Oestrone sulphate, progesterone, total protein, Na and K concentrations in mammary secretions of Friesland sheep have been determined from 11 days before until 8 days after parturition. Mammary secretions were obtained on most days for at least 1 week before parturition in 9 of 14 ewes, and in all animals after lambing. Oestrone sulphate concentration had doubled on the morning of parturition compared with the value 24 h earlier, and this sharp rise was a useful indicator that delivery was imminent. Values continued to rise during the day of delivery, remained high for a further 24 h and then declined over the next 2 days. Progesterone, in contrast, decreased linearly between day –2 and day +2 when it reached baseline values.

Total protein concentration in pre-colostral and colostral mammary secretion (10–15 g/100 ml) was higher than that in goats, and decreased to a mean value of about 6 g/100 ml by day +8 after delivery. Na declined from about 55 mM on day –10 to 36 mM on day 0, whereas K increased from 20 to 29 mM. There was a sharp rise in K/Na, but this occurred after rather than before parturition and was not a useful predictor of parturition.

The onset of copious milk secretion occurred when oestrone sulphate in mammary secretions was high and progesterone was low, which is consistent with the hypothesis that the cessation of progesterone secretion is an important regulator of the onset of lactogenesis in sheep. Efficiency of milk secretion in the first 14 days of lactation was correlated, however, with the maximum oestrone sulphate concentration in colostrum on the day of parturition.

The adequacy of the Agricultural Research Council (1980) recommendations for phosphorus for pregnancy and lactation has been investigated in ewes given a plentiful supply of dietary calcium.

The efficiency of absorption of P remained high and fairly constant throughout the whole experimental period and the rate of P absorption varied in direct relation to the P intake.

The endogenous faecal loss of P also varied with P intake and at all stages of pregnancy and lactation was higher than the value assumed by the Agricultural Research Council (1980) in their calculations of P requirements.

Bone mineral stores of Ca and P were lost in the normal way during late pregnancy and early lactation but were not replaced, as normal, in mid- to late lactation. At the end of the lactation, ewes were still in deficit of 125 g P and 100 g Ca.

It is argued that the Agricultural Research Council (1980) recommendations for P, particularly in mid- to late lactation, are too low and it is recommended that future calculations of requirements for pregnancy and lactation allow for the inevitable loss and subsequent replacement of skeletal mineral stores and also for the increased endogenous faecal losses of P that appear inevitable at the high P intakes needed to meet the increased demands.

Field experiments were conducted in a zinc-deficient flood plain alluvial soil to study the effect of amounts, methods and sources of zinc application on the yield and uptake of zinc by wheat. Zinc was applied at 0, 5 and 10 kg Zn/ha as zinc sulphate and zinc oxide either broadcast and mixed in the soil or drilled below the seed. Spray application of zinc was also tested. Irrespective of the source, grain yield and zinc uptake significantly increased up to 10 kg Zn/ha. Soil-applied zinc was highly correlated with yield and zinc uptake in the two field experiments. Grain yield was also found to be significantly correlated with zinc content of grain (r = 0·78), straw (r = 0·72) and flag leaf (r = 0·66). When applied at the rate of 10 kg Zn/ha, broadcasting of zinc sulphate and drilling of ZnO below the seed were equally effective in increasing grain yield of wheat. Foliar spray of zinc sulphate was an effective emergency method, but in highly zinc-deficient soils it did not compare well with soil application of zinc.

The variability revealed in a half-diallel cross between nine diverse genotypes of winged bean (Psophocarpus tetragonolobus (L.) D.C.) in regard to yield and yield components was studied in the F1 generation. The results indicated that high genetic variability existed for all traits. With respect to seed size, general combining ability effects alone were adequate to predict the performance of hybrids. For numbers of pods per plant and seeds per pod, both general and specific combining ability effects were of equal importance, while the performance of hybrids for grain yield was mainly dependent on specific combining ability effects. Heterosis was clearly evident for number of seeds per pod and grain yield. Of the yield components, number of pods per plant exhibited a positive genotypic association of appreciable magnitude with grain yield, showing its usefulness as an indicator of yield in selection.

