Long-term N fertilization reduces uptake of N from fertilizer and increases the uptake of N from soil.

Long-term supply of synthetic nitrogen (N) has the potential to affect the soil N processes. This study aimed to (i) establish N response curves to find the best balance between inputs and outputs of N over four ratoons; (ii) use N-labeled fertilizer to estimate the N recovery efficiency of fertilizer applied in the current season as affected by the N management in the previous three years. Nitrogen rates (control, 60, 120, and 180 kg ha N) were applied annually in the same plots after the 1st, 2nd, 3rd, and 4th sugarcane cycles.