Records on 884 litters and 3051 bunnies of the Bauscat (B) and Giza White (G) breeds were used to construct different selection indices.

A series of selection indices and subindices were constructed for both B and G does. An index or subindex based on litter size at weaning, mean bunny weight at weaning, litter size at birth and litter weight at birth could be practically applied to improve the productivity of B and G does, under local Egytian conditions. Preweaning mortality did not contribute significantly to the different selection indices and subindices. Litter weight at birth made a large contribution to the different indices and subindices constructed. Litter size at weaning contributed little in the subindices to be used to select for mean bunny weight at weaning. Mean bunny weight at weaning made a lower contribution to the subindices to be used to select for litter size at weaning. The expected genetic gain in litter size at weaning was slight in all of the selection indices and subindices constructed because of low heritability values for this trait. Considerable genetic improvement for doe productivity of the G breed might be achieved through selection for mean bunny weight at weaning.

Four selection indices and subindices were constructed for B and G rabbits. The index or subindex based on 6-week weight and 8-week weight was the best criterion for selection for the genetic improvement of 6-week weight and 12-week weight. Six- and 8-week weight contributed substantially while 12-week weight contributed little to the value of most of the selection indices and subindices constructed. The highest total genetic gain attributable to 6- and 12-week weight was obtained when the selection indices or subindices including 6-week weight and 8-week weight were used.

The relationship between seed rate and use of pesticide (chlorpyrifos and aldicarb) on tiller density and herbage yield of a conventionally established autumn re-seed (i.e. grass sown after a previous grass crop) of Italian ryegrass (cv. RvP) was investigated in small plot trials at three sites in Yorkshire, Berkshire and Devon in August 1984. Plots were also sampled for pests and earthworms. Pesticide enhanced yield at all sites at the first harvest in October 1984, particularly at the low seed rates, but this effect did not persist until the spring harvest in 1985. Tiller density and herbage dry-matter yield increased logarithmically with increasing seed rate. Frit fly was the major pest and the proportion of infested tillers increased linearly with seed rate. Low seed rate in combination with appropriate insecticide was more cost effective than untreated higher seed rates in the establishment of autumn re-seeded Italian ryegrass.

The analysis of Perkins & Jinks (1971) was applied to 360 progeny families of three chickpea F2 triple test crosses, namely, F 378 × ICCC 1, P 1198–1 × ICCC 1 and US 613 × BG 203, to detect and measure the interaction of additive, dominance and epistatic gene effects with sowing dates. The families were grown in completely randomized blocks in three replications with two sowing dates, and data were recorded for plant height, number of branches per plant, number of days from sowing to flowering, number of days from sowing to maturity, number of pods per plant, number of grains per plant, 100-grain weight and grain yield per plant. The i type epistasis and additive genetic component were relatively more important than j and l type epistasis and dominance component, respectively. The j and l type epistasis and additive gene effects were more sensitive to environmental differences than the i type epistasis and dominance gene effects, respectively.

In an intermediate deepwater (15–50 cm) situation, the number of tillers increased with increase of nitrogen fertilizer from 0 to 40 and 80 kg/ha and of seed rate from 100 to 200, 300 and 400 seeds/m2. The tiller mortality due to higher water depth was higher under no-N treatment and under higher seed rates. The number of panicles and grain yield increased significantly with increase in N. Similarly, an increase in the seed rate increased the number of panicles and decreased the number of grains per panicle and panicle weight. The grain yields of the different seed rates were similar. The interaction between N levels and seed rates was not significant.

Observations are presented from a crop of sugar beet grown in Cambridgeshire during 1978, and a field trial at Sutton Bonington during 1985 in which the influence of synthetic plant growth regulators (PGRs) daminozide, chlormequat, GA4+7 and ethephon were compared.

Several distinct patterns of growth were evident, being similar for both growing seasons and described by two intersecting straight lines. Early development was characterized by a slow rate of biomass accumulation, a dominance of foliage production with a constant but small root fraction (around 40%), a low specific leaf area and a slow but conservative rate of sucrose fractionation. Later in the season the rate of stand growth was both constant and maximal, the root fraction doubled, specific leaf area increased and the rate of sucrose accumulation rose markedly.