Triple test cross progenies arising from F2 of three crosses, namely, C164 x EB1556 BG25 x NP21 and BH15 x RD103, were used for investigating their interactions with macro- and micro-environments for number of days to heading, plant height, number of tillers per plant, ear length, number of grains per ear, 100-grain weight and yield per plant in barley. The analysis indicated, in general, that the additive component of genetic variance was more sensitive to macro-environment than non-additive components. In order to have a more precise estimate of this component, an experiment repeated over a larger number of locations and years would be desirable. The ‘j and l’type of epistasis showed sensitivity equal to the dominance components in response to the change of soil conditions. Covariances between family means and variances were used to detect the interactions of genetic components with the micro-environmental differences. The additive and the dominance components showed sensitivity to microenvironmental changes and were not differentially affected by the adverse soil condition compared with normal soil. The additive gene effects were relatively more sensitive, indicating the probable superiority of heterozygotes over the corresponding homozygotes with regard to stability.

Amongst the three populations, the population resulting from BH15 x RD103 was found to be most sensitive. Although the genotype x environment interaction for a character was population-specific, number of grains per ear and yield per plant were invariably the most sensitive.

Root and shoot growth and nutrient uptake have been monitored for several winter wheat crops which gave a mean grain yield of 9·5 t/ha (85% D.M.) when grown on three soil types in 1980 and 1981. Averaged over all crops, maximum growth rates were 170 kg/ha/day for shoots and 14 kg/ha/day for roots; maximum nutrient uptake rates for N, P, K, Ca and Mg were 2·75, 0·47, 341, 0·60 and 0·18 kg/ha/day respectively. Maximum uptake of K and Ca occurred at anthesis with values of 239 and 38 kg/ha respectively, whilst for the other nutrients maximum uptake was at final harvest with values of 200, 39 and 14 kg/ha for N, P and Mg respectively. The grain contained 141 kg N, 27 kg P, 41 kg K, 3·2 kg Ca and 7·1 kg Mg/ha.

The quantity of nutrients arriving at root surfaces by mass flow was calculated for one of the crops from measurements of soil solution concentration and potential evapotranspiration data. The potential supply of nutrients by mass flow, as a percentage of that actually taken up between 19 March and 29 June, was 25% for N, 4% for K, 800% for Ca and 32% for Mg.

Manganese-tolerant strains Mnr-1 and Mnr-5 of Azospirillum brasilense (RAU 1075) were isolated through step-wise transfer to higher levels of manganese chloride. One of the strains (Mnr-5) showed more growth at low pH and greater nitrogenase activity in 10 mM MnCl2. 4H2O than parental and Mnr-1 strains. These tolerant strains also showed cross-resistance to antibiotics such as gentamycin and neomycin but not to streptomycin. Mn-adapted strains also tolerated elevated levels of aluminium (2·5–3·5 mg/kg) and the stability of the Mn-resistance required the presence of Mn2+ ions in the growth medium. It has been demonstrated that the effect of inoculation with Mn-adapted strains was variable with different genotypes of rice in acid soil and that initial low level of nitrogen was essential for maximum associative N2-fixation.

Chaffed lucerne hay was fed to wether sheep at two feeding frequencies (once a day (daily) and once an hour (hourly)) and at two levels of dry matter (D.M.) intake (700 (L) and 1020 (H) g/day). Sheep fed daily were slaughtered either prior to eating, immediately after eating ceased or 10 h after eating ceased to compare rumen, reticulum, omasum and abomasum pool sizes and particle size distributions within pools.

Effects of level of intake, feeding frequency and time after feeding were confined mainly to the rumen which contained 77–91% of stomach D.M. Once-daily feeding resulted in a 2·6 fold variation in rumen D.M. pool size. Sheep fed hourly had a relatively small rumen and comparatively large reticulum D.M. pool. Diurnal changes in reticulo-rumen particle size pools are discussed in relation to the effectiveness of chewing.

Particle size distribution in digesta was estimated by wet sieving. On average the proportion of D.M. retained on a sieve 1 mm or larger comprised 35, 28, 4 and 4% of D.M. in the rumen, reticulum, omasum and abomasum, respectively, D.M. passing a 0·25 mm sieve comprised 40, 46, 57 and 61% of D.M. in the respective organs.

