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 32P 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.
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