Abstract

Phosphorus losses from soils have been reported to impair the water quality, resulting in deaths of fish and other marine animals, and can harm human health. The objective of this study was to determine the seasonal distribution of P forms and losses in leachate collected from intact soil monoliths (70-cm depth, 50-cm diam.) of a Lismore stony silt loam soil (fine-loamy, mixed, superactive, frigid Aquic Cumulic Hapludoll) during a 2-yr period. The experiment included different combinations of mineral P fertilizer at 45 or 90 kg P ha−1 yr−1 and/or farm dairy effluent (FDE) at 200 or 400 kg N ha−1 yr−1, which contained 41 to 95 kg P ha−1 yr−1 Amounts and forms of P in leachate collected during the irrigation (IR; November–April) and nonirrigation (NIR; May–October) seasons were compared. Results showed that P losses were higher in particulate forms (mainly particulate unreactive phosphorus, PUP) during the IR seasons. This may be because of regular inputs of high intensity flood IR (92 mm per application), which increased the dislocation of particles in the soil profile, thereby resulting in higher PUP losses. On the other hand, the amount of natural rainfall was much lower (usually <20 mm per event) during the NIR seasons that resulted in less dislocation of particles compared with the IR seasons; hence, lower P losses as PUP but higher losses as dissolved unreactive phosphorus (DUP). Variation in P losses during the different seasons suggest the need to develop mitigation strategies that should focus on reducing DUP losses during the NIR and PUP losses during the IR season.

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