Maize was grown on the same Clay-with-Flints site at Rothamsted for 14 years (1974–87) in an experiment which tested cumulatively all combinations of three rates of N fertilizer (50, 100 and 150 kg N/ha) and six agrochemical treatments (aldicarb, benomyl, dazomet, phorate, benomyl + dazomet + phorate and none). Permethrin and pirimicarb were also tested in 3 of the years. The crop was grown for forage from 1975 to 1987 and for grain from 1974 to 1976. With 150 kg N/ha, the average forage yield was 10·5 t dry matter/ha and there was no overall decline during the experiment; annual yields ranged from 5·9 to 14·5 t/ha. From 1975 to 1983, yields were on average 0·2 t/ha less with 100 kg N/ha and 1·0 t/ha less with only 50 kg N/ha than with 150 kg N/ha. The crop grown for grain in 1974 failed but in 1975 it gave 3·5, 3·6 and 3·8 t/ha with 50, 100 and 150 kg N/ha, respectively, and 3·3 t/ha in 1976 with all N rates. The cultivars grown, Cargill Primeur 170, Caldera 535 and Fronica, matured too late to ensure a grain harvest at Rothamsted.

Pests observed on the crop included nematodes of the genera Pratylenchus, Tylenchorhynchus and Tylenchus/Ditylenchus and initially some Heterodera avenae, the aphids Metopolophium dirhodum and Sitobion avenae, and frit fly (Oscinella frit). Common smut (Ustilago maydis) was the only fungus disease recorded and Microdochium bolleyi, possibly a minor pathogen, occurred on roots. There was no overall increase in the incidence of pests and pathogens during the experiment. Agrochemical treatments increased yields in all years; the most effective was the combined treatment with benomyl + dazomet + phorate which gave on average 1·4 t/ha more forage than the untreated crop with the largest N rate.

Forage yields were generally larger with sowing in early May rather than later and maturity was earlier in years with the most accumulated day-degrees.

To study the effect of soil texture, aggregate size and initial moisture content on soil water diffusivity, D(θ), and unsaturated hydraulic conductivity, K(θ), horizontal absorption experiments were conducted on samples of loamy sand, sandy loam and clay–loam soils as well as on artificially prepared water-stable aggregates of a clay–loam sample (sizes 0.·25–0–25, 0·25–0·5, 0·5–1, 1–2, and 2–4 mm). For comparable moisture contents, D(θ) followed the order loamy sand > sandy loam > clay–loam. The effect of initial moisture content on D(θ) varied with soil texture. K(θ), which was evaluated using D(θ) for air-dry initial moisture content and the slopes of the water retention curves, also varied with soil texture.

The D(θ) function for air-dry initial moisture content increased with the decrease in aggregate size, the increase being more pronounced below a size of 1 mm. Values of D(θ) obtained from initially airdry soil and at 10% of saturation moisture content did not differ greatly from one another. The K(θ) function was almost the same for aggregate sizes 1–2 and 2–4 mm. In the size ranges of < 1 mm, K(θ) increased with the decrease in aggregate size. The particle/aggregate size range of 0·1–0·5 mm was the most conducive to unsaturated water flow.

In two trials the effect on D.M. intake of applying flavouring agents to grass silage at feeding time was examined using a total of 89 British Friesian cows in mid to late lactation. The flavouring agent used in Expt 1 was Simax 100 (5 ml/cow per day), while in Expt 2 Palatol (20 ml/cow per day), molasses (0·7 kg D.M./cow per day) and molasses + Talin (0·7 kg D.M./cow per day) were added to both lowand high-quality grass silage.

Both Simax (significantly) and Palatol increased silage D.M. intake by an average 0·67 kg/day. The total D.M. intake of the cows fed the molasses and molasses + Talin was similar to that obtained by those receiving the silage treated with Simax and Palatol. However, in the case of the cows receiving the molasses and molasses + Talin, the increased D.M. intake was obtained mainly from the additional molasses and not by an increased silage intake. This result indicates a very low substitution rate for molasses.

