Long-term impact of fertilizer sources on cyclic P budget and soil P status under ley farming system

Abstract

Optimal phosphorus (P) management is essential in order to achieve sustainable crop production under ley farming system. Manure-based fertilizer represents an alternative to mineral fertilizer to produce forage across tillage systems. Our objective was to investigate the effects of mineral fertilizer [MIN] vs. liquid dairy manure [LDM]) and chisel plough [CP] vs. moldboard plough [MP] on soil P dynamics under a long-term ley farming system. Cumulative P inputs, P offtake and P budget were determined by summing cyclic values across eight 3-yr cycles (1993–2016). Soil test P was determined across six 3-yr cycles (1999–2016) by the Mehlich3 method. Crop P offtake was similar between CP and MP or between LDM and MIN. Phosphorus inputs accumulated across cycles were higher under LDM (65–610 kg P ha−1) than under MIN (54–446 kg P ha−1). The cumulative P budget ranged from − 20 to + 150 kg P ha−1 with LDM and from − 33 to + 3 kg P ha−1 with MIN. Despite a tend of decrease of Mehlich3P in upper layers, a higher accumulation in the 0–0.15 m soil depth under MIN than LDM, and under CP than MP was observed. Discrepancies between P budget and soil test P highlighted the complex mechanisms regulating P cycling. Our findings suggest the importance of complete assessment of soil P reserves in soil profile to sustain P management. Long-term experiment is a useful tool for monitoring effects of agricultural practices on soil P dynamics.