Long-term effects of five ameliorants on a saline-sodic soil of South Africa

The effects of five ameliorants for saline-sodic soil reclamation on certain chemical and physical soil properties over a four-year period of observation are reported. Of these ameliorants, three are conventionally used (gypsum, sulphur, manure); the other two are for this purpose either unusual (potassium sulphate) or relatively unknown (molasses meal). Results published in a previous paper demonstrated that molasses meal had a very rapid-acting favourable effect on most soil physical properties whilst soil chemical conditions remained essentially unchanged. The effect on physical properties was presumably due to soil aggregation by the polysaccharide component of molasses meal. As a follow-up this paper shows, however, that this aggregation does not last long; the rigidly arid climatic conditions under which this experiment was carried out apparently do not favour the preservation of structural bonds consisting of polysaccharide gums. Consequently, a gradual decline of structural conditions took place after the second year. Although initially not as effective as molasses meal, gypsum and sulphur retained their favourable influence on physical properties over a longer period. Potassium sulphate and farmyard manure provided virtually no benefits.     

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.     

Adsorption sur les argiles de deux lipopolysaccharides rhizosphériques

The adsorption with time has been measured of two well characterized lipopolysaccharides onto aqueous suspensions of a montmorillonite, a kaolinite and an illite at one fixed polymer-clay ratio. The clays were prepared in the Fe⁺⁺⁺ or Ca⁺⁺ forms by washing with FeCl₃ or CaCl₂ followed with water. The competitive sorption of the two polymers was measured also in the presence of an equal concentration of a protein or a basic amino-acid. Sorption of the polymers by themselves was approximately proportional to the external areas of the three clays and independent of the exchangeable cation. The presence of the protein inhibited completely the adsorption of both polymers onto the Ca⁺⁺ clays, but usually enhanced sorption onto the Fe⁺⁺⁺ clays. Sorption in the presence of the amino-acid differed both for each polymer and according to the form of the clay. Possible reasons for the various sorption patterns are discussed.     

Factors influencing the loss of organic carbon from wheat roots

Wheat plants were grown in an atmosphere containing ¹⁴CO₂ at temperatures of 10°C or 18°C for periods from 3–8 weeks. The plant roots were maintained under sterile or non-sterile conditions in soil contained in sealed pots which were flushed to displace respired ¹⁴CO₂. The ¹⁴C content of the shoots, roots and soil was measured at harvest. The loss of ¹⁴C from the roots, expressed either in terms of total ¹⁴C recovered from the pots or ¹⁴C translocated to the roots, ranged from 14.3–22.6%, mean 17.3% or 29.2–44.4%, mean 39.2%, respectively. The presence of soil microorganisms significantly increased ¹⁴CO₂ release from the rhizosphere but had no effect on the ¹⁴C content of the soil. Fractionation of 6 m HC1 hydrolysates from sterile and non-sterile soils showed the presence in all soils of material behaving as neutral sugars and amino acids, in quantities representing 5.9–9.2% and 13.4–17.2% of the soil ¹⁴C content for the sugar and amino acid fractions respectively. It is proposed that a major loss of root carbon resulted from autolysis of the root cortex. Root lysis was increased by soil microorganisms, apparently without penetration of the plant cell walls.     

Diurnal changes in acetylene reduction in field-grown cowpeas and soybeans

The effects of five environmental factors on variation in the rate of C₂H₂ reduction in two cowpea (Vigna unguiculata L. Walp.) and two soybean (Glycine max L. Merrill) cultivars were examined at two stages of growth in the field. Diurnal changes in C₂H₂ reduction, estimated as μmoles C₂H₄ produced·g^?1 nodules·h^?1, over a 30 h period were compared with changes in soil, canopy and air temperatures, global radiation, and vapour pressure deficit. Although the environmental factors showed one maximum and one minimum during a diurnal cycle, the C₂H₂ reduction rate in nodulated cowpea roots showed two peaks: one between 0600–1200 and another between 1800–2400 and two minima: one between 1200–1600 and another between 2400–0600. Variation in C₂H₂ reduction in soybean nodules did not show any definite pattern. Vapour pressure deficit appeared the most likely factor influencing the decline in C₂H₂ reduction between 1200–1600.The rate of C₂H₂ reduction in cowpeas was greater at the pre-flower than at the early pod-fill period; the rate in soybeans was not greatly different at early flower or early pod-fill.     

Soil protozoan dynamics in a shortgrass prairie

Soil Protozoa (primarily small naked amoebae and flagellates) were counted under control conditions and with stresses of nitrogen, water, or nitrogen and water under field conditions (Ecosystem Stress Area, Pawnee Site, northeastern Colorado, USA) in the summer of 1974. Protozoan populations were also measured in soil cores removed from the field and incubated under a wet-dry cycle. Protozoan numbers were higher in the top 1 cm of soil and overlying litter than at a depth of 5–6 cm in all treatments. After rainfall totaling 35 mm, the control and fertilized only treatments showed population increases with the fertilized only treatment showing the greater change. Protozoa showed marked responses to the addition of water to soil cores, with the largest numbers appearing after peak CO₂ evolution. Numbers of active (trophic) forms ranged from about 20.000. g^?1 dry soil in the control treatment under dry conditions to over 100,000. g^?1 dry soil in the irrigated plus fertilized plot. There were few (<5%) cystic (dormant) forms in all treatments contrary to earlier studies in mesic climates. A rough estimate of protozoan production is presented.     

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.     

The utilisation of poison hoppers designed for grey squirrel (Sciurus carolinensis Gmelin) control

The grey squirrel is recognised as a pest species of economic importance but the justification of the view appears to be founded on local areas of severe damage. Despite evidence that damage may not be alleviated by squirrel population destruction, Warfarin poisoning was introduced as an alternative to trapping.The utilisation by wildlife of a poison hopper designed for grey squirrel control was investigated by automatic photography. Results confirmed that a number of species may feed from the grain presented via the hopper. However, the majority of the bait was removed during the hours of darkness when grey squirrels were not active. It is a conservative estimate that between 55 and 65% of the grain entered the environment via animals other than squirrels.In addition, the removalof bait by night visitors resulted in the accumulation of large quantities of bait at and around the entrance to the hopper tunnel. This increased accessibility to the potentially poisoned bait by animals other than squirrels.Until such time as evidence is produced to show these results as exceptional, it can only be concluded that fears expressed over the lack of specificity of this method of control are justified.     

Management of the Northern Chesapeake Bay American shad fishery

The Shad fisheries of the Chesapeake Bay in Maryland have been declining since an 1897 peak of 7860 × 10³kg. No periods of stability have been recorded. Data are presented to trace the decline not only as a function of specific areas within the Northern Chesapeake Bay but also in terms of environmental problems and recruitment overfishing.The problem is related to improving the commercial fishing yield. An estimation of a maximum effort of 200,000 man-hours is suggested if a stable yield is to be approached. Methods for obtaining this goal include alternating of closed fishing areas, adoption of rest days, enforcement of fisheries regulations and reduction of the number of metres of gill net used per fisherman.