ON pC, pS, AND pN AS INDICATING FUNCTIONS OF ELECTRICAL SOIL CONDUCTIVITY

The colourless complexes with other polyphenols are soluble in 70% aqueous alcohol, but are precipitated when the alcohol concentration is raised. I t appears that the simpler polyphenols form complexes, in the fresh beans, with the more complex polyphenolic compounds, which are stable in neutral but not in acid solution. This is of considerable interest, since a major feature of the commercial fermentation of cacao is the production of acetic acid by the flora fermenting the pulp, so that at an early stage the cotyledons are permeated with acetic acid and any such complex will be broken up.Severe damage to lettuce involving tip-burn of the leaves, wilting and death has occurred in several tomato glasshouses in west Scotland. Soils from such houses lose their capacity to cause damage if their soluble-salt content is reduced by leaching or liming. The damage was produced experimentally when mixed artificial fertilizer was added to normal soil in amounts equivalent to four tons and more per acre. It is therefore concluded that the diseased condition results from over-manuring, i e. too high a content of soluble salts in the soil. Heavy manuring of the preceding tomato crop may contribute to this over-manuring of the lettuce. Only one extreme case of actual damage to a tomato crop has been reported, but the yield of tomatoes begins to fall a t higher levels of soluble mineral matter than for lettuce. It is suggested that the yield of tomatoes begins t o fall at lower values of soluble-salt content when added manures are grossly unbalanced than when they are attuned to the needs of the crop.The plant pathologist is familiar, in the course of his work, with instances of abnormal functioning of crop plants for which no parasitic cause can be found. One such instance concerned nine glasshouses of winter lettuce, from which not one plant was marketable (Fig. I). Botrytis sp. and aphides could be found, but were so scant that they could not have caused the extensive damage.Affected plants first showed a drying or wilting of the leaf margins, without loss of green colour. This initial appearance has been called ' tip-burn ' or ' leaf-burn ' in this paper, without prejudice to similar symptoms possibly due to other causes (e.g. Greer, 1946 ;Anderson, 1946). Whole leaves wilted, later becoming brown or black, and the plant ultimately died (Fig. I). The roots were often discoloured.Manuring of the preceding tomato crop had been on a generous scale, and ammonium sulphate had, moreover, been applied to most houses at the surprising rate of one ton per acre, before the lettuce was planted. One house to which this heavy dressing had not been given showed less damage. This gave a @ima facie indication that the diseased condition was related either to excessive ammonium sulphate, or to excessive manuring in general. The present investigation was therefore undertaken to test these suppositions, to see what practical

Damage to glasshouse crops by over‐manuring

Grainger

1952

Carbon‐nitrogen relationships in soil. III.—Comparison of Immobilization of Nitrogen in a Range of Soils

Winsor

Pollard

1956

WINSOR d POLLARD-CARBON-NITROGEN RELATIONSHIPS. I I I 613spectrum obtained from a freeze-dried secretion sample, and confirms the muco-protein nature of this material. In this spectrum, the broad structure of the OH-bending vibrations may also be due in part to the complex mixture of sugars which form the polysaccharide parts of the molecules. ConclusionAs indicated earlier, the quantitative analysis of dairy products by infra-red absorption methods presents a number of special problems. Attempts are being made to study dried materials using the potassium bromide pressed-disc technique, but the preparation of clear uniform discs of materials containing fat often proves difficult. Such samples are not usually hard enough to be ground up to the requisite fine particle size by a vibratory ball-mill operating at room temperature and do not mix intimately with the potassium bromide powder. If the fat content is not very high and the sample has been dried carefully, it is sometimes possible to prepare satisfactory discs, but samples from which the fat has been first removed by a suitable solvent generally provide good potassium bromide discs.Immobilization of nitrogen in the presence of sucrose has been compared in 24 soils differing widely in origin and composition. Marked differences were found in the amounts of nitrogen immobilized in the various soils, these being correlated with the pH, phosphate content and carbon/nitrogen ratios of the soils.

Sulphur in soils. III.—A study of the readily soluble sulphate content and of the total sulphur content of soil

Little¹

1958

Results are given of a survey of the readily soluble sulphate content and of the total sulphur content of soils of various categories. These results have been correlated with the results of ‘routine’ analytical determinations. The close relationship found to exist between pC and readily soluble sulphate stresses the importance of the sulphate ion in the physico‐chemical equilibrium of soil. Published results of other workers are reviewed, and comparisons drawn with the results obtained in the present survey. A deficiency of sulphur is considered unlikely in plants growing on the soils included in the present survey, although in a few cases the readily soluble sulphate content may be approaching a deficiency level.