Studying Tillage Effects on Physical Factors Affecting Plant Growth Using LLWR Index

Plant growth is directly affected by soil water, soil aeration, and soil resistance to root penetration. Least limiting water range (LLWR), a proposed soil structural quality index, is the range of soil water content at which plant growth is least limited by water potential, aeration, and soil mechanical resistance. In this study, the effect of tillage on the physical factors controlling plant growth in the LLWR index was investigated. Sixty undisturbed soil samples were collected from two contiguous fields cultivated by no-tillage and conventional tillage. Then, soil water retention curve, soil resistance curve, and bulk density were determined. The results showed that in conventional tillage system LLWR was significantly higher (P <0.01). In no-tillage system, θSR (soil moisture equivalent to 2 MPa penetration resistance) was the lower limit of LLWR in 63% of the samples and replaced θPWP (soil moisture at permanent wilting point), while this value was 53% in conventional tillage.