The suitability was assessed of various designs for field experiments investigating plant diseases caused by airborne pathogens that can be subject to interplot interference. Use of a model to describe such interference showed that the treatments with the most dissimilar effects on controlling the disease should be allocated to experimental plots furthest apart in each block, in order to minimize the interplot interference within a block. When using large square plots, rectangular blocks were more efficient than square blocks in minimizing treatment-comparison biases due to interference between neighbours. For rectangular blocks with the square plots side by side, less biased treatment comparisons were obtained from designs with complete blocks than from designs with incomplete blocks, especially when larger numbers of treatments were included in the experiment. However, when interplot variance is taken into account, incomplete blocks may give better treatment comparisons. Similarly, unbalanced designs composed only of incomplete blocks that yield less biased treatment comparisons may be better than balanced incomplete block designs when interplot variance is low. For high levels of variation, balanced incomplete block designs may be more appropriate, as increasing the precision of the treatment comparisons becomes more important than reducing the bias.

RAPD (Randomly Amplified Polymorphic DNA) assay of 32 cultivar accessions from the ryegrass–fescue (Lolium–Festuca) complex was accomplished using ten decamer primers to assess (i) the power of RAPD technology to discriminate between individual commercial accessions and to produce cultivar fingerprinting, (ii) the degree of relatedness of accessions based on RAPD profiles in comparison with other existing classifications, and (iii) the possibility of automation of RAPD technology.

The variation of the correlation coefficient r as the primary output from the automated RAPD-profile processing summarizes variability derived from DNA isolation, the RAPD reaction, and final computer-image processing of RAPD profiles. The AII (Accession Identity Interval) of r for accession Festuca arundinacea cv. Lekora was determined experimentally and the value obtained was accepted as a valid interval for all the other accessions studied. In order to evaluate the discrimination potential of all ten primers together, a pooled-similarity matrix was computed. Employing this approach, we achieved 100% discrimination between all 35 accessions when using all ten primers. A dendrogram for all 35 accessions was obtained using average linkage cluster analysis (UPGMA – Unweighted Pair Group Method with Arithmetic Means). This procedure successfully produced smaller groups of higher taxonomic homogeneity. The relationships between the Lolium–Festuca accessions were also revealed by principal coordinate analysis (PCO) based on absorbance profiles from the RAPD assay. Again, all accessions were well separated, recognising even subspecies relationships. In general, PCO analysis confirmed the inferences made from the UPGMA method.

We successfully applied the computer-aided system of RAPD assay, based on an IBM PC computer, for discrimination of cultivars as well as for description of DNA-based relationships of accessions from various taxonomic groups of the Lolium–Festuca complex.

Lucerne (Medicago sativa L.) is the most common forage species in the world. In Italy it is grown on c. 1 million ha and is one of the most important crops for restoring soil fertility and for low-input agriculture. Landraces are still common (73% of the seed market) and 14 are registered in the National Register of Varieties. However, by 2002, landraces will be removed from the Register, seed certification will terminate and seed marketing will be forbidden. The collection, agronomic evaluation and characterization of farmer-landraces, still widespread in central Italy, were the objectives of the present work, particularly of the most important morphological and physiological characters useful for their identification. From 1993 to 1995, 20 landraces were evaluated for dry matter and seed yield in dense stands, and compared with Casalina, a local landrace, Boreal, an improved variety, and Italia Centrale, the registered landrace from central Italy. From 1992 to 1994, six landraces were evaluated as spaced plants and 48 morphophysiological characters were recorded.

Several landraces, not differing from the local control, were significantly more productive than Boreal. Univariate analysis of variance indicated that although differences were found in several characters, they could not be used to distinguish between populations. Discriminant analysis was more powerful, and five landraces out of six were clearly distinguished, with an average of correct classification of individuals in the group of origin as high as 82%.

The ex situ and in situ conservation of lucerne landraces, their potential role in future breeding programmes, and the most important characters to be used in discriminant analysis in the landrace/variety characterization of allogamous species in Hardy–Weinberg equilibrium are discussed.

