Tine-influenced infiltration patterns and informing timing of liquid amendment applications using brilliant blue dye tracers

Abstract

Tillage associated with slurry applications, as well as soil physical properties at time of application, imparts strong control over resulting slurry application-induced infiltration patterns and contaminant flow pathways. This field-based study used Brilliant Blue-dyed water applied to tine-influenced silty-clay loam soil, at different antecedent soil water contents, to investigate the nature of infiltration patterns that might be expected to occur during a typical liquid manure or biosolid land application. The tines were associated with a furrow-based Kongskilde Vibro-Flex S-tine slurry application system and a soil pocket-forming AerWay ® SSD rolling aerator-type slurry application system. For the furrow-based approach, liquid was applied to a small furrow stretch at a nominal rate of 180,000 l ha −1 . For the AerWay treatment, a nominal liquid application rate of 180,000 l ha −1 was applied to individual soil pockets. Dye infiltration attributes were determined in 10 cm depth increments to over 1 m beneath the application area. Attributes included: dye infiltration depth, dye spread, and area coverage of dye. The attributes were determined for each depth via image processing software. Experiments were conducted at soil water conditions ranging from 15% v/v to 39% v/v. For furrow-based methods, dye was primarily absorbed above 30 cm depth (above a plough pan which, was approximately 20 cm depth) for all water content conditions. Dye spread:area ratios were generally larger below the pan than above it. Dye penetration depth for all water content conditions exceeded 60 cm depth. With the soil pockets caused by the AerWay treatments, the depth of dye penetration was non-linearly related to the soil water content where greatest dye penetration depth occurred at lower surface soil water contents ( 29% v/v). Overall, for the lower soil water content conditions, desiccation cracks and soil fractures facilitated by tillage action augmented bypass-based preferential flow to continuous sub-pan macropore networks. The greater infiltration depths achieved for the wetter soil conditions were due to greater intrinsic pore sizes that are operative at lower soil tensions and reduced dye sorption. The area covered by dye was greater above the plough pan; but beneath the pan, discrete macropore-based flow (e.g., worm burrows, root channels) dominated infiltration to the deepest observed depths as supported by observations of relatively higher dye spread:area ratios. This study underscores the importance of basing liquid amendment timing regulations not only on an upper water content limit but also on a lower limit as well. In addition, the study supports the impact of plough pans augmenting sorption in the tillage layer, thus minimising the degree of preferential flow to depth during a typical land application.