Nitrogen fertilization and potassium requirement for cereal crops under a continuous no-till system

Nitrogen (N) and potassium (K) are the most required nutrients for corn and wheat production. Increasing the N application rate usually boosts crop yields. However, many uncertainties remain for K management. Potassium deficiency results in yield losses, but K application rate based on the percentage of K+ in the cation exchange capacity (CEC) is doubtful, especially in soil with high CEC. A field trial was conducted to examine the effects of KCl application before sowing corn and wheat, by raising the percentage of K+ in CEC at pH 7.0 (CECpH7.0) to approximately 2.5%, 3.5%, and 4.5%, and adding N as a topdressing (75, 150, and 225 kg ha(-1) to corn and 40, 80, and 120 kg ha(-1) to wheat) on the nutrition and yield of corn and wheat under a continuous no-till system (30 years). Exchangeable K+ content increased in the topsoil (0-20 cm depth) up to 7.2 mmol, dm(-3) after K application at the highest rate, which, however, did not result in significant increases in nutrient uptake and yields for both corn and wheat. The N application rate positively affected the uptake and removal of all macronutrients by corn and wheat. Applying N as a topdressing increased yields of corn and wheat by up to 83% and 22%, respectively. Our results suggest that in the soil with a high CECpH7.0 (162.1 mmol, dm(-3)), the recommendation for K application made by considering the percentage of K+ in the CEC(pH7)(.0 )may result in excessive application of K fertilizer to crops with high K-recycling potential grown under a continuous no-till system.