Effects of herbicides on soil microflora in WDSR [wet direct-seeded rice] fields: biochemical analysis
2003
Malabayabas, M.D. | Xuan, T.H. | Santin, C.A. | Nazar, J.S. | Juliano, L.M. | Casimero, M.C. | de Dios, J.L. (Philippine Rice Research Inst., Maligaya, Munoz, Nueva Ecija (Philippines). Central Experiment Station)
In the DS [dry season], microbial (ETS) activity decreased 11 days after herbicide application (DAHA) in plots with pretilachlor and pretilachlor +2,4-D including the control. At 18 DAHA, activity increased in soils treated with pretilachlor + 2,4-D. Activity lagged in untreated plots, and those sprayed with pretilachlor only at 1 DAS [days after seeding]. A logarithmic increase in microbial activity followed at 25-46 DAHA. In another batch of samples, almost the same trend was observed, except those plots treated with Bispyribac sodium and Benthiocarb, 2,4-D where microbial activity logarithmically increased with time. This could be a result of flooding and application of fertilizer N particularly at 25 DAHA. Microorganisms could have also occurred resulting in increased activity. Herbicide treatment with pretilachlor only, and pretilachlor + 2,4-D had comparable trends to the control at 4-18 DAHA. However, herbicide application significantly reduced chlorophyll content at 25 DAHA. The same trend was noted in the rest of the treatments except that the decrease was observed at 18 DAHA. The results indicate that the chlorophyll contents were degraded at the later stage due to herbicides. During the WS [wet season], microbial biomass was determined as biomass N, which dropped in the 5 DAHA in all treatments, then increased at 12 DAHA including the control due to N application at 15 DAS. In the other treatments, almost the same trend was observed, although biomass N with pretilachlor was significantly higher at 54 DAHA. Microbial activity was not significantly affected by pretilachlor, butachlor, and pretilachlor + WCAI treatments. Based on these results, herbicides applied at the recommended rates have no detrimental effects on soil microbial biomass activity and phototrophic biomass
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