Effect of Different Long-Term Potassium Dosages on Crop Yield and Potassium Use Efficiency in the Maize–Wheat Rotation System

Potassium (K) is the second most important plant nutritional element and is used for numerous physiological processes. We established an eight-year experiment comparing the effects of five K fertilization treatments (0, 48, 84, 120 and 156 kg K ha⁻¹) on crop yield, K use efficiency and soil apparent K balance under the maize–wheat rotation system in the North China Plain. The highest maize and wheat yields were achieved in the K₁₂₀ treatment, increasing by up to 16.7% and 25.1%, respectively. The increase in grain yield and K agronomic efficiency (AE_K) with K application was greater in wheat than in maize. The K recovery efficiency (RE_K) and K accumulative recovery efficiency (ARE) significantly decreased with the increase in K fertilization in the maize and wheat seasons. However, the soil apparent K balance and soil available K content increased; the former was deficiency (−24.3 kg ha⁻¹ yr⁻¹) in the K₀ treatment, but the latter did not decrease significantly compared with that in the initial year of the experiment. The soil available K content increased by 10.9 mg kg⁻¹ per 100 kg ha⁻¹. In conclusion, the yield response to K fertilization was greater in wheat than in maize and alleviated soil K depletion, but the K fertilizer efficiency was lower. We believed that K fertilizer can be increased moderately in the wheat season and decreased in the maize season.