Abstract:
The search for microorganisms to improve soil fertility and crop production has continued to
attract attention to offset the negative impacts of fertilizers in the environment in an eco friendly way. The objectives of this study were to screen beneficial bacterial strains from onion
(Allium cepa L.) rhizosphere from Thiruvaiyaru area in Kilinochchi district for the ability to fix
nitrogen, solubilize phosphorus and/or to produce indole-3-acetic acid; and to select efficient
strains in terms of onion productivity. Seven bacterial strains were screened for their N fixing
and P-solubilization potential. The selected isolates together with previously screened three
bacterial isolates were tested in a pot experiment under greenhouse conditions to evaluate their
efficiency in improving growth, and yield of onion. The treatments were arranged in a
completely randomized design with four replicates. The treatments were T1 (Non-fertilized), T2
(Rec NPK), T3 (Azo1), T4 (Azo3), T5 (Azo4), T6 (Azo5), T7 (Azo6), T8 (TSA1), T9 (TSA2), T10
(Azoj2), T11 (Azoj4), T12 (OD) and T13 (Cattle manure: CM). T2 (Rec NPK) was treated with
recommended dose of CM (10t/ha) and NPK fertilizers; Urea (195kg/ha), Triple supper
phosphate (100kg/ha) and Muriate of potash (75kg/ha). For the treatments T3 to T12 were
treated with respective inoculum, CM (20t/ha) and Muriate of potash (75kg/ha). T13 was treated
with CM (20t/ha) alone. All the inoculated plants showed significantly comparable height and
number of leaves /plant with T2 (Rec NPK) throughout the growing season except T9 (TSA2).
The highest and the lowest dry matter were produced in T7 (Azo6) and T9 (TSA2) respectively.
The onion yield was increased by 24%, 25%, 20%, 20% and 31% in T3 (Azo1), T4 (Azo3), T6
(Azo5), T7 (Azo6) and T11 (Azoj4), respectively compared to T2 (Rec NPK). There was a positive
correlation observed between yield and uptake of nutrients, nitrogen and phosphorus.
Therefore, the bacterial strains Azo1, Azo3, Azo5, Azo6 and Azoj4 have the potential to improve
the growth and yield of onion compared to other tested strains. It is also suggested that further
studies under the field conditions are needed to confirm the efficiency of screened strains.