The reticulum usually contained significantly less D.M. retained on a 4 mm sieve than the rumen, and reticulum D.M. percentage was usually 3–5 units lower than rumen D.M. percentage. Reticulum digesta composition is discussed in relation to the efflux of particulate D.M. to the omasum.

Chemical composition of rumen particulate D.M. retained on sieves > 0·25 mm was comparatively unaffected by intake level and feeding frequency. Analyses of particle composition showed a rapid loss of non cell wall constituents after feeding and an increasing contribution of rumination toward particle size reduction.

Nutrient inflows, that is the amount of nutrient absorbed per unit root length per unit time, have been determined for several winter wheat crops (cv. Hustler) with grain yields in the range 8–11 t/ha (85% D.m.). Inflows reached a maximum in April or May with values in the range 13–34, 0·5–1·6, 3·5–13, 0·9–1·8 and 0·35–0·60 × 10–14 mol/cm root/sec for N, P, K, Ca and Mg respectively. The concentration in the soil solution necessary to maintain inflows by diffusion of nutrient through the soil was calculated using a nutrient uptake model. For an October-sown crop the model predicted that soil solution concentrations of 165 μΜ N, 14 μΜ P and 56 μΜ K were needed to sustain the observed maximum inflows, whereas for a September-sown crop, with a larger root system, even lower values of 106 μΜ N, 8 μΜ P and 36 μΜ K were needed. It appears that nutrient transport is unlikely to limit uptake by winter wheat crops growing in moist, well fertilized soils, at least for crops up to about 17 t/ha of total dry matter.

Experiments on winter wheat were made from 1980 to 1982 to test fungicide and aphicide sprays in factorial combination with four amounts of nitrogen fertilizer, applied in either one or two dressings in spring. The wheat was grown on three farms with contrasting calcareous clay soils from three soil series; each year it followed a 2-year break on one farm, a cereal rotation on the second and continuous wheat on the third. Soils were sampled to a depth of 0·9 m at seedling emergence in autumn, and again in February and April, to determine the NO3-N and NH4-N in each 0·3 m horizon. Crops were sampled for growth analysis at monthly intervals from March onwards and analysed for nitrogen content. Measurements of stem sap NO3-N concentration were also made at 2-weekly intervals from February or March to late June.

Measurements of soil mineral N were used to calculate the fertilizer nitrogen dressings used in the experiments. The concentration of NO3-N in the stem sap was related to NO3-N in soil; concentiations remained high until most of the soil NO3-N had been removed by the crop. The time at which stem sap NO3-N concentration declined therefore acted as an index of soil N supply, and the data showed that fertilizer-N was needed when the NO3-N concentration fell below a 200 μg/ml threshold. Yields benefited from N applied in February or March only when stem sap NO3-N concentration fell below the threshold at this time.

Apparent fertilizer nitrogen efficiency exceeded 70 % where yields were very large, but ranged between 53 and 64% where yields were smaller because either soil physical problems or disease restraints were present.

A severe attack by take-all (Gaeumannomyces cerealis) caused premature senescence at one centre in 1980; this apparently prevented previously assimilated nitrogen from moving into the grain.

Four factorial experiments made in 1982 and 1983 tested the effect of 10 t CaCO3/ha, applied either in autumn 1981 or spring 1982, on the response of established grassland to 360 kg N/ha per year applied either as ammonium sulphate, calcium nitrate, urea or a mixture of ammonium nitrate and calcium carbonate.

Lime did not increase yield in the short term. It also reduced herbage Mn and, to a lesser extent, herbage N, P and Mg. The mixture of ammonium nitrate and calcium carbonate gave about 0·5 t D.M./ha per year more herbage than did the other forms of N.

Lime had no effect on the recovery in the herbage of N from calcium nitrate, but it reduced N recovery from the other three fertilizers in 1982, and from urea also in 1983. Soil pH, which initially ranged from 4·9 to 5·7 at the four sites, was raised by lime to almost 7·0 in the top 5 cm soil. This pH is probably not high enough to cause serious losses due to NH3-volatilization.

Application of fertilizer prone to loss from NH3-volatilization is not recommended soon after liming. However, the practice is not likely to cause detectable yield loss in established grassland in Northern Ireland.

