THERMODYNAMICS OF CATION EXCHANGE ON CLAY: Ca-K-MONTMORILLONITE

Radioactive elution and batch equilibration techniques have been used to obtain isotherms at 30° C, 50°C, and 70° C for the exchange of Ca for K on K-montmorillonite. From these the changes in enthalpy and entropy were + 3.87 kcal/mole and +6.7 e.u./mole of Ca respectively. The activity coefficient for K decreased from approximately 1.5 to 1 and for Ca from 1 to approximately 0.5 as the fraction of K on the clay increased from 0 to 1. The results are discussed especially in relation to hydration of the ions and adsorption of water on the clay. The entropy of adsorbed water is inferred, from the results, to be less than that for liquid water.     

Effects of fungicides on long-term cropping and fruit quality of apple

The effects on cropping of 24 applications, over a 3-year period, of each of five fungicidal programmes to control powdery mildew ( Podosphaera leucotricha ) were examined on the apple cultivar Cox's Orange Pippin. Trees receiving programmes based on ergosterol biosynthesis inhibitors (EBIs)-fenarimol, a triadimefon/bitertanol mixture and an experimental compound coded PP 347-each applied at 2-week intervals during the growing season had significantly ( c . 40%) less yield than those receiving the standard programme of binapacryl (not an EBI), applied weekly. Yield with a fourth EBI programme-based on penconazole-was also less than with binapacryl, but not significantly so. Both binapacryl and penconazole were used mixed with captan.
The lower yields were due to fewer apples harvested rather than to lower individual fruit weight. Possible reasons underlying these effects are discussed: the anti-gibberellin action of EBI compounds may be involved.     

sulphur isotope composition of stream water,moss and humus from eight arctic catchments in the Kola Peninsula region (NW Russia,N Finland,NE Norway)

In summer 1994, stream water, moss and humus samples were collected for sulphur isotopic analysis from eight catchments located in the western Kola Peninsula region, where several industrial centres emit high loads of SO₂ and other elements to the atmosphere. Three potential sources of sulphur and their isotopic signatures were identified: (1) marine (δ ³⁴S+20 to +21‰ CDT), (2) anthropogenic emissions (<+10‰), and (3) geogenic (variableδ ³⁴S, mostly <+10‰). Averaged per catchment, the sulphur isotopic composition varies between +6.0 and +16.3‰ for stream water sulphate, +6.0 and +8.4‰ for moss sulphur, and +5.2 and +12.2‰ for humus sulphur. Theδ ³⁴S composition of stream water from the more remote catchments is quite variable, reflecting several natural (geogenic) sources, but it becomes restricted to the range +8 to +10‰ near the pollution sources. A plot ofδ ³⁴S vs. 1:SO₄ in stream water suggests that sulphate originating from the smelters has aδ ³⁴S value ≈+9.5‰, and is a dominant source. Sulphur isotope values for moss and humus are consistent with the deduced composition for the emitted sulphur, though for humus a component of geogenic sulphur incorporated via vegetation uptake may play a role. Further isotopic characterisation of atmospheric emissions, together with environmental samples, is needed to better understand sulphur sources and sinks in the area.     

Fungicide and nitrogen applications in relation to the improvement of disease control and yield in winter barley

In crops of winter barley, cvs Igri and Halcyon, crop structure and intensity of foliar diseases were altered by delaying the main top dressing of nitrogen until mid-April. A single application of fungicide then was sufficient to decrease substantially the severity of fungal disease and improve grain yield at harvest.
Disease control and yield responses were greatest when fungicides were applied during a 3-week period after the main nitrogen application in April. No additional yield benefits were obtained by making two fungicide applications at growth stage (GS) 31 and GS 39.     

Fireblight at Long Ashton: a case history, 1971–1983

At Long Ashton Research Station serious outbreaks of fireblight (caused by Erwinia amylovora ) occurred on apples in 1978, 1980 and 1982. and on pears in 1979, Mid-season and late-flowering cider apple cultivars were particularly affected. On cider apple, outbreaks were associated with years of profuse blossom coinciding with unusually warm temperatures during bloom. Spread of infection between hosts, including hawthorn and cotoneaster, was undoubtedly important. These and other factors underlying the outbreaks are discussed.