Effects of native leaf litter amendments on phosphorus mineralization in temperate floodplain soils

As phosphorus (P) losses from Midwestern crop fields degrade water quality in downstream water bodies, the assessment of natural P immobilization in floodplain soils is imperative to reduce P input to the Gulf of Mexico. While the organic C:P ratio of soil is widely accepted as an important indicator of P immobilization, roles of the quality/type of C sources (i.e., foliar C composition and degradability) on soil P dynamics are not clearly understood. The objective of this laboratory incubation study was to assess the influence of leaf residue of native trees (e.g., hackberry, and silver maple) on P reaction dynamics in floodplain soils as a function of C composition (i.e., carbonyl-, alkyl- and aromatic-C) and soil organic C:P ratios. Conventional wet chemical analyses and P-31 NMR spectroscopy were used to understand changes in P speciation and phosphatase activities. During the incubation, at a soil organic C:P of similar to 200, residues with low aromaticity promoted P mineralization, as evidenced by a sustained increase in labile inorganic P and decrease in microbial P. Conversely, residues with high aromaticity and hydrophobicity (i.e., silver maple) caused a decrease in labile inorganic P and increase in microbial P under the same soil organic C:P, indicating the dominance of P immobilization. At a soil organic C:P of 300, both sugar maple and silver maple promoted P immobilization. Mineralization rates were of lesser magnitude in the soils amended with silver maple, which interestingly contained the largest proportions of recalcitrant C and the highest ratios of aromaticity and hydrophobicity. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study demonstrated that the carbon composition of plant leaf residue can affect phosphorus reaction dynamics in floodplain soils under different soil organic carbon to phosphorus ratios. Residues with low aromaticity promoted phosphorus mineralization, while residues with high aromaticity and hydrophobicity caused phosphorus immobilization.