Weed - fertilizer interactions in rice

This paper presents data from worldwide field trials on the effects of nutrients, especially nitrogen (N), on weed growth and rice production. Given that weeds usually grow faster and thus absorb available nutrients first, application of fertilizers can cause a greater increase in weed growth than in rice yield. Data on rice yields in weeded and non-weeded and in fertilized and non-fertilized fields show variable, sometimes contradictory results. The magnitudes of nutrient absorption by different weed species are indicated. Maximizing the actual benefits to rice of high N fertilization is examined with regard to: (1) the timing of fertilizer application (application to a previous crop, before planting, or after planting) and the relation of application to the type of rice planting (transplant, wet-seeded, dry-seeded wetland, or dryland); (2) the method of land preparation (no tillage, stale-seedbed, or conventional tillage); (3) the rice cultivar grown (modern or traditional variety); (4) crop canopy, plant population, and plant density; and (5) the composition of the weed flora (i.e., the effect of added fertilizer on 14 different weeds and comparison of the competition caused by different weeds). Because increased fertilizer application is most effective only if improved cultural practices are used simultaneously, weed control -- both chemical and manual -- takes on added importance. The authors discuss several herbicide-fertilizer mixtures (e.g., phenoxy herbicides, propanil, butachlor), and explore the use of ferns (Azolla) and blue-green algae as natural weed contollers. The authors conclude with a brief review of research on nutrients other than N. The text is highlighted by numerous tables, graphs, and charts and a 128-item bibliography (1927-81) is included.