Soil Texture and Residue Addition Effects on Soil Phosphorus Transformations

Abstract

AbstractThe effect of soil texture on P transformation and the extent and timing of crop residue decomposition affects both P availability and the fate of the P added in the residue. Our objectives were to examine P transformation in sand, sandy loam, and loam soils during surface or incorporated wheat (Triticum aestivum L.) straw decomposition with and without N and P addition. Packed soil cores (4.8 cm diameter by 2.5 cm deep) were incubated in the dark for 10, 30, 60, and 90 d at 25°C and −0.033 MPa initial soil water pressure. We determined CO2 respiration, labile inorganic P (Pi), labile organic P (Po), microbial P, NaOH‐extractable Pi and Po, and HCl‐extractable Pi. Soil texture had a greater effect on P transformation than did residue placement. Microbial P was greatest at 10 d and was 13.0, 9.8, and 6.5 mg kg−1 for the loam, sandy loam, and sand, respectively. Labile Pi was lowest at 10 d and was 22.9, 18.0, and 11.5 mg kg−1 for the loam, sandy loam, and sand, respectively. More of the nutrient P added remained as labile Pi when the residue was surface applied. Residue placement did not affect microbial P, indicating that the effect of placement was indirect. Phosphorus transformations were closely linked to microbial activity and C dynamics.