Long‐Term Effects of Conservation Agriculture on Soil Properties in Calcareous Soils Under a Rice–Maize System

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Abstract
Soil degradation, driven by intensive tillage and faulty agronomic management practices, poses a major challenge to sustainable agriculture in South Asia. Conservation agriculture (CA) has been proposed as a viable strategy to restore soil health; however, long‐term evidence from calcareous soils is limited. A 17‐year field experiment was conducted to evaluate the effects of CA on soil physical, chemical, and biological properties, and system productivity under a rice–maize system. This study provides novel long‐term evidence from calcareous soils by integrating soil health indicators with multivariate analyses, which remain limited in rice–maize systems. The experiment comprised four treatments in a randomized complete block design: zero tillage with residue (ZT + R ; T1), permanent bed with residue (PB + R ; T2), permanent bed without residue (PB − R ; T3), and conventional tillage (CT; T4). After 17 years, CA treatments (T1 and T2) significantly ( p < 0.05) improved soil properties compared with conventional tillage (T4) at two depths (0–15 and 15–30 cm), with the strongest effects under PB + R (T2). Bulk density under T2 decreased by 12.1% and 10.3%, while water‐stable aggregates increased by 48.8% and 36.6% at 0–15 and 15–30 cm, respectively. Soil organic carbon increased by 44.1% and 39.8% across the respective depths, accompanied by improved nutrient availability. CA treatments also enhanced cationic micronutrients (Mn, Fe, Cu, and Zn) and reduced soil pH and electrical conductivity relative to T4. Biologically, fluorescein diacetate activity increased by 78.2% and 53.2%, and fungal populations by 174% and 152% at 0–15 and 15–30 cm, respectively. System productivity was highest under T2, with a 40.2% increase over conventional tillage. Soil organic carbon showed strong positive correlations with wet aggregate stability ( r = 0.75**), micronutrients (Mn: r = 0.81**, Fe: r = 0.80**, Cu: r = 0.85**, Zn: r = 0.65**), fluorescein diacetate activity ( r = 0.73**), and bacterial population ( r = 0.70**). Multivariate analyses further supported these findings, with principal component analysis explaining 77.4% of total variance and clearly separating CA‐based treatments from conventional systems, while heatmap clustering indicated strong co‐association of soil quality indicators and productivity under PB + R . Overall, the study provides long‐term evidence that conservation agriculture, particularly permanent beds with residue retention, influences soil health and productivity in calcareous soils, with implications for sustainable intensification in South Asia.

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