[Nutrient balance between N, P, and K in flue-cured tobacco production under different preceding crops planting]

A field experiment was conducted to study the nutrient balance between N, P, and K in flue-cured tobacco production in Shilin County of Yunnan Province under the effects of different preceding crops including rape, wheat, barley, and green manure planting. Overall, there existed significant differences in the soil nitrogen availability, tobacco plant dry matter accumulation, plant uptake of N, P and K, residual amounts of soil N, P, and K, apparent soil N loss, and apparent soil P- and K surplus during tobacco growth period under different preceding crops planting. Under preceding crop green mature planting, the soil mineral N content before tobacco plant transplanting, the soil N net mineralization rate during tobacco growth period, and the tobacco plant dry matter accumulation and N- and K uptake at maturation were all the highest, followed by under preceding rape planting, and under preceding barley or wheat planting. The P uptake by tobacco plant was also obviously higher under the preceding green manure or rape planting than under preceding barley or wheat planting. After the harvest of tobacco leaves, the soil residual mineral N content was the highest under the preceding green manure planting, followed by under preceding rape planting, and by preceding barley or wheat planting, while the soil available P and K contents were in adverse, being the highest under preceding barley or wheat planting and the lowest under preceding green manure planting. The apparent soil N loss during tobacco growth period was the highest under the preceding green manure planting, whereas the apparent soil P- and K surplus was obviously higher under preceding wheat or barley planting. It was suggested that an appropriate adjustment should be made on the fertilization rates of N, P, and K for tobacco production based on the preceding crops, i. e., lesser N application when the preceding crop was green manure or rape, and lesser application of P and K when the preceding crop was wheat or barley.