Fertilizer value of phosphorus in different residues

Abstract

AbstractThe phosphorus (P) fertilizer effect of a range of commonly available manure, waste treatment and by‐product residues was tested in pot, field and incubation experiments. The effect of the residues on P offtake was compared with that of commercial mineral P (super phosphate) to calculate the mineral fertilizer equivalent (MFE). Possible relationships between MFE and P extractable from residues using different agents (ammonium lactate, citrate, water) were examined. Dry matter yield and P concentration were measured in ryegrass grown in pots amended with 14 different residues. The effect on the first cut (after 5 weeks) was significantly higher for residues with a low organic matter content, for example ash and biogas residues (MFE = 74–85%), than for many other products with higher organic matter content, for example meat meal (MFE = 44%), cattle slurry (MFE = 57%) and sewage sludge (MFE = 0–37%). However, the effect on two combined cuts (after 11 weeks) was more similar between residues (MFE = 40–60% for most residues). Ammonium lactate‐extractable P (P‐AL) in residues correlated better with MFE (r2 = 0.48) than water‐extractable or citrate‐extractable P. Grain yield and P concentration were measured in a field experiment with spring wheat fertilized with four different residues. Pelleted meat meal had a similar effect on yield and P offtake as mineral fertilizer P, whereas two different sewage sludge and chicken manure had approximately 50% of the mineral fertilizer effect. The effect of residues on soil P‐AL (the Swedish measure of easily available soil P) in the incubation experiment showed no correlation with MFE from the pot experiments.