Three kinds of organic fertilizer (sawdust manure, rice straw manure, liquid slurry from dairy cow waste) and a chemical fertilizer were used for 6 consecutive years (1986-1991), and their effects on green-cut corn yield and soil properties were investigated. There was a considerable variation in the year to year foliage dry weight of the corn yield, and it was considered appropriate to determine the ratio of fertilizer effectiveness of organic fertilizer in the field in which it had been consistently used to that in which the chemical fertilizer was applied. The dry weight yield of the field in which the respective fertilizer had been used was found to be 80-90% of that in the fields in which the chemical fertilizer had been applied.
After 3 successive years of organic fertilizer application, we added to the organic fertilizer-applied fields ammonium sulfate, fused phosphate and potassium chloride so that the 3 major components in each field were equal to thet of the chemical fertilized field (N:20kg/10a, P2O5:18kg/10a, K2O:20kg/10a). The results were increased foliage yield (dry weight) in the organic and chemical fertilized fields, with the yield reaching the level in the chemical fertilized fields (N:20kg/10a, P2O5:18kg/10a, K2O:20kg/10a) by the fifth year of constant application successively (1990). The application of 11t of slurry proved to be especially effective for consistently high yield. The sixth-year (1991) yield was highest, and vigorous growth was observed in 6-8 weeks after sowing.
Porosity (void ratio) was reduced in all fields tested, whether organic or chemical fertilizers had been used. Harrowing tented to be easier in the organically fertilized fields. In the slurry-applied fields in particular, the proportion of tiny clods was quite high after rotary tilling.
