Stabilization of new light fraction and humified C in >250 µm aggregates after conversion from no-till to fall conservation deep tillage

WINGEYER, ANA B.; DRIJBER, RHAE; OLK, DAN

Mar del Plata

Congreso; XIX Congreso Latinoamericano y XXIII Congreso Argentino de la Ciencia del Suelo; 2012

Asociación Argentina de la Ciencia del Suelo

Aggregate size classes represent distinct niches for soil organic matter (SOM) protection. Light Fraction (LF), mobile humic acid (MHA) and calcium bound humic acid (CaHA) were extracted from slake-resistant aggregates (>250 µm, and 250-53 µm). Soil samples from 0-5, 5-15 and 15-30 cm depths from an irrigated continuous maize field were collected under no-till (2005) and after 3 years (2008) of fall conservation deep tillage (FCDT). The change in management resulted in the redistribution of aggregates (and their SOM) between the 0-5 and 5-15 cm depths. From 2005 to 2008, aggregate-C and -N contents in SOM fractions of the 0-5 cm depth decreased from 7 to 35%, while increases of 9 to 120% were observed for the 5-15 cm depth and of 2 to 110% for the 15-30 cm depth. In addition, LF distribution with soil depth indicated preferential protection of plant-derived C in larger aggregates as well as a shift to more homogenous distribution of residue inputs across all depths in 2008 compared to 2005. From 2005 to 2008, a reduction in the light absorption at 465 nm of MHA and CaHA in the 5-15 and 15-30 cm depths of the large and mid-size aggregates indicated humification of new C inputs with change in management. The trends observed after three years of FCDT indicates loss of C in the 0-5 cm depth was counterbalanced by preferential stabilization of new C with soil depth by both physical protection and humification into >250 μm aggregates and largely humification in mid-size aggregates