Abstract

Soil water fluxes influences inorganic nitrogen (N) because their transport, transformation, storage and potential losses from an agroecosystem are determined by the hydraulic gradients that occur in the soil, as being a result of drying and wetting cycles (D-W cycles). The objective of this research is to evaluate the temporal availability of N physically stored in the range of matric potentials corresponding to pore diameters between 0.2 and 50 μm, in five volcanic ash soils under permanent grassland during continuous D-RW cycles. Undisturbed soil samples were collected at two depths: 0-10 and 10-20 cm (n = 5), using stainless steel cylinders (610 cm3, with Ø=8.8 cm and h=10 cm). Soil samples were pre-incubated for 24 hours added 5 ml solution with K15NO3 (98 atom %15N). The labeled solution was added evenly over the soil surface. All soil samples (cores) were subjected to five D-W cycles. Dry conditions were determined when the core is equilibrated to 100 kPa. Rewetting conditions were performed by applying distilled water to the top of the soil cores and leaving the soil to equilibrate until the soil water content reaches - 6 kPa of matric potential. The water that was drained for ~10 days until reaching an equilibrium equivalent to ~ 100 kPa (50% of PAWC according to water retention curve) was collected in a plastic bottle from the pressure chamber and stored cold until analysis of isotopic ratios. The physical soils' capacity to store available nutrients in time and space (mineral N movement in depth is approximately 1 cm per day in volcanic soils) forms part of a new line of study that includes the dynamic nature of soil, which depends on the hydraulic properties of the soil, the functionality of the pore system, and the spatial arrangement of its particles and aggregates. Therefore, the “physical soil condition” plays a fundamental role plays a fundamental role in the sustainable management of soil fertility