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

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 (θ_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 (θ_2MPa) were obtained by drawing soil resistance curve (SRC) and also soil water contents at field capacity (θ_fc), permanent wilting point (θ_pwp-) and at 10% aeration porosity (θ_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 θ_w was appreciable. Computed θ_2MPa from SRC was higher for CL than for LS and SL. Among all four parameters of LLWR, θ_fc and qpwp did not vary much, whereas θ_ap reduced significantly and θ_2MPa increased appreciably with increase in BD. Trends of LLWR-BD curve showed that LLWR was more than 20% (m³m⁻³) at lower BD, which is indication of good structural condition and decreased with increase in BD. At BD >1.75 Mg m³ for LS and SL and at BD>1.68 Mgm⁻³ for CL the value of LLWR became less than 10% (m³m⁻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 structural condition.