LAUSR

Introducing specific microorganisms into the soil ecological system is an important strategy for improving nutrient use efficiency. Two experiments were conducted in the greenhouse to evaluate the effect of nitrogen (N) source and inoculation with plant growth-promoting rhizobacteria (PGPR) on plant growth and N and phosphorus (P) uptake in tomato (Lycopersicon esculentum Mill.) grown in calcareous soils from South Florida. Treatments included urea (UF), controlled release urea (CRF) each at low N (F1) and high N (F2) and with or without inoculation of PGPR. A mixture of PGPR strains Bacillus amyloliquefaciens IN937a and B. pumilus T4 was applied to the soil during growing periods of tomato. Treatments with PGPR inoculation increased plant height compared to treatments without PGPR in both experiments. Inoculation with PGPR increased dry shoot weight compared to the treatments without PGPR at equivalent N rates. Only CRF and UF at F2 with PGPR had significantly (P < 0.05) greater shoot biomass than that from CRF and UF alone in both experiments. For N uptake in tomato shoot, treatments with PGPR increased N uptake compared to the treatments without PGPR in the same N rate and N source. Only CRF2 with PGPR significantly increased N uptake by 39.0 and 10.3% in shoot compared to CRF2 alone in experiment 1 and 2, respectively. Meanwhile, presence of PGPR in the soil increased total P uptake in shoot for all treatments in experiment 1 and for most of treatments in experiment 2. In experiment 1, only CRF treatment at F1 level with PGPR significantly increased total P uptake in shoot compared with CRF without PGPR. In experiment 2, a significant increase in total P uptake in shoot by inoculation of PGPR was only observed in CRF at F2. Results from this study indicate that inoculation with PGPR may increase plant growth and N, P uptake by tomato grown in calcareous soils. However, the effect of PGPR varied and was influenced by many factors such as N source, N rate, and soil fertility. Further investigations are warranted to confirm the effect of PGPR under different soil conditions.