Leaching losses of nitrogen, phosphorus, and carbon in diverse 7-year crop rotations including annual and perennial crops

Nutrient leaching is a major pathway for nitrogen (N), phosphorus (P), and carbon (C) losses in agroecosystems. This study quantified year-round leaching of nitrate-N (NO 3 -N), dissolved organic N (DON), dissolved reactive P (DRP), particulate P (PP), and dissolved organic C (DOC) across six 7-year crop rotations, using zero-tension lysimeters. Rotations varied in crop types (perennial versus annual), forage composition [pure grass (timothy and tall fescue) stands with or without alfalfa], and fertilizer sources (mineral or organic) for the first five years, and were all transitioned to corn and soybean for two years. For the first five-year period ending with perennial crop termination, effects of crop type, forage composition, and fertilizer sources were significant, while only forage composition affected leaching in the two-year legacy phase following perennial crop termination. For the whole 7-year period, perennial-based rotations resulted in lower NO 3 -N (–50%) and PP (–39%) but greater DRP (+52%) losses compared to annual-based rotations. Compared to pure grass stands, an alfalfa-grass mixture increased NO 3 -N (+79%) but decreased DOC (–19%) and DRP (–41%) losses. Additionally, in pure grass stands, organic fertilizer increased DON (+79%) and DRP losses (+210%) compared to mineral fertilizer. These results highlight 1) the strong ability of perennial crops to limit N losses; 2) the trade-offs between N, P, and C losses; 3) the importance of tailoring nutrient management strategies to crop type; and 4) the need to leverage the residual fertility of alfalfa to sustain the environmental advantages of perennial-based rotations.