Highlights of the study on aeolian dust emitted from agricultural soils of Argentina

PANEBIANCO ESTEBAN; AVECILLA FERNANDO; ITURRI ANTONELA; MENDEZ MARIANO; DE ORO LAURA; AIMAR SILVIA; BUSCHIAZZO DANIEL

Simposio; blowing south southern hemisphere dust symposium; 2021

Although some precedents exist, strong research on wind erosion in Argentina started around 1995. The first works focused on the measurement of wind erosion. Some mass flux profile models turned out not to be mathematically feasible to calculate the horizontal mass transport, hence producing important biases. Even when using the models that can represent better the mass distribution with height, such as exponential functions or linear interpolation, we found differences of up to 50% in the calculated mass transport depending on the sampling set up. Considering this, soil losses measured in loessic soils from central Argentina were up to 1.5 kg m-2 day-1 (or 27 Mg ha-1 year-1 ). Generally, much lower values were measured in other soil types across the country. Mean threshold wind speed was 7.5 m s-1for loessic soils, but generally higher for other soil types in more arid and windy regions. After studying wind erosion, work was oriented towards dust or particulate matter less than ten microns in diameter (PM10) emitted from agricultural soils and from other wind-erosion prone surfaces in rural areas. Very sandy surfaces such as unpaved roads were found to emit less dust per unit of transported mass, but to emit much more absolutequantities because horizontal mass transport was much higher than on soils. Using concentration gradients, average potential PM10 vertical emission for loessic soils from central Argentina was estimated to be between 2x10-4 g m-2 s-1 and 8x10-4 g m-2 s-1. According to our findings, abrasion predominates in sandy surfaces, and lifting of loose particles prevails in finer surfaces. Higher emission values were observed for loamy textures due to the overlapping of abrasion, lifting, and fragmentation of aggregates during saltation. Aggregates that move most actively by saltation on loamy-textured soils are, on average, 110 microns in diameter. We also observed that around 250 metres of bare surface are needed for the development of a dust plume from full fragmentation of the saltating soil aggregates on a loamy sand soil. Particles that we have consistently found to actively contribute to the emission of dust are up to around 62.5 microns, because particles in this size range are much more affected by vertical forces than bigger ones. On average, 12% of these particles were found to be lost by vertical movement over a distance of 200 meters. The highest PM10 emission rates under field conditions were observed when relative humidity was below 20% and the air temperature was higher than 30°C, especially when the wind speed exceeded 8 m s−1. Interaction between climate, soil and tillage produces high variability of dust emission. Dust is generally enriched in chemical elements as compared to the bulk soil. Nutrient content in PM10 from eroded sediment from these soils was found to be up to 60 g/kg C, 5 g/kg N, 900 mg/kg S; and up to 250 mg/kg Ca and Mg. C y N are transported15 higher than Ca and Mg, especially on less structured surfaces, and S showed a more homogenous distribution with height.