Contribution and fate of maize residue-¹⁵N and urea-¹⁵N as affected by N fertilization regime - Fig 1

Effect of N regime on nitrogen recovery efficiency, residual rate and loss rate for15N-labelled residue (a) and15N-labelled urea (b), respectively. G1, G2, G3, and G4 represent the after-dormancy, heading and maturity stages of winter wheat, and maturity stage of summer maize, respectively. Vertical bars represent the standard errors and different letters above the bars indicate significant differences between treatments at p < 0.05.