Stolon death, often caused by grazing or winter-kill, is a major factor determining the survival and persistence of white clover (Trifolium repens L.), the most important forage legume in UK agriculture. Since stolon morphology apparently affects stolon survival, this study was designed to assess the genetic variation for stolon characters within a white clover population from Switzerland and to assess the effects of two generations of selection for stolon characteristics on that population. Bidirectional selection was carried out simultaneously for stolon diameter (as the primary criterion of selection) and total stolon length i.e. the product of the length of the longest stolon and stolon number. Four selection lines were established: (a) plants with thick sparse stolons, (b) plants with thick profuse stolons, (c) plants with thin sparse stolons and (d) plants with thin profuse stolons. Realised heritabilities for stolon diameter, estimated in both directions and over both generations of selection, were found to lie within the range 0·28–0·44; significant shifts in population means for stolon diameter were demonstrated. Selection for thin profuse stolons and for thick sparse stolons was effective, but because of negative correlations between stolon diameter and both stolon length and number, selection for thin sparse stolons or thick profuse stolons was ineffective.

The changes in weight and quality of sugarbeet roots stored in 18 clamps, mostly in eastern England during the winters of 1992/93 to 1994/95, were studied on farms using best commercial practice. Storage usually started in early December, at about the last recommended date of harvesting, and continued until the end of the beet-processing campaign at the local sugar factory (usually in February). Random samples of beet, in open-weave nets, were either analysed at the outset or were buried in a predetermined pattern in the clamp for up to 84 days. Periodically, samples were removed from the clamps for analysis. Beet weight hardly changed but sugar was lost as a reduction in sugar concentration: this declined at c. 0·02% per day. The concentration of reducing sugars, which are important impurities, increased fourfold during storage. Most other beet quality parameters remained unchanged. Sugar and adjusted weight was lost at 0·143 and 0·187% per day respectively. This relationship was highly significant, but a relationship between sugar loss and accumulated thermal time (0·0188% per °C day) accounted for more of the variation (73%). Temperature changes within the clamps, and the differences between clamps in accumulated thermal time, were not predictable. Some clamp insulation materials appear to allow more heat to accumulate than is desirable.

Results of an experiment conducted during the summer seasons of 1990 and 1991 in North West India revealed that a Spanish semi-spreading type groundnut cultivar ICGS 1 produced 93% higher pod yield than a Valencia bunch type MH 2. Application of chlormequat chloride (CCC) to both cultivars at 0·5 ml/l water enhanced yield by 17%. An input of 13 kg P/ha increased the pod output significantly over control.

Studies were conducted from 1993 to 1995 in Southern Spain to determine the feasibility of controlling broomrape (Orobanche crenata Forsk.) in broad bean (Vicia faba L.) and lentil (Lens culinaris L.) by treating seeds with imazethapyr and imazapyr. In the broad bean, soaking for 5 min in 0·01–0·1% herbicide solutions or coating at 20–40 g ha−1 (seed sowing rate 160 kg ha−1) with imazethapyr (Pursuit-10) did not affect seed germination and crop growth, and resulted in 60–80% broomrape control. Furthermore, broad bean seeds treated with imazethapyr followed by an additional late post-emergence application of imazapyr (Arsenal-25) at 5 g ha−1 resulted in excellent broomrape control (>95%). Similarly, lentil seed treatments with imazapyr by coating seeds at rates equivalent to 5–10 g ha−1 or by soaking for 5 min in 0·25% solutions did not affect germination or crop growth, and controlled 85–95% of broomrape. As a result, with broomrape-efficient herbicide treatments, crop biomass/seed yield increased as compared to broomrape-infested, non-treated controls. Herbicide seed treatments with imazapyr in broad bean and with imazethapyr in lentil were less well tolerated and were less effective in controlling broomrape than treatments with imazethapyr and imazapyr, respectively.

