The land used for the experiments had not been cultivated in the previous 10 years. All
plots containing the experimental treatments were 30 m long and 5 m wide. Fertilizer was
applied to the treatment plots prior to each cropping season in the form of 15-15-15 NPK
mixed fertilizer at a nominal rate of 330 kg/ha. Planting each year was in mid to late May,
with fertilizer being applied within a month of planting. All plots were weeded twice during
the growing season, normally in June and August.