum aestivum and T. durum genotypes of spring habit, short stature derived from Norin 10 genes, and contrasting plant type. Measurements included dry-matter production, photosynthetic area index, and light interception during one experiment, total dry matter at maturity in most others and grain yield and its numerical components in all experiments.

Grain yield and most other crop characters were unaffected by row spacings within the range 10–45 cm interrow width. The optimal seeding density for maximum grain yield was 40–100 kg/ha (80–200 plants/m2). Yield reductions at lower densities (20, 25 kg/ha) were slight and accompanied by reduced total dry-matter production. Yield reductions at higher densities (160–300 kg/ha) were also slight and were associated with more spikes/m2 but fewer grains/m2 and reduced harvest index. It is suggested that lower than normal preanthesis solar radiation or weather conditions leading to lodging can magnify these yield depressions at higher densities.

Measurements showed rapid approach of crops to 95% light interception, reached even at a density of 50 kg/ha within 50 days of seeding. It is suggested that provided this occurs before the beginning of substantial dry-matter accumulation in the growing spikes (60 days after seeding) there will be no loss of grain yield with reduced seeding density. Results point to a ceiling photosynthetic area index for maximum crop growth rate although there was a tendency for rates to fall at very high indices (> 9). This tendency was associated with very high density, high maximum numbers of shoots, poor survival of shoots to give spikes (< 30%) and reduced number of grains/m3;. The relatively low optimal densities seen here may be characteristic of genotypes derived from Norin 10.

Genotype × spacing, genotype × density and spacing × density interactions were generally non-significant and always small. There was a tendency for the presence of non-erect leaves or branched spikes to reduce the optimal density, but large differences in tillering capacity had no influence. Differences in lodging susceptibility can however lead to substantial genotype x density interactions.

A comparison was made between an intensive system of lamb production based on Italian ryegrass RvP and one based on perennial ryegrass S. 24, over 2 years, each at three stocking rates (14, 17, 20 ewes/ha). More grass was grown in the first year than in the second when the yield of RvP was particularly reduced. The ewes and lambs ate more RvP than S. 24 but there was no difference in lamb growth rate. The lambs grew faster at the low stocking rate from 0 to 18 weeks and from 0 to slaughter than at the medium and high stocking rates, in both years. Ewe intake and lamb growth rate were higher in the second year than the first. The Masham ewes with two lambs ate significantly more grass per unit of body weight than the Finnish Landrace × Scottish Halfbred and Finnish Landrace × Scottish Blackface ewes, and their lambs grew significantly faster. It was concluded that for an intensive system of lamb production from grass, S. 24 was more suitable than RvP.

Examples of response surfaces for pairs of nutrients and results of 41 multi-level experiments with N only were used to compare the goodness-of-fit of polynomial, inverse polynomial, exponential and intersecting-straight-lines models.

Whereas no one model fitted best at every site, many results were well represented by two intersecting straight lines and on average, this model had the least residual mean square. Of 17 experiments with spring barley in south western England the few results best represented by smooth curves were from crops much affected by leaf diseases.

Fertilizer response was poorly represented by models without a falling asymptote, like the simple exponential and inverse linear. Study of residuals after fitting the quadratic showed that this widely used model consistently over-estimated both the amount of fertilizer needed for maximum yield and the yield loss when too much fertilizer was given.

When fitted to the mean yields of each nitrogen treatment, most models had residual mean squares equal to or less than the error mean square, repeating a result obtained at Rothamsted as early as 1927. We question the validity of some well-known evidence for block and treatment additivity.

For 12 experiments in 1970, between-site differences in the parameter values of the two straight lines representing grain yield were related to leaf area at ear emergence.

The effects of paraquat (l, 1'-dimethyl-4, 4'-dipyridylium dichloride or Gramoxone) and diquat (l,1'-ethylene-2, 2'-dipyridylium dichloride or Reglone) on inhibition of flowering and the effect of such an inhibition on improvement of cane yield and juice quality in late maturing sugarcane varieties Co. 853 (early-season flowering) and Co. 419 (mid-late season flowering) planted in February were studied under field conditions at Coimbatore (latitude 11° N). In Co. 419, the spray of paraquat @ 0·35 kg a.i./ha and diquat @ 0·45 kg a.i./ha (diluted in 3000 1 of water) in two equal doses at 3–4 day intervals during the 1st and 2nd week of August suppressed the flowering almost completely, while in Co. 853 flowering could not be checked successfully by chemical spray. Flowering in Co. 853 could be checked only when the spindle leaves were cut continuously from 15 July to 12 August at 4–5 day intervals. In Co. 419, cutting leaf spindles at any day between 1 August and 12 August prevented flowering totally.

The sprayed non-flowered crop of Co. 419 gave 13·84–15·69 t/ha more cane yield in February and 16·14–18·07 t/ha in April, whereas sugar yield increased by 1·16 t/ha in February and 3·56 t/ha in April compared with the control flowered crop. There was practically no difference in paraquat and diquat sprays. Suppression of flowering by defoliation in Co. 853 also increased the cane and sugar yield in and after February.