Although D.M. intake was increased by the addition of flavouring agents, milk production remained unaltered because of the relatively late stage of lactation of the cows in both trials.

Statistically sound methods for analysing the results of germination tests were used to quantify and assess differences between seed lots of perennial ryegrass (Lolium perenne L.) subjected to accelerated ageing. Ageing altered not only the proportion of seed not germinating but also the mean germination time and the synchrony of germination. Seed lots differed in these three parameters before and after ageing. The responses to ageing of mean germination time and synchrony were not regular and a simulation of trie possible effects of ageing on germination suggested this irregularity might be due to changes in the proportion of viable seeds and to a non-normal distribution of seed ages.

In field experiments in 1983–85 in Northumberland, UK, early sowings achieved a leaf area index (LAI) of 3·5, capable of intercepting 90–95% total incident solar radiation, earlier than late sowings. As there was a close relationship between total dry weight, bud dry weight and amount of intercepted solar radiation, early sowings invariably outyielded later ones. The efficiency of energy conversion of radiation was 1·28, 2·05 and 2·11 g/MJ for total dry weight and 0·97, 0·83 and 0·67 g/MJ for bud dry weight in 1983, 1984 and 1985, respectively. Harvest index ranged from ca. 25% in 1985 to 40% in 1984.

Increasing plant density from 2·22 to 6·66 plants/m2 advanced and increased maximum LAI and total and bud dry weight per m2 but had an adverse effect on distribution of dry matter. Maximum total dry weights were achieved at or slightly after maximum LAI. The onset of rapid bud growth coincided with maximum total standing dry weight and was advanced by early sowing but largely unaffected by plant density.

Early-sown crops produced more buds than late-sown ones because of a longer growing season. Plant density had a large effect on the number of buds per m2, which was almost directly proportional as the number of buds per plant was not severely affected. However, individual bud size was restricted as a result of competition for assimilates. Approximately 80% of buds finally recorded had been produced before significant bud growth had occurred.

Total bud fresh yields averaged over all sowing dates reached 17 t/ha in 1983 and 31 t/ha in 1984. The lower yield in 1983 was the result of late sowing caused by unfavourable weather. Early sowings significantly outyielded late ones because of earlier onset of rapid bud growth which gave a longer growing period. The effect of plant density on total sprout yield was less pronounced than that of sowing date but effects on yield per plant were large.

Yields of buds in the freezing grade (20–30 mm) increased rapidly between late September and early to mid-November in both 1983 and 1984 and reached 7·5 and 8·8 t/ha, respectively. The difference between freezing-grade yields in the two years (1·3 t/ha) was much less than the difference between total yields (14 t/ha). Late sowing in 1983 restricted bud growth resulting in a higher proportion in the freezing grade. Plant density had a greater effect on freezing-grade yield than on total yield. Low planting densities gave high yields of small buds at early harvests but denser planting gave higher yields at later harvests. Generally, increases in bud fresh weight over the harvest period were greater than those in bud dry weight because of water uptake. The average dry matter content of buds declined by 2–5 % from October to January.

The experiments confirmed that manipulation of sowing date and planting density is an effective way of spreading harvest date throughout the season in order to achieve an orderly sequence of crops for the fresh market and for processing.

Ammonia (NH3)-N fluxes from three swards, grazed by cattle and with different N managements, were measured using the mass balance micrometeorological method after a 7-day grazing period in the spring of 2 years. At the same time the impact of the sward managements on N returns in dung and urine was examined in housed animals and the effects of the changes in excreted returns on NH3-N losses examined. The treatments were ryegrass swards receiving either 420 or 210 kg N/ha per year, and a mixed ryegrass/white clover sward receiving no mineral N. There was little difference in the faecal N returns between treatments but there were differences in the N returned in urine, thus 74, 60 and 56% of the excreted returns from 420 N, 210 N or grass/clover treatments, respectively, were in urine. The fluxes of NH3-N from the grazed swards were greatest whilst the animals were present and there were large differences between treatments, the ratio of total NH3 losses from 420 N grass to those from 210 N grass and grass/lover being 7·8:1. The NH3-N losses were equivalent (i) to 12,5 and 7 % of the urinary N returns to 420 N, 210 N grass and grass/clover swards, or alternatively (ii) to 9 and 3% of the fertilizer addition to 420 and 210 N swards and 3% of the estimated rate of N2 fixation in the grass/clover sward. Throughout the investigation there was little difference between the effects with the 210 N grass swards and those with grass/clover.

