Short‐term (5 years) impact of conservation agriculture on soil physical properties and organic carbon in a rice–wheat rotation in the Indo‐Gangetic plains of Bihar

Short‐term (5 years) impact of tillage and residue management practices on physical properties and organic carbon (OC) of a silty clay soil was evaluated in a rice–wheat rotation in the Indo‐Gangetic Plains of Bihar. The experiment had three conservation agriculture (CA) practices: one full (direct‐seeded rice (DSR)–no‐tilled wheat (NTW)–no‐tilled mung bean (NTMB); fCA) and two partial (puddled transplanted rice (PTR)–NTW–conventionally tilled mung bean (CTMB); pCA1 and unpuddled transplanted rice (UPTPR)–conventionally tilled potato+maize (CTP + M)–NTMB; pCA2), which were evaluated against full conventional practice (puddled transplanted rice (PTR)–conventionally tilled wheat (CTW); TA). Subsurface compaction reduced and soil aggregation improved under both full and partial CA. Macro‐ and water‐stable aggregates increased to a large extent (26 and 11%, respectively) in full CA and to a lesser extent in partial CA, mostly due to increase in coarse macroaggregate (2–8 mm) contents in the 0–10 and 10–20‐cm depth soil layers. Steady‐state infiltration rate nearly doubled under full CA, with larger pore volume recorded in 10–20 and 20–30‐cm depth soil layers. The CA increased OC associated with all size fractions of aggregates in the surface soil layer (0–10 cm), but a higher amount of C was associated with macroaggregates, indicating relative stabilization of OC in the soil under CA. Change in bulk soil OC was larger in the 0–10‐cm depth soil layer in favour of CA, which also had an 11% increase in OC stock in the 0–30‐cm depth soil layer. Improvement in soil physical condition did not effectively translate into increased rice or wheat yields, but the system productivity increased largely. Highlights Conservation agriculture (CA) resulted in 11–12% higher macro‐aggregation compared to conventional practice (CT). Macro‐ and total pores reduced in the 0–10 cm depth soil layer but increased in the 10–20 cm depth soil layer under CA. CA resulted in 27–35% higher aggregate‐associated OC content and 11% increase in OC stock at 0–30 cm. Full/partial CA improved soil physical condition and the productivity of rice–wheat systems in the Indo‐Gangetic Plains.