Studies on Weed Vegetation in Non-cultivated Paddy Fields : I. The vegetation of non-cultivated paddy fields in the north-western parts of Fukuoka prefecture

Abstract

To make clear the weed vegetation of paddy fields left off cultivation on account of government paddy acreage-control policy, the investigation were carried out in autumn of 1975. The 25 surveyed plots were located at the north-western parts of Fukuoka prefecture. Coverage and height of plants in their paddy fields were measured and Summed Dominance Ratio (SDR2), which was proposed by NUMATA, was calculated from those two factors. All the species appeared were classified into the following four plant groups from their habitat type: that is, A; perennials in lowlands, B; annuals in lowlands, C; perennials in uplands and D; annuals in uplands. And then, the relations between the SDR2 of these plant groups and the difference of soil moisture, and years of fallow were compared with each vegetation. Results are as follow. 1. At the beginning one or two years after left off cultivation, species number and SDR2 of annuals were dominative. With increase of years of fallow, species no. and SDR2 of perennials became dominative. 2. In the former case, the dominant species were annuals such as Aster subulatus, Aeschynomene indica, Panicum bisulcatum, Echinochloa spp., Leptochloa chinensis, Digitaria adscendens and so on. In the latter case, they were perennials such as Aliscanthus sinensis and Solidago altissima under upland condition, or Isachne globosa, Phragmites communis, Leersia japonica and Paspalum distichum under lowland condition. 3. The vegetation consisting of four groups were largely affected by the difference of soil moisture and years of fallow. The vegetation of paddy fields left off cultivation for many years were mostly composed by the specics of C group under upland condition and by the species of A group under lowland one. On the other hand, that of paddy fields left off cultivation for few years were composed by the species of D group under upland condition and by the species of B group under lowland one, although the relationships were not so clear as in the former. 4. The increase of number of species and SDR2 of perennials were controlled by means of managing methods such as plowing, cutting of weeds and herbicide application. The repressive effects of management against weeds varied depending on the kind of managements and the characteristics of weed species.