This study was carried out to maximize the fertilization efficiency of mixed organic fertilizer (OF) for
organically managed onion (AlliumcepaL.) productionduring the one growing season of 2005–2006. The
organic fertilizer was made of organic materials like sesame oil cake, rice bran and molasses and
minerals like illite and mountainous soil. Four organic topdressing treatments, which all followed the
same basal fertilization with solid OF, consisted of solid OF without mulch (OF/OFnM), liquid organic
fertilizer without mulch (OF/LOFnM), liquid organic fertilizer under mulch (OF/LOFuM) and liquid
organic fertilizer over mulch (OF/LOFoM). Chemical fertilizer (CF) and no fertilizer (NF) were treated as
controls. The solid organic fertilization base was 2.0 ton ha
1
, and 4.57 ton ha
1
and was used for
topdressing. The total amount of liquid organic fertilization was 133.2 ton ha
1
, which was divided into
6 applications from February through March. The OF/LOFuM and OF/LOFoMtopdressings did not reduce
onion height, leaf number or bulb diameter as compared to chemical fertilizer, whereas no mulch
treatmentsmade onion growth significantly poorer. Onion top weight inCFwas significantlyhigher than
that inOF groups at the peak growth stage, while therewas not much difference in bulb weight between
the CF and OF/LOFoM treatment. Finally, the onion marketable yield was 45.9 ton ha
1in the OF/LOFoM
treatment, which exceeded that in the CF treatment by up to 1.9 ton. Furthermore, OF/LOFoM was the
most effective among all the treatments in transferring the nutrients from sink to source. CF made the
soil pH more acidic than OF did, and the electrical conductivity (EC) remained higher with CF than OF as
well. While organic fertilizer helped to keep the NO3-N content stable throughout the growing season,
the concentration rapidly oscillated up and down according to CF fertilization. Organic fertilizer
increased population number of soil microorganisms like aerobes, actinomycetes in the field