This paper presents a series of 20 two-replicate row-and-column designs for field trials comparing between 25 and 100 varieties on small plots.

The in sacco, in vitro and in vivo effects of feeding proteins partially coated with calcium soaps of longchain fatty acids were examined.

In sacco, 84–90% of whey powder and soya-bean meal coated with calcium salts of fatty acids remained after 20 h incubation in the rumen of sheep. In vitro tests revealed no effects on volatile fatty acid or ammonia production.

In vivo sheep balance studies, where soya-bean meal coated with calcium soaps was substituted for soya-bean meal, showed no effects on ammonia or volatile fatty acid production in the rumen due to the calcium soap coated proteins. No changes were observed in digestibilities of dry matter, nitrogen or acid detergent fibre; total fatty acid digestion increased. Nitrogen balance was improved slightly in sheep fed the protected protein.

It appears that proteins coated with calcium soaps are not degraded in the rumen and thus energy and non-degradable protein can be supplied to ruminants by this route.

The mineralogy of the clay fraction (<2 μm) of nine soil samples representing three physiographic positions of a toposequence in Ochon, south-eastern Nigeria, was determined by transmission electron microscopy and X-ray diffraction.

Soils in the crest and middle slopes (pedons TE1 and TE2, respectively) of the toposequence, formed over fine-grained sandstone, were coarse-textured, well-drained and acidic and had low effective cation exchange capacity and percentage base saturation. Kaolinite, mica, quartz, goethite and gibbsite were the principal minerals identified in the clay fraction of these soils. Soils in the valley bottom (pedon TE3) formed over arenaceous shale were, on the other hand, fine-textured, poorly drained and weakly acidic with higher cation exchange capacity and percentage base saturation. Their clay fraction mineralogy was similar to that of the well-drained upland soils but additionally included feldspar and smectite/vermiculite mixed layer minerals.

Mixed cropping of yam, cassava, maize and other annuals under traditional methods was carried out on the drier, well-drained crest and upper slopes while sole cropping of lowland rice occurred in the poorly drained, more fertile valley-bottom site. The valley-bottom soils show greater potential for improvement in agricultural productivity under good management than the upland soils.

The mechanisms by which phosphorus homoeostasis is achieved in growing calves in response to changes in P supply ranging from deficient to excess were investigated in three studies in which additional P was given in the diet, infused into the abomasum, or infused directly into the blood.

Whereas the rate of P absorption was directly related to P supplied, the efficiency of absorption of P differed according to the supply. Thus, the absorption efficiency was low from the P-deficient basal diets, increased with P supplementation until the supply was sufficient to meet requirements and then decreased at higher rates of P supply, possibly as a result of homoeostatic control.

The serum P concentration, which was directly related to the rate of P absorption, appeared to determine the rates of P retention, salivary P secretion and urinary P excretion. Urinary P excretion was negligible at P intakes below those needed to supply requirements, and any additional P absorbed was partitioned between retention and salivary P secretion in the ratio 0–88:1, these two processes continuing to have equal priority for absorbed P until retention reached a maximum, approximately equal to the postulated growth requirement. Only when the growth requirement for P had been met, did urinary P excretion occur, increasing progressively as the serum P concentration exceeded the renal threshold.

The endogenous faecal loss of P increased in direct relation to salivary P secretion and hence to the rate of P supply, the increase occurring even in P-deficient animals. This finding supports the claim that the inevitable endogenous faecal loss of P is not maintained at the constant rate expected at zero P intake until all requirements are met, as assumed by the Agricultural Research Council (1980) in their calculations of P requirements, but varies in direct relation to the P intake needed to supply a particular requirement. Indeed, these results suggest that the ARC (1980) recommendations for P, particularly for growing animals, are too low.

