Plant bioassays to detect herbicides residues in intensive rice-based cropping patterns under Conservation Agriculture

Avoiding the negative effect of herbicide residues in soils on the growth of subsequent crops is especially challenging in intensive cropping sequences involving numerous crop species and short fallow periods between crops. For intensive rice cropping patterns in Bangladeshthe residual effect of six herbicides: glyphosate, pendimethalin, ethoxysulfuron-ethyl, carfentrazone-ethyl + isoproturon, isoproturon, and fenoxaprop-p-ethyl were investigated in the following crops of mungbean and mustard through plant bioassay approach. These herbicides in ten different combinations were applied to mustard, mungbean, summer rice, winter rice, and wheat in an on-farm Conservation Agriculture experiment, which was conducted for three consecutive years (2013–2016). No detrimental residual effects of any herbicides applied to the prior crops in the rotation were detected on the plant population, root, shoot growth, and chlorophyll content in the leaves of test crops. Moreover, plant biomass, seed production, and the germination rate of the harvested seeds of both crops were not hampered by the residues of tested herbicides. It is concluded that these six herbicides examined for controlling weeds in the prior rice, wheat, mustard, and mungbean crops under the minimum soil disturbance and crop residue retention could be considered safe for cultivating crops in the next season. Under the increased prevalence of herbicide use for controlling weeds in intensive rice-based cropping sequences in South Asia, the systematic assessment of herbicide residual risk to crops needs to be instituted as a routine practice in this region.