Nine years continuous tobacco monocropping compared with alternative cropping frequencies and sequences. Part 1. Effect on leaf yield and quality
Flue-cured tobacco (Nicotiana tabacum L.) was grown on a granitic soil in Queensland for a total of 9 years. Following a pre-trial bedding in tobacco crop, an 8-year tobacco cropping rotation experiment with cropping frequencies of tobacco every one (1:1), two (1:2), and four (1:4) years was planted. With the exception of alkaloids and Mg, no significant long-term changes were evident in flue-cured leaf chemical characteristics. Alkaloid concentration appeared to increase in the first 6 years and then decrease with the introduction of a new flue-cured tobacco variety (resistant to soil-borne bacterial wilt (Pseudomonas solanacearum (Smith 1896) and (Smith 1914)) in the last 2 years of the experiment. The application of the soil fumigant EDB was observed to alter very slightly, but not significantly, macroelement chemical composition of the tobacco leaf. Continuous tobacco cropping for 9 years reduced total yield by 495 kg/ha and flue-cured leaf quality by 18-20 cents (A)/kg as compared with a 1:2 crop sequence. Withholding the soil fumigant treatment under continuous tobacco cropping lowered total yield by 1040 kg/ha and cured leaf quality by 17-31 cents(A)/kg. Fallowing land under a weed cover for 1 or 3 years had a beneficial effect on subsequent tobacco crop performance. Gatton panic grown in continuous or 1:2 rotation with tobacco was also noted to enhance leaf yield and quality. The poorest returns were seen for peanut and soybean, likely because of erosion during row crops, and for signal grass grown 1:2 rotation with tobacco.