Effects of tillage reversal and crop rotation on soil health and soil organic carbon fractions and stocks in wheat-based cropping systems under dryland Morocco

Tillage and cropping systems can influence strongly soil health and soil organic carbon (SOC). We studied the effects of permanent shifting from no-tillage (NT) to reduced tillage (RT) and crop rotation on soil health indicators, soil organic carbon (SOC) fractions and stocks, and soil health index (SHI). We implemented a field experiment including 12-year continuous NT (“NT12”) and 7-year NT converted to 5-year RT (“NT7RT5”, i.e., tillage reversal), both combined with three wheat-based diversified crop rotations. A 12-year conventional tillage (“CT12”) system under wheat monoculture served as a reference. Soil samples were collected at 0–7.5, 7.5–15, and 15–30 cm depths. SOC fractions included particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). Compared to NT12, NT7RT5 did not affect the contents of SOC and its fractions and SOC stocks at 0–30 cm but modified the vertical distribution of SOC and its fractions, with NT7RT5 having lower contents of SOC (1.74%) and POC (0.65%) at 0-7.5 cm but greater contents of SOC (1.68%) and MAOC (1.05%) at 7.5-15 cm and higher POC content (0.70%) at 15-30 cm; NT7RT5 lowered the available water capacity (-22%) at 0-30 cm; but SHI values at 0-30 cm were comparable between NT12 (0.5) and NT7RT5 (0.54). CT12 resulted in lower SOC content and stock, and POC content at 0-30 cm compared to cropping systems in NT12 and NT7RT5. Under NT12 and NT7RT5, crop rotation influenced total nitrogen, cation exchange capacity, bulk density, and total porosity, with “Rotation 3”, including wheat, pea, triticale, and faba bean showing the best results. These results provide evidence on the possibility of shifting from long-term NT to RT without harming, in the short term, the overall soil health status and SOC storage in the topsoil, but with the risk of reducing water retention in the soil, which may penalize crop productivity. • We evaluated the effects of tillage reversal from 7-year no-tillage to 5-year reduced tillage (NT7RT5) vs 12-year continuous no-tillage (NT12), both tillage systems combined with three wheat-based diversified crop rotations, on soil health indicators including soil organic carbon (SOC) fractions, i.e., particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), SOC stocks, and soil health index (SHI). A neighbouring 12-year conventional tillage (CT12) system under wheat monoculture was taken as a reference. • Compared to continuous no-tillage (NT12), tillage reversal (NT7RT5) did not significantly (p>0.05) influence SOC stock or SHI at 0-30 cm but altered the vertical distribution of SOC and its fractions, with NT7RT5 recording lower SOC and POC contents at 0-7.5 cm and higher SOC and MAOC contents at 7.5-15 cm and higher POC content at 15-30 cm. NT7RT5 lowered available water capacity and cation exchange capacity but increased total nitrogen and available sulfur at 0-30 cm compared to NT12. • Despite its higher nutrient (N-P-K) inputs, the conventional tillage system (CT12) recorded significantly lower SOC content and stock, and POC content, and slightly to significantly SHI values at 0-30 cm compared to cropping systems under NT12 and NT7RT5. • Under NT12 and NT7RT5, “Rotation 3”, a wheat-based rotation including triticale, faba bean, and pea, showed overall the best results in terms of soil health attributes, particularly for total nitrogen, cation exchange capacity, bulk density, and total porosity. • Our findings: (1) suggest a flexibility under conservation tillage management with the possibility of shifting from no-tillage to reduce tillage without damaging SOC storage and the overall soil health status in the topsoil in the short term, and (2) support the role of conservation tillage practices associated with diversified rotations in maintaining SOC and soil quality.