Variation of Least Limiting Water Range with Compaction for Divergent Textured Soils

摘要

Least limiting water range (LLWR), an indicator of soil structural quality is dynamic in nature and varies inversely with bulk density (BD) changes; its effects are further modified by variation in soil texture. Hence, in order to relate LLWR with compaction and soil type, a column study was carried out with three soil types i.e. sandy loam (SL), loamy sand (LS) and clay loam (CL), five soil water contents (theta_W) (5, 10,15, 20 and 25% by weight) and three compaction levels (10, 20 and 30 blows). Components of LLWR i.e. soil water content at soil penetration resistance (PR) of 2MPa (theta_(2MPa)) were obtained by drawing soil resistance curve (SRC) and also soil water contents at field capacity (theta_(fc)), permanent wilting point (theta_(pwp).)and at 10% aeration porosity (theta_(ap)) determined by drawing soil water release curve (SWC). The SRC showed that as compared to higher BD, at lower BD the magnitude of PR was low and its reduction with increase in theta_W was appreciable. Computed theta_(2MPa) from SRC was higher for CL than for LS and SL. Among all four parameters of LLWR, theta_(fc) and q_(pwp) did not vary much, whereas theta_(ap) reduced significantly and theta_(2MPa) increased appreciably with increase in BD. Trends of LLWR-BD curve showed that LLWR was more than 20% (m3m3) at lower BD, which is indication of good structural condition and decreased with increase in BD. At BD >1.75 Mg m~3for LS and SL and at BD>1.68 Mg m~(-3)for CL the value of LLWR became less than 10% (m~3m~(-3)) which indicated poor structural conditions. For all soil types, available water capacity (AWC) did not vary appreciably with BD, whereas LLWR decreased appreciably with increase in BD, which indicated that LLWR was a true indicator of soil structuralcondition.