Abstract:

To explore the potential of chemical nitrogen substitution by ploughing and returning Vicia villosa as the preceding crop of flue-cured tobacco in Lijiang tobacco-growing area of Yunnan Province, this study conducted a systematic analysis through three experiments: (1) measuring the degradation rate of Vicia villosa after ploughing; (2) using the δ¹⁵N isotope labeling technique to precisely quantify the amount of nitrogen transferred from Vicia villosa to tobacco plants; (3) verifying the substitution effect of chemical nitrogen by returning Vicia villosa to the field under field conditions. The research results showed that Vicia villosa could naturally decompose and release nutrients in the soil after ploughing, and the decomposition rate was the fastest within two weeks after ploughing. The appropriate ploughing time should be 90 to 100 days before tobacco transplanting. At this time, more than 50% of Vicia villosa could decompose, and nitrogen, phosphorus and potassium were released by approximately 48.75%, 52.00% and 83.65% respectively. The isotope tracking results showed that among the fertilizer nitrogen absorbed by tobacco, the nitrogen from Vicia villosa accounted for 10.15% of the total fertilizer nitrogen, and the nitrogen utilization rate of green manure in the current season was approximately 3.66%. Therefore, after returning Vicia villosa to the field, the application amount of chemical nitrogen fertilizer should be appropriately reduced, and the optimal nitrogen fertilizer dosage was 80% of the conventional dosage. The research indicated that planting Vicia villosa as the preceding crop of flue-cured tobacco and ploughing it over could not only increase the yield and economic value of tobacco leaves but also effectively reduce the usage amount of chemical fertilizers, achieving the goal of reducing fertilizer application and increasing efficiency.

Key words: green manure, Vicia villosa, decomposition, nutrient migration, flue-cured tobacco, ploughing and returning to field, chemical nitrogen substitution, reducing fertilizers and increasing efficiency