Australian researchers recently studied the reaction of both liquid and granular phosphorus (P) fertilizers in soil that was either dry or wet (at field capacity). They measured the movement of P from the application site as well as the amount of P that was in available and non-available forms.
They found that when soils were dry, very little diffusion occurred away from the site of application, and the P interactions with soil were negligible. This resulted in phosphorus remaining relatively unchanged and still in a plant-available form.
Another key finding was that granular sources resulted in higher amounts of available P compared with liquid P sources. However, when soils were wet, both granular and liquid P fertilizer experienced significantly more diffusion away from the application site and much more interaction with the soil. Consequently, when applied in wet soils, neither source differed in labile P.
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These results show that there can be a distinct difference in how much P is soil available, based on which form is applied into dry and wet conditions. Keeping this research in mind can go a long way toward helping growers maximize their investment in P fertilizer.