In experiments harvested in 1985 and 1986 the grain yields of 61 F1 hybrids among winter wheat varieties and advanced breeding lines were 5·9% greater than the yields of the best parents. In a trial with 430 hybrids in 1986, the hybrids yielded 3·6% more grain than the best parents. Among these 430 hybrids heterosis for yield was greatest for those from the lowest yielding parents. This result is taken to indicate that among these genotypes most genes for high yield have been fixed in the highest yielding parents.

The hybrids had slightly fewer ears/m2, but more grains per ear and heavier grains than the highest yielding parents. They yielded more straw as well as more grain.

The results are compared with those from other studies and it is concluded that yield advantage of F1 hybrids so far tested is not generally sufficient to justify their introduction into U.K. agriculture.

The frost hardiness of 5-month-old seedlings of 12 white clover cultivars was examined at – 4, – 8, – 12 and – 16°C and in a subsequent study the frost hardiness of 6-month-old seedlings of 190 experimental lines and 23 cultivars and ecotypes was determined at – 12°C. There were large differences among cultivars and lines in frost tolerance based on the percentage of plants damaged and the percentage of leaves killed. The most frost-hardy were the cultivars Podkowa and Undrom and ecotypes collected from Kaikoura and Nelson Lakes. There was no significant, correlation between the percentage germination of cultivars at 4 °C and their subsequent frost hardiness.

Large-leaved, erect cultivars tended to be more frost sensitive than small-leaved, prostrate cultivars. Frost-tolerant cultivars and lines tended to be acyanogenic. Selection for low winter growth did not increase frost tolerance. However, lines derived from crosses between genotypes of cold-hardy lines selected for rapid germination at 4 °C were more frost-hardy than lines from genotypes selected in a similar way that had been crossed with unselected Huia genotypes.

Experiments are described in which a range of seed beds was created in each of 5 years. The weather in these years produced wet, dry and capping seed-bed conditions. The time course of sugar-beet seedling emergence on each seed bed was recorded each year and the differences were considered in terms of soil physical characteristics: much of the year-to-year variation was accounted for by considering thermal time above 3 °C. The differences in emergence between seed beds were large only when conditions were dry, but in all years it was advantageous to level the seed bed in autumn or winter. Seed beds with a dense soil below the seed and fine aggregates above gave the most suitable conditions for rapid and successful emergence.

Ninety-six young rabbits (48 males, 48 females) each weighing 08 kg were offered one of six diets to appetite (n = 8 per treatment) or at one of four restricted feeding levels (n = 2 per treatment). All animals were culled at ca. 2 kg body weight and carcass analysis was carried out. Nutrient retention was estimated by the comparative slaughter technique.

Five of the experimental diets (A–E) were formulated to contain increasing concentrations of a poor-quality grassmeal (0, 100, 300, 500 and 700 g/kg, respectively), the remainder of the diet consisting predominantly of ground oats and soya-bean meal. A sixth diet (F) was based on a common laboratory rabbit diet (SGI). All diets contained similar digestible crude protein (DCP): digestible energy (DE) ratios of ca. 13·1 g DCP/MJ DE. Acid detergent fibre concentrations in diets A–F were 146, 158, 213, 264, 321 and 180 g/kg dry matter (D.M.), respectively.

When feeding to appetite, growth rates were depressed at the highest inclusions of grassmeal (diets D and E). Growth rates (GR) and voluntary food intakes (VFI) for diets A–F were: GR (g/day): 40, 41, 43, 36, 30 and 40; VFI (g D.M./day): 93, 103, 120, 137, 159 and 111, respectively. The depression in growth rate on diets D and E was associated with a reduction in total daily DCP and DE intake. The data suggested that, when the DE content of the diet falls below 10·5 MJ/kg D.M., the young rabbit is unable to compensate further by increasing daily VFI. Males grew significantly faster than females (40 cf. 37 g/day) and females had fatter carcasses at slaughter (301 cf. 274 g fat/kg carcass D.M.).

Relationships between daily N and energy intake and their retention in the body of the growing rabbit were calculated using data from both restricted and ad libitum-fed animals. Daily energy retention (ER, kJ) was related to daily DE intake (DEI, kJ) by the equation: ER = –227 + 6 x DEI (b ranged from 0·407 to 0·502, according to diet).

The estimated maintenance energy requirement of the growing rabbit ranged from 351 to 434 kJDE/kg0·75 per day and the average value across all diets was 377 kJ DE/kg0·75 per day.

Daily N retention (NR, g) was related to daily digestible nitrogen intake (DNI, g) by the equation: NR = –0·398 + 6 x DNI (b ranged from 0·589 to 0·667, according to diet).

