Crack closure and flow regimes in cracked clay loam subjected to different irrigation methods

Abstract

Soil cracks, which are common in farmland, typically serve as preferential paths for water movement or solute transport and potentially result in deep percolation and groundwater contamination during crop production. The major objectives of this study were to investigate crack variation and flow regimes in cracked soil under different irrigation methods. Dye experiments were conducted in cracked soil columns using three different irrigation methods, i.e. surface irrigation, spray irrigation and drip irrigation. Superficial crack networks and dye patterns in soil profiles were photographed and quantified by image processing techniques. Soil water content was measured by Time Domain Reflectometry. Evaluation of irrigation efficiency was conducted based on the dye patterns and measured soil water content. The results showed that the cracks rapidly closed under surface irrigation but partially closed under spray irrigation, which was mainly attributed to the difference in application rate. Crack flow occurred under surface irrigation and caused striking ‘V’-shaped regions of preferential flow in profiles, markedly increasing the infiltration depth compared with spray irrigation. Under drip irrigation, crack closure degree decreased with the distance from drip center. Cracks restricted the horizontal infiltration, giving rise to an inverted pear-shaped wetted zone in soil. Our results indicate that application rate and infiltration geometry of irrigation have substantial effect on crack closure degree, and flow regimes in upper soil are closely associated with both irrigation methods and soil cracks, which can appreciably affect the irrigation efficiency. These findings could bear management recommendation for irrigation in cracked fields to promote irrigation efficiency. Besides, this study implies that spraying at appropriate application rates may be able to facilitate crack closure without inducing large water loss via crack flow, which needs to be further investigated.