Objectives Effects of fertilizer application patterns and rates on content of soil potassium of different forms and wheat root vigor were investigated to provide a technical basis for increasing soil potassium use efficiency.

Methods In two growing seasons of 2018–2020 in Henan, a split-split plot design was employed with combined application patterns of nitrogen fertilizer and chicken manure in main plots (A1: 20% chicken manure plus 80% nitrogen fertilizer, A2: 100% nitrogen fertilizer), potassium fertilizer application rates in sub-plots (B1: CK, B2: 80 kg K₂O/hm², B3: 120 kg K₂O/hm², B4: 160 kg K₂O/hm²), and wheat cultivars in sub-sub-plots (C1: Xi’nong 979, C2: Yu’nong 202). Potassium-releasing rhizosphere microorganisms, content of soil potassium of different forms, wheat root vigor, and potassium use efficiency were all investigated and analyzed during wintering and at growth recovering, jointing, anthesis, grain-filling stage, and mature, respectively.

Results It was showed by complex variance analysis that influence of chicken manure, potassium fertilizer application rate, wheat cultivar, and growing season on potassium-releasing rhizosphere microorganisms, content of soil available potassium, wheat root vigor, potassium use efficiency, and grain yield were all significant at either 5% or 1% level. During the whole growing period, compared with the treatments with sole potassium fertilizer, potassium-releasing rhizosphere microorganisms, content of soil readily available potassium, and root vigor were significantly increased, and contents of both slowly available potassium and relatively inactive potassium were decreased in treatments with chicken manure combined with chemical fertilizer. Potassium-releasing rhizosphere microorganisms, content of soil available potassium, and root vigor, and potassium use efficiency increased with potassium application rate, but decreased to some extent when potassium application was excessive. Potassium-releasing rhizosphere microorganisms, content of soil available potassium, and root vigor were significantly increased and content both of slowly available potassium and mineral potassium decreased in treatments of common potassium application rate combined with chicken manure, compared with those in other treatments. Potassium use efficiency was increased by 2.24% in treatments of chemical fertilizer application combined with manure, compared with single chemical fertilizer application, The utilization efficiency of potassium in 2 years under conventional potassium application increased by up to 75.15%, and the utilization efficiency increased by 4.66%, compared with that in treatments with sole chemical fertilizer application. Correlation analysis also showed that there was a significant (5% or 1%) and positive correlation between potassium-releasing rhizosphere microorganisms and wheat root vigor, content of available potassium, slowly available potassium, and mineral potassium at different growth stages.

Conclusions The study indicated that combined application of manure with chemical fertilizer could increase potassium-releasing rhizosphere microorganisms and content of soil available potassium, and decrease content of both slowly available potassium and mineral potassium. Under the condition of reduced potassium fertilizer, combined application of manure (organic) with fertilizer (inorganic) could improve soil potassium utilization and increase wheat root vigor. It may be concluded from this study that the suitable potassium application strategy is a combined application of a certain manure with potassium fertilizer of 120 kg/hm² in the typical wheat field in the Huang-Huai Plains.