The estimated N requirement for maintenance ranged between 0·464 and 0·525 g DN/kg0·75 per day and the average value across all diets was 0·497 g DN/kg0·75 per day.

The analysis of Kennedy et al. (1985) was applied to 150 individuals from each of six plots containing mixtures of the perennial ryegrass (Lolium perenne L.) cultivar Grasslands Nui and the resident ryegrass population at Rawhiti, Central Wairarapa, New Zealand. Four alleles (A, B, C and D) were identified at the phosphoglucoisomerase-2 allozyme locus in the two ryegrass populations. Using the maximum likelihood method, non-linear models were fitted to calculate the percentage contribution of Grasslands Nui to the mixtures. The contribution of Grasslands Nui to the six evaluation plots ranged from 5 to 44%, with S.E.S of 11–17%. The lowest contribution occurred under set stocking with sheep and a low fertilizer regime. The persistence of Grasslands Nui under contrasting grazing managements and fertilizer regimes in this dry environment, and aspects of enzyme electrophoresis application to field trials, are discussed.

Volatilization of ammonia from urea applied to rice on a soil of pH 9·3 was measured during 1982 and 1983 at Karnal. For three moisture regimes (continuous submergence, and irrigation 1 day and 4 days following subsidence of ponded water) mean ammonia losses varied from 28·2 to 31·8 kg N/ha. For urea applications between 40 and 120 kg N/ha, mean ammonia losses varied from 26.1 to 33.7 kg N/ha. Ammonia losses were highest on the second day following urea application and dropped to near zero 7–8 days after application.

In a field study at exchangeable sodium percentage (ESP) values of 11 and 32, subjecting a wheat (Triticum aestivum L.) crop to waterlogging for 1, 2, 4 and 6 days at the time of first irrigation (25-day-old plants), significantly reduced tillering and plant height, delayed ear emergence and resulted in 8, 17, 27 and 39% reduction in grain yield, respectively. Waterlogging decreased oxygen diffusion rate (ODR), restricted root growth and reduced ion uptake, especially of N, P, K., Ca, Mg and Zn, and led to higher absorption of Na, Fe and Mn. However, the effects of waterlogging were more pronounced at higher alkalinity values. The results indicated that, to ensure optimum wheat yield in alkaline soils, waterlogging must be avoided.

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.

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.

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.

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.

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.

Experiments were carried out in 1985 and 1986 on a sandy clay–loam to investigate the effects of above average rainfall in May and early June on the growth of the spring barley cv. Klaxon in three systems of cultivation. The cultivation treatments, ploughing (P), shallow-tine cultivation (S) and direct drilling (D), had been repeated on the same plots and cropped with spring barley each year since 1971.

A total of 112 mm water was applied to the waterlogged subplots in 1985 and 168 mm in 1986.

Compared with plots receiving the normal seasonal rainfall, extra water had no effect on shoot or grain yield in 1985 (mean grain yield 6·38 t/ha) and there were no significant differences between cultivation systems. In 1986, in contrast, water, in excess of normal rainfall, depressed both shoot growth and grain yield (mean grain yields 4·49 and 4·07 t/ha for the normal rainfall and the additional water treatments, respectively), the effect being greater on P than on either S or D.

In both years, saturation was achieved in the topsoil for a prolonged period during May and early June in the waterlogged subplots. In 1985 this was associated with a period of low oxygen flux and low redox potential, but this did nothave a significant effect on root or shoot growth. In 1986 there was no comparable period of reduced aeration, nor any significant differences in oxygen flux or redox potentials between water and cultivation treatments. In 1986, reduced growth and yield were directly associated with a mean reduction in N recovery by shoots of 36 kg N/ha, the effect being greatest on the ploughed plots where water was added. The results do not support the hypothesis that waterlogging per seaffects the growth of barley more on ploughed than on direct-drilled land.

In a field experiment on a typic hapludoll in 1983 and 1984, deep placement of urea supergranules at 40 and 80 kg N/ha proved to be the best N source, of five tested, for grain production, but at 120 kg N/ha it was similar to neem-cake-coated urea. The results showed that deep placement of urea supergranules can save fertilizer use by 60% compared with prilled urea to obtain the same yield. Shellac-coated urea and dicyandiamide-coated urea was more effective than prilled urea in 1984. Differences in dry-matter production and grain yield were directly related to N uptake by the plants. On average, apparent recovery of applied N increased from 35% for prilled urea to 55, 52·5,46·5 and 37·5% for urea supergranules, neem-cake-coated urea, shellac-coated urea and dicyandiamide-coated urea, respectively.