Effect of irrigation regimes on mobilization of nonreactive tracers and dissolved and particulate phosphorus in slurry‐injected soils

Abstract

Understanding the mobilization processes of phosphorus (P) in the plow layer are essential to quantify potential P losses and suggest management strategies to reduce P losses. This study is aimed at examining nonequilibrium exchange dynamics on the mobilization of slurry‐amended Br−, and dissolved and particulate P in slurry‐injected soils. We compared leaching from intact soil columns (20 cm diam., 20 cm high) under unsaturated flow (suction at the lower boundary of 5 hPa) subjected to continuous irrigation at 2 mm hr−1, and intermittent irrigation at 2 mm hr−1 and 10 mm hr−1 to with interruptions of 10 h duration simulate periodic precipitation events. Suction was increased to 20 hPa during interruptions to allow drainage of the largest pores. Irrigation interruptions induced fluctuations in leaching of nonreactive tracers, particles, and particulate P indicating nonequilibrium transport. A nonreactive tracer, 3H2O, applied with irrigation water, diffused from mobile to less mobile pore regions during interruptions, leading to a lower mass recovery during low‐intermittent (76.4%) compared with continuous irrigation (86.6%). In contrast, mass recovery of slurry‐injected Br− increased as Br− diffused from less mobile to mobile pore regions during low‐intermittent (53%–64%) compared with continuous irrigation (42%–47%). Despite high fluctuations during the leaching of particles and particulate P during low‐intermittent irrigation, accumulated values did not differ from continuous irrigation. Increased preferential flow during high‐intermittent irrigation lowered the mass exchange between pore regions of nonreactive tracers, particles, and particulate P compared with low‐intermittent irrigation. The leaching of dissolved inorganic and organic P was low during all of the experiments and scarcely affected by the irrigation regime. These results highlight that nonequilibrium exchange dynamics are important when evaluating processes affecting mobilization and transport in structured soils. Leaching experiments, including cycles of irrigation interruptions and gravitational drainage, thus, adds significantly to the understanding and interpretation of processes affecting mobilization and transport under natural conditions.