Nitrogen Fate of ¹⁵N-labeled Sugarcane Leaves in Furrow Application and Its Contribution to Nitrogen Uptake of the Subsequent Sugarcane Crop

Objective The aim was to investigate the fate of nitrogen (N) from sugarcane leaves under furrow application in the subsequent two sugarcane seasons, in order to provide a basis for the efficient utilization of sugarcane leaf incorporation into the soil.

Method Using the sugarcane variety Guitang 44 as the experimental material, the N utilization and fate of ¹⁵N-labeled sugarcane leaves were analyzed with four treatments in the field: 100% leaves applied at the bottom of furrows (R1), 100% leaves applied on the surface of furrows (R2), 50% leaves applied at the bottom of furrows + 50% leaves applied on the surface of furrows (R3), and 100% leaves mixed with furrow soil (R4).

Result Across the four treatments, 5.00% - 6.48% and 5.55% - 6.25% of N from sugarcane leaves were absorbed by newly planted sugarcane and first-ratoon sugarcane, respectively. The N from sugarcane leaves contributed 3.10% - 3.33% and 2.02% - 2.20% to the N requirements of newly planted sugarcane and first-ratoon sugarcane, respectively. The utilization rate of N from sugarcane leaves in R4 was cumulatively 0.25 - 1.97 percentage points higher than that in the other treatments. After two crops, the N from sugarcane leaves was retained in the soil layer above 40 cm for all treatments, with a residual rate of 55.00% - 61.65%, where R1 had higher residues and R4 had lower residues. The loss rate of N from sugarcane leaves was 27.80% - 32.48%, with R4 having higher losses and R1 having lower losses. In two crops, the cumulative dry matter accumulation in sugarcane stalks was the highest in R4, increasing by 5.48% - 20.36% compared with the other treatments.

Conclusion The absorption and utilization rate of N from incorporated sugarcane leaves was very low, with a large amount of residue remaining, and its contribution to the N requirements of sugarcane was limited.