Fertilizing maize croppings with blends of slow/controlled‐release and conventional nitrogen fertilizers

Abstract Background : Blends of controlled‐release and slow‐release urea may help to synchronize N release from fertilizers and N uptake by maize to improve the plant nitrogen use efficiency. Aim : We aimed to investigate the effects of slow‐release urea and controlled‐release urea and their blends with uncoated urea to release N for maize uptake over time in comparison to urea and ammonium nitrate. Methods : The experiment was performed under greenhouse conditions, and the treatments consisted of conventional urea, ammonium nitrate, three controlled‐release ureas (Multicote 4M®, Nitrocote®, and polyurethane‐coated urea), one slow‐release urea, and mixtures of controlled‐ release urea and slow‐release urea with uncoated urea. These treatments were applied at concentrations of 0, 150, 300, and 450 mg N kg −1 of soil. We evaluated the dry mass, nitrogen accumulation in the shoots, agronomic efficiency index and applied nitrogen recovery after each of three maize croppings. Furthermore, we characterized the N release pattern of the controlled‐release ureas and their coating thicknesses by using scanning electron microscopy. Results : The N release curves showed that Multicote 4M®, Nitrocote® and urea + polyurethane reached 80% of the N released in water at 40°C at 36, 30, and 13 d after incubation. The highest cumulative nitrogen accumulation (1127.4 mg pot −1 ), agronomic efficiency index (122.3%), and applied nitrogen recovery (69.3%) occurred with ammonium nitrate, with a low residual effect of only 25.4% of the total N accumulated after 35 d of cultivation. The highest cumulative dry mass was produced when the maize was fertilized with a blend in which 40% of the N came from Nitrocote® (44.8 g pot −1 ). Conclusions : The results showed that ammonium nitrate is an important option as an N source, but it has no residual effect. Controlled‐ release ureas and their blends have a delayed N release and promote constant N uptake after 70 d. After 70 d, the applied N rates were also more important than the N fertilizer technologies. An adequate mixture of N fertilizers could be an interesting option to help synchronize N release and uptake by maize. Technologies involving urea blends could be an option to improve the nitrogen use efficiency in comparison to that obtained by using uncoated urea while decreasing costs in comparison with the application of 100% controlled‐release urea or slow‐release urea.