Mechanism of Competition between Barley and Weeds in Winter Cropping on Drained Paddy Fields, and a Diagnosis Method of the Weed Damage

Abstract

Experiments were carried out under various cultural and weed conditions in cropping of barley (and of wheat in some cases) on drained paddy fields with either of the two culture methods, i. e. the tiller-seeding method and the drill-seeding method. In the former, seeds are put in the upper soil layers of the field in broad bands by plowing with a rotary power tiller, and in the latter, seeds are sown in drill rows with narrow spaces between them by a drill-seeder. In the study by the present authors, however, seeds were sown by a rake and by hands respectively instead of machinery. The results obtained were as follows: 1) The competition between barley (or wheat) plants and weeds (mainly Alopeculus aequalis S_OBOL.) became serious from about the beginning of the internode elongation period of the crops, but was stabilized after the heading time, the process reflecting the competitive characteristic of the crop and that of the weed, each associated with its growth habit, plant height and so on (fig. 1). 2) The mechanism of competition between crop plants and weeds was analysed from the viewpoint of the "density-effect" in mixed plant population as proposed by K_IRA, et al. The final productive relations in the community including crop plants and weeds changed almost proportionally to the increase of the weed-density (fig. 2). That is to say, the production of weeds, increased along a curve very akin to a straight line, while the production of barley (or wheat) plants decreased almost perfectly linearly in proportion to the increase of the weed-density. As the result of the fact that the decrease in barley (or wheat) production was greater than the increase in weed production, the total production of the community decreased also slightly in higher densities of weeds. Then, the ratio of barley (or wheat) plants to the total production of the community declined linearly as the weed-density increased. Finally, the yield decrease of barley (or wheat) caused by weeds was highly related first to lowering of the ratio of weeds to the total production of the community, and secondly to the decrease of the total production of the community, but was little related to lowering of the ratio of the grain weight to the whole plant weight of the crop. Then, these competitive relations differed with cultural conditions such as rate of seeding, amount of fertilizers, width of the planting row, and mutual relations between the kind of crop (barley or wheat) and the kind of weeds in the community; these differences had a plainly visible effect on the ratio of weeds to the total production of the community (table 2). 3) Considering the weed-density, the ratio of weeds to the total production of the community and the weight of weeds in comparison with each other as an index for diagnosing the weed damage (table 3), it is evident that the weed damage of winter barley (or wheat) on drained paddy fields, the weed community being nearly uniform, can be diagnosed most accurately in an early stage by examining the weed-density.