Effects of tobacco nicotine on maize yield and soil bacteria in Tabora western Tanzania

Abstract

Tobacco (Nicotiana tabacum L.) is globally known to be a primary source of nicotine worldwide. This study was conducted to determine the effects of nicotine on the rhizosphere and subsequent maize crop yield. Pot experiments were carried at the Nelson Mandela African Institution of Science and Technology (NM-AIST), using levels of root and leaf extracts drenching to maize seedlings. In the first year, the field experiment comprised of six treatments (a) fertilized tobacco, (b) fertilized maize, (c) fertilized tobacco incorporated with tobacco stalks, (d) unfertilized maize, (e) unfertilized tobacco and (f) fallow with a plot size of 6 m x 6 m, 1.2 m from the ridge to ridge and 0.50 m from plant to plant. In the second year, all plots with exception to fallow plots were planted with maize to observe the effects of tobacco on soil nutrients, bacteria diversity and maize yield. Soil samples were taken to measure nutrients, nicotine and study bacteria diversities. Results showed that fertilized tobacco, released higher nicotine into the soil (10.27 mg ha -1 ) than unfertilized tobacco (3.07 mg ha -1 ). High levels of nicotine released in soils 7.59 mg kg -1 were found at a depth of 30 - 50 cm and lowest level 5.50 mg kg -1 at a depth of 0 - 10 cm. Maximum adsorbed and desorbed nicotine were found to be 4.61 and 2.21 mg kg -1 , respectively. Maize absorbed nicotine but at a very low concentration (0.001%) in maize grain. Maize planted not after tobacco had the highest grain yields (3.86 t ha -1 ), but maize planted as subsequent crop after tobacco had the lowest grain yields (3.53 t ha -1 ). The low yields were due to the low absorption of P and K nutrients following extreme uptake of these nutrients by the tobacco plant. In tobacco rhizosphere, bacteria under Proteobacteria, influence solubilization of P, K, S, Cu 2+ , Fe 2+ , Zn 2+ , Mn 2+ hence increased uptake of macronutrients and reduced their levels in soils; and less uptake of micronutrients and increased their levels in soils. This study recommends further studies to re-calibrate new recommendations for P and K on maize crop planted after tobacco.