Effects of cultivation practices on root development and weed tuber propagation in organic paddy rice field

To confirm the effects of tilling practices with organic material incorporation on weed flora, we conducted an experiment in the paddy field, where organic rice had been grown successively for more than 30 years, in Hatamachi, Nagano, and examined root system formation of weed and rice under tillage practices with organic matter as soil amendment from 2003 to 2005. A factorial experiment was carried out with split plot design of 1) fall tillage (done and none), 2) timing of spring tillage and fertilization (0 day and 40 days before water immersion) and 3) fertilization and tilling depth (5 cm and 15 cm), The fresh mass of Sagittaria trifolia L, Scirpus hotarui Roxb. var. ohwianus T. Koyama Ohwi, and other small broad leaved weeds decreased under the cultivation practices. Although the soil available nitrogen was decreased by the fall tillage, the rice yield in plots without weeding increased, along with the weeds root dry mass and tuber dry mass of Eleocharis kuroguwai Ohwi reduced. Available nitrogen emission from soil tilling at the time of water immersion increased in comparison with that 40 days before immersion, which then made new tuber enlargement if no plowing was done before water immersion. It was suggested that the plowing practice of fall tillage with straw incorporated, then spring shallow tillage with organic fertilized immediately before transplanting and early weeding after transplanting, could decrease nutrient supply quantity in addition to weeding effect, exert influences on the root system development of the paddy rice, and avoid the weed domination and rice yield decrease.