Abstract
Potassium (K) depletion of soils in the intensively-cropped Ganges River Floodplains is a key challenge for maintaining crop productivity. Both increased residue retention and decreased soil disturbance (i.e., Conservation Agriculture) can decrease negative K balance but not fully reverse it in typical rice-based cropping patterns. Our research question was whether CA could fully reverse negative K balance in the high K input potato-maize-rice cropping sequence. A two-year experiment was conducted with an annual potato-maize-rice rotation that involves a wide range of K input along with CA practices. Treatment factors were: (a) soil disturbance (conventional = CT and strip planting = SP); (b) crop residue retention (low, LR = 15 cm and high, HR = 40 cm by height); and (c) K application (100% K (recommended level, RD; K 255 kg ha−1 yr−1), 50% or 75% K of RD (low dose, LD), and 125 or 150% K of RD (high dose, HD)). After two years and six consecutive crops, soil pH, total soil organic carbon, total nitrogen, extractable phosphorus, sulfur, and K increased while soil bulk density decreased significantly due to CA practices. In year 1, HR increased REY by 7% over LR, while SP-HD and SP-RD produced 25% and 15% higher REY, respectively, than CT-RD. However, K balances during year 1 were consistently negative although less negative for the SP and HR combination than for the CT and LR applications. In year 2, the combined treatment SP-HR-HD produced a 34% greater rice equivalent yield (REY) than CT-LR-RD and the only positive K balance (24 kg ha−1 yr−1), whereas CT-LR-RD, which mimics conventional practice, showed a strongly negative balance (–96 kg ha−1 yr−1). Hence, even in the high K input potato-maize-rice rotation, while strip planting and higher residue retention significantly reversed negative K balances, improved soil fertility and increased cropping system yield, additional K fertilizer was necessary to prevent soil K depletion.