Autumn-calving cows on a complete diet system were given a similar amount of concentrates over two winter periods in the years 1980–1 and 1981–2. Two feed allocation systems were examined: step (different diets given at different stages of lactation) and uniform (one single diet given over all the winter period).

The yield of fat-corrected milk (FCM) was similar (P > 0·05) in both systems with 5·32 and 5·37 t/cow for the step and uniform system respectively in the 1st year and 4·75 and 4·35 t/cow in the 2nd year.

There is an indication that adult cows or cows with a higher potential for yield can respond to the higher energy concentration diet given in early lactation but with the main effect on milk, not in FCM yield.

No effect of diet distribution was found on overall weight gain but cows given the uniform system lost less weight in early lactation and this may lead to better conception for cows in such a system.

In 1980 a field of winter wheat at Little Raveley, Cambridgeshire (U.K.) suffered a bad attack of take-all, which was confined mainly to areas dominated by Ragdale series, one of five soil types on the field. Take-all and yield were assessed on experimental areas within the field in the three subsequent years (1981–3). On a strip 50 m wide, which was sown with wheat in each of these years, take-all was in decline and although slight differences in take-all occurred between some of the soil types, they had no effect on grain yield. Following a break crop of beans in 1981, the remainder of the field carried wheat in 1982 and 1983. Here take-all was generally less and yields generally greater in the area that suffered the 1980 attack, probably because it had developed a natural partial immunity to the disease. However, measurements of takeall in relation to soil characteristics on 1 m2 plots suggested that the disease was becoming more prevalent on soils that are less well drained in winter, are more deeply decalcified, and contain less extractable phosphorus or more exchangeable potassium.

Poaching damage to a new grass ley was measured over a period of time using a surface profile meter. Individual profiles obtained on different drainage treatments in the ley showed little change over 3 years of measurements. Poaching could be denned visually as a depression greater than 4 cm depth on this site. Degree of poaching was adequately described by the standard deviation of the soil surface. Typically, standard deviations along a poached, undrained transect were twice those of an unpoached, drained one. In this experiment drainage with pipes alone at 12 m spacing controlled poaching as well as mole drainage at 2 m with pipes at 40 m spacing even though watertable levels were usually not lower than those of the undrained control.

In 1976–7, 1977–8 and 1978–9 plots of winter-sown field beans, either irrigated in June and July or unirrigated, were treated with one or more sprays of benomyl or were untreated. The amounts of chocolate spot on field bean leaves and flowers were increased by irrigation and decreased by benomyl in all seasons. These effects were greater in 1977 and 1978, when there was respectively 76·5 and 82·4 mm rainfall in June, than in 1979, when there was 30 mm rainfall in June and less chocolate spot developed. Leaves half-way up stems of plants in irrigated, unsprayed plots had 11% of their area affected in July 1977, 17% affected in July 1978, but only 4% affected in August 1979. By contrast, middle leaves of plants in unirrigated, sprayed plots had 3, 4 and 0·3% of their leaves affected in 1977, 1978 and 1979 respectively. Irrigation increased the number of pods per stem in 1977 and 1979 and decreased it in 1978; it decreased grain yield in 1977 and 1978, but increased yield in 1979. Benomyl treatments affected the number of pods little in any year; they increased yield in 1977 and and 1978, but not in 1979.

Prilled urea, with or without a nitrification inhibitor (dicyandiamide, DCD) or urease inhibitor (hydroquinone), was compared with ‘Nitro-Chalk’ as a nitrogen fertilizer for winter oil-seed rape in field experiments on a clay loam soil at Rothamsted in 1984 and 1985. Each was tested when supplying 50 kg N/ha to the seed bed; each was also broadcast in early spring to supply 150 kg N/ha as either a single dressing or two equal dressings, the form of nitrogen being the same as that applied in the seed bed.

Seed-bed nitrogen increased plant growth during autumn and winter in both years but increased yield only in 1985.

