Soil and erosion features of the central plateau region of Tigrai,Ethiopia

The results of reconnaissance soil surveys covering 6,000 km² are used to describe the Central Plateau region, which lies at elevations of 2,000 to 2,800 m in northern Ethiopia. Landform and soil sequences on calcareous shales, dolerites and sandstones are described, in which the principal soil units are Lithosols, Luvisols, Cambisols, Arenosols and Vertisols. Detailed morphological and analytical data are presented for a profile representative of arable soils in each sequence.Small-scale subsistence cultivation of cereals is the dominant land use; all land which is physically cultivable is at present cultivated. Settlement patterns are closely related to soil type, nucleated settlement occurring on fine textured soils but dispersed settlement on coarser textured and more freely draining soils.Erosion and soil moisture features of the three landforms described were investigated and compared. Empirical methods and suspended sediment measurements indicate high rates of regional soil loss (17–33 t ha^?1 yr^?1), accounted for by seasonally high rates of rainfall erosivity, steep terrain and poor land use. The recent development of gully erosion is seen to be linked to the disintegration of waterfall tufas. Application of the universal soil loss equation to arable lands indicates potential annual soil losses in the range of 400 t ha^?1 on Vertisols to 200 t ha^?1 on Cambisols: differences in rates are ascribed principally to differences in crop planting dates, which affect the degree of vegetative protection during periods of high rainfall erosivity.Soil moisture is shown to be in the available range for less than three months in the year. The time at which moisture in the profile enters the available range differed between the three soils monitored and was found to be closely related to the crop planting date, thus indirectly affecting the erosion hazard.     

Dopamine: mediator of brain polysome disaggregation after L-dopa

The disaggregation of brain polysomes which is produced by giving large doses of (L)-dopa to rats is not reproduced by administering its metabolite, 3-O-methyldopa, by giving D-dopa, which also depletes the brain of S-adenosylmethionine but is not converted to catecholamines, or by giving the L-dopa after a decarboxylase inhibitor. Polysome disaggregation is potentiated by the prior administration of a monoamine oxidase inhibitor, indicating that formation of a catecholamine is an obligatory requirement. These observations suggest that the mechanism by which L-dopa disaggregates brain polysomes involves its conversion to dopamine within the majority of brain cells.     

MECHANICAL TREATMENT FOR IMPROVING UPLAND GRAZING

The botanical changes in a wet ( Molinia ) and a drier ( Nardtts ) upland pasture that followed a single defoliation by a forage harvester are briefly described. Without fertilizer the bare and litter-covered areas were soon recolonized by the original dominants; with lime and fertilizer the recolonization was mainly by Agrostis spp., even when Agrostis was a minor element in the original sward. These changes were markedly accelerated by the forage-harvester treatment. The results of surface seeding after the forage-harvester treatment are compared with those obtained after rotary cultivation. Contrasting moisture regimes and competitive thresholds led to considerable differences in sward balance and in establishment of sown species, and seeding was successful only on the wetter site. Too rapid regeneration of undesirable remnants was prevalent, but this and other hazards are related to the uneven deposit of litter left by the forage harvester; thick, slowly-rotting accumulations inhibited the redevelopment of rapidly-growing species and germination on seeded areas.