Transitions between developmental phases occurred at various times dependent on variate under consideration. The onset of the main growth period began at the end of June, followed by an increase in the rate of sucrose accumulation about 2 weeks later. Finally, near the end of July, partition of assimilate into the root assumed a faster rate. Changes in the partitioning into both roots and sucrose are discussed in relation to the development of the secondary cambium.

Generally there were no effects of PGRs on biomass accumulation, dry-matter partitioning, specific leaf area and sucrose accumulation. However, daminozide increased early canopy expansion and early dry-matter production but failed to influence biomass or sugar yield.

Behavioural oestrus was studied using 32 Friesian × Bunaji and 29 Bunaji heifers standing for mounts by either vasectomized bulls or heifer herdmates. The study was conducted from 06.00 to 12.00 h and from 13.00 to 18.00 h local time for 96 days. All the 61 heifers showedoestrus. The mounts received by the heifers ranged from 68 to 170, being few between the first 24 days but increasing later. A total of 171 oestrous cycles were recorded, 85·4% of which had a mean oestrous cycle length (± S.E.) of 22·6 ± 0·9 days, while the average duration of oestrus (± S.E.) was 5·9 ± 0·2 h. Results showed significant differences between the mounts made by the teasers as well as mounts received by the heifer groups (both P = 0·01), but the teaser x heifer group interaction was not significant (P > 0·05). As all the heifers showed oestrus at least once, observation for oestrus between 06.00 and 18.00 hwould be reliable for supporting an artificial insemination scheme in the Guinea Savannah of Nigeria.

The effects of applying phosphorus, farmyard manure (FYM) and nitrogen on some soil properties were studied at the end of 2 years of field experimentation at New Delhi, India. Each year a crop of soya bean sown in the rainy season received phosphorus and farmyard manure and maize sown in winter received nitrogen fertilizer. Phosphorus was applied to soya bean at 0, 40 and 80 kg P2O5/ha, farmyard manure at 0 and 15 t/ha and nitrogen to maize at 0, 60 and 120 kg N/ha. Phosphorus application increased organic C, total N and available P status of the soil. It also improved bulk density and water-holding capacity of the soil. Farmyard manure increased organic C, total N, available P and K and pH of the soil, but decreased EC and bulk density of the soil. Water-holding capacity of the soil was increased by FYM. N fertilizer increased organic C and total N only.

Blood samples were taken from 428 Friesian (Holstein) bulls on three occasions, on average at approximately 3-monthly intervals, between 3 and 15 months of age, and also from 214 of them on three occasions at 6-monthly intervals when they were between 2 and 6 years of age.The average concentrations of blood glucose and haemoglobin and of serum cholesterol, urea, albumin, globulin, inorganic phosphate, Ca, Mg, Na, K and Cu were calculated for each of these periods and correlated with improved contemporary comparisons of milk yield and quality.

Repeatability estimates were similar within each of the two periods but were lower when mean concentrations calculated between 3 and 15 months of age were compared with those between 2 and 6 years. The main exceptions were cholesterol (0·52) and Cu (0·54) for which repeatability estimates were similar to those derived within the above two periods. The constituents with the next highest levels of repeatability were magnesium (0·44), globulin (0·43) and inorganic phosphate (0·39), which were approximately 30% lower than those obtained within the two periods.

Correlations between blood concentrations and improved contemporary comparisons were negligible, indicating that it is not possible to use these blood constituents to predict the milk production potential of a bull's daughters.

Spores of Pyrenopeziza brassicae, which are mostly dispersed by rain splash, were trapped 4 m above and 20 m downwind of an oil-seed rape crop. This suggests that not all trapped spores were transported in ballistic splash droplets (100–2000 μm); indeed some were airborne during periods of dry weather following closely after rain. Vertical and horizontal spore concentration gradients corresponded to the gradients expected for spores with fall speeds of between 2 and 5 cm/sec. Atmospheric dispersal calculations suggest that such spores have the potential for transport over considerable distances to other susceptible crops.

The study was designed to compare the agronomic performance of progenies of barley plants (cv. Golden Promise) regenerated from immature zygotic embryos (IE) with these originating from embryos produced after chromosome elimination (Hordeum bulbosum technique). Conventionally derived seed material was used as control.

