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The rhizosphere is a highly biogeochemically active site influencing several soil processes that are crucial for soil formation (e.g., mineral weathering). We studied weathering processes in embryonic Technosols constructed with limestone mine spoils, cultivated with sugarcane for two and six years (illitic siltstone areas: SC2 and SC6) and forage grasses (mainly Urochloa spp.) for 20 years (smectitic black shale area: P20). Rhizosphere and bulk soils were characterized through biological, chemical, and mineralogical analyses. We found contrasting biogeochemical environments when comparing rhizosphere and bulk soils. The pH values were about 1 unit lower, dissolved organic carbon concentrations were up to 3 times higher, and the average enzymatic activity was about 3 times higher in the rhizosphere soils compared to the bulk soils of the studied Technosols. A higher biological activity in the rhizosphere triggered the weathering of primary minerals (dolomite, feldspar, muscovite, quartz), causing the release of K, Ca, Mg, and Si from the mineral structure into the soil solution. The enrichment of the rhizospheric soil solution with Si and bases (mainly Ca and Mg) triggered the transformation of clay minerals and led to the formation of amorphous Si phases. Under sugarcane, smectite content increased from 18% in the siltstone to 44% in the SC6 rhizosphere. Under forage grasses, there was an increase in smectite contents from 58% in the black shale to 75% in both the rhizosphere and bulk soils. The main clay transformation process was a topotactic transformation from illite to smectite through progressive interstratification, supplied by the high availability of Si, Ca, and Mg in the rhizosphere. Our results highlight the pivotal role of rhizospheric processes in mineral weathering of Technosols developed from limestone mine waste. These processes may accelerate pedogenesis, and, consequently, the recovering of the soil functions essential for mine reclamation processes.

The origins, history, and recent advances in Conservation Agriculture (CA) are reported. CA is now practiced worldwide on some 200 million hectares, important for mitigating climate change and ensuring food security. Its bedrock is Zero Tillage (ZT) with crop rotation and retention of crop residues. CA approaches Or-19 ganic Agriculture (OA) when coupled to biological control providing opportunity for OA to become truly sustainable. Ley Farming (LF) and agroforestry with ZT are important for carbon sequestration and land use intensification. Hidden cost: each ton of carbon immobilizes 83 kg of N, 29 kg of P, and 14 kg of S. Industry-backed Regenerative Agriculture (RA) variants have no scientific definition, but generally adopt CA. Sustainable, profitable, and compatible new technologies are emerging and CA needs to embrace them to present a holistic, sustainable package to the farmer. How? A single definition for agricultural sustainability via a multi-stakeholder world congress would standardize certification and de-confuse the market. RA describes exactly what CA does for soil health and all farmers need to unite around a new "Combined Regenerative Agriculture" (CRA) to lobby for adequate payments for environmental services. Expansion of CA is critical for world sustainability. Many gaps and constraints exist, especially for smallholders. Made available in DSpace on 2022-01-16T01:55:43Z (GMT). No. of bitstreams: 1 Next-steps-for-conservation-agriculture-2021.pdf: 332738 bytes, checksum: 192f05da6a9dd45aed4dc1d3b9654d61 (MD5) Previous issue date: 2021