Soil samples at 0–20cm layer were collected on 11 May (32DAT,
fruit enlarging stage), 15 June (67DAT, fruit maturity stage) and 20
July (102DAT, later fruit harvesting stage), respectively.
Soil organic matter was analyzed using potassium dichromate
volumetric method (external heating method). Soil available N
content was determined using 1mol/L NaOH solution diffusion
method. Available P content was extracted using 0.5 mol/L NaHCO3
(pH 8.5) and determined according to the method of Olsen and
Sommers (1982). Other soil properties were determined according
to the methods of Lu (1999).