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Penetrometer resistance is one of the important soil physical properties that can determine, or be strongly correlated with, both root elongation and yield. We used a field experiment, which was designed to explore the effects of no-tillage (NT) and ridge tillage (RT) on a Mollisols in Northeast China, to test an approach for predicting the effects of soil bulk density, matric potential of water, and depth on penetrometer resistance. The field experiment was initiated in the fall 2010 on a clay loam soil. Soil bulk density, water content, water release curve, and penetrometer resistance were measured during the corn growing seasons in 2012 and 2013. Compared with the RT treatment, NT significantly increased soil bulk density and reduced the fraction of macropores in the 0–20 cm soil layer. The increase in density under NT resulted in a higher soil penetrometer resistance, which was associated with a lower water uptake by roots compared with the RT treatment. It was possible to use a relatively simple model for penetrometer resistance to explain the effects of soil bulk density, water status and depth on penetrometer resistance. Depth was included by relating it to overburden pressure. In a penetrometer resistance model that excluded overburden pressure, or depth empirically, penetrometer resistance in deeper layers (>35 cm) could not be fitted accurately. The effects of depth on penetrometer resistance from this study were consistent with published data. Our data suggests that at the assessment of soil conditions for root growth, ignoring the effects of depth is likely to give misleading penetrometer resistance. [ABSTRACT FROM AUTHOR]

Soil structure influences the soil hydraulic properties, aeration and resistance to root penetration. Many indicators can be used to investigate the changes of soil structure, but using a single indicator or method has limitations. This study evaluates the effects of 15-years tillage management on soil structure with soil bulk density (BD) , penetrometer resistance (PR), soil water retention curve (SWRC), least limiting water range (LLWR) and X-ray computed tomography (CT). The treatments include no-tillage (NT), rotary tillage (RT), and mouldboard plough (MP). Soil bulk density of the 0–30 cm soil profile was measured after the establishment of tillage treatments for 7, 9, 12 and 14-years. The values of PR , SWRC, LLWR, and 3-D pore geometry of the 5–10 and 15–20 cm layers were determined in the 15th year of the experiment. The greater BD in the 0–5 cm layer of NT was not observed after 9 years, but an increased BD in the 5–20 cm layer was found in most years. Tillage had no effect on PR in wet soil. When soil had dried, the NT treatment had a greater PR and it was the lower limiting factor of LLWR, ultimately leading to a narrower LLWR of NT. Both NT and RT showed lower proportions of structural but higher textural pores. The macroporosity (> 50 µm) from X-ray CT was greater than that estimated from SWRC of the 15–20 cm layer. The characteristics of pore morphology were similar under three tillage treatments. Therefore, NT resulted in a narrower LLWR due to the denser soil layer, yet similar macropores may alleviate the negative impacts on crop growth caused by lower LLWR. It was suggested that using LLWR and characteristics of macropores from X-ray CT at the same time is a suitable way to assess soil structure under various tillage practices. • After 15-years no-tillage, the physical quality is poor in 5–20 cm layer reflected by greater BD, PR, and lower LLWR. • Similar properties of macropore weak the usefulness of LLWR for assessing soil structure under no tillage treatment. • Combining LLWR with macropores from X-ray CT is a suitable way to assess soil structure under various tillage practices. [ABSTRACT FROM AUTHOR]

• Soil water retention curve (WRC) shape is influenced by variable bulk density. • Available pedotransfer functions (PTFs) fail to account for bulk density effects. • New PTFs for WRCs are developed to better account for bulk density effects. • The accuracy of New PTFs is comparable to widely-used ones. Pedotransfer functions (PTFs) describing soil water retention curves (WRCs) have been widely used in crop, soil, and land surface models. A limitation of the available PTFs is that they fail to account for shape changes in WRCs due to bulk density variations caused by soil tillage, compaction, and other processes. This study develops new PTFs that include bulk density effects on the WRC shape. A new framework is introduced to build the bulk density-associated PTFs based on a widely-used WRC dataset. The new PTFs were validated by comparing the performance with two common PTFs from the literature using two independent datasets. The results show that the newly developed PTFs provide reliable WRC estimates for the validation datasets, with mean RMSE values of 0.055 and 0.059 m3 m-3, respectively. The accuracy of the new PTFs is comparable or in some cases better than the common PTFs. While the literature PTFs investigated do not always properly describe bulk density effects on WRC changes, the new PTFs effectively account for such effects on the WRC shape, thus have the potential to be integrated into crop and soil management models to represent bulk density impacts on WRCs due to anthropogenic (e.g., plowing and compaction) and natural (e.g., wetting/drying) processes. [ABSTRACT FROM AUTHOR]