Long-term effects of potassium fertilization on yield, efficiency, and soil fertility status in a rain-fed maize system in northeast China

• We investigated the long term effects of K application on K use and soil status.
• K increased grain yield, but this effect decreased with excessive application.
• Returned straw, deep soil K utilization, weathering soil K pools may alleviate soil K deficits.

The effects of 20 years of potassium (K) fertilization (in two treatments: 113 and 225 kg K2O ha−1) on grain and stover yields, plant K concentrations, aboveground K uptake, K use efficiencies, soil K pools, and the K balance were examined in a Haplic Phaeozem soil under a rain-fed mono-cropped spring maize (Zea mays L.) system in the province of Jilin, northeast China. The indigenous K supply (zero K application) maintained an average grain yield of 7.0 t ha−1 per year, but the year-to-year variation was large. Application of K significantly (P < 0.05) increased the average grain yields by 15.1 and 13.8% in the 113 and 225 kg K2O ha−1 treatments, respectively, over the experimental period. The mean K recovery efficiency, K agronomic efficiency, and K partial factor productivity decreased from 37.3 to 28.5%, 10.8 to 4.9 kg kg−1, and 86.8 to 43.1 kg kg−1 when the K application rate increased from 113 to 225 kg K2O ha−1. The effect of K application was larger on stover K concentrations than grain K concentrations. In the top 100 cm of the soil profile, excessive or non-synchronized K application significantly (P < 0.05) increased the leaching of exchangeable K in comparison with the control, but K application had little effect on soil non-exchangeable K and total K. K fertilizer, therefore, plays an important role in increasing grain yields in China, but the K application rate can be reduced if farmers return stover to the soil and make full use of K below the soil surface.