Alluvial Soils

Study area consists of the alluvial plains of Kothari River, which is the tributary of Banas and situated in Eastern Rajasthan Upland. The area surrounded by Aravalli hills where sand constituted the major part of the soil. This study is concerned with the relationship of the soil moisture retention and release properties with irrigation scheduling and land use plan along with their texture, particularly the clay and silt fraction. Twelve pedons representing various topographic positions and zone of rainfall were sampled to study the soil-plant-water relationship in alluvial soils. viz., upper rolling plains, middle sloping plains, lower plains. Soil moisture retention characteristics explained that the soils of the upper rolling plains have capacity to retain low amount of plant available water (AWC 7.31cm/m) as compared to the soils of middle sloping plain (AWC 12.87 cm/m) and lower plain (AWC 14.02 cm/m). Volumetric water content at different suction pressures viz. 33, 100, 500, 800, 1000, 1200 and 1500 kPa were studied in the alluvia of the river. About 75 percent of available water found to be released below the suction pressure of 500 kPa. The amount of available moisture for plant between 33 to 100 kPa was 59, 55 and 51 per cent while between 100 to 500 kPa it was 16, 20 and 22 per cent in upper rolling plains, middle sloping plains and lower plains, respectively. Silt and clay fractions were found to be the major factor controlling the available moisture. Coefficient of variation in moisture retention was noted from moderate (15–35%) to high (>35%) magnitude within the plains. In present investigation moisture retention of soils depleted to about 50 per cent at 100 kPa suction pressure so that irrigation should be delivered to replenish the soil moisture storage at this stage to keep target of maximum economic yield.

GOLD PLACER OF THE MILANO SUBSOIL

Gold is a mineral widespread throughout the Alps and in the northern Apennines, but economically interesting concentrations are very scarce and are found only in the central-western Alps: they generally consist of quartz vein with native gold or gold-containing sulphides. The Po plane placers are made up of recent alluvial sediments of many rivers, containing very fine dust and scales. On the Po river southern side, the Orba is the only rich stream; on the northern side there are the rich rivers Orco, Dora Baltea, Elvo, Ticino and Adda, and many minor tributaries, which do not take gold directly from primary gold ores and related eluvial and alluvial deposits, but from the glacial sediments that carried them for many kilometers to the south. In addition, all these rivers received, and transport downstream, the gold particles lost during the Celtic and Roman exploitations of the highest gold-bearing alluvial terraces.

The city of Milan is located at the confluence of three small streams (Olona, Seveso, Lambro) responsible for the considerable thickness - almost 400 feet - of the alluvial layers below, made up of sand and gravel rich in aquifers: the entire requirement water supply of the metropolitan area is completely satisfied by many wells.

The systematic collection of samples, in large sand quarries operating around the city, has made it possible to obtain interesting samples of natural sands and its concentrates composed of heavy minerals. The estimated gold content in the extracted sediment, up to 30 m deep, is a few centigrams per cubic meter. Gold is made up of thin flakes, some ten millimeters large, of an intense yellow color, with a rough surface and irregular edges: the average composition is 92.3% pure gold, 6% silver, 1.7% other metals. The concentrates are mainly composed of garnets (30-50% by weight), magnetite (20-40%) and ilmenite (12-20%), with a gold content rancing from 0,1 to 0,4%.

The study area consists of the alluvial plains of Kothari River, a tributary of Banas and situated in Eastern
Rajasthan Uplands. The area is surrounded by Aravalli hills. Sand constituted the major part of the soils of
Kothari river plains. Quartz was the dominant mineral followed by feldspars and mica in all the plains. There
was a mixed mineralogical makeup of clay fraction. Mixed mineralogy of alluvial plains revealed that the soils
of the area were formed by mafic and felsic igneous rocks under moderate precipitation with higher base
status. Higher cation content or base saturation with low rainfall (<1000 mm) favour the formation of smectites.
Decreasing order of minerals (estimated semi-quantitatively) in the soils of alluvial plains could be depicted
as: Illite/mica > smectite > kaolinite > feldspars > quartz > vermiculite = chlorite. Smectite content was highest
in the soils of lower plains and least in upper rolling plains while illite/mica was highest in the soils of middle
sloping plains. The ratio of 001 and 002 basal reflections of mica was more than unity, suggesting the
presence of both biotite and muscovite mica minerals. Other minerals were found randomly distributed
without any specific pattern. Youthful nature of the soils of upper rolling plains was indicated due to the
presence of talc in their clay fraction. Mineralogy of silt size fraction was very similar to clay mineral
framework except the higher content of quartz and feldspars and an equivalent reduction in 2:1 or 1:1
minerals. Smectite, mica, kaolinite, quartz, feldspars with trace amount of chlorite and vermiculite were found
in silt size fraction.