Controlled-release urea combined with potassium chloride improved the soil fertility and growth of Italian ryegrass

A field experiment with a split-plot design was conducted to study the effect of nitrogen fertilizer type combined with different potassium fertilizer rates on the soil fertility and growth of Italian ryegrass. The main plots were assigned to controlled-release urea (CRU) and common urea, while low, moderate and high potassium chloride (KCl) rates (150, 300 and 450 kg ha −1 , respectively) were assigned to the subplots. The results showed compared with the common urea, the CRU significantly increased the SPAD value, plant height, leaf area, and photosynthetic index. Moreover, the dry and fresh yields of the CRU increased by 10.9-25.3% and 11.8-17.7%, respectively. At the same time, compared with the KCl150 and KCl450 treatments, the KCl300 treatment resulted in better plant growth. Overall, the CRU×KCl300 maximized the soil inorganic nitrogen and different soil potassium forms. The root length, volume, surface area, average diameter, tips and branches were also improved, and there was a significant N×K interaction effect on the tips. Our analysis corroborated the CRU combined with 300 kg ha −1 KCl fertilization enhances crop growth by improving leaf photosynthesis, soil fertility, and yield and should be recommended as the best fertilizer ratio for Italian ryegrass production.