Effect of Shading on Weed Emergence in Paddy Fields

Abstract

Asynchronous emergence of seedlings is a problem in the management of paddy field weeds. This phenomenon is caused by the heterogeneous germination characteristics of buried seeds and non-uniform environmental factors affecting them. To identify the environmental factors associated with asynchronous weed emergence, the influence of shading was investigated in paddy fields.
1. The overall number of weed seedlings decreased with the increase in the shading rate. The numbers of emerging plants in each weed species also decreased. In Ammannia multiflora Roxb., the correlation between the shading rate and emergence number was especially high: the coefficient of correlation was -0.985** (Table 1)
2. After the end of the shading treatment, 852/m² weed plants emerged in the plot with 0% shading. The lower the emergence during the shading period, the higher the post-shading emergence. The higher total emergence, 1, 705/m², was obtained in the 0% shading plot. Besides, the difference between the total amounts for 0-40% shading plots and 81-100% shading plots was significant at 5% according to Turkey's test (Fig. 2).
3. In A. multiflora Roxd., when the shading was severe, then was a high seedling emergence after shading, which was statistically confirmed by Tukey's test at 5% for 0-94% shading. The coefficient of correlation between the shading rate and emergence number for post-shading was 0.847** (Table 2).
4. Shading strongly affected the emergence of Lindernia procumbens (Krock.) Borbas, Ludwigia epilobioides Maxim., Elatine triandra Scjk. var. pedicelata Krylov., Rotala indica (Willd.) Koehne var. uliginosa (Miq.) Koehne, Cyperus difformis L., Ammannia multiflora Roxd., and Dopatrium junceum (Roxd.) Hamilt.