Effects of Long-Term Fertilization and Deep Plough on Crop Potassium Utilization and Soil Potassium Forms in Maize-Sorghum Rotation System

The effects of long-term different fertilizations and deep plough on grain yield, potassium utilization, potassium forms in soil profile and non-exchange potassium release in maize-sorghum rotation system was evaluated to provide the theoretical basis for potassium nutrient management.

The experiment was conducted in Jinzhong city of Shanxi Province from 2011 to 2022. There were 6 treatments: no fertilizer (CK), NP, NPK, straw return and manure (MS), NPK with MS (NPKMS) and NPKMS with deep plough for 30 cm (NPKMSD). The influences of different treatments on grain yield, potassium uptake, potassium apparent utilization efficiency (KUE), potassium agronomy utilization efficiency (KAUE) and kinetics of non-exchange release were investigated.

Compared with NP and NPK treatments, the accumulative grain yield was increased 6%-8% under MS, NPKMS and NPKMSD, whereas potassium uptake was promoted 22%-43%. Moreover, the values of PAUE produced by NPKMS and NPKMSD were only half under NPK and MS treatments. The available K content of 0-20 cm soil layer under MS, NPKMS and NPKMSD treatments were 2.2 to 2.8 times higher than those under CK, NP and NPK treatments. Meanwhile, the slow available K was increased 8%-10%. The deep plough enhanced available K content of 20-40 cm soil layer. The K uptake aboveground was more related to available K content of both 0-20 cm and 20-40 cm soil layer and slow available K content of 20-40 cm soil layer. When the soil non-exchangeable K was extracted by CaCl₂, the accumulative amount of K released under NPK, MS, NPKMS, and NPKMSD were 1.04, 1.77, 1.99, and 1.81 times than that under NP treatment, respectively, while these values were 1.05, 1.41, 1.85, and 1.63 times under NP treatment when soil non-exchangeable K was extracted by citric acid.

Taken together, straw return and manure could activate soil potassium. Thus soil available K content, slow available K content, KUE and KAUE were improved relative to NPK treatments when total potassium input was comparative for 12-years. NPK with MS treatments could induce potassium luxury absorption and resulted in low values of KUE and KAUE. Deep plough could increase subsoil available K content, but its impact on accumulative grain yield was not noticed. Straw return and manure increased cumulative non-exchangeable potassium release amount and release rates. Therefore long-term combination of straw return and appropriate amount manure could substitute chemical potassium fertilizer.