Weeding Performance of the Intra-row Weeders: (I) Weeding Effects of Soil Covering

A soil covering test was conducted to investigate the killing effect of weeds. The weeds tested were chenopodium album, stellaria media, polygonum nodosum and echinochloa crus-galli. The seeds of the weeds were sown in experimental plots, and they were covered with a loose soil layer of 1.0, 1.5, 2.0 times the weeds height by hand after emergence. Three types of intra-row weeders with different weeding mechanisms were examined to evaluate the width and the depth of soil covering and the rate of weeds exterminated by one weeding operation in an azuki-beans field in 1992. The results obtained were as follows: 1) The killing effects were seen when the ratio of soil covering depth to the weed heights were 1.5 or more, and the rates of weed extermination were over 97% for chenopodium album, stellaria media and polygonum nodosum with the exception of 50-57% for echinochloa crus-galli. 2) When each weeder was used in the field, the range of the soil covering widths were 18-32cm, and the range of the soil covering depths were 10-25mm. Therefore, weed heights which could be exterminated by the soil covering effects were considered to be less than about 10mm for each weeder. However, weeds over 10mm were exterminated by the multiple effects of pulling, breaking and soil covering at the field tests. 3) The rate of weed extermination was over 80% immediately after one weeding operation of each weeder. But, 15-72% of the weeds regenerated and/or emerged on the thirteenth day after the weeding operation.