Tensions in tillage: Reduction in tillage intensity associates with lower wheat growth and nutritional grain quality despite enhanced soil biological indicators

Dryland ecosystems are particularly susceptible to the adverse effects of intensive agriculture, with intensive tillage exerting a major impact on soil health and its biotic components. The implementation of less disturbing soil management practices can be essential for preserving the soil environment and maintaining the diverse communities of microorganisms, micro- and mesofauna, which are vital contributors to soil fertility. In this study, we assessed soil chemical properties, soil biodiversity and functionality, and wheat crop growth across a tillage gradient encompassing no-tillage (NT), minimum tillage (MT), and standard tillage (ST). Results showed that reducing tillage intensity increased soil macronutrient levels and the abundance of soil biota. Overall, higher levels of bacterial and fungal marker genes and higher abundance of predatory acari were observed in MT and NT compared to ST. Also, nematode abundance increased by 25 % in MT and 50 % in NT, compared to ST. Similarly, community structure analysis revealed that tillage strongly influenced bacterial, fungal and acari community composition, reflecting a gradient of soil disturbance intensity. Corresponding to the increased abundance of soil biota, reducing tillage intensity increased microbial activity and soil functionality along the disturbance gradient. In addition, evidence of the formation of biocrust as a possible source of carbon input was found. Despite enhanced soil biological indicators in less intensive tillage systems, wheat growth, nitrogen uptake and grain B vitamin contents were higher in ST compared to NT. In addition, we observed a shift in technological grain properties across tillage practices. The higher root:shoot ratio (an indicator of nitrogen deficiency) and median root diameter (hormone-driven lateral expansion) in NT suggest that soil compaction could be a potential cause of reduced wheat performance. These results suggest that despite improved soil biological indicators, other factors such as low rates of N mineralization potential due to drought conditions during the study year and the prevalence of soil compaction may limit wheat performance in NT systems.