Gibbsite and halloysite decomposition in strongly acid podzolic soils developed from granitic saprolite of the Bayerischer Wald

The present study reports the occurrence of gibbsite and halloysite in soils derived from granitic saprolites and from glacial deposits formed from granitic saprolites of the Bayerischer Wald (Germany). Both minerals are common in soils of this area. They were formed in the initial stages of weathering, most probably before the Pleistocene and in a warmer climate. Under present conditions halloysite and gibbsite are unstable in the surface soils, as indicated by a decrease in gibbsite concentration towards the surface and by an undersaturation of the equilibrium soil solution with respect to both minerals. It is assumed that the strongly acid conditions and the high concentration of organic compounds in the surface horizons lead to dissolution of gibbsite and possibly to transformation of halloysite to kaolinite.     

Some observations on plant lectins and Rhizobium specificity

The ability of fluorescein isothiocyanate (FITC) labelled lectins extracted from the legumes Aspalathus linearis, Glycine max, Lotononis bainesii, Phaseolus vulgaris and Pisum sativum, respectively, to react with strains of various Rhizobium spp. was studied. With the exception of six out of ten strains of R. phaseoli and two out of ten strains of R. japonicum, none of the Rhizobium strains tested were able to bind lectin from their normal host plants. Many strains of R. leguminosarum, R. trifolii and R. phaseoli bound each of the plant lectins studied with the exception of the P. sativum lectin. This lectin was only bound by two strains of R. meliloti and a slow-growing strain isolated from Macroptilium atropurpureum. These results do not support suggestions by other workers that plant lectins play an important role in Rhizobium specificity.     

Vital staining of fungi in pure cultures and in soil with fluorescein diacetate

A method for vital staining of fungal mycelium with fluorescein diacetate (FDA) is described. In experiments with pure cultures, good correlation was obtained between relative staining efficiency, growth rate, and respiration. FDA thus appears to be a true vital stain, in that it stains only metabolically active mycelia.In fresh soil suspensions stained with FDA, brightly fluorescent hyphae and portions of hyphae were observed. The applicability of the method for measurement of active mycelium in the soil is discussed.     

A comparison of some red and yellow earths in tropical queensland and northeast Brazil

Red and yellow earths are kaolinitic and generally sesquioxidic soils having massive B horizons with porous, earthy fabrics and weak profile differentiation but usually displaying a gradual increase in clay content with depth. They are widespread in tropical Queensland and northeast Brazil where comparable climates prevail although the vegetation is markedly different. Their parent materials are mostly quartzitic sedimentary rocks or unconsolidated sediments and the soils occur in a wide variety of topographic and geomorphic situations. In both regions it is probable that many of the soils have not formed under the present climatic conditions.Profile morphology, drainage, silt and clay contents, clay mineralogy, and soil chemistry have been compared and contrasted between the red and yellow earths within and between the two regions. Canonical variate analysis has shown that, on the basis of surface soil chemical attributes, the red earths can be separated from the yellow earths within each region and that the Queensland soils can be separated from the Brazilian soils.     

Hyphal density as a measure of suppression of Gaeumannomyces graminis var. tritici on wheat roots

Runner hyphae of Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker on seminal roots of wheat seedlings were photographed and their length measured. As well, their length was estimated using the line-intercept method. The correlation of 0.904 between measured and estimated lengths of hyphae was highly significant. This line intercept method was used to estimate the density (length/unit area) of hyphae on roots of plants growing in the presence and absence of a soil suppressive to G. graminis var. tritici. Estimations were made eight times during 28 days growth at 15°C. In fumigated soil (non-suppressive) inoculated with 0.1% ground oat grain infested with G. graminis var. tritici, the density of hyphae on roots started to increase at five days compared with 15 days when soil there was a 10.8% cover of the root surface after 15 days when the hyphae had reached maximum density. Suppression to G. graminis var. tritici is normally detected by a difference in disease rating of roots at 28 days but this study has shown that suppression can be demonstrated by the difference in the density of hyphae if roots are examined between seven and 19 days.