Abstract

The dynamics of water in the soil permit the movement, storage and redistribution of nitrogen (N) within productive and natural agro-ecosystems. The objective of this research was to determine the functionality of the soil's porous system, using capacity and intensity parameters in two volcanic soils (Andisol and Ultisol) under agricultural use and to present a new approach of how soils have the capacity to store inorganic N throughout time. Undisturbed soil core samples (230 cm(3) and 250 cm(3)) were collected at four depths: 0-20; 20-40; 40-70; 70-100 cm. Capacity parameters: air capacity (AC) and plant available water (PAW) and intensity parameters: saturated hydraulic conductivity (Ks) and pore connectivity index (C2) were measured and calculated. Greater average PAW (48%) was determined at the previously mentioned depths in the Andisol as compared to the Ultisol (32%). Calculated values-diffusive NO3-fluxes (DNF) as a function of soil water content (SWC) were determined in the pF curve (R-2 = 0.98; p 0.0001; fitted model proposed by Clunes, 2020). As SWC increased in PAW, the DNF did as well (DNF in Andisol, from 480 nmol N cm(-2) h(-1) to 710 nmol N cm(-2) h(-1)). An inverse relationship was observed between the DNF and the air-filled porosity (ea); the slope was about -1.02 in both soils. The DNF presented a significant relationship with the C2 index in the Andisol (R-2 > 0.80; Sy.x > 0.02). In contrast, the Ultisol at the depth of 0-20 cm presented a highly negative relationship between DNF and C2 (R-2 = 0.99), due to tillage. The relationship observed here between intensity parameters and DNF revealed a dynamic factor of N availability in the soil. As water increased in PAW and the continuity values between the pores augmented, this allowed for an increase in the available N in a soil volume. We propose that soils have the capacity to physically store inorganic N in the PAW and the functionality of the pore system (their ability to transport water and distribute nutrients throughout the profile). Improving our comprehension in this regard will allow us to increase fertilization efficiency and could also contribute to closing nutrient cycles within an agro-ecosystem.