Development ofbioconsortia for optimizing nutrient supplementation through microbes for sustainable tobacco production

Increased interests in low-input agriculture in recent years has seen the growing development in the use of commercial biological inoculants to increase the mobilization of key nutrients such as nitrogen (N), phosphorus (P) and potassium (K) to enhance their availability to crop plants. The objectives of this field experiment with tobacco were to determine i) reduced rates of inorganic fertilizer coupled with microbial inoculants that produce plant growth, ii) yield and nutrient acquisition levels equivalent to those with full rates of fertilizers and iii) the minimum level to which fertilizer could be reduced with the use of bioinoculants. The microbial inoculants used were plant growth promoting bacteria viz., Azospirillum, Azotobacter, Bacillus subtilis and Frateuria aurantia alone or a mixture of them in combination with 75% chemical fertilizer. Results showed that supplementing 75% of the chemical fertilizer rate with inoculants produced plant growth, yield and nutrient (N, P and K) acquisition that were statistically equivalent to the full fertilizer rate without inoculants. When inoculants were used in single, double or triple with 75% RDF the beneficial effects were usually not consistent. However, inoculation with the mixture of PGPR (N, P and K mobilizers) at 75% RDF produced significantly superior yield better than the full fertilizer dose without inoculants. Without inoculants use of fertilizer rates lower than the recommended resulted in significantly less plant growth, yield and nutrient uptake. The results suggest PGPR based inoculants can be used and should be further evaluated as components of integrated nutrient management strategies.