Finally, these studies show that bone resorption, salivary P secretion, P absorption and urinary P excretion all play a part in P homoeostasis in the growing ruminating calf, and that the relative importance of each of these processes depends upon the P status of the calf.

The effects of irrigation, nitrogen fertilizer, cutting three or six times per year and a combined pesticide treatment that included aldicarb, phorate, benomyl and methiocarb on ryegrass (Lolium perenne) cv. S.23, either alone or in mixtures with white clover (Trifolium repens) cvs S.I00 or Blanca, and on lucerne (Medicago sativa) cv. Vertus grown on a silty clay–loam at Rothamsted and a sandy loam at Woburn were studied in 1977–81.

Benefits from irrigation were greater for six-cut than three-cut swards, with pesticides than without, for ryegrass with clover S. 100 than ryegrass with Blanca and at Woburnthan at Rothamsted. Lucerne did not benefit.

Responses of ryegrass to fertilizer N were best fitted by the model y = a + b/1+cx+dx2; and those of ryegrass–clover by the model y = a+bx (where y = yield, x = amount of N; a, b, c and d are constants). Without N, yields of ryegrass–Blanca clover mixtures considerably exceeded those of ryegrass–S.100. The former gave yields equivalent to those of ryegrass given 270 kg N/ha at Rothamsted and 330 kg N/ha at Woburn.

Lucerne without irrigation, N or pesticides gave yields in excess of all other unirrigated crops, even when these received pesticides and maximum N. Yields from three cuts of ryegrass greatly exceeded those from six cuts but yields of ryegrass–Blanca were greater from the six-cut regime.

Pesticides substantially improved the yields of ryegrass and clover, whether grown separately or mixed, but not those of lucerne. Pesticides not only controlled pests and diseases but also increased the incidence of vesicular–arbuscular mycorrhizas. The relative magnitude of yields of the different swards at the two sites differed, depending on treatment with irrigation, N fertilizer and pesticides. Differences between sites were removed or reversed by appropriate combinations of treatments.

Ryegrass–Blanca given no N fertilizer and cut six times removed 300 kg N/ha, an amount that was increased by irrigation and decreased by less frequent cutting; ryegrass–S.100 clover contained less N. Removals of P and K. often exceeded 35 and 300 kg/ha, respectively, each year. Herbage containing Blanca clover had much more Ca than that containing S.100 but at comparable yields all swards contained similar amounts of Mg.

Five experiments in harvest years 1980–2 tested the effects of straw inoculum and fungicides on leaf blotch (Rhynchosporium secalis), growth and yield of winter barley. Inoculating plots with rhynchosporium-infected straw increased the rate of disease development and greatly decreased seedling growth but inoculating plots with wheat straw or sterilized barley straw had no effect. In 1982, plots inoculated with infected straw gave less grain than uninoculated plots, but in all years fungicide sprays applied in winter or early spring had mostly small effects on grain yield that were only poorly related to their effects on leaf blotch and seedling growth.

Yields from lucerne cultivars grown on land infested with Verticillium albo-atrum, a cause of wilt disease, were studied over the period 1969–77. Field experiments established in 1969, 1971, 1972 and 1973 were maintained for periods of 4–6 years. Reactions by cvs Europe and Vertus were of principal interest. Europe is considered to be moderately susceptible, initially producing yields exceeding those of resistant types on uninfested land. In comparison cv. Vertus has considerable resistance derived from a polygenic system. In the first 2 cropping years on infested land, Europe yielded similarly to Vertus with only slight symptom expression. In year 3, Europe maintained comparable yields to Vertus but with increasing disease expression. During succeeding years Europe was badly affected by discase and yields were below those achieved by Vertus. Data from other cultivars indicated a positive correlation between symptoms in years 4 and 5, a negative correlation between dry-matter yield in year 5 and symptom severity in year 4, and a negative correlation between symptom severity and yield in year 5. Symptom expression and pathogen build-up appear to occur at similar rates in the latter years of a lucerne crop. Disease development in one season has a considerable effect on future productivity. These findings are discussed in terms of the primary (extra-vascular) and secondary (intra-vascular) determinants of resistance to wilt pathogens. It is suggested that the apparent moderate susceptibility of cv. Europe in seasons two and three relates to a rapid growth rate.