Scorching of plant leaves was severe in spring after application of urea or urea plus DCD given as a single dressing, but was much less with urea plus hydroquinone or when the dressings were divided. DCD inhibited nitrification of fertilizer nitrogen but had little effect on yield compared with urea alone. Ammonia volatilization losses were reduced by urea plus hydroquinone but, irrespective of the type of fertilizer applied, loss was always less than 3% of the nitrogen applied. Soil pH rose rapidly after urea application and thereafter fell slowly, whereas pH fell immediately after application of ‘Nitro-Chalk’. Neither dicyandiamide nor hydroquinone affected the pH changes after urea application. Overall, grain yields from urea were 90%, whereas those from urea plus hydroquinone were 97%, of those obtained from ‘Nitro-Chalk’. Dividing the spring dressings of urea-nitrogen increased yield in 1985 compared with a single dressing, but not in 1984. Yields from divided and single dressings of ‘Nitro-Chalk’ were similar. Oil and protein yields generally showed the same patterns of response to the fertilizer treatments as were shown by grain yields.

Batcombe series soils readily break down to good tilths, Beccles series soils form cloddy seed beds that are resistant to weathering, and Stackyard series soils form unstable tilths that readily break down. The soils differ in their particle-size distribution. The proposition that such differences contributed to the differences in field behaviour was examined by forming artificial soils, each of which was made up from particles of one of the soils, but redistributed with respect to size in the proportion in which they occurred in one of the other soils.

As a measure of the relevant physical properties, breaking strengths and bulk densities of cylindrical ‘clods’ moulded from the artificial soils were determined. To aid interpretation of the observed soil properties, similar measurements were made on individual fractions, on various other mixtures and on the parent soils.

The breaking strengths of the soils made up to a given particle-size distribution from particles from the different parent soils were reasonably close to each other, with those for the Beccles distribution being more variable. There was a significant difference between the two. The strength of the reconstituted Batcombe soil was markedly greater than that of its parent soil, whereas that for Beccles soil was markedly less. There was little difference for the Stackyard soil.

The bulk densities of saturated soils reconstituted from all nine fractions could be estimated reasonably accurately from the properties of the separate components. The structure of each of these soils in the air-dry state was inferred from comparisons between measured and calculated bulk densities. The breaking strengths of air-dry reconstituted soils were estimated from the properties of the separate components, and agreed reasonably well with the measured values for soils in which the clay and fine silt fractions predominated.

Whereas it was generally possible to predict various physical properties of the reconstituted soils from those of the separate fractions, it was not possible to extrapolate the results to explain field behaviour.

Field assessments of varietal contamination from entomophilous outcrossing in okra revealed that the plant characters employed in such assessments influenced the estimate of contamination expressed as percentage of offtypes. In Nigeria, complex cropping systems, land use patterns and the abundance of insects associated with okra flowers make the effective isolation of seed crops difficult. Also, the largely subsistence production where annual seed purchase is infrequent, and consumers' acceptance of variable and ungraded edible okra fruits, imply that breeding for uniform or pure varieties may not be appropriate. Consequently, a composite bulk variety is proposed for growing or seed multiplication in areas where edible fruit production is envisaged. In this way, the difficulty of pure seed production or unwanted adulteration of varieties will not pose problems to breeders or farmers.

The relationships between pairs of characters are investigated using F1 and F2 derived doubled haploids as well as single seed descent lines from spring barley (Hordeum vulgare) crosses. It is shown that linkage disequilibrium and pleiotropy are factors affecting the relationship between characters in barley. In fact, the linkages found are in general in the coupling phase and pleiotropy is usually positive. The consequences of such relations for plant breeding are discussed.

Seven experiments on winter barley, made during 1979–81, measured the effects of several amounts of nitrogen, applied at different times in spring, on grain yield and nitrogen content. All of these experiments also tested a growth regulator applied in spring, and five of them tested fungicide sprays. In 1980 the experiment at Rothamsted also tested sowing dates, and an eighth experiment, also at Rothamsted in 1980, tested sowing dates and mildew fungicides applied in autumn or spring. In all the experiments treatments were tested in factorial combination.

N applied in February was less effective than N applied in March and both were less effective, in terms of grain yield, than N applied in April. Divided dressings were best applied in February and April or March and April; effects on % N in grain followed the same pattern and so, therefore, did the efficiency of uptake of fertilizer N. The growth regulator consistently reduced the length of the straw and diminished lodging; it increased yields in five of the seven experiments in which it was tested.

Responses to fungicides were inconsistent from year to year. Sowing in September rather than in October 1979 increased yield in both of the experiments at Rothamsted in 1980, especially of the 6-row variety Hoppel.