Effects of tri-functional catch rapeseed (for vegetable, forage and manure) on soil nutrients and flue-cured tobacco growth in tobacco fields

To further enhance the economic benefits of the "tobacco-rapeseed" integrated development mode in fluvo-aquic soil tobacco fields of the Huanghuai region, this study investigated the economic effects of tobacco field, soil nutrient dynamics in the 0~40 cm soil profile, as well as flue-cured tobacco growth, resulting from the use of multi-purpose rape (for vegetable, forage and green manure) as a catch crop. The results showed that: (1) The yields of rape flower stalks and fresh forage reached 11.74 t/hm² and 45.97 t/hm², respectively, the corresponding profits of which were 1.88 10⁴yuan/hm² and 1.10 10⁴ yuan/hm², yielding a total profit of 2.68 10⁴ yuan/hm². (2) Through the harvesting of rape flower stalks and fresh forage, 201.12, 74.15, 215.64 and 73.96 kg/hm² of N, P, K and Cl^- were respectively removed from the tobacco field soil. (3) Compared with the winter fallow control, at the time of rapeseed harvest, soil organic matter and total nitrogen contents in the 0-20 cm soil layer increased by 2.02 and 0.07 mg/g, respectively, while soil nitrate nitrogen, available phosphorus, and Cl^- contents across all soil layers decreased significantly (p<0.05). (4) Compared with control treatment, at the critical growth stages of tobacco, soil organic matter and total nitrogen contents across all soil layers in rapeseed treatment increased by 2.15-4.47 and 0-0.16 mg/g, respectively; Contents of all forms of soil available nutrient increased at the topping stage of tobacco, but subsequently decreased at its maturity stage, with the exception of soil alkali-hydrolyzable nitrogen in the 0-20 cm soil layer; At the topping stage of tobacco, the biomass and the nutrient accumulation amounts of N, P, K and Cl^- in all tobacco organs were decreased, but at its maturity stage, the biomass of the stems and leaves, and the accumulation amounts of N, P, and Cl^- in leaves were increased; The proportion of premium-grade cured leaves, average price and output value (by 1.00 10⁴ yuan/hm²) were increased. In conclusion, employing multi-purpose rape (for vegetable, forage and green manure) as a catch crop to develop "tobacco-rapeseed" integrated mode, not only improved the comprehensive economic benefits of tobacco field and removed a large amount of Cl^- from soil, but also promoted soil health and mitigated soil degradation by increasing annual contents of soil organic matter and total nitrogen. Additionally, it also promoted biomass accumulation in mature tobacco leaves and thereby enhanced its output value by increasing the availability of soil nutrients at the topping stage of tobacco. Consequently, this mode is suitable for popularization in the tobacco-growing areas of the Huanghuai region.