Revisiting soil infiltration and its controls after long-term intensive agricultural management in contrasting soils

Soil infiltration controls the partitioning of water between surface runoff and recharge into the soil and, thereby, influences a range of biogeochemical processes, including soil erosion, carbon and nutrient cycling. However, long-term intensive soil management (e.g. irrigation and grazing) can substantially alter soil infiltration capacity, with responses strongly dependent on soil type and associated soil water regimes. In this study, we evaluated the effects of more than 30 years of contrasting land use, namely dryland pasture (DryPast) and irrigated pasture (IrrPast), on surface steady infiltration rate (IRs) across three representative soils with increasing soil water-storage capacity: silt loam Lismore soil (LIS), silt loam Templeton soil (TEM), and Waterton/Temuka clay loam soil (WAT) in the Canterbury Plains of New Zealand. The greater reduction in IRs after DryPast conversion to IrrPast was observed in WAT soils with higher water-holding capacity, followed by LIS and TEM soils. Across soil types, the response of IRs to land-use change was primarily determined by the characteristics of smaller macropores, particularly their volume and tortuosity within the 60–300/430 µm size range. However, the macropores that control IRs did not remain static; instead, they underwent structural changes, either through reductions in pore size or increases in tortuosity, following conversion from DryPast to IrrPast. Overall, the alterations in macropore characteristics (e.g., decrease in size or increase in tortuosity), driven by interactions between management practices (e.g., irrigation and grazing) and inherent soil type (e.g., soil water-holding capacity), are important for interpreting steady infiltration responses to land-use change.