Diffusion, Adsorption, and Predicted Longevity of Banded Phosphorus Fertilizer in Three Soils

Diffusion of banded P fertilizer influences the residual P effect, root/P‐fertilizer contact, fertilizer‐P longevity (the time after which the contribution of applied band to plant P uptake is insignificant) and the probability that the P‐affected soil will be collected during soil sampling. An experiment was conducted to determine the extent of P diffusion from banded P application, diffusion coefficients, and the longevity of banded P fertilizer. Six P rates of 15, 22.5, 30, 37.5, 45, and 60 kg P ha −1 tagged with 32 P were applied in a band in three soils and allowed to diffuse under field conditions for 94 d. Phosphorus‐fertilizer movement from the injected band centers (30‐cm spacing) after 94 d ranged from 1.8‐cm radius at the 15 kg P ha −1 rate in the Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll) and Coly (fine‐silty, mixed [calcareous], mesic Typic Ustorthent) soils to 3.9 cm at the 60 kg P ha −1 rate in the Nora (fine‐silty, mixed, mesic Udic Haplustoll) soil. The diffusion distances and apparent diffusion coefficients increased in a linear manner as the P application rate increased. The calculated longevity of banded P fertilizer ranged from 2.6 yr at 15 kg P ha −1 in the Sharpsburg soil to 6.5 yr at 60 kg P ha −1 in the Coly soil. The longevity of banded P fertilizer was shortest for the Sharpsburg soil with the highest P‐adsorption capacity and was longest for the Coly soil with the lowest P‐adsorption capacity. The probability of P‐affected soil being collected during soil sampling ranged from 11.7% at 11.7% at 15 kg P ha −1 in the Sharpsburg soil to 25.9% at 60 kg P ha −1 in the Nora soil. Soil sampling and soil‐test P calibration should be altered to account for the residual nature of applied P bands.