Phosphorus fractions and phosphorus delivery potential of a luvisol derived from loess amended with organic materials

摘要

In a long-term field experiment, started in 1962, the fate of P applied with different organic materials [farmyard manure (FYM), compost and sewage sludge] in comparison to mineral fertilizer was investigated. Soil samples were collected after 38 years' continuous addition of these amendments to a luvisol derived from loess and cultivated to a cereal-root crop sequence. The total P (Pt) content of all treatments increased compared with the original soil; NaOH-inorganic P (NaOH-Pi) representing Fe- and Al-bound P was the dominant inorganic fraction. At the beginning of the experiment the various P pools could be quantitatively ranked in the following order: NaOH-Pi-PiO-P>HCl-P. The order changed as follows: NaOH-Pi-PiO-P>HCl-P, with transformations of non-labile residual P to the labile NaHCO3-Pi pool with continued P fertilization and cropping. In addition, the content of organic P (Po) forms (NaOH-Po and NaHCO3-Po) increased. Pt delivery potential (desorbable P pool) increased between 35% and 185% compared to the P delivery potential in 1962. Compared to mineral fertilizer application, the application of organics resulted in a significantly higher, and FYM in a lower, P adsorption capacity of soils. The calcium lactate-extractable P (plant-available P) increased from 43.1 mg kg–1 soil in 1962 to 175.9 mg kg–1 soil in the treatment with 49 t compost ha–1. The increase in the citrate-dithionate Fe-O ranged between 44% and 154% in the different treatments compared to the Fe-O content in 1962. In a pot experiment with soil from the field experiment, P removal by ryegrass was in the following sequence: FYM>compost=sewage sludge>mineral fertilizer.