Changes of Wewd Communities by Methods of Cultivation in Winter Cropping on Drained Paddy Fields : (3) Influence of methods of spring and autumn tillage on the structure of weed community and the quantity of weeds with special reference to the analysis of the quantity of weeds by the distributioh in soil of Alopeculus aequalis Sobol. seeds

Abstract

Combinating each of three tillage methods, shallow tillage by power tiller, deep tillage by power tiller and deep plowing, in spring and autumn, nine plots were laid in 1957. After weeds had ripened and scattered seeds, spring tillage was practiced in the middle of June and then lowland rice was planted, and after its harvest autumn tillage was made in the middle of November. In each plot, the vertical distribution of viable buried seeds of Alopeculus aequalis was surveyed before and after tillage times and at drainage time and number of weeds emerged during the period from autumn to the next spring was counted. Before spring tillage, most of Alopeculus aequalis seeds were placed in the top layer, and this distribution of seeds was changed by the tillage as shown in Fig. 1. The changes in the distribution differed with the three tillage methods. Many viable buried seeds emerged or sprouted under soil to die during the period from drainage to autumn tillage. And number of the viable seeds was reduced by so much in upper layer of soil than in lower (Fig. 3). Accordingly, the distribution was changed as shown in Fig. 4. In the plot of spring shallow tillage, where many seeds were placed in upper layer, total number of seeds within all soil layers was less at the time of autumn tillage than in others. These patterns of the distribution were changed by autumn tillage as shown in Fig. 2. Number of seedlings of Alpeculus aequalis was proportional to number of seeds in the upper emergenable layer (0∼4 cm) (Fig. 5). Consequently, number of seedlings (Table 1) was reduced in the plots combinated deep plowing-shallow tillage, shallow tillage-shallow tillage, and deep plowing-deep tillage, and increased in deep tillage-deep plowing and deep tillage-deep tillage. Moreover, it was shown that deep plowing in spring and shallow tillage in autumn had a tendency to reduce the number of seedlings. Number of seedlings of Stellaria uliginosa was few in the plots deep plowed in either spring or autumn. This fact seems to be very reasonable, based on that few decrease in viable buried seeds took place during the time from the drainage to autumn tillage. The other kinds of weeds hardly emerged. As the result, the structure of weed community differed in each plot as shown in Fig. 6, that is in the plots of autumn deep plowing the proportion of Alopeculus aequalis was high and in the plots of autumn shallow tillage the proportion of Stellaria uliginosa was high.