Abstract

ROLDAN, María Florencia et al. Distribución De Tamaño y Estabilidad De Agregados En Molisoles Bajo Labranzas Contrastantes. Cienc. suelo [online]. 2014, vol.32, n.2, pp.247-257. ISSN 1850-2067.

Tillage systems affect soil aggregation and aggregate stability, both directly and by affecting other factors such as organic matter content (MO). Changes in both variables may be good soil health indicators. The aim of this work was to evaluate aggregate size distribution and stability in two sites representative of the Southeastern Buenos Aires province (Balcarce and Barrow, soils with different texture and MO) and under two tillage systems (no- (SD) and conventional (LC) tillage). Soil samples were taken (0-5 and 5-20 cm) from two long-term experiments started in 1997 with continuous cropping under SD and LC after four-year old grass-based pastures. Besides, in each site soil samples were taken from undisturbed situations. Soil was sieved in water to separate large (>2000 µm) and small (2000-250 µm) macroaggregates (MA), microaggregates (mA, 250-50 µm) and the fraction <50 µm, after 2 re-wetting methods: 1) capillary (MC) and 2) by immersion (MV). Mean weight diameter change (CDMP) between re-wetting methods was determined as a measure of aggregate stability. There was a greater proportion of MA (large+small) under SD respect to LC in both sites and re-wetting methods. The amount of MA tended to change less between re-wetting methods under SD, especially in the top layer, and in Barrow, whereas the amount of mA increased more under LC and with a like trend in Balcarce. Similar trends were observed when changes were expressed relative to the undisturbed situations. No significant differences (P>0.05) were observed in CDMP between tillage systems nor sites. For both soils under study, SD increased aggregate stability in the surface layer possibly due to the greater MO content. Likewise, the greater clay content in Barrow could be the cause of the greater stability of the different aggregate fractions.

Keywords : Aggregation, soil health indicator, no tillage, conventional tillage, continuous cropping.

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