ALBERT

Description: SummaryExperiments on winter barley at Rothamsted, testing different sowing dates, were sampled in 1987–89 to measure effects on take-all caused by the fungus Gaeumannomyces graminis var. tritici. The experiments used the same plots in each year, and in 1988 and 1989 the randomization was restricted so that sowing dates were balanced for sowing dates in the previous year.The site had been used to grow barley since at least 1979 (spring barley from 1979 until 1985), and take-all was much more severe than expected. It was usually most severe in the earliest-sown plots and decreased almost linearly as sowing was delayed. There was also evidence that the sowing dates of the preceding crop had a continuing, residual effect. In the two years that the effects of previous sowing dates were tested, there was usually least take-all in plots where the crop followed one sown very early or very late in the previous year, and most where it followed one sown at the end of September or in early October. These effects probably reflect differences in amounts of inoculum and in the rate of development of take-all decline.

Description: The effects of supplying the fertilizer nitrogen (N) as a recommended quantity of ammonium nitrate or as a commonly used dose of poultry manure on yield of sugarbeet infected with Beet mild yellowing virus (BMYV) or Beet yellows virus (BYV) were studied in field experiments at IACR-Broom's Barn in 1990, 1991 and 1992. Three N fertilizer treatments comprising Zero (N0), standard rate of 110 kg N/ha (N1) and poultry manure equivalent to c. 300 kg/ha of available N (N2) were applied to plots which were uninoculated or were subsequently inoculated with either BMYV or BYV. Averaged over virus treatments, N1 increased sugar yields by 23% relative to N0: there was no further increase when N2 was applied. When averaged over N treatments, early virus yellows infection reduced the sugar yields by 23%. Generally there was no significant interaction between N supply and virus infection. There was no evidence that the large N supply could reduce the yield effect of virus yellows infection, as had previously been thought. Crops infected from late July produced similar yields to uninoculated controls. The main effect of virus yellows was to reduce the efficiency of radiation conversion even when account was taken of the light intercepted by yellow foliage. Whilst the N2 treatment helped to maintain a green leaf cover throughout the season on virus yellows infected crops, it had no effect on virus replication. Beet processing quality was impaired by increasing the N supply and by virus infection, but again there were generally no significant interactions between infection and N rate.

Description: Results from field experiments with mobile pests and air-borne pathogens are subject to bias as a result of inter-plot interference. Serially balanced designs (SBDs) allow interference to be estimated but other designs may be better for decreasing such effects. To investigate this, systematic replicated designs, comparing sprays applied at different times to control powdery mildew of spring barley, were sited in 2 years alongside SBDs testing similar treatments. Yields of grain and assessments of mildew on the leaves were analysed. Results from the balanced designs provided strong evidence of interference in both years but not in a third (when the systematic design was omitted). Estimates of treatment effects from the systematic designs were often, but not consistently, greater than corresponding estimates from the SBDs. A method of analysis from Draper & Guttman (1980) was adapted to produce estimates of the differences between treatments as if applied to all plots of an experiment; this showed larger differences between treatments than the conventional analysis in 1975 and 1976 (when there was appreciable interference), but failed in 1977 when interference was slight. This method fails when applied to the systematic designs; SBDs (which are a subset of all designs in randomized blocks) are probably optimal for this type of analysis. The difficulties of analysing data in the form of percentages or proportions (with consequent non-orthogonality) are discussed.

Description: SUMMARYExperiments in 1985 and 1986, at Woburn Experimental Farm in Bedfordshire, tested the effects of fungicides, applied in autumn, and a growth regulator, applied at GS3O–31 or GS32–33 in spring, on winter barley grown on two contrasting soil types in each year. Leaf diseases did not become severe in any of the experiments but take-all (Gaeumannomyces graminis var. tritici) was prevalent in 1985. Triadimenol (‘Baytan’) was more effective than flutriafol (‘Ferrax’) in decreasing the severity of takeall and its activity against the disease was related to earliness of sowing.Mean responses in grain yield to the fungicide treatments were mostly small and not significant but did not conflict with the hypothesis that crops on lighter soils benefit more from autumn fungicides than those on heavier soils. Mean effects of the growth regulator sprays were also small but they interacted with both soil type and season. Over the 2 years the later spray applied to crops on the heavier soil gave the largest mean response. Sprays applied to crops on lighter soils were often detrimental to yield, especially in 1985.

Description: SUMMARYMultifactorial experiments at Rothamsted Experimental Station in two contrasting seasons, 1985/86 and 1986/87, tested the effects of treatment combinations that varied the supply of nitrogen at important stages of crop development in autumn and spring on the grain yield and nitrogen content of September- and October-sown winter wheat. Treatments that altered the nitrogen supply in autumn were an application of winter fertilizer N and sowing the wheat after rape or oats, which left different amounts of residual N. These were combined with treatments which tested the effects of 200 kg N/ha in spring applied as early or late dressings and as single or divided dressings. The effect of applying an additional 50 kg N/ha in summer was also tested in 1985/86.In both experiments, larger yields were obtained from sowing in September than in October. The September-sown wheat grew better over winter in 1986/87 than in 1985/86 but the early advantage in size and N uptake resulted in enhanced production of straw rather than grain. Residues of N from previous crops were smaller after oats than rape in both years. This difference in soil N did not affect the over-winter growth and N uptake of the October-sown wheats. Neither this difference in residual N nor an application of fertilizer N in winter affected the yield of the following September-sown wheat in 1985/86 because autumn growth and N uptake were restricted by adverse weather. In 1986/87, however, wheat that followed oats yielded 0·42 t/ha less grain than wheat that followed rape, and the deficit in yield was removed by an application of fertilizer N equivalent to the deficit in soil N.Yields were decreased when the spring N was applied as a delayed, single dressing in April especially if the wheat was sown in September after oats, or was not given winter N. Yields were not affected by any of the other combinations of single v. divided dressings or early v. late applications of spring N, despite these being given at very different stages of apical development.The percentage of N in the harvested grain was greatly increased by winter applications of fertilizer N, especially to wheat grown after oats, by applying the spring N as a late, single dressing and, in 1986, by applying N in summer.