Effects of herbicides on in-situ net mineralization of nitrogen in wheat field

In conservation agricultural practices, adoption of herbicide has increased for crop protection but increased herbicide uses for soil health are being questioned. Two experiments were conducted to examine the effect of herbicide on net nitrogen mineralization rates in situ under field conditions. Both experiments were conducted at different treatments of post and pre emergence herbicides in the research farm of Bangladesh Agricultural University under Old Brahmaputra Floodplain (AEZ 9). Experiment-1 comprised of three post emergence herbicides and one control treatment [T₁-Control, T₂-2,4-D Amine, T₃-Carfentrazzone-ethyl+isoproturon (Affinity), T₄- Carfentrazzone-ethyl (Hammer)]. Composite soil sampling for post emergence herbicides was done at day 21 (days after planting, DAP) which was the day of herbicide and fertilizer application, day 22, 23, 24 and 25 (DAP) after herbicide application. Experiment-2 comprised of one most popular pre-emergence herbicides Pendimethalin (Panida) with manual weeded control treatment. Composite soil sampling for pre emergence herbicides was done at day 3 (DAP) which was the day of herbicide and fertilizer application; day 4, 5, 6 and 7 (DAP) after herbicide application. Both experimental designs were Randomized Complete Block Design (RCBD) with four replications. Herbicides were tested at their label rate compared with manual weeded control treatment. Tested post-emergence herbicides had no significant effect on N mineralization. The numerically higher concentration of NH₄⁺-N and NO₃^--N was found in treatment T₄ (Carfentrazzone-ethyl). Tested pre- and post-emergence herbicides had no significant effect on soil NH₄⁺ and NO₃^--N content. Similarly, pre-emergence herbicides Pendimethalin (Panida) had no significant effect on NO₃^--N production. The study revealed that commonly used herbicides have no short term inhibitory effect on nitrogen mineralization and nitrifying microorganism. The increase in nitrification process is an indication of increasing nitrifying microorganism and positive effect to the soil microbiota. Although tested herbicide did not differ significantly with respect to wheat grain, yet the higher grain yield was produced by Carfentrazzone-ethyl+isoproturon (Affinity).