The fractile diagram of bulk density of the soil constructed by the use of a probability density distribution/unction showed a normal distribution. Four stage balanced hierarchical (nested) analysis of variance showed that the samplesfrom 0.67 ha contributed 44 to 54% of the total variance, an increase in sampling area to 2 and 6 ha increased the contribution but by smaller amounts of 26 to 35% and 15 to 26%, respectively. Two dimensional geostatistical analysis of bulk density showed the anisotropic nature of its distribution with the maximum gradient of semivariance in west direction. The recommended tillage systems were disc plough tillage system and chisel plough tillage system for the sub-blocks having bulk densities greater than 1.62 Mg m−3 up to 0.30 m and 0.45 m depths, respectively, to reduce the mechanical impedance for root growth.
Bulk density, probability density, variance, semivariance, anisotropic, mechanical impedance
