Conservation agriculture in intensive rice cropping reverses soil potassium depletion

Intensive cropping in the Eastern Gangetic Plain has progressively depleted soil potassium (K) over time due to negative K balances. There is limited understanding of how alternative soil and crop management practices under Conservation Agriculture (CA) will alter the soil K pools in such soils. We hypothesized that long-term CA will reduce K depletion in soils through recycling and storing soil K. A split plot experiment with two factors—(A) soil disturbance (strip planting = SP and conventional = CT), and (B) residue retention (low, LR = 20 cm and high, HR = 50 cm) commenced in 2010 with three crops per annual cycle for 24 consecutive crops. Soil samples were then collected in December 2018 at 0–5, 5–15, 15–30, 30–45 and 45–60 cm to analyse fractions of K along with soil physical and chemical properties. All K fractions were higher in SP (by 300, 26, 7.8 and 2.4 mg kg −1 for total, non-exchangeable, exchangeable and soil solution K, respectively) than in CT while HR was higher (by 267, 243, 18, 28.8 and 15.9 mg kg −1 for total, mineral non-exchangeable, exchangeable and soil solution K, respectively) than in LR. While increased crop residue retention recycled more K to the soil which partly explains higher concentrations in K fractions, both increased residue retention and decreased soil disturbance increased SOC that can positively increase exchangeable K. Hence, the core components of CA, minimal soil disturbance and increased residue retention, resulted in larger K pools in soil and appear to be effective means for reversing negative K balances in these intensive rice-based cropping systems.