2.2. Plant and soil sampling
Sampling for onion growth, plant nutrients and soil chemical analysis were performed from 26 to 28 April (at the initial bulbing stage), and from 3 to 9 June (at harvest). Ten plants were pulled at 3 replications from each field at the initial bulbing stage,and fifty plants were pulled at three replications at harvest. Soil samples were collected from the surface soil (0–20 cm) and the subsoil (20–40 cm), at the same site and date as the plant sampling.