Crop residue application at low rates could improve soil phosphorus cycling under long-term no-tillage management

A field experiment was conducted in northeastern China to study the effects of no-tillage (NT) and residue application rates (NT and residue application at 0% (NTR0%), 33% (NTR33%), 67% (NTR67%), and 100% (NTR100%)) on soil phosphatase activities and P species determined by 31 P NMR, and their relationships at 0–10 and 10–20 cm depths. The NTR33% treatment showed significantly higher available P, microbial biomass P, pyrophosphate, scyllo -inositol hexakisphosphate ( scyllo -IHP), and corrected diester contents than the NTR0% treatment. The myo -IHP concentration under the NTR33% treatment at the 0–10 cm depth was significantly greater than in all treatments except the NTR100% treatment at the 0–10 cm depth and the NTR67% and NTR100% treatments at the 10–20 cm depth. The corrected monoester content under the NTR33% treatment at the 0–10 cm depth was not significantly different from the NTR67% at the 0–10 cm depth and the NTR100% treatment at the 10–20 cm depth, but was significantly greater than in all other treatments. Both NTR33% and NTR100% treatments significantly increased acid phosphomonoesterase activity. Structural equation modeling suggested a relationship of organic P compounds with phosphodiesterase and acid phosphomonoesterase at 0–10 cm, and with alkaline phosphomonoesterase at 10–20 cm.