Soil physical quality (SPQ) is an important parameter for crop growth. Tillage management is widely recognized to affect SPQ remarkably, but such an effect is complicated in Vertisols by shrinking and swelling soil structure. The objectives of this study were to (i) investigate how tillage practices affected SPQ as indicated by the S index, least limiting water range (LLWR) and water stress percentage (WSP); and (ii) determine the relationship between these SPQ indicators and crop yield. A 4-year field experiment, which was conducted in a Vertisol under wheat-maize rotation system in the North China Plain, consisted of four tillage treatments: no tillage (NT), rotary tillage (RT), subsoiling (SS), and deep ploughing (DP). Soil water retention curve (SWRC), soil shrinkage curve (SSC), penetration resistance (PR), and bulk density (BD) of the 0−10 and 10−20 cm layer were measured during wheat and maize seasons, and soil water content was continuously monitored in situ. The S index, LLWR and WSP were determined. Our results showed that SSCs were parallel to each other among four tillage treatments, indicating that tillage did not impact shrinkage capacity (P > 0.05). Relative to NT and RT treatments, the SS and DP treatments improved soil physical quality (higher S index and larger LLWR), particularly in the 10−20 cm layer. The S index presented a poor relation with wheat (P > 0.05) and maize yields (P > 0.05), while LLWR had a significant correlation with wheat yield (P < 0.05) but not with maize yield (P > 0.05). A new proposed SPQ indicator, WSP, is defined as the percentage of the period when the soil water content is above the field water capacity (waterlogging stress percentage, WLP) or below the wilting point (drought stress percentage, DSP) to the entire crop season period. The WLP presented a significantly negative relation with maize yield (P < 0.01) but not with wheat yield (P > 0.05), whereas the DSP had no relation with wheat and maize yield (P > 0.05). Moreover, the WSP was observed to be independent of the volume change in the Vertisol. Our results demonstrate that LLWR and WLP can be regarded as suitable indicators for evaluating SPQ in wheat and maize seasons, respectively, but the latter is more conveniently applied in a Vertisol.

土壤物理质量（SPQ）是作物生长的重要参数。耕作管理已被广泛认为会显着影响SPQ，但是在Vertisols中，由于土壤结构的收缩和膨胀，这种影响变得复杂。这项研究的目的是（i）研究耕作方式如何影响S指数（如S指数，最小极限水位（LLWR）和水分胁迫百分比（WSP））；（ii）确定这些SPQ指标与作物产量之间的关系。在华北平原小麦-玉米轮作系统下的Vertisol上进行了为期4年的田间试验，包括四种耕作处理：免耕（NT），旋耕（RT），深耕（SS）和深耕犁（DP）。土壤保水率曲线（SWRC），土壤收缩率曲线（SSC），耐渗透性（PR），原位。确定了S指数，LLWR和WSP。我们的结果表明，在四种耕作处理中，SSC彼此平行，表明耕作不会影响收缩能力（P  > 0.05）。相对于NT和RT处理，SS和DP处理改善了土壤物理质量（较高的S指数和较大的LLWR），尤其是在10-20 cm的土壤层中。S指数与小麦的关系不佳（P  > 0.05）和玉米单产（P  > 0.05），而LLWR与小麦的产量具有显着的相关性（P <0.05），而与玉米的产量则无相关性（P > 0.05）。新提出的SPQ指标WSP定义为土壤水分在整个作物中高于田间持水量（渍水压力百分比，WLP）或低于枯萎点（干旱压力百分比，DSP）的时期的百分比季节期间。WLP与玉米产量呈显着负相关（P  <0.01），而与小麦产量无显着负相关（P  > 0.05），而DSP与小麦和玉米产量无关（P  > 0.05）。此外，观察到WSP与Vertisol中的体积变化无关。我们的结果表明，LLWR和WLP可以分别用作评估小麦和玉米季节SPQ的合适指标，但后者在Vertisol中更方便地应用。