Annual liveweight gain of beef cattle (steers) grazing grass pasture fertilized with 200 kg N/ha was compared over a period of 7 years (1989–95) with that of steers grazing grass/white clover pasture given no artificial N fertilizer at North Wyke, Devon, UK. Nitrogen lost by leaching over the ensuing winter drainage periods was monitored from both pastures. Nitrogen leaching loss from the fertilized pasture over an extended period of 13 years (1983–95) is also reported.

The average annual liveweight gain of the steers grazing the grass/clover pasture (0·81 t/ha) was 19% lower than that of the steers grazing the N-fertilized grass pasture (1·00 t/ha). The average annual loss of nitrate-N by leaching in winter drainage from the grass/clover pasture (13 kg/ha) was only 26% of that recorded from the fertilized grass (50 kg/ha). A possible reason for this difference may arise from the previous history of the grass/clover pasture which had been ploughed in 1982, causing a flush of N mineralization and consequently greater immobilization of N in the soil in subsequent years.

Losses of N each winter by leaching measured over a 13-year period from the fertilized grass were highly correlated (P<0·001) with the preceding summer's soil moisture deficit, with the highest losses following dry summers. The nitrate-N concentration in the drainage water exceeded the European Union limit in drinking water (11·3 mg/l) in the initial 25 mm of drainage during 11 of the 13 autumns. The average loss of N each winter (53 kg/ha) was equivalent to 26% of the fertilizer-N applied annually. Immediate losses of N by leaching of fertilizer applied in early spring and throughout one very wet summer (1993) were minimal.

The Cu, Zn and Mn status of 44 fields from the Canterbury region of New Zealand under winter wheat was investigated in Spring 1993. Micronutrient status was assessed using EDTA, DTPA and HCl as extractants. The Mn status of soils was generally high and unaffected by soil development. However, when samples were separated according to soil series, it was found that extractable Cu and Zn levels in both the 0–15 and 15–30 cm soil layers generally decreased with increasing soil development (increasing soil age and annual rainfall). Twenty-three percent of fields had EDTA-extractable Cu levels <1 μg g−1 whilst 34% had EDTA-extractable Zn levels <1 μg g−1.

Twenty-two of the soils were used in a glasshouse experiment in which wheat was grown in the soils with or without the addition of added Cu and/or Zn. Plant dry matter responses to added Cu were recorded in soils with extractable Cu levels <1·1 μg g−1 EDTA, 0·4 μg g−1 DTPA and 0·9 μg g−1 HCl. Responses to added Zn occurred in soils with extractable Zn levels <0·8 μg g−1 EDTA, 0·25 μg g−1 DTPA and 1·4 μg g−1 HCl. Significant linear correlations were found between EDTA-, DTPA- and HCl-extractable Cu and Zn and Cu and Zn uptake respectively by wheat. Correlation coefficients were closer for Cu than for Zn uptake. It was concluded that many sites on the more strongly developed soils of the Canterbury Plains are potentially deficient in Cu and/or Zn and that these can be identified using conventional micronutrient soil tests.

Field trials were conducted at six sites throughout Ireland in 1992, 1993 and 1994, to assess the efficiency of utilization of N in cattle slurry treated with nitric acid. Slurries were left untreated or were acidified to pH 5·5 with 12 m nitric acid immediately prior to spreading. Slurries were either band-spread or splashplate-spread using an automated tanker system. The efficiency of N (NH+4-N+NO−3-N) in slurry for grass production (Eff-N%) was measured by comparing N offtake values with those from a range of rates of inorganic fertilizer N (ammonium nitrate/calcium carbonate) treatments. Slurry was applied at rates (13–28 m3/ha) which supplied N (NH+4-N+NO−3-N) below the highest inorganic fertilizer treatment. In all experiments, untreated cattle slurry was compared with nitric acid-treated cattle slurry at the same rate of application. The Eff-N% values for unacidified or acidified slurries were highly variable by both spreading methods. The effect of spreading method depended on whether or not the slurry was acidified. On average the Eff-N% value of the band-spread unacidified slurry (59%) was significantly higher than the Eff-N% value of the splashplate-spread slurry (37%). For acidified slurry, the average Eff-N% value of the band-spread slurry (85%) was not significantly different from the Eff-N% value of the splashplate-spread slurry (81%). The overall average Eff-N% value of the acidified slurry was 83% which was significantly less than 100%. Cattle slurry acidified with nitric acid to pH 5·5 was more variable and less efficient than inorganic fertilizer N under the soil and climatic conditions tested.