Characterization of accessions of Lolium perenne collected in Romania, using naturally hardened tillers in an artificial freezing test, is described. Accessions showed contrasting hardening response to variation in the winter environment at Aberystwyth. Cold tolerance of the accessions, measured as lethal temperature for 50% of the tillers (LT50), was positively correlated with the mean temperature of the coldest month at the sites of origin and with persistence in swards after three winters. Superior populations were identified within this collection and are being used as a source of winter hardiness in a breeding programme.

The role of temperature and irradiance in the contrasting hardening responses of three accessions was investigated in controlled-environment studies with seedlings.

The advantages of environmental simulation techniques for characterization of genetic resources are discussed.

Experiments of balanced design in harvest years 1981 and 1982 were used to measure interactions between plots of winter barley with different amounts of leaf blotch, caused by the splash-dispersed pathogen Rhynchosporium secalis. On the appropriate transform scales (logarithms of counts and logits of percentages), the effects of extreme treatments on neighbouring plots were up to 30% of the effects of the same treatments on the plots to which they were applied. Powdery mildew (Erysiphe graminis f.sp. hordei) was commonly least severe in plots with most leaf blotch except soon after fungicide sprays had been applied which, although chosen to decrease leaf blotch, also had short-lived effects on mildew. Consequently, contrasts in mildew between differently treated plots changed sign during the season. The effects of the same treatments on neighbouring plots similarly changed with time but not necessarily in phase with their direct effects. Analyses of the rhynchosporium data that recognized the effects of neighbouring treatments typically had much smaller residual mean squares than analyses that ignored neighbour effects but assumed randomized block designs.

Treatments had mostly small effects on grain yield but these data from two of the experiments showed marked positional variation. Individual plots yields from one of these experiments, testing five treatments, are quoted in the appendix so that they are available to others with an interest in alternative methods, such as nearest-neighbour models, to adjust for local correlations between plots.

Rates of intake of herbage and grazing time of beef cattle are essential components of simulation models of grassland agroecosystems. We studied the effects of herbage allowance on rates of intake and ingestive behaviour of twelve 2-year-old Angus heifers (Bos taurus)(364 ± 12 kg) grazing pastures of tall fescue (Festuca arundinacea Schreb.). A balanced change-over design and a novel tethering technique were used to estimate direct, residual and permanent effects of three herbage allowances on intake per bite, rate of biting and rate of intake. Herbage dry matter (D.M.) allowances, which were established by varying tether lengths, were 5, 9 and 13 kg (1·4, 2·5 and 3·6 kg/100 kg of live weight) and made available in circular plots of 15, 27 and 38 m2, respectively, for a single measured 2 h grazing session each day. Heifers grazing Kenhy tall fescue swards, composed of vegetative tillers and free from the endophyte Acremonium coenophialum, with herbage D.M. masses (> 5 cm) of 2000 kg/ha and D.M. allowances of 9 and 13 kg/2 h per heifer, ingested D.M. at 1·9 kg/h by taking bites averaging 800 mg D.M. at 38 bites/min. Allowances of 5 kg/2 h per heifer slowed the rate of intake to 1·3 kg/h by limiting D.M. intake per bite to 654 mg and biting rate to 35/min. Rate of D.M. intake of cattle grazing vegetative temperate grass swards appears to be ca. 0.5% of live weight per hour when allowance and availability of herbage are not limiting.

