Abstract: Effect and recommended NPK fertilization for mustard green were studied with field experimentations.Thirty tests were conducted and the results showed that the average rate of soil fertility contributed to the mustard yield was merely 26.3%.The effect of yield increase by individual fertilizers was 55.5%, 14.1% and 15.3% for the applied N, P and K, respectively.The fertilization benefits as shown by the output/input ratios were 36.9 and 21.3 and 12.2 for N, P and K, respectively.The result indicated that there was a remarkable effect on yield with the applied fertilizers.Maximum yield was achieved by using Olsen-P and available K at the rate of 42 mg·kg^-1 and 88 mg·kg^-1, respectively.Optimal application rate and NPK proportion varied for soils of different fertilities.On average, the application rates for the soil of "high fertility grade" were N 315 kg·hm^-2,P₂O₅ 85 kg·hm^-2 and K₂O 146 kg·hm^-2; those for the soil of"medium fertility grade" were N 348 kg·hm^-2, P₂O₅ 127 kg·hm^-2 and K₂O 196 kg·hm^-2; and, those for the soil "low fertility grade" were N 319 kg·hm^-2, P₂O₅ 146 kg·hm^-2 and K₂O 241 kg·hm^-2.The regression equations between the available NPK in soil and fertilizer application rate were established to facilitate proper fertilization according to soil testing results.

Key words: Mustard green, soil, NPK, fertilization effect, fertilization index