The effects of exogenous purine supply on plasma concentration and urinary excretion of purine derivatives (PD), which include allantoin, uric acid, xanthine and hypoxanthine, were studied. Five sheep, totally nourished by intragastric infusion of volatile fatty acids and casein, were given an abomasal infusion of a mixture of adenosine and guanosine at three levels (5·0, 10·0 and 20·0 mmol/day) each in four infusion patterns (as one, two, or four 3-h infusion periods per day or infused continuously, P1 to P4 respectively). Urine was collected hourly over 24 h, and plasma samples were collected hourly for 7 h from the start of purine infusion. Both the plasma concentration of PD and its urinary excretion changed rapidly in response to the start and termination of purine infusion with a lag time of 2–3 h. Individual sheep differed considerably in the relative proportions of the different purine derivatives in the urine. The endogenous urinary PD excretion averaged 176 (±S.E. 28) μmol/kg W0·75 per day. Daily PD excretion in urine increased with the amount of purine infusion, but at each level the output decreased significantly in a gradient from P1 to P4. The response of total PD excretion (Y, mmol/day) to daily purine input (X, mmol/day) was predictable and followed the equation: Y=0·81 (±0·02)X+3·07(±0·81) × (u e−0·27X/u +1−u), where u is the duration over which the daily input was infused expressed as a proportion of 24 h. The recovery of the infused purines averaged 81%. When the infusion was given continuously, plasma PD concentration was relatively stable and was linearly correlated with the purine entry rate and daily PD excretion in the urine. The estimated glomerular filtration rate was 150 (±S.E. 16) litres/day and the estimated tubular transport maximum was 2·6 (±S.E. 1·3) mmol/day. It is concluded that due to the rapidity in the response of plasma and urinary PD to changes in the exogenous purine supply, spot measurements of PD in urine or plasma can be of no value for the estimation of exogenous purine uptake unless the purine supply is relatively constant throughout the day. Daily PD excretion in urine related to the exogenous purine uptake in a predictable and reproduceable manner and provides a reliable index for the estimation of the exogenous purine uptake.

Annual variation in the feeding value of barley straw (Hordeum vulgare L. subsp. vulgare) is economically significant in the Mediterranean region. The relationship between the feeding value for sheep of several winter-planted barley cultivars and monthly meteorological data was analysed at Tel Hadya, northwest Syria (mean annual precipitation 330 mm) in 11 years. Indicators of feeding value included contents of neutral detergent fibre, acid detergent fibre and nitrogen (11 years), voluntary straw intake by sheep (10 years), voluntary digestible organic matter intake (9 years), in sacco dry matter loss and lignin content (8 years), in vitro digestibility (7 years) and in vitro gas production (6 years). Monthly meteorological data included total precipitation, mean minimum and mean maximum air temperatures.

Conditions likely to decrease grain yield tended to increase the feeding value of straw. Low mean minimum temperature in February, low precipitation in January, February, March and April, and high mean maximum temperature in March, April and May increased one or more indicators of straw feeding value (by both bivariate and multiple regression, P<0·05). Precipitation before January affected grain and straw yield but had little effect on the feeding value of straw.

Genotype × year interactions had a meteorological component; the superior feeding value of the straw of locally-adapted cultivars v. exotic cultivars was only seen in years with cool or wet springs. This has implications for the genetic selection of crops with better straw feeding value.

Models based on monthly precipitation and temperature, calibrated for locations in the Mediterranean region, can predict the nutritive value of straw and aid the planning of rations for small ruminants.