Abstract
Shifts in weed vegetation during maturation process of farms were studied in relation to chemical characters of the soils. Vegetations in unclutivated land, mature field and immature field were found to consist of wild plants, arable weeds and both, respectively. Immature fields tended to have a larger number of species, greater biomass, and higher population density, larger plant height and coverage. Among soil chemical characters, exchangeable acidity, degree of calcium saturation, pH (KCL) remarkably varied between those three types of fields.
Effect of the artificial disturbances after the field reclamation on weed vegetation was investigated. As the results it proved that most cf the cultural practices contributed only to quantitativfi change but little to qualitative change except for the weed shift by heavy application of calcum carbonate.
Fifteen-year trials on the successive applications of calcium carbonate and barnyard manure indicated that critical points in soil exchangeable acidity, degree of calcium saturation and pH which couldcause the shift from “wild plants” to “wild plant+weeds” and further shift to “weeds” were around 10.0, 20% and 4.40, and 1.0, 50% and 5.00, respectively.
The degree of resistance to soil acidity was rated on 54 species of weed. The classification was referred to soil acidity at the place where a pure stand was formed.
Index for degree of field maturation was feasibly calculated from the correlation between an avreage responsiveness index of weed community and soil acidity, concerning 15 areas with five different soil types. Quantitative index of weed corresponding to field maturation could be given by the equation for the relation between weed biomass and soil acidity, under the various conditions in the essential factors that affect the weed emergence.
Cropping systems in old slash-and burn method were investigated with particular reference to weed control, and one of the interesting weed control method was the cropping of perilla (Perilla frutescens Brit.) in a series of rotation expecting its phytotoxic ability for inhibiting weed emergence and growth.
