Profile distribution of extractable phosphorus following a knife-applied subsurface phosphorus fertilizer band

A field experiment was initiated to characterize the soil profile distribution of Bray-I extractable orthophosphate-phosphorus (PO4-P) after a knife-applied liquid fertilizer P application. Fertilizer P was applied at a 25 kg P/ha rate to both undisturbed and chisel plowed field strips at either a 10 cm or 20 cm depth. Exttactable-P levels after 20 days were significantly higher 4 cm below the intended P placement position mainly because the bottom of the slot created by the knife applicator was 2.5 cm below the fertilizer distribution tube. This permitted fertilizer to move deeper into the soil than intended. However, further vertical movement and some lateral movement was observed by 70 days and was attributed to a combination of fertilizer moving into macropores as well as some diffusion in field strips not disturbed by tillage.