Fate of P from organic and inorganic fertilizers assessed by complementary approaches

Abstract

Long-term field experiments (LTFEs) can provide an extensive overview on the effectiveness of phosphorus (P) management. In order to have a detailed insight into the availability and distribution of the P in soil as affected by organic and inorganic fertilizers (no P, triple-superphosphate (TSP), compost and compost + TSP), soil samples collected at a LTFE established in 1998 in Northern Germany at different sampling dates and soil depths were subjected to P characterization including the double-lactate method (P-dl) as standard soil test, the degree of P sorption (DPS), the sequential P fractionation and isotopic exchange kinetics. While the type of fertilizer had rarely an effect on the soil P pools, higher amounts of P applied resulted in increased values of P-dl, labile P fractions and P that was isotopically exchangeable within 1 min (p < 0.05). The DPS values varied from on average 40.2% (no P) to 47.2% (compost + TSP) with small variations during the experimental time. In contrast, significant shifts from less available to readily available P pools were measured between the sampling in autumn 2017 and spring 2019. The differences in the P budgets between the treatments corresponded to the differences of the total P stocks in 0–90 cm, yet with an estimated upward or downward movement of P between the soil depths as consequences of long-term deficit or surplus of fertilizer P. The use of complementary methods in this study contributed to a better understanding of the potential availability of P in soil in a long term perspective.