The latter two processes occur selleck in the soil matrix, predominantly in sandy textured soils. Therefore, preferential flow can occur in almost all types of soils caused by heterogeneities at scales ranging from the single pore to the pedon [12]. The extent of preferential flow and transport depends on factors such as soil texture, structure, initial soil water content (SWC), and application rate [13,14]. Even though flow is uniform in deep and uniform sandy soils, finger flow is observed in layered sandy soils having different particle sizes [15]. Infiltration is higher in non-tilled or undisturbed soils than in tilled or disturbed soils [13,16,17]. There is no consensus among the researchers about the effect of initial SWC on the preferential flow and transport [18�C21].
Chloride-tagged water with lower application rates in sandy and sandy loam soils reach deeper depths than in clayey soil [22,23]. They reported that high rainfall intensity after herbicides application caused considerable amount of them to leach deeper depths in a sandy loam soil. In the case of higher application rate, the more preferential flow was observed [24]. These studies show that the effects of individual factors affecting preferential flow and transport need to be further investigated. The interaction of the controlling parameters may help better understanding of these processes.Since the transport of water and solute in the vadose zone is not uniform due to soil heterogeneity, classical models using the Richards Equation Anacetrapib do not produce acceptable results [1,25�C28].
Therefore, different approaches are new post required for reliable simulations of flow and transport in this zone. A variety of approaches are available for modeling preferential flow and transport in the vadose zone like dual-porosity [29], dual-permeability [30], multi-porosity, and multi-permeability models [31]. In the dual-porosity and dual-permeability modeling approaches, the total soil porosity consists of two regions, macropore and micropores. Water flows through only macropores in a dual-porosity model, but it flows through both regions in a dual-permeability model. Accurate or reliable measurement of water flow and solute transport in the vadose zone is a key factor in better understanding the mechanisms of flow and transport processes and modeling these processes.Enabling to measure both SWC [32] and soil bulk electrical conductivity, EC [33] simultaneously makes time domain reflectometry (TDR) a valuable tool for studying the transport processes of water and chemical movement in the unsaturated zone in laboratory or field under steady-state or transient conditions.