Residual Phosphorus Distribution and Sorption in Starter Fertilizer Bands Applied in No‐Till Culture

Banding fertilizer P in no‐till culture results in a heterogeneous soil P distribution for months to years. This study's objective was to quantify the spatial distribution and temporal dynamics of banded P to improve assessment of soil P availability. In three trials for no‐till corn (Zea mays L.) and from four replicated plots each, we collected a grid of 1.3 by 1.3 cm samples around 10 and 20 kg P ha−1 starter fertilizer bands at ∼6, 12, and 18 mo after application. Soils were Mexico silty clay loam (Mollic Epiaqualf), Putnam silty clay loam (Vertic Albaqualf), and Dockery silt loam (Aquic Udifluvent). Band affected soil was defined as having a Bray‐1 P concentration of at least 1.5 times that of adjacent soil. Band dimensions varied from 5 to 8 cm (horizontal) and 5 to 12 cm (vertical), and tended to be largest at the 12‐mo sampling. Cross‐sectional area of bands ranged from 18 to 63 cm2 Band P concentrations decreased logarithmically from the band center, and were largest at either 6 or 12 mo, and varied substantially along the direction of band application. Band P concentrations ranged from 100 to 313 mg P kg−1 at 6 mo, 56 to 415 mg P kg−1 at 12 mo, and 63 to 237 mg P kg−1 at 18 mo (avg. of the six most concentrated samples of the 20 kg P ha−1 bands). Soil in the band center was weakly buffered and appeared to be more easily extracted by the Bray‐1 extractant than nonband affected soil. Inclusion of bands in soil samples would increase the risk to overestimate available P to a crop.