The effect of a pharmacological dose of testosterone propionate, administered by intramuscular injection, on feed intake, live-weight change and fasting metabolism of steers was determined in two experiments. The first consisted of three growth phases: normal weight-gain on a long-chopped lucerne (Medicago sativa) hay diet ad libitum (8 weeks), live-weight loss on a low-quality pasture (Dichanthium aristatum) hay diet ad libitum (12 weeks) and recovery gain on a lucerne hay diet ad libitum (8 weeks). During normal weight-gain, the testosterone-treated steers had significantly (P < 0·01) higher weight gains than untreated steers (1·48 v. 0·95 kg/day, respectively). Feed intakes and fasting metabolic rates of treated and control steers were not significantly different, being 28·2 and 29·1 g dry matter/kg live weight and 85·6 and 91·0 KJ/kg per day, respectively. The efficiency of feed conversion was significantly (P < 0·01) better in the treated steers (6·7 v. 9·6 feed/kg weight-gain). There was no significant effect of treatment on any of these characters during live-weight loss or recovery gain. The weight changes during these periods were ca. –0·7 kg/day and 1·5 kg/day, respectively. After 12 weeks of severe weight loss, metabolic rate per unit live weight had decreased by 25% compared with that at the start of the weight-loss period.

The second experiment examined the effect of the same dose of intramuscular testosterone propionate on another group of steers fed the low-quality roughage diet during a period of weight loss. Again there was no significant effect of treatment on weight loss, feed intake or fasting metabolism.

It was concluded that the growth response to pharmacological doses of testosterone in well nourished steers was greater than that usually observed in comparisons between bulls and steers, and that testosterone was ineffective when administered to steers losing weight or in recovery gain after severe weight loss.

An experiment in which all combinations of four rates of N fertilizer soon after sowing, four in early spring and nine in late spring were applied to the same plots of winter wheat for 6 years is described and the effects discussed.

It was found that although the yield varied considerably from year to year the regime leading to greatest yield was fairly consistent. If the farmer had used the regime which gave the greatest average yield (0, 90, 180 kg N/ha in autumn, early spring and late spring, respectively) he would have averaged only 0·12 t/ha less than the maximum attainable each year.

Application of N increased protein concentration in the grain more or less linearly but the latest application increased it most. Since the regime which gave greatest yield on average produced grain which qualified for bread-making premium from the protein point of view in all years except 1981, adopting the regime which gave maximum yield would reduce the potential maximum gross margin by only £30/ha.

Analysis of the soil showed a reduction in pH down to 15 cm and of available P2O5 down to 10 cm.

The effects of different severities of continuous grazing imposed during the spring, followed by a uniform continuous grazing management from mid-summer onwards, were examined in relation to changes in tiller demography and leaf growth of perennial ryegrass (Lolium perenne). Two grazing severities were imposed, based upon maintaining a constant sward height of either 35 mm (severe) or 75 mm (lenient). From 1 June onwards, a uniform grazing pressure with a sward height of 60 mm was imposed.

Differences in the age class structure of the tiller populations developed during the spring between the two grazing treatments, principally through the suppression of daughter tiller development under the more lenient grazing. The demographic differences between the treatments were further increased during the remainder of the grazing season, under the common grazing management, largely because of the greater production of secondary daughter tillers in the sward which had been leniently grazed. The demographic differences between the swards had little effect on net pasture production during the treatment season, with lamina growth rates being virtually unaffected across a wide range of steadystate, continuous-grazing pressures. However, longer-term effects on pasture development, due to the demographic differences between the swards, did appear in the following season; the more severe grazing pressure treatment resulted in earlier inflorescence development in the subsequent season.

In field experiments, infections by okra mosaic virus (OMV) and okra leaf curl virus (OLCV) reduced trie growth of okra more than when the plants were infected singly by either virus. The critical growth component responsible for low performance was leaf area in OLCV-infected plants and chlorophyll content in OMV-infected plants. However, the two viruses had a synergistic effect in mixed infection.

Expressed as percentage yield loss, mixed infections significantly reduced edible fresh fruit weight more than single infections in all okra cultivars. In single infections, OLCV caused higher yield loss than OMV. Since both viruses cause more damage in mixed infections, it may be preferable to breed for combined resistance, particularly if the genes for resistance are linked.