Residual value of the phosphate added to ecuadorian and chilean soils with different phosphorus retention capacity

The residual value of phosphorus addition is described by two reactions: a quick initial reaction followed by a slower reaction over time. In this study, the residual effect of two P sources was evaluated: monopotassium phosphate (MKP) and triple superphosphate (TSP) added to soils from Ecuador and Chile with contrasting soil P retention capacity. Olsen-P extractability was measured and compared in soil samples 1, 2, 4, 8, 15, 45, 90, 180 and 360 days after the addition. The Olsen-P extracted at 24 hours after the P addition varied among soils, and extracted between 10 and 66% of the P added depending upon the soil, with lower extraction values in soils with high P retention capacity. When the source was TSP, only approximately 70% of P was extracted compared to that extracted when MKP was added. After the phosphate addition there was a clear initial effect followed by a progressive loss of Olsen-P extractability. Furthermore, over time, a state of quasi-equilibrium or a stationary state become evident in which the loss of P extractability was minimal. When the initial effect was removed, as a point that characterizes different types of soils, the loss of P extractability was similar among soils, and reflects the amount of phosphate added despite the type of fertilizer used.