In a randomized complete block design with two replicates, plants were scored for mildew reaction (Erysiphe graminis f.sp. hordei), number of days to awn emergence, height and yield. Data showed no evidence of variation for mildew reaction and although significant differences between lines for the other three characters were observed in the IE-derived sample these were not significantly greater than that observed in the control samples.

Twenty field site3 were selected for their potential sulphur-deficient status. The effect of sulphur at 10 kg S/ha per cut as gypsum or kieserite on the yield and composition of grass for silage given intensive fertilizer was measured at two or three cuts in 1985. Other incidental sulphur inputs in P and K fertilizers and organic manures were minimized. There were significant increases (P < 0·05) in dry-matter yield at ten harvests on five sites. At seven of the ten harvests gypsum and kieserite were equally effective, but at three harvests only kieserite gave significant yield increases. The drymatter yield increases occurred at all three cuts.

Using soil analyses to predict sulphur-deficient sites had limited success. The conclusions from this study were that soils with extractable sulphate values < 10 mg S/l had adequate reserves for three-cut silage while soils with values > 10 mg S/l had a 1 in 3 chance of being sulphur deficient. Using plant analyses to diagnose sulphur-deficient herbage had also limited success. In this study herbage with an N/S ratio > 14 was sulphur deficient while herbage with a ratio > 12 had a 1 in 2 chance of being deficient.

The proportion of sulphur responsive sites in this study is an overestimate for Northern Ireland as a whole. Most soils in this country have higher clay and organicmatter contents than the field sites. The application of organic manures in normal agricultural practice is likely to be an important source of sulphur to grass for cutting.

Four experiments are reported in which the effects of a range of physiological ages of seed tubers on growth and yield in seed crops and regrowth of the progeny seed were studied. Increasing the age of seed in Home Guard, Arran Comet, Pentland Javelin and Désirée advanced emergence, tuber initiation and early growth but restricted leaf area index and reduced the number of tubers and seed tuber yield. In these varieties increasing the physiological age of seed shortened the dormancy of the progeny seed and slightly increased sprout lengths at replanting but in Home Guard had no effects on field growth and tuber yield.

In a further series of experiments at Tenby seed of five varieties (Home Guard, Red Craigs Royal, Désirée, Maris Piper and Stormont Enterprise) was multiplied over 2 years using husbandry methods designed to produce seed of contrasting ages. Once-grown seed from Tenby which had been planted and harvested early in the season was stored at either 4 or 12 °C and grown again at Tenby before being stored again at either 4 or 12 °C. The seed resulting from this multiplication over 2 years was compared with seed imported from seed-growing areas stored at the two temperatures. The seasons for the two multiplications at Tenby (1975 and 1976) were hot and were followed by an especially cold and late spring yet few differences between seed from Tenby and other areas could be detected. Where seed from different areas entered sprouting temperatures at different times and therefore produced different ages of seed at replanting large effects on yield were found. Storage temperature had large effects on regrowth of tubers in Home Guard, Red Craigs Royal and Stormont Enterprise for storage at 12 °C produced ‘little potato disorder’ in the majority of plants in one storage phase while storage at lower temperature produced full plant stands and yields. The results provided no support for the suggestion that repeated multiplication in warm lowland areas may lead to cumulative deterioration in the performance of seed.

Two Rhizobium strains were studied for their chemotaxis, nodulation, nitrogenase activity and other endosymbiotic N2-fixing characteristics with two genotypes of Cicer arietinum. Root exudates were found to attract Rhizobium strains. Nodule-specific root proteins (nodulins) and leghaemoglobin were found to be host-range specific between two strains of Cicer Rhizobium. Physiologically active iron content was more important for nodule functioning than total iron concentration of nodules.

The effects of recalculating P concentrations in spring barley (Hordeum vulgare L. cv. Georgie or Julia) on the basis of tissue water were investigated. Expressing P concentrations in this way altered their apparent behaviour with time. Whereas % P in dry matter declined during growth, P concentrations in tissue water decreased initially but then increased. The rate of increase became more rapid during senescence. Nitrogen and water supplies induced differences in % P in dry matter but these were reduced when P concentrations were expressed on the basis of tissue water. Like % P in dry matter, P concentrations in tissue water were lower in crops grown on a soil that had not received P since 1852. It is suggested that P concentrations in tissue water can provide a method for assessing crop P status that has some advantages over % P in dry matter.

Nine experiments are reported in which effects of site of seed production on dormancy, sprout and field growth of progeny tubers were recorded. The experiments used early varieties, Home Guard (four experiments), Red Craigs Royal (three experiments) and Arran Comet (two experiments) and in each, seed crops were grown with similar husbandry at sites differing in altitude and location in western England and Wales. There was no consistent effect of site of seed production on the timing of the end of dormancy, and the maximum effect in any year was 11 ± 1·2 (S.E.) days. The small effects of site on dormancy influenced initial sprout lengths, and this effect usually persisted up to planting in Home Guard and Red Craigs Royal, although the effects were small in magnitude. There was no effect of site of seed production on sprout lengths at planting or on field growth and yields in Arran Comet. In the other two varieties there was no effect of site of seed production on yield at early harvests, but at later harvests seed from cooler upland sites sometimes significantly outyielded lowland seed. There was, therefore, no evidence to support the view that locally produced seed was advantageous for early potato production. The results, together with those of the concurrent series with maincrop varieties reported by Wurr (1979), show that on half the occasions on which yields were measured covering the whole of the harvesting period, site of seed production had no effect on yields. In these experiments with early varieties effects of site occurred only at harvests later than the commercial harvesting of such old seed. It is therefore suggested that site of seed production is a much less important determinant of tuber yield than hitherto suggested, and of little practical significance.

FARZ 27, a high-yield maize variety, was grown in 1984 and 1985 over a wide range of density treatments (1·9– 11·1 plants/m2) and with four rates of nitrogen application (0, 75, 100 and 150 kg N/ha) in Ibadan. south-western Nigeria.

There was no significant density or fertilizer effect on morphological characters of number of leaves per plant, height or stem diameter. For total dry-matter yield, the highest density of planting gave the highest yield although less dry matter was obtained in the 1985 experiment than in the 1984 experiment. Optimum density for grain production in both years was 8·8 plants/m2. There is an indication that there is no need to increase density of planting of maize beyond 80000 plants/ha in the south-western part of Nigeria. Plants without applied nitrogen fertilizer gave significantly lower total dry-matter and grain yields than plants with applied nitrogen. Highest grain yield was obtained with 150 kg N/ha in both years. By doubling the nitrogen application rate from the present recommended level of 75 kg N/ha to 150 kg N/ha an average increase of 0·42t/ha of maize was obtained in both years. With the present prices of fertilizer and maize, this increase is economical. It seems therefore that more revenue would accrue to the farmers by using 150 kg N/ha on the ‘FARZ series’ of maize instead of the present recommendation of 75 kg N/ha.

Three experiments, carried out in 3 years (1972–5), which examined the effects of a wide range of rates of nitrogen fertilizer applied to seed crops of Home Guard on seed and progeny crop growth are reported. There was little effect of increasing rate of N application over the range 0–300 kg/ha on seed yield, and the results suggested that very low rates of nitrogen fertilizer (< 75 kg/ha) were required for maximum seed yield in mid-Wales. Increasing the rate of nitrogen fertilizer above 304 kg/ha delayed growth and decreased yield in seed crops. Although increasing the rate of nitrogen fertilizer in seed crops delayed senescence and increased the nitrogen concentration of tubers, there were few consistent effects on sprouting or growth of progeny crops.

Close negatively quadratic relationships were found between the dry-matter content of tubers and their size. The dry-matter content of all sizes of tubers increased during growth, but there were no effects of nitrogen on dry-matter content.

A comprehensive study of how age and weaning affect intestinal structure and enterocyte ability to digest and absorb nutrients has been carried out in 4- and 6-week-old piglets.

Villus length, which did not change significantly in unweaned piglets 4–6 weeks after birth, was halved 5 days after weaning. Crypt depth, which increased normally in unweaned piglets, is further increased by weaning in both 4- and 6-week-old animals.

Lactase activity, which decreased normally with age, was inhibited more than a-glucosidase by weaning. Weaning of 6-week-old piglets also caused a significant increase in maltase II and III activities. Alkaline phosphatase activity was unaffected by age or weaning in 4- and 6-week-old piglet intestine.

Na-dependent alanine transport was reduced in 6- compared with 4-week-old unweaned piglet intestine. Weaning inhibited Na-dependent alanine transport in 4- but not 6-week-old pigs. Na-independent alanine transport, which was considerably less than that found in the presence of Na, was not noticeably affected by age or weaning.

Weaning-induced problems in intestinal function appear from the present results to be caused more by changes in intestinal structure and specific loss of digestive enzymes rather than by any gross change in absorptive function. The possible role of immune as well as nutritional factors in causing these weaning-dependent changes in intestinal function is discussed.

Laboratory studies were conducted on four soils to ascertain the effect of P content and texture on the capacity factor (P buffering capacity) of soils and in turn the effect of these factors combined with moisture content of soil on the diffusion coefficient of P (Dp). A glasshouse experiment was conducted to study the relationship of Dp with P uptake by maize and wheat. The buffer capacity decreased by the application of P in all four soils. There was a significant negative correlation between buffer capacity and Olsen's extractable P but positive correlation with other soil factors. The relative influence of different soil variables on the buffer capacity was in the order: free iron > percentage clay > exchangeable aluminium. The Dp value increased significantly with applied P, the maximum (3·2-fold over control) being in Tolewal loamy sand. The increase in clay and moisture content of soil also increased the Dp value. The drymatter yield and P uptake was significantly correlated with Dp, the r value being higher at later stages of growth of maize and wheat.

15N-labelled nitrogen fertilizer (containing equal quantities of ammonium-N and nitrate-N) was applied in 4 consecutive years (1980–3) to different microplots located within the Broadbalk Wheat Experiment at Rothamsted, an experiment which has carried winter wheat continuously since 1843. Plots receiving 48, 96, 144 and 192 kg N/ha every year were given labelled fertilizer in mid-April at (nominally) these rates.

Grain yields ranged from 1–2 t/ha on plots given no N fertilizer since 1843 to a maximum of 7·3 t/ha with 196 kg N/ha. On plots given adequate P and K fertilizer, between 51 and 68% of the labelled N was recovered in the above-ground crop; only about 40% was recovered where P deficiency limited crop growth. In 1981 fertilizerderived N retained in soil (0–70 cm) at harvest increased from 16 kg/ha, where 48 kg/ha was applied, to 38 kg/ha, where 192 kg/ha was applied. More than 80% of this retained N was in the plough layer (0–23 cm).

Overall recovery of fertilizer N in crop plus soil ranged from 70 % to more than 90 % over the 4 years of the experiments. Losses of N were larger in years when spring rainfall was above average and when soil moisture deficits shortly after application were small.

Crop uptake of unlabelled N derived from soil increased from 28 kg N/ha on the plot given no fertilizer N to 67 kg N/ha on the plot given 144 kg N/ha. The extra uptake of unlabelled N was mainly, if not entirely, due to greater mineralization of soil N in the plots that had been given N fertilizer for many years. Presumably fertilizer N increased the annual return of crop residues, which in turn led to an accumulation of mineralizable organic N, although there was only a small increase in total soil N content.

Wheat given NH4-N grew less well and took up less N than wheat given N08-N in the relatively dry spring of 1980; there was little difference between the two forms of N in the wetter spring of 1981. In both years more fertilizer N was retained in the soil at harvest when fertilizer was applied as NH4-N than as N03-N.

The N content of the soil in several plots of the experiment has been constant for many years, so that the annual removal of N is balanced by the annual input. A nitrogen balance for the plot given 144 kg fertilizer N/ha showed an average annual input of non-fertilizer N of at least 48 kg/ha, of which N in rain and seed accounts for about 14 kg/ha. The remainder may come from biological fixation of atmospheric N2 by blue-green algae, or from dry deposition of oxides of nitrogen and/or NH3 onto crop and soil. The overall annual loss of N from the crop–soil system on this particular plot was 54 kg N/ha per year, 28% of the total annual input from fertilizer and nonfertilizer N.