The Trifluralin (TFN) is a pre-emergent herbicide which is widely used in agriculture. Usually, this pesticide is directly applied to the soil, where it can remain for long periods or can be transported. In this sense, knowing the dynamics of an herbicide soil transport is essential to avoid environmental contamination problems and risks to human health. Thus, this study aims to model and simulate TFN movement on soils with two different textures, a sandy loam and clay loam soil. It was considered that the herbicide was applied via chemigation trough a subsurface drip irrigation system, under a non-steady regime. Therefore, the transport parameters of TFN in these soils and physical-hydric characteristics of these were used, while the physical environment modeling were conducted using the Hydrus 2D software. The results showed that both in sandy and clayey soils, the TFN tends to be retained by the soil, close to where it was applied, not exceeding a layer greater than 2.5 mm outside the dripper radius, even in more favorable conditions such as the presence of irrigation. Finally, it could be concluded that this herbicide movement in the soil is of low potential, due to this product high solid-liquid partition coefficient (Kd), even in sandy soil, which has low cation exchange capacity (CEC).

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Subsurface drip irrigation success depends on surpassing the backpressure obstacle, a phenomenon which occurs when the water application intensity exceeds the infiltration rate of soil, which reduces the emitter flow rate. Thus, this study aimed to determine the flow rate variation, in relation to surface flow, of four drip emitters when buried at two depths in a loam soil (Yolo Loam soil), and the backpressure generated by the soil on subsurface condition. The cavity radius developed around the emitters outlet was also obtained. The experiment was conducted in a completely randomized design, in a strip-plot scheme, with three treatments: installation depth of driplines (two levels: 0.10 and 0.20 m); dripline type (four levels: D5000, JardiLine, TalDrip and and Hydro PCND) and irrigation time (three levels: 0.5, 1.0 and 3.0 h). The results showed that the flow rate variation between the surface and subsurface application on Yolo Loam soil, with inlet pressure of 145 kPa, was greater the higher was the emitter flow rate. For pressure-compensating emitters, even under backpressure influence, this was not enough to cancel the pressure-compensating device operation, of the emitters. The emitters installation depth, as well the irrigation time, did not affect the backpressure and, consequently, the flow rate variation.