Unearthing Soil Structure Dynamics under Long-Term No-Tillage System in Clayey Soils

Soil structure is a sensitive and dynamic soil physical property that responds rapidly to different tillage systems, and thus it requires constant monitoring and evaluation. The visual evaluation of soil structure (VESS) and subsoil visual evaluation of soil structure (SubVESS) methods were used to assess the soil structure quality of clayey soils subjected to different tillage systems. The tillage systems were no-tillage (NT) and conventional tillage (CT), with virgin fields (VGs) used as controls. The study was conducted at Tshivhilwi and Dzingahe in Thohoyandou, Vhembe District, Limpopo Province, South Africa. The soil structure quality at Tshivhilwi, as determined by VESS and SubVESS, was found to be poor. However, at Dzingahe, both the VESS and SubVESS scores responded to the impact of tillage. VESS showed a fair (Sq = 2.25) soil structural quality in the NT system, poor quality (Sq = 3.57) in the CT system and moderately poor quality (Sq = 3.05) in the VG. Similarly, at the same location, the SubVESS scores were moderately good in the NT system, moderately poor for the CT system and fair in the VG. The differences in the responses of VESS and SubVESS at the two locations were attributed to differences in the duration of the NT system. The VESS and SubVESS results were supported by selected measured soil physico-chemical properties such as bulk density and porosity. In conclusion, the findings of this study showed that VESS and SubVESS were able to effectively differentiate between the impacts of tillage systems on soil structural quality. The soil structure quality was better under NT than CT at Tshivhilwi and Dzingahe.