Phosphorus dynamics in peat-based substrates

Abstract

The mobility of nutrients in soils is well characterized, whereas little information is available for common horticultural substrates based on peat. Aim of the current study was to investigate the mobility and dynamics of phosphorus (P) as well as the parameters involved in P transport to plant roots in peat-based substrates. A series of experiments was run to determine the impedance factor (f) and the buffer power (b). The impedance factor was determined for black peat and black peat mixed with 20% and 40% (v/v) of mineral component at volumetric water content (θ) of 40%, 50%, 60%, and 70% and at different diffusion time. Buffer power was calculated for black peat and black peat mixed with 20% (v/v) of seven different mineral components. Phosphorus was applied at rates of 0, 35, and 100 mg (L substrate-1), respectively. The impedance factor was not affected by addition of the mineral component to peat. However, f increased from 0.03 to 0.2, by increasing θ from 40% to 60%, indicating that water content has a significant effect on this parameter. Substrate-solution P ranged from 0.3 to 27 and from 1 to 95 mg P (L solution)-1 for the P-application rate of 35 and 100 mg P (L substrate)-1, respectively. Buffer power of the substrates ranged from 1 to 17.25 depending on the mineral component, and it was positively correlated with oxalate-soluble Fe and Al in the substrate. The calculated effective diffusion coefficient for P in the substrate was in the range of 10-7 to 10-8 cm2 s-1. This high value could be attributed mostly to the low buffer power rather than to the high impedance factor. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.