An investigation was carried out to study the physical and chemical properties of soils and its relationship with water holding capacity along altitudinal gradient for cultivated soils of South Sikkim. The physiography of the study area was mainly hilly terrain with closely spaced contour on steep sloppy lands. The soil texture ranged from sandy loam to clay with slightly acidic (6.6) to highly acidic (4.2) in reaction. The organic carbon content varied from 1.22 to 3.45 per cent with a mean value of 2.31 per cent. The bulk density, particle density, porosity, volume expansion and water in air dry soils ranged from 1.08 to 1.54 gm/cc, 2.05 to 2.77 gm/cc, 42.44 to 61.73 per cent, 2.95 to 11.9 per cent and 0.68 to 4.32 per cent, respectively. The water holding capacity (WHC) ranged from 33 to 73.86 per cent with a mean value of 54.18 per cent. The results revealed that 80 per cent of the soil samples have medium to high WHC while only 20 per cent are of low category. A significant positive relationship was observed between WHC and organic carbon, clay and porosity, while, a negative relationship was found with pH and bulk density with sand and silt content.
A study was conducted with 24 piedmont soils of Arunachal Pradesh (India) to estimate the critical limit of available boron (B) in soil and cowpea plant for predicting the response of cowpea (Vigna unguiculata L. Walp.) to B application. The critical concentration of available B in these soils was established by graphical procedure at 0.48 mg kg −1 for soil and at 24.5 mg kg −1 in the plant tissues. Soil containing available B below the critical limit responded appreciably to B fertilization. A negative response to B application was also observed in soils at higher level of available B. The average dry matter yield increased with the increasing level of B application up to 1.5 mg kg −1 . The yield response to B application in cowpea on B deficient soils was 34.5%. Based on the critical value of 0.48 mg kg −1 , 10 soils were rated to be adequate and 20.0% soils belonging to this category responding to B application, whereas 85.7% soils below the critical value showed a positive response to B application. The hot water soluble B was significantly and positively correlated with organic carbon, cation exchange capacity and clay contents and negatively correlated with pH, silt and sand contents of soils.
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