Phosphorus sorption dynamics in soils cropped with silage corn at Agassiz

Unravelling the mechanisms controlling P sorption during early growth stages of corn is crucial to refine starter fertilizer P rates. The objective of this study was to assess P sorption characteristics to estimate P sorption maximum (Smax) of a range of soils under silage corn with contrasting P levels. We used composite soil samples collected from eight silage corn experiments at Agassiz and Rosedale for P sorption experiments. Initial equilibrating solution P concentrations were 0, 5, 10, 20, 30, 40, 50, 100, 200 and 300 mg P L–1 as KH2PO4. The experimental data of the sorption study for all eight sites were best fitted by the Langmuir equation, with R2 values ranging between 0.90 and 0.99. The Smax varied between 982 and 2532 mg P kg–1 and the binding energy of P onto sorption sites (ka value) also varied between 0.008 L mg P–1 and 0.041 L mg P–1. The Pearson’s correlation coefficient between the Smax and Mehlich-3 aluminum (AlM3) was 0.46, and the Pearson’s correlation coefficient between the Smax and organic matter content was 0.59. The close association between Smax and AlM3 was further highlighted by the significant and positive correlation between Smax and P sorption capacity confirming the role of Al and Fe oxyhydroxides on P sorption characteristics. From these results, we can conclude that soils at Agassiz and Rosedale have a maximum capacity to fix newly applied P through fertilizer or manure, and therefore excess P inputs should be limited to reduce the risk of potential P loss to the environment.