Evolution of soil fertility in long-term design with Oriental tobacco (1982 - 2002)
The experiments were conducted in a four-year rotation, of the type oats - tobacco - corn - corn, fertilizing with compost or compost added with PK, compared with the unfertilized control and a variant fertilized with mineral products (N25P100K50). The plot with tobacco had the same variants in the crop rotation and in the single-crop system also. The tested cultivars were Djebel 252 (1990 - 1993), Djebel 212 (1994 - 1997), Djebel 144 (1998 - 2001). In the year 2002, the single-crop system was 21 years old (from 1982). The organic or mixed fertilization ensures a faster ripening of the upper leaves with 2 - 5 days in the crop rotation and with 4 - 5 days in the single-crop system, compared with the mineral fertilization with N25P100K50. Compared with the single-crop system, the crop rotation ensured yield profits of 416 - 520 kg/ha for the unfertilized control, of 601 - 824 kg/ha for the variant with mineral fertilization - N25P100K50 and of 873 - 1038 kg/ha for the best variant (compost 15 /ha + P50). The yield profits favour the crop rotation system and draw serious critical attention to those who assert the single-crop system for Oriental tobacco. The long-term single-crop system leads to a poor use of fertilizer, which is emphasized during the drought periods in summer with obvious repercussions upon the yield and even upon the industrial and chemical smoking quality of the tobacco. For the tobacco obtained in the single-crop system, the nicotine and albumin content is higher, and that of carbohydrates is lower, compared with the tobacco in the crop rotation. The correlation of the enzymatic activities of the soil with the yield of cured tobacco shows the importance of organic fertilization with compost in the crop rotation. The 4 year crop rotation, after 21 years of experiments (the first tests began in 1982), visibly contributed to the improvement of the alluvial soil at the Experimental Field - Voicesti, county Vâlcea, the unfertilized variant obtaining high values of the enzymatic activities and maintaining the soil fertility. At the same time, the control of weeds, diseases and pests was